Spherical Submicron Powders with a Nanopolycrystalline Superstructure—a Promising Raw Material for Obtaining Fine-Grained High-Density Ceramics

Abstract

The unique properties and possible fields of application of submicron powders from refractory oxides obtained by aerosol-spray pyrolysis are considered. Analysis of experimental results obtained by researchers at different times convincingly proves the prospects of using nonagglomerating aerosol submicron spherical powders to produce ceramic materials with a high-density, uniform, and fine-grained structure that does not contain pores. The uniqueness of aerosol powders is due to the presence in particles of a nanopolycrystalline substructure with a developed network of grain boundaries, which during the sintering process, has a significant impact on the efficiency of diffusion mass transfer and promotes to increase the rate and completeness of pore overgrowth. Aerosol powders acquire these properties through the use of ultrasonic spray pyrolysis, where equilibrium physical and chemical processes occur in ultra-small local volumes of aerosol droplets ensuring a high degree of homogeneity of the resulting powder. Being formed ultra-thin substructure of aerosol powders ensures their complete sintering at low temperatures allowing the formation of a high-density, nonporous ceramic material with extreme physical and mechanical characteristics. The practical use of nanostructured aerosol powders does not require the use of operations related to their preliminary preparation (grinding–crushing, classification, purification from impurities, etc.), and, unlike ultrafine powders, such powders are easily molded using traditional methods of powder technology (uniaxial pressing, hot casting, etc.).