Mn-Zn ferrite crystals were fractured along the main low-index planes, (100), (110) and (111) to obtain fracture toughness (K_Ic) for each plane. Controlled surface flaw (CSF) technique and indentation fracture (IF) technique were used. In the CSF technique, microplastic zones around Vickers impressions were identified by slip traces. Removal of the zones by surface grinding resulted in elimination of residual stress. In the IF technique, the proposed expressions for K_Ic evaluation and effects of surface treatment were discussed. The plane of lowest toughness was (110) with K_Ic of 1.14±0.06MN/m^3/2 in CSF technique. For IF techique, there was a difference in K_Ic between chemically and mechanically polished surfaces: K_Ic=0.73±0.02 MN/m^3/2 for the former, K_Ic=1.09±0.09MN/m^3/2 for the latter (indentation load: 100gf to 300gf, crack to impression ratio: 3 to 4). Etching after indentation resulted in underestimation of K_Ic because of crack growth. It was difficult to fracture the crystal along a (100) plane without causing fractures along the other planes (mainly (110)) both in the CSF and IF techniques. Only small loads (≤50gf) could yield Palmqvist-type cracks along (100). For a (111) plane, fractures were necessarily deviated from the intended planes in the IF technique. K_Ic for near (111) was obtained by CSF technique to be 1.40±0.21MN/m^3/2. The lowest toughness plane of the spinel ferrite was (110), which was inconsistent with the prediction from the single crystal elastic anisotropy. Furthermore, this plane was a slip plane at higher temperatures (>1000°C). These results were different from those reported on MgAl₂O₄.

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Al₂O₃-SiC-C refractories are used in ladle for hot metal pretreatments. In the Al₂O₃-SiC-C refractories used in such treatments, the surface of SiC grains is corroded in a comb-like shape, and deposits of carbon are found in the affected section. The Na₂O-Al₂O₃-SiO₂ compounds also deposited on the surface of Al₂O₃ grains and inside the micropores. The following remarks have been obtained based on the microscopic observation of the refractories used and the thermodynamic study in the system SiO₂-SiC-C.
(1) Carbon is oxidized at the hot surface to generate CO(g), forming a reducing atmosphere. A part of the generated CO(g) reacts with SiC(s) to deposit carbon in the refractories by the following reaction.
SiC(s)+CO(g)→SiO(g)+2C(s)
(2) SiC grains in the refractories are corroded by the reaction with CO(g) within the refractories to form SiO(g) and carbon. Consequently, the affected section is filled with carbon.
(3) The generated SiO(g) is oxidized by CO(g) to SiO₂(s), which reacts with Na₂O and Al₂O₃ to form Na₂O-Al₂O₃-SiO₂ compounds on the surface of Al₂O₃(s) grains and inside the micropores. These compounds, which create a denser structure, prevent the gases from passing through the refractories and suppress the oxidation of carbon.

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The equimolar spinet powders have been synthesized by spray-pyrolysis of the water-methanol solutions of magnesium and aluminum nitrates, and their sinterability was studied. The specific surface area and pore volume of the powder depended on the calcination temperature and showed maximum values when calcined at 400°C. Although the primary particle size and the specific surface area of the powder calcined at 400°C were 150Å and 120m²/g, respectively, the lattice parameter of the powder was 8.081Å, suggesting that the particles are composed of the nearly perfect spinel lattice. The as-sprayed powder showed poor sinterability, but the grinding increased the sinterability to a great extent. As the methanol content in the solvent was increased, the agglomerated particles became fragile and tended to fracture more easily by compression. Censequently, the bulk density of the sintered body increased with decreasing of the ratio of water/methanol ratio in the solvent. A sintered body with 97% of theoretical density was obtained when the spinel powder was prepared under the optimum conditions and sintered at 1500°C for 4h. The sinterable powder was obtained when a water-methanol (1:1) solution containing 0.3mol/l Mg and Al was spray-pyrolyzed at 800°C, followed by grounding and calcination at 800°C for 1h. and calcined at 800°C for 1h.

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The strength of sintered β-sialon was measured at room temperature. The average strength was 534MPa. The Weibull modulus calculated from 25 measurements was 6.5. The value excluding two abnormally low strength specimens was 8.8, comparable to that of hot-pressed β-sialon. The fractures were originated from surfaces or interior defects. The average strength and Weibull modulus of specimens fractured from surfaces were 490MPa and 4.7, respectively, while those fractured from the interior was 564MPa and 10.6, respectively. Almost all of the interior defects were large voids or clustered pores. The surface defects were flaws or interior defects exposed to surfaces by polishing.

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Density, elastic moduli, Vickers hardness and thermal expansion coefficient for CaO-P₂O₅ (47.5-55.0mol% CaO) and MgO-P₂O₅ (47.5-57.5mol% MgO) glasses have been studied. Mean molar volumes calculated from mean molecular weight and density were compared with ideal mixed molar volumes estimated from the molar volumes of the constituent oxides in the phosphate glasses. The relationship between these two kinds of molar volumes for CaO-P₂O₅ glasses was a linear over the entire range of composition, whereas the relationship for MgO-P₂O₅ glasses was not linear with maximum deviation at the metaphosphate composition relative to the linear line for CaO-P₂O₅ glasses. The deviation decreased with a decrease in MgO content and the curve agreed with the linear line for CaO-P₂O₅ glasses about 33mol% MgO. There were definite relationships between elastic moduli (bulk modulus K, Young's modulus E, shear modulus G and Poisson's ratio ν) and mean atomic volume as follows; K=K₁V^f, E=K₂V^g, G=K₃V^h, 1+ν=K₄V^j, where f=-9.0, g=-5.1, h=-4.4, j=-0.7, for CaO-P₂O₅ glasses, f=-5.0, g=-3.4, h=-3.1, j=-0.3 for MgO-P₂O₅ glasses, There was a linear relationship between Poisson's ratio and density and also between Vickers hardness and void fraction φ for CaO-P₂O₅ glasses as well as MgO-P₂O₅ glasses; where φ=1-V₀/V_m, V₀=4/3π∑r_i³n_i, V_m: mean molar volume, r_i: ionic radius and n_i: number of i-ion. Vickers hardness decreased with increasing void fraction. Thermal expansion coefficient for compostions from 47.5 to 57.5mol% CaO or MgO increased with an increase in CaO or MgO content. The thermal expansion coefficients of CaO-P₂O₅ glasses (11.0-11.8×10^-61/K) were larger than those of MgO-P₂O₅ glasses (7.66-8.47×10^-61/K).

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Fine powders of alumina-zirconia mixtures were prepared by hydrothermal oxidation of Al-Zr alloys which were fused in an arc image furnace. The hydrothermal oxidation of Al-Zr alloys proceeded above 500°C under 100MPa for 3h, and the obtained powders consisted of monoclinic zirconia, tetragonal zirconia and alpha-alumina. The average crystallite sizes of these phases were 13-24nm, 9-12nm, 27-35nm, respectively, smaller than that of monoclinic zirconia or alpha-alumina (which was) prepared by hydrothermal oxidation of Zr or Al metal under the same condition. Alumina-zirconia powders prepared by this method were homogeneous mixtures of alumina and zirconia particles of which sizes were around 30nm as determined by Transmission electron micrograph (TEM) observation.

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The growth of potassium titanate fibers was studied by a new growth technique called “slow-cooling calcination method”. By this method, a specific composition is incongruently melted into a solid phase and liquid phase, and then is slowly cooled to a temperature region below the incongruent-melting temperature. Fibrous crystals are grown by a incongruent melt-association reaction between the solid and liquid phases during the cooling precess. In the system K₂Ti₂O₅-K₂Ti₆O₁₃, a stating material having the n value between 2<n<6 in the K₂O⋅nTiO₂ formula was incongruently melted into a liquid phase and K₂Ti₆O₁₃ solid phase at above the incongruent-melting temperature (1114°C±15°C) of K₂Ti₄O₉, and then was slowly cooled to a temperature region below 1114°C. During the slow-cooling process, the incongruently melted K₂Ti₆O₁₃ solid phase and liquid phase again reacted to associate. This association reaction plays a very important role to grow potassium titanate fibers, especially K₂Ti₄O₉ fibers. Relatively long fibers were grown in the mixed fibers of K₂Ti₄O₉ and K₂Ti₂O₅ when a starting material of K₂O⋅2.8TiO₂ composition was calcined at 1150°C for 4h, and then was slowly cooled to 950°C with a rate of 16°C/h, and was followed by quenching to room temperature. Consequently, the K₂Ti₄O₉ fibers in them were grown by an incongruent melt-association reaction, and the K₂Ti₂O₅ fibers were crystallized from the liquid phase during the quenching process. The growth of K₂Ti₄O₉ fibers was mainly depended upon three factors of starting composition, calcination temperature and cooling rate, and furthermore was also promoted by repeating the incongruent melt-association reaction.

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