TG-MS simultaneous measurement on a nominally chromium deficient lanthanum calcium chromite, (La0.7Ca0.32)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(CrOx) = 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.
- Chromium deficiency
- Lanthanum calcium chromite
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry