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(NH4)2RuCl6 is an important precursor in the synthesis of Ru powder with high-purity requirement. In this study, high-purity (>99.999 wt%) micro-sized (NH4)2RuCl6 pieces were synthesized by distillation and precipitation from crude Ru powder. Then, the thermal decomposition behavior of the (NH4)2RuCl6 pieces was investigated. The decomposition process included two stages. First, (NH4)2RuCl6 was decomposed from 255.0°C to 314.0°C, with the endothermic peak located at 309.4°C. At this stage, HCl and NH3 were released, while the dense micro-pieces were transformed to loosened micro-pieces due to the thermal decomposition. Then, the solid phase [(NH3)4Ru3Cl12] kept decomposing from 314.0°C to 352.7°C, HCl and N2 were released, and agglomerated Ru particles were achieved. Thermogravimetric analysis-differential thermal analysis-mass spectrum coupling (TG-DTA-MS) was used to monitor the thermal decomposition process and identify the released gaseous phases, respectively. The solid phases in different stages were characterized by high-temperature X-ray diffraction (HTXRD). A good understanding of the processing and thermal decomposition of (NH4)2RuCl6 is crucial in the creation of Ru products.

Ceramic/metal composites, as high-temperature structural materials, have limited applications because of their poor machinability. AlN/Mo/Mo 2 B machinable composites were fabricated by adding h-BN to AlN/Mo composites by plasma-activated sintering at various temperatures and at an axial pressure of 30 MPa under argon atmosphere. The sample sintered at 1500 °C exhibited excellent machinability for cemented carbide tools, with a bending strength of approximately 500 MPa and a Vickers hardness value of 9.34 GPa. The effects of sintering temperature on the microstructure, mechanical properties, and machinability were investigated, and the reactions introduced by adding h-BN were studied. These reactions reinforced the composite and newly introduced a Mo 2 B phase, which showed better ability to deflect cracks and prevent them from moving deep inside the composite, thus improving its machinability. This research provides a possible solution for improving the machinability of ceramic/metal composites without sacrificing the strength. [ABSTRACT FROM AUTHOR]

IrO2 is an important material in numerous applications ranging from catalysis to the microelectronics industry, but despite this its behaviour upon annealing under different conditions has not yet been thoroughly studied. This work provides a detailed investigation of the annealing of IrO2 thin films using in situ high‐temperature X‐ray diffraction and X‐ray reflectivity (HTXRR) measurements from room temperature up to 1000°C in oxygen, nitrogen, forming gas and vacuum. Complementary ex situ scanning electron microscopy and atomic force microscopy measurements were conducted. The combined data show the dependencies of crystalline properties and surface morphology on the annealing temperature and atmosphere. The reduction of IrO2 to Ir takes place at a temperature as low as 150°C in forming gas, but in oxygen IrO2 is stable up to 800°C and evaporates as a volatile oxide at higher temperatures. The IrO2 crystallite size remains constant in oxygen up to 400°C and increases above that, while in the more reducing atmospheres the Ir crystallites grow continuously above the phase‐change temperature. The role of HTXRR in the analysis is shown to be important since its high sensitivity allows one to observe changes taking place in the film at temperatures much below the phase change. [ABSTRACT FROM AUTHOR]

IrO2 is an important material in numerous applications ranging from catalysis to the microelectronics industry, but despite this its behaviour upon annealing under different conditions has not yet been thoroughly studied. This work provides a detailed investigation of the annealing of IrO2 thin films using in situ high‐temperature X‐ray diffraction and X‐ray reflectivity (HTXRR) measurements from room temperature up to 1000°C in oxygen, nitrogen, forming gas and vacuum. Complementary ex situ scanning electron microscopy and atomic force microscopy measurements were conducted. The combined data show the dependencies of crystalline properties and surface morphology on the annealing temperature and atmosphere. The reduction of IrO2 to Ir takes place at a temperature as low as 150°C in forming gas, but in oxygen IrO2 is stable up to 800°C and evaporates as a volatile oxide at higher temperatures. The IrO2 crystallite size remains constant in oxygen up to 400°C and increases above that, while in the more reducing atmospheres the Ir crystallites grow continuously above the phase‐change temperature. The role of HTXRR in the analysis is shown to be important since its high sensitivity allows one to observe changes taking place in the film at temperatures much below the phase change. [ABSTRACT FROM AUTHOR]

• Thermally efficient carbon neutral process to synthesise nanoparticles of Ho 2 Zr 2 O 7. • TGA/DTG/DSC of metal alginate beads is in confirmation with HT-XRD data. • Effect of cationic (Zr4+, Hf4+) radius on XRD peaks positions and lattice parameters. • Raman spectroscopy and Rietveld refinement of XRD data of Ho 2 Zr 2 O 7 nanopowders. • Crystallite size and d-spacing obtained from XRD and TEM-SAED are in excellent agreement. The pyrochlore oxides are of potential interest as ion conducting electrolyte for intermediate temperature solid oxide fuel cell (SOFC). Nanopowders of holmium zirconate have been synthesised through ion-exchange between sodium alginate gel and metal complex solution followed by its thermal decomposition. Nanoparticles of Ho 2 Zr 2 O 7 were obtained by calcining the dried gel beads at 700 °C for 2 h and 6 h duration respectively. An insight into calcination has been obtained employing simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). Thermal decomposition was also followed using High Temperature X-ray Diffraction (HTXRD) in static ambient atmosphere. Results from TGA/DSC and HTXRD corroborate with each other. Fine crystalline nanopowders of single phase Ho 2 Zr 2 O 7 could be obtained after thermal decomposition at relatively low temperature (600–700 °C). Powder X-ray diffraction (XRD) revealed that the material has crystallized as single phase cubic Ho 2 Zr 2 O 7 with defect fluorite structure. XRD and Raman spectroscopy were used to analyse the local structure of holmium zirconate. XRD scans of holmium zirconate and holmium hafnate prepared through identical method have been compared and the effect of cationic radius of Zr4+ and Hf4+ on B-site was studied. The crystallographic data obtained from XRD and transmission electron microscopy (TEM) are in good agreement with each other. This sol-gel method also referred as Leeds Alginate Process (LAP) is simple, cost effective, energy efficient and carbon neutral for the preparation of pyrochlore oxides (A 2 B 2 O 7) solid electrolyte material for SOFC. [ABSTRACT FROM AUTHOR]

Abstract Thermal diffusion characteristics in naturally grown ultra-nanoscale superlattice structures have been studied. In absence of any suitable direct experimental tool due to the physical resolution limit, here we rely on the theoretical analysis of x-ray rocking curve simulations coupled with the diffusion equation to arrive at the diffusion characteristics across the interfaces of spontaneously grown Al x Ga 1-x As/Al y Ga 1-y As superlattice structures. The simulation approach presented here is a combination of a virtual interdiffusion code and a code on x-ray diffraction. We have obtained the variation in the actual diffusion coefficient as a function of time at different temperatures from the decay rates of the integrated satellite peak intensities. We have also found the diffusion coefficient to be highly nonlinear across the interface with time. The satellite decay equation could fit the experimental data taking the maximum Al composition alone at each time step. The pre exponential factor and the activation enthalpy values for interdiffusion are found out to be 0.17–0.25 cm2/s and 0.5–0.6 eV for Al diffusion whereas 0.01–0.11 cm2/s and 3.45–3.5 eV for Ga diffusion, respectively in the studied temperature range of 500 °C–700 °C. The interdiffusivity increases with temperature from 500 °C to 625 °C and decreases for further rise in temperature as the compositional contrast between the two layers decreases significantly at higher temperatures. Highlights • Natural superlattice ordering in MOVPE grown Al x Ga 1-x As/GaAs(100) in a length scale of 54 Å has been observed. • Combined XRD and interdiffusion study to analyze interfacial diffusion in AlGaAs/GaAs superlattice structures. • The diffusion coefficient has been found to be highly nonlinear across the interface with time. • Significant difference in activation enthalpy 0.5–0.6 eV and 3.45–3.5 eV for Al, Ga diffusion respectively. [ABSTRACT FROM AUTHOR]

High temperature crystal chemistry and thermal behavior of the boron minerals bear special attraction, owing to the increase in their application areas requiring elevated temperature. Colemanite (2CaO.3B2O3.5H2O) is one of the most commonly found and used compound among the boron minerals. In this study, therefore, thermal and mineralogical characterization of the colemanite was performed by X-ray Diffractometer (XRD) and Thermal Gravimetric Analysis (TG-DTA). Also, mineralogical changes in crystal structure were measured and recorded during heating from room temperature up to its melting temperature for each 50°C by using High Temperature XRD device. By this way, structural changes in the colemanite up to melting point were determined with increasing temperature for the first time. Results indicate that the thermal decomposition of colemanite has revealed a multi stage internal process; i) moisture removal, ii) dehydration- dehydroxylation, iii) amorphization of the crystal structure, iv) recrystallization of the amorphous solid (gradual reconstitutions). [ABSTRACT FROM AUTHOR]

Fluorapatite is being contemplated as a potential host for the incorporation of fluoride bearing radioactive nuclear waste. Ca 10 (PO 4) 6 F 2 and Sr 10 (PO 4) 6 F 2 are two fluorapatites which are studied extensively for the purpose of radioactive waste immobilization. Here, in this work a series of solid solutions having compositions Ca 10-x Sr x (PO 4) 6 F 2 (x = 2, 4, 6 and 8) were synthesized by solid state chemistry route. The detailed structural properties of these solid solutions were analysed by powder XRD, FTIR and Raman spectroscopy. Rietveld refinement was used to determine the structural changes as well as micro-structural strain in these compositions. At lower loading of Sr2+, there is a preference on site occupation of Sr2+ between two crystallographic Ca2+ sites as evidenced by Rietveld refinement. The calculated average strain values in the calcium rich compositions (x = 2 and 4) are higher than the strontium rich compositions (x = 6 and 8). Thermo-physical properties such as heat capacity and thermal expansion of Ca 10-x Sr x (PO 4) 6 F 2 (x = 2, 4, 6, 8) solid solutions were experimentally measured for the first time.Heat capacity values follow the usual solid solution behaviour. Electron beam irradiation studies show that these substituted solutions are resistant to phase degradation up to 1000 kGy as revealed by powder XRD. Moreover, combined FTIR, Raman and EPR studies confirmed that higher strontium content is detrimental to the fluorapatite through surface modification. This study further gives insight into design of better matrix in terms of 90Sr loading capacity and stability. Structural, thermodynamics and electron beam radiation studies on strontium substituted calcium fluorapatire matrix were carried out in view of radioactive waste immobilization. After strontium substitution, extent of non-ideality in terms of V mixing , strain, polyhedral distortion was explored by X-ray diffraction. Effect of temperature on these substituted apatites was ascertained by High temperature X-ray diffraction and calometric studies. [Display omitted] • Fluorapatite was explored as fluoride bearing nuclear waste form. • Ca 10-x Sr x (PO 4) 6 F 2 solid solution series synthesized by solid state route. • Strontium distribution is not random throughout the concentration range. • The extent of non-ideality was demonstrated by Rietveld refinement. • Thermophysical properties of these compositions were explored for the first time. [ABSTRACT FROM AUTHOR]

Nano-particles of NiAl 2 O 4 were prepared by co-precipitation and their bulk and surface were characterized by XRD, Raman spectroscopy, N 2 -adsorption-desorption analysis, SEM-EDS and XPS. The reducibility was studied by TPR and HTXRD techniques under H 2 atmosphere. The synthetized catalyst was made of NiAl 2 O 4 spinel oxide as main phase and of NiO (10%) free oxide. Interestingly, it was shown that the surface was richer in Al species. The catalytic performances in methane dry reforming were evaluated without H 2 -pretreatment of catalyst. A very high activity was observed with conversion of methane and CO 2 at 750 °C of 84 and 90 mol%, respectively and high H 2 /CO ratio. The amount of coke deposited during the reaction on this spinel was ∼3.6%. The physico-chemical properties of the catalyst on their behavior in the dry reforming of methane are discussed. [ABSTRACT FROM AUTHOR]

High-temperature X-ray diffraction and infrared emission spectroscopy have been applied to measure the thermal stability of the sulphate mineral kröhnkite NaCu(SO)·2HO. Kröhnkite shows a low thermal stability. The mineral decomposes into a complex mixture of sulphates below 500 °C and sulphides below 650 °C, before melting. Broad emission infrared bands at 3350 and 3105 cm are assigned to the stretching vibration of the water units. The intensity of these two bands decreases as the temperature is raised. The intensity of these bands is lost by 250 °C. The sharp IES band at 992 cm is assigned to the ν SO symmetric stretching vibration. Intensity in this band is lost by 200 °C. New IES bands are noted. The important aspect of this work is the use of high-temperature X-ray diffraction to determine the thermal decomposition of a mineral, in this case kröhnkite. [ABSTRACT FROM AUTHOR]

Thermal stability and expansion behavior of ThWO and UWO were studied using thermogravimetry and high-temperature X-ray diffraction techniques. ThWO and UWO showed positive thermal expansion in vacuum from ambient to 1273 and 1073 K, respectively. Heat capacity for ThWO(s) and UWO(s) was measured in argon atmosphere using heat flux-type differential scanning calorimeter, and thermodynamic functions of these compounds have been computed from the measured heat capacity data. The structural study of UWO was also carried out from powder X-ray diffraction data using Rietveld profile method. [ABSTRACT FROM AUTHOR]

The Toarcian Posidonia shale from Dotternhausen, Germany, is quarried and burnt in a fluidized bed reactor to produce electricity. The combustion residue, namely burnt oil shale (BOS), is used in the adjacent cement work as an additive in blended cements. The starting material is a typical laminated oil shale with an organic matter content ranging from 6 to 18%. Mineral matter consists principally of quartz, feldspar, pyrite and clays. After calcination in the range, the resulting product, burnt oil shale, keeps the macroscopic layered texture however with different mineralogy (anhydrite, lime, iron oxides) and the formation of an amorphous phase. This one, studied under STEM, reveals a typical texture of incipient partial melting due to a long retention time (ca. 30 min) and quenching. An in-situ high temperature X-ray diffraction (HTXRD) allowed studying precisely the mineralogical changes associated with the temperature increase. [ABSTRACT FROM AUTHOR]

The lattice thermal expansion and specific heat capacity of the C15–Cr 2 Zr Laves phase intermetallic compound were investigated using high temperature X-ray diffraction (HTXRD) and differential scanning calorimetry (DSC). All these alloys were prepared by arc melting. Through various heat treatments, the intermetallic compound Cr 2 Zr with both C14/C36–Cr 2 Zr and cubic C15–Cr 2 Zr Laves phase structure was obtained from these ingots. Room temperature XRD profile and scanning electron microscope (SEM) along with energy-dispersive X-ray (EDX) experiments on 1573 K/8h homogenized samples have confirmed the homogeneity and C15 (Fd-3m) crystal structure of Cr 2 Zr. The lattice parameters and relative phase fraction of the constituent phases were evaluated by using Rietveld refinement. The lattice thermal expansion behaviour of the compound was investigated in the temperature range 298 K–1073 K, and the result shows that its unit cell parameters increased exponentially when the temperature increased. The average thermal expansion coefficients were found to be α a i = 1.03 × 10−5 K−1 and α v i = 3.08 × 10−5 K−1. The specific heat capacity of the Laves phase Cr 2 Zr has been measured by using heat-flux DSC by employing the classical three-step method and is being reported for the first time. The heat capacity data obtained in this study have been compared with the theoretical model using quasi-harmonic Debye Grüneisen formalism in the temperature range 0–860 K and shown the various contributions to total heat capacity. The measured heat capacity data was used to obtain enthalpy increment as a function of temperature, which was effectively modelled by first principles based quasi-harmonic approximation and revealed different contributions to total enthalpy. To the best of our knowledge, this is the first experimental report on the thermal expansion and specific heat capacity of C15–Cr 2 Zr. A comprehensive set of thermodynamic parameters for C15–Cr 2 Zr has been established using a combination of measurement and modelling. • Cr 2 Zr with C14/C36 and C15-Cr 2 Zr Laves phase structures were synthesized from arc melted ingots using various heat treatments. • XRD and SEM along with EDX on 1573 K/8h homogenized samples have confirmed the homogeneity and C15 (Fd-3m) crystal structure. • The lattice thermal expansion and C p of the C15–Cr 2 Zr Laves phase were investigated by HTXRD and DSC for the first time. • The C p and H T - H 298 as a function of temperature have been successfully modelled by quasi-harmonic Debye-Grüneisen formalism. [ABSTRACT FROM AUTHOR]

Highlights: [•] Highest levels of homogeneity and clarity in the synthesized C12A7 solution. [•] Sol–gel formulation of binary C12A7 in stoichiometrical ratio of 12:7. [•] High temperature XRD to study effect of the heating rate on crystallization. [•] In situ investigation in to crystallisation of C12A7 with temperature rise. [•] Raman and FTIR spectra for crystal structure of annealed C12A7. [ABSTRACT FROM AUTHOR]

ABSTRACT The reaction pathways and phase evolution during synthesis of CuInSe2 (CIS) by a novel bilayer approach were investigated using in situ high-temperature X-ray diffraction. Two bilayer precursor structures, glass/Mo/γ-In2Se3/β-CuSe + β-Cu2Se/Se and glass/Mo/γ-In2Se3/β-Cu2Se/Se, were examined in this study. Temperature ramp experiments revealed that the phase transformation sequence for each bilayer precursor qualitatively follows that predicted by the phase diagram and that the onset temperatures for decomposition of the sub-binary compounds depend on the Se partial pressure. Measurement of the isothermal rate of formation of CuInSe2 at six temperatures in the range 260 to 310 °C for the γ-In2Se3/β-CuSe + β-Cu2Se/Se bilayer suggests relatively slow nucleation followed by diffusion-limited reaction with estimated activation energy of 162(±7) and 225 (±16) kJ/mol from Avrami and parabolic models, respectively. Interestingly, the measured activation energy for the same precursor in a 4 mol % H2/He ambient (108 (±8) kJ/mol) was lower than that observed in pure N2 (158 (±16) kJ/mol). The results of isothermal measurements in the temperature range 250 to 300 °C for the γ-In2Se3/β-Cu2Se/Se precursor film in an inert ambient are consistent with one-dimensional diffusion-limited growth with estimated activation energy from the Avrami and parabolic models of 194 (±10) and 203 (±12) kJ/mol, respectively. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The transformation of mixed sodium manganese ferrite into manganese ferrite induced by carbon dioxide was investigated. The reaction was performed in controlled conditions at different temperatures (600°C and 800°C). Transformation kinetics were followed in terms of powder composition evolution and weight gain by in-situ high temperature X-ray diffraction and thermogravimetric analysis respectively. Differently than expected by the reaction stoichiometry, the comparative analysis of the obtained experimental results reveals that sodium carbonate and manganese ferrite compounds formation is asynchronous. A mechanism describing mixed sodium manganese oxide transformation into manganese ferrite following sodium extraction by carbon dioxide is proposed and discussed. [Copyright &y& Elsevier]

Dysprosium hafnate is a candidate material for as control rods in nuclear reactor because dysprosium (Dy) and hafnium (Hf) have very high absorption cross-sections for neutrons. Dysprosium hafnate (Dy2O3·2HfO2-fluorite phase solid solution) was prepared by solid-state as well as wet chemical routes. The fluorite phase of the compound was characterized by using X-ray diffraction (XRD). Thermal expansion characteristics were studied using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1973 K. Heat capacity measurements of dysprosium hafnate were carried out using differential scanning calorimetry (DSC) in the temperature range 298–800 K. The room temperature lattice parameter and the coefficient of thermal expansion are 0.5194 nm and 7.69 × 10−6 K−1, respectively. The heat capacity value at 298 K is 232 J mol−1 K−1. [ABSTRACT FROM AUTHOR]

The phase transition of metavariscite into berlinite has been studied by means of different techniques, namely electron probe micro analysis, environmental scanning electron microscopy, high-temperature X-ray diffraction, differential thermal analysis, thermogravimetry, thermoluminescence, and thermo Raman. The application of these techniques indicates that: (i) from room temperature to 150°C metavariscite (monoclinic dimorph AlPO4 ⋅ 2H2O) appears as the main phase, (ii) in the range of 100-300°C metavariscite starts to lose the water molecules giving rise to form α-berlinite (trigonal AlPO4) that is the stable phase up to ca 540°C, and (iii) from 550°C onwards the structure adopts the more stable configuration, tetragonal β-berlinite. [ABSTRACT FROM AUTHOR]

Abstract: In the present investigations we have carried out the high temperature X-ray diffraction (HTXRD) studies on the metallosilicate molecular sieves iron silicalite-1 (FeS-1) samples of different Si/M ratios (Si/Fe=50, 75, 100 and ∞) for their negative thermal expansion (NTE) behavior. All the samples exhibit NTE behavior in the temperature range 373–773K. Systematic increase in negative thermal expansion coefficient is observed as a function of increasing Fe content in the MFI framework. Strength of the negative thermal expansion increases in the order Si/Fe=∞<100<75<50. It is concluded that by changing the composition of the framework of MFI, enhanced negative thermal expansion can be obtained. [Copyright &y& Elsevier]

In this work, the synthesis of Nd-doped SrSnO3 by the polymeric precursor method, with calcination between 250 and 700 °C is reported. The powder precursors were characterized by TG/DTA and high temperature X-ray diffraction (HTXRD). After heat treatment, the material was characterized by XRD and infrared spectroscopy. Ester and carbonate amounts were strictly related to Nd-doping. According to XRD patterns, the orthorhombic perovskite was obtained at 700 °C for SrSnO3 and SrSn0.99Nd0.01O3. For Sr0.99Nd0.01SnO3, the kinetics displayed an important hole in the crystallization process, as no peak was observed in HTXRD up to 700 °C, while a XRD patterns showed a crystalline material after calcination at 250 °C. [ABSTRACT FROM AUTHOR]

Abstract: Cr-based coatings were prepared by cathode arc-evaporation technology using N2 and C2H2 as reactive gases. Three compositions were investigated, Cr60N40, Cr41N27C32 and Cr67C33. The present investigation is centred on the structural stability via coatings tempering up to 1000 °C, by in situ X-ray diffraction in protective atmosphere. As-deposited coatings present low order structure with a medium feature size less then 10 nm. The hexagonal β-Cr2N phase, characteristic of binary Cr60N40 coating, was stable up to 900 °C, before recrystallization and grain growth takes place. For Cr41N27C32 film the phase transition varies from the metastable δ-Cr(N,C) to orthorhombic chromium carbonitride Cr3(C x N1− x )2 phase up to 800 °C and then to chromium carbide phase. No chromium nitride phases were detected in spite of the similar N and C contents after the deposition. The Cr–C coating recrystallizes into a mixture of carbide phases, mainly Cr3C2 and Cr23C6 after 1000 °C annealing treatment. [Copyright &y& Elsevier]

Abstract: Non-isothermal decomposition of the tetrapropylammonium cations (TPA+) intercalated in silicalite-1 framework has been carried out using thermogravimetric (TG) analysis and high temperature powder X-ray diffraction (HTXRD) techniques. Conversion factor for template decomposition is calculated using two methods viz., % weight loss from the thermogravimetric analysis and changes in the intensities of the Bragg reflections 101/011 and 200/020 in the HTXRD patterns scanned at different temperatures (range 298–823K). The calculated apparent activation energy for template decomposition in air was 129 and 125kJmol−1, respectively, for the two techniques TG and HTXRD, calculated using the Kissinger method. By Flynn–Wall–Ozawa approach of isoconversion, apparent activation energy for template decomposition in air was 123 and 124kJmol−1, respectively, for TG and HTXRD data. The reaction order was determined using the method of Kennedy and Clark and it is ∼2 by both the techniques. The second order of template decomposition can be attributed to the fact that TPA+ is positioned in two different orientations inside the silicalite-1 framework. Template removal occurs with a contraction in unit cell dimensions. There is a decrease in the lattice parameters of the as-synthesized silicalite-1 sample after removal of template from the framework. [Copyright &y& Elsevier]

Abstract: The measurement of the thermal expansion behavior of silica polymorph of zeolite MFI (Silicalite-1) was carried out in greater detail in the temperature range 373K–673K using high temperature X-ray diffraction (HTXRD) technique. The sample shows negative thermal expansion (NTE) in the temperature range studied, which is related to the transverse vibrations of the bridging oxygen atom between the two rigid polyhedrons. There is an anisotropy in the negative thermal expansion of this material that is contracting more along a axis than along the b and c axes. The bond angles and bond distances were determined from the Rietveld refinement data to look for any structural changes taking place as a function of temperature. The Si–O bond distances seem to play no role in the NTE, as there is no change in their distances as a function of temperature. It was observed that the Si–Si non-bonding distances for which the interatomic vectors are parallel to any of the crystallographic axes is responsible for the negative thermal expansion along the respective axes. The strong anisotropy in the expansion along a axis as compared to b and c directions is likely due to the stacking of the 2-dimensional layers in the bc direction. The observed decrease in Si–Si non-bonding distances with the constituent Si–O bond distances remaining constant, supports the correlation that the transverse vibrations of the bridging oxygen atoms in the structure are responsible for the NTE in this material. [Copyright &y& Elsevier]

Abstract: Nanocrystalline titania was synthesized by the hydrolysis of titanium iso-propoxide using ultrasonication. The powder XRD patterns of the sample were recorded in static air and vacuum using a Philips X-pert Pro diffractometer equipped with a high-temperature attachment (HTK16) from room temperature (298K) to 1173K and were analyzed by the Rietveld refinement technique. The anatase to rutile phase transformation was observed at 1173K for the data collected in static air. Only 3% of anatase titania transformed to rutile when the experiments were carried out at 1173K in vacuum. The phase transformation from anatase to rutile is accompanied by a continuous increase in the crystallite size of the anatase phase from 9nm at room temperature to 28nm at 873K and then to 50nm at 1173K in air while the process of crystallite growth was suppressed in vacuum. A linear increase in the unit cell parameters ‘a’ and ‘c’, and thus, an overall linear increase in the unit cell volume was observed as a function of temperature in static air as well as vacuum. The lattice and volume thermal expansion coefficients (TEC), αa, αc and αV at 873K are 8.57 × 10-6, 8.71 × 10-6 and 25.91 × 10-6K-1 in air and 18.01 × 10-6, 14.95 × 10-6 and 51.13 × 10-6K-1 in vacuum, respectively. [Copyright &y& Elsevier]

LaMnxV1−xO4−δ(0≤x≤1) samples were characterized using thermogravimetry, thermo-dilatometry, high-temperature X-ray diffraction (HTXRD) and temperature-programmed reduction techniques, with an objective to explore the role of substitution on their thermo-physical properties, which may have a direct bearing on their catalytic behavior. Even though the substituted compositions (x<0.8) were of a single phase, their reduction occurred in two steps, a lower temperature step corresponding to Mn4+→Mn3+/Mn2+ and another higher temperature one related to V5+→V3+. The dilatometric measurements gave similar values of linear thermal expansion coefficient (α1) at temperatures up to 600 °C, both for LaVO4 and substituted samples. A different behavior was, however, observed at higher temperatures, whereas thermal contraction was observed in case of LaVO4 for measurements at temperatures above 700 °C, the value of α1 remained almost constant in case of the substituted samples. Furthermore, the HTXRD data revealed expansion in cell volume for all temperatures up to 950 °C, irrespective of the substitution. These results therefore point to a higher degree of sintering in LaVO4 as compared to Mn-doped samples on heating at temperatures above 700 °C. It is inferred that the resistance to sintering and the lowering of the reduction temperature are both responsible to the higher catalytic activity of the substituted samples and their compositional stability during the repeated cycles of reduction–reoxidation, as reported earlier [Appl. Catal. A 205 (2001) 295]. [Copyright &y& Elsevier]

The thermal behaviour of the intercalation complex of a dickite from Tarifa, Spain, with dimethylsulfoxide was studied by high-temperature X-ray diffraction, differential thermal analysis and thermogravimetry, and attenuated total reflectance infrared spectroscopy. The ATR-FTIR study indicated that the heating between room temperature and 75°C produced the elimination of adsorbed molecules. Above this temperature the elimination of intercalated molecules occurs through several stages. Loss of 6.5% of the intercalated DMSO first causes a slight contraction of the basal spacing at 90şC due to a rearrangement of the DMSO molecules in the interlayers positions. This contraction is followed by the formation of a single layer complex and the restoring of the dickite structure, at 300°C, when the loss of intercalated species have been completed. [ABSTRACT FROM AUTHOR]

• Presents the fundamentals pertaining to the microwave treatment of ultramafic ores. • High temperature X-ray diffraction analysis showed the transition to heazlewoodite. • Conventional heating tests and thermodynamic modelling supported the microwave tests. The mining of ultramafic ores is required to meet society's continued demand for nickel. These deposits, however, are difficult to process due to their high serpentine content. Serpentine, a gangue mineral, increases slurry viscosity, slime-coats the valuable Ni-bearing mineral pentlandite, and reports to and dilutes the froth during flotation via the formation of bubble-fibre aggregates. Microwave pre-treatment can be used to convert the serpentine gangue to olivine, which should improve ore processing. However, the fundamental microwave properties and heating behaviour of ultramafic ores must be understood to develop a robust process. Microwave heating curves were developed for, and high temperature permittivity analysis was conducted on, two ultramafic nickel ores (Pipe and OK ore). Subsequently, TGA/DSC (thermogravimetric analysis/differential scanning calorimetry) and HTXRD (high-temperature x-ray diffraction) tests, along with a thermodynamic analysis using FactSage 7.3, were done to explain the heating behaviours and permittivity data. An unusual peak in the permittivity data was detected at 950 °C for the Pipe ore with both increasing and decreasing temperature; however, no phase transitions were detected in the TGA/DSC analysis. HTXRD of the Pipe ore revealed the presence of heazlewoodite at higher temperatures (950 to 1100 °C). Thermodynamic modeling of the Pipe ore system suggests that melting at higher temperatures is responsible for the decrease in the permittivities of this ore. To mitigate the melting and clumping of the ore particles, it is necessary to ensure that the processing temperature does not exceed 800 °C during microwave treatment. The OK ore, which contained less microwave response minerals than the Pipe ore, reached a maximum temperature of 500 °C after only 5 min of heating time, and therefore overheating was not an issue. [ABSTRACT FROM AUTHOR]