Investigation of thermal decomposition of CrOx (x≥2.4)

The phase transitions and thermal effects occurring during annealing in air of material with general formula CrO_x (x≥2.4) have been investigated. The investigations were performed with TG, DTA, DSC, EGA, XRD and other spectral techniques. The formation of an amorphous phase with average composition Cr₅O₁₂ in the range 300-400°C has been observed. Further heating leads to partial loss of oxygen, simultaneous decay of Cr₂O₅ and CrO₂ phases and formation of nonstoichiometric Cr₂O_3+x. The distinct loss of mass is observed in the range 415-428°C, connected with evolving oxygen and small amount of nitric oxides. Thermal effects accompanying the mass changes depend on the mass of the sample. When the mass decreases, the transition from exothermic to endothermic effects is observed. This phenomenon can be explained as the competition between two processes: reconstruction of the crystalline lattice (endothermic effect) and recombination of the evolved atomic oxygen (exothermic effect). This revised version was published online in August 2006 with corrections to the Cover Date.