The variations of microhardness in aluminum oxide crystals were examined; (1) the effects of loading conditions in a single crystal of ruby and (2) characteristics of crystal grains in a polycrystal of corundum with 0.8mol per cent MgO. The ruby was produced by the Verneuil method and the corundum was prepared by a molten method in argon atmosphere at 2100°C.
A thin section was used for the measurement of microhardness in the corundum, since subgrain boundaries and precipitates in grains could not be observed under a microscope attached in a microhardness tester, but detected under a polarized microscope.
The results are summerized as follows:
(1) The diagonal of indentation figures d (μ) for the (0001) surface of ruby varied according to a formula, P=1.82d^1.85, depending on the load applied P(g).
(2) A temperature higher than 250°C was preferable for the measurement of microhardness in the ruby, since cracks or fractures around the indentation marks disappeared at such temperature.
(3) The microhardness numbers (300g) on (0001) and (1010) surface of the ruby at room temperature were 2065±95kg/mm² and 2230±140kg/mm², respectively. As the temperature increased, from room temperature to 1000°C these numbers decreased almost lineary.
(4) The microhardness of grain boundaries in the corundum tended to become lower than that of grain centers.
(5) On the plane nearly parallel to c-axis in the corundum, the microhardness of subgrain boundaries tended to become lower than that of subgrain centers. On the plane nearly perpendicular to c-axis, the microhardness of subgrain boundaries tended to become slightly higher than that of subgrain centers.
The effects of loading conditions on the variation of microhardness were almost neglegible as far as cracks or fractures were not formed. It will be deduced from the above observations that subgrain boundaries and precipitates in the grains caused a marked variation of microhardness in the corundum.

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In previous paper (Yogyo-Kyokai-Shi 77, 1 (1969)), the synthetic conditions of the hexagonal boron nitride from ammonium thiocyanate (NH₄SCN) and orthoboric acid (H₃BO₃) were reported. In present paper, the formation mechanisms and some properties of the hexagonal boron nitride were reported.
The heat-treated samples were examined by a chemical analysis, heating-loss measurement, X-ray diffraction, infrared spectroscopy, and polarizing and electron microscopy.
In an ammonium atmosphere, the formation mechanism of hexagonal boron nitride could be shown as follows.
nH₃BO₃+n/2NH₄SCN160°-200°C→[-HN⋅BO(OH)]_n→[HN=BH]_n
[I] [III]
250°C→[BNH]_n300°-440°C→[BNH_0.8]_n450°-500°C[BNH_0.3]_n→800°C→[BN]_n
[IV] [V] [IV]
Borazin ring was observed to grow gradually from 250°C. A structure [IV], structure [V] and structure [VI] had eight, about eighteen, about one hundred and fifty borazin rings, respectively.
In a flowing atmosphere of nitrogen, on the other hand, gas almost not played an important role on synthesis of hexagonal boron nitride, therefore while it was partially followed the same process as above mentioned, but boron oxide was simultaneously formed.
The average distance of layer-plane (L_a) and the average distance of layer interval (L_c) values were gradually increased from 800°C and rapidly increased from about 1450°C. When samples synthesized (previous paper) were heat treated at 1450°C and 20kbar, L_a and L_c values became about 290 and 275 (Å), respectively, and a lattice parameter C₀ value was nearly equal to that of a complate hexagonal boron nitride. It was clear that pressure was much effective to grow boron nitride crystal.

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Solubilities and physical properties of phosphate glasses in the systems, alkaline earth oxides-phosphorous pentoxide, were measured. Glass systems concerned in the present study are CaO-P₂O₅, MgO-P₂O₅, SrO-P₂O₅, BaO-P₂O₅, CaO-MgO-P₂O₅ and CaO-MgO-SrO-BaO-P₂O₅. The composition of the glass specimens covered from 0.7 to 1.7 in mole ratio RO/P₂O₅. The subjects tested in this paper are solubility of P₂O₅ component in various solvents, chain-length distribution of phosphate ions, mineral composition of the devitrified specimens obtained by heat-treatment, density and refractive index. As the solvents for the solubility test, N/2 hydrochloric acid, 2% citric acid, 10% neutral sodium citrate, 10% sodium hydroxide and 10% ammonium hydroxide etc. were used.
The solubility of P₂O₅ in the acid solvents increased with the increase of mole ratio RO/P₂O₅, whereas the reverse change was observed in the case of the basic solvents. It was recognized that the solubility by using the neutral solvents gave a maximum value at a composition of RO/P₂O₅=1. For the sodium hydroxide solvent, MgO-P₂O₅ glass resulted in a considerably high solubility comparing with the other glasses.
The anomalies of some physical properties and solubility in a system MgO-P₂O₅ glass disappeared by adding other alkaline earth oxide to a original system. For instance CaO-MgO-P₂O₅ and CaO-MgO-SrO-PaO-P₂O₅ glasses had no anomalies concerning density and refractive index curves. When the system contained the mixed alkaline earth oxides, glass formation was observed even in high alkaline earth oxide region. The inclusion of RO in the melt of a sample up to 1.7 in mole ratio RO/P₂O₅ gave the vitrifaction of the specimen. In these mixed alkaline earth glasses, only two kinds of phosphate ions with short size, i.e. ortho and pyro, were detected by paper chromatographic test and their acid solubilities were higher than those of the other phosphate glasses.
No change in the size-distribution of the phosphate ions was seen in the process of dissolution of the glasses in the various solvents except for the acid solvents in which the hydrolysis of phosphate ions occured considerably and rapidly. It seems that when these glasses are heat-treated and then devitrified no reaction among the phosphate ions arises and the phosphate ions with the various size in the original glass make the correspondingly crystalline phosphates.

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Basic properties of domestic agate and of foreign agate were studied by an X-ray method, polarization microscope, thermal analysis and emmission spectrochemical analysis. The agate is a family of quartz with minute amount of Al and Fe or Mg ions as ingredients without any bonding materials such as amorphous glass or opal. The agate held a small amount of structural water which was eliminated off at the temperature ranging from 400°C to 600°C on heating. The values of thermal expansions of agate in principal axes, which were determined by high temperature X-ray diffractometer, were smaller than those of rock-crystal, especially in the direction of c axis. The agate transformed into cristobalite below 1025°C and the corresponding activation energy of crystal growth were evaluated to be about 60 kcal/mol. This value is smaller than that of siliceous stone. It was supposed that the broadning of five-fold lines in the vicinity of 68° in Cu K_α radiation, the broadning of α-β inversion peak in DTA curves, the structural water and the size of crystallites in agate were closely related to each other.

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