Na_2O-MgO-MgF_2-SiO_2系ガラスからの四珪素雲母の析出

概要

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The glass forming region in the system Na_2O-MgO-MgF_2-SiO_2 was examined, and the crystallization of fluor-tetrasilicic mica from the glass when it was heat-treated was studied by the methods of DTA and X-ray powder diffraction and the electron microscopy. The results were summarized as follows; 1) The clear glass was obtained from the melt containing a lower amount of SiO_2, F or a higher amount of Na_2O than the composition of fluor-tetrasilicic mica (Na・Mg_<2.5>・Si_4O_<10>F_2). 2) A larger amount of the mica crystallized from the glass having the composition nearer to Na・Mg_<2.5>・Si_4O_<10>F_2. 3) The mica crystallized from the glass had the composition of Na・Mg_<2.5>・Si_4O_<10>F_2 and the lattice constants of a=5.17 Å, b=9.08 Å, c=9.81 Å and β=100゜. 4) The nucleation and the crystal growth of the mica started after the glassy phase separation. The rate of crystallization of the mica from the glass depended mainly on the rate of nucleation at the earlier stage of the crystallization. The mica phase which nucleated at the earlier stage decomposed during the heat-treatment for a long time at the comparative higher temperature, on the other hand fluor-richterite crystallized. 5) Activation energies for the nucleation and the growth of the mica phase from the glass were obtained as 115 kcal/mol and 151 kcal/mol, respectively.
1973-10-01