Structural and Optical Ceramics: Yesterday, Today, and Tomorrow
Ceramics contributes to progression of civilization. Yet advancement of ceramic science and technology benefits from the improved infrastructure and productivity. This paper assesses the development of structural and optical ceramics in the last quarter century. For example, structural ceramics such as silicon carbide whisker reinforced alumina matrix and titanium carbide dispersed silicon carbide matrix composites have made possible high-speed, wear-resistant, specialty tools. Designing of the structural materials involved consideration of thermodynamic compatibility of phases during fabrication, and consideration of the initiation and propagation of fracture. Mechanisms of the observed toughening have been proposed on a scale ranging from continuum to microstructure to atomistics. Optical ceramics including translucent polycrystalline alumina have facilitated the construction of high-pressure sodium and ceramic metal halide lamps. The microstructure and properties such as transmittance and sodium resistance of polycrystalline alumina have improved. The starting powders improved in purity, particle size, and de-agglomeration. Sintering of alumina advanced through optimization of dopants and sintering atmosphere. Densification involves grain-boundary diffusion; retardation of grain growth is due to solute drag. The solid solubility of magnesia sintering aid in alumina is a function of grain size. During grain growth and sintering of magnesia-doped alumina, both the enriched dopant level at grain boundaries and the equilibrium dopant content in the lattice alter, resulting in boundary pinning and pore annihilation. Oxygen vacancies when in motion significantly influence the boundary transport, and when stationary are important to optical properties of the sintered alumina. Further development of improved and new functional ceramics involves consideration of energy and environmental renewability. Prior achievements and outstanding challenges will be discussed.
Wei Pan and Jianghong Gong
G. C. Wei "Structural and Optical Ceramics: Yesterday, Today, and Tomorrow", Key Engineering Materials, Vols. 336-338, pp. 905-910, 2007