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The reaction between equimolar silica and barium carbonate powders in oxygen, air or carbon dioxide was studied by means of TG and DTA. The particle size of the silica showed appreciable effects on the reactivity of the silica, on the activation energy of the reaction, and on the formation of an intermediate silicate, Ba2SiO4. The formation of Ba2SiO4 is depressed by a decrease in the silica particle size or by an increase in the partial pressure of carbon dioxide in the ambient atmosphere.

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Abstract  

The mutual reactivity in mixtures containing Nasicon (Na3Zr2Si2PO12) or YSZ (ZrO2:Y2O3) solid electrolytes with Li2CO3 or Li2CO3:BaCO3 sensing electrode materials was investigated using simultaneous DTA and TG and ex situ XRD techniques. The uncontrolled chemical reaction is suspected to be responsible for the instability of electrochemical gas sensors constructed from these materials. DTA and TG results obtained for Nasicon-carbonate mixtures indicate the possibility of reaction in the temperature range from about 470 to 650C, which overlaps the sensor operating temperature range (300–525C). The results obtained for YSZ-carbonate mixtures indicate that reaction between carbonate and the ZrO2 takes place at higher temperatures and cannot explain the instability drift of investigated sensors. The mechanism of observed reactions in systems studied is also discussed.

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The thermal decomposition in air of iron(II) sulphate heptahydrate in the presence of calcium, strontium and barium carbonates has been carried out. The decomposition path varies from carbonate to carbonate. Also, these decompositions are different from those of basic beryllium carbonate and basic magnesium carbonate. The results obtained for the kinetics of thermal decomposition have also been presented.

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Journal of Thermal Analysis and Calorimetry
Authors: E. Charsley, C. Earnest, P. Gallagher, and M. Richardson

Abstract  

The ICTAC Committee on Standardisation has formed a Task Group to investigate the suitability of the ICTAC Certified Reference Materials for DTA, covering the temperature range 450°–1100°C, for accurate temperature calibration purposes and to evaluate their potential as enthalpy calibrants for DTA and DSC equipment. This paper reports the results of preliminary round-robin studies on barium carbonate and strontium carbonate, using a dual-point calibration method based on the melting points of aluminium and gold. In addition the fusion of ICTAC potassium sulphate has been investigated as a possible calibration transition.

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The binary system Li2CO3–BaCO3 was studied by means of differential thermal analysis (DTA), thermogravimetry (TG) and X-ray phase analysis. The composition of carbonate and CO2 partial pressure influence on the thermal behavior of carbonate were examined. It was shown that lithium carbonate does not form the substitutional solid solution with barium carbonate, however the possible formation of diluted interstitial solid solutions is discussed. Above the melting temperature the mass loss is observed on TG curves. This loss is the result of both decomposition of lithium carbonate and evaporation of lithium in Li2CO3–BaCO3 system. Increase of CO2 concentration in surrounding gas atmosphere leads to slower decomposition of lithium carbonate and to increase the melting point.

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Synthesis of perovskite-type oxides Ln1-xAxBO3 (Ln: lanthanoid; A: alkaline earth; B: transition metal) by heating at low temperature with large ratio of alkaline earth element, especially barium, easily involves impurity of alkaline earth carbonate. We succeeded to prepare the precursor without the formation of barium carbonate even at a large content of barium. The chemical state and structure of Ln1-xAxBO3- d (Ln: La, Eu; A: Ca, Sr, Ba: B: Fe, Mn) perovskite-type oxides prepared by using those precursors have been studied by Mössbauer spectroscopy and X-ray powder diffraction. The X-ray powder patterns showed many types of crystal system depending on x.

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The thermolysis of strontium and barium tris(maleato)ferrates(III), M3 [Fe(C2 H2 C2 O4 )3 ]2 ·x H2 O has been investigated from ambient temperature to 800 °C using simultaneous TG-DTG-DTA, XRD, Mössbauer and IR spectroscopic techniques. After dehydration the anhydrous complexes undergo decomposition to yield an iron(II)maleate/oxalate intermediate in the temperature range of 240-280 °C. An oxidative decomposition of iron(II) species leads to the formation of -Fe2 O3 and respective alkaline earth metal carbonate in the successive stages. Finally at 540-590 °C, a solid state reaction occurs between -Fe2 O3 and strontium/barium carbonate resulting in the formation of SrFeO2.5 and BaFe2 O4 , respectively.

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This paper discusses a novel application of PIGE for the determination of13C in breath. Samples of human breath, urea, glucose, benzamide, barium carbonate were analyzed against cylinder CO2 and graphite standard. An accuracy check of the13C determination (with reference to mass spectrometric True results) gave a relative error of only –0.4% for PIGE. The performance of different standards in this determination was assessed. Relative standard deviation for the determination of13C isotopic abundance in breath samples were <20%. Then, if a 25% change is conservatively assumed observable in13C abundance, an increase in13C percent isotopic abundance from the natural 1.11% (average) to only 1.39% may be detected.

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Journal of Thermal Analysis and Calorimetry
Authors: Latifa Al-Hajji, Muhammad Hasan, and Mohamed Zaki

Abstract  

The formation of Barium monotungstate (BaWO4) particles in equimolar powder mixtures of BaCO3 and WO3 was examined under isothermal and non-isothermal conditions upon heating in air at 25–1200 °C, using thermogravimetry. Concurrence of the observed mass loss (due to the release of CO2) to the occurrence of the formation reaction was evidenced. Accordingly, the extent of reaction (x) was determined as a function of time (t) or temperature (T). The xt and xT data thus obtained were processed using well established mathematical apparatus and methods, in order to characterize nature of reaction rate-determining step, and derive isothermal and non-isothermal kinetic parameters. Moreover, the reaction mixture quenched at various temperatures (600–1,000 °C) in the reaction course was analyzed by various spectroscopic and microscopic techniques, for material characterization. The results obtained indicated that the reaction rate may be controlled by unidirectional diffusion of WO3 species across the product layer (BaWO4), which was implied to form on the barium carbonate particles. The isothermally determined activation energy (118–125 kJ/mol) was found to be more credible than that (245 kJ/mol) determined non-isothermally.

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