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We coupled first principles calculations and the quasiharmonic approximation combined with experiments (X-Ray diffraction and dilatometry measurements) to determine the thermal properties of NiTiSn (half-Heusler) and Ni2TiSn (Heusler) compounds. These properties are important especially if they are to be used in thermoelectric applications. First, the calculation of their mode Gruneisen parameter shows that it is positive throughout the first Brillouin zone. This suggests that these compounds undergo a regular thermal expansion. Then, the calculation of the Ni2TiSn thermal expansion shows an excellent agreement, even in the high temperature range, with our high energy powder X-Ray diffraction measurements (ESRF) and dilatometry experiments. In the case of NiTiSn, this agreement is less impressive. This could be due to stronger phonon-phonon interactions that are not considered within the quasiharmonic approximation, but also to the difficulty of making high-quality NiTiSn samples. Finally, the constant-pressure and constant-volume heat capacities have been calculated for both compounds and compared with the experimental data reported in the literature. In particular, we have decomposed the constant-volume heat capacity of Ni2TiSn into a purely electronic and a phonon-mediated contribution, and we discuss each of them., Comment: 22 pages, 6 figures

The mechanical energy absorption ability of the highly flexible; MIL-53(Al) MOF material was explored using a combination of; experiments and molecular simulations. A pressure-induced transition; between the large pore and the closed pore forms of this solid; was revealed to be irreversible and associated with a relatively large; energy absorption capacity. Both features make MIL-53(Al) the first; potential MOF candidate for further use as a shock absorber.

Gallium orthophosphate, GaPO 4 , is a piezoelectric material isostructural with α -quartz, SiO 2 , with better piezoelectric characteristics: higher coupling coefficient for its temperature compensated cut and wider thermal stability (up to 933°C). A new investigation of the solubility of GaPO 4 in different acids and their mixtures allows to determine the metastable zone of which the knowledge is primordial for a good growth restart. The comparison of experimental growth results obtained in horizontal glass vessels ( T c T c >170°C) leads to specify a necessary minimum value of the solute supply at the interface crystal/solution. On the other hand, natural large seeds being not available, the seed lengthening is carried out with the splicing technique followed by crossed crystal growths to decrease the density of structural defects. At the same time, characterizations of crystals have been undertaken to check: the OH content by infrared spectroscopy; the crystalline quality (specially crystals after splicing) and the growth restart by X-ray topography; the piezoelectric properties.

GaPO4 cystals were obtained by hydrothermal solution crystal growth. The retrograd solubility of the material was investigated in different solvents. In static growth vessels, good quality crystals can be obtained only if the solute supply is higher than about 0.06M/L. Crystal characterization by infrared spectroscopy showed that dilute solvents at high temperature decrease the “-OH” group content. Seed lengthening by splicing along the Y-axis was designed. The AT cut angle and the C44 elastic constant were determined. Compared to quartz-type materials, the C0/C1 calculation shows the high ability of GaPO4 for manufacturing BAW devices.

Previous X-ray crystal structure refinement of GaAsO4 gave spurious As–O (1.72 A) and Ga–O (1.77 A) bond distances by comparison with theoretical values and with experimental values from AlAsO4 and GaPO4 ([As–O]≅1.67 A and [Ga–O]≅1.82 A). Therefore, a complete structural reinvestigation of gallium arsenate was carried out between 15 and 1073 K by both neutron and X-ray diffraction. All new analyses led to experimental bond values in agreement with those predicted, i.e., close to 1.67 and 1.82 A. This new structural investigation of GaAsO4 over a wide range of temperatures emphasizes the high thermal stability of the α-quartz packing in this compound, the best amongst quartz-like materials. The experimental relation between structural deformation and piezoelectric properties of these quartz-like materials also allows us to predict that GaAsO4 would have the best piezoelectric characteristics for its AT-cut. Conversely, its higher covalent character should imply a greater pressure sensitivity, with a crystal structure transition around 9 GPa. Thus, GaAsO4 would be the best piezoelectric candidate for high temperature applications but not for high pressure devices.

The adsorption of benzene in the cation-containing metal–organic framework (MOF) MIL-141(Cs) was explored by manometry measurements coupled with Monte Carlo simulations. This joint experimental/modeling approach demonstrates that this solid shows a high affinity for benzene that does not result from a direct interaction between the guest molecules and the Cs+ cations, in contrast to what is commonly observed in zeolites. This behavior was attributed to the high degree of confinement of Cs+, which prevents any cation detrapping upon adsorption, as revealed by dielectric relaxation spectroscopy and molecular dynamics simulations. This peculiar adsorption behavior is further discussed in relation to that of other alkali extraframework cations including Li+, Na+, K+, and Rb+.

The breathing of the flexible metal organic framework MIL-53(Cr) has been widely explored by both experimental and modeling approaches upon the inclusion of different guest molecules within its porosity. This spectacular phenomenon has been only partially tackled by force field based simulations mainly due to the complexity of deriving a set of accurate potential parameters able to capture the associated structural transition implying a unit cell volume change up to 40%. Here, a new parametrization of a flexible force field for the MIL-53(Cr) framework is realized from an iterative procedure starting with the experimental structural data collected in the presence of CO 2 as the guest molecule. Hybrid osmotic Monte Carlo simulations based on this refined force field are then successfully conducted to reproduce for the first time the complex shape of the CO 2 adsorption isotherm in the whole range of pressures. The structural behavior of the MIL-53(Cr) under a wide range of applied temperature and pressure is then followed by molecular dynamics simulations. It is established that these two stimuli also induce a similar reversible structural transition toward a contracted phase, with the presence of a hysteresis. Each of these predictions is confirmed by experimental evidence issued from either the literature for the impact of the temperature or from our own high pressure neutron diffraction measurements. This permanent experimental/modeling interplay allows a full validation of the derived flexible force field, a prerequisite for further understanding the microscopic key features that govern the spectacular breathing of such a material. © 2012 American Chemical Society.

The potential of the porous crystalline titanium dicarboxylate MIL-125(Ti) in powder form was studied for the separation in liquid phase of xylene isomers and ethylbenzene (MIL stands for Materials from Institut Lavoisier). We report here a detailed experimental study consisting of binary and multi-component adsorption equilibrium of xylene isomers in MIL-125(TO powder at low (= 0.8 M) concentrations. A series of multi-component breakthrough experiments was first performed using n-heptane as the eluent at 313 K, and the obtained selectivities were compared, followed by binary breakthrough experiments to determine the adsorption isotherms at 313 K, using n-heptane as the eluent. MIL-125(Ti) is a para-selective material suitable at low concentrations to separate p-xylene from the other xylene isomers. Pulse experiments indicate a separation factor of 1.3 for p-xylene over o-xylene and m-xylene, while breakthrough experiments using a diluted ternary mixture lead to selectivity values of 1.5 and 1.6 for p-xylene over m-xylene and o-xylene, respectively. Introduction of ethylbenzene in the mixture results however in a decrease of the selectivity.

The synthesis of the microporous crystalline titanium(IV) 2-amino-terephthalate (MIL-125(Ti)_NH2; MIL stands for Materials from Institut Lavoisier) was improved at the laboratory scale (40 g) in order to be evaluated as powder for the selective adsorption and separation of xylene isomers and ethylbenzene in liquid phase using n-heptane as eluent. Multi-component breakthrough experiments, conducted at 313 K, have shown a preferential adsorption of ethylbenzene or para-xylene depending on the ethylbenzene concentration. Thus, MIL-125(Ti)_NH2 solid is para-xylene selective in liquid phase in presence of low ethylbenzene concentrations while at higher ethylbenzene concentrations it becomes ethylbenzene selective.

The adsorption of n -hexane and n -nonane in MIL-53(Cr) and MIL-47(V) was first investigated by gravimetric measurements. While MIL-53(Cr) exhibits a sub-step during the sorption process induced by the breathing ability of this solid, the adsorption isotherm for MIL-47(V) is of type I. This different shape of the so-obtained isotherms was then interpretated in light of complementary experimental tools including thermogravimetry and X-ray thermodiffraction. We thus evidenced the occurrence of different structures in presence of n -hexane or n -nonane in the case of MIL-53(Cr) identified as the narrow pore (NP) phase and large pore (LP) phase. One noticed the existence of a swollen NP form which spans in a broad range of temperature. A computational assisted structure determination allowed us to elucidate the structures for both NP and LP forms in presence of each investigated alkane. From these structures, the adsorption enthalpies of n -alkanes over MIL-53(Cr) have been computed. It was shown that the NP phase leads to higher enthalpy of adsorption as compared to the LP phase which is related to a higher degree of confinement.

Using the electrocrystallization process, silver iodide particles were embedded into bulk Vycor7930 porous glass (VPG) to obtain ionic conductor composite. X-ray microdiffraction (μXRD) was carried out on the composite. AgI was found to be in its β-form with nanometric crystallite size. Microstructure has also been investigated by scanning electron microscopy (SEM). The ionic conductor was found to be embedded in the center of the VPG disk, into the 4 nm diameter pore network. Electron probe for micro analysis (EPMA) has shown the homogeneity of the silver iodide precipitate inside the VPG. Electrical conductivity was measured by complex impedance spectroscopy (CIS). A large hysteresis phenomenon in the conductivity versus temperature curve at a temperature close to the transition β ↔ α-AgI was observed. At low temperature, the conductivity of the composite was found to be higher than that of pure β-AgI by 1 order of magnitude.

Foam glass manufacture is a promising mode for re-using cathode ray tube (CRT) glasses. Nevertheless, because CRTs employ glasses containing heavy metals such as lead, barium and strontium, the leaching behaviour of foam glasses fabricated from CRTs must be understood. Using the AFNOR X 31-210 leaching assessment procedure, the degree of element inertization in foam glasses synthesized from waste CRT glasses (funnel and panel glasses, containing lead and barium/strontium respectively) were determined. The amount of leached lead from foam glasses prepared from funnel glass depends on the nature and concentration of the reducing agent. The effects of the reducing agents on the generation of cellular structure in the fabrication of foam glass were studied. The fraction of lead released from foam glass was less than those extracted from funnel glass and was lower than the statutory limit. Leached concentrations of barium and strontium were found to be approximately constant in various tests and were also below regulatory limits.

As a possibility to clean waste CRT glass, treatment of lead-containing glass with a reducing agent, SiC or TiN, leads to a porous material containing metallic lead, Pb(0), located on the surface of the pore, and unreduced lead, Pb(II). The influences of reducing agent content, of the time, and at last of the temperature on lead reduction were analysed. Our investigations have pointed out significant differences as a function of the used reducing agent. CRT glass heat treated with SiC lead to less Pb(0), compared to TiN as shown by X-ray diffraction, and differential scanning calorimetry (DSC). It has been also evidenced that lead reduction occurs on randomized zones inside the sample leading to macroscopic lead beads inside glassy samples. XPS and XAS measurements were also carried out to investigate the local structure of lead and have evidenced a change of role of lead inside the glassy framework in function of the used conditions.

Synthesis and characterization of porous Vycor (R) 7930-MI (M = Li, Ag) composites are discussed. Two types of composites were prepared: sintered composites obtained by classical sintering (CS) and composites obtained by electro-crystallisation (EC). In the case of Lil composites all increase of the conductivity of two orders of magnitude as compared to the conductivity Of pure Lil was observed. In Such a case good coating of insulating particles and filling of the pores was observed. In the case of Agl the main important finding is the presence of an hysteresis phenomenon in the conductivity versus temperature Curve at a temperature close to the transition alpha beta

International audience; Silver-containing chalcogenide glasses are potential candidates for electrical memory manufacturing. In order to study the glasses under dynamic conditions, using the temperature as the main parameter, a neutron thermodiffraction study of three Agx(Ge0.25Se0.75)100−x glasses (x = 5, 15 and 25) was carried out. Two in situ diffraction experiments were performed: a first series including heating ramps from room temperature up to 350 C and a second one comprising the measurement of an isotherm at about 300 C for 5 h. For the three studied glasses two stable crystalline phases were formed during the heating process: the cubic Ag8GeSe6 appeared first, followed by the crystallization of monoclinic GeSe2. The crystallization process for the Ag-rich (x = 15 and 25) glasses was more complex, with the appearance of a new unstable phase at high temperature, i.e. Ag2GeSe3. Such a phase decomposed with time or temperature to produce a new phase, Ag10Ge3Se11, along with the stable GeSe2. This phase has never been reported to date while the existence of Ag2GeSe3 was still controversial.

Cathode-ray tubes (CRTs) are made of two different kinds of glasses. The front part, panel, or screen, is made of barium- and strontium-containing glasses, while the rear part, the funnel, is made of lead-containing glasses. The structure and the role of these elements in the glasses are different: lead oxide is generally considered as a network intermediate whereas barium and strontium oxides as network modifiers. To study the local structure around the three aforementioned heavy elements we have used X-ray absorption spectroscopy (XAFS) on Pb and Ba LIII-edges and Sr K-edge as well as X-ray photoemission spectroscopy (XPS) analyzing the Pb 4f, Sr 3p, Ba 3d, Si 2p and O 1s core peaks. Due to the complex formulation of these glasses the coordination of lead and strontium could be affected compared with the local structure of binary glassy systems. We demonstrate that the average coordination number of lead is close to three (Pb–O distances being 2.24 A) as in other lead silicate glasses. In case of strontium, the coordination number is found close to five (Sr–O distances being 2.52 A) similar to that in Sr-containing glasses.

International audience; Cellular glasses were synthesised by heat treatment (750–850°C for 60–120 min) of waste cathode-ray tube (CRT) glasses (funnel and panel) with a SiC or TiN reducing agent. Macro-size pores with a single distribution were formed after reduction with SiC, whereas a double distribution was observed for TiN. The intrinsic properties of these materials were investigated.We found that the flexural strengths of the samples varied from 4 to 68 MPa depending on their porosity, and that the compressive strengths varied from 4 to 267 MPa. Our analysis shows that Ashby's model is more appropriate for these porous materials because their Poisson ratios are porosity-independent. The thermal conductivities of the materials were determined from their thermal diffusivities at room temperature, obtained by means of laser flash experiments. We also determined the variation of the conductivity with the porosity of the cellular glasses. The samples were found to have thermal conductivities in the range 0.08– 0.43 W/m/K. The dielectric constants of the materials were determined by impedance spectroscopy, and indicated that the materials are insulators. The samples were found to have permittivities in the range 2.6–3.1 S/cm. These values varied with sample thickness, and appeared to tend towards a limiting value determined by the porosity of the material, or more particularly, by the relationship between the volumes of air and matter in the sample.

New re-use applications are needed to address the relatively large quantity of waste electronic products generated in the world. Cathode-ray tubes (CRTs) from computer monitors and TV sets are a large component of such waste. The three glass components of CRTs are the funnel, panel and neck, which are produced by various manufacturers and are now collected by asset-recovery centres. In this paper, we characterize waste funnel and panel glass from dismantled cathode-ray tubes with a view to assisting the development of new re-use applications. The heavy metal (lead, barium, and strontium) content of such glass represents an acute risk to the environment. Our results of the chemical composition for different kinds of waste CRT glass including black & white and color CRTs show that CRT glass from different producers have generally similar chemical compositions. In particular, the compositions of funnel and panel black & white CRT glass are similar, but are different to those of panel and funnel color CRT glass. We also measured the following specific properties of each type of CRT glass: density, glass transition temperature, and linear coefficient of thermal expansion. It was found that the coefficients of thermal expansion of CRT glass do not vary with their composition. In contrast, the measured densities and glass transition temperatures do vary with composition. On the basis of our experimental data and data found in the literature, we outline the main properties of several waste CRT glass currently in circulation. The aim of this study was to provide the data required to determine if this kind of waste could be entirely (or partially) re-used and to aid the search for promising methods of treatment.

Display tubes such as those used in TV receivers and computer monitors have an evacuated glass envelope, which consists mainly of a screen (front component) and a funnel (back component hidden inside the TV set or monitor). These two components have different compositions: the screen is composed of lead-free glass with strontium and barium oxides, whereas the funnel is composed of glass with lead oxides. In order to comply with future government measures, a method is required for the recycling or re-utilisation of CRT (Cathode Ray Tube) glasses in end-of-life electronic goods. One open-loop recycling method is to create foam glasses from CRTs using a reducing agent. The results for the chemical compositions of these glasses and their physical properties showed that foam glasses can be prepared from glasses from various CRT glassmakers. In this paper, we use several methods to determine the structures of these foam glasses. We use helium pycnometry, Hg porosimetry, specific surface area measurements and scanning electron microscopy as direct methods for determining foam glass structure. These methods provide information about the morphologies and reactivities of these porous materials. Densities, porosities and pore size distributions were measured, which enable us to suggest some potential applications for the fabricated foam glasses.

Research into the recycling of electronics waste materials, such as cathode ray tubes (CRTs) and in particular their component glasses, is required by both French and European legislation. One possible solution to the problem of CRT glass waste is to convert it into foam glass, a material with very promising properties. Foam glasses can be prepared from CRT glasses containing heavy elements (lead, barium) through reaction with a reducing agent such as TiN or SiC. The present experimental study sought to determine the mechanism of foam glass formation and the structural differences between bulk and foam glasses. Additionally, the specific characteristics of bulk and foam glasses such as density, porosity, thermal and mechanical properties were determined, as well as their structural characteristics, using X-ray diffraction, differential scanning calorimetry, photoelectron spectroscopy and scanning electron microscopy with energy dispersive spectroscopy. The results indicate that reutilisation of CR...

Foam glasses can be prepared from lead silicate glasses through reaction with a reducing agent such as TiN or SiC. The environmental impact and specific characteristics of the final product (e.g., density, porosity, and thermal and mechanical properties) depend on the reaction processes that occur during expansion. The mechanisms of foam glass formation are determined in this study from experimental results, which we also use to determine the structural differences between the bulk (lead silicate glass before treatment) and foam glass (after heating the lead silicate glass with a reducing agent). This paper also presents measurements of the variation of the concentration of the divalent cation Pb(II) in the vitreous network (which initially contains 2–5 mol% PbO) during the expansion process. These results were obtained with various methods, including X-ray diffraction, differential scanning calorimetry, photoelectron spectroscopy, and scanning electron microscopy with energy dispersive spectrometry. Our results show that a small proportion (about 20%) of the initial Pb(II) in network modifying sites is reduced to Pb metal, and the remaining proportion is present in the vitreous network as Pb(II) with another particular environment. Increasing the amount of SiC or TiN results in increased reduction of Pb(II). The quantity of the reducing agent can be optimized with respect to the temperature, pressure, and reaction rate.

Gallium arsenate (GaAsO4) is a new α-quartz-type piezoelectric material. Large single crystals (8 mm along the c-direction) were grown for the first time by hydrothermal methods. The different crystal faces were indexed by X-ray diffraction. The crystal quality was characterized by infrared measurements. X- and Z-cut crystals were prepared in order to perform dielectric measurements. The dielectric constants of GaAsO4 (e′11=8.5, e′33=8.6) are the highest found among α-quartz type materials. A linear relationship has been established between a structural property, the tetrahedral tilt angle δ, and the dielectric constants for the well-known α-quartz homeotypes. These results indicate that gallium arsenate should have the highest piezoelectric coupling coefficient of any material of this family.

A joint experimental–modelling study has demonstrated a large flexibility of the MIL-47(VIV) upon mechanical pressure which strongly deviates from its rigid behaviour in presence of guest molecules. A structural transition suspected by mercury intrusion and further confirmed by X-ray powder diffraction and molecular dynamics simulations, leads to a closed MIL-47(VIV) form never observed so far corresponding to a cell contraction of up to 43%. The microscopic key features that govern this transition are then elucidated from complementary Raman experiments.

This paper reports an x-ray absorption spectroscopy (XAS) analysis of the local structure around lead contained in foam glasses prepared with waste funnel cathode-ray tube glasses (CRT) and three reducing agents AlN, TiN and SiC. The XAS data were collected at the Pb-L(III) edge to measure the influence of the reducing agent concentration on the unreduced lead content present in the glass. XANES spectra have been demonstrated to be a linear combination of both pure metallic lead and funnel glass spectra, with a significant modification of the funnel spectra for the highest contents of reducing agent. We have shown that the average coordination number of lead decreases in the case of TiN and SiC but remains constant in the case of AlN. The coordination number was found to be more affected for TiN than for SiC. Nevertheless, Pb-O bond lengths were determined to be constant close to 2.23 Å whatever the reducing agent and its content.