Transparency is a key property of alumina ceramics, which is not only related to the basic chemical composition of the material but also depends on the microstructure of the material. Therefore, the transparency of alumina ceramics depends on factors such as porosity, grain size, grain boundary structure, and surface finish of the ceramics.
The preparation process of alumina ceramics is essentially a densification process that eliminates microscopic pores during the sintering process. The size, number, and type of pores in the material will have a significant impact on its transparency. In addition to porosity, the diameter of the pores also has a great influence on the transmittance of alumina ceramics. When the diameter of the pores is equivalent to the wavelength of the incident light, the transmittance is the lowest.
The grain size of the alumina ceramic polycrystal also has a great influence on the light transmittance. When the incident light wavelength is equivalent to the grain diameter, the light scattering effect is the largest and the light transmittance is the lowest. Because of this, to improve the light transmittance of alumina ceramics, the grain size should be controlled outside the wavelength range of incident light.
It is understood that the grain boundary is one of the important factors that destroy the optical uniformity of the alumina ceramic body, thereby causing light scattering and reducing the light transmittance of the material. Moreover, the greater the composition difference of the materials, the greater the difference in refractive index, and the lower the light transmittance of the entire alumina ceramic.
In addition, the transmittance of alumina ceramics is also affected by the surface roughness, which is not only related to the fineness of the raw materials, but also related to the machining finish of the ceramic surface. The surface of the untreated alumina ceramic after sintering has a large roughness, so the light incident on this surface will have diffuse reflection, resulting in light loss.
