Simultaneous thermogravimetry-mass spectrometry for a solid oxide fuel cell interconnect, (La_0.7Ca_0.32)CrO₃

TG-MS simultaneous measurement on a nominally chromium deficient lanthanum calcium chromite, (La_0.7Ca_0.32)CrO₃, has been made in a helium flow and the results were compared with its shrinkage behavior in air and also with TG-DTA results on related calcium chromium oxides ( n(CaO) n(CrO_x) = 1:1 and 5:3) in air. In addition to evolution of water (320-920 K and 1020-1120 K) and carbon dioxide (340-1120 K), four distinct oxygen evolution peaks were observed from 900 to 1600 K; this oxygen evolution can be ascribed to the successive reduction of chromium ions in second phases which were estimated as about 1 mol% of Ca₅ (CrO₄)₃ or 2 mol% of Ca₃(CrO₄)₂. With the aid of available phase diagrams, a peak of simultaneous water and oxygen evolution at 1020-1120 K was attributed to the decomposition of an intermediate reaction compound, Ca₅(CrO₄)₃OH. Similarly, the water evolution at 320-920 K and CO₂ evolution can be ascribed to the decomposition of hydrated calcium chromates, CaCrO₄·nH₂O and calcium carbonate which were considered to be formed as reaction products of Ca₅(CrO₄)₃ with water, oxygen, and carbon dioxide. These features were discussed in relation to the sintering behavior of chromium deficient lanthanum calcium chromite.