Shigetaka Wada

Facile catalytic combustion of rice husk and burning temperature dependence of the ashes.

In this work, it was discovered and demonstrated that the combustion of rice husk is a catalytic process by the thermoanalytical technique. The catalyst involves the oxides of such transition metals as Mn, Fe, and Cu, which are mainly formed in the initial stage of rice husk combustion and remain in the rice husk ash as an impurity. Mn(2+) ions of various concentrations were reloaded into the HCl-washed husk for cocombustion. As a result, the complete combustion temperature of the husk was decreased exponentially depending on the Mn(2+) concentration. By the facile Mn loading technique using a 0.5 M solution, the combustion temperature can be decreased by approximately 100 degrees C, and the resulting ashes themselves can be a good catalyst in the complete combustion of many other organic compounds. The physicochemical properties and amorphous structure of the ashes from both the raw and HCl-washed husks were found to be strongly dependent on the burning temperature. A decreased complete rice husk combustion temperature can be beneficial in preparing porous amorphous silica with high surface area, high densification, and small Si-O-Si band angles.

Thermal Conductivity Improvement by Heat-Treatment in Si3N4 Ceramics Using SiO2-MgO-Y2O3 Additive System

Silicon nitride (Si3N4) ceramics have been interested for electrical substrate applications, because the ceramics can be made highly mechanical strength, fracture toughness, electrical resistivity and high thermal conductivity. Generally, relatively large amount of additives are required to obtain dense Si3N4 ceramics. During sintering, additives react with SiO2 including surface oxide of Si3N4 raw powder to form a liquid phase. Most of liquid phase changed into glassy phase during cooling down. In this study, Si3N4 ceramics were fabricated by gas pressure sintering. Yttrium oxide (Y2O3), silica (SiO2), and magnesia (MgO) were used for liquid-phase-enhanced sintering process. Dense materials were sintered by this process, but their thermal conductivities were not so high (30-40 W/m·K). Therefore, post-sintering heat-treatment process was performed to reduce the excess amount of glassy phase. An additive system (3 mass% SiO2 with 3 mass% MgO and 1-5 mass% Y2O3) was selected as the sintering aid. These ceramics could be sintered to almost full density at relatively low temperature as 1650oC for 2 h under 0.1 MPa-N2 without packing powder. The resulting materials have high bending strength, about 1 GPa, when 5mass% of Y2O3 was added. Based on the creation of low temperature pressureless sintering without packing powder, a novel two-step sintering (once firing) was proposed. The two-step sintering conducted by sintered at 1650oC under 0.1 MPa-N2 for 2 h for densification in the first step. Followed by heated up to and kept at 1950oC for 8 h under 1.0 MPa-N2 in the second step. The Si3N4 ceramics could be fabricated with relatively high thermal conductivity of 90 W/m·K. Mass loss, microstructure, mechanical properties, oxygen content and chemical composition were discussed.

Preparation and Characterization of Fly Ash and Aluminium Waste Geopolymer

Geopolymeris an alumino-silicate material with three dimensional amorphous structures. The main compositions are silica and alumina which were decomposed by alkaline solution. Geopolymer materials not only have comparable or superior properties to portland cement, but also have lower greenhouse emission. In this study, Preparation and characterization of geopolymer were investigated. The main composition of fly ash from Mae Moh power plant is SiO2 and Al2O3. The major composition of Aluminium waste from aluminium frame industry is Al2O3.The geopolymer pastes were mixed at various proportions of FA:Al-waste of 100:0 80:20 60:40 and 40:60 by weight. Sodium hydroxide and sodium silicate were used as alkali activators.A mass ratio of 2.5 Na2SiO3/NaOH and three concentrations of NaOH (5 10 15 M) were used. Geopolymer were cured at ambient temperature for 7days. Properties of geopolymer specimens were measured for example compressive strength, bending strength, phase by XRD, and bonding by FT-IR.