Upon PXRD analysis, it was found that signals at 2θ values of 12.3 and 24.7 gets sharper after the calcination of 7Å halloysites. Can anyone explain me the reason. I know that unfolding of halloysites tubes can happen due to the water loss on calcination. Does it affect the sharpening?
Dear Anish Philip, Heating at 300-400 °C often increases the height of XRD peaks of halloysite that results in XRD spectrum similar to kaolinite pattern (due to tubes unfolding), and increasing crystallinity. See the attached paper, discussion and references cited in. Best wishes, Anicet
Anish,
the main reason is that even "7Å" halloysites usually still contain some interlayer water, i.e. 10Å layers, it typically takes quite high temperatures (300C) and prolonged heating to drive it all out. Unrolling during heating is not really a factor.
sincerely,
steve
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