2.1 - Synthesis of Compound and Individually Separated Ultra-Fine Particles

Abstract

This chapter discusses the methods for producing UFPs and describes the morphology and catalytic properties of Cu-Zn compound UFPs as well as the morphology of isolated UFPs and their applications. One of the methods for producing UFPs is the gas evaporation method and it has been shown that when an alloy having elements with similar vapor pressures is evaporated from a single crucible, alloy UFPs with uniform compositions can be obtained. UFPs produced via the gas evaporation method are of high purity and are produced under conditions of quasithermal equilibrium and have good crystallinity. The size of the particles can be controlled by adjusting the evaporation source temperature and the helium gas pressure and any element that can be vaporized can be made into UFPs. In the gas evaporation method the UFPs aggregated to form black powders. The diameters of the individual particles ranged from 30–70 nm, and the nearly spherical particles were fused together due to sintering. There were no rectangular platelets characteristic of zinc particles present among the particles. By modifying the conventional gas evaporation method, Cu-Zn UFPs with little inhomogeneity in their compositions can be produced. Such materials are normally difficult to produce due to the large difference in their vapor pressures. These UFPs have a complex morphology and exhibit superior catalytic activity for methanol synthesis.