Effects of nickel(II) oxide on the thermal decomposition of alkali persulfates

Abstract

The thermal decomposition of Na 2S 2O 8 and K 2S 2O 8 has been studied derivatographically in the presence of NiO at various molar mixtures. Experiments have proved that the first decomposition stage (persulfate into pyrosulfate) is independent of the amount of the oxide present. During the second decomposition stage (pyrosulfate into sulfate) which occurs in the melt, NiO plays the role of lowering the melting, the initial and final decomposition temperatures of pyrosulfates. The lowest melting temperatures recorded for Na 2S 2O 8 and K 2S 2O 8 are 320 and 280°C, respectively. A mechanism has been proposed to describe the catalytic action of NiO on the thermal decomposition of alkali pyrosulfates. The mechanism makes use of the semiconductivity of NiO and the availability of electron-rich centers in the pyrosulfate group to help the formation of an adsorption complex between them. NiO reacts to some extent with alkali pyrosulfates forming the yellow NiSO 4 and alkali sulfates as separate products. NiO and NiSO 4 form eutectic mixtures with alkali sulfates melting at temperatures lower than those of the pure salts.