Densification processes and microstructural changes of kaolin bodies during firing were examined and their co-relations were discussed.
From the results of the firing shrinkage, bulk density and apparent porosity measurements, following results were obtained. Degree of densification increased with the temperature. The longer the grinding time of the kaolin, the lower the densification of the bodies when fired at 1000°C. However, when fired at temperatures higher than 1100°C, the effect of grinding time on the densification of kaolin resulted inversely.
Shrinkage behaviours were also examined kinematically, and the following results were inferred. The kaolin body shrank at about 500°C, 900°C and 1100°C. Shrinkage occurred at about 900°C might be due to the diffusion sintering process of metakaolin grains. Shrinkage occurred at slightly lower temperatures than 1100°C might be attributed to the viscous flow mechanism and partly diffusion process in the spinel intermediate phase.
Microstructural changes of the fired bodies were also examined by means of X-ray diffraction, polarizing microscope and scanning electron microscope. Further, it was shown that the densification processes and accompanied phenomena of the fired bodies were clearly explained by these microstructural observations.

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The reactivity of phosphoric acid and dihydrogen phosphate additives with expanded vermiculite aggregates and with bond clays at firing temperatures of 800° and 1000°C was investigated from the measurements of X-ray diffraction, water absorption and pH value. The aggregates were prepared by the calcination at 1050°C of the vermiculites from Fukushima Prefecture, Japan and from Palaboroa area, N. E. Transvaal, S. Africa. The bond clays were Mitsuishi-pyrophyllite from Okayama Prefecture and kibushi-clay from Aichi Prefecture. The effect of the additives on the compressive strength of fired insulators of the expanded vermiculite-bond clay system is discussed in connection with the above reactivity investigation. A remarkable increase in strength was observed when magnesium dihydrogen phosphate was added as an additive: The strength was about 22kg/cm² for the test-specimens obtained by the firing at 1000°C of the mixture of 15 expanded vermiculite, 10 kibushiclay and 75 pyrophyllite by wt%, whereas the strength of about 39kg/cm² was achieved when 1.5wt% magnesium dihydrogen phosphate was added into the mixture. This is attributed to the formation of bridge bonds due to both reactions of magnesium dihydrogen phosphate with magnesium oxide component in vermiculites and with aluminum oxide component in bond clays. Little or no change in strength was observed when aluminum dihydrogen phosphate was added. This is connected with the X-ray diffraction evidence that aluminum dihydrogen phosphate does not appreciably react with vermiculites though reacts with bond clays. The thermal conductivity shows a small decrease with increasing the content of additives. This corresponds to the porosity increase due to the dehydration condensation of the additives on firing.

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The vapor phase reaction between silicon tetrachloride and ammonia was carried out at 1050°-1500°C with an intention to produce finely divided silicon nitride, Si₃N₄. The reaction products were examined by means of X-ray diffraction, infra-red spectroscopy, chemical analysis and electron microscopy. The results are as follows:
(1) The reaction products were amorphous powders containing excess nitrogen and hydrogen such as Si(NH)₂, Si₃N₅H₃ or (SiN)₂NH. The degree of the excess decreased as reaction temperature increased.
(2) The products were finely divided and nearly sphere-shaped particles with diameter of 10 to 100mμ.
(3) By heat treatment at 1400°C for 80 to 250min., the amorphous reaction products crystallized partly into α-Si₃N₄ with an evolution of ammonia, but the excess nitrogen and hydrogen decomposed so slowly that the crystallization was incomplete. This fact suggests a high thermal stability of NH groups. On the other hand, a reaction product at -78°C, Si(NH₂)₄, transformed into stoichiometric silicon nitride more easily than the products at high temperature reactions. The less regular structure of high temperature products may perphaps be responsible for their larger resistance to crystallize into silicon nitride.
(4) The reaction products between Si(CH₃)₄ and ammonia were also amorphous as well as those from SiCl₄. In the heat treatment, howeve, the products crystallized into both α- and βforms of silicon nitride.

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The growth rate of silver halide (AgX) liquid particles was measured in the alkali alumino borosilicate glass which could be converted to the photochromic glass with excellent light sensitive properties by appropriate heat treatment.
The size of AgX liquid particles was mainly determined using X-ray line broadening technique assuming the size of liquid particles is equal to that of AgX crystallite found in quenched glass. Three compositions of particles, AgCl, AgCl_xBr_1-x(x-0.79) and AgBr, were selected for measurement. The results were summarized as follows.
(1) The maximum temperature below which the particles could deposit depended upon the composition of liquid. It was approximately 940°C in AgCl, 980°C in AgCl_xBr_1-x(x-0.79) and 1080°C in AgBr, respectively.
(2) Mean diameter of liquid particles of AgCl and AgBr increased in proportion to the cube root of heating time except initial period of time. In consequence the growth was considered to be performed according to the principle that larger particles grew by the dissolution of smaller ones. In case of AgCl_xBr_1-x(x-0.79), the growth rate of liquid particles was smaller at lower temperature and larger at higher temperature than that expected from the cube root relation.
(3) The growth rate for mean volume of liquid particles was approximately expressed by following equation, respectively.
AgCl (510°-600°C)
v/t=4.99×10²exp-92500/RT (cm³⋅sec^-1)
AgCl_xBr_1-x(x-0.79) (530°-700°C)
v/t=1.00×10²exp-96100/RT (cm³⋅sec^-1)
AgBr (585°-705°C)
v/t=1.74×10^-3exp-80000/RT (cm³⋅sec^-1)

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Stress distribution in severely quenched thick plate glasses was examined. Three kinds of glasses (thermal expansion coefficient: 37-94×10^-7/°C) were quenched by air blast from softening ranges of temperature. Photoelastic observations indicated that: 1) Stress distribution in the direction of thickness was not parabolic; stresses and stress gradients were extremely high near the blasted surfaces, 2) Stress distribution was not simple; in some blasting conditions tension at surface layers and saw-teeth-shaped stress distribution were found; 3) The glass with relatively low thermal expantion (60×10^-7/°C) could be stressed as effectively as a soft lead glass; glass transition temperature multiplied by expansion coefficient seemed to be a measure of possible stressing.
Thus we have found non-parabolic stress distribution which had been forecast theoretically but not found experimentally. The results indicate that stress distribution depends on both the degree of air quenching and the deformation of glass plate during blasting.

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[in Japanese]

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