Structured zinc oxide powder materials: Synthesis and further investigations of their thermal morphological stability

Abstract

ZnO is a versatile metal oxide with a wide range of applications in optoelectronics, catalysis, medicine and lightweight technology. Recently, two powder crystalline structures of ZnO were produced from an aqueous amine-containing zinc salt solution in a 30 to 120min reaction under atmospheric pressure. The novelty concerns the synthesis of the particles. Such particles have been produced in a low temperature synthesis under atmospheric conditions and the synthesis route follows not the conventional hydrothermal route in an autoclave, but in an open vessel. Nevertheless, it is possible to produce particles with a specific structure and small size distribution. On the one hand, rod-like particles with a size up to 1.5μm in length and 0.3μm in width and on the other hand star-like particles with a size up to 0.7μm in diameter and branches <0.3μm were produced. The identification was carried out by means of Raman spectroscopy, the morphology by scanning electron microscopy, and its crystallinity by means of X-ray diffractometry. To explain the structure formation, we developed schematically the formation mechanism starting from a zinc embryo. To improve the suitability of these materials in composite materials, e.g., as an additive in sintered metals or in foundry processes, these structures were further exposed in a 2h annealing process from 500°C to 900°C. The effects on morphology and crystal size are investigated by FE-SEM and XRD-measurements. In both cases, aluminum and magnesium are suitable candidates as matrix material since they have their melting points in the above-mentioned temperature interval. In addition to the chemical resistance, the stability of the particles at these temperatures is a major factor in the first testing. The star-like shaped particles showed a temperature resistance of up to 500°C, and the rod-like shaped particles even up to 700°C, confirming the possibility of use in the above mentioned applications.