Formation of rod-like zinc oxide microcrystals in homogeneous solutions

Abstract

The formation of zinc oxide microcrystals obtained from hydrolysis of zinc nitrate and zinc chloride in the presence of hexamethylenetetramine has been studied by X-ray diffraction, electron microscopy and IR spectroscopy. Prisms, needles and spherulitic aggregates are formed depending on several factors such as reactant concentrations, pH and temperature. It is shown that the formation of prisms and needles is mainly determined by kinetic conditions with prisms favoured at lower temperatures (< 80 °C), where faces can be developed from the solution complexes. The formation mechanism of the monodispersed prisms and needles occurs by coupling of microcrystalline spheres through their c axes forming embryonic rod particles which later grow. On the other hand, the formation of spherulitic aggregates is more the consequence of solution heterogeneity, i.e. high reactant concentrations.