Studies of the Hydrous Tin(IV) Oxide Ion Exchanger. IV. The Effect of Heat Treatment

The effects of heat treatments in air or water at high pressure have been studied regarding the properties of a hydrous tin(IV) oxide ion exchanger. The exchanger in a H+ form was stable against heat treatments in both air and water up to around 80 °C; thereafter the exchange capacity progressively decreased with temperature until 300 °C, at which point it was reduced to about a quarter of the initial value. The exchanger began to crystallize at 300 °C, and formed nearly-complete cassiterite crystals at 500 °C (where the capacity disappeared). In contrast, the exchanger in a Na+ form was more stable against heat treatment than the H+ form; at 400 °C, the Na+ form retained 40 per cent of the initial exchange capacity. An examination of the uptake curves showed that more acidic exchange sites were stronger than less acidic sites against heat treatment. The existence of three kinds of water in the exchanger (adherent, zeolitic, and bound) has been suggested on the basis of the ion-exchange capacity, the thermal-analysis curves, and the recovery of water brought about by humidifying.