Blackwell Publishing Journal Backfiles 1879-2005
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
The compound Ba3Ca1.18Nb1.82O9-delta (BCN18) has been discussed recently as a promising high-temperature proton conductor. Oxygen loss under very reducing conditions has been determined quantitatively using thermogravimetry. The thermodynamic parameters DeltaH°O= 2.58 ± 0.06 eV and DeltaS°O= 1.06 × 10-3 eV/K provide a suitable thermodynamic description for the equation O×O right arrow ½O2+V··O+ 2e´. Enthalpy and entropy of the hydrogen absorption reaction have been determined indirectly for BCN18: DeltaH°H= -0.8 eV and DeltaS°H= -6.6 × 10-4 eV/K. Hydrogen absorption is, therefore, an exothermic process. Valence changes where Nb5++e´ right arrow Nb4+ also have been taken into account under reducing conditions.
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