Showing papers by "Sumio Sakka published in 1964"

Change in Refractive Indices of Glasses under High Pressure

Abstract: H. M. Cohen and Rustum Roy reported that silica glass densified under ultrahigh pressures with the opposed anvil apparatus shows no relaxation effects even when heated at 600°C (J. Am. Ceram. Soc., 44 [10] 523 (1961)). J. D. Mackenzie, however, has found recently that marked relaxation occurs at the beginning of reheating at above 300°C for silica glass densified with the high-pressure “Belt” apparatus (J. Am. Ceram. Soc., 46 [10] 461, 470 (1963)). In the present work Mackenzie's result has been confirmed for silica glass and a borosilicate glass both densified with the same opposed anvil type pressure apparatus as used by Cohen et al.Samples of the silica glass were taken from a commercial clear grade silica glass rod. The borosilicate glass with the composition of Na2O 7.5, B2O3 22.5, and SiO2 70% in weight, was melted in a platinum crucible. The glasses were pulverized to 40-50μ, pelleted into a disc of approximately 6-mm diameter and 0.2-mm thickness, wrapped in a platinum foil, and pressed between two opposed anvils of the high-pressure apparatus at temperatures ranging from 25°C to 300°C for various periods. The pressure was released after the temperature of the sample was lowered to room temperature. The annealing of the densified glasses was made by reheating under atmospheric pressure at temperatures ranging from about 130°C to 900°C for various periods. Refractive indices of the reheated glasses were measured as the indication of relaxation.The results showed that the relaxation becomes noticeable by reheating above approximately 300°C for the silica glass and at much lower temperatures than 300°C for the borosilicate glass. In both cases the relaxation completes almost in a few minutes at the beginning of reheating.The activation energies of the relaxation process calculated from the initial changes in refractive indices were approximately 10 and 3kcal/mol for the silica- and borosilicateglasses respectively, which were both much lower than the activation energy of viscous flow in these glasses.

Magnetic Materials Obtained from Silicate Melts in the System Fe2O3-MnO-Alkali Oxide-Al2O3-SiO2

Abstract: Most commercial products of ferrites are made by firing preformed powder mixtures of raw materials. This conventional method, however, is not adapted for obtaining products of the special shapes such as fiber and film. In this study we undertook to examine the possibility of obtaining magnetic materials from melted silicates containing Fe2O3 and MnO and of forming the melts into desired shapes by the ordinary glass-forming technique.The compositions of the melts studied were of 7.5-20% Fe2O3, 7.5-20% MnO (or CoO and NiO), 0-5% Li2O (or Na2O and K2O), 0-15% Al2O3, and 55-70% SiO2(mole). The raw materials were ferrous oxalate, manganese dioxide, cobaltic oxide, nickel oxide, lithium-, sodium- and potassium carbonates, aluminium hydroxide and potter's flint powders. Their mixtures to yield about 50 gram of melts were heated in sintered-alumina crucibles in an electric furnace at temperatures from 1300° to 1400°C. Their melting behaviors and the workability of their melts into shapes of fiber or plate during cooling were investigated. X-ray diffraction analysis and magnetic measurement were made on materials quenched in air.The results obtained are as follows:1) The melts of the compositions, 7.5-15% Fe2O3, 7.5-20% MnO, 0-5% Li2O (or Na2O and K2O), 5-15% Al2O3, 55-70% SiO2 (mole) were fluid at temperatures 1300°-1400°C, and were able to be formed into desired shapes during cooling.2) The intensity of magnetization of quenched specimens reached up to 18 gauss/g at the field of 10, 000 oersteds. Magnetization increased with increasing the content of Fe2O3 or Fe2O3+MnO, and decreased with increasing the content of Al2O3. The specimens of high Fe2O3 content saturated magnetically at a fairly weak magnetic field whereas the specimens of Fe2O3 content less than 15mole% did not saturate even at the field as strong as 5, 000-10, 000 oersteds. The followings are some examples of the composition which showed high magnetization and magnetic saturation at a weak magnetic field.3) Separation of fine crystallites of spinel-type ferrites was confirmed by X-ray analysis in some of quenched specimens containing high amount of Fe2O3. The average size of the crystallites estimated from the broadening of X-ray diffraction peaks was 60-150A.4) Reheating quenched specimen generally increased the intensity of magnetization and also accelarated magnetic saturation at weak magnetic field.