Preparation of ultrafine particles (chemical method).

Abstract

Needs for ultrafine and homogeneous ceramic powders have increased and many nonconventional powder preparation techniques have been developed. In the preparation of powders, it is important to control both chemical and physical characteristics of the powders to meet the requirements in their applications. An example of requirements for the starting powders for sintering is that the powders are consisted of small, spherical, and unaggregated particles with a narrow size distribution and to have a uniform and controlled chemical composition. In the present paper, the some of the recent preparation techniques of ceramic powders from solution and vapor phases will be described.Preparation of ceramic powders from solution can be classified into precipitation and solvent-evaporation techniques. Among precipitation methods, the alkoxide process is receiving an increasing attention as a method to produce fine monosized and monodispersed spherical oxide particles. There are two methods for the powder preparation from vapor phase : evaporation-condensation (PVD) and vapor phase reaction (CVD). The application of PVD method is limited because of less volatile nature of refractory materials. CVD method as powder preparation technique can be characterized by : (1) highly discrete particles; (2) ultrafine powders with narrow particle size distribution; and (3) direct preparation of powders of metals and nonoxides in addition to oxides. In CVD method, applications of plasma and laser to the powder production is also recieving an increasing attention.