The application of rare earths and rare earth oxides in ceramic materials is mainly used as additives to improve the sintering, compactness, microstructure and crystal phase composition of ceramic materials, thereby greatly improving their mechanics and electrical , Optical or thermal properties to meet the performance requirements of ceramic materials used in different occasions. This article briefly reviews the application of rare earth oxides in structural ceramic materials and functional ceramics.
Rare earth oxides can promote sintering as a flux.
Rare earth oxides can improve the ceramic microstructure.
Rare earth oxide plays a role of doping modification.
Structural ceramics refers to a type of ceramic material in which the crystal grains are mainly ionic bonds and covalent bonds, which have good mechanical properties, high temperature properties and biocompatibility. Structural ceramics are widely used in daily life, and have now expanded to high-tech fields such as aerospace, energy and environmental protection, and large and medium-sized integrated circuits.
Alumina ceramics are widely used in the manufacture of circuit boards, vacuum devices and semiconductor integrated circuit ceramic packages. In order to obtain ceramics with good performance, it is necessary to refine the crystal grains and distribute them in equiaxed crystals, reduce the porosity of the ceramics, and increase the density. It is best to reach or approach the theoretical density. The high sintering temperature of alumina ceramics and the high price of high-purity alumina firing materials limit its promotion and application in certain fields. Studies have shown that the addition of rare earth oxides can form a liquid or solid solution with the matrix oxide, reduce the sintering temperature and improve its mechanical properties. Commonly used rare earth oxide additives include Dy2O3, Y2O3, La2O3, CeO2, Sm2O3, Nd2O3, Tb4O7 and Eu2O3.
Zirconia (ZrO2) has three crystal types: monoclinic phase, tetragonal phase and cubic phase. At a certain temperature, zirconia is accompanied by volume expansion and shear strain when the crystal form transformation occurs, and the volume expansion may cause the product to crack. Zirconia has a high melting point, strong acid and alkali corrosion resistance, good chemical stability, and high bending strength and fracture toughness. The mutual transformation of the three crystal forms will be accompanied by volume expansion or contraction, resulting in unstable performance, and stabilization measures must be taken. Adding rare earth oxides as stabilizers to zirconia can form a stable cubic zirconia solid solution after high temperature treatment, and can also improve its toughness, strength and conductivity. Zirconia ceramics have been widely used in refractory materials for converter steelmaking, medical artificial teeth, various sensors and high-temperature heating elements.
