Quantitative Analysis of Crystalline Silica in Sintered Amorphous Spherical Silica by X-ray Diffraction Method and its Phase Transformation Behavior

概要

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Crystalline silica contents in sintered amorphous spherical silica with Li_2O or K_2O or Cs_2O additive were determined by X-ray diffraction method. Results obtained were as follows. (1) The calibration curves for determining quartz or cristobalite contents were made from X-ray peak intensity ratio using CaF_2 as an internal standard material. The accuracy of the quantitative analysis by X-ray diffraction method was estimated to be below 1%. (2) From the results of the relative values of crystalline silica contents in the sintered silica, the route of the phase transformation was classified into the three paths. path 1 : amorphous silica ⇒ keatite or quartz path 2 : amorphous silica ⇒ cristobalite or tridymite path 3 : quartz ⇒ cristobalite or tridymite The lower relative values of crystalline silica contents in the sintered silica suggested that amorphous silica existed there. (3) The phase transformation of the sintered silica was considered thermodynamically. Because the gap of standard free energies among these silica phases closes each other, the transformations among silica phases occurred readily by changing free energy barriers by external causes. Quartz was formed form amorphous silica because it has the lowest free energy among the crystalline silicas. When adding alkali metal ion, the energy barriers of cristobalite and tridymite decreased. Therefore, amorphous silica transformed to cristobalite or tridymite.
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