Relation between the synthetic condition of NH₄AlO(OH)HCO₃ and the sinterability of thermally decomposed α-alumina from the compound was studied.
Results were as follows;
1) The most sinterable α-alumina was obtained from the NH₄AlO(OH)HCO₃ which was formed under conditions such as molar ratio of ammonium hydrogen carbonate/ammonium aluminum sulfate as 10-15; dropping rate of about 1l/h and reaction temperature as 30-35°C.
2) The sintered density of the above mentioned α-alumina fired at 1600°C for 1h was 3.8-3.9.
3) Sinterable α-alumina powders were obtained only by the above described conditions. It was ascribed to the formation of the other aluminum compounds or to high crystallinity of NH₄AlO(OH)HCO₃.
4) The size of primary particle of α-alumina was 0.3-0.4μ, independent of the synthetic conditions of NH₄AlO(OH)HCO₃.

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The exothermic reaction observed in the thermal decomposition of basic magnesium carbonate was studied by DTA and X-ray.
The DTA taken in air and CO₂ shows occasionally a very sharp exothermic peak at about 500°C in addition to the rather broad endothermic ones.
The relative heights of the exothermic peaks depend on the experimental conditions such as the amounts of the samples, the atmosphere (air or CO₂) and the amounts or kinds of the additives (alkali or alkaline earth halides), among the examined additives magnesium chloride showed a remarkable effect.
From these results of the analyses the decomposition process could be explained as follows. The crystalization of MgO proceeds slowly through amorphous state corresponding to the first endothermic peak up to above the exothermic peak. At 500°C, MgCO₃ is formed suddenly and the amounts of MgCO₃ are nearly proportional to the heights of the exothermic peaks emerged at this temperature. From above this temperature, however, MgCO₃ decomposes immediately into MgO.
The mechanism of these processes under various conditions are shortly discussed.

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Dielectric constants (DC), infrared (IR) spectra, and Raman spectra of glassy Fe₂O₃-PbO-SiO₂ (Fe₂O₃, 0-20mol%) system were measured. The composition of samples was changed such as xFe₂O₃⋅(1-x) PbO⋅SiO₂ (a-series) or x Fe₂O₃⋅(1-x) (PbO⋅SiO₂) (b-series). The values of DC in a-series increased rapidly from 15.5 (10⁶Hz) of PbO⋅SiO₂ glass up to about 19 of the sample which contained 2mol% of Fe₂O₃. The values of DC in b-series were equal to those in a-series. In the composition range over 2mol% of Fe₂O₃, the value of DC increased slowly up to 15mol% of Fe₂O₃ for a-series and up to 10mol% of Fe₂O₃ for b-series. As Fe₂O₃ content increased moreover, the values of DC for both series increased markedly again. The difference of IR spectra between the samples in both series could not be recognized. IR absorption band shifted from about 950cm^-1 for PbO⋅SiO₂ glass to 920cm^-1 for the sample which contained 20mol% of Fe₂O₃. The shift appeared relatively large at about 2mol% of Fe₂O₃. Raman band of the sample contained Fe₂O₃ under 2mol% showed a similar pattern to that of PbO⋅SiO₂ glass which corresponds to ν₃ mode of SiO₄ vibration. However some split of Raman band occurred when Fe₂O₃ content was larger than 2mol%.
On the basis of above experimental results, the following consideration was given. When Fe³⁺ ion in the glassy system has 6-oxygen neighbors, the Fe³⁺ ion can contribute to the ionic polarization of the system. The induced dipole moment and the change in the ionic field also become effective for the dielectric polarization. Owing these effects, the value of DC increases rapidly with increasing Fe₂O₃ content. IR and Raman bands would not be affected very much since Fe-O interaction is weak when the Fe³⁺ ion has 6-oxygen neighbors. Consequently, in the composition range under 2mol% of Fe₂O₃, it can be suggested that the Fe³⁺ ion in the glassy system has 6-oxygen neighbors. If we assume that the strength of Fe-O bond increases, above effects for the dielectric polarization become relatively few, namely the value of DC would vary gradually with increasing Fe₂O₃ content. Since the symmetry of the SiO₄ vibration is decresed by the increase in the strength of Fe-O bond, the split of its vibrational band would be given rise. As the measured results showed these phenomena, it can be considered that the Fe³⁺ ion having above strong Fe-O interaction also exists when Fe₂O₃ is over 2mol%.

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The periclase solid solution with the sesquioxides (Al₂O₃, Fe₂O₃ and Cr₂O₃) was formed with cation vacancies due to the ion substitution 3Mg²⁺_??_2Al³⁺ at high temperatures. The solid solution became separated into two phases by the exsolution reaction which equilibrates at annealing temperatures lower than that of the preparation of the solid solution. The exsolotion reaction caused the coherent precipitation of MgO⋅R₂O₃ spinel on the periclase grain boundaries, and then spinel became filled up pores among the grains.
For the purpose of making clear the exsolution phenomenon, the distribution of the elements and the identification of the phases were studied by using the electron probe microanalyzer and the X-ray powder diffractometer, respectively.
The significance of its industrial application on the mechanism of direct intergrain bonds in the magnesia-chrome bricks was discussed.

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“Shirasu” is a sort of volcanic ash broadly deposited in southern Kyushu and consists mostly of glassy alumino-silicate.
In this paper, the authors describe the crystallizing behavior of some glasses produced by using “Shirasu” as a raw material without addition of any crystal nucleus and discuss the correlations between the structures of crystallized glasses and their strengths.
The results obtained are summarized as follows:
1. Heat treatments of the glasses in the systems “Shirasu-CaO-MgO”, Shirasu-CaO-ZnO” and “Shirasu-CaO-MgO-ZnO” caused the formation of the crystals of diopside, hardystonite-β-wollastonite and diopside-hardystonite-β-wollastonite respectively. An unknown crystal was detected in each of almost all of the specimens. All the crystals grew from the surface to the inside of the glass specimens.
2. By the crystallization, the softening temperature of all of the glasses examined rose from about 870°C to about 1200°C and their hardness in Mohrs increased from 5 to 8.
3. The glasses in the systems “Shirasu-CaO-MgO” and “Shirasu-CaO-MgO-ZnO”, in which diopside precipitated on heating, did not show an increase in strength by any crystallization procedure, whereas the strength of the glasses in the system “Shirasu-CaO-ZnO” heat-treated for 2 hours were 2 to 3 times as high as those of the original glasses respectively. As the heating time was further increased, however, their once increased strengths dropped rapidly, regaining their original values.
4. The high strengths achieved by crystallization were discussed in terms of the shape of the formed crystals, the processes of the crystal growth, the appearance of crystal grain boundary, etc.

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Polycrystalline Ni_0.5Zn_0.5Fe₂O₄ (density, 99%; average grain size, 60 microns) was deformed under the compressive load. The brittle-ductile transition temperature was about 1200°C under the loading rate of 11kg/cm²⋅min. In the compressive deformation at higher temperatures than 1400°C, straight slip lines, interpenetration of 60° and 120° slip systems as well as wavy slip lines, were observed. Grain boundary slip was not large enough to be observed by the off-set of the marker line even in the temperature range of ductile fracture. During the compressive deformation, grain boundary migrated to the perpendicular direction to the grain boundary plane and lost the flatness of the boundary. And also, corrugation and rumpling of grain boundary were observed during the deformation process. These seem to be the causes of the difficulty of grain boundary slip. In the vicinity of grain boundary, the deformation by dislocation movement was active as seen by corrugation and rumpling of grain boundary. However, the piled-up dislocations near the grain boundary and ensuing strain were not relaxed by a mechanism like polygonization in the temperature range of this research.

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Infrared absorption spectra of some silicate glasses containing TiO₂ were measured in the range of 400-1400cm^-1 by KBr pellet method. In this paper the absorption band in the range of 890-1100cm^-1 due to the streching vibration (v₃) of Si-O tetrahedron is mainly discussed, because this absorption band is considered to reflect the polymerization state of tetrahedral SiO₄^4- anion. The results indicate that the absorption peak tends to shift to lower wave number until 930cm^-1, when TiO₂ is added to the glasses showing the peak at higher wave number than 930cm^-1. On the other hand the shift of absorption peak to higher wave number is observed when TiO₂ is added to the silicate glasses having the peak at lower wave number than 930cm^-1. Addition of TiO₂ to the glasses having the peak around 930cm^-1 gives little effect on the peak shift.
It may be concluded that the Ti ion has a role of cation as a network modifier in SiO₂ rich glasses, whereas the TiO₂ tends to act as an acidic oxide for the glasses poor in SiO₂ content.
For example the following equations will be presented.
in SiO₂ rich glasses: TiO₂+Si₄O₁₂^8-=2Si₂O₇^6-+Ti⁴⁺
in SiO₂ poor glasses: TiO₂+2SiO₄^4-=Si₂O₇^6-+TiO₃^2-

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The effects of HCrO₂ seed crystals were investigated in the hydrothermal synthesis of chromium dioxide from chromic anhydride.
Dissociation sequence of CrO₃ in a closed vessel was CrO₃→liquid→Cr₃O₈→undetermined phase→Cr₂O₅→CrO₂→Cr₂O₃, while with HCrO₂ seed crystals the sequence being CrO₃→Cr₂O₅→CrO₂→Cr₂O₃.
It may be concluded that the seed crystals HCrO₂ supply nuclei for the formation of CrO₂ crystals from liquid CrO₃. The CrO₂ crystals thus obtained were acicular with the length of 0.1-0.2μ.

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