The object of the present study is to prepare the cement suitable for particularly urgent construction work. This is “blended cement” consisting of aluminous cement-lime system. Our experiment showed that setting time could be controlled by using some kind of setting retarder. We found the suitable proportion of the mixture and the most effective setting retarder. In this paper, we dealt with the blended cements that set during from several ten seconds to a few minutes, and developed high compressive strength.
The results are summarized as follows:
(1) When lime is added to aluminous cement, it comes to flash setting which makes the cement useless practically.
(2) Under the condition of high alkalinity, the setting time can be retarded when about 1% of the setting retarder that formed coordination compounds with Ca²⁺ is added into the cement. The most effective setting retarder is Ca-2 keto gluconate.
(3) Composition of the mixture to develop desirable high compressive strength is as follows;
aluminous cement, 100g and Ca(OH)₂, 20g, or dolomite plaster, 25g. Water cement ratio is 35%.
(4) Setting time can be also a little retarded by means of addition of portland cement or CaSO₄⋅2H₂O to aluminous cement-lime system.
In addition to this experiment, we discussed the mechanism of hydration and hardening reaction on the basis of the results on X-ray diffraction and differential thermal analysis.

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By the solid state reaction of the mixture 3PbO+ZnO+Nb₂O₅ a pyrochlore-type (Pb, Zn)₂Nb₂O₇, was obtained, while perovskite-type A²⁺(B²⁺_1/3Nb⁵⁺_2/3)O₃ (A²⁺=Ba, Sr and B²⁺=Zn, Mg, Co, Ni; A²⁺=Pb²⁺ and B²⁺=Mg, Co, Ni) can be prepared by usual solid state reactions. To obtain a perovskite-type Pb(Zn_1/3Nb_2/3)O₃, a pressure higher than 25 kbars at 800°-1000°C was necessary. Another method to obtain the perovskite form was quenching the molten solution from the temperatures higher than 1200°C. These conditions are considered to favor Zn coordination number to change into 6.

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1) A thick-film capacitor having a dielectric constant of 94 and tan δ of 0.0130 (at 10⁶c/s) was obtained by firing powder of a PbO-TiO₂-Al₂O₃-SiO₂-B₂O₃ glass on an alumina substrate to approximately 600°C. The layer of glass powder was changed to a glass-ceramic film in this firing process. The temperature dependence of the dielectric constant of the capacitor was almost linear in the range from room temperature to 270°C with temperature coefficient of 0.00083/degree.
2) It was found that glass powders which soften before crystallization are suitable for preparing capacitors of high dielectric constant. Otherwise, many cracks were formed in the thick-film dielectrics, which resulted in the lowering of its apparent dielectric constant.

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Powder mixtures of zirconium diboride and molybdenum disiliside were hot-pressed at the temperatures ranging from 1500° to 2200°C in graphite dies under the pressure of 200kg/cm² in order to improve densifying and oxidation resistance properties. Pressure was applied through out the experiment and shrinkage of the compact was measured by a dilatometric method during hot-pressing at the temperatures below 2000°C.
Final density was measured and density change of the compact during hot-pressing was calculated. Microstrctures were also observed with microscope and electron micro-probe. The compacts were heated in air at the temperatures ranging from 860° to 1600°C and weight changes were measured to estimate the oxidation resistance of the compacts.
Densification of zirconium boride was strongly accelerated by addition of small amount of molybdenum siliside. No other compound except zirconium boride and molybdenum siliside was detected in the compacts by X-ray diffraction. Wetting of molybdenum siliside to zirconium boride was considered to be good by observation of the microstructures.
When the densification data were processed with Murray's equation for hot-pressing ceramics based on plastic flow mechanism, fairly good linearities were observed in the relations between log (1-ρ) and t expect early period. From these relations, viscosities of the compacts were able to be calculated and it was found that the viscosity decreased with increasing content of molybdenum siliside. The densification data were also processed with the rate equations based on stress enhanced diffusion mechanism. It was found that there were two steps in the densification process. First step of the densification was considered to be a deforming process of the particles at the contact area between them. This step corresponds with the early period in Murray's relations. Although second step which corresponds with the linear period in Murray's relations was not decided to be either plastic flow or stress enhanced diffusion mechanism, this step was considered to be a diffusion process. For the compacts containing molybdenum siliside, these steps were not able to be distinguished clearly.
The compacts showed good oxidation resistance with increasing content of molybdenum siliside.

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Two compounds, K₂O⋅Al₂O₃⋅SiO₂ and K₂O⋅Al₂O₃, were studied in order to identify the corrosion products of the mullite exposed to K₂CO₃ vapor. The compounds of various ratio of K₂O⋅Al₂O₃⋅SiO₂ and K₂O⋅Al₂O₃ were prepared from the fired mixtures of K₂O⋅Al₂O₃ and SiO₂. From the results of the powder X-ray diffraction analysis, the following were obtained. The K₂O⋅Al₂O₃⋅SiO₂ and K₂O⋅Al₂O₃ were cubic. Their lattice constants were 7.650±0.005Å and 7.720±0.005Å, respectively, and between these compounds a complete series of solid solution was formed. The corrosion products of the mullite consisted mainly of this solid solution and with prolonged time of exposure to the K₂CO₃ vapor, the solid solution changed into that rich in K₂O⋅Al₂O₃.

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