Thermal behavior of the kaolin minerals

H. Insley, R.H. Ewell
1935 Journal of research of the National Bureau of Standards  
When minerals of the kaolin group are heated at constant rates there are two principal heat effects, a broad, pronounced endothermic effect near 5.'50 0 C and a sharp, intense exothermic effect near 950 0 C. New evidence, based largely on X-ray patterns of the kaolin minerals and of artificial alumina-silica gels after various heat treatments, leads to the following conclusions: (1) The endothermic effect is due to the dissociation of the kaolin m inerals into water vapor and an intimate
more » ... an intimate mixture of amorphous Ah03 and amorphous Si02; (2) The exothermic effect is caused by the crystallization of /,-Al,03 from amorphous AI. Oa; (3) The delay in the crystallization of /,-AhOa until higher temperatures are Teached and the resultant intensity of the effect produced are due to the restraining action of the rigid amorphous SiOz network with which the AhOa is closely a~~ociated.
doi:10.6028/jres.014.037 fatcat:7ed7ufuwbbbfjp4vy6buwmvv3m