Papers by Author: S. Koda

Abstract: The effect of surface modified Si-Al-C® fibre with carbon interface (SA/C fibre) addition on the densification of silicon carbide (SiC) composite was examined. An acid treatment (H2SO4 and HNO3) was carried out at 50°C for 3 h in order to add COO- group to the surface of SA/C fibre and to enhance the dispersibility of SA/C fibre in the SiC powder due to the mixing operation in the polar solvent. Commercially available ultrafine SiC powder (specific surface area: 47.5 m2∙g-1) was mixed with acid-treated SA/C fibre and sintering aid (4.8 mass% Al4C3 and 1.2 mass% B4C) in the presence of acetone. The relative density of the SiC composite with non-acid-treated SA/C fibre addition hot-pressed at 1800°C for 1 h in Ar atmosphere under a pressure of 62 MPa was 98.4%, whereas that of the SiC composite with acid-treated SA/C fibre addition increased to 98.7%. Furthermore, the fracture toughness increased from 5.6 MPa∙m1/2 to 7.0 MPa∙m1/2 for the acid-treated SA/C fibre addition.

Abstract: The luminescence properties of rare-earth doped Gd4Si2O7N2 with cuspidine structure were examined. The Gd4Si2O7N2 powder, i.e., a host material, was prepared by mechanically mixing α-Si3N4, SiO2, Gd2O3 and rare-earth oxide (activator) powders (in the stoichiometric ratio Si3N4 : SiO2 : Gd2O3 = 1 : 1: 4) by heating the mixtures at 1700°C for 2 h in N2 atmosphere. When Ce3+ was doped to Gd4Si2O7N2, the emission peak of (Gd0.98Ce0.02)4Si2O7N2 appeared at 457 nm (excitation wavelength: 393 nm) where the blue light was emitted (the relative emission intensity = 0.11 against the standard substance: YAG: Ce3+ (P46-Y3)). When Tb3+ was doped to Gd4Si2O7N2, the emission peak of (Gd0.98Tb0.02)4Si2O7N2 appeared at 545 nm (excitation wavelength: 266 nm) where the green light was emitted (the relative emission intensity = 1.01 against the standard substance: YAG: Ce3+ (P46-Y3)). When both Ce3+ and Tb3+ were co-doped to Gd4Si2O7N2, the emission peak of (Gd0.79Ce0.01Tb0.20)4Si2O7N2 appeared at 545 nm (excitation wavelength: 393 nm) where the greenish yellow light was emitted (the relative emission intensity = 0.95). Such emitting behavior was discussed based upon the energy transfer from Ce3+ and Tb3+.