Preparation of glass and ceramics by sintering colloidal particles deposited from the gas phase

Abstract

With the increasing demands being made on the properties of glass and ceramics, conventional preparation techniques are reaching technical limits. New methods which start from highly dispersed powders now offer better possibilities. As the diffusion lengths are short in submicron particles, green bodies made from these powders can be easily purified. Furthermore, considerably reduced sintering temperatures are possible due to the high sintering activity of powder with large surface areas. These powders can be deposited from the gas phase as compact particles with a diameter between 7 and 100 nm. SiO2, AI2O3, and TiO2 are already commercially available at a moderate price. Unfortunately, some problems with the ceramic processing of the highly dispersed powders have to be weighed against these advantages. In this paper the influence of the particle diameter on each processing step is discussed in more detail. SiO2 and AI2O3 serve as examples. In the case of AI2O3 another problem arises from the shrinkage during the phase transition from the δ- and γ- to the A-modification. It is shown that highly dispersed A-Al2O3 can be prepared via the deposition from the gas phase, resulting in a material which should solve this problem.