Surface characterization of some selected zinc oxide samples II: Zinc oxide prepared by thermal decomposition of zinc carbonate

Abstract

Zinc oxide was thermally dehydrated in vacuo at different temperatures in the range 100 – 500 °C. Nitrogen adsorption measurements were carried out on the different samples; the specific surface areas, the total pore volumes and other surface parameters were estimated and correlated. The adsorption isotherms were characterized by hysteresis phenomena over the entire temperature range. The initial increase in the area of the hysteresis loop up to 300 °C is attributed to the increase in molecular water loss. The high temperature (greater than 300 °C) dehydration resulted in the appearance of high pressure hysteresis loops which are attributed essentially to the sinterability of the zinc oxide sample. The specific surface area initially increases at 200 °C and then gradually decreases to the maximum temperature studied (500 °C). The early increase in nitrogen surface area is due to the loss of physisorbed water together with a contribution revealed by the increase in the magnitude of the Brunauer-Emmett-Teller C constant. The gradual decrease in nitrogen surface area above 200 °C was followed by different methods of analysis, the V 1- t method, the n S- n R method and pore size distribution curves. The change in porosity characteristics accompanying the development of some narrower (or micro) pores was interrelated with the estimated adsorption values.