The semiquantitative estimations of 980°C exothermic reaction products of kaolinite by quantitative X-ray diffraction (QXRD) and chemical leaching techniques show the formation of a significant amount of amorphous aluminosilicate p h a s e (-30 t o 40 wt%). T h e t h e o r e t i c a l l y e x p e c t e d A104/A106 ratio in the 980°C reaction is in close agreement with the value measured by the X-ray fluorescence (XRF) technique and the experimental radial electron distribution (RED) profile agrees with the suggested 980°C formation of Si-A1 spinel with mullite-like composition. Mullitization of kaolinite has been compared with a synthetic AIzO3-SiO2 mixture. In synthetic mixtures development of a n intermediate amorphous aluminosilicate phase is a n essential step prior to mullitization. Kaolinite forms mullite in two ways: (i) by polymorphic transformation of cubic mullite a t 1150" to 1250°C and (ii) by nucleation of mullite in the amorphous aluminosilicate phase and its subsequent growth above 1250°C. Thus chemical continuity is maintained throughout the reaction series and the intermediate spinel phase is silicon bearing and its subsequent transformation to mullite confirms the topotactic concept in the kaolinite transformation. [
Earlier works of mullitization through the gel route have been reviewed and the results show 980°C DTA and erystalline phases. Some AI2O3-SiO2 gels have been synthesized by using different precursors and by varying pH and water content during the gelification process. Thermal changes of these coherent gels were studied by DTA and X-ray powder diffractometry. The results demonstrate that two types of aluminosilicate gels form. The first type produces orthorhombic mullite directly on heating at 98OoC, whereas the second type forms cubic mullite first at 980°C and then transforms to the orthorhombic variety on further heating. Lastly, the cause of the 980°C exotherm is explained with reference to kaolinite.(4)
In the present work the authors have developed a finite difference method of analysis for any circular plate with any kind of loading on semi‐infinite elastic foundations. No assumption regarding the contact pressure distribution has been made. The equations have been developed in non‐dimensional form and also the results have been obtained in non‐dimensional form. These results have been compared with the available experimental results and the agreement between them is found to be much better than that of the previous works. The same method with slight modification can be applied for Winkler type foundations and problems of circular plates with varying thickness.
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