Infra-red Spectra of High-temperature Phases of Kaolinite and Halloysite


KAOLINITE and halloysite in the temperature-range 650–900° C. do not show any pronounced X-ray interference. In this range metakaolinite is formed; its Si—O hexagonal network remains more or less unchanged, while the octahedral sheet is deformed in absence of OH-groups1,2. In kaolinite and halloysite, dehydration brings about a random arrangement in the direction of the c-axis. In pure and perfectly crystallized kaolinite, heated in the differential thermal apparatus at a velocity of 10 deg. C. per min. just above the exothermal maximum, X-ray examination reveals γA12O3 and mullite, whereas in halloysite only γ-alumina appears. In halloysite heated in the same way, mullite is observed3 only above 1,100° C. As the X-ray diagrams of mullite and sillimanite resemble each other closely, it is not certain which of these two phases is formed during the heating of kaolinite and halloysite.

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STUBIČAN, V., GÜNTHARD, H. Infra-red Spectra of High-temperature Phases of Kaolinite and Halloysite. Nature 179, 542 (1957).

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