Stress relaxation mechanisms of sodium phosphate glass were studied in the vicinity of T_g. The materials were linearly viscoelastic and time-temperature superposition were successful. The temperature dependence of shift factor is of the WLF type. In the ultra-region the half-width of the distribution of relaxation times becomes narrower with an increase of crosslinking. In the poly-region the relation between the maximum relaxation time and molecular weight shows that the entanglement of polyionic molecules does not occur. In the ultra-region the relaxation between logτ_m and 1/T have an Arrhenius-type behavior. This suggests that the bond interchange does occur in the molecular P-O-P frameworks rather than in the interchain ionic linkages.

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An effect of grinding on the negative charges of the clay minerals has been studied, paying attention to the distribution of the charges on basal and edge surfaces.
The negative charges on the basal surface resulting from the isomorphous substitution were assessed from the C. E. C. values at pH 4, whereas those on the edge surfaces which vary with pH values of the ambient aqueous media were computed from the difference in C. E. C. values at pH 10 and pH 4.
Dickte from Hiraki-mine and kaolinite (Soft Georgia kaolin), chosen as samples, were dry ground or wet milled. Dry grinding produced particles on which the edge surfaces occupied a relatively greater proportion of the total surface area.
The obtained conclusions are as follows.
1. The negative charge densities on edge-faces of the ground samples were larger than those on basal surfaces.
2. The negative charge densities decreased gradually as grinding proceeded, which may suggest that the isomorphous substitution diminishes from the outermost surfaces toward the interior of the unground particles.

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In order to study on the densification mechanism of the system which retains open pores until the final stage of densification in hot pressing, a model system has been proposed. A theoretical equation
D_h.p.={1+nπ[2r₀η/(Pt+2η)]²}^-1
has been derived for the system on the basis of Shaler's theory which has treated the rate of shrinkage of the capillary pores of a glass tubing in normal sintering.
The validity of the equation has been confirmed experimentally using the compacts of the orientated glass filaments.

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1. The processes in the solid state reaction on the formation of perovskite type Pb(Mg_1/3Nb_2/3)O₃ from its component oxides have been investigated by a powder X-ray diffraction measurement. As a result, it is found that pyrochlore phase exists in three types, and that an interchange of these phases occurs at about 790°C, accompanied with the melting phenomena.
2. In the formation of the perovskite type, it seems that there are two processes involving the solid reaction on the bases of 2PbO⋅Nb₂O₅ and 3PbO⋅Nb₂O₅, respectively, and the composition of the product from 3:1:1 mixture (PbO:Nb₂O₅:MgO in molecular ratio) is an intermediate state of these in the two processes. Lattice constant of rhombohedral pyrochlore phase gradually approaches that of cubic one as the amount of Pb substituted by Mg increases, and the transformation to cubic type is completed in the substituted amount about five mole per cent, and above this amount the substitution by Mg does not occur.
3. When MgO contained in the mixture is in excess (e.g., 3:1:1.2), the amount of PbO volatilized decreases, and simultaneously the yield of perovskite increases. It is considered that the existence of excess MgO promotes the reactivity of MgO to the (NbO₃) network and drives the free PbO into the stable lattice.
4. By the hydrothermal treatment, cubic pyrochlore is obtained at relatively low temperature although no perovskite is formed.
5. For tetragonal pyrochlore, two atomic configurations are hypothetically suggested. Based on these configurations, the calculated powder X-ray patterns are compared with the observed one. It is concluded that the network-vacant configuration is more probable.

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The glass having fluor-richterite (Na⋅NaCa-Mg₅⋅Si₈:O₂₂F₂) composition was crystallized by various heat treatments and the relation between microstructure and bending strength of the crystallized material was studied. The results obtained were as follows:
1) The difference of microstructure between the outer surface and the internal part of the crystallized material was observed. A small amount of enstatite coexisted with fluor-richterite (main crystalline phase) on the surface, whereas only fluor-richterite was found in the internal part.
2) The amount of crystalline phase and the crystallite size varied with the heat-treating conditions.
3) Microcracks formed on the surface of the specimen when it was heated up to crystallization temperature at a comparatively high heating rate.
4) Secondary grain growth of fluor-richterite crystalline particle occurred during the heat treatment for crystal growth at a comparatively high temperature.
5) The bending strength of the crystallized material decreased with the increase of crystallite size. However, no quantitative relation between them was obtained, presumably due to the influences of microcrack and inhomogeneity of the microstructure resulting from secondary crystal growth.

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Factors, which essentially govern properties of casting slips, seemed to be the distribution of size and shape of particles, their surface activities and their dispersion states. If we could determine appropriate fundamental parameters to these factors, and if we could understand relationships between fundamental parameters and practical properties of casting slips, we could make more progress in casting slip control. As fundamental parameters, the author chose the solid fraction of dry bodies (F₃), the effective specific surface area for water movement through cast bodies (S_a), and the hydration degree of solid surfaces (d_s). The practical testing methods of these parameters were introduced and variation of their values for various conditions were discussed. The results were as follows.
1) F₃ which relates to the arrangement of particles in cast bodies was much influenced by the particle size distribution and the dispersion state.
2) S_a which could be determined from the casting rate of the slip on the basis of the equation by Adcock et al. was also influenced by the fineness and the dispersion state.
3) d_s could be calculated from the moisture content of cast bodies, and their values decreased with increasing degree of deflocculation.

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