In order to study the characteristic properties of fired high Al₂O₃ ceramics formed by injection molding their physical, mechanical, and electrical properties were compared with those of the same composition but formed by pressing and casting.
The conditions of processing whose variation being least influential on the properties of the fired articles were:
(1) Composition,
Nonplastic ceramic material 81.7%
Polystyrene 12.3%
Stearic acid 4%
D. E. P. plastizer 2%
(2) Pressure 1000kg/cm²
Temperature of the mixture 140°C
Temperature of the mold 40°C
Some properties of the articles formed by injection molding, i.e., mechanical strength, coefficient of thermal expansion, specific gravity were in the same level with those formed by conventional means, i.e., by pressing or casting.
The author concluded that the process of injection molding may be applied to the production of the various kinds of articles such as high grade insulators, ceramic cutting tools, etc.

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Many researchers have attempted various model experiments as a method to study the flow patterns or the characteristics of the convection current of molten glass in a tank furnace, as well as the theoretical considerations of the law of similarity. However, the adaptation of the similarity criteria may still be open to criticism.
Standing on the experiences obtained from the previous model experiments the authors intend in this paper to scrutinize the law of similarity and to get the practical and convenient method for determining the experimental conditions, with which the law may be satisfied as much as posible. In the last part of this paper some results of model experiments are indicated and the applicability and its limitations are discussed.
Considering the conditions which make the three equations governing the behavor of liquid in scale model, i.e., Navier-Stokes equation, the equation of continuity and the equation of energy, similar to those of the actual tank, the similarity criteria being Pr, Gr and Re for the pull current were derived. Furthermore, the authors pointed out that some quantites in these formulae for the model should have the proportional relations to those of the actual tank and the other such as pressure, temperature and time have the linier relations, so these quantities must be selected initially to satisfy the demands.
As a model liquid glycerin was used and Gr and Pr numbers for this liquid were determined for vaious concentrations, scales of model and the maximum and minimum temperatures in model. The results are summerized in Fig. 6 which shows the experimental conditions to satisfy the similarity criteria. The maximum and minimum temperatures used above were so determined that the ratio of the viscosities of glycerin at these temperatures in model is equal to that of glass in actual tank. Consequently it is found that, for instance, using 88% glycerin as the working liquid in the 1/30 scale model the applicable temperatures of the liquid are 18.5°C and 56°C against 1200°C and 1500°C in the proto type, and for the 1/50 scale model using 82% glycerin they are 14°C and 57°C.
On the experimental technique it is convenient that the temperature distribution of liquid in model is made similar to that of actual tank by the method of adjusting the heating and cooling conditions.
From the observations of flow patterns in our experiments it is believed that for the most part of tank the model has a posibility to represent the behavor of molten glass in actual tank fairly well.

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In previous paper (Part III) the author gave the results of the investigations on the deterioration phenomenon of steatite bodies making use of the ternary equilibrium diagram, BaSi₂O₅-Mg₂SiO₄-SiO₂, constructed by himself. And the work contained in this paper refers to the extension to the quaternary system, MgO-BaO-Al₂O₃-SiO₂.
Combining the ternary systems, BaO-Al₂O₃-SiO₂ (R. H. Thomas), MgO-Al₂O₃-SiO₂ (G. A. Rankin, H. E. Merwin), and MgO-BaO-SiO₂ (author) the author investigated the constitution of the domain of primary crystalls appearing in the cross section at BaO⋅2SiO₂-Al₂O₃⋅2SiO₂-MgO⋅2SiO₂ of the tetrahedron representing the system MgO-BaO-Al₂O₃-SiO₂, and three other vertical planes chosen appropriately.
Based on the phase equilibrium of the system MgO-BaO-Al₂O₃-SiO₂, the author was able to confirm that the domain of the separation of protoenstatite primary crystals, being essential for the production of stable steatite articles, is occupying a wide fan-shaped area sandwiched between those of trydimite and forsterite.
Furthermore, the correlation of the composition of steatite bodies with the deterioration phenomenon was investigated in the light of the transition of phase equilibrium making use of the vertical cross sections of the quarternary diagram.

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A new ceramics, including Pyroceram, Fotoceram etc. studied in Corning Glass Works, has recently been developed in many countries. The new ceramics, the crystalline materials, devitrified from glass by heat treatment named by authors as “Devitrified Ceramics” (“Devitroceram” in abbreviation).
In our laboratory, studies were made in order to produce the heat resisting devitroceram of superior quality by means of the devitrification of glass. The devitroceram has been obtained by the following two stage heat treatment of special glasses.
The glasses whose composition (Table 1) may be regarded as the mixture of mica, Li1/3Na2/3Mg₃ (Si₃Al₁₀)F₂ and spodumene, Li₂O⋅Al₂O₃⋅4SiO₂, were subjected to the heat treatments:
(1) The glass was heated in 1 hour up to the temperature slightly higher than that of exothermic peak in thermal analysis and kept constant for 2 hours.
(2) In order to stabilize sufficiently the micro-crystals separated out the specimen was heated to 950°C in 1 hour and then to 1000°C in 2 hours.
The specific gravity and expansion coefficient of glassy and crystalline specimens given in Table 3. Although M₁₀₀ (pure mica) turned out an unstable glass having inferior workability, M₇₅S₂₅ (75 Mol. % mica, 25 Mol % spodumene) gave a mass of uniform texture composed of submicroscopic crystalls from which may be expected the highest mechanical strength among this group.
The X-ray spectrometer pattern was able to separate into two groups, one belongs to β-spodumene and the other, probably, to mica. In order to study the process of crystallization the samples of M₃₀S₇₀ and M₇₅S₂₅ were drawn out from furnace at intermediate stages of the heat treatment and then subjected to X-ray analysis. It was confirmed that from M₃₀S₇₀ came out β-spodumene as primary crystal which was followed by the separation of mica, while the order was reverse with M₇₅S₂₅.
Furthermore, the glasses were heated for 24 hours at a temperature below that of the first stage of the heat treatment. The samples taken out from time to time were analyzed by X-ray. On referring to the results of both X-ray analysis it was concluded that the separation of β-spodumene proceeds more and more easily with the increasing amount of mica composition leading to the texture of uniform and compact assembly of submicroscopic crystalls which gives higher strength.

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[in Japanese]

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