種々のカオリン鉱物の分析電子顕微鏡による化学組成の分析

抄録

Chemical compositions of kaolin group minerals, i.e. two kinds of dickite, three kinds of kaolinite and two kinds of halloysite, having various stacking orders and particle shapes, were examined by analytical transmission electron microscope (AEM). Analysed data using the spot mode in probe size of approximately 10 nm were apparently richer in SiO₂ than the ideal value of SiO₂ obtained by wet chemical analysis except for spheroidal halloysite. On the other hand, analysed chemical data by picture mode for 0.2μm×0.2μm region were in good agreement with ideal value, although those of disordered type kaolinite showed a little SiO₂ rich composition. The most probable interpretation for the difference observed between the spot mode and picture mode data was the channeling effect which occurs in the specific orientation between an incident electron beam and a crystal lattice. Furthermore, this effect results in the enhancement of an X-ray intensity for a specific element, although, probability due to the contamination and/or beam damage was also considered. Contents of Fe₂O₃ in kaolin minerals varied fairly widely among the specimens : Takabatake dickite (poorly ordered) < Red Mountain dickite (well ordered) < Oguni kaolinite (well ordered) < Georgia kaolinite (poorly ordered) < Indonesia halloysite (short tubular) < Motoyama Kibushi clay (disordered) < Ina hallysite (spheroidal).