Zirconium carbide was hot-pressed at the temperature ranging from 1450°C to 1950°C in graphite molds with nickel added by the amount of 3-10% in order to improve its sinterability and oxidation resistance.
Density-time relation during hot-pressing obtained by a dilatometric method wass consistent with the rate equation proposed by Murray et al. for hot-pressing ceramics. The equation was dD/dt=3P/4η⋅(1-D). The activation energy for densification of ZrC derived from experiments was calculated to be about 50kcal/mole.
Densification of ZrC compact was strongly accelerated by Ni addition. A body with higher density was formed with increasing amount of Ni addition. Little grain growth was observed in ZrC-Ni compacts. X-ray microanalyzer analysis showed that in specimen hot-pressed with 3% Ni at 1750°C, Ni element was not always limited to be on grainn boundaries, but was distributed rather uniformly through the specimen. Mobility of Ni element in ZrC compact seems to be great. Chemical analysis showed that residual amount of Ni decreased with increasing hot-pressing temperatures in ZrC-10% Ni compact. Nikel metal and zirconium carbide were recognized in specimen by X-ray diffraction, but no other compound of nickel was observed in the diffraction pattern. With optical microscope it was observed that most of pores in compact were distributed in the surface layer which was distinguished from inner layer. The abnormal grain growth and growth of pores in coarse grains were observed. Although open pores decreased easily and almost disappeared at the end of firing process, some of closed pores remained even at the end of the firing process, and this fact was considered to be due to the existence of Ni metal.

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In relation to three hydrated phases which were obtained by the reactions between the water vapor and the solid phases of nepheline=carnegieite compositions in the foregoing paper, attempts were made to establish a correlation between the structure of the starting solid and the product with a hope that the structure of the starting solid might be inherited to the product. Dehydration experiments of the products were carried out also in relation to clarifying their structural relationships.
X-ray powder diffractions of the nepheline hydrate I and the species Y obtained in the previousp aper and of the nepheline hydrate II which is of a low-water type closely relating to these hydrates and obtained by hydrothermal reaction after Barrer's method, were examined and are listed in Table 3-6. All these patterns can be tentatively indexed based on orthorhombic cells which are shown in the tables and also summarized in Table 7. Indexing was made by trial and error based on the available electron diffraction patterns. Some discrepancies, however, are still observed, which may suggest that dehydration occurs to some extent under high vacuum and also by electron bombardment during the electron optical observation.
The high temperature X-ray diffraction patterns and thermal analysis curves are illustrated in Fig. 1-8 for the nepheline hydrate I, the species Y, and the hydroxy-sodalite of the present experiments and for a nepheline hydrate II. It seems that in the former three species, some lattice distortion takes place upon partial dehydration as shown by the splitting of the diffraction peaks. The original structure, however, is nearly resumed by further dehydration and eventually goes to a nepheline structure. At the final stage of dehydration double exothermic effects in D. T. A. curves are characteristic for all of these three hydrated phases, which seems to be due to complicated transformation processes including the formation of intermediate sodium aluminosilicate phases. As compared with these, the thermal change of nepheline hydrate II is so simple that dehydration brings about the direct formation of nepheline structure as low as at 600°C. Though little can be said of the actual structures of these phases at present, close relationships between the original solid phase and hydrated product can be demonstrated by a comparison between the lattice parameters as illustrated in Fig. 13 and 15. The lattice dimensions suggest that the structural units of aluminosilicate as illustrated in Fig. 14 are inherited throughout the hydrothermal processes.

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By putting a small droplet of etchant solution on the surface of optical glass were studied topographic marks produced thereon with the aid of a microscope and a multiple-beam interferometer. Small droplets (about 0.01ml) of water, acid and alkaline solutions, and alkaline solutions containing some quantity of dissolved SiO₂ were put on two samples of polished surfaces. One of them was kept in air and another was kept in mineral oil, for example gasoline, during various times at room temperature.
Several types of corrosion were observed (see Table 2. and Fig. 3). In the case of water corrosion, the dissolution was uniform (Type B) (see Fig. 8). Thereafter the type of corrosion turned from B to C (see Fig. 9) with increasing time of attack. The reason for this phenomena is explained by the change of pH values. In alkaline solution, the degree of corrosion became deeper and that type was observed to be C (see Fig. 12). In acid solution, it was deepest and that type was A (see Fig. 4, 5). And in alkaline solutions with different quantities of dissolved SiO₂, there appeared peculiar corrosion marks of type F (see Fig. 14, 15, 17) caused by precipitating supersaturated SiO₂.
When gasoline was used for immersion liquid, the interference color appeared on glass surface in all etchant solutions used. On the other hand, when the glass was kept in air, the depth of corrosion was smaller than that in gasoline and large number of microcrystals were observed on the corroded surface (see Fig. 7).
The cause for producing the stain on the surface of glass during the process of polishing was cleared up and the method for protecting the glass against stain was found; from practical point of view, it is very important to evaporate up traces of water droplet condensed on the surface of glass (lens) before dipping the glass into gasoline (or other organic solvents) for removing pitch or similar adhesives.

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