A new aluminum compound, NH₄AlO(OH)HCO₃ (AACH), was synthesized by adding an ammonium aluminum sulfate (AA) solution to an ammonium hydrogen carbonate (AHC) solution.
Because the large amount of HCO₃- ion is required during the reaction, the initial concentration of AHC more than 1mol/l is essential for the formation of the AACH. The lower the concentration of AA and/or the higher the reaction temperature, the larger the concentration range of AHC required for the formation of the new compound.
When an AHC solution is added to the AA solution, the formation of the new compound is rather difficult.
Identification of the new compound as NH₄AlO(OH)HCO₃ is achieved by X-ray diffraction, infrared spectroscopy, DTA, TGA and chemical analysis.

View full abstract

Smoking process of rooftiles has been reviewed and discussed relating to the problems in the manufacturing process. Three types of carbons were observed by SEM. One is the smooth plane carbon layered parallel to the basal plane which contributed to the luster of smoked tiles. The others were droplet-like and fibrous carbons which decreased the surface luster. It was found that smooth plane carbon layer was formed mainly by the direct decomposition of hydrocarbon in contact with the heated clay surface. Droplet-like and fibrous carbons were considered to be formed by partial decomposition of hydrocarbon in gas phase. Hence dilution of hydrocarbon by inert gas and lowering the decomposition temperature were useful for the prevention of the formation of droplet-like and fibrous carbons. Smoking propane at 900-950°C for 30-40min after dilution by nitrogen to one-fouth and passage through water has given the best silver-luster tiles. The so called “rust” in the smoked tiles was also discussed.

View full abstract

The orientation of chrysotile in the asbestos products was studied by X-ray diffraction method. The X-ray diffraction profiles from the chrysotile with various degree of orientation were theoretically calculated using a probability function and the diffraction profiles from a given section of specially prepared specimen with one-dimensionally oriented chrysotile. X-ray diffraction profiles thus calculated changed systematically. It was clarified that the half-maximum breadth of diffraction band at about 20° (Cu K_α 2θ) is good indicator of the orientation of chrysotile. Using the relation between the half-maximum breadth of the diffraction dand and the degree of orientation, the orientation of chrysotile in the asbestos products was determined.

View full abstract

(Pb, La) (Zr, Ti) O₃ is a highly transparent ferroelectric ceramic fabricated by doping La into PZT. However, the mechanism to achieve its high transparency has not been adequately clarified yet. In order to substantiate the concept in the preceding study concerning the optical transparency of ferroelectric ceramics PLZT, the optical transparency and the crystal-lattice anisotropy of the hot-pressed Sm-, Sr- and Ba-doped PZT were investigated.
As in the case of PLZT, the optical transmittance of the above ferroelectric ceramics and the anisotropy of individual grains are closely related. That is, the optical transmittance of solid solution system (PbZrO₃-BaZrO₃) increases with the decrease in the lattice anisotropy of grains within the range of ferroelectric phase (BaZrO₃ concentrations: 15-35mol%) in the phase diagram. On the other hand, in the case of the Sm-doped PZT, this tendency was observed only with respect to less concentration than the solubility limit (4 at %) of Sm in PZT. From these results, it was thought that crystal-lattice anisotropy apparently has a great effect on optical transmittance in ferroelectric ceramics, although optical anisotropy directly controls the optical transmittance of polycrystalline solids.
In general, the light scattering in anisotropic ceramics is affected by grain size, optical anisotropy and crystal imperfections such as pores and precipitates. In the PbZrO₃-BaZrO₃ solid soution, the grain sizes were nearly equal, and photomicrographs showed that porosity was negligible. No precipitated second phase was detected by electron microscopy. Therefore, it was suggested that light scattering in the present ferroelectric ceramics is also caused mainly due to the variation in refractive index at domain and grain boundaries as in the case of the PLZT system. In line with the above consideration, the Sr- and Ba-doped PZT were fabricated to highly transparent bodies (transmittance 70%, thickness 0.25mm, wavelength 0.7μm) by the hot-pressing technique (condition: 1400°C, 5h, 150kg/cm²). This means that the anisotropy of these materials can be decreased by doping Sr or Ba in PZT and consequently the light scattering at domain boundaries is decreased.
The present work suggests that ferroelectric ceramics other than PLZT and modified PLZT can be fabricated to highly transparent substances by decreasing their optical anisotropy and by selecting a sintering process which eliminate pores, to a considerable extent.

View full abstract

The electrical resistivity of sintered bodies of TiO₂ doped with Al₂O₃ or Nb₂O₅ was measured in air in the range from 30° to 1000°C.
The resistivity of Nb-doped specimen sintered in air showed extrema (a minimum at ≈ 270°C and a maximum at ≈ 440°C) but not on Al-doped specimen. This suggests that the extent of chemisorption of oxygen is different with dopant.
The atmosphere for sintering had a remarkable effect on the resistivity of the specimen; more significant effect of solid solution of Nb₂O₅ on the resistivity was observed in the specimen sintered in Ar than in air.
When the resistivity of Nb-doped specimen sintered in Ar was measured in air during heating, two step extrema was observed. The first extrema in the low temperature was explained in terms of the desorption of the chemisor bed oxygen and the oxidation (Ti_i^...→Ti_Ti^×or V₀^..→O₀^×), and the second extrema in the high temperature was by the precipitation of Nb₂O₅.

View full abstract

The strengths of various abrasive grains were experimentally obtained by means of two components grinding wheel using epoxy resin as a bond. From the test results, it becomes clear that the grain strength is considerably low and, in the extreme case, the value here obtained differs by a figure down from that of the old way of thinking. The use of ultra high speed grinding using conventional grinding wheels must be reconsidered. The estimation of the grain strength by means of this method enables us to predict the maximum possible bursting strength of grinding wheels.

View full abstract

In order to make clear the origin of the flake which is present, sometimes, in the water contained in thermos flask, the effects of character of the water and composition of the glass on the flake-formation have been studied.
The flake-formation depends upon Mg²⁺ concentration, pH value, temperature of the water, and alkalinity of the glass. In the thermos flask made from boro-silicate glass, the flakeformation does not occur in such the water as its Mg²⁺ content <5ppm, pH value (after boiling) <8.0 or temperature <70°C. A main component of the flakes is identified as magnesium silicate hydrate by analysis.
Judging from the results obtained, it is reasonable to say that the flake found in the thermos flask is generally produced due to break-down of the film of magnesium silicate hydrate formed on the glass surface.

View full abstract