Browsing by Author "MacKenzie, Kenneth John Dallas"

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The kinetics and mechanism of the high temperature solid state reactions of kaolinite minerals
(Te Herenga Waka—Victoria University of Wellington, 1965) MacKenzie, Kenneth John Dallas
This thesis describes a kinetic study of the solid state reactions of kaolinite minerals at high temperatures. These reactions can be represented by the idealized equations: The formation of mullite and cristobalite from metakaolinite has been studied in the temperature range 1060°C - 1220°C using several different but well characterized starting materials. A method of X-ray analysis for mullite has bean developed for following the reaction. The experimental data, which suggest that the mechanism is independent of the starting materials, have been compared with several theoretical models for nucleation and diffusion processes. The data up to 90% conversion of mullite can be explained satisfactorily by exponential nucleation followed by rapid crystal growth. Rate constants for the reactions of kaolinite, halloysite, and copper halloysite have been determined. The corresponding enthalpies of activation (87-96 K cal. mole.-1), free energies of activation (108-130 K cal. mole.-1) and entropies of activation (-15.3- -28.8 cal. deg.-1 mole.-1) are independent of the starting materials.
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Studies on the Solid State Reactions of Aluminosilicates at High Temperatures
(Te Herenga Waka—Victoria University of Wellington, 1967) MacKenzie, Kenneth John Dallas
This thesis describes a study of the high temperature reactions of the class of hydrous aluminosilicates typified by the kaolinite group of minerals. The work was carried out using X-ray diffractometry, infrared spectroscopy and electrical conductance measurements. The effects of impurity cations and anions and of the reaction atmosphere was also studied, using infrared and Mossbauer (γ-ray) spectroscopy. The high temperature reaction sequence of kaolinite can be represented by the following idealized equations:- The kinetics of mullite formation from metakaolinite and related clay minerals have been determined by X-ray and I.R methods, and the corresponding thermodynamic function compared with theoretical disorder entropy value calculated from idealized structural models. A comparison has also been made with activation energies for the conduction process. The slow step in the reaction has been identified as the formation of mullite from the spinel via a number of intermediate mullite-like phases differing from each other only in the arrangement of the octahedral aluminium atoms. This mechanism is supported by a normal co-ordinate analysis of the mullite "molecule" and the assignment of the infrared frequencies of mullite. The behaviour of cationic impurities can also be explained in terms of the influence of metal-oxygen interactions is confirmed by electric conductance measurements on cation-doped clays.