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Abstract  

The study of the system xSb2O3–(1 − x)Bi2O3–6(NH4)2HPO4 has been carried out to identify the phases and simulate the mechanisms of their formation, using the technique of thermal analysis in association with X-ray diffractometry. The main stages observed during thermal treatment of the samples include: (1) elimination of water and ammonia leading to the formation of (NH4)5P3O10; (2) reaction of the latter with M2 IIIO3 and the formation of acidic polyphosphates M2 IIIH2P3O10; (3) their dehydration with the formation of the polyphosphates MIII(PO3)3. Then Sb(PO3)3 decomposes giving SbPO4 and P2O5. In the presence of excessive P2O5, two moles of Bi(PO3)3 condensate into oxophosphates Bi2P4O13 and BiP5O14. The data of thermal analysis match with the composition of intermediate and final products. The hygroscopicity of the samples diminishes with growing bismuth content.

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Abstract

Sb(VO3)3 has been synthesized by interaction between NH4VO3 and Sb2O3. The compound crystallizes in monoclinic system with lattice parameters: a = 17.150; b = 15.940; c = 14.600 Å and angle β = 90.50°. The scanning electronic microscopy shows thin flat plates measuring ~20 μm along with detritus material. The synthesis was simulated by thermal analysis and the final product identified by X-ray diffraction. Thermal analyses of the ternary system xNH4VO3 + (1 − x)(NH4)2HPO4 + Sb2O3 lead to the formation of Sb(VO3)3 and SbPO4 at 500 °C. At high temperature (900 °C), SbVO4, SbOPO4, VO and SbP5O14 are formed. The data of thermal analysis match with the composition of intermediate and final products. No solid solutions containing simultaneously PO4 −3 and VO4 −3 ions have been found.

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Abstract  

A vitreous form of antimony orthophosphate has been obtained using antimony polyphosphate as a precursor. Morphologically, it is composed of small uniform grains having ellipsoidal shapes. Prolonged thermal treatment leads to the transformation into a crystalline variety. According to TG curves, both forms start to evaporate at 920°C without decomposition. Melting point of crystalline SbPO4 has been determined to be 877°C. Thermomechanical study reveals plastic behavior due to the capacity to flow under shearing stress. Ceramics formation in the system Sb2O3-SbPO4 is discussed. The presence of glass domains in this system has not been confirmed.

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Abstract

It is well established that gallium insertion into the hydroxiapatite matrix as practiced in orthopedics protects bone from resorbtion and improves the biomechanical properties of the skeletal system. The research presented in this article is an investigation into the thermal decomposition of gallium nitrate, which is part of a complex process leading to the preparation of a hybrid matrix. It was demonstrated that after melting of the hexahydrate in its own water there occurs a simultaneous condensation of 4 mol of initial monomer Ga(NO3)3·6H2O into a tetramer Ga4O4(NO3)4. The resulting inorganic cycle gradually loses N2O5 and, through the formation of unstable oxynitrates, is transformed into gallium oxide. The use of molecular mechanics for comparing the potential energies of consecutive products of thermal decomposition permitted an evaluation of their stability and an appropriate interpretation of the experimental data.

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Abstract  

Mechanisms of formation of polyphosphates MeIII(PO3)3, where M III=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc, Fe, Ga, Al and Cr has been simulated by thermal analysis technique. MeIII oxides and ammonium dibasic phosphate (NH4)2HPO4 were used as starting materials. For M III=La-Lu, Y and Fe three main stages were observed: 1. elimination of water and ammonia leading to the formation of ammonium tripolyphosphate (NH4)5P3O10; 2. reaction of the latter with Me2 IIIO3 and formation of acidic polyphosphates MeIIIH2P3O10 or their isomers MeIII(PO3)3·H2O; 3. final loss of water and formation of MeIII(PO3)3. For Me III=Sc and Ga the second stage is prolonged and the polyphosphates form at higher temperatures. Aluminum and chromium polyphosphates are unstable. It is suggested that thermal behavior of the compounds is determined by MeIII ionic radii.

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Abstract  

Xerogels were prepared from zirconium, barium, aluminum, lanthanum and lithium acetates, corresponding to a Li containing ZBLA composition. The study of their thermal properties (DSC, TG/DTG, FT-IR) showed that they might be used as chemically stable precursors in the preparation of fluoride glasses. Hydrofluoric acid in solution was chosen as a mild fluorinating agent. This newly proposed technique of fluorinating allowed to obtain high quality ZBLALi glass which presents the advantage of higher thermal stability and homogeneity in comparison with the glass obtained using individual commercial fluorides.

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Journal of Thermal Analysis and Calorimetry
Authors: P. Melnikov, F. J. dos Santos, S. B. Santagnelli, M. A. C. Secco, W. R. Guimarăes, A. Delben, and J. R. Delben
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Journal of Thermal Analysis and Calorimetry
Authors: J. R. J. Delben, S. S. Rojas, K. Miazato, P. Melnikov, A. A. S. T. Delben, C. X. Cardoso, and A. Job
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