Adsorbed Water on Needle-like Zinc Oxide

Abstract

The needle-like ZnO was prepared by gas-phase oxidation of zin c metal vapor, and the adsorbed water on its surface was investigated by means of DTGA and active hydrogen analysis. Adsorbed state of water on the crystal surface was studied by comparing the needlelike powders with the granulated powders by French process. The, results obtained are as follows. ( 1 ) The proportion of water vapor evolved from the needle-like ZnO around 500°C (isolated hydroxyl) is less than that froth the granulated ZnO. ( 2 ) Around 400°C, it (doused hydrogen bonding hydroxyl) is almost equal to zero. ( 3 ) On the contrary, around 80°C, it is more than that from the granulated ZnO. This water is considered to be molecular type water on the crystal surface. ( 4 ) The amount of physisorption water on the needlelike ZnO is less than that on the granulated ZnO. This seems to be due to the lower concentration of surface hydroxyl on the needle-like crystal.