TEXTURAL ANALYSIS OF PITCH COKE BY OPTICAL MICROSCOPY AND IMAGE PROCESSING

摘要

Coal tar pitch-based coke (pitch coke) is used widely in several industrial fields as raw material for aluminum cathodes and carbon specialties such as electrical discharge machining electrodes, crucibles for semiconductors, hot press molds and atomic core material. Pitch coke requires various properties for each application and this is done by designing the optical texture and porosity. It is well known that there is a close correlation between the texture of pitch coke and their bulk properties. However this correlation is only tacit knowledge based on human perception and it provides only qualitative properties of pitch coke. The coefficient of thermal expansion (CTE) is one of the most important qualities of pitch coke and is evaluated qualitatively by polarized light microscope observation (depended on a qualified operator). On the other hand, quantitative CTE data of pitch coke can be obtained by an actual measurement of a laboratory size graphitized electrode, which requires significant effort and expense. Therefore, quick and strictly unbiased evaluation method is desired instead of this laborious work. Polarized light microscopy (PLM) is a commonly used technique to observe the optical texture of carbon materials [1-3] and image processing has been applied in order to make the polarized light microscope observation quantitative [4-7]. In this paper, we report about the color image analysis method of pitch coke texture and about the quantitative correlation between pitch coke texture and the CTE.