The dense Y₂O₃-PSZ ceramics with 2-6mol% Y₂O₃ (>99% of theoretical density) were fabricated using fine powders prepared by the co-precipitation method. The thermal and mechanical properties of these ceramics were studied by the following methods.
(1) STEM and SEM observation of microstructure, (2) fracture toughness and 3-point bend strength, (3) the 230°C aging test of 3mol% Y₂O₃-PSZ controlled their grain size, (4) thermal conductivities and thermal expansion coefficients. The following results were obtained:
(1) 2mol% Y₂O₃-PSZ contained only a tetragonal phase, and 6mol% Y₂O₃-PSZ almost a cubic phase. PSZ ceramics with 2-6mol% Y₂O₃ were composed of a tetragonal phase with 2mol% Y₂O₃ and a cubic phase with 6-7mol% Y₂O₃.
(2) The mean values of 3-point bend strength were 1000-1200MPa for PSZ with 2-3.5mol% Y₂O₃, and 900MPa for 4mol% Y₂O₃-PSZ. The fracture toughness decreased with increasing Y₂O₃ content, which corresponded to the relation between the amount of tetragonal-tomonoclinic stress induced transformation and Y₂O₃ content.
(3) The grain-size dependence of thermal stability in temperature range of 200°-300°C was confirmed by the 230°C aging test of 3mol% Y₂O₃-PSZ ceramics controlled their grain size. 3mol% Y₂O₃-PSZ containing large grain more that 1μm occurred microcracking due to T-M transformation, resulting in a decrease of strength, but those composed of fine grain under 0.5μm exhibited no significantly change even after 1500h aging.
(4) The values of thermal conductivities and thermal expansion coefficients decreased gradually with increasing Y₂O₃ content.

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The type or shape of the polymers produced in the course of hydrolysis of silicontetraethoxide Si(OC₂H₅)₄ has been investigated. Four solutions in the Si(OC₂H₅)₄-H₂O-C₂H₅OH-HCl system were prepared. In those solutions the molar ratios of water to Si(OC₂H₅)₄, r, were 1.0, 2.0, 5.0 and 20.0, respectively, while the ratio of HCl to the alkoxide was kept constant at 0.01. The polymerized products or siloxane polymers were trimethylsilylated and subjected to the measurements of number-average molecular weight M_n and intrinsic viscosity [η]. Based on the relation between M_n and [η], namely, [η]=KM_n^a where K and a are constants, type of the siloxane polymer was discussed. The exponent a's for solutions with r's of 1.0 and 2.0 were 0.75 and 0.64, respectively, showing that linear polymers are produced in those solutions. The exponent a for the solution with r of 20.0 was 0.34, corresponding to the three-dimensional or spherical polymer. Intermediate value of a was obtained for the solution with r of 5.0. These results corresponded with the authors' previous assumption that the occurrence of spinnability in a Si(OC₂H₅)₄ solution containing a small amount of water is closely related to the formation of linear polymers in the course of hydrolysis.

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In the glass industry it is recognized that bottles with oval cross-sections are not suitable if the bottles are to be subjected to internal pressure. We investigated theoretically and experimentally the effect of slight ovality on the stresses developed in nominally circular glass bottles under internal pressure. The results obtained are summarized as follows:
(1) When the stresses were measured with strain gauges on bottles of oval cross-section under internal pressure, they showed good agreement with elasto-mechanical calculations.
(2) The new method of stress calculation was investigated under the conditions of known wall thickness and internal radius of curvature of an oval cross-section, and this calculation agreed closely with that obtained by experimental measurements.
(3) The resistance to internal pressure of sample bottles decreased with increasing ellipticity, and it is interesting to note that a origin of the bottle fracture by a bursting test concentrated on the part of minor axis of oval cross-sections at the ellipticity of over ca. 1.5%.

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The phase relation in the system Ta-N was studied in the temperature range of 1400°-1700°C and in the nitrogen partial pressure range of 10^-3-1atm. Two one-phase nitrides, β-Ta₂N and ε-TaN, were obtained, and the N/Ta ratios were between 0.470 and 0.524 for β-phase, and between 0.990 and 0.996 for ε-phase. The c-axis of β-phase increased with increasing nitrogen content but the a-axis remained unchanged. This behavior was discussed based on the structure of β-Ta₂N. The relative partial molal enthalpy and entropy of nitrogen in β-Ta₂N were calculated from the nitrogen partial pressure-composition isotherms.

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The effects of Fe₂O₃ addition on the formation of Al₂TiO₅, microsttucture and bending strength of Al₂TiO₅ ceramics were investigated. Various amounts of Fe₂O₃ from 0.01 to 5wt% were added into equimolar mixture of corundum and rutile, and compacts of these mixtures were fired at 800°C to 1500°C in air. During heating, pseudobrookite solid solution, (Fe_1-xAl_x)₂TiO₅, x<<1, was formed at about 900°C. The composition of the solid solution gradually shifted to Al₂TiO₅-rich composition with rising firing temperature. At 1500°C for 4h, added Fe₂O₃ dissolved almost completely into the Al₂TiO₅ solid solution and corresponding amount of Al₂O₃ coexisted with the Al₂TiO₅ solid solution as corundum phase. The pseudobrookite solid solution which might act as nuclei of reaction lowered the formation temperature of Al₂TiO₅, accelerated the formation rate and affected the formation of domains in which Al₂TiO₅ grains orientated preferentially. With increasing Fe₂O₃, the amount of the solid solution, i.e., the number of nuclei of reaction, increased and size of domains decreased. Especially in fired specimen containing 5wt% Fe₂O₃, the domain size decreased to nearly the same order as that of Al₂TiO₅ grains i.e., 3-5μm, and clear domain structure was not observed. Many cracks were observed on boundaries of domains and of grains of Al₂TiO₅ due to the thermal expansion anisotropy of Al₂TiO₅. In fired bodies having a domain size less than 35μm, crack length on the boundaries decreased and their bending strength increased, but high strength specimens could not be obtained in this work because of many cracks in the fired specimens.

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The thermally stimulated exoelectron emission (TESS) of Li₂B₄O₇ glass ceramics was investigated for its application to the dosimetric use. It has been found the TSEE glow patterns of Li₂B₄O₇ glass ceramics and of the thin layer of LiF evaporated on Li₂B₄O₇ glass ceramics depend on the kind of radiations irradiated. The TSEE glow pattern of the duplicated structure sample indicated a possibility of determining the dose of each kind of radiation separately in the mixed radiation field.

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Statistical analysis based on slow crack growth is necessary to deal with design problems involving fatigue of brittle materials like ceramics under some environments. A new theory is formulated by combining the inert strength distribution (Weibull's bi-modal function) with slow crack growth, under non-uniform stress state. Four-point bending tests in air and vacuume environments were performed on steatite specimens under the constant loading rate so that the inert strength distribution and the crack growth parameter might be obtained. The surface-crack model was selected as the most suitable one from three-models-a newly obtained Weibull's distribution function for surface cracks and/or internal cracks-using failure diagnosis data and Akaike's Information Criterion, AIC. The predictions using the surface-crack model were in satisfactory agreement with experiments.

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The failure probability of the ceramics in use which are proved their life time by a proof test was studied on the basis of the fracture mechanics of ceramics. Especially the influence of the safety factor, k, for the level of test stress on the probability was studied. The study proved that the probability depends much on the value of n, m, g and k, where n is the material constant connecting the crack propagation velocity v and the stress intensity factor K_I as v=AK_Iⁿ, m is Weibull modules, g is the ratio of the required fracture stress of the ceramics to possess the required life time, σ_g, to the mean fracture stress, σ, (σ_g=g·σ), and k is the safety factor or the ratio of the test stress, σ_k, to σ_g (σ_k=k·σ_g). And it was shown that the probability is the minimum at the optimum value of k, and that the probability can be 1ppm or less at suitable values of k (1.2-1.5), in most ceramics having n-80, m-15 and g-0.5 or less. The efficiency of the proof test, however, is not always so high, especially for the ceramics of low n. Therefore, some care must be paid on the application of the test.

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An accurate and convenient method was developed for analysis of K₂O-FeO-Fe₂O₃-CaO-P₂O₅ glass ceramics. Sample was dissolved in hydrochloric and nitric acid. Potassium in the sample solution was determined by gravimetry as potassium tetraphenylborate. Calcium, iron (II and III) and phosphorus were determined successively by complexometry with CyDTA (trans-1, 2-cyclohexanediamine-N, N, N′, N′-tetraacetic acid). Iron (II) was separately determined by redox titrimetry with potassium permanganate after the dissolution of the sample in sulfuric acid in an inert atmosphere. A trial has been made to extended to those glass and glass ceramics containing aluminum.

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