Studies of the Hydrous Niobium(V) Oxide Ion Exchanger. III. The Effect of Heat Treatment

The effects of heat treatments in air have been studied regarding the properties of a hydrous niobium(V) oxide ion exchanger in H+ form. The exchanger lost 17 per cent of the initial ion-exchange capacity when it was heat-treated at 110 °C; thereafter the exchange capacity decreased progressively with temperature until 400 °C, at which point it retained about a half of the initial value. The exchanger began to crystallize into γ-phase at a temperature between 450 to 500 °C where the capacity disappeared. The γ-phase transformed to α-phase at a temperature above 800 °C. An examination of the uptake curves showed that less-acidic exchange sites were more resistant than more-acidic sites to 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 water recovery brought about by humidifying.