A pressure of 55kbar was applied to three cobalt-containing glasses by the use of a high-pressure apparatus of the simple squeezer type at room temperature for 30min. Compositsons of the glasses are; 72.0SiO₂, 10.2CaO, 13.9Na₂O, 1.54K₂O, 1.33B₂O₃, 0.25mole% Sb₂O₃ with 2.0wt% CoO to 100g of glass, 25.0K₂O, 75.0mole% B₂O₃ with 2.0wt% CoO to 100g of glass and 10.0K₂O, 90.0mole% B₂O₃ with 5.0wt% CoO to 100g of glass. Light absorption spectrum in the visible range of the specimens before and after application of the pressure were determined with a microspectrophotometer. From the experimental results changes in ionic distance between the Co²⁺ ion and its neighbouring O²⁺ ions and also changes in numbers of the O^2- ions coordinated around the Co²⁺ ions were calculated by the Ligand Field Theory. Changes in refractive index of the specimens before and after the compression were also measured to determine the residual shrinkage of the glasses in bulk.
The results obtained are summerized as follows:
1) The three absorption peaks characteristic for both the four- and six- fold coordinated Co^2- ions in all of the glass specimens were shifted toward the shorter wave length by the compression; the three peaks at 535, 597 and 633mμ for the silicate glass were shifted to 532, 595 and 630mμ, those at 530, 595 and 633mμ for the high-alkali borate glass to 500, 573 and 613mμ, those at 463, 503 and 555mμ for the low-alkali borate glass to 440, 480 and 530mμ, each respectively.
2) The local shrinkage of the glass structure in the neighbourhood of the Co²⁺ ions calculated from the shift of the absorption peaks were 0.005 for the silicate glass, 0.073 for the high-alkali borate glass and 0.078 for the low-alkali borate glass, whereas the shrinkages of the glasses in bulk calculated from their changes in refractive index were 0.02-0.05, 0.03-0.07 and 0.03-0.06 for the silicate and the high- and low-alkali borate glasses, respectively.
3) Besides the shift of the absorption peaks, developement of the new peaks at 440, 480 and 525mμ, which are probably attributed to the change in coordination number of the Co²⁺ ions from four to six, were observed for the high-alkali borate glass.

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This research was carried out as a part of the study on the synthesis and the stability region of cobalt garnet (Co₃Al₂(SiO₄)₃). Mixtures of SiO₂, Al₂O₃, Y₂O₃ and CoO corresponding to the compositions m[Co₃Al₂ (SiO₄)₃](1-m)[Y₃Al₂(AlO₄)₃](m: mole ratio) were treated at 1200° and 1400°C for 48 and 18 hr, respectively, at the ambient pressure. The heat-treated samples were examined by a X-ray diffractometer and under a polarizing microscope.
Only garnet appeared in the mixtures of m=0.0-0.32, indicating that the crystalline solution phase of Co₃Al₂(SiO₄)₃-Y₃Al₂(AlO₄)₃ series was stable in this range of m. In the mixtures of m=0.40-0.475 treated at 1200°C granet coexisted with spinel, Y₂O₃-SiO₂ minerals and very minute amount of silica (?), and garnet coexisted with spinel and minute amount of Y₂O₃-SiO₂ minerals in the mixtures treated at 1400°C. No garnet was found in the heat-treated products of the mixtures of m=0.55-0.675. Spinel, cristobalite, Y₂O₃-SiO₂ minerals and minute amounts of unidentified minerals were found in the mixtures treated at 1200°C and only spinels seemed to be stable at 1400°C. Spinel, olivine and cristobalite were found in the mixtures of m=0.75-1.0 treated at 1200°C. At 1400°C spinel was the only crystalline phase.

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The development of forsterite by solid state reaction in mixed powders of MgO and enstatite in various mole ratios at the temperature range 1100°-1300°C and times up to about 100 hrs is followed by quantitative X-ray diffraction measurement. Powders are used consisting of coarse (10μ) particles of one component in a fine-grained (mostly 1μ) matrix of the other component. The results are consistent with a diffusion-controlled mechanism and up to about 80% reaction to agree with the Ginstling-Brounshtein equation. Reaction constants are evaluated and activation energies in the range 100-110kcal/mole are obtained.
Studies, using mixed powders and reaction couple with platinum markers, indicate that Mg is main diffusing species.
Comparison of these results with our previous study of MgO-SiO₂ solid state reaction makes it possible to presume that the rat-controlling process of MgO-SiO₂ reaction arises from diffusion of Mg through the thin enstatite layer which forms between the main reaction product (forsterite) and the SiO₂ component.

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[in Japanese]

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