Some problems on chemical composition analysis of clay minerals by analytical transmission electron microscope.

Chemical compositions of kaolinite, crocidolite, chlorite, sepiolite, chrysotile, beidelite and montmorillonite were analysed by analytical transmission electron microscope (AEM) and were compared with their bulk compositions measured by wet chemical method. Most of the data by AEM using approximately 10 nm probe size showed apparently richer in SiO2 than those by wet chemical method. No significant influence by K-factors of water was recognized by the comparison of the data of kaolinite and metakaolinite, which was prepared by dehydration of kaolinite. Data by picture mode for approximately 0.2μm×0.2μm region for kaolinite showed in good agreement with ideal composition whereas data by spot mode analysed in the same region showed apparently SiO2 rich composition, and were scattered very widely among particles. This anomaly in spot mode data was considered to be due to the channeling effect and possibly to the contamination and/or damage for the specimen by the incident electron beam.