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The formation of substitutional solid solutions of the isostructural oxyhydroxides α-FeOOH-α-AlOOH (goethite-diaspore and γ-FeOOH-γ-AlOOH (lepidocrocite-boehmite) was investigated by X-ray powder diffraction technique and by thermal analysis.

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Selenium and cadmium sulphide react in the temperature range 250‡–350‡ to form a solid solution CdSe/CdS. Thermogravimetric (in N2) and chemical analyses show that this reaction occurs with the elimination of equimolecular amounts of Se and S. The thermal stability of the s.s. (2CdS · CdSe) in an atmosphere of N2 was studied.

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Abstract  

Al2O3-Cr2O3 solid solutions with 0, 4, 7, 10 and 20 mol% of corundum were synthesized using a high-pressure/high-temperature apparatus and characterized by X-ray powder diffraction. Calorimetric measurements were carried out using DSC-111 (Setaram). Heat capacity was measured by the enthalpy method in a temperature range of 260–340 K, near magnetic phase transition in pure Cr2O3 (305 K). Magnetic contribution into the heat capacity was derived and found to change irregularly with the composition. Heat capacity of solid solutions remains constant in a relatively wide range of composition, while the C p values of the end members differ significantly. This phenomenon is very important for the modeling of the thermodynamic functions of intermediate solid solutions.

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DTA and XRD studies of the Fe2V4O13–Cr2V4 O13 system have shown that continuous solid solutions of a Fe2–xCrxV4O13 type, bearing a Fe2 V4 O13 structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe2 V4 O13 structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe2–x Crx V4 O13 type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr3+ ion incorporation. The solid product of melting Fe2–x Crx V4 O13 solid solutions for 0.2<x >1.2 is the Fe1–x Crx VO4 solution phase, and for x ≤0.2 and x ≥1.4 – the Fe1–x Crx VO4 phase as well as FeVO4 or CrVO4 , respectively.

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The systems CaHPO4−MHPO4−H2O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca1−xSrxHPO4 for 0.95<X<0.75 and CaxSr1−xHPO4 for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca2Ba(HPO4)3 has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Electrical conductivity of solid systems AgX-MX2 (where M=Cd, Co, Zn and X=Cl, Br) were measured in a large range of temperature and compositions. Activation energies and conductivity values vs. composition are presented and discussed in relation to phase equilibria in the respective systems. Maximum of the conductivity value and stabilization of the activation energy have been found for silver halides doped heavily with divalent cation e.g. in the systems forming solid solutions on the silver halide side. Disorder in AgBr on the approach to melting, expected to be higher than in AgCl, has been shown by means of original DSC curves presented for both halides.

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In this paper the influence of alkaline-earth admixtures on the synthesis of lanthanum chromites of La1–xMxCrO3 (x=0; 0.3; M=Ca, Sr, Ca+Sr) type was studied. The formation mechanism as well as the phase composition evolution, under non-isothermal and isothermal conditions, were investigated by thermal analysis and X-ray diffraction. The structure of the compounds and of the solid solutions formed depends on the solute type by means of the structural distortion induced. The crystallinity of the chromites obtained is obviously influenced by both the temperature and the thermal treatment plateau.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Touboul, E. Le Samedi, N. Sephar, F. Broszniowski, P. Edern, and E. Bétourné

Abstract  

Six binary systems were studied using DTA with supplementary XRD. In Li2SO4−MSO4 systems (M=Mg, Co, Ni), a primary solid solution with α-Li2SO4 structure (high-temperature form) and an incongruent melting compound Li2My(SO4)1+y exist:y=2 with Mg andy=1 with Co and Ni. In Li2SO4−Li3XO4 systems (X=P, V), which are very different from one another, only primary solid solutions exist. In the Li2SO4−Li2B4O7 system there is neither a solid solution nor an intermediate compound. Comparisons with previous investigations are made.

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Journal of Thermal Analysis and Calorimetry
Authors: N. K. Labhsetwar, V. Balek, S. Rayalu, T. Terasaka, A. Yamazaki, J. Šubrt, H. Haneda, and T. Mitsuhashi

Summary Studies on ruthenia-titania based materials have been attractive because of their catalytic properties as well as due to the possibility of solid solution formation. Samples of pure ruthenia and ruthenia containing various amounts of titania (10-70 mol%) were investigated during heating of their hydroxide precursors from 20 to 800°C in air using emanation thermal analysis (ETA), thermogravimetry (TG), and differential thermal analysis (DTA). The resulting mixed oxide type materials were characterized by X-ray diffraction (XRD), which indicate the presence of three ruthenia-titania phases. The onset temperature of the crystallization of materials was identified by ETA results, whereas DTA effects characterized the crystallization in bulk of the samples. A good agreement was found between the ETA results and other characterization techniques used. ETA results, indicating the microstructural changes in surface and subsurface of ruthenia-titania based catalytic materials, can be used for optimization of their synthesis protocols to achieve the better physical properties.

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The solid–solid interactions in pure and MoO3-doped CuO/MgO system were investigated using TG, DTA and XRD. The composition of pure mixed solids were 0.1CuO/MgO, 0.2CuO/MgO and 0.3CuO/MgO and the concentrations of MoO3 were 2.5 and 5 mol%. These solids were prepared by wet impregnation of finely powdered basic magnesium carbonate with solutions containing calculated amounts of copper nitrate and ammonium molybdate followed by heating at 400–1000C. The results revealed that ammonium molybdate doping of the system investigated enhanced the thermal decomposition of copper nitrate and magnesium hydroxide which decomposed at temperatures lower than those observed in case of the undoped mixed solids by 70 and 100C, respectively. A portion of CuO present dissolved in the lattice of MgO forming CuO–MgO solid solution with subsequent limited increase in its lattice parameter. The other portion interacted readily with a portion of MoO3 at temperatures starting from 400C yielding CuMoO4 which remained stable up to 1000C. The other portion of MoO3 interacted with MgO producing MgMoO4 at temperatures starting from 400C and remained also stable at 1000C. The diffraction peaks of Cu2MgO3 phase were detected in the diffractograms of pure and MoO3-doped 0.3CuO/MgO precalcined at 1000C. The formation of this phase was accompanied by an endothermic peak at 930C.

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