Interdiffusion coefficient of Mg²⁺ and Al³⁺ in the defective spinel, MgO⋅nAl₂O₃, was measured using the couple of spinel pieces, MgO⋅1.1 Al₂O₃ and MgO⋅1.6 Al₂O₃. Interdiffusion coefficient of the MgO⋅1.1 Al₂O₃ side and the MgO⋅1.6 Al₂O₃ side were separately analyzed as shown in Table 1 by applying the Fick's law tothe concentration distribution measured by EPMA. The Arrhenius plot is shown in Fig. 6 and so-called activation energy, 73kcal/mol, was obtained. The Matano's analysis for one example was carried out as shown in Fig. 7. Two values of the interdiffusion coefficient were calculated and compared with the experimental values, by substituting the self-diffusion coeffisients of Mg²⁺ and Al³⁺ estimated on some assumptions, into the Wagner's formula of interdiffusion coefficient,
D=D₁D₂(z₁²c₂)/z₁²c₁D₁+z₂²c₂D₂, and Yamaguchi and Nakano's,
D=D₁D₂(z₁²c₁+z₂²c₂)/z₁²c₁D₁+z₂²c₂D₂{1+c₁c₂(z₁-z₂)²(1-p)/(z₁²c₁+z₂²c₂)(c₁+c₂)p}
And it was clarified that the values calculated from the Yamaguchi and Nakano's formula can well interpret the actual phenomena so that the formula is proper to analysis of diffusion with gradient of vacancy concentration as in the defective spinel.
According to our previous paper, in the reaction of spinel formation, the rate constant, k, is expressed as follows;
k=D256(n-1)(3n+1)²/(21n+11)(3n+5)(7n+1) Where n comes from the ofrmula, MgO⋅nAl₂O₃, which represents the composition of a spinel in equilibrium with Al₂O₃. Fig. 9 shows k calculated from D obtained in this experiment and n obtained from the phase diagram, comparing with the observed k in the previous papers. These calculated and observed rate constants are consistent with one another fairly well. Therefore, it was numerically proved that the dominant mechanism of spinel formation is the interdiffusion of Mg²⁺ and Al³⁺ through the formed spinel layer owing to the concentration gradient expected from the solid solution range and to the interdiffusion coefficient.
The so-called activation energy for the spinel formation is 92kcal/mol, while that of interdiffusion is 73kcal/mol, and the difference between them is about 20 kcal/mol. The cause of that difference is that k and D are connected by the terms of the concentration gradient and the mean composition of formed spinel which are functions of n depending upon a temperature. Therefore, it should be noticed that the “so-called activation energy” for the solid state reactions may have meanings different from the original meaning of “activation energy”.

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Fundamental properties of agate from Yamagatajuku, Ibaragi, Japan and that from Minas Gerais, Brazil were studied by using an X-ray, a thermogravimetric and a chemical analysis with the B. E. T. method.
a₀ and c₀ of Brazil agate with 0.56% of Al₂O₃ and a₀ of Yamagatajuku agate without Al₂O₃ became larger than those of rock crystal, when they were heated at higher temperatures than the α_??_β inversion point. Thus, it was concluded that most impurities of Brazil agate occupied the substitutional sites, while most impurities in Yamagatajuku agate were interstitial.
It was found that the crystallite sizes of agate did not change while the R. M. S. strains changed when the specimens were heated at 300°-900°C for one day.
An activation energy of dehydration process of agate was estimated to be 6-7kcal/mol. It was concluded that such a small value of the apparent activation energy resulted from the sluggish dehydration due to the presence of micropores or channels.

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An approximate structure of lithium boro-germanate has been determined from three dimensional X-ray data. It is orthorhombic (pseudo tetragonal) with two formula units in the unit cell of dimensions,
a=6.371±0.008, b=6.365±0.008, c=6.885±0.009Å.
The space group is Fmm2. The germanate network can be described as a two-dimensional linkage of boron-oxygen tetrahedra and germanium-oxygen tetrahedra. Each boron-oxygen tetrahedron is linked only to germanium-oxygen tetrahedra, and each germanium-oxygen tetrahedron is linked only to boron-oxygen tetrahedra. The lithium atoms serve to hold the networks together through coordination with oxygen atoms.

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Thermal expansion characteristics of green bodies composed of Toseki, Roseki and Kibushi clay as the fundamental raw materials and limestone as an additive constituent are discussed in relation to content of limestone added and to the particle size.
The thermal expansion curves for low limestone bodies show that a profound shrinkage due to sintering following after decomposition of limestone occurs at about 900°C, and it proceeds on into the higher temperature range. Those for the bodies containing limestone much more than 10.5% show a drastic change from shrinkage to expansion at about 960°C. The expansion proceeds on up to 1050°C, but it is succeeded by shrinkage at the temperature. Since the expansion can be observed only within the definite range of temperature (960°-1050°C), it is named in term of “temporary expansion”. The temporary expansion is observable only for the sample containing limestone much more than 10.5% and increases its intensity with increasing amount of limestone added. The sample containing 15% of the fine limestone (content of particles smaller then 10μ in size, 83%) has no expansion, but a little shrinkage in the temperature range corresponding to the temporary expansion. When the coarse limestone (content of particles smaller than 10μ in size, 40%) is used, however, the sample has temporary expansion in a great extent.
Furthermore, identification of minerals newly formed in the green bodies by heating was made by means of D. T. A. and X-ray analysis with the results that they were the calcia-containing minerals such as gehlenite, wollastonite and anorthite. On the other hand, the mixtures corresponding to gehlenite, wollastonite and anorthite in chemical composition was prepared in advantage of limestone, quartzite, alumina and china clay. They were submitted to dilatometry in order to compare with the limestone containing green bodies.
Discussion of these experimental results leads to the conclusion that the temporary expansion observable for the green bodies containing limestone is attributed to formation of calcium compounds such as gehlenite and wollastonite.

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Measurements were made of the tensile strength, Vickers hardness, Young's modulus and surface tension in lead borate glasses and sodium borosilicate glasses. The data of the tensile strength had small variation and no size effect as Thomas' results. NMR spectra of B¹¹ were measured in borosilicate glasses and the fraction of 3- and 4-coordinated boron were determined. From these measurements, the following conclusions were obtained.
1) It was observed that the tensile strength of B₂O₃ glass is 60kg/mm², which is very small compared to that of SiO₂ glass. The reason for this weakness may be that the glass has weak cohesive force between the layers in which boron atoms form planar BO₃triangles.
2) The tensile strength of these glasses shows the change with the composition similar to Vickers hardness and Young's modulus. NMR measurements of B^II in the borosilicate glasses can explain the change of the observed tensile strength with the composition. From these facts, it is proper to consider that there is a relation between the strength and the structure of glass.
3) The experimental values of the tensile strength of sodium borosilicate glasses were compared with the theoretical values calculated by using the observed values of Young's modulus and surface tension in Orowan's equation. The experimental values are about one fourth of the theoretical values, although the dependence of both values on the composition are similar. It may be said that the experimental values have not yet reached the intrinsic strength.

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硼珪酸塩ガラスの構造を明らかにするために, SiO₂-Na₂O-B₂O₃三成分系ガラスのうち組成の異なる数個のガラス試料を選び, それらの急冷した試料とさらに580℃で30時間熱処理した試料とについてKBr錠剤法で赤外線吸収スペクトルを測定した. BO₃三角形配位による吸収と考えられている1400cm^-1附近の吸収スペクトルを定量的に測定し, その値を解析することによって, 硼素の配位状態を調べ, ガラスの化学組成の構造依存性を検討して, 次の結果を得た.
(1) R(Na₂とB₂O₃のモル比) ≦0.5の場合, 実験値 (試料中でBO₃群を形成している硼素原子の割合) は急冷試料のとき直線にのった. (図-8参照)
直線の方程式: N₃=1-R
このことからNa₂OはSiO₂と結合せず, B₂O₃とのみ結合する.
(2) R>0.5の場合, 急冷試料の実験値は直線より上にずれるから, Na₂OはSiO₂とB₂O₃の両方に結合する.
(3) 熱処理した試料では, R≦0.5の場合, 実験値は直線にのり, R>0.5の場合, 急冷試料の実験値より減少するが直線より上にある. このことからR>0.5の場合, 熱処理によってNa₂O・B₂O₃形成が進行する.

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Phenomena in the devitrifying process of phosphate glasses containing both CaO and MgO were studied by DTA, X-ray diffraction and chemical resistivity test. Crystals formed by heat-treatment of the glass were identified to be magnesium metaphosphate in CaO/MgO mole ratio smaller than 1 and β-calcium metaphosphate larger than 4. A schematic phase diagram of CaP₂O₆-MgP₂O₆ system in which the existence of a double salt 2CaP₂O₆⋅MgP₂O₆ was assumed from the results was given. The gush of a melt through a crevice formed in the crystallized layer was observed during the heat-treatment of a cylindrical specimen. Such strongly separating tendency seems to occur because of difference of the anion structure between CaP₂O₆ and MgP₂O₆. A considerable difference of the chemical resistivity between the crystal part and the glassy part in a specimen was detected by a dissolution test by using 1:1 hydrochloric acid.

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