Synthesis of long chrysotile fibers was studied under hydrothermal dehydration process with an addition of magnesium iodide which had the same structure as the bromide and was found to be effective in the formation of the fibers.
In this experiment free iodine appeared in the slurry by decomposition of hydrogen iodide formed by hydrolysis of magnesium iodide. When the slurry was subjected to hydrogen pressure at initial stage of the reaction, satisfactory results were obtained. The product was a layer like natural chrysotile ore bundled from fibers of the almost same length. Therefore, it was deduced that iodide contained in the intermediates was easily dissociated and the bundling of fibers was carried out at a smaller degree of disturbance as compared with the bromide.
Crystal growth may be controlled by initial hydrogen pressure and dehydration velocities. The velocities were also controlled by the reactivity of metallic iron added to the outside of the slurry container.

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A glass containing Li₂O, Al₂O₃ and SiO₂ as the principal components and P₂O₂ of about 2 wt% and TiO₂+ZrO₂ of about 4 wt% as the so-called nucleating agents can be converted by suitable heat treatment to a transparent glass ceramic material whose average transmission of 5mm thick plate is 80% or over in visible region. It is the purpose of present paper to examine the structural change of the glass during the heat treatment putting the stress on the nucleation phenomenon.
The study was made by electron microscope observation (mainly direct transmission method), electron and X-ray diffraction methods, differential thermal analysis and measurement of thermal expansion coefficient. The results are summarized as follows:
1) The tendency toward phase separation of glass was increased by the addition of nucleating agents.
2) The crystalline nuclei whose mean diameter was 30-80 Å were confirmed to precipitate before the main crystals-β-Quartz solid solution-crystallize out. The position of diffraction peak due to the nuclei in both electron and X-ray diffraction patterns agreed with that of the strongest one of ZrO₂ (cubic system) or ZrTiO₄.
3) It was found that some incubation period (about 40 min at 750°C) was required for the nuclei to precipitate and thereafter the nuclei tended to grow by the diffusion controlled mechanism and to approach to a certain constant size. The higher the temperature at which the glass was heat treated, the larger was the mean size of nuclei.
4) The approximate number of nuclei per unit volume was of the order of 10¹⁶-10¹⁷ and the volume fraction seemed to be less than 2%.
5) The mean size of main crystals which was estimated from the broadening of X-ray diffraction peak increased with increasing heat treatment temperature and time, depending more strongly upon the temperature.
6) The degree of crystallinity which was calculated using an equation proposed by Ohlberg et al. increased in S-shape with increasing heat treatment temperature and time. This change was similar to that in thermal expansion coefficient.
7) A probable mechanism for formation of main crystal was suggested, that is, the region which is close to main crystal in composition but still remains in amorphous state is formed first around nucleus and then the region transforms rapidly to crystalline state after it grew to fairly large size in comparison with nucleus.
8) It was also elucidated that probably one main crystal was formed from one nucleus by the analysis of the relationship between the number of nuclei per unit volume, the mean size of main crystals and the degree of crystallinity which were determined independently each other. This seems to be supported by the direct observation of thin glass films by electron microscope.

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[in Japanese]

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AlN, TiN, ZrN, HfN and Si₃N₄ were synthesized by nitrogen plasma torch in a short time. The identification of products were carried out by Xray diffraction. Their physical properties as well as the behavior at high temperature of them were examined. Moreover, using optical means, their structures were examined.
AIN was most easily synthesized while Si₃N₄ was the most difficult.
In Si₃N₄ it was seen that the silicon melted at high temperature coagulated again to prevent nitrogen from diffusion into it.
Based upon X-ray diffraction patterns, these five nitrides were identified with hexagonal AlN, cubic TiN, cubic ZrN, face centered cubic HfN, and hexagonal Si₃N₄, respectively. A small quantity of β-Si₃N₄ mixed with α-type. Lattice constants calculated mostly agreed with values reported hitherto. To the contrary, density was more close to theoretical density than any other reported values.
A crystal growth of TiN was minutely observed under the optical microscope. It seemed that the crystal grew into dendritic pyramid starting from skeletal crystal.
AlN was oxidized rapidly at 1000°-1200°C changing into Al₂O₃ although over 700°C oxidation carried out gradually. By means of high temperature X-ray diffraction, two characteristic peaks of Al₂O₃ appeared at 1120°C and at 1200°C, respectively. In the lattice of AlN, diminishing of peaks of (100) and (110) planes were remarkable.
In comparision with powdered AlN, pressed AlN obviously more impeded the diffusion of air at 1000°C.
Wettability of AlN to fused glass was much smaller than that of any other nitrides.
As mentioned above, synthesized nitrides showed no great difference on their properties compared with hitherto reported products except that the synthesis period was shortened. Therefore when a small quantity of nitrides are urgently required, this procedure is considered to be of good use.

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The relationship between the growth temperature and the polytype of SiC crystals has been studied experimentally in the range from 2200°C to 2600°C at the condition of low supersaturation.
The results are summarized as follows;
1) In all region of the present experiments, excluding one example in which 4 H-type was involved, the structure of all crystals consisted of 6H-, 15R- and other long c-period types exceeding 21. Among the elemental structures of SiC, 2H, 3C, 4H, 15R, 6H, and 21 R, only the 6H and 15R were found.
2) From the results stated in 1), it was concluded that in the range of 2200°-2600°C, 6H and 15R have the most thermal stability among the structures considered as elemental. In this conclusion, however, the effect of impurity in the crystal and the shift from the stoichiometry were neglected.
3) The relative amount of 15R increased with decreasing temperature; 6H showed an opposite tendency.

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In the previous paper, the authors confirmed that addition of glass powders rich in BaO and TiO₂ to BaTiO₃ crystal powders was effective to extend the firing range of the pressed mixture and to obtain BaTiO₃ ceramics with dielectric properties little influenced by sintering temperature (J. Ceram. Assoc. Japan 75, 278 (1967)). In the present study, temperature characteristics in dielectric properties were measured at 1 kc/sec (applied voltage, 2V) by means of Bridge method in the cooling process of the specimens from 160°C to -60°C. On the same specimens, observation of microstructure by electron microscope was made in order to investigate structure dependency of the temperature characteristics.
The results obtained are summarized as follows: 1) By addition of glass powders of a BaO-Mg(Ca)O-TiO₂-SiO₂-Al₂O₃ system, the BaTiO₃ ceramics with temperature characteristics of dielectric properties little affected by sintering temperature were able to be prepared. 2) The temperature characteristics in dielectric properties of the BaTiO₃ ceramics thus prepared are much influenced by the composition of the glass powders added. The MgO component is especially effective in decreasing the temperature changes of their dielectric properties. 3) Addition of the MgF₂ crystal powders together with the BaO-TiO₂-SiO₂-Al₂O₃ glass powders (glass 7.5, MgF₂ 2.5 by wt%) to BaTiO₃ powders is effective in decreasing temperature changes of dielectric properties and also in raising dielectric constant near room temperature of the BaTiO₃ ceramics. 4) Effects of addition of the glass powders on temperature characteristics of dielectric properties can be reasonably explained on the basis of the electron microscopic observation of the microstructure of the specimens.

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Zirconium diboride (ZrB₂) was deposited on the heated graphite substrate by the chemical vapor reaction of zirconium tetrachloride, boron trichloride and hydrogen. Under certain condition, the resulting deposit was found to have a high density (higher than 99% of theoretical density), a high purity (total impurity less than 100ppm), a high hardness (H_V=2200±100kg/mm²), and to have a preferred orientation in which the (110) or (100) plane of the ZrB₂ crystalline lied parallel to the surface of the graphite substrate.

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