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In this work, the structure and microstructure of Nd:KY3F10 nanoparticles was probed using X-ray synchrotron diffraction analysis. Rietveld refinement was applied to obtain cell parameters, atomic positions and atomic displacement factors to be compared with the ones found in literature. X-ray line profile methods were applied to determine mean crystallite size and crystallite size distribution. Thermoluminescent (TL) emission curves were measured for different radiation doses, from 0.10 kGy up to 10.0 kGy. Dose-response curves were obtained by area integration beneath the peaks from TL. The reproducibility of the results in this work has shown that this material can be considered a good dosimetric material.

Iron-excess Mn-Zn ferrite nanoparticles were prepared by coprecipitation with sodium hydroxide (NaOH) at different concentrations (0.1, 0.2, 0.5 and 1.0 mol/L). The results of X-ray diffraction (XRD) analysis using Whole Powder Pattern Modeling (WPPM) showed that higher concentrations of NaOH promote crystallite growth and broader dispersion in crystallite sizes. Energy dispersive X-ray spectroscopy indicates that zinc loss is noticeable when [NaOH] ≥ 0.2 mol/L. XRD revealed also a significant less-crystalline phase contribution alongside the main peaks of the nanocrystalline cubic spinel ferrite phase. The less-crystalline fraction is lower for the ferrite obtained with 0.2 mol/L of NaOH, being about 50% and more than 70% for the other samples. Despite of the less-crystalline fraction and the excess of iron, no secondary phases were detected. The Warren curves showed that the concentration of NaOH significantly influences the microstrain in the crystallites, being smaller for the sample obtained with NaOH at 0.2 mol/L. The sample prepared with this condition presented the better properties to be used as magnetic tracer in clinical diagnoses combining small mean crystallite size, low microstrain, which resulted in materials with higher magnetic saturation and high surface charge under blood pH.

Sugar and alcohol industries generate large amount of wastes that could produce ashes of great reactivity with pozzolan properties. The objective of this paper is to evaluate the pozzolanicity of Sugar Cane Straw Ashes (SCSA), thermal treated, at different curing times. Employing Synchrotron X-ray radiation for XRD measurements, scans from 10 ° to 110 ° ( θ - 2 θ setup) allowed the quantification of several phases of the cement pasts through Rietveld analysis. The SCSA substitution of 20% (weight) in Ordinary Portland Cement (OPC) has improved the AFt (Ettringite) formation up to 47% for 90 days curing time. The Portlandite concentration analysis allowed concluding that this addition of SCSA in OPC has caused a delay in the cement setting time. Moreover, the behaviour of the C3S and Calcite contents in both OPC and OPC/SCSA samples were determined by refinement of the XRD pattern using the Rietveld method.

There are many commercially important multiphase materials which contain amorphous phases, such as cement pastes, porcelains, glass-ceramics or pharmaceutical compounds. However, the analysis of amorphous phase(s) within cement matrices that contain high amounts of crystalline phase(s) is a challenge. Here, we report measurements of total scattering data quantitatively analyzed by Pair Distribution Function (PDF) minimization and Rietveld methodology to determine phase compositions including both amorphous and nanocrystalline phase contents in cement-related samples. Furthermore, laboratory techniques were used to complement the sample characterization. In addition to five reference materials, the main phase of calcium aluminate cements, CaAl2O4 hydrated at 50 °C to yield crystalline hydrogarnet, Ca3Al2(OH)12, (43wt%) and nanocrystalline aluminum hydroxide gel, Al(OH)3·0.1H2O (50wt%) was also investigated. The PDF analyses revealed that the hydroxide gel has a gibbsite local structurewith an average particle size close to 5nm. PDF and Rietveld quantitative phase analysis results fully agree. This work has been supported by Spanish MINECO through BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, which is cofunded by FEDER, research grants. R.U.I. acknowledges funding of CNPQ, grant no. 206983/2014-0/SWE. We also thank CELLS-ALBA (Barcelona, Spain) for providing synchrotron beamtime at BL04-MSPDand Dr. Oriol Vallcorba for his assistance during the synchrotron experiment. 2018-07-01

Mullite formation from kaolinite was studied by means of high-temperature in situ powder neutron diffraction by heating from room temperature up to 1370 °C. Neutron diffractometry under this non-isothermal conditions is suitable for studying high-temperature reaction kinetics and to identify short-lived species which otherwise might escape detection. Data collected from dynamic techniques (neutron diffraction, DTA, TGA and constant-heating rate sintering) were consistent with data gathered in static mode (conventional X-ray diffraction and TEM). The full process occurs in successive stages: (a) kaolinite dehydroxylation yielding metakaolinite in the ∼400–650 °C temperature range, (b) nucleation of mullite in the temperature range ∼980–992 to ∼1121 °C (primary mullite) side by side with a crystalline cubic phase (Si-Al spinel) detected in the ∼983–1030 °C temperature interval; (c) growth of mullite crystals from ∼1136 °C, (d) high (or β) cristobalite crystallization at T > ∼1200 °C and (e) secondary mullite crystallization at T > ∼1300 °C. The calculated activation energy for the kaolinite dehydration was 115 kJ/mol; for the mullite nucleation was 278 kJ/mol and for the growth of mullite process was 87 kJ/mol; finally for cristobalite nucleation the calculated apparent activation energy was 481 kJ/mol.

In order to elucidate the mechanism of reaction during the cordierite synthesis a kinetic study has been carried out by means of X-ray diffraction and neutron thermo-diffraction. It was thus possible to elucidate between the reactions leading to the cordierite synthesis and those that gave rise to the undesired phases generated during this process. Depending on the reactants used these reactions are different. The present paper presents results obtained during the cordierite synthesis starting from talc, kaolin and hydromagnesite as reactants. This synthesis from natural raw materials takes place through a complex mechanism that has been described. In this kind of synthesis, at the end of the entire process the obtained cordierite is always accompanied by a second phase: spinel. This is the first time that the presence of the μ-cordierite phase has been observed when the synthesis is carried out in solid state from non-submicronic natural raw materials.

Publicación versión impresa: diciembre de 2008, In-situ monitoring of the changes that take place in the phase composition of cement pastes during accelerated carbonation (100% CO2) for different binders, has been carried out, by taking Neutron Diffraction patterns in parallel with the carbonation experiments. The variation of the intensity of chosen reflections for each phase along the experiment has been used to monitor concentration changes and has supplied data, in real time, for fractional conversion of different phases (Portlandite, Ettringite and CSH gel) of the hydrated cement pastes. Fitting of these results has allowed to make a qualitative approach to the kinetics of the carbonation of the different phases and extracting conclusions on the microstructural changes that takes place during the carbonation of cement pastes., The experiments reported here were done thanks to the beamtime (Exp 5-25-50) granted by the Institute Max von Laue- Paul Langevin (ILL). The authors are especially grateful to the staff of D20. The authors also acknowledge the funding provided by the Spanish MMA through the project n° 005/2006/2-3.1.

The transformation b-a in Mg-substituted Ca3(PO4)2 was studied. The results obtained showed that, contrary to common belief, there is, in the system Mg3(PO4)2–Ca3(PO4)2, a binary phase field where b1a-Ca3(PO4)2 solid solutions coexist. This binary field lies between the single-phase fields of b- and a-Ca3(PO4)2 solid solution in the Ca3 (PO4)2-rich zone of the mentioned system. In the light of the results and the Palatnik–Landau’s Contact Rule of Phase Regions, a corrected phase equilibrium diagram has been proposed. The practical implications of these findings with regard to the synthesis of pure a- and b- Mg-substituted Ca3(PO4)2 powders and to the sintering of related bioceramics with improved mechanical properties are pointed out

Intermetallic compounds in the Al–Ni system were prepared by Self-propagating high-temperature synthesis (SHS). The front high speed in the range of 1–100 mm/s – typical of these processes made necessary the use a very intense synchrotron source (ESRF) coupled to a very fast acquisition system. Finely divided powders of Ni and Al were intimately mixed in a 1:1 mole ratio, and then compressed to form compact cylindrical of the right density to assure a steady combustion front. Diffraction patterns were acquired every 100 ms. As the reaction proceeded, patterns from the preheated, reaction front, post-heated and cooling zones were sampled. The crystal phases appearing were identified. Similarly, reaction mechanisms and nucleation kinetics were established. Also, high speed pyrometers were used to obtain combustion front temperature profiles and its propagation was video recorded. Finally, SEM images were taken to characterize the microstructure of end products.

The hydration behaviour of Ca3Al2O6 ,C a 12Al14O33 and CaAl2O4 with added amorphous silica at 40, 65 and 901C has been studied for periods ranging from 1 to 31 days. In hydrated samples crystalline phases like katoite (Ca3Al2(SiO4)3� x(OH)4x) and gibbsite, Al(OH)3, were identified, likewise amorphous phases like Al(OH)x, calcium silicate hydrates, C–S–H, and calcium aluminosilicate hydrates, C–S–A–H, were identified. The stoichiometry of Ca3Al2(SiO4)3� x(OH)4x (0p3� xp0.334), which was the main crystalline product, was established by Rietveld refinement of X-ray and neutron diffraction data and by transmission electron microscopy.

TiC–WC composites have been obtained in situ by self-propagating high-temperature synthesis (SHS) from a mixture of compacted powders of elemental titanium, tungsten and graphite. The Rietveld method has proved to be a useful tool to quantify the different phases in the reaction and calculate the cell parameters of the solid solution found in the products. The reaction has also been followed in real time by X-ray diffraction at the European Synchrotron Radiation Facility (ESRF ID-11 Materials Science Beamline). The mechanism of the reaction is discussed in terms of the diffusion of liquid titanium to yield titanium carbide with a solid solution of tungsten. The microstructures of the materials obtained by this method are presented.

Composites of TiC and TiB2 were prepared by self-propagating high-temperature synthesis (SHS). Two routes were attempted; from the elements and from a mixture of anatase, boron oxide, graphite and magnesium. The reactions were monitored in situ by synchrotron X-ray diffraction ( lambda = 0. 26102 Angstrom). The powder mixtures were compacted as cylindrical pellets and upon ignition diffraction patterns were collected every 65 ms with a CCD camera. TiC was the first phase to form, followed by TiB2. The reactions take place in time scales of 0.1 s. The temperature profile for the first route was established from the peak position and the known thermal expansion coefficients. The microstructure of the final products was different: particles of 10 mum for the first and submicron for the second. The viability of the second route to produce ceramic powders in a cheaper way was confirmed. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. (Less)

The reaction process to obtain CaZrO3/MgO specimens in the ZrO2–CaO–MgO system from two mixtures of natural and synthetic raw materials were analyzed by neutron thermodiffractometry; differential thermal analysis–thermogravimetry (DTA-TG) also was used. The results from the different techniques provided a complete description of the decomposition and reaction process in the samples and proved that high-temperature neutron diffraction is a powerful tool for analyzing in situ reactions up to 1250°C in both mixtures. In the present work, the evolution of the crystalline phases, the mechanism and temperature of formation of CaZrO3, and the activation energy were properly established in terms of the neutron thermodiffraction study.

Composition and microstructure changes of cement pastes when heating until 620 °C and cooling afterwards have been monitored on site by neutron diffraction. The parameters involved in the study have been the heating ramp, the state of the sample (in block or ground) and the type of cement. The residual state of the samples has also been studied by mercury intrusion porosimetry (MIP) and thermogravimetry analysis (TGA). As a result, it has been possible to monitor the major features of the experiments, i.e., the phases existence domains and their growing and decaying for portlandite, ettringite, calcite, lime, larnite, and hydrated calcium silicate (CSH gel), as well as the loss of free and bounded water during the experiments. In addition, the different residual phases in the matrix depending on the experimental set up have been established, which might have a significant influence in the durability of a concrete after a fire.

Self-propagating high-temperature synthesis (SHS) has been performed in the quaternary Al–Ni–Ti–C system in order to obtain intermetallic–ceramic composites. These kind of reaction synthesis are very fast (linear velocity of the synthesis front is in the range 1–100 mm/s) and the productivity would be very high from the industrial point of view. Nevertheless,this characteristic is a negative point when synthesis mechanism and kinetics must be studied. There are only a few tools with enough time resolution in order to study these kinds of fast reactions. Synchrotron radiation (ESRF,Grenoble) has been employed to follow the reactions in situ on a time-scale of 100 ms. Powder diffraction patterns were recorded in this time-interval using a high-speed CCD camera coupled to an image intensifier X-ray sensitive detector with 10241024 pixels frames. As the reactions proceed patterns from the pre-heated, reaction front,post-heated and cooling zones of the reaction were sampled. The phases occurring during the reactions were identified and information of the reaction mechanism and the nucleation kinetics were obtained. SEM was used to characterize the final microstructure. # 2002 Published by Elsevier Science Ltd.

The reaction mechanism that takes place in ZrSiO4–Mg Ca(CO3)2 mixtures was studied in air up to 13001C by collecting neutron diffraction patterns during the heating ramp. Neutron diffraction intensities were used to monitor and establish the mechanism of reaction that occurs in successive stages. (a) MgCa(CO3)2 decomposition yielding MgO and CaCO3; (b) CaCO3 decomposition; (c) reactions between CaO, MgO, and ZrSiO4 involving the formation of phases such as: tetragonalZrO2, a-Ca2SiO4, and Ca3MgSi2O8, some of them acting as transitory phases; and (d) formation of CaZrO3. The results obtained by this technique agree with data obtained by differential thermal analysis and thermogravimetry. The final product has a porous structure, due to the release of CO2, with a very narrow pore size distribution (E1 lm). This open-porosity can be controlled by tailoring the reaction sintering process. # 2002 Elsevier Science (USA)

Synchrotron energy-dispersive diffraction has been employed to monitor the hydration of CaAl2O4. Diffraction intensities of neat pastes, with a water-to-solid ratio (ws) of 0.4, were employed to follow the hydration progress at temperatures ranging from 60°C to 90°C. The hydration rate of CaAl2O4 increased with temperature according to a three-dimensional diffusion-controlled model expressed by [1 − (1 − α)13]2 = kt, with reaction constants k ranging from 7.4 × 10−1 min−1 at 70°C to 3.2 × 10−2 min−1 at 90°C. The activation energy was 84 kJ mol−1 K−1. The onset of Ca3Al2O6.6H2O diffraction peaks from CaAl2O4, at 90°C, was within 3 min whereas at 60°C it was after 8 min. The results show that Ca2Al2O5.8H2O is the intermediate in the hydration of CaAl2O4 to Ca3Al2O6.6H2O, in all cases. The hydration is explained in solid-state kinetics terms, Ca2Al2O5.8H2O playing a key role in CaAl2O4 hydration for triggering the hydration to form Ca3Al2O6.6H2O.

The thermal decomposition of ettringite in the presence of water and impurity gypsum has been observed by energy-dispersive synchrotron X-ray diffraction and FTIR spectroscopy. The decomposition occurs rapidly at 114 °C to produce a monosulfate, with 0.96 nm interlayer spacing, and bassanite. The thermal expansion of ettringite from 70 to 110 °C is 42 × 10–6 K–1 in the a direction and 22 × 10–6 K–1 in the c direction. The gypsum acts as a transient intermediate in the decomposition. The mechanism of this rapid decomposition is discussed.

Zirconia is an important component material for several industrial applications. In these studies we have used intense radiation sources, primarily synchrotron radiation, to shed new light on the properties of zirconia and its synthesis via existing industrial routes. Certain “static” techniques have been used to probe the atomic structure of precursor compounds used in the synthesis of zirconia, whereas time-resolved techniques were required to dynamically capture the various calcination stages during the heating section of the synthesis cycle. Finally the important tetragonal to monoclinic zirconia transformation during cooling was studied in detail using time resolved energy dispersive diffraction. Altogether what emerges is a new unfolding story on the various stages of zirconia synthesis, in which synchrotron radiation has played a vital role.

A rapid in situ diffraction technique, synchrotron radiation–energy dispersive diffraction, has been used to obtain direct information on the kinetics of the tetragonal-to-monoclinic transformation temperatures for zirconia synthesized by heating the hydroxide up to temperatures between 900 and 1300 °C. In all cases the monoclinic phase appears only during the cooling stage. The effects of chemical (hydroxide preparation–pH) and heat treatments (top dwell temperature and dwell time) have been investigated. The transformation temperature increases with both top temperature and dwell time. For the lesser heat treatments (generally temperatures 1000) the low-pH material displays the higher transformation temperatures. These data do now give reliable indications on how to design a required metastability into the final room temperature product.

Neutron [l-31 and X-ray [4,5] techniques have been used to study the formation of zirconia from zirconium hydroxide. Synchrotron radiation can now, using dynamic energy-dispersive diffraction (DEDD), shed light on the kinetics of both the hydroxide-to-oxide crystallization and tetragonal-to- monoclinic conversion. Furthermore, different rates of crystallization and conversion have been linked [5] to the preparative conditions of the hydroxide; in particular the final pH of the solution coexisting with the precipitate of zirconium hydroxide. The results here represent an important extension of our dynamic studies. The special advantage of neutron thermodiffractometr!~ (NTD) [6] is that the high scattering/diffraction background associated with incoherent scattering by hydrogen is an effec- tive monitor of the chemical composition of the hydroxide; the scattering background reflects the amount of hydrogen-containing species in the sam- ple. Zirconium hydroxide can be considered as an intermediate between a hydroxide and a hydrated oxide [7]. One possible model [H] depicts the hydroxide as an open polymer in which individual units are linked by double h!.droxy bridges (Fig. 1). Clearly, if such a model were essentially correct, NTD would be expected to monitor the combined loss of H,O and OH during calcination. Zirconium hydroxides were prepared under care- fully controlled conditions [9] at pH 8.37 and 10.35, since these preparations display extremes of crystal- lization behaviour [5]. Aqueous ammonia solution was added to an aqueous suspension of zirconium basic sulphate (Magnesium Elektron Ltd, Man- chester, UK) to the desired pH. the suspension was filtered and washed with distilled water. The sam- ples were dried at 130 "C to produce zirconium hydroxide. Thermal analysis was carried out in both samples at a heating rate of 2 "C min-' in static air. Synchro- tron experiments were undertaken at Daresbury Laboratory, station 9.7, using pellets of thickness approximately 0.5 mm. The pellets were heated at a rate of 20 "C min-' to 400 "C, and the ramp then reduced to 5

Synchrotron energy-dispersive diffraction has been employed to monitor the hydration of CaAl2O4. Diffraction intensities of neat pastes, with a water-to-solid ratio (ws) of 0.4, were employed to follow the hydration progress at temperatures ranging from 60°C to 90°C. The hydration rate of CaAl2O4 increased with temperature according to a three-dimensional diffusion-controlled model expressed by [1 − (1 − α)13]2 = kt, with reaction constants k ranging from 7.4 × 10−1 min−1 at 70°C to 3.2 × 10−2 min−1 at 90°C. The activation energy was 84 kJ mol−1 K−1. The onset of Ca3Al2O6.6H2O diffraction peaks from CaAl2O4, at 90°C, was within 3 min whereas at 60°C it was after 8 min. The results show that Ca2Al2O5.8H2O is the intermediate in the hydration of CaAl2O4 to Ca3Al2O6.6H2O, in all cases. The hydration is explained in solid-state kinetics terms, Ca2Al2O5.8H2O playing a key role in CaAl2O4 hydration for triggering the hydration to form Ca3Al2O6.6H2O.

The synthesis of DPA-VPI-5 and TBA-VPI-5 and their phase transformation to AlPO 4 -8 have been studied by X-ray diffraction in situ. The synchrotron radiation-energy dispersive diffraction is shown to be able to monitor these two fast reactions in real time. The results indicate that nucleation may occur already during the aging of the synthesis gel. The different rates of transformtion of DPA-VPI-5 and TBA-VPI-5 show that the microstructure of the two materials is different.

The structural phase transitions and electrical properties of Ti3O5, the pseudobrookite series LixTi3 –xO5 and MgxTi3 –xO5, and of V3O5 structure type CrTi2O5 have been studied by high-temperature X-ray diffraction, differential scanning calorimetry, and d. c. conductivity measurements. Ti3O5 undergoes a complex transformation between 440 and 515 K from semiconducting α-Ti3O5 to metal-like β′-Ti3O5 with orthorhombic pseudobrookite structure. The intermediate formation of the monoclinic β-Ti3O5 polymorph involves a martensitic transition at 467 K. The following continuous β- to β′-type transition is accompanied by a small polaron order–disorder process. In the series LixTi3 –xO5 and MgxTi3 –xO5 the pseudobrookite-related phases are stabilised. Electrical conductivities are as high as 170 S cm–1 at 1073 K for CrTi2O5. The materials of the MgxTi3 –xO5 series and CrTi2O5 are promising candidates for anodes in solid-oxide fuel cells.

Partially deuterated Ca3Al2(SiO4)y(OH)12−4y–Al(OH)3 mixtures, prepared by hydration of Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7) and CaAl2O4 (CA) phases in the presence of silica fume, have been characterized by 29Si and 27Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca3Al2(OH)12 and Al(OH)3 phases were detected. From the quantitative analysis of 27Al NMR signals, the Al(OH)3/Ca3Al2(OH)12 ratio was deduced. The incorporation of Si into the katoite structure, Ca3Al2(SiO4)3−x(OH)4x, was followed by 27Al and 29Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of 27Al MAS–NMR components associated with Al(OH)6 and Al(OSi)(OH)5 environments. The 29Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C–S–H and C–A–S–H for short. From 29Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures., This research was partially supported by MCYT under the project MAT-2006-12749-C02-01 and MAT-2004-04923-CO2-01. Neutron diffraction data were acquired at the SINQ (experiment number no II/025-18, Swiss Spallation Neutron Source-Paul Scherer Institute Villigen, Suisse). We thank Dr. D. Sheptiakov for the experimental assistance in collecting the ND data.

International audience; The ability of gypsum, a common sulfate mineral, to host arsenic atoms in its crystalline structure, is demonstrated through experimental structural studies of the solid solutions formed upon synthetic coprecipitation of gypsum (CaSO4 ·2H2O) and arsenic. Neutron and X-ray diffraction methods show an enlargement of the gypsum unit cell proportional to the concentration of arsenic in the solids and to the pH solution value. The substitution of sulfate ions (SO42-) by arsenate ions is shown to be more likely under alkaline conditions, where the HAsO42- species predominates. A theoretical Density Functional Theory model of the arsenicdoped gypsum structure reproduces the experimental volume expansion. Extended X-ray Absorption Fine Structure (EXAFS) measurements of the local structure around the arsenic atom in the coprecipitated solids confirm solid state substitution and allow some refinement of the local structure, corroborating the theoretical structure found in the simulations. The charge redistribution within the structure upon substitutions of either the protonated or the unprotonated arsenate species studied by means of Mulliken Population Analyses demonstrates an increase in the covalency in the interaction between Ca2+ and AsO4 3-, whereas the interaction between Ca2+ and HAsO4 2- remains predominantly ionic.

Hydrogarnet (Ca12Al2(OH)12) and katoite of composition Ca3Al2(SiO4)0.176(OH)11.3 were obtained by hydration of tricalcium aluminium oxide, and for katoite synthesis, by addition of amorphous silica. The thermal dehydration was monitored in situ, by neutron thermodiffractometry, from room temperature to 700 °C at atmospheric pressure and at a heating rate of 2 °C/min. On heating, powder neutron diffraction patterns were collected every 300 s. Cell parameters were fitted by the Pawley method. Hydrogarnet decomposed to yield Ca12Al14O32(OH)·mH2O and Ca(OH)2 that eventually transformed to CaO. For katoite, phases of formula Ca12Al14−ySiyO32(O,OH)1+y/2 related to mayenite were formed. Complementary annealing experiments, for 10 h, at higher temperatures and subsequent quenching lead to the formation of mayenite and traces of Ca3SiO5. Thermogravimetric curves were in agreement with the thermodiffractometry experiments. Also, neutron diffraction data allowed to measure thermal expansion coefficients, at atmospheric pressure, between 25 and 250 °C for hydrogarnet and katoite: 1.89 × 10−5 ± 0.09 and 1.63 × 10−5 ± 0.07 °C−1, respectively., This research was supported by MCYT under the projects MAT-2003-08331-CO2-01 and MAT2006-12749-C02-01-02. We thank ILL for beam time granted (experiment number 5-25-83) and Dr. J. Campo for his assistance in collecting ND data. We also thank to Dr. D. Sheptyakov for experimental assistance in collecting the neutron diffraction data at SINQ (experiment number II/02 S-18).

Here we report on two structural studies performed on As-doped gypsum (CaSO4 2H2O) and calcite (CaCO3), using neutron (D20-ILL) and x-ray (ID11-ESRF) diffraction data and EXAFS (BM8-ESRF). The aim of this study is to determine whether As gets into the bulk of gypsum and calcite structures or is simply adsorbed on the surface. Different mechanisms of substitution are used as hypotheses. The combined Rietveld analysis of neutron and x-ray diffraction data shows an expansion of the unit cell volume proportional to the As concentration within the samples. DFT-based simulations confirm the increase of the unit cell volume proportional to the amount of carbonate or sulphate groups substituted. Interpolation of the experimental Rietveld data allows us to distinguish As substituted within the structure from that adsorbed on the surface of both minerals., Comment: Proceedings of the Eighth International Conference on Neutron Scattering

Sorption of As(III) by calcite was investigated as a function of As(III) concentration, time and pH. The sorption isotherm, i.e. the log As(III) vs. log [As(OH)3 degrees / Assat] plot is S-shaped and has been modelled on an extended version of the surface precipitation model. At low concentrations, As(OH)3 degrees is adsorbed by complexation to surface Ca surface sites, as previously described by the X-ray standing wave technique. The inflexion point of the isotherm, where As(OH)3 degrees is limited by the amount of surface sites (ST), yields 6 sites nm-2 in good agreement with crystallographic data. Beyond this value, the amount of sorbed arsenic increases linearly with solution concentration, up to the saturation of arsenic with respect to the precipitation of CaHAsO3(s). The solid solutions formed in this concentration range were examined by X-ray and neutron diffraction. The doped calcite lattice parameters increase with arsenic content while c/a ratio remains constant. Our results made on bulk calcite on the atomic displacement of As atoms along [0001] direction extend those published by Cheng et al., (1999) on calcite surface. This study provides a molecular-level explanation for why As(III) is trapped by calcite in industrial treatments., Comment: 9 pages

10 pages, 12 figures, 3 tables., Even though the electroosmotic flux through hardened cementitious materials during laboratory realkalisation trials had been previously noticed, it has never been in-situ monitored, analysing at the same time the establishment of the electroosmotic flux and the microstructure changes in the surroundings of the rebar. In this paper, two series of cement pastes, cast with CEM I and CEM I substituted in a 35% by fly ash, previously carbonated at 100% CO2, were submitted to realkalisation treatments followed on line by simultaneous acquisition of neutron diffraction data. As a result, it has been possible to confirm the electroosmosis as the driving force of carbonates towards the rebar and to determine the range of pH in the anolyte in which most of the relevant electroosmotic phenomena takes place. On the other hand, the behaviour of the main crystalline phases involved in the process has been monitored during the treatment, with the precipitation of portlandite as main result., The authors also acknowledge the funding provided by the Spanish MMA through the project n- 055/2004/3.

The defect pyrochlore (H3O)SbTeO6 oxide is an excellent proton conductor, showing a conductivity value of 10(-1) S cm(-1) at 30 degrees C under saturated water vapor partial pressure. It can be prepared by ion exchange from KTeSbO6 pyrochlore in sulfuric acid at 453 K for 12 h. The full characterization of the structure of the (H3O)SbTeO6 pyrochlore, including the location of the H3O+ units within the three-dimensional framework, has been carried out by neutron powder diffraction. A first Rietveld refinement of the [SbTeO6]- framework was performed in the Fd3m space group (a= 10.1510(1) A); a difference Fourier map enabled the unambiguous location of the O2 atoms from the H3O+ ions at 32e (x,x,x) positions, and subsequently the H atoms at 96g (x,x,z). The (H3O)SbTeO6 crystal structure is constituted by a network of randomly distributed Sb(V)O6 and Te(VI)O6 octahedra linked by their corners with (Sb,Te)-O1-(Sb,Te) angles of 136.2 degrees. Hydronium ions are located off-center around the large 8a cages of the pyrochlore. The geometry of the (O2)-H3 units is that of an almost regular tetrahedron, with O2 atoms at the center and the three H atoms in three of the vertices; the fourth vertex is supposed to be occupied by the O2 lone pair. The three O2-H bonds have equal distances of 1.020(8)A. The H3O+ units are linked to the O1 framework oxygens by weaker hydrogen bonds, with O1-H bond lengths of 1.649(7) A. The relatively large thermal factors of O2 and H, of 2.5 and 3.7 A2, respectively, suggest that both kinds of atoms are not static at fixed positions but could be dynamically fluctuating between crystallographically equivalent sites.

The influence of an external DC voltage in an aluminous cement paste has been studied by in situ neutron diffraction, by monitoring the evolution of CaAl2O4 and Ca3Al2(OH)12 at different distances from the electrodes. The microstructure of the whole aluminous paste becomes dramatically altered. Both phases have been more attacked in zones closer to the electrodes. Major changes took place in the zone next to the positive electrode, in which the anhydrous phase has disappeared completely and the Ca3Al2(OH)12, has decreased significantly. In the cathodic zone, a decrease is also noticed due to the aluminium amphoteric character. The noticeable background diffraction increase in the area close to the positive electrode has been attributed to the formation of an amorphous alumina-like-gel that incorporated water to its composition.

Previous studies [l-41 on calcium aluminate cement (CAC), formerly known as high alumina cement (HAC), have shown that on reaction with water the initial hydrate formed at lower temperatures, par- ticularly below 15 "C, is the metastable, hexagonal hydrate CAHlo (see Table I for cement nomen- clature system) CA

An external dc voltage was applied to cured cement pastes to simulate their natural degradation over time; i.e. migration of ions and dissolution of solid phases. The presence of crystalline phases before and after applying a voltage was quantified by powder diffraction using synchrotron X-ray radiation. The results were refined by the Rietveld method. The specimens were also analysed by mercury intrusion porosimetry. Results indicated that a portion of the crystalline phases dissolved and later precipitated as amorphous phases in smaller pores. This accelerated treatment led to the formation of a larger proportion of amorphous phases in the specimens studied.

We show that a number of processes involved in the field of industrial solid-state chemistry can be successfully studied in situ, using a range of crystallographic and related techniques. The adaptation of relevant equipment to reproduce the process environment at the sample is a crucial part of the approach. Examples are given, involving the synthesis of zirconia-based ceramics, hydration of cements, and dehydration of zeolites, where successful applications of this approach have uncovered new structural/kinetic aspects concerning seemingly well established industrial processes.

Dolomite powder from Coin (Spain) was heated in air at a constant rate of 2°C/min to 1000°C, while neutron diffraction patterns were collected every 150 s. Rietveld refinement was applied and raw intensity data were used to monitor decomposition. The full process happened in two stages: dolomite decomposition to give calcite and periclase, and calcite breakup. The first stage activation energy was 47 kcal·mol−1 from fitting to a contracting sphere model. The dolomite mean thermal expansion coefficients were (6.7 ± 0.4) × 10−6 and (2.7 ± 0.2) × 10−5 K−1 along the a and c axes, respectively. Changes in the Ca–O and Mg–O bond distances were also measured.

We show that 25–140 keV X-rays from high-brilliance synchrotron sources can penetrate through 25 mm of intact rock. Powder diffraction patterns are obtained rapidly by energy-dispersive detection. Data acquisition time is reduced by a large factor (say 102–103) compared with standard laboratory powder diffraction methods. Data are presented on sedimentary rock cores and mineral standards. Full-pattern fitting is used for quantitative modal analysis of the composition. Using acquisition times of only 20 s for each pattern, we show the feasibility of line traverse (conveyor-belt) X-ray diffraction analysis and compositional tomography with sub-millimeter resolution.