Abstract
The effects of three corundum structure oxides, α-Al 2O 3, α-Cr 2O 3, and α-Fe 2O 3, on the thermal decomposition of sodium and potassium peroxodisulfates (persulfates) under non-isothermal static air conditions and using various oxide/persulfate molar ratios, have been thermoanalytically investigated. Compounds such as Na 3Al(SO 4) 3, K 3Al(SO 4) 3, Cr 2(SO 4) 3, K 3Cr(SO 4 3, and Na 3Fe(SO 4) 3 are identified by X-ray diffractometry and conventional chemical analysis. The molar ratios as well as temperatures of the stoichiometric formation for these compounds have been established. At higher temperatures, α-Al 2O 3 acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate, whereas α-Cr 2O 3 behaves as a retarder for the decomposition of persulfate. A eutectic mixture is formed between K 3Al(SO 4) and K 2SO 4 at 675°C. Also, K 3Fe(SO 4) 3 is identified as two crystalline phases.
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