Thermal decomposition and creation of reactive solid surfaces

Abstract

Three chromia precursors, namely CrO a, (NH4)2Cr207 and chromia gel, were subjected to thorough thermal analysis by means of TG and DTA. The thermal decomposition products obtained by calcination of these precursors at various temperatures (150-500 ~ for 5 h were investigated by infrared and X-ray techniques. The results obtained allowed a thorough physicoehemical characterization of the intermediate steps and products throughout the thermal decomposition.

Non-isothermal kinetics of CrO3 decomposition pathways in air

“…The results of studies conducted in this laboratory [1,2] are in line with those of other studies [3][4][5][6] in showing that the thermal decomposition of CrO3 into Cr203 at 523-753 K in air involves the formation of three detectable intermediate CrO~ phases. These are CrO2.66, at 523-593 K, CrOz5, at 593-623 K, and CrO2.z~, at 658-703 K. X-ray diffractometry revealed [ The XRD-verified compositions for the intermediates CrO~ are indicative of composite material bulks containing mixed valency (in the range from Cr 6 § to Cr 3+) chromium-oxygen species [2,7].…”

“…Decomposition course and products Similarly as in earlier investigations [1,2], the present results demonstrate the occurrence of four thermal events (denoted I-IV) in the course of CrO3 decom- position. These events were previously [2] characterized physicochemically by means of X-ray diffractometry, and UV/Vis diffuse reflectance and infrared spectroscopy.…”

“…As concerns the activation energy, the high value cannot be credited, since it was obtained by using a single method (Kissinger's). Nevertheless, it might account for a slow process due to the chain-structure assumed by solid-phase CrO3 [ 1 ].…”

Thermal decomposition of silver chromate complex with 1, 10 phenanthroline, Ag2(phen)2CrO4

“…As the oxydation state of chromium is supposed to be lower than six, the anion has been presented in the quotation marks. Moreover, various chromium to oxygen stoichiometry can not be excluded [3,5]. Generally, stage I can be identified as partial decomposition of the complex, volatilization and decomposition of phen and finally oxidation of its products.…”

“…This paper reports details on the thermal behaviour of the phen complex together with the analysis of the intermediate products of its decomposition. As various Cr(VI) compounds were found to be precursors of widely adopted chromia catalysts [3,4], M(HB)xCrO4 type complexes can be also interesting from this point of view. …”