Electron diffraction and lattice image observations have been applied to study the high-index crystallographic shear (CS) phases derived from rutile-type structure in the system Cr₂O₃-TiO₂. At 1390°C, there existed many CS phases where the orientation of the CS planes continuously changed from (121)_r to (5, 12, 7)_r and the spacing of CS planes increased from 12.9Å to 18.2Å according to the decrease of Cr₂O₃ contents in the range of 13.7-24.1wt% Cr₂O₃. The high-index (5, 12, 7)_r CS phase coexisted with rutile solid solution in the range of 7.5-13.7wt% Cr₂O₃. The highest end member of (121)_r CS phase appeared to be Cr₂Ti₆O₁₅ instead of Cr₂Ti₇O₁₇ which was previously regarded as a member of (121)_r CS phase by X-ray diffraction analysis. The crystals had ordered features with equal spaced CS planes within each fragment, whereas the structures of high-index CS phases were slightly different from one fragment to another obtained from a bulk specimen with constant composition.
The structural model for (5, 12, 7)_r CS plane was presented on the basis of the structural units for (011)_r and (121)_r boundaries and it seemed that (5, 12, 7)_r CS plane had zig-zag feature rather than straight line along CS plane.

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The freeze-dried salt was prepared from the mixed solution of magnesium and aluminum sulfates in composition of spinel. The thermal decomposition processes of the resultant salt were studied with DTA, TG and X-ray powder diffraction methods, and the formation processes of spinel were discussed.
The results obtaind were as follows:
(1) The salt seemed to be composed of the mixture of two compounds of MgSO₄⋅6H₂O and Al₂(SO₄)₃⋅17H₂O, in which magnesium sulfate was amorphous and aluminum sulfate crystalline.
(2) On heating the freeze-dried salt, the crystalline Al₂(SO₄)₃⋅17H₂O decomposed to a crystalline anhydride which then decomposed to an amorphous alumina. In contrast, the amorphous MgSO₄⋅6H₂O decomposed to an amorphous anhydride. This anhydride was then crystallized, and finally decomposed to an amorphous magnesia.
(3) Once the amorphous magnesia was formed, some part of this reacted to form spinel immediately with non-crystalline alumina which had been already formed.
(4) The amorphous magnesia which did not react with this alumina then crystallized as the temperature raised. This crystalline magnesia did not completely react with alumina up to higher temperature.
Thus the spinel has been formed at two stages. The temperature of the first stage to give spinel was as low as 840°C in this study which was very low when compared with the case of the solid-solid reaction, for example, as of alumina and magnesia pellets.

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Growth of single crystals of alkaline earth metal hexaborides (CaB₆, SrB₆ and BaB₆) in molten aluminum in an argon atmosphere has been investigated.
Results obtained are as follows.
The optimum growth conditions of single crystals:
The mixing atomic ratios of raw materials: for CaB₆: (B/Ca)=3.20-5.70, (Al/Ca)=10.50-50.50, for SrB₆: (B/Sr)=2.00-3.50, (Al/Sr)=25.98-77.94, and for BaB₆: (B/Ba)=3.00-5.70, (Al/Ba)=34.81-76.28. The heating temperature and time: at above 1450°C for longer than 10h in any case.
Cubical single crystals composed of {100} faces, and needle-like and thick-plate-like crystals having well-developed (100) faces, respectively, were grown.
The lattice constants (a₀) and densities (D) of single crystals:
CaB₆: a₀=4.15215±0.00008(Å), D=2.44±0.02g/cm³ SrB₆: a₀=4.19756±0.00009(Å), D=3.37±0.03g/cm³ BaB₆: a₀=4.26961±0.00008(Å), D=4.26±0.03g/cm³
Values of Knoop-microhardness determined on (100) faces of single crystals:
CaB₆: 1840-1940kg/mm² SrB₆: 1680-1960kg/mm² BaB₆: 1770-2010kg/mm²
As-grown single crystals were used for the oxidation in air at temperatures between 700° and 1200°C. Oxidation began to proceed at 720°-730°C, and noncrystalline oxidation products were always obtained.
The oxidation proceeded in two stages. The initial stage of oxidation was found to be expressed by the general oxidation rate equation, (dw)ⁿ=kt, and apparent activation energies of CaB₆, SrB₆ and BaB₆ single crystals calculated on the basis of the equation were 56kcal/mol, 55kcal/mol and 64kcal/mol, respectively.

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The effects of applied pressure on the densification during hot-pressing of β-SiC compacts were investigated. β-SiC powder used in this study is Starck made and has the average particle size of about 0.7μm. Hot-pressing experiments were carried out in graphite dies at the temperatures of 1700° to 2300°C and at the pressures up to 1000kg/cm². Experiments were also done with the compacts containing 1wt% B₄C. Sintered compacts were then subjected to the observation of microstructure and to the measurement of Rockwell A-scale hardness.
(1) The densification of the compacts was accelerated by increasing pressure. This pressure effect was clear in hot-pressing at around 2000°C for β-SiC. However, to obtain the compacts of sufficiently high density, over 3.0g/cm³, severe hot-pressing condition, above 2200°C at 200kg/cm² or 2100°C at 600kg/cm², is needed. B₄C addition was very effective to mitigate the hot-pressing conditions.
(2) Empirical relations between hot-pressing temperature and pressure to realize 95% density were deduced as follows: T=2610-185logP for β-SiC and T=2780-280logP for β-SiC containing B₄C, where T is hot-pressing temperature (°C) and P is pressure (kg/cm²). These relations mean a ten-fold change in pressure was equivalent to 185° and 280°C in hot-pressing temperature for β-SiC and for β-SiC containing B₄C, respectively.
(3) The compacts of high densities near the theoretical value showed Rockwell A-scale hardness of about 96. Compared with microvickers or knoop hardness, rockwell hardness is thought to be macroscopic and to reflect the bonding strength between the particles of the compacts. The hardness of the compacts was simply dependent on its density, not on hot-pressing condition. In other words, the compacts prepared under different conditions but having the same density have the same hardness. These mean that the densification takes place accompanying the strengthening of the bonding and is not likely to occur by the deformation of the particles due to concentrated stress.

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Electronic ceramics, which require the cofiring for metalization and sintering, are fired in a reducing atmosphere to prevent the oxidation of metals. The burning out of an organic binder used for forming the ceramic materials in the reducing atmosphere is recognized as one of the most difficult processes in this industry. Considering this, the firing phenomena of the 92% alumina ceramics (Al₂O₃-MgO-SiO₂) and the polyvinyl butylar binder system in the reducing atmosphere, which are generally used in a semiconductor package, are discussed. These include the mechanisms of the burning out of the binder, sintering of the ceramics and the interaction of both.
In the theoretical equilibrium of carbon in a H₂+N₂+H₂O gas atmosphere, the decomposition of remaining carbon produced from the binder begins at 680°C. This is a much lower temperature than the sintering temperature for the ceramics. However, the actual burning out temperature was found to be from 1000°C to 1200°C in the same atmosphere.
At the heating rate of 500°C/h in the same atmosphere, the remaining carbon from the binder became enclosed in the ceramics during sintering. As a result, the ceramic bulk density was found to be lower than that of pre-burned out samples.
The reason for this phenomenon was interpreted as follows: Under such quick heating conditions, for instance, 500°C/h, the ceramic sintering rate was shown to be more rapid than the burning out rate of the remaining carbon from the binder. The remaining carbon was trapped in the ceramics, and it was partially burned by oxygen in the ceramics. To produce ceramics with the same density as the pre-burned out samples, the preferable heating rate for burning out of the binder in the atmosphere was lower than 200°C/h in the temperature range of 680°C to 1450°C.
The phenomena of interaction between burning out of the polyvinyl butylar binder and sintering of the alumina ceramics in a H₂+N₂+H₂O gas atmosphere could be defined by an analysis of the problems encountered during the study.

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Trace amounts of α-emitters, such as U and Th, in sintered alumina LSI-packages are known to be the cause of the soft-error of dynamic memory. The behavior of these α-emitters in the preparation of alumina by the Bayer process was studied using nondestructive neutron activation analysis of U and Th, γ-ray spectrometry for Ra-226 and Pb-210, and colorimetry of U. Almost entire part of Th and most portion of Ra in bauxite ore are confirmed to go into the red mud, whereas considerable portion of U was found to enter into the sodium aluminate solution and coprecipitate with the aluminum hydroxide. Probable form of uranyl ion in the solution has been deduced to be HUO₄^- from the solubility data of U, 2.06±0.03mg/l. From the γ-ray spectrometry, trace amounts of Pb-210 was detected in freshly precipitated aluminum hydroxide.

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A Pt crucible 50ml in capacity and 35mm in depth charged with a γ-6Bi₂O₃⋅SiO₂ crystal aggregate was placed in a SiC furnace with a temperature gradient (Fig. 1). Firstly, the temperature of the top of the crucible was kept at 1250°C for five hours while that of the bottom of the crucible was kept cooled with a water-cooled jacket so that the charge near the bottom of the crucible remained unmolten. The temperature of the top of the crucible was then lowered at a rate of 5 or 25°C/h, so that the melt was solidified upwards at a rate of 0.4 or 2.0mm/h. The unmolten crystals acted as seed crystals. Throughout the solidification, the thermal gradient in the melt was kept at 115°C/cm. A homogeneous transparent ingot was obtained when the melt was solidified at a rate of 0.4mm/h. Some inclusions were observed in the ingot solidified at a rate of 2.0mm/h (Fig. 3). The former ingot was composed of γ-6Bi₂O₃⋅SiO₂ columnar crystals 1 to 5mm in diameter which elongated parallel to the solidification direction. The crystallographic orientation of the columnar crystals, however, was random. Its polished transverse section 1.0mm thick showed a high transmission (40 to 60%) for the light of 500 to 5700nm in wavelength and a high photo conduction almost comparable to that of a single crystal of γ-6Bi₂O₃⋅SiO₂ (Fig. 5 and 6). For preparation of the section with homogeneous optical activity, the use of the seed crystals (γ-6Bi₂O₃⋅SiO₂) with the same sign of optical activity in the process of solidification of the melt was found necessary. The section with homogeneous electrooptic effect, however, could not be prepared because of the random orientation of the crystallographic axes of the constituent columnar crystals (Fig. 8 and 9).

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Effects of thirty additives on sintering AlN were investigated. The addition of alkali earth oxides and rare earth oxides gave fully densified aluminum nitride. This is due to the formation of nitrogen-containing aluminate liquid in the system aluminum nitride-alkali earth oxides or rare earth oxides. Microstructural studies of the sintered specimens with the above two types of additives suggested that the densification was due to the liquid phase sintering. Additions of silicon compounds resulted in poor densification by the formation of highly refractory compounds such as AlN polytypes.

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