It is difficult to obtain dense Y₂O₃ pieces using an ordinary sintering method without any additives. The effect of sintering conditions were investigated in order to facilitate obtaining dense pieces by the above mentioned method. Conditions such as sintering temperature and atmosphere on sinterability of Y₂O₃ were examined.
The total impurity of the Y₂O₃ powder was less than 0.1% and the average grain size was 4-6μm. The compacting pressure was 10t/cm². The green compacts were sintered at 2, 100-2, 300°C for 30-60min in a H₂ (d. p. -36, 20°C) atmosphere.
In-line transmittance of the pieces sintered in a H₂ (d. p. -36°C) atmosphere was higher than that for pieces sintered in a H₂ (d. p. 20°C) atmosphere. The maximum in-line transmittance was obtained from the piece sintered in a H₂ (d. p. -36°C) atmosphere at 2, 270°C. This maximum was 80% with 0.76mm thickness at a wave-length of 550m nm.
The calorific changes of the Y₂O₃ powder were measured with a DTA apparatus. The changes seemed to be due to the phase transition (cubic←→hexagonal) noted at 2, 280°C. The “Hedvall effect” appeared to be helpful in grain growth and for removal of pores in the pieces.
Measurement of the “Thickness effect” suggested that the grain growth was abnormal. When the diameter of the grains in the sintered pieces was below 0.5mm, the porosity decreased with the diameter.

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The present study was undertaken in an attempt to better understand the decomposition behavior of Al₂TiO₅, known as one of the materials with negative thermal expansion coefficient. Techniques employed are X-ray diffraction analysis, dilatometry and SEM. The eutectoid temperature has been estimated to be 1295±10°C by isothermal heating of sintered β-Al₂TiO₅ with or without preliminary decomposition anneal.
Decomposition isotherms are characterized by sigmoidal shape with a miximum rate at approximately 1150°C, and kinetics has been best described by the Avrami equation ln (1-α)=-ktⁿ(n=2), where α, t, k and n are fractional decomposition, time and proportionality constants respectively. It is shown that the preliminary annealing at low temperatures promotes the decomposition with the maximum-rate temperature increased by approximately 30°C. Arrhenius plot of ln k vs. 1/T yielded an activation energy, of 90±5kcal/mol below the maximum-rate temperature, regardless of the preliminary annealing, and the value has been considered to comprise with the growth or phase boundary process. Results of dilatometry revealed that the effect of preliminary annealing is more pronounced in the cooling run. Summarizing with the results of SEM, it is proposed that nucleation rather than growth plays an important role in the process.

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Alumina ceramic-to-nickel metal seals were formed by reactive alloying method utilizing Ti-Ni-Ag solder and the interfaces between the materials were examined by an optical microscope and an electron probe microanalyzer.
The results were as follows:
(1) Vacuum-tight seals were formed by this technique.
(2) The highest seal strength was 140kg/cm² for the samples sealed at 1000°C for 7 minutes.
(3) The intermediate layar and Ti-Ni-Ag solder layer were formed between the ceramic and nickel metal by sealing operation. Ti and Ni in the solder segragated at ceramic-solder interface, and in particular, Ti was adsorbed selectively at ceramic surface.
The intermediate layer about 7μm thick was made up of two layers. The ceramic side layer about 3μm thick was composed of SiO₂, Ti and their reaction products.
The solder side layer about 4μm thick was composed of Ti and Ni.
The solder layer was composed of two parts which were rich in Ti-Ni and Ag, respectively.
(4) These evidences and thermodynamical consideration showed that SiO₂ could react with Ti to form titanium oxides and elemental Si. The interdiffusion and reaction between Si, Ti and the oxides of Si, Ti formed intermediate and diffusion layers giving vacuumtight and mechanically stable seals.

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Effects of zirconium compounds on the hot-pressing were studied at about 1800°C using Si₃N₄ powder of low oxygen content (particle size<3μm total oxygen content:0.52 wt%, Al₂O₃:0.30 wt%). Any effective result was not observed with 5 wt% addition of ZrO₂, ZrN, ZrC and 10 wt% of ZrSiO₄ to the Si₃N₄. Then, ZrO₂ additions together with Al₂O₃, MgO, AlN and ZrN were tried and effective results were found in Al₂O₃-ZrO₂-Si₃N₄ ternary system.
Added ZrO₂ in the system was considered to lower the melting point of X-phase and/or melts which appeared in Al₂O₃-Si₃N₄ system and to increase the amounts of those melts. Zirconium oxide in the ternary system remained as zirconia in the sample hot-pressed, but ZrO₂ in MgO-ZrO₂-Si₃N₄ and AlN-ZrO₂-Si₃N₄ systems was converted to ZrN forming Mg₂SiO₄ and Al₃NO₃ spinel respectively.
From the results of experiments, following systems were considered to be in equilibrium at about 1800°C.
ZrO₂-β-Si₃N₄
ZrN-β-Si₃N₄
ZrO₂-ZrN-Al₃NO₃
ZrO₂-ZrN-β-or β′-Si₃N₄ (Si₃N₄-Al₃NO₃ solid solution)
ZrO₂-β′-Si₃N₄-molten X-phase soln.
ZrO₂-ZrN-β-Si₃N₄-molten Mg₂SiO₄ soln.

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Solid state reaction between a sintered disk of Al₂O₃ and a sintered disk of Nb₂O₅ was investigated. Closely joined couples of four different relative densities of Al₂O₃ (60, 70, 80 and 90%) with sintered disk of Nb₂O₅ were heated in Ar gas at the temperature between 1250°C and 1350°C.
Observation by an electron microscope, X-ray diffraction measurement, electron probe X-ray microanalysis and differential thermal analysis were used to analyse the reaction products between Al₂O₃ and Nb₂O₅.
The following results were obtained.
(1) Two kinds of the reaction layer were formed at the Al₂O₃-Nb₂O₅ interface. The one was thicker of Al₂O₃⋅2Nb₂O₅, the other was thinner layer contained Al₂O₃ of 2-4mol%. Due to the difference in thermal expansion between the two reaction layers, they cracked and came off each other by cooling.
(2) An experiment with a Pt wire as a innert marker showed that the reaction process was a one-way transfer of Nb₂O₅ to Al₂O₃.
(3) Reaction layer thickness of the product increased parabolically with time in the temperature range 1250°C to 1350°C, and it showed that the reaction process was diffusioncontrol.
(4) The reaction rates depended remarkably on the densities of sintered disks of Al₂O₃. The larger the density of Al₂O₃, the slower the reaction rate, because the volume diffusion played an important role in the reaction process. In the smaller density of Al₂O₃, the densification of Al₂O₃⋅2Nb₂O₅ layer occurred remarkably at temperature above 1325°C, and the volume diffusion controlled the reaction rate. However, at temperature below 1325°C, the reaction process was affected remarkably both the surface and grain boundary diffusion.

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The plasma flame coating of alumina baloon on the metal substrate was used to prepare η alumina. The formation of η alumina from the molten state was discussed on the schematic P-T diagram.
This phenomenon can be understood only through the hypothetical melt which consist of prototypes of η alumina with the octahedral and tetrahedral atomic group.
The structural analysis of the η alumina was performed using a program of the least square computation for the X-ray powder data. The result of this analysis is noted as given below.
Space group; Fd 3m
0 32e x=0.370 atomic ratio; 4.000
Al (4-1) 8a atomic ratio; 0.503
Al (4-2) 48f x=0.250 atomic ratio; 0.497
Al (6-1) 16d atomic ratio; 1.128
Al (6-2) 16c atomic ratio; 0.539

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Possibility of fiber drawing in the course of hydrolysis has been examined to prepare refractory oxide fibers of the TiO₂-SiO₂ and Al₂O₃-SiO₂ binary systems from metal alcoholates. The liquid mixtures of Ti (O-isoC₃H₇)₄+Si(OC₂H₅)₄ and Al(O-isoC₃H₇)₃+Si(OC₂H₅)₄+C₂H₅OH were slowly hydrolyzed and became increasingly viscous when exposed to ambient atmosphere at room temperature, and so the fibers could be drawn after varying periods of time of holding. The promotion of the hydrolysis by the addition of pure water to the alcoholate mixtures could not be applied to the present method of fiber drawing, because it caused the precipitation of the hydrolyzed product. Mixture of the alcoholate solutions and water added as alcoholic solution showed no precipitation and promoted hydrolysis of the alcoholates, but it did not show spinnable state in the course of hydrolysis. Heating the drawn fibers at 500°C led to the formation of oxide glass fibers.

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Clay bodies for rooftiles have been usually fired at high temperature over 900°C. Consequently, fired clay bodies have some defects in style and accuracy of size, etc. In this paper, in order to improve these defects, clay bodies were fired at low temperature under 900°C. However, when clay bodies were fired at low temperature, water absorption of fired clay bodies increased and bending strength of those decreased. So, unsaturated polyester was impregnated into them in order to cover these weak points. In this investigation, we studied the effects of admixture on Torigai clay, the forming methods of bodies, firing temperature of ones, and curing conditions of monomer in fired clay bodies, considering burning quality and cost of clay bodies impregnated resin. From these results, the bodies, of which bending strength was over 250kg/cm² and water absorption was about 0.5%, were obtained, when Torigai clay was mixed with 30% of glass beads and 7% of water, and the mixture was formed by press forming method at 200kg/cm², and then these bodies were fired at 500°-600°C, and polyester monomer was impregnated into them, and was cured in pressure cell at 3kg/cm² and 85°C.

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