Abstract
A study on improvement of transmittance through optimization of Y2O3 transparent ceramic microstructure using a spark plasma sintering

Cheol Woo Park
Advisor: Prof. Kwang Bo Shim
Graduate School of Hanyang University

With the rapid development of industries, there is a growing demand for the improvement of the functionality of existing materials and the development of new highly functional materials. Since nano technology has been highlighted as a core technology of the 21st century, more precise control of the microstructure has been required, and interest in the development of new sintering process technology has increased. In particular, transparent window materials using the wavelengths of mid-infrared light are key materials that act as the eye under extreme conditions. Such transparent ceramics are widely applied in military and civilian fields where infrared transmitting materials are used. The applications of transparent ceramics include infrared domes, sensor windows, jigs for semiconductor display process equipment, touch panels, and medical thermotherapy. The transparent ceramic materials currently being used and studied include Y2O3, AlON, YAG, and MgAl2O4. In contrast to the fact that the mid-infrared transmittance of most transparent ceramics begins to decrease in the 5 μm wavelength region, the light transmittance of yttria has been reported to remain 80% or higher even beyond the 5 μm wavelength region. The infrared emission intensity directly depends on the temperature of the emission source, and the intensity peaks in the 3-5 μm wavelength region near 800 K, which is the jet engine exhaust temperature. To maximize the object identification ability of a sensor targeting projectiles such as air crafts and missiles, the ability to transmit mid-infrared light in the 3-7 μm region is most important. Because the transmittance of yttria in the 3-7 μm region is higher than that of any other materials, it is currently in focus as the most suitable window material. In this study, the spark plasma sintering method, which allows very fast sintering at low temperatures and precise control of the microstructure by tuning process parameters, was used to produce Y2O3 transparent ceramics. The objective was to maximize the transmittance by tuning various process parameters and optimizing the microstructure of the ceramics. The sintering behaviours and microstructures were analysed to evaluate the properties required for the Y2O3 transparent ceramic material. Via spark plasma sintering, the characteristics of the Y2O3 transparent ceramic material were improved and the problems of the long-duration conventional sintering methods were avoided, thus preventing abnormal grain growth and resulting in a uniform microstructure.