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Capacity degradation and voltage fade of Li2MnO3 during cycling are the limiting factors for its practical use as a high-capacity lithium-ion battery cathode. Here, the simulated amorphisation and recrystallisation (A + R) technique is used, for generating nanoporous Li2MnO3 models of different lattice sizes (73 Å and 75 Å), under molecular dynamics (MD) simulations. Charging was carried out by removing oxygen and lithium ions, with oxygen charge compensated for, to restrain the release of oxygen, resulting in Li2−xMnO3−x composites. Detailed analysis of these composites reveals that the models crystallised into multiple grains, with grain boundaries increasing with decreasing Li/O content, and the complex internal microstructures depicted a wealth of defects, leading to the evolution of distorted cubic spinel LiMn2O4, Li2MnO3, and LiMnO2 polymorphs. The X-ray diffraction (XRD) patterns for the simulated systems revealed peak broadening in comparison with calculated XRD, also, the emergence of peak 2Θ ~ 18–25° and peak 2Θ ~ 29° were associated with the spinel phase. Lithium ions diffuse better on the nanoporous 73 Å structures than on the nanoporous 75 Å structures. Particularly, the Li1.00MnO2.00 shows a high diffusion coefficient value, compared to all concentrations. This study shed insights on the structural behaviour of Li2MnO3 cathodes during the charging mechanism, involving the concurrent removal of lithium and oxygen.

The perpetual acceleration of the lithium demand combined with its relatively low abundance and uneven concentration on the Earth’s crust might dramatically increase its price in a near future. Mg batteries are a promising alternative to Li-ion batteries thanks to Mg high abundance, low cost and capacity. Yet, metallic Mg reacts with conventional electrolytes to form a barrier on its surface, preventing cation exchange. An interesting alternative is to replace Mg metal with a host negative electrode, overcoming the electrolyte compatibility problem. The objective of this work is to study the electrochemical behaviour and reaction mechanisms of two p-block elements alloys used as a negative electrode in Mg-ion systems: In-Pb:C and InSb made by ball-milling.A strong synergy between In and Sb is evidenced in InSb with the electrochemical activation of Sb with Mg, inactive as a pure element. This synergetic effect is only present on the first magnesiation for In-Pb:C. By coupling operando and ex situ XRD with XAS, we followed the phase transformations during (de)magnesiation. Especially, an amorphization of MgIn is induced by the first magnesiation of InSb and In-Pb:C. To improve the performance of InSb, the morphology of the powder was modified via a reduction synthesis. Although performances are slightly improved, the crystallization of the MgIn phase is favored for nanostructured particles. This behavior suggests a competition between crystallization and amorphization depending of the material’s morphology.; L’accélération continuelle de la demande en lithium, combinée à son abondance limitée et sa concentration inhomogène dans la croûte terrestre risque d’augmenter considérablement son prix dans un futur proche. Les batteries au Mg sont une alternative prometteuse aux batteries Li-ion du fait de la grande abondance, du coût et des capacités du Mg. Néanmoins le Mg métal réagit avec les électrolytes conventionnels pour former une couche de passivation à sa surface rendant l’échange de cations impossible. Une alternative intéressante réside dans le remplacement du Mg métal par une électrode négative hôte, surmontant le problème de compatibilité avec les électrolytes. L’objectif de ce travail est d’étudier le comportement électrochimique et les mécanismes de réactions de deux alliages d’éléments du bloc p en tant qu’électrode négative de batteries Mg : In-Pb:C et InSb, synthétisés par broyage.Une forte synergie entre In et Sb est mise en évidence dans InSb avec la promotion de l'activité électrochimique du Sb avec Mg, impossible dans le cas de Sb seul. Cet effet synergique n’est présent qu’au premier cycle électrochimique pour In-Pb:C. En couplant des caractérisations DRX ex situ et operando et XAS, nous avons suivi les transformations de phases durant les processus de (dé)magnésiation. En particulier, une amorphisation de la phase MgIn est induite par la première magnésiation de InSb et In-Pb:C. Afin d’améliorer les performances de InSb, la morphologie des poudres a été modifiée via une synthèse par réduction. Bien que les performances soient peu améliorées, la cristallisation de la phase MgIn est favorisée quand les particules sont nanostructurées. Ce comportement suggère une compétition entre cristallisation et amorphisation dépendante de la morphologie.

The influence of the amorphization technique on the physicochemical properties of amorphous lactulose was investigated. Four different amorphization techniques were used: quenching of the melt, milling, spray-drying, and freeze-drying, and amorphous samples were analyzed by differential scanning calorimetry, NMR spectroscopy, and powder X-ray diffraction analysis. Special attention was paid to the tautomeric composition and to the glass transition of amorphized materials. It was found that the tautomeric composition of the starting physical state (crystal, liquid, or solution) is preserved during the amorphization process and has a strong repercussion on the glass transition of the material. The correlation between these two properties as well as the plasticizing effect of the different tautomers was clarified by molecular dynamics simulations. 17

A novel processing method for amorphous Al50Ti50 alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al50Ti50 powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7&ndash, 8 kA) and processing times (0.8&ndash, 1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al50Ti50 powder. The hardness results are compared with the values found in the literature.

Among the many methods available for solubility enhancement, mesoporous carriers are generating significant industrial interest. Owing to the spatial confinement of drug molecules within the mesopore network, low solubility crystalline drugs can be converted into their amorphous counterparts, which exhibit higher solubility. This work aims to understand the impact of drug overloading, i.e., above theoretical monolayer surface coverage, within mesoporous silica on the release behaviour and the thermal properties of loaded drugs. The study also looks at the inclusion of hypromellose acetate succinate (HPMCAS) to improve amorphisation. Various techniques including DSC, TGA, SEM, assay and dissolution were employed to investigate critical formulation factors of drug-loaded mesoporous silica prepared at drug loads of 100&ndash, 300% of monolayer surface coverage, i.e., monolayer, double layer and triple layer coverage. A significant improvement in the dissolution of both Felodipine and Furosemide was obtained (96.4% and 96.2%, respectively). However, incomplete drug release was also observed at low drug load in both drugs, possibly due to a reversible adsorption to mesoporous silica. The addition of a polymeric precipitation inhibitor HPMCAS to mesoporous silica did not promote amorphisation. In fact, a partial coating of HPMCAS was observed on the exterior surface of mesoporous silica particles, which resulted in slower release for both drugs.

This work is devoted to establishment of the chemical composition and conditions of formation and stability of the amorphous phase arising in the Fe-Si-Cu-Mn-Mg-O system in the course of high-temperature annealing. The materials used for research cold rolled strips 0,70 mm of alloy thick, containing were used (in % on weight): Si – 3,1, Cu – 0,5, Mn – 0,3, other iron and inevitable impurity. The main methods used of a research the high-temperature x-ray phase analysis, the scanning electronic microscopy with electron probe analyses. Upon studying the processes occurring on the surface of a Fe-3%Si-0,5%Cu alloy sample with a heat resistant MgO coating during continuous annealing at a temperature range of 600…1060 °C, the formation of an amorphous phase in the form of a Fe-based solid solution was observed using the non-ambient XRD technique. This phenomenon was observed in a layer composed of α-Fe and (MgFe)2SiO4, (MgFe)O, SiO2 oxides upon heating in the temperature range corresponding to α→γ transformation, that is, 920…960 °C. The amorphous state of the thin film was preserved during the subsequent annealing, both during heating and during cooling to a temperature of 20 °C. Данная работа посвящена установлению химического состава и условий формирования стабильной аморфной фазы, возникающей в системе Fe-Si-Cu-Mn-Mg-O в процессе высокотемпературного отжига. В качестве материала для исследования использовались холоднокатаные полосы толщиной 0,70 мм сплава, содержащего (в % по массе): Si – 3,1, Сu – 0,5, Mn – 0,3, остальное железо и неизбежные примеси. В качестве основных методов исследования использовались высокотемпературный рентгеновский фазовый анализ, сканирующая электронная микроскопия с электронно-зондовым (МРСА) анализами. Интегральный химический анализ слоев материала от поверхности вглубь образцов проводился с применением анализатора тлеющего разряда GDA-750. При исследовании процессов, происходящих на поверхности сплава Fe-3%Si-0,5%Cu c термостойким покрытием MgO, при непрерывном отжиге в интервале температур 600…1060°C методом терморентгенографии обнаружено образование аморфной фазы в виде твердого раствора на основе Fe. Эффект наблюдался в слое, состоящем из α-Fe, оксидов (MgFe)2SiO4, (MgFe)O, SiO2, при нагреве в температурном интервале, соответствующем α→γ превращению: 920…960 °C. Аморфное состояние тонкого слоя сохраняется в процессе дальнейшего отжига, как при повышении температуры, так и при охлаждении до 20°C.

International audience; In order to improve the understanding of the microscopic phenomena occurring during irradiation in zirconium alloys, ion beam irradiations are performed at 350 DC (dose-rate of 2 × 10-5 dpa/s) on recrystallized Zy-4 and M5 alloys, with 2 MeV protons. The aim of this study is to determine in which way proton irradiations can be representative of neutron irradiations, considering the second phase particle changes and the influence of these changes on the microstructural evolution of the material during irradiation. The 2 MeV proton irradiation at 350 DC, performed here, seems to reproduces well what happened in Zy-4 in PWR conditions with a progressive amorphisation of the Zr(Fe,Cr)2 Laves phases, but with a lower growth rate and a higher Fe/Cr ratio of the amorphous rim. The Zr(Fe,Nb)2 s phase particles in M5 undergo a uniform amorphisation, while the native βNb precipitates remain fully crystalline as evidenced in neutron irradiation at very low irradiation temperature. No radiation-enhanced precipitation of nanometric BETA-Nb particles was observed. Thus, for M5 alloy, the present irradiation seems to be representative of neutron irradiations at a very low irradiation temperature. Nevertheless it does not reproduce what happens in PWR conditions, where no amorphisation and a drastic loss of iron is reported for the Zr(Fe,Nb)2 Laves phase SPPs. Despite the lower iron rejection from the particles into the matrix during proton irradiation than during neutron irradiation, -component loop distribution is found to be similar after both types of irradiations. These results underline the influence of both dose-rate and temperature on second phase particles behavior under irradiation and point out the complexity of iron rejection influence on the basal -component loops. Indeed, although the -component loop nucleation and growth seem locally correlated to iron dissolution into the matrix, they do not seem to be directly correlated to the global amount of iron rejected.

Tablets are the most common forms of drug administration. They are convenient to administer and easy to manufacture. However, problems associated with the adhesion of the powders to the tableting tools are common. This phenomenon is known as sticking and even though it has been well documented and studied, it remains poorly understood. The many factors that contribute to good performance of the powders make the sticking problem difficult to solve. The goal of this study is to establish a relationship between the properties measured at the nanoscale to the overall tablet mechanical properties, tablet performance and powder pre-processing induced modifications. By using atomic force microscopy (AFM) we aim to develop an analytical method to characterize the mechanical and adhesive properties of the pharmaceutical powders at the nanoscale. Other methodologies such as scanning electron microscopy (SEM), thermal analyses (DSC, TGA) and tablet strength test were also used. The materials used in this study are commonly used excipients, a sticky drug and magnesium stearate (MgSt). Two different approaches offered by AFM were employed: sharp tip imaging and colloidal probe force measurements. Nano-mechanical properties of the materials were evaluated with a sharp tip cantilever showing that higher adhesion correlates with higher tablet cohesion and that both are significantly affected by the presence of MgSt. AFM characterization of the particle surface mechanical properties at the nanoscale was also used to detect the crystallinity and amorphicity levels of the materials. New approaches to presenting such data considering the particle heterogeneity and to track the dynamics of surface recrystallization are revealed. Adhesive interactions between a steel sphere and sticky and non-sticky powders were performed with the colloidal probe technique. Sticky materials presented a higher adhesion against the steel surface, and reveal the mechanism of stickiness. This work thus contributes to the provision of predictability of the performance of formulations at an early stage of the development process. QC 20170315

One of the most important prerequisites in the drug development is to attain a reproducible and robust product in terms of its nature, and its chemical and physical properties. This can be challenging, since the crystalline form of drugs and excipients can be directly transformed into the amorphous one during normal pharmaceutical processing, referred to as process-induced amorphisation or process-induced disorder. The intention of this thesis was to address the mechanisms causing disorder during powder flow and milling and, in association with this, to evaluate, the ability of Raman spectroscopy and atomic force microscopy (AFM) to quantify and characterize process-induced disorder. The amorphisation mechanisms were controlled by stress energy distribution during processing, which in turn was regulated by a series of process parameters. Compression and shearing stress caused by sliding were stress types that acted on the particles during powder flow and ball milling process. However, sliding was the most important inter-particulate contact process giving rise to amorphisation and the transformation was proposed to be caused by vitrification. The plastic stiffness and elastic stiffness of the milling-induced particles were similar to a two-state particle model, however the moisture sorption characteristics of these particles were different. Thus the milled particles could not be described solely by a two-state particle model with amorphous and crystalline domains. Raman spectroscopy proved to be an appropriate and effective technique in the quantification of the apparent amorphous content of milled lactose powder. The disordered content below 1% could be quantified with Raman spectroscopy. AFM was a useful approach to characterize disorder on the particle surfaces. In summary, this thesis has provided insight into the mechanisms involved in process-induced amorphisation of pharmaceutical powders and presented new approaches for quantification and characterization of disordered content by Raman spectroscopy and atomic force microscopy.

Silicon carbide based composites are candidates for structural components and fuel claddings in nuclear power plants. In the frame of accident tolerant fuel research, the effective through-thickness thermal conductivity of SiC/SiC prototype claddings is investigated. This property, which is both material and geometry dependent, has been measured with a custom-made radial heat flow apparatus. Conductivities ranging between 0.5 and $\sim4$~W$\cdot$m$^{-1}\cdot$K$^{-1}$ have been measured, well below the literature values of 8 to 15~W$\cdot$m$^{-1}\cdot$K$^{-1}$. This significant difference is due to several factors. Firstly, with the method used here, the components of the conductivity, parallel, and perpendicular to the fibre weave, are fully separated. Secondly, the complex multilayered architectures of the tubes are detrimental, acting as barriers against heat transport. Indeed, in order to be water- and gas-tight, the tubes have to include dense ceramic or metallic layers. The poor adhesion between these and SiC/SiC results in a severely reduced heat transfer. Moreover, the matrix of the composite shows a heterogeneously distributed porosity --~ about 20 to 45\%. This leads to an inhomogeneous thermal conductivity, along both the length and the circumference of the cladding. Although the total porosity should be lessened in future development steps, it currently contributes to the transport of heat through Mie forward scattering of infrared radiation, an effect known as radiation thermal conductivity. In parallel to these activities, a specific component of SiC/SiC, the pyrolytic carbon interphase, has been investigated using analytical electron microscopy. This work showed that this layer, linking the fibres to the matrix, becomes partially amorphous after irradiation. In-situ ion irradiations evidenced radiation-induced dimensional changes of the said layer, the impact of which would mostly be on the mechanical properties of the composite. Using continuous medium modelling, the effect of a partial amorphisation of the PyC is estimated to a thermal conductivity loss of 20 to 25\%. In their current state, SiC/SiC clads do not have a thermal conductivity high enough for them to used in power plants. Indeed, a thermal conductivity locally as low as 1~W$\cdot$m$^{-1}\cdot$K$^{-1}$ results in fuel temperatures high enough for \ce{UO2} to reach its melting point.

The purpose of the study was to investigate the relationship between comminution and amorphisation of alpha-lactose monohydrate particles during ball milling under different milling conditions, including ball-to-powder mass ratio, milling time and ball diameter. The results revealed that at a constant ball filling ratio, ball-to-powder mass ratio of 25:1 resulted in the lowest minimum particle diameter of similar to 5 mu m and the highest degree of apparent amorphous content of 82%. The rate of comminution was high during early stage of milling whereas the degree of apparent amorphous content increased gradually at a slow rate. An increased ball-to-powder mass ratio during milling increased both the rate of comminution and the rate of amorphisation. Using a given ball-to-powder mass ratio, the ball diameter affected the degree of apparent amorphous content of the particles while the particle diameter remained unchanged. The relationship between comminution and amorphisation could be described as consisting of two stages, i.e. comminution dominated and amorphisation dominated stage. It was proposed that the rate constant of comminution and amorphisation are controlled by stress energy distribution in the milling jar and the stress energy distribution is regulated by the ball motion pattern that can be affected by the process parameter used. Title in dissertation list of articles: "Comminution-amorphisation relationships during ball milling of lactose at different stress energies"

Characterisation of mechanochemically activated Tsagaan-tsav zeolite has been performed. Tsagaan-tsav zeolite has been activated with a vibration mill for 2, 3, 5, 10 and 20 minutes. Ball to powder ratios were varied 1:10, 1:20, 1:50 and 1:100. Efficiency of milling determined based on amorphisation rate and cation exchange capacity changes. The highest efficiency was obtained for zeolite milled with ball to powder ratio of 100. Structural characterisation was performed with XRD, SEM, BET and particle size analyzer. Mechanochemical activation improves cation exchange capacity of natural zeolite.DOI: http://dx.doi.org/10.5564/mjc.v12i0.181 Mongolian Journal of Chemistry Vol.12 2011: 98-101

Mechanically induced reactivity of gibbsite in an attrition mill is focused in this paper. Reactivity of milled gibbsite, assessed in terms of its dehydroxylation and dissolution in alkali solution, is found to increase with the increase in milling time. Besides analysing the increased reactivity in terms of the changes in physicochemical characteristics, an attempt has also been made to correlate the reactivity with physicochemical changes. Changes in the physicochemical characteristics of gibbsite during milling in an attrition mill and corresponding change in reactivity are compared with that observed for gibbsite milled in a planetary mill, described in Part 1; thus a comparison of two different types of mills in terms of their efficiency in bringing out structural/reactivity changes is illustrated using the same feed stock, gibbsite., by S.P. Mehrotra et al.

Boron carbide B4C is a material considered as neutron absorber for the Sodium Fast reactors SFR of the fourth generation. This type of reactor is the reference for the future of the nuclear technology in France. A first prototype of SFR, called ASTRID, should be built around 2025. The aim of this study is to understand, from a fundamental point of view, the effects induced by ion irradiation on the crystallographic structure of B4C, in different energy ranges. So, boron carbide samples were sintered by Spark Plasma Sintering (SPS) technique at the SPCTS laboratory in Limoges (France) and then irradiated with ions of different natures and energies, favoring: (i) the nuclear stopping power, creating ballistic damage in the material, or (ii) the electronic stopping power, creating mainly electronic damage. For the irradiations in the ballistic regime, we used C+, Ar+ and Au+ ions with energies below 1 MeV, on the accelerator VdG 4 MV of the IPNL and on the JANNuS-Orsay plateform. The structural modifications of B4C were studied between 0 and 9 dpa. The irradiations in electronic regime were performed with S9+ and I9+ ions with energies of 60 and 100MeV, at the 15 MV Tandem accelerator of the IPNO. The electronic excitations values corresponding to those conditions are ranging between 4 and 15 keV.nm-1. The irradiations were carried out at room temperature, 500°C and 800°C to study the coupled effects of temperature and irradiation. The structural characterizations of the samples after irradiation were performed by Raman spectrometry at CEA Saclay and by in situ Transmission Electron Microscopy at the JANNuS-Orsay facility. Our study demonstrated the existence of an amorphisation threshold in boron carbide in both irradiation regimes at room temperature. In the ballistic regime, the amorphisation of the material is reached around a value of 9 dpa. In the electronic regime, from a stopping power in between 9 and 10 keV.nm-1 an amorphisation process, induced by the formation of latent tracks and their overlapping at high fluences was observed. Moreover, at 500°C, we showed that the temperature slowed down the damage induced by the irradiation in B4C, and almost totally prevented it at 800°C, Le carbure de bore B4C est envisagé en tant qu'absorbeur de neutrons dans les réacteurs nucléaires à neutrons rapides et à caloporteur sodium, RNR-Na, de génération IV. Cette filière de réacteur constitue aujourd'hui la référence pour l'avenir du nucléaire en France. Ainsi, un premier concept de réacteur RNR-Na, nommé ASTRID, devrait être construit aux alentours de 2025. L'objectif de notre étude est de comprendre, d'un point du vue fondamental, les effets induits par les irradiations aux ions, sur la structure cristallographique de B4C, dans différents domaines de pouvoirs d'arrêt. Pour cela, des échantillons de B4C, frittés par Spark Plasma Sintering (SPS) au SPCTS de Limoges, ont été irradiés par des ions de différentes natures et de différentes énergies, nous permettant de favoriser: (i) le pouvoir d'arrêt nucléaire Sn, afin d'induire un endommagement dit balistique dans le matériau, ou (ii) le pouvoir d'arrêt électronique Se, pour induire un endommagement dit électronique. Les irradiations en régime balistique ont été réalisées à l'aide d'ions C+, Ar+ et Au+ à des énergies inférieures au MeV, sur le VdG 4 MV de l'IPNL et auprès de la plateforme JANNuSOrsay. Les modifications structurales de B4C dans des gammes d'endommagement compris entre 0 et 9 dpa ont ainsi pu être étudiées. Les irradiations en régime électronique ont été effectuées par des ions S9+ et I9+ de 60 et 100 MeV sur l'accélérateur Tandem de l'IPNO. L'impact des excitations électroniques sur B4C à des pouvoirs d'arrêt électronique compris entre 4 et 15 keV.nm-1 a été déterminé. Afin d'étudier également les effets couplés de l'irradiation et de la température, toutes les irradiations ont été réalisées à température ambiante (RT), à 500°C et à 800 °C. Les caractérisations microstructurales des échantillons irradiés ont été effectuées principalement par microspectrométrie Raman au CEA Saclay et par Microscopie Electronique en Transmission (MET) in situ à JANNuS-Orsay. Nos études ont permis de mettre en évidence un seuil d'amorphisation du B4C dans les deux régimes d'endommagement à RT. En régime balistique, l'amorphisation du matériau est atteinte pour un taux de 9 dpa environ. En régime électronique, un pouvoir d'arrêt de 9 keV.nm-1 a permis de mettre en évidence une amorphisation du matériau induite par la formation de traces latentes nanométriques amorphes, et leur recouvrement à hautes fluences. De plus, nous avons également montré que la température permettait de limiter l'endommagement dès 500°C dans B4C, voire de l'inhiber presque totalement à 800°C

Silicon carbide is one of the candidate materials for core components of some nuclear reactor projects (Gen-IV). In order to improve their thermo-mechanical properties, materials with nanometric grain size are considered. For such materials, nearly no data concerning their behaviour under irradiation are available. In this paper, we study the damage and subsequent recovery of a nanostructured 3C–SiC ceramic. Samples were irradiated at room temperature with 4 MeV Au ions and subsequently annealed. Their structural modifications are analysed with a grazing incidence X-ray diffraction method. Results show that these nanoceramic materials present the same damage kinetics during irradiation as conventional micrometric grained SiC, with total amorphisation at the highest fluence. However, while the recrystallisation of a conventional ceramic is expected to occur through an epitaxial recrystallisation from the non-damaged parts of the large grains, the nanometric material is healed only after annealing at 1000 °C through mechanisms that can be attributed to a heterogeneous nucleation and growth of β crystallites in the totally amorphised grains.

International audience; Graphite response to irradiations has been widely studied in the past because of its importance for nuclear engineering. Although its behavior under irradiation has been widely investigated, the very details of the underlying mechanisms are still under debate and several scenarios are available [1,2,3]. With molecular dynamics simulations using empirical potentials we investigate in this paper the creation of damages by single irradiation event and the effect of the irradiation dose until complete amorphisation of the graphite structure.Two methodologies are used displacement cascades to investigate the primary damage and Frenkel pair accumulations to study the dose effect. We show that graphite is not amorphised by a direct impact mechanism for initial energies of the primary knocked-on atoms (carbon and chlorine) up to 40 keV. Instead, various defects stabilize and remain after a single irradiation event. However, amorphisation is reached by accumulation of defects. Before amorphisation, we show that graphite follows a three stages evolution characterized by (1) an increase of point defects (2) a pinning and wrinkling of the graphene planes at small amorphous pockets and (3) an amorphisation by percolation of the small amorphous pockets. These three stages all together constitute an alternative scenario to those already existing [4]. We also show the mechanisms of each stage drive the change of lattice dimension of graphite. Interstitials contribute as expected to the swelling of the c-axis, while vacancies link the shrinkage of the basal plane in the first stage. The point defects contribution of the first stage is replaced by the dimension change induced by the rippling of the graphene planes. This topological change is depicted by a power law relation between the c-axis swelling and the basal-plane shrinkage as a function of the irradiation dose. [1] K. Niwase, Phil. Mag. Lett. 82 (2002) 401.[2] M.I. Heggie, I. Suarez-Martinez, C . Davidson, and G. Haffenden, J. Nucl. Mater. 413 (2011) 150.[3] B.J. Marsden, and G.N. Hall, in Comprehensive Nuclear Materials, chap. 4.11 (2012) 325.[4] A. Chartier, L. Van Brutzel, B. Pannier, and P. Baranek, submitted in Carbon (2014)

The use of Tyranno SA3 (TSA3) and Hi Nicalon S (HNS) SiC fibers as reinforcement for ceramic composites for nuclear applications requires the characterization of its structural stability and mechanical behavior under irradiation. Ion-amorphization kinetics of these fibers have been studied and compared to the model material, i.e. 6H-SiC single crystals, with no significant differences. For all samples, full amorphization threshold dose yields ~0.4 dpa at room temperature and complete amorphization was not achieved for irradiation temperatures over 200 ºC. Successively, ion-amorphized samples have been thermally annealed. It is reported that thermal annealing at high temperatures not only induces the recrystallization of the ion-amorphized samples but also causes cracking and delamination. Cracking is reported to be a thermally driven phenomenon characterized by activation energy of 1.05 eV. Regarding the mechanical irradiation behavior, irradiation creep of TSA3 fibers has been investigated using a tensile device dedicated to in situ tests coupled to two different ion-irradiation lines. It is reported that ion-irradiation (12 MeV C4+ and 92 MeV Xe23+) induces a time-dependent strain under loads where thermal creep is negligible. In addition, irradiation strain is reported to be higher at low irradiation temperatures due to a coupling between irradiation swelling and irradiation creep. At temperatures near 1000 ºC, irradiation swelling is minimized hence allowing the characterization of the irradiation creep. Irradiation creep rate is characterized by a linear correlation between the ion flux and the strain rate and square root dependence with the applied load.; L'utilisation des fibres SiC Tyranno SA3 (TSA3) et Hi Nicalon S (HNS) pour le renforcement de composites céramiques dédiées aux applications nucléaires impose l'étude de leur stabilité microstructurale et de leur comportement mécanique sous irradiation. La cinétique d'amorphisation des fibres a été étudiée et comparée à celle d'un matériau modèle, 6H-SiC monocristallin, sans que des différences significatives puissent être observées. La dose seuil d'amorphisation totale a été évaluée à ~0,4 dpa à température ambiante et aucune amorphisation complète n'a pas être obtenue pour des températures d'irradiation supérieures à 200 ºC. Les échantillons amorphes ont ensuite été recuits thermiquement ce qui a conduit, pour des températures élevées, à leur recristallisation mais également à une fissuration et une délamination de la zone irradiée. Ce processus d'endommagement était activé thermiquement avec une énergie d'activation de 1,05 eV. En ce qui concerne le comportement mécanique, le fluage d'irradiation des fibres TSA3 a été étudié en utilisant une machine de traction in situ implantée sur deux plateformes d'irradiation aux ions. On montre que sous irradiation ces fibres se déforment en fonction du temps avec des chargements thermique et mécanique où le fluage thermique est négligeable. Cette déformation est plus élevée pour les faibles températures d'irradiation en raison d'un couplage entre le gonflement et le fluage d'irradiation. Pour des températures voisines de 1000 ºC, le gonflement devient négligeable ce qui permet l'étude spécifique du fluage d'irradiation dont la vitesse de déformation présente une dépendance linéaire au flux d'ions.

International audience; Multiple energy aluminum (Al) implantations were performed at room temperature in n-type epitaxial 6H-SiC layers, aiming at amorphizing the material from the surface up to a depth inferior to 0.5 mum. Annealings were then carried out in an induction furnace. The goal of this paper is to optimize the furnace geometrical configuration, in order to reduce the surface degradation and improve the crystal reordering. This optimization was established for one-side amorphized wafers, which need restricting annealing parameters, and is therefore supposed to be valid for less crystal damaging implantations. Two types of geometrical parameters were essentially studied: the internal configuration, which tends to increase the silicon partial pressure inside the reactor, and the position of the sample, which has a direct influence on the recrystallization and on the dopant electrical activation. The annealings are compared for the same thermal parameters: the plateau temperature (1700degreesC), the annealing duration (30 min), and the heating rate (60degreesC s(-1)). The surface roughness was evaluated by using atomic force microscopy. Two final configurations were retained, leading to satisfactory results with respect to the as-implanted material: (i) Rutherford backscattering spectrometry in channeling geometry revealed a very good recrystallization in both cases, giving a signal level similar to the virgin crystal one; (ii) secondary ion mass spectrometry showed two distinct results depending on the sample position: one position led to some material etching, especially the SiC part which was amorphizcd by the implantation, and the second position gave rise to the deposition of a crudely monocrystalline SiC layer on the surface of the sample implanted side. This coating was found to prevent from any dopant loss by exodiffusion or material etching. Electrical measurements (four-point probe at 300 K) proved an Al substitutional ratio of 97 and 78% depending on the configuration, giving room temperature sheet resistances of about 2 x 10(4) and 4 x 10(4) Omega sq.(-1), respectively, for 4 x 10(19) cm(-3) Al implanted samples.

Chalcogenide glasses are used as optics for the IR cameras thanks to their transparence in the two atmospheric windows [3 – 5 µm] and [8 – 12 µm]. In order to reduce their price and to increase the panel of compositions which may be produced, a new method of synthesis has been elaborated in the Glass and Ceramics group. Thus, this manuscript presents the development of the new way of synthesis of chalcogenide glasses and glass-ceramics by mechanical milling and SPS sintering, and the study of the structure and mechanical properties of glass-ceramics. The different milling and sintering parameters have been studied and the possibility to produce bulk samples with a structure and properties similar to those of glasses synthesized by melt-quenching method has been demonstrated. Also, it has been shown that the generation of crystalline particles in the glassy matrix increases mechanical properties of the samples without spoiling their optical transmission. Finally, a theoretical study, based on the DFT method, has been initiated in order to access more precise information concerning glass and glass-ceramic structure and mechanical properties.; Les verres de chalcogénures sont utilisés en tant qu'optiques pour les caméras IR grâce à leur transparence dans les deux fenêtres atmosphériques [3 – 5 µm] et [8 – 12 µm]. Afin de diminuer leur prix et d'augmenter la gamme des compositions qui pourraient être produites, une nouvelle méthode de synthèse a été élaborée au laboratoire Verres et Céramiques. Les travaux présentés dans ce manuscrit ont ainsi porté sur le développement de la technique de synthèse des verres et vitrocéramiques de chalcogénures par mécanosynthèse et frittage flash, ainsi que sur l'étude de la structure et des propriétés mécaniques des vitrocéramiques. Les différents paramètres de broyage et frittage ont été étudiés et la possibilité de produire des matériaux massifs, avec une structure et des propriétés similaires à celles des verres obtenus par voie classique de fusion-trempe, a été démontrée. Egalement, il a été constaté que la génération des particules cristallines dans la matrice vitreuse permet d'améliorer les propriétés mécaniques sans altérer la transmission optique des échantillons. Finalement, une étude théorique, basée sur la méthode DFT, a été initié pour accéder à des informations plus précises concernant la structure et les propriétés mécaniques des verres et vitrocéramiques de chalcogénures.

Complex oxides with the spinel structure often called spinels belong to the group of strategic materials which are used in the wide area of modern technologies. They exhibit excellent magnetic, refractory, semiconducting, catalytic and sorption properties. Spinels based on magnesium aluminate (MA spinels) are used for the preparation of refractory ceramic materials and bricks. Due to its good properties MA spinel is predestinated for special applications in electronics.Several methods and precursors for the synthesis of MA spinel have been studied experimentally. The conventional process of MA spinel preparation based on the high temperature solid state reaction of precursors is connected with the difficulty to obtain the high spinel phase purity required for its special applications. From the viewpoint of final material properties and of intensification of solid state reactions, the non-standard mechanochemical techniques are suitable.In the paper, results of the mechanochemical modification of the mixture of crystalline hydroxide precursors caused by the high-energy milling and subsequent heating in the temperature range 300-1500 °C are presented.Mixtures of brucite and gibbsite in the molar ratio 1:2 were submitted to grinding in a planetary mill using the corundum chamber for various milling times (0.5-12 hours). The specific surface area of the milled samples was determined by the BET method. Changes in the structure of mechanosynthesized products and the evolution of the spinel phase during the subsequent calcination of both mechanosynthesized samples and reference homogenised mixtures were monitored by the X-ray diffraction analysis and IR spectroscopy. The degree of conversion of hydroxide mixture to the MA spinel was determined by chelatometry.During the early stage of grinding (up to 1 hour), a considerable refinement of hydroxide mixture occurs. With the increasing grinding time, amorphisation of structure as well as a gradual mechanochemical dehydration and formation of aggregates take place. A structural metastability of high reactive products of dehydration and a large area of particle contacts lead to the solid state mechanochemical reaction with the formation of nucleation centres of amorphous magnesium aluminate. By the combination of mechanosynthesis with the subsequent thermal treatment, crystalline magnesium aluminate with the spinel structure is prepared at temperatures which are by 300 K lower than those at which the spinel is synthesized by conventional ceramic method.

A substantial number of new chemical entities and marketed drugs show poor solubility characteristics and amorphisation is one of the favorable approaches to enhance solubility characteristics of such poorly soluble drugs. Formulation efforts in the present study were devoted to investigate amorphisation of a model poorly soluble drug, atorvastatin calcium by molecular complexation with anion exchange resin, Duolite(®)AP 143/1093 and hence enhancement in its solubility characteristics. Drug resinates in 1:1, 1:2, and 1:4 weight ratios were prepared by simple batch operation and subsequently studied for drug content, residual solvent content, molecular interactions, solid state characterisation and solubility characteristics. During initial characterisation, all the proportions of drug resinates, except 1:1 proportion showed partial amorphisation of the drug, whereas 1:1 proportion showed complete amorphisation of the drug. This proportion reported distinctly enhanced solubility characteristics over pure drug and other proportions. Such amorphisation and solubility enhancement could be attributed to the binding of individual drug molecules to the functional sites of the resin molecules, either partially or completely, resulting in reduction of crystal lattice energy, a main barrier to dissolution. Hydrophilic nature of ion exchange resin matrices also assisted in enhancing dissolution of the drug from the resinates. During accelerated stability study, there was an insignificant decrease in solubility characteristics of the drug and its amorphous form was also found to be stable in 1:1 proportion. Atorvastatin resinates formed in 1:1 weight ratio were in stoichiometric proportion and such drug resinates in stoichiometric proportion showed to have tremendous potential in conversion of crystalline form of drug substances to its amorphous form and subsequent stabilisation. It hence proved to be a very effective, yet simple approach for improving solubility characteristics of poorly soluble actives.

Understanding the formation of bulk metallic glasses (BMG) in metallic systems and finding a reliable criterion for selection of BMG compositions are among the most important issues in condensed matter physics and material science. Using the results of magnetic susceptibility measurements performed on both amorphous and crystallized Cu-Hf alloys (30-70 at% Cu) we find a correlation between the difference in magnetic susceptibilities of corresponding glassy and crystalline alloys and the variation in the glass forming ability (GFA) in these alloys. Since the same correlation can be inferred from data for the properties associated with the electronic structure of Cu-Zr alloys, it seems quite general and may apply to other glassy alloys based on early and late transition metals. This correlation is plausible from the free energy considerations and provides a simple way to select the compositions with high GFA., Comment: 11 pages, 3 figures

In this paper the results of optical properties investigations on plastically deformed copper are presented. The optical properties of the plastically deformed copper were studied using spectroscopic ellipsometry in the ultraviolet-visible (UV-VIS) range. Chemically pure copper was deformed by applying the Equal Channel Angular Pressing (ECAP) technique. During the last decade, equal-channel angular pressing procedure was used for the fabrication of ultrafine-grained metals and alloys. The plastic deformation of metallic materials leads to the production of bulk nano-scale structures with ultrafine grains and cross-sections, which remain about equal before and after deformation. The parameters of the sample were calculated using a two-film model together with the Bruggeman effective medium approximation. V članku so predstavljeni rezultati raziskav optičnih lastnosti plastično deformiranega bakra. Te so bile raziskane s spektralno elipsometrijo v območju vidne UV-svetlobe. Kemijsko čist baker je bil deformiran z uporabo ECAP-metode (enakokotno koničasto stiskanje). V zadnjem času se ECAP-postopek uporablja za izdelavo ultra udrobnjenih kovin in zlitin. Takšna plastična deformacija kovinskih materialov vodi k izdelavi masivnih nanostruktur z ultra drobnimi zrni in prečnim prerezom, kar omogoča približno enakost pred deformacijo in po njej. Parametri preiskanih vzorcev so bili izračunani na osnovi uporabe dvojne plasti - filma skupaj s Bruggemanovo srednjo efektivno aproksimacijo.

Jorgensen, Anders D. Jensen, Susanne L. Ziegler, Gregory Pandeya, Anuranjan Buleon, Alain Svensson, Birte Blennow, Andreas 34 WILEY-V C H VERLAG GMBH; International audience; The interaction and physical/structural effects of aroma compounds, at high concentrations on dry native starch granules were studied using eight selected model compounds: acetaldehyde, dimethyl sulphide, diacetyl, allyl isothiocyanate, ethyl butyrate, citral, octanol and butyric acid. The maize, potato and pea starches used represent different typical structural and chemical starch characteristics. Retention of the different aroma compounds varied from a few to one hundred percent and starch was found to induce as well as reduce aroma evaporation depending on the aroma compound and the starch type. As deduced from DSC, powder XRD and SEM analyses, citral, butyric acid and octanol exerted specific effects on the starch granules manifested in local melting of crystalline layers and partial disruption of the granular meso structure. The most prominent effect was obtained with citral that generated surface wrinkles on B- and C-type polymorphic granules and aggregation of A-type polymorphic granules, decreased the melting temperature and suppressed the crystallinity of the starch.

The studies presented in this manuscript deal with the synthesis and characterization of new rare-earth based magnetocaloric materials for magnetic refrigeration applications. The first chapter is an introduction to the concepts of magnetocaloric effect and magnetic refrigeration and establishes a review of the magnetocaloric materials existing today. Two research axes were explored in order to obtain materials with a high refrigeration capacity (RC) and to identify strategies for improving this performance criterion: the enlargement of magnetic transition and the effect of transition element M and p-element X in the metallic glasses Gd60M30X10 (M = Mn, Fe, Co, Ni, Cu et X = Al, Ga, In) on one hand, and the synthesis of new ternary silicides in the RE-M-Si systems (RE = Nd, Gd, Tb et M = Co, Ni) with high magnetocaloric potential on the other hand. The second chapter of this thesis presents the magnetic properties of Gd-based amorphous ribbons synthesized by the melt-spinning technique, in which the structural disorder induces a very strong enlargement of the magnetic transition (compared to that of pure Gd for instance). In a first part, it shows the weak influence of the p element (X) on the magnetic properties of Gd60Mn30X10 (X = Al, Ga, In) ribbons. A second part presents the very strong influence of the transition element M, either on the nature of the magnetic transition and on the magnetocaloric properties of Gd60M30In10 (M = Mn, Fe, Co, Ni, Cu) metallic glasses with, in particular, a Curie temperature varying between 86 (M = Ni) and 220 K (M = Fe) and the occurrence of a cluster-glass behavior below 35 K when M = Mn. The third chapter of this thesis is composed of three parts. The first one describes the synthesis conditions of RE5MSi2 (RE = Nd, Gd, Tb), Gd5Si3 and of the compound with existence domain Gd3Co2.5 ± xSi1.5 ± y. These syntheses are sometimes delicate, particularly in the choice of annealing temperatures. The use of the Rietveld method to refine the X-ray and neutron powder diffraction patterns allowed showing that RE5MSi2 compounds adopt a Cr5B3 type structure, with a mixed occupation of 8h site by Co and Si at 50 %/50 % and that Gd3Co2.5 ± xSi1.5 ± y adopts an Er4Ge4 type structure with mixed Co/Si occupation in 4a et 4c positions. The second part presents the magnetic and magnetocaloric properties of the Gd5CoSi2 silicide. This compound exhibits a ferromagnetic transition at the Curie temperature TC = 169 K that is accompanied by a magnetic entropy change of -4.7 and 8.7 kg-1 K-1 at 2 and 5 T, respectively, as calculated by the application of Maxwell's relationship. The third part is this chapter describes the magnetic properties of Nd5CoSi2 and Nd5NiSi2 which order ferromagnetically at 55 and 44 K, respectively. It also presents the refinement of the canted ferromagnetic structure on Nd5CoSi2, obtained by neutron diffraction measurements. These study show that evaluating the magnetocaloric materials by only considering the criterion of refrigeration capacity does not lead to the elaboration of the best materials for the applications. It could be more efficient to target more pragmatic criteria, for each considered refrigeration cycle, such as a temperature window of use around the Curie temperature or an optimal specific heat value in order to lead the research of new magnetocaloric materials at best.; Les travaux présentés dans ce manuscrit portent sur la synthèse et la caractérisation de nouveaux matériaux magnétocaloriques à basse de terres rares pour la réfrigération magnétique. Le premier chapitre constitue une introduction aux notions d'effet magnétocalorique et de réfrigération magnétique et dresse un état de l'art des matériaux magnétocaloriques existants. Dans le but d'obtenir des matériaux à forte capacité de réfrigération (RC) et d'identifier des stratégies d'amélioration de ce critère de performance, deux voies de recherche ont été explorées : l'élargissement de la transition magnétique et l'effet de l'élément de transition M et de l'élément p (X) dans les verres métalliques Gd60M30X10 (M = Mn, Fe, Co, Ni, Cu et X = Al, Ga, In) d'une part, et la synthèse de nouveaux siliciures ternaires dans les systèmes R-M-Si (R = Nd, Gd, Tb et M = Co, Ni) à fort potentiel magnétocalorique, d'autre part. Le second chapitre de cette thèse présente les propriétés magnétiques des rubans amorphes à base de gadolinium synthétisés par la technique de melt-spinning, dans lesquels le désordre structural induit un très fort élargissement de la transition magnétique (vis-à-vis de celle du gadolinium par exemple). Il montre dans un premier temps, la faible influence de l'élément p (X) sur les propriétés magnétiques des rubans Gd60Mn30X10 (X = Al, Ga, In). Une seconde partie présente la très forte influence de l'élément de transition M, tant sur la nature de la transition magnétique que sur les propriétés magnétocaloriques des verres métalliques Gd60M30In10 (M = Mn, Fe, Co, Ni, Cu), avec en particulier une température de Curie variant entre 86 (M = Ni) et 220 K (M = Fe) et l'existence d'un phénomène de type cluster-glass en dessous de 35 K lorsque M = Mn. Le chapitre trois de cette thèse se décline en trois parties. La première décrit les conditions de synthèse parfois délicates, notamment dans le choix des températures de recuit, des siliciures R5MSi2, Gd5Si3 et du composé à domaine d'existence Gd3Co2,5 ± xSi1,5 ± y. L'utilisation de la méthode Rietveld pour l'affinement des diffractogrammes de rayons X sur poudre et monocristaux et neutrons a permis de montrer que les composés R5MSi2 adoptent une structure de type Cr5B3 avec la particularité de l'occupation mixte du site 8h par Co et Si à 50 %/50 % et que Gd3Co2,5 ± xSi1,5 ± y adopte une structure de type Er3Ge4 avec des sites mixtes Co/Si en positions 4a et 4c. La seconde partie présente les propriétés magnétiques et magnétocaloriques du siliciure Gd5CoSi2. Ce composé subit une transition ferromagnétique à la température de Curie de 169 K qui s'accompagne d'une variation d'entropie magnétique calculée par l'application de la relation de Maxwell, de -4,7 et 8,7 J kg-1 K-1 pour des variations de champ magnétique respectives de 2 et 5 T. Le troisième volet de ce chapitre décrit les propriétés magnétiques de Nd5CoSi2 et Nd5NiSi2 qui présentent une transition ferromagnétique respectivement à 55 et 44 K. Il décrit également l'affinement de la structure ferromagnétique cantée de Nd5CoSi2 obtenue par des mesures de diffraction neutronique. Il ressort de ces travaux que l'évaluation des matériaux magnétocaloriques par le seul critère de capacité de réfrigération ne mène pas vers les matériaux les plus adaptés à l'application. Il faudrait cibler plus spécifiquement, pour chaque type de cycle de réfrigération envisagé, des critères pragmatiques tels qu'une fenêtre de température d'utilisation autour de la température de Curie ou une valeur de chaleur spécifique optimale afin de mieux guider la recherche de nouveaux matériaux magnétocaloriques.

International audience; The structural changes induced by ball-milling of near-equiatomic σ-FeCr and α-FeCr in vacuum were followed. Besides the α-phase, an amorphous phase appears when milling the σ-phase for times longer than 20 h. An amorphous phase forms too, but at a slower rate than the latter, when milling the α-phase. The partial amorphisation of σ-FeCr and α-FeCr ball-milled in vacuum is concluded to be a phenomenon of intrinsic origin. The amorphous phase crystallizes into a bcc Cr-rich phase and a bcc Fe-rich phase during short annealing steps.

http://www.sciencedirect.com/science/article/B6TWY-4V34RFW-N/2/c9147c3fe84413d6b8e8875146fc1b0b

Irradiation defects in minerals present at the earth surface gave rise to an important number of studies. Among these minerals, clays possessed properties (cationic exchange capacity, swelling properties) which make them suitable candidate for the retention of actinides in the context of high level radioactive waste storage. In order to insure the stability of the clay located around the waste, it is necessary to study their physico-chemical properties after irradiation. This thesis is divided in three parts that are related to this thematic. In the first part, we will discuss the effect of ionizing irradiation of alpha particles on the specific surface area of kaolinite and the consequences of such an irradiation on the observed spectra by IRTF. The second part is dealing with the solubility of amrophized smectite in alkaline conditions and more especially with the dissolution kinetics. We will present new results on this process. Finally, in the third part, we studied a natural analogue geosysteme Nopal which is located in Chihuahua (Mexico). We will discuss how the kaolinite dosimeter can be a powerfool tool to asses' ancient uranium migration in the U-deposit.; Les défauts d'irradiations dans les minéraux présents à la surface de la terre ont donné lieu à de nombreuses études. Parmi ces minéraux, les argiles ont des propriétés (capacité de rétention des radioéléments, gonflement...) qui les rendent utiles dans le cadre du stockage des déchets radioactifs. Afin de s'assurer de la stabilité des argiles se trouvant autour du colis de déchets, il est nécessaire d'étudier leurs propriétés physico-chimiques après irradiation. Cette thèse est séparée en trois parties qui sont axées autour de cette thématique. Dans une première partie, nous verrons quels sont les effets des rayons alpha sur la surface spécifique de la kaolinite et nous exposerons les phénomènes physique induits par ces rayonnements ionisants. La seconde partie traitera de la solubilité des smectites amorphisées dans un milieu basique et plus particulièrement de la cinétique de dissolution. Nous verrons que cette dissolution est favorisée par l'amorphisation. Enfin dans une troisième partie, nous nous sommes intéressés au géosystème analogue naturel de Nopal (Chihuahua, Mexique), où le dosimètre kaolinite peut permettre d'étudier les migrations anciennes de l'uranium au sein de la roche.

The energy saving produced by the equalization of Fermi energies of a crystal and a melt has been associated to the crystal formation in undercooled melts to determine the new homogeneous-nucleation critical-temperature T 2 and the new nucleation critical barrier as a function of the temperature T . Small unmelted clusters act as nuclei by reducing the critical energy barrier and the nucleation times; the glass transition temperature T g occurs near T = T 2 . The temperature dependence of the specific heat difference of the undercooled melt with the glass, the viscosity weakening below T g and the nose of the temperature–time–transformation diagrams are successfully predicted.

We compare, through first-principles pseudopotential calculations, the structural, electronic, and optical properties of different size silicon nanoclusters embedded in a ${\text{SiO}}_{2}$ crystalline or amorphous matrix with that of freestanding, hydrogenated, and hydroxided silicon nanoclusters of corresponding size and shape. We find that the largest effect on the optoelectronic behavior is due to the amorphization of the embedded nanocluster. In that, the amorphization reduces the fundamental gap while increasing the absorption strength in the visible range. Increasing the nanocluster size does not change substantially this picture but only leads to the reduction in the absorption threshold, following the quantum confinement rule. Finally, through the calculation of the optical absorption spectra both in an independent-particle and a many-body approach, we show that the effect of local fields is crucial for describing properly the optical behavior of the crystalline case while it is of minor importance for amorphous systems.

Isometric Gd2Zr2O7 with the ordered, pyrochlore structure has an extremely high resistance to radiation-induced amorphization. Ion-beam irradiations at keV to GeV energies result in a disordered, defect-fluorite structure that remains crystalline to very large fluences. However, we report liquid-like phase formation of droplet-like surface hillocks and quenched molten tracks in Gd2Zr2O7. The extremely high energy density of 12-MeV C60 clusters creates tracks with substantial volumes of amorphous material, accompanied by the formation of nanocrystals of the disordered, defect-fluorite structure. This is the first evidence of irradiation-induced amorphization of Gd2Zr2O7. In contrast, irradiation of Gd2Zr2O7 pyrochlore with swift heavy ions of U resulted in an order-disorder transformation to defect-fluorite without any evidence of amorphization. Thermal-spike calculations highlight the dominance of the effect of deposited energy density, controlled by the projectile velocity, as compared with the energy loss.

Silicon carbide is envisaged as a cladding material for the nuclear fuel in the fourth generation reactors. The aim of this work is to study the capacity to retain fission products and the structure evolution of this material under the combined effects of temperature and irradiation. The low energy ion implantations and the incorporation of stable analogues of fission products (Cs and I) in single crystalline 6H-SiC samples were performed by using the ion implanter or the accelerator of the CSNSM. The high energy heavy ion irradiations were made at GANIL. The evolution of the implanted ion profiles and the crystal structure were studied by RBS and Channeling. Complementary information were obtained by using the UV-visible absorption spectroscopy. The low energy ion implantations at room temperature induce a fast structural damage in the crystal. On the other hand, it is possible to attain a small disorder rate in the crystal during implantation by increasing the implantation temperature (600 °C). The high energy heavy ion irradiations do not damage the SiC crystals. On the contrary, they cause an annealing of the disorder created by the low energy implantations. The implanted ions (I) do not diffuse during low or high energy ion irradiations at room temperature and at 600 °C. However, a diffusion of Cs ions was observed during a post-implantation annealing at 1300 °C. At this temperature, the crystal which had an extended amorphous layer starts to recover a single-crystal structure.; Le carbure de silicium est un matériau envisagé pour le conditionnement du combustible dans les réacteurs de quatrième génération. Ce travail a pour objectif d'étudier la capacité de confinement des produits de fission et l'évolution de la structure de ce matériau sous les effets combinés de la température et du rayonnement. Les implantations d'ions de basse énergie et l'incorporation d'analogues stables de produits de fission (Cs et I) dans des monocristaux de 6H-SiC ont été réalisées sur l'implanteur ou l'accélérateur du CSNSM. Les irradiations avec des ions lourds de haute énergie ont été effectuées au GANIL. L'évolution du profil des ions implantés et de la structure du cristal a été étudiée par RBS et canalisation. Des informations complémentaires ont été apportées par la spectroscopie d'absorption UV-visible. Les implantations d'ions de basse énergie à température ambiante conduisent à l'endommagement rapide du cristal. Par contre, une élévation de la température d'implantation (600 °C) permet de conserver un faible taux de désordre dans le cristal. Les irradiations avec des ions lourds de haute énergie n'endommagent pas les cristaux de SiC mais au contraire, elles provoquent une guérison du désordre créé préalablement par l'implantation d'ions I de basse énergie. Ces marqueurs d'iode ne diffusent pas lors d'irradiations avec des ions lourds de basse ou de haute énergie à température ambiante ou à 600 °C. Cependant, une diffusion des ions Cs a été observée lors d'un recuit thermique post-implantation à 1300 °C, température à laquelle le cristal qui comportait une couche amorphe étendue commence à retrouver une structure monocristalline.

The combination of microbeam implantation and in-situ micro RBS/channeling analysis in the Rossendorf nuclear microprobe facility enables crystal damage studies with high current densities not achievable in standard ion implantation experiments. Si(1 0 0) samples were implanted with 600 keV Si + ions and a fluence of 1 × 10 16 cm −2 . Using a beam spot of 200 μm × 200 μm current densities from 4 to 120 μA/cm 2 were obtained. The substrate temperature was varied between RT and 265 °C. The implanted regions were subsequently analysed by micro RBS/channeling with a 3 MeV He + beam having a spot size of 50 μm × 50 μm. Crystal damage up to amorphisation was observed in dependence on the substrate temperature. Above a critical temperature T C no amorphisation occurs. T C was determined for each series of samples implanted with the same ion current density j . It was found that the empirical Arrhenius relation j ∼ exp(− E a / kT C ), known from standard implantation experiments, is also valid at high current densities. The observed Arrhenius law can be derived from a model of epitaxial crystallisation stimulated by defect diffusion.

Silicon carbide is envisaged as a cladding material for the nuclear fuel in the fourth generation reactors. The aim of this work is to study the capacity to retain fission products and the structure evolution of this material under the combined effects of temperature and irradiation. The low energy ion implantations and the incorporation of stable analogues of fission products (Cs and I) in single crystalline 6H-SiC samples were performed by using the ion implanter or the accelerator of the CSNSM. The high energy heavy ion irradiations were made at GANIL. The evolution of the implanted ion profiles and the crystal structure were studied by RBS and Channeling. Complementary information were obtained by using the UV-visible absorption spectroscopy. The low energy ion implantations at room temperature induce a fast structural damage in the crystal. On the other hand, it is possible to attain a small disorder rate in the crystal during implantation by increasing the implantation temperature (600 °C). The high energy heavy ion irradiations do not damage the SiC crystals. On the contrary, they cause an annealing of the disorder created by the low energy implantations. The implanted ions (I) do not diffuse during low or high energy ion irradiations at room temperature and at 600 °C. However, a diffusion of Cs ions was observed during a post-implantation annealing at 1300 °C. At this temperature, the crystal which had an extended amorphous layer starts to recover a single-crystal structure., Le carbure de silicium est un matériau envisagé pour le conditionnement du combustible dans les réacteurs de quatrième génération. Ce travail a pour objectif d'étudier la capacité de confinement des produits de fission et l'évolution de la structure de ce matériau sous les effets combinés de la température et du rayonnement. Les implantations d'ions de basse énergie et l'incorporation d'analogues stables de produits de fission (Cs et I) dans des monocristaux de 6H-SiC ont été réalisées sur l'implanteur ou l'accélérateur du CSNSM. Les irradiations avec des ions lourds de haute énergie ont été effectuées au GANIL. L'évolution du profil des ions implantés et de la structure du cristal a été étudiée par RBS et canalisation. Des informations complémentaires ont été apportées par la spectroscopie d'absorption UV-visible. Les implantations d'ions de basse énergie à température ambiante conduisent à l'endommagement rapide du cristal. Par contre, une élévation de la température d'implantation (600 °C) permet de conserver un faible taux de désordre dans le cristal. Les irradiations avec des ions lourds de haute énergie n'endommagent pas les cristaux de SiC mais au contraire, elles provoquent une guérison du désordre créé préalablement par l'implantation d'ions I de basse énergie. Ces marqueurs d'iode ne diffusent pas lors d'irradiations avec des ions lourds de basse ou de haute énergie à température ambiante ou à 600 °C. Cependant, une diffusion des ions Cs a été observée lors d'un recuit thermique post-implantation à 1300 °C, température à laquelle le cristal qui comportait une couche amorphe étendue commence à retrouver une structure monocristalline.

This thesis deals with molecular alloys mechanosynthesis obtained by co-milling. The compounds studied are used as excipients in pharmaceutical industry. It concerns lactose, trehalose and mannitol. We show that co-milling of crystalline powders of trehalose/mannitol and of lactose/mannitol generate, for some composition range, homogeneous glass solutions. These studies show, from original way, the influence of milling temperature regard to glass transition temperature (Tg) on the nature of the final states obtained by milling : we have changed the glass transition temperature by changing the chemical composition of molecular alloys. The effect of milling on the pure compounds has also been studied. Ball milling of lactose and trehalose below their Tg induces a direct crystal - > glass transformation. Ball milling above Tg of mannitol ß, stable form, and of mannitol d, the most metastable form, induces a polymorphic transformation towards mannitol a, which is of intermediate stability. These results show that states obtained under ball milling are stationary states rather than thermodynamic equilibrium states. Moreover, our investigations permit to determine some specific properties of the systems studied which are not accessible from liquid states. We have characterised in details mutarotation of lactose. Binary phase diagrams trehalose/mannitol and lactose/mannitol are also proposed. All the results have been obtained by XRD, NMR, DSC and TGA experiments.; Ce mémoire est consacré à la mécanosynthèse d'alliages moléculaires par cobroyage. Les composés étudiés sont des composés utilisés comme excipients dans l'industrie pharmaceutique. Il s'agit plus particulièrement du lactose, du tréhalose et du mannitol. Nos investigations ont montré la possibilité d'obtenir, sur une certaine gamme de concentrations, des solutions solides vitreuses homogènes tréhalose/mannitol et lactose/mannitol par cobroyage des poudres cristallines correspondantes. Elles ont aussi permis de montrer de manière originale l'influence de la position relative de la température de broyage par rapport à la température de transition vitreuse (Tg) sur la nature des états obtenus par broyage en faisant varier la zone de Tg des alliages par changement de composition chimique. Les transformations sous broyage des composés purs ont également été étudiées en détail. Le broyage du lactose et du tréhalose en dessous de Tg est à l'origine d'une transformation directe cristal -> verre à l'état solide. Par contre, le broyage des formes cristallines d et ß? du mannitol au dessus de Tg engendre une transformation polymorphique vers la forme cristalline a de stabilité intermédiaire montrant, de ce fait, le caractère stationnaire des états atteints au cours de ce type de transformations. De plus, nos investigations ont permis de déterminer un certain nombre de propriétés spécifiques de ces systèmes inaccessibles à partir des liquides purs et des mélanges liquides. La mutarotation du lactose a pu être caractérisée en détail. Les diagrammes de phases des mélanges lactose/mannitol et tréhalose/mannitol ont pu être établis. L'ensemble de ces résultats a été obtenu par DRX, RMN, DSC et ATG.

International audience; Defect production and amorphization due to energetic uranium recoils in zircon (ZrSiO$_4$), which is a promising ceramic nuclear waste form, is studied using molecular dynamics simulations with a partial charge model. An algorithm that distinguishes between undamaged crystal, crystalline defects and amorphous regions is used to develop a fundamental understanding of the primary damage state. The damage consists of under-coordinated Zr and polymerised Si leading to amorphization and phase separation on a nanometer scale into Zr-and Si-rich regions. This separation could play an important role in the experimentally observed formation of nanoscale ZrO$_2$ in ZrSiO$_4$ irradiated at elevated temperatures. The observed amorphisation and the associated volume expansion have the potential to enhance leaching of cations by providing diffusion pathways for cations and water molecules.

Angle-dispersive monochromatic x-ray diffraction spectra from a perfect single-grain AlPdMn quasicrystal have been obtained under hydrostatic pressure in a diamond anvil cell up to 35 GPa. More than 50 Bragg peaks with sharpness comparable to that at ambient conditions were observed up to the maximum pressure, indexed and used to measure the hypercubic 6D lattice parameter, providing the most accurate determination of the equation of state in this pressure range to date. Within the instrumental resolution, the absence of broadening of the diffraction peaks indicates the absence of structural transition and/or unusual configurational entropy change expected from previous studies through pressure-induced amorphization or phason defects.

Reactive ion-beam sputtering has been used to prepare iron nitride over a wide composition range. It is found that the samples deposited at room temperature exhibit amorphous phase in the composition range from $12\phantom{\rule{0.3em}{0ex}}\mathrm{at}.\phantom{\rule{0.2em}{0ex}}%$ nitrogen to $23\phantom{\rule{0.3em}{0ex}}\mathrm{at}.\phantom{\rule{0.2em}{0ex}}%$ nitrogen. For samples deposited at liquid nitrogen temperature the system is amorphous up to $35\phantom{\rule{0.3em}{0ex}}\mathrm{at}.\phantom{\rule{0.2em}{0ex}}%$ nitrogen. Amorphization can be understood in terms of a frustration in the system due to a competition between $\ensuremath{\alpha}$ and $\ensuremath{\epsilon}$ phases. Kinetic constraints are also found to play a role in the amorphization process. M\"ossbauer measurements suggest that the local order in the amorphous phase consists of a mixture of $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Fe}$--like and $\ensuremath{\epsilon}\text{\ensuremath{-}}{\mathrm{Fe}}_{3}\mathrm{N}$--like short-range orders. On the iron rich side the amorphous phase exhibits two-step crystallization, with a primary $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Fe}$ phase precipitating out in the first step. Around $22\phantom{\rule{0.3em}{0ex}}\mathrm{at}.\phantom{\rule{0.2em}{0ex}}%$ nitrogen the system exhibits a single step isomorphous transformation to $\ensuremath{\epsilon}$ phase. Thus, amorphous iron nitride phases exhibit behavior very similar to the conventional transition metal-metalloid amorphous alloys. In the remaining composition range nanocrystalline phases are formed. The amorphous magnetic iron nitride phases are expected to have distinct advantages over their crystalline counterparts in terms of soft magnetic applications.

The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Métallurgie Physique of the Direction de l'Energie Nucléaire in Saclay are presented in this Habilitation thesis.These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica.The second part tackles the modelling of displacement cascades created by Α disintegration recoil nuclei in various crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects.Finally the prospects of these studies are discussed.; Dans ce mémoire d'Habilitation à Diriger des Recherches sont présentées les études menées par Jean-Paul Crocombette entre 1996 et 2005 au Service de Recherches de Métallurgie Physique de la Direction de l'Energie Nucléaire à Saclay. Le travail se place dans le cadre général des recherches en sciences des matériaux sur le vieillissement des oxydes d'intérêt pour le nucléaire, en particulier sous irradiation. Dans ce contexte, on a mené des études de modélisation à l'échelle atomique en abordant deux ingrédients élémentaires du vieillissement sous irradiation : les défauts ponctuels et les cascades de déplacements à l'aide de deux techniques de simulation complémentaires : les calculs de structure électronique dits ab initio et la dynamique moléculaire en potentiels empiriques.La première partie du mémoire est consacrée aux études de défauts ponctuels : auto-défauts (lacune, interstitiel) ou dopants hétéro-atomiques. Après avoir rapidement rappelé l'énergétique des défauts ponctuels dans les oxydes, les particularités des calculs de défauts et la précision que l'on peut attendre de ce type de calcul, on présente les résultats obtenus sur le dioxyde d'uranium, l'oxygène dans l'argent et la silice amorphe.La deuxième partie du mémoire s'intéresse aux cascades de déplacements atomiques créées par les noyaux de recul des désintégrations Α dans diverses matrices cristallines de stockage des actinides radioactifs. Les calculs de cascade donnent des éléments pour comprendre les mécanismes d'amorphisation sous irradiation de ces oxydes. On a ainsi prédit que l'amorphisation dans le zircon a lieu dans le coeur de chaque trace alors que dans le zirconate de lanthane, l'amorphisation se produit par accumulation de défauts ponctuels.En fin de mémoire, on présente les perspectives ouvertes par ces études et les travaux en cours.

The studies done by Jean-Paul Crocombette between 1996 and 2005 in the Service de Recherches de Métallurgie Physique of the Direction de l'Energie Nucléaire in Saclay are presented in this Habilitation thesis.These works were part of the material science researches on the ageing, especially under irradiation, of oxides of interest for the nuclear industry. In this context simulation studies at the atomic scale were performed on two elementary components of ageing under irradiation : point defects and displacement cascades ; using two complementary simulation techniques : ab initio electronic structure calculations and empirical potential molecular dynamics. The first part deals with point defects : self defects (vacancies or interstitials) or hetero-atomic dopants. One first recalls the energetics of such defects in oxides, the specific features of defects calculations and the expected accuracy of these calculations. Then one presents the results obtained on uranium dioxide, oxygen in silver and amorphous silica.The second part tackles the modelling of displacement cascades created by Α disintegration recoil nuclei in various crystalline matrices for actinide waste disposal. Cascade calculations give access to the amorphization mechanisms under irradiation of these materials. One thus predicts that the amorphization in zircon takes place directly in the tracks whereas in lanthanum zirconate, the amorphization proceeds through the accumulation of point defects.Finally the prospects of these studies are discussed.; Dans ce mémoire d'Habilitation à Diriger des Recherches sont présentées les études menées par Jean-Paul Crocombette entre 1996 et 2005 au Service de Recherches de Métallurgie Physique de la Direction de l'Energie Nucléaire à Saclay. Le travail se place dans le cadre général des recherches en sciences des matériaux sur le vieillissement des oxydes d'intérêt pour le nucléaire, en particulier sous irradiation. Dans ce contexte, on a mené des études de modélisation à l'échelle atomique en abordant deux ingrédients élémentaires du vieillissement sous irradiation : les défauts ponctuels et les cascades de déplacements à l'aide de deux techniques de simulation complémentaires : les calculs de structure électronique dits ab initio et la dynamique moléculaire en potentiels empiriques.La première partie du mémoire est consacrée aux études de défauts ponctuels : auto-défauts (lacune, interstitiel) ou dopants hétéro-atomiques. Après avoir rapidement rappelé l'énergétique des défauts ponctuels dans les oxydes, les particularités des calculs de défauts et la précision que l'on peut attendre de ce type de calcul, on présente les résultats obtenus sur le dioxyde d'uranium, l'oxygène dans l'argent et la silice amorphe.La deuxième partie du mémoire s'intéresse aux cascades de déplacements atomiques créées par les noyaux de recul des désintégrations Α dans diverses matrices cristallines de stockage des actinides radioactifs. Les calculs de cascade donnent des éléments pour comprendre les mécanismes d'amorphisation sous irradiation de ces oxydes. On a ainsi prédit que l'amorphisation dans le zircon a lieu dans le coeur de chaque trace alors que dans le zirconate de lanthane, l'amorphisation se produit par accumulation de défauts ponctuels.En fin de mémoire, on présente les perspectives ouvertes par ces études et les travaux en cours.

7 pages, 5 figures.-- PACS: 64.70.Dv; 81.30.Fb; 61.80.Ba; 78.66.Fd; 61.82.Fk, Laser-induced melting and resolidification of single-crystalline indium phosphide (InP) upon irradiation with 150 fs laser pulses at 800 nm has been investigated by means of real-time-reflectivity measurements with subnanosecond time resolution. Melting of the surface is observed to occur very rapidly on a time scale shorter than our experimental resolution while the lifetime of the liquid phase is several tens of nanoseconds. As a result of the subsequent rapid solidification process, a thin layer of amorphous material with a thickness of several tens of nanometers is formed on the surface. The formation of this amorphous layer has been observed for every fluence above the melting and below the ablation threshold. The evolution of the reflectivity has been modeled for several different solidification scenarios and compared to the experimental results. This comparison shows that solidification proceeds interfacially from the solid interface towards the surface. A lower limit for the critical solid-liquid interface velocity for amorphization in this compound semiconductor has been estimated to be in the range of 1–4 m/s., This work has been partially supported by the EU in the frame of the TMR Project XPOSE (Grant No. HPRN-CT- 2000-00160). S.M.W. acknowledges the funding in the frame of the same project. J.B. acknowledges the funding of the CSIC through a contract in the frame of the I3P programme (Ref. I3P-PC2002), co-funded by the European Social Fund.

Smectite is a major component of bentonite, a material considered for engineered barriers in high level nuclear wastes repositories (HLNWR). In order to predict the long-term performance of the bentonite, various physical and chemical factors such as, e.g., thermal gradient, redox potential or mechanical stresses are currently considered. By contrast, little is known about radiation effects in smectite, although it might affect the properties of this mineral through cumulative radiation damages produced by ionizing radiations. The present study focuses on radiation damage in montmorillonite considered herein as a simplified model of bentonite. Two reference clays have been selected, one from Liaoning (China, CHI), containing native radiation-induced defects, and the other (called MX) separated from the MX80 reference bentonite (Wyoming, USA). They are distinguished by layer composition, particularly iron content (1 % and 4 % for CHI and MX, respectively). Radiation effects have been studied by combining X-ray diffraction, Fourier transform infrared spectroscopy, Electron Paramagnetic Resonance (EPR) and Mössbauer spectroscopies. Ionizing irradiation induces two main effects. First, several paramagnetic point defects are identified as trapped holes located on oxygen atoms of the smectite structure. These defects are characterized by different thermal stabilities, according to annealing experiments. Their creation is limited by saturation curve with maximum damage around 100 MGy. The response of the two montmorillonites is different in terms of nature and production of point defects, indicating a role of layer composition and structural precursors. Besides, EPR and Mössbauer results show substantial modifications of the oxidation state of structural iron, which are sample and dose-dependent. Irradiation induces reduction and oxidation of iron in CHI and MX samples, respectively. Moreover, physico-chemical treatments show that intensity of redox effects varies significantly with the nature of the interlayer cation and less with the interlayer water content. The radiation effects in MX are expected to strongly modify the layer charge of the montmorillonite owing to the production of positive holes and oxidized iron. This is confirmed with the variations of cationic exchange capacity with He ion irradiation. Amorphization absorbed dose was measured for electronic (TEM) and ionic (ions Kr+) radiations. It was found to vary with the nature of interlayer cations and density charge. Results will be compared with data on of radiation effects in montmorillonite. Discussion will focus on the evolution and reversibility of smectite surface properties relevant for HLNWR.; Les smectites sont des matériaux envisagés pour le stockage des déchets radioactifs en tant que barrière ouvragée et encaissant géologique en raison de leurs propriétés physiques et chimiques particulières. Dans ce contexte, il est important de connaître leur comportement sous irradiations afin de pouvoir estimer la sûreté et la durabilité de l'ouvrage de stockage. Pour cette étude, deux montmorillonites ont été choisies. L'une des argiles provient de la province de Liaoning, en Chine (CHI) et présente la particularité de contenir des défauts d'irradiation stables. La seconde smectite (notée MX) a été extraite de la bentonite de référence méthodologique MX-80 et purifiée à l'aide de différentes techniques chimiques. La spectroscopie par Résonance Paramagnétique Électronique (RPE) a permis d'identifier plusieurs défauts d'irradiations qui se différencient par leur stabilité thermique et leurs caractéristiques RPE. Tous ces défauts peuvent être décrit comme des trous localisés sur une orbitale d'un oxygène lié à un silicium dans le feuillet argileux. Leur concentration augmente avec la dose jusqu'à atteindre une valeur de saturation, mais des différences sont observées entre les deux échantillons. La production de défauts ponctuels est également sensible au type de rayonnements et à la composition de l'espace interfoliaire (nature du cation compensateur, quantité d'eau interfoliaire). L'utilisation conjuguée de la RPE et de la spectroscopie Mössbauer a permis de mettre en évidence deux effets d'irradiation sur le fer structural. La montmorillonite MX purifiée est oxydée alors que la montmorillonite de Chine et la montmorillonite MX non déferrifiée sont réduites. Les irradiations modifient également l'environnement du fer structural. L'intensité du changement d'état d'oxydation dépend du type de rayonnement et de la nature du cation interfoliaire. En revanche, l'influence de l'eau interfoliaire semble être secondaire. Enfin, une variation de la Capacité d'Échange Cationique en fonction de la teneur en fer trivalent a été enregistrée. L'amorphisation de la montmorillonite MX a également été étudiée en fonction de la température. Elle dépend du rayonnement et de la nature du cation interfoliaire. Une dépendance de la dose maximale d'amorphisation en fonction de la masse du cation a été mise en évidence pour l'irradiation avec des ions Krypton.

Smectite is a major component of bentonite, a material considered for engineered barriers in high level nuclear wastes repositories (HLNWR). In order to predict the long-term performance of the bentonite, various physical and chemical factors such as, e.g., thermal gradient, redox potential or mechanical stresses are currently considered. By contrast, little is known about radiation effects in smectite, although it might affect the properties of this mineral through cumulative radiation damages produced by ionizing radiations. The present study focuses on radiation damage in montmorillonite considered herein as a simplified model of bentonite. Two reference clays have been selected, one from Liaoning (China, CHI), containing native radiation-induced defects, and the other (called MX) separated from the MX80 reference bentonite (Wyoming, USA). They are distinguished by layer composition, particularly iron content (1 % and 4 % for CHI and MX, respectively). Radiation effects have been studied by combining X-ray diffraction, Fourier transform infrared spectroscopy, Electron Paramagnetic Resonance (EPR) and Mössbauer spectroscopies. Ionizing irradiation induces two main effects. First, several paramagnetic point defects are identified as trapped holes located on oxygen atoms of the smectite structure. These defects are characterized by different thermal stabilities, according to annealing experiments. Their creation is limited by saturation curve with maximum damage around 100 MGy. The response of the two montmorillonites is different in terms of nature and production of point defects, indicating a role of layer composition and structural precursors. Besides, EPR and Mössbauer results show substantial modifications of the oxidation state of structural iron, which are sample and dose-dependent. Irradiation induces reduction and oxidation of iron in CHI and MX samples, respectively. Moreover, physico-chemical treatments show that intensity of redox effects varies significantly with the nature of the interlayer cation and less with the interlayer water content. The radiation effects in MX are expected to strongly modify the layer charge of the montmorillonite owing to the production of positive holes and oxidized iron. This is confirmed with the variations of cationic exchange capacity with He ion irradiation. Amorphization absorbed dose was measured for electronic (TEM) and ionic (ions Kr+) radiations. It was found to vary with the nature of interlayer cations and density charge. Results will be compared with data on of radiation effects in montmorillonite. Discussion will focus on the evolution and reversibility of smectite surface properties relevant for HLNWR., Les smectites sont des matériaux envisagés pour le stockage des déchets radioactifs en tant que barrière ouvragée et encaissant géologique en raison de leurs propriétés physiques et chimiques particulières. Dans ce contexte, il est important de connaître leur comportement sous irradiations afin de pouvoir estimer la sûreté et la durabilité de l'ouvrage de stockage. Pour cette étude, deux montmorillonites ont été choisies. L'une des argiles provient de la province de Liaoning, en Chine (CHI) et présente la particularité de contenir des défauts d'irradiation stables. La seconde smectite (notée MX) a été extraite de la bentonite de référence méthodologique MX-80 et purifiée à l'aide de différentes techniques chimiques. La spectroscopie par Résonance Paramagnétique Électronique (RPE) a permis d'identifier plusieurs défauts d'irradiations qui se différencient par leur stabilité thermique et leurs caractéristiques RPE. Tous ces défauts peuvent être décrit comme des trous localisés sur une orbitale d'un oxygène lié à un silicium dans le feuillet argileux. Leur concentration augmente avec la dose jusqu'à atteindre une valeur de saturation, mais des différences sont observées entre les deux échantillons. La production de défauts ponctuels est également sensible au type de rayonnements et à la composition de l'espace interfoliaire (nature du cation compensateur, quantité d'eau interfoliaire). L'utilisation conjuguée de la RPE et de la spectroscopie Mössbauer a permis de mettre en évidence deux effets d'irradiation sur le fer structural. La montmorillonite MX purifiée est oxydée alors que la montmorillonite de Chine et la montmorillonite MX non déferrifiée sont réduites. Les irradiations modifient également l'environnement du fer structural. L'intensité du changement d'état d'oxydation dépend du type de rayonnement et de la nature du cation interfoliaire. En revanche, l'influence de l'eau interfoliaire semble être secondaire. Enfin, une variation de la Capacité d'Échange Cationique en fonction de la teneur en fer trivalent a été enregistrée. L'amorphisation de la montmorillonite MX a également été étudiée en fonction de la température. Elle dépend du rayonnement et de la nature du cation interfoliaire. Une dépendance de la dose maximale d'amorphisation en fonction de la masse du cation a été mise en évidence pour l'irradiation avec des ions Krypton.

Plus de la moitié des composés pharmaceutiques sont sujets au phénomène de polymorphisme ou de pseudo-polymorphisme, c'est-à-dire qu'ils existent sous plus d'une structure cristalline (polymorphes vrais, hydrates, solvates) ou comme produit plus ou moins amorphe. À ce titre, il présentent, à l'état solide, des caractéristiques physico-chimiques (point de fusion, point de transition, plasticité, solubilité, hygroscopicité, réactivité chimique) différentes, qui à leur tour peuvent avoir des incidences sur les propriétés pharmaco-techniques et biopharmaceutiques des principres actifs ou des excipients (comprimabilité, vitesse de dissolution, biodisponibilité, activité pharmacologique, stabilité). Considérant une substance chimiquement bien définie, on peut se trouver en présence de tel ou tel état cristallin ou forme polymorphe en fonction de la source d'approvisionnement ou simplement du lot en question. Mais il se peut aussi que l'on observe des changements de propriétés pharmaco-techniques ou biopharmaceutiques dus à des phénomènes de transformations polymorphes, selon le traitement mécanique, thermique ou les conditions environnementales (intervention d'un solvant, désolvatation) qu'a subi le produit ou la forme médicamenteuse. Le présent article passe en revue les aspects fondamentaux liés à ces phénomènes et présente des exemples de la littérature, classiques ou récents, de transformations observées lors d'un broyage ou d'une trituration, d'une compression, de la mise en suspension d'un principe actif, d'une granulation, de tests de dissolution ou de libération, d'essais de stabilité, d'une nébulisation, d'une lyophilisation ou encore de la préparation d'adsorbats ou de complexes.

International audience; 6H- and 4H-SiC n-type layers were amorphised by multiple Al implantations at room temperature, in order to study the annealing process. This paper deals with the influence of specific annealing conditions, such as furnace atmosphere and heating rate, on SiC reordering and Al profile. Below a certain deposited nuclear energy, solid phase epitaxy (SPE) is possible and leads to recrystallisation under precise conditions (high heating rate, silicon partial pressure prescribed). Above that, partial reordering is only observed for 4H-SiC layers, and leads to some increasing roughness, even though annealing has proven to be efficient for avoiding surface impairment (due to a specific cleaning process). Some Al oscillations have been observed near the junction in case of SPE, whereas a flat homogeneous profile is formed in amorphised layers. (C) 2001 Elsevier Science B.V. All rights reserved.

Ion beam induced crystallisation (IBIC) of preamorphised surface layers of 6H–SiC has been stimulated by high dose Al implantation (0.3−3×10 17 cm −2 ) at elevated temperatures (300–500 °C) Randomly oriented 3C–SiC nanocrystals with diameters between 2 and 25 nm are formed depending on the implantation parameters as proved by XRD and XTEM. Spreading resistance measurements have been performed at bevelled as-implanted and annealed (1500 °C, 10 min) samples in order to study the electrical behaviour of the Al acceptors in the nanocrystalline layer. Reference experiments have been carried out on single crystalline 6H–SiC wafers implanted at the similar conditions. It has been found that in the as-implanted state Al doped fine granular SiC has much lower spreading resistance than the corresponding single crystalline SiC. Only minor differences have been observed between the nano- and single crystalline samples after annealing.

Not available, Des alliages MT-C avec MT = Ni, Co ou Mn ont été élaborés par pulvérisation cathodique en mode radiofréquence. Leur stabilité thermique et l'évolution de leurs structures sont suivies par analyse enthalpique différentielle, diffraction des rayons X et microscopie électronique à transmission in-situ. Les principaux résultats sont les suivants: système Ni-C: des alliages essentiellement cristallins Ni1-xCx avec 0,10 x 0,67 ont été élaborés. Le carbure Ni3C à sites octaédriques est toujours présent. Le comportement thermique du dépôt Ni0, 33C0,67 laisse supposer la présence d'une phase amorphe métallique dont l'un des produits de cristallisation est Ni3C. Système Co-C: des alliages amorphes Co1-xCx avec 0,07 x 0,42 ont été élaborés. Leur cristallisation montre qu'il y a compétition entre le carbure à sites octaédriques Co2C et le carbure à sites prismatiques Co3C pour x < 0,34. Pour x > 0,34, le carbure à sites octaédriques devient majoritaire. Système Mn-C: des alliages amorphes Mn1-xCx avec 0,20 x 0,37 ont été, pour la première fois à notre connaissance, obtenus. Le suivi de leur cristallisation montre l'existence d'une concentration remarquable en carbone xr = 0,34, en dessous de laquelle les carbures obtenus sont à nappes prismatiques (CNP) et au dessus de laquelle se forme un nouveau carbure Mn2C à sites octaédriques, dont nous avons déterminé la structure et les paramètres de maille. Parmi les carbures CNP, nous identifions Mn5C2 et nous constatons des intercroissances entre ce carbure et Mn3C et/ou d'autres carbures CNP. Nous mettons en évidence des carbures métastables CNP de structures : périodiques correspondant à la formule Mn2n+1Cn. Ainsi deux nouveaux carbures Mn7C3 et Mn9C4 sont identifiés. Ce type de structure conduit à un carbure limite Mn2C à nappes prismatiques également observé ; apériodiques à une dimension de formule Mn1-x'Cx'. En ce qui concerne la cristallisation des alliages amorphes, la composition x = 0,33 semble remarquable quelque soit le système exploré et traduit vraisemblablement un changement de l'ordre local dans l'état amorphe.

Not available, Les verres métalliques sont intrinsèquement le siège de transformations structurales très importantes qui constituent l'une des raisons fondamentales de leur fragilisation; ce qui freine leur utilisation industrielle. Afin de comprendre ces effets, l'objectif principal de cette étude est de décrire les structures atomiques et leurs évolutions par des mécanismes clairs et maitrisables. Nous proposons d'abord un modèle bidimensionnel d'amorphisation fondé sur des transformations topologiques subies par une structure de référence. Ensuite, nous traitons le cas plus réaliste d'un modèle tridimensionnel de l'alliage ni#8#1b#1#9. Ce modèle permet de souligner les paramètres influant sur les phénomènes de relaxation structurale. Nous attribuons la fragilité d'origine expérimentale aux fluctuations de composition chimique dont l'effet revient à appliquer la structure du verre sur celle du cristal le plus proche. Il en résulte une perte de volume libre qui met le réseau amorphe en tension et, par conséquent, est favorable à la propagation de fissures. Pour les compositions étudiées ici, cet effet parait inévitable. Ces simulations utilisent une méthode originale d'optimisation numérique d'usage général. Cet algorithme est particulièrement adapté au parallélisme; une implantation performante sur réseau de stations de travail est décrite dans cette étude. Il est applicable sans difficulté de principe à de nombreux problèmes d'optimisation: problèmes de placement, gestion boursière, commande optimale et bien sur à d'autres types de simulations atomiques en science des matériaux (cristallisation, transitions ordre-désordre, transformation martensitique, etc.)

Comminution, amorphization and surface properties of minerals The comminution of minerals involves energetic, mechanical, structural and superficial phenomena. According to the principles of fracture mechanics, the propagation of cracks can be favoured by lowering the surface free energy of their walls (Rebinder's effect). It is also possible to promote breaking by modifying the electrical surrounding of discontinuities, for example by increasing the surface charge (Westwood's principle). However both these theories give only a partial explanation of experimental facts. Here it is proposed to consider that the elasticity of strongly structured layers of the medium to the solid-liquid interface protects the structure and spreads the stresses. Then, the mineral breaks according to its intrinsic weak strength directions. If the structured layers do not exist (apolar liquids) or are disordered (using hydrogen bond disruptors), the material amorphizes without breaking and the formation of amorphous substances can generate aggregation. The variation of surface properties of minerals resulting from grinding can be described by measuring the dispersive component of the surface free energy ; this measurement is achieved using inverse gas chromatography., La fragmentation des minéraux met en cause des phénomènes énergétiques, mécaniques, structuraux et superficiels. D'après les principes de la mécanique de la rupture, on peut favoriser la propagation des fissures en abaissant l'énergie libre de surface de leurs parois (effet Rebinder). On peut aussi promouvoir la rupture en modifiant l'environnement électrique des discontinuités, par exemple en augmentant la charge superficielle (principe de Westwood). Cependant ces deux théories ne rendent qu'imparfaitement compte des faits expérimentaux. On propose de considérer que l'élasticité des couches de medium fortement structurées à l'interface solide-liquide protège la structure et répartit les contraintes. Alors le minéral se rompt selon les directions de faiblesse qui lui sont propres. Si ces couches structurées n'existent pas (liquide non polaire) ou sont perturbées (à l'aide de rupteurs de liaisons hydrogène), le matériau s'amorphise sans se rompre ; la formation d'amorphes peut conduire à une réagglomération. La mesure de la composante dispersive de l'énergie de surface par Chromatographie gazeuse inverse permet de décrire la variation des propriétés superficielles des minéraux lors du brogage., Papirer Eugène. Fragmentation, amorphisation et propriétés superficielles de minéraux. Comminution, amorphization and surface properties of minerals. In: Sciences Géologiques. Bulletin, tome 46, n°1-4, 1993. Minéraux finement divisés, sous la direction de Jacques Yvon. pp. 35-44.