Kinetics and Mechanism of High‐Temperature Reactions of Kaolinite Minerals

Abstract

The kinetics of mullite growth from kaolinite and halloysite at high temperatures were studied by quantitative X-ray diffraction analysis. The evidence in both cases is consistent with a nucleation-controlled model.

Crystal‐chemical investigation of the “cubic Al–Si spinel” issued from the thermal transformation of kaolinite and halloysite

“…At first, de‐hydroxylation between 400 and 650°C yields metastable metakaolinite Al 2 Si 2 O 7 that decomposes at 947°C 15 into an amorphous silica‐based phase and nanocrystalline needle‐shaped aluminum‐rich primary mullite, along with a nanocrystalline “Al–Si spinel” phase that will be the main topic of this work. A similar transformation is observed for related 1:1 phyllosilicate clays like halloysite, imogolite, dickite, and allophane 5,10 . On further heating, secondary mullite grows by reaction between the spinel and the amorphous phase.…”

“…Naturally aluminum‐rich and low in impurities, it is appreciated for its refractory properties and its whiteness. At high temperature, kaolinite undergoes a series of irreversible chemical and structural transformations known through an abundant literature 1–14 . At first, de‐hydroxylation between 400 and 650°C yields metastable metakaolinite Al 2 Si 2 O 7 that decomposes at 947°C 15 into an amorphous silica‐based phase and nanocrystalline needle‐shaped aluminum‐rich primary mullite, along with a nanocrystalline “Al–Si spinel” phase that will be the main topic of this work.…”

A Mossbauer study of the role of iron impurities in the high temperature reactions of kaolinite minerals

“…The two clays used in the present study were an English china clay and a New Zealand halloysite. Both have been fully described elsewhere (Duncan, MacKenzie & Foster, 1969). The principal impurities in both clays were iron (0"8%) and titanium (0"8 and 1.1%).…”

Mullite Phase

“…He inferred that mullite nucleation followed by subsequent Fig. 21.6 Ln(1-a) versus firing time for kaolinite (after Duncan et al 1969). Reprinted by permission of the American Ceramic Society grain growth, which is diffusion controlled in case of KGa-1 whereas phase boundary controlled in case of KGa-2.…”