Hydrothermal reaction of slurries made from homogeneous Si-Mg precipitates, lithium hydroxide and sodium hydroxide yielded hectorite-like smectite products. The transmittance measured on 1% dispersions and the rheological properties of a 2.5% gel solution were easily controlled by adjusting the chemical composition of the slurry, the hydrothermal synthesis temperature, and the reaction time. The transmittance and rheological properties attained their maxima for materials synthesized at 200°-225°C in 2 h and at a system composition of Si: Mg: Li: Na =8: 5.4: 0.6: 0.7. The hectorite produced from a composition of Mg/Si=5.5/8 showed optimum transparency and apparent viscosity, whereas transmittance and rheological properties decreased with increasing amount of Mg in the Mg/Si range (5.5-6.5)/8. Additional Li and Na improved both properties. The average particle size of the products correlates well with the transmittance (r=-0.883) and apparent viscosity at a high shear rate of 1022/s (r=-0.714), and the apparent viscosity at a low shear rate of 10.2/s correlates well with gel strength after 600 s (r=0.949), which is apparently controlled by the total alkali metals (Li+Na) content.

抄録全体を表示

Three kinds of n-CH₃ (CH₂) _nNH₃⁺-montmorillonite-polyacrylonitrile intercalation compounds (n=3, 5, 11) were prepared and converted to nitrides to investigate the effect of the amine chain length on carbothermal reduction and the subsequent nitridation. With n=3 and 5, the similar intercalation compounds having the basal spacings of ca. 19 Å were obtained. On the contrary, the intercalation compound with n=11 showed the basal spacing of 27.1 Å and contained the larger amount of the organic materials than the other intercalation compounds. After the decomposition of the n-alkylammonium ions, the basal spacings of the complexes with n=3 and 5 decreased to the value corresponding to the monolayer of carbon, whereas the spacing corresponding to the multilayer of carbon was observed in the complex with n=11. By heating these intercalation compounds in N₂ at 1100-1500°C, β-sialon, A1N, and SiC formed without the crystallization of the oxides. From the intercalation compounds with n=3 and 5, β-sialon formed by the treat-ments above 1100°C. On heating above 1200°C, SiC was obtained. AIN was detected in the products heated above 1300°C. In spite of its greatest organic content, the intercalation compound with n=11 showed the higher threshold temperatures, indicating its lowest reactivity. Therefore, the longer amine chain was disadvantageous for nitrides formation by carbothermal reduction, since the structural conditions in the interlayer space of the intercalation compounds influenced their reactivities to a great extent.

抄録全体を表示

The 2: 1 type clay minerals of pyrophyllite and talc were converted into nitrides by carbothermal reduction. The mixtures of the minerals and carbon black were heated at 1200-1600°C in an N₂ flow. Pyrophyllite was converted into β-sialon and α Si₃ N₄. As oxides, mullite, α-quartz, and cristobalite were detected. On the other hand, α and β-Si₃ N₄ were obtained from talc. MgSiN₂ and Si₂ N₂ O were also formed as intermediates. Forsterite and enstatite were detected as oxides. The variation in the compositions of the products suggests that both the minerals were converted into the nitrides via the decomposition to the oxides and their subsequent reduction.

抄録全体を表示

Calculation of rigorous one dimensional X-ray powder patterns of various interstratified minerals are tried by using Kakinoki and Komura's equation. In this first paper, theoretical aspects on both the interstratified structure and its X-ray powder diffraction patterns are given.

抄録全体を表示

The solid solution between beryllosilicate and aluminosilicate mordenites was synthesized at 423K, and the Be end-member has BeO/(Al₂O₃ + BeO) mole fraction of 0.75 because of the contamination of impurity alumina in the silica source. The lattice constants a, b and c of the solid solution decrease with the replacement of Al by Be atoms, and are 1.808, 2.044 and 0.750nm for the Al end-member and 1.803, 2.027 and 0.744nm for the Be end-member. However, the existence of a continuous solid solution between 0.4 and 0.5 for BeO/(Al₂O₃ + BeO) mole fraction of product is somewhat uncertain.
A part of benzyltrimethylammonium base in the structure of the solid solution plays a role of cations to neutralize negative framework charge, and the remainder is supposed to be present as a molecule

抄録全体を表示