Thermochemistry of GaBO3 and phase equilibria in the Ga2O3–B2O3 system |
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Authors: | Heiko Pelzer,Franz Mü ller |
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Affiliation: | Institut für Gesteinshüttenkunde, RWTH-Aachen, D52064 Aachen, Germany |
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Abstract: | Employing a Tian-Calvet-type calorimeter operating in the scanning mode at temperatures from 1120 to 1220 K, the enthalpy change, ΔdH, associated with the decomposition of GaBO3 (=1/2β-Ga2O3+1/2B2O3(liq.)) and the corresponding decomposition temperature, Td, were determined: ΔdH=30.34±0.6 kJ/mol, Td=1190±5 K. Using the transposed-temperature-drop method the thermal enthalpy, H(T)−H(295 K), of GaBO3 was measured as a function of temperature, T, in the region from 760 to 1610 K; the results obtained are[H(T)−H(295 K)]/(J/mol)=104.8·(T/K)−31 300 (760 K<T<1190 K), [H(T)−H(295 K)]/(J/mol)=138.8·(T/K)−41 480 (1190 K<T<1590 K). On the basis of the experimental results, the enthalpy and entropy of formation, ΔfH and ΔfS, respectively, of GaBO3 from the component oxides were derived:ΔfH=−30.34 kJ/mol,ΔfS=−25.50 J/(K·mol) at 1190 K, ΔfH=−10.55 kJ/mol,ΔfS=−5.48 J/(K·mol) at 298 K. The enthalpy versus temperature curve shows, apart from a step associated with the decomposition of GaBO3, a further step at 1593 K which is attributed to a monotectic equilibrium. |
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Keywords: | Thermodynamics Ga2O3–B2O3 System Ga2O3 |
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