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Journal of Thermal Analysis and Calorimetry
Authors:
M. Hampl
,
J. Leitner
,
K. Růžička
,
M. Straka
, and
P. Svoboda

Abstract

The heat capacity and the heat content of bismuth niobate BiNb5O14 were measured by the relaxation time method, DSC and drop method, respectively. The temperature dependence of heat capacity in the form C pm=455.84+0.06016T–7.7342·106/T 2 (J K−1mol−1) was derived by the least squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m=397.17 J K−1mol−1 was derived from the low temperature heat capacity measurement.

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-0037 0.3 SbP 5 O 14 36-0006 0.2 SbP 5 O 14 36-0006 0

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A DTA study of the thermal properties of Tl2V6O16, showed that its structure is not decomposed up to 475 °C. It melts at 505 °C. Tl2V8O21 and Tl3V5O14 crystallize successively from the melt.

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Abstract  

The electrical properties of ZnO varistors are induced by a sintering step. The phenomena occurring during this thermal treatment have been studied through model systems whose nature and composition are well defined. The pure BiSbO4 and Bi3 Zn2 Sb3 O14 phases have been synthetised by Direct Oxidation of a Precursory Alloy (DOPA) and characterized using XRD method. Each one of these phases can react with zinc monoxide through an invariant isobaric reaction in the ZnO–Bi2 O3 –Sb2 O3 system: – at 998C 17/3<ZnO>+2/3<Bi3 Zn2 Sb3 O14 > arrow <Zn7 Sb2 O12 > + ((Bi2 O3 )) – at 1058C 7<ZnO>+2<BiSbO4 > arrow <Zn7 Sb2 O12 >+((Bi2 O3 )) These thermodynamic considerations can explain the thermal domain of the sintering reaction described in the literature.

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Abstract  

Pb(1,4-BDC)·(DMF)(H2O) (1,4-BDC=1,4-benzenedicarboxylate; DMF=dimethylformamide) has been synthesized and investigated by elemental analysis, FTIR spectroscopy, thermogravimetry (TG), derivative thermogravimetry (DTG). TG-DTG curves show that the thermal decomposition occurs in four stages and the corresponding apparent activation energies were calculated with the Ozawa-Flynn-Wall (OFW) and the Friedman methods. The most probable kinetic model function of the dehydration reaction of the compound has been estimated by the Coats-Redfern integral and the Achar-Bridly-Sharp differential methods in this study.

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Physicochemical properties of bismuth vanadate catalysts with varying compositions, e.g., Bi4V6O21-6 1/2H2O·12 1NH3; Bi6V2O14·3 H2O; Bi6V4O19·6 H2O have been studied by chemical analysis, differential thermal analysis, thermogravimetry, infrared, X-ray diffraction, surface area and magnetic susceptibility techniques.

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Thermoanalytical investigations of the V2O5-K2S2O8 system have revealed that, in the presence of excess amounts of V2O5, the initial decomposition temperature is lowered compared to that of the pure salt. An explanation for this lowering is based on the interaction between V2O5 and the peroxo group of the persulfate ion. The reaction however, is, not unimolecular. The presence of an unknown potassium sulfate complex of V(V) with a catalytic character is indicated by XRD patterns obtained for samples heated up to 410°. It has been found that the formation of K3VO8, KV(SO4)2, K3V5O14 and K4V10O27 depends on whether V2O5 or K2SO4 is present in excess during thermal decomposition.

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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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.83 0.57 0.56 35.98 36.47 0.220 0.211 B 6 O 14 T′ 9 D 124 D 31 vi M′ 17 14

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