The semi-hot wall of MHD generation duct is constructed with many rectangular elements that are made of dense refractory ceramics.
In the steady state running of MHD generator, one side of the element is heated at constant temperature (T_w) by working fluid of MHD generator and the opposite side is cooled at constant temperature (T₀) by the element holder that is kept at constant temperature (T_b). Heat flux is flowed from the latter side of the element to the holder. The value of the heat flux is decided by temperature difference (T₀-T_b) and heat transfer coefficient between them (h). The thermal stress in the element is caused by temperature distribution and temperature-dependent physical properties of the element material.
The critical conditions of the element are determined in order to avoid the fracture caused by the steady thermal stress. The critical conditions are shown by the minimum values of T₀ or the maximum values of h, and decided by T_w and ratio of thickness to width (γ) of the element.
Results are as follows:
(1) The critical values of h became infinite whether γ>4 for magnesia ceramics or γ>1 for alumina ceramics when T_w=1150-1400K and T_b=300-310K. This indicated that the maximum values of tensile stress in the elements are always smaller than the strength of the element materials when T₀=T_b.
(2) A simplified method is developed in order to calculate the critical conditions when γ=0 (infinite plate). Results obtained by this method are almost the same as the critical conditions obtained by the method previously developed by the author when γ<0.5. This indicated that the maximum values of the tensile stress in a duct element where γ<0.5 is nearly the same as those in the infinite plate.
(3) The parameter Γ=(1-ν)Et/(Eα), (ν: Poisson's ratio, E_t: tensile strength, E: modulus of elasticiy, α: thermal expansion coefficient) is found to be a rough measure of the resistive strength against fracture caused by thermal stress under the steady state. The Γ values are about 19.5K for magnesia ceramics and about 46.7K for alumina ceramics which are kept at 1000K. This indicated that alumina ceramics is stronger than magnesia ceramics against fracture caused by steady thermal stress.
(4) The method described in the previous paper is only useful for T_w lower than the temperature (T_c) at which creap or plasticity of the element material occurs. The method described here, however, is available for T_w larger than T_c.

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Hot-pressing was carried out with NbB₂ powder in graphite die under the conditions of 1650° to 2240°C and 50 to 900kg/cm², in the atmosphere (CO+N₂) or in vacuum. The microstructures, densities and Rockwell hardness of the compacts were investigated.
The microstructures were mainly dependent on hot-pressing temperature, and to less extent on hot-pressing pressure. The grain growth was observed in the compacts hot-pressed above 1740°C. In the compacts hot-pressed above 2000°C, the grain growth was intensive and a number of microcracks transversing the grain boundaries were observed.
The density can be expressed as a function of hot-pressing temperature and the logarithm of hot-pressing pressure as follows:
ρ(g/cm³)=-3.58+0.00336T(°C)+1.19logP(kg/cm²)
The Rockwell hardness increased with increasing densities of the compacts. However, the compacts hot-pressed at higher temperatures and lower pressures showed rather higher hardness than those of the same densities hot-pressed at lower temperatures and higher pressures.
The compacts hot-pressed in vacuum had higher densities than those hot-pressed in the atmosphere at the same conditions. On the other hand, the compacts hot-pressed in vacuum showed much lower hardness compared with those of the same densities hot-pressed in the atmosphere.

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The flushing method was adopted to separate the very fine sulfide mineral particles of sphalerite and arsenopyrite from the sericite which is formed in the zinc ore deposit at Tagokura mine, Fukushima prefecture. Since the sulfide minerals of fine particle size concentrate at the oil/water interface more easily than at the air/water interface, the method which transferred directly the fine sulfide mineral particles from the sericite slurry into kerosene was very favorable compared with the conventional flotation. method
The most important factor influenced the efficiency for separation of sulfide minerals was the dispersing state of the slurry. On this factor the elimination of the influences caused by the oxidized substances of sulfide minerals formed in natural circumstance or in condition of ore storage increased remarkably the dispersion of the slurry by addition of reductant and chelating agent with the pH control. Sphalerite showed the best condition for removing at pH 8 and the presence of sodium citrate. However, arsenopyrite was removed more effectively at the conditions of pH 3 and the presence of sodium citrate where the dissolved metal ions can exist favorably in solution than at the condition of pH 8.
Aerofloat 208 and fatty acid soap were used to increase the lyophilic property of the surface of the sulfide minerals. MIBK did the promotive action of separating sulfide-oil drops smoothly from the sericite slurry and controlled the emulsification of the slurry by the excess addition of the collector. By the refining treatment, more than 90% of zinc and arsenic were removed from the raw sericite and each contents were decreased less than 100 ppm and 5 ppm, respectively.

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The influence of sodium aliphatic carboxylic acids, having different hydrophobic chains, on the hydration of alite and portland cement was studied by means of conduction calorimeter (see Fig. 3, Table 3). And the wettabillty of cement with sodium carboxylic acid was discussed by means of the rate of capillary rise (see Fig. 4, 5). Amount of compound adsorbed on cement was determined by Total Organic Carbon analyser (see Table 5).
Sodium aliphatic carboxylic acids consisting of long hydrophobic chains slightly retarded the very early stage of hydration (see Fig. 3) but the hydration of alite or the main hydration of cement was less affected as compared with sodium aromatic sulfonate addition (see Table 3).
The hydrophilic properties of -COONa and -SO₃Na were different each other. -COONa was less hydrophilic than -SO₃Na. Sodium aliphatic carboxylic acids having long hydrophobic chains formed insoluble calcium salts. The very early hydration of cement was retarded and the wettability of cement decreased due to the precipitation of these calcium salts on cement particle (see Fig. 5). But as the time proceeded, these precipitates separated out from cement to form scum. Therefore, sodium carboxylic acids having long hydrophobic chains unappreciably retarded t₁.
Consequently, the balance between hydrophobic and hydrophilic properties plays an important role in the retarding mechanism by organic compounds.

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Thermal stress fracture behavior of various refractories was studied using an acoustic emission technique and a panel spalling method. Effects of thermal shock conditions such as heating rate on acoustic emission characteristics, that is, on crack propagation process were also studied.
As heating rate, specimen dimension or restraining force increased, magnesia refractory exhibited more and more unstable crack propagation. On the other hand, magnesia-dolomite refractories exhibited stable crack propagation and the propagation behavior was scarcely affected by the difference of the thermal shock conditions.
Measurements on magnesia, magnesia-dolomate, magnesia-chromite and high-alumina refractories have demonstrated that each specimen material exhibited different acoustic emission characteristics corresponding to the difference of thermal shock damage behavior. These acoustic emission characteristics were classified into five patterns in the present study.
Because good correlation was obtained among AE total rinddown count, service performance and thermal shock damage resistance parameter R_st for magnesia-dolomite refractories, it is effective to use the acoustic emission technique for evaluating thermal shock damage resistance of refractories such as magnesia-dolomite.

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Compacts of highly pure β-SiC powder with an average size of about 0.1μm were heated up to 2100°C at a heating rate of 5.5°C/min in helium (O₂<1ppm and dew point -74°C). Although no apparent shrinkage was observed on the compacts, scanning and transmission electron microscopic observation revealed remarkable microstructural changes during the heating.
The results obtained were as follows:
(1) After heating up to 1630°C, joining and coalescence among particles were observed in the compact. It was found that the coalesced grain was polycrystalline and consisted of many differently oriented grains, of which size was in the range of 0.1 to 0.3μm.
(2) In the compact heated up to 1900°C, the grain growth by about ten times in size was observed, although extensive morphological change among particles occurred without appreciable grain-boundary migration.
(3) During heating up to 2100°C, some parts of the compact was densified almost to its theoretical density, and development of pores took place in other parts. Thus no densification occurred as a whole.
(4) A distribution of dihedral angles was measured from the transmission electron micrographs, and the most frequently observed angle was 92°, which gave a value of 1.39 as the ratio of grain-boundary energy to surface energy. This suggests that virtually no thermodynamic limitation would exist for densification of SiC.

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Vaporization experiments for 3Y₂O₃⋅WO₃ were carried out by using the Langmuir and the Knudsen methods from 1630° to 1755°C, and also effects of oxygen partial pressure on the vaporization rate were determined at 1660°C. WO₃ component only vaporized selectively with a zero-order reaction in an initial stage and then with control by diffusion through remained Y₂O₃ layer in a later stage.
The vaporization rate of 3Y₂O₃⋅WO₃ exhibited a dependence of -0.079 on the oxygen partial pressure. Therefore, the vaporization reaction is assumed as follows:
3Y₂O₃⋅WO₃(s)→3Y₂O₃(s)+9/64W₃O₉(g)+6/64W₄O₁₂(g)+2/64W₂O₆(g)+3/64W₃O₈(g)+3/128O₂(g)
The standard enthalpy and the entropy changes of the reaction were 28±4kcal/mol and 3.1±1e.u., respectively, from the Knudsen vaporization.

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The phase separation in the glass of the system Na₂O-B₂O₃-SiO₂-MoO₃ has been investigated as the basic study on the solidification of high level radioactive waste with glass.
The amount of MoO₃ or sham-waste to be introduced without phase separation into the glass increased with the substitution of B₂O₃ for SiO₂ in the basic glass composition.
Parameters for estimating the limiting amount of MoO₃ to be introduced into a glass of given composition were determined from experimental data, assuming the melt of the system Na₂O-B₂O₃-SiO₂-MoO₃ to be the regular solution of pseudo-binary system consists of two end members, Na₂MoO₄ and the remaining oxides. The limiting amount of waste to be introduced, estimated using the parameter for respective structural unit which is expected for a melt of given composition, agreed to the experimental result.

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