TG-DTA-MS of chromium(III) formate

The thermal decomposition of chromium(III) formate pentahydrate, Cr-3(OH)(2 )(HCO2)(7). 5H(2)O, in helium atmosphere and 20% O-2 in helium atmosphere h as been successfully studied by means of TG-DTA-MS, i.e., thermogravimetry- differential thermal analysis (TG-DTA) coupled with evolved gas analysis (E GA) using mass spectrometry (MS). The TG-DTA-MS is useful to interpret the complicated successive reactions and to determine the mechanism of the ther mal decomposition. The thermal process in Iie atmosphere proceeded by four steps, while in 20% O-2-He atmosphere it proceeded by three steps, The deco mposition scheme of Cr-3(OH)(2)(HCO2)(7). 5H(2)O in He atmosphere was propo sed by the following decomposition mechanism via formation of three interme diates: Cr-3(OH)(2)(HCO2)(7) . 5H(3)O --> Cr-3(OH)(2)(HCO2)(7) . 2H(2)O + 3H(2)O Cr-3(OH)(2)(HCO2)(7) . 2H(2)O --> Cr-3(OH)(2)(HCO2)(7) + 2H(2)O Cr-3(OH)(2)(HCO2)(7) --> Cr2O3 + Cr(HCO2)(3) + CO + 3CO(2) + 3H(2) 2Cr(HCO2)(3) --> Cr2O3 + 3CO + 3CO(2) + 3H(2). After the decomposition, a slight mass loss was observed with a sharp exoth ermic crystallization of Cr2O3 due to evolution of H-2. In 20% O-2-He atmos phere, a drastic exothermic mass loss accompanying evolution of CO2, H2O an d H-2 was explicable by one step combustion of the dehydrated formate, and a small amount of mass loss observed with a crystallization of Cr2O3 was at tributed to evolution of O-2. The decomposition process without an intermed iate was indicated by the temperature increase of the specimen produced by combustion heat. (C) 2000 Elsevier Science B.V, All rights reserved.