High-temperature microscopic observation of MgO-FeO solid solution reaction and MgO-Al₂O₃ combining reaction in the state of crystallities aggregates were conducted.
In the MgO-FeO solid solution reaction, crystal growth of MgO took place at 700°C when the distance between both crystals was within about 1μ. But crystals separated beyond 1μ did not react.
The MgO-Al₂O₃ combining reaction took place at 1500°C when the distance between both crystals was within about 3μ. The reaction seemed as evaporation-like phenomenon from MgO toward Al₂O₃. But crystals separated beyond 3μ did not react.

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In order to improve the electrical conductivity of zirconia, the systems ZrO₂-MoSi₂ and ZrO₂-SiC up to 40wt% of MoSi₂ and SiC have been studied.
Sintering atmosphere of hydrogen was the best among 3 sorts of atmosphere of combustion gas of city gas, vacuum, and hydrogen. Values for electrical conductivity and energy for conduction of the both systems did not differ markedly from values of stabilized zirconia. The systems ZrO₂-MoSi₂ and ZrO₂-SiC had less advantages in comparison with stabilized zirconia as an oxide heating element.
Zircon was coexisted with MoSi₂ in the samples sintered at 1300°C, 1400°C and 1500°C in H₂ and with SiC in the samples sintered at 1300°C in H₂. ZrC was formed in the mixtures of ZrO₂ and SiC sintered at 1600°C in H₂.
After oxidation in air at 1400°C, appearance of zircon and its growth was recognized in all samples and stabilized zirconia was changed into monoclinic zirconia in the sample sintered at 1600°C in H₂.

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Al³⁺, Fe³⁺ and Cr³⁺ are similar in their chemical properties, and their coordination number to O^2- is six. Their ortho-phosphates are able to have an isostructure with SiO₂, because the ratios of the average ionic radii of the positive ions to that of oxygen ion are nearly equal to each other, -0.30, 0.31, 0.35 and 0.35 for SiSiO₄, AlPO₄, FePO₄ and CrPO₄ respectively. In practice, the quartz type, the tridymite type and the cristobalite type, have been found for AlPO₄ and only the quartz type for FePO₄, but the isostructure with SiO₂ is not yet known even now for CrPO₄. The solid solutions between AlPO₄-FePO₄ and AlPO₄-CrPO₄, which were synthesized above 1100°C, were studied in this paper.
In the AlPO₄-FePO₄ system perfect solid solutions were made, and their crystals had the structure of the cristobalite type and the quartz type when [Al³⁺/Fe³⁺]≥3/7, and ≤2/8 respectively.
In the range [Al³⁺]=0.55-0.3 molar fraction, the crystals were in the transition state from the cristobalite type to the quartz type.
In the AlPO₄-CrPO₄ system the crystal structure was of the cristobalite type with the exception that β-CrPO₄ was isolated when [Al³⁺/Cr³⁺] was below 8/2.

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To obtain highly refractory mineral wool (glass fiber), authors tried to produce those which crystallize without softening during heating. The wool, the composition of which is within the system CaO⋅Al₂O₃⋅2SiO₂-2MgO⋅2Al₂O₃⋅5SiO₂-CaO⋅TiO₂⋅SiO₂, was easily produced by arc smelting of raw materials and by blowing compressed air to the melt. These samples, however, softened between 700°C and 800°C during heating before the crystallization took place. Surface treatment with various salts, especially such as Cu(NO₃)₂ and AgNO₃, was found to be effective to accelerate the crystallization and decrease the shrinkage during heating (compare Fig. 1 and 2).
By X-ray analysis it was observed that these nitrates decompose to the oxides at relatively lower temperatures and react with the glass fiber at the surface and accelerate the crystallization (Fig. 4, 5, 6 and 7). Microscopic observation showed also the decomposition of the nitrate and the reaction with the glass fiber at the surface. It was observed that the reacted oxides diffused into glass phase and formed dense metallic nuclei (Fig. 3 and 8). The reaction at the surface seemed also to remove Griffith flaw and to decrease the effect of the orientation of crystals by the crystallization from these flaws. Dense core of crystals thus formed around each fiber seemed to support the inner glass which should soften at high temperature by itself.
The shrinkage of the properly salt-treated wool was only within a few per cent at 1000°C.

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D. c. conductivities and dielectric losses in BaO-P₂O₅ glasses having various water contents were measured. Water was assumed to be contained in the form of OH group in the glasses as has been shown in our previous works, and its effects on the electrical properties were discussed in terms of proton diffusion in an electrical field;
(1) Contrary to the usual alkali free glasses, the BaO-P₂O₅ glasses showed a clear dielectric dispersion in very low frequency region. Its correlation with d. c. conductivity was similar to that of dispersion of ionic relaxation loss observed in usual alkali containing glasses. The spectral shape was also nearly identical to that for the alkali containing glasses. These facts suggest that the movement of some ions in BaO-P₂O₅ glasses is responsible for both of d. c. conduction and dielectric relaxation.
(2) D. c. conductivities (σ) and magnitudes of dielectric dispersion (Δ ε), which should be closely related to carrier ion concentration, were roughly proportional to the water content. The findings and the acidic nature of OH bond in polymeric phosphates led us to a conclusion that the carrier ion in BaO-P₂O₅ glasses is a proton.

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