The technique to make calcium carbonate a photocatalyst by the surface treatment which used the fatty acid zinc and the surface oxidation was studied. The relationship between the kind of the fatty acid zinc and the state of the zinc introduced on the surface was investigated. In addition, the relation between the state of zinc and the photocatalytic ability was discussed. The surface of calcium carbonate was able to make a photocatalyst by using the process of the adsorption of the fatty acid zinc and the surface oxidation. It has been understood that the structure of the zinc oxide generated with the change of an organic chain length of the fatty acid zinc is different. The grainy zinc oxide in the sample which used zinc stearate was generated, and layered zinc oxide in the sample which used zinc acetate was generated, respectively.The layered zinc oxide was excellent in the photocatalytic ability compared with the grainy zinc oxide. It was presumed that this cause was a difference of degree of crystallinity of the zinc oxide. It has been understood that the calcium carbonate covered with one layer of zinc oxide onto the surface has the same degree of photocatalytic ability as a zinc oxide.
To clarify the disinfecting properties of lime compounds such as calcium hydroxide, calcium oxide and calcium carbonate, the kinetics of disinfection by the lime compounds were studied using a bacterium, Eschericia coli. The disinfection effects were found to be expressed by “Chick's low”. The disinfection rate constants of the lime compounds were compared with those of disinfection effect in NaOH solution. The disinfection rate constants of both systems increased with pH increasing, but the disinfection rate constants of the lime compounds appeared to be higher than those in the alkaline solution. Furthermore, the disinfection rate constants were increased with increasing specific surface area of the lime compounds. These results suggest that the contact phenomenon of the bacteria to the strong alkaline surfaces on these lime compounds is most important factor of the disinfection mechanism. To evaluate the disinfective efficiency of the lime compounds, the C·t values were calculated from the time for 99% disinfections and the concentrations of the disinfectants were compared with those of usual disinfectants. The lime compounds were found to be stronger disinfectants than Ag and the efficiency of the disinfection by calcium hydroxide was almost same as that by chloramine. Thus, the lime compounds seem to have the feasibility as practical water disinfectants instead of chlorine.
The effect of bimodal particle size distribution on the sintering of magnesium oxide (MgO) powder was examined using seven kinds of powders with average primary particle sizes of 11, 25, 32, 44, 57, 107, and 261 nm. The binary-phase MgO powder mixtures were prepared using two of these MgO powders (quantity : 0.75 g for each powder). These binary-phase MgO powder compacts were fired at 1700°C for 5 h in air. The relative densities of the sintered binary-phase MgO powder compacts were lower than those (97-98%) of the sintered single-phase MgO powder compacts. Appreciable decreases in relative density were observed after the firing of binary-phase MgO powder compacts with average primary particle sizes below 57 nm. The densification of such binary-phase MgO compacts appeared to be restricted by the entrapment of pores into grains, due to the rapid inhomogeneous grain growth.
The effects of thermal decomposition on the surface properties and the chemical activity of rice husk ash were investigated by XRD, XRF, BET, chemical analysis, and electrical conductivity method. The results show that with simple hydrochloric acid pretreatment of rice husks, white rice husk ash comprising of pure amorphous silica with high specific surface area (145-311 m2·g-1) was obtained from the heating rice husks at the temperature 550-900°C. The metallic impurities in rice husk ash were substantially reduced, and decrease of impurities resulted in difficult formation of crystalline phase from amorphous silica in rice husk ash. The crystalline phase of distorted quartz structure was formed above 1000°C. The surface properties and the chemical activity of silica in rice husk ash strongly depended on the soaking temperature and were slightly affected by the soaking time at a given temperature.
The rapid preparation of a series of RBa2Cu3Oy (R=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er and Yb) superconductors on the microwave processing was studied. All of the RBa2Cu3Oy superconductors were prepared as orthorhombic compounds and it was found that these compounds, except for the case of La, have revealed the superconductivities with the superconducting transitions, (Tcmag), ranging from 83 to 93 K. The Tcmag for compounds RBa2Cu3Oy (R=Dy, Y and Ho) remained essentially constant at 93 K, independent of R. However, the Tcmag decreased with increasing R radius andwith decreasing R radius. Further we have attempted to prepare NdxYb1-xBa2Cu3Oy of two rare earth elements with different ionic radii and also have investigated the superconducting properties of the synthesized compounds in various compositions of x (0≤x≤1). The cell parameters showed linear dependence on the composition (x). In the range of x=0.2-0.4, a homogeneous phase superconductor with Tcmag=93 K was formed, while for the range of x≥0.5, the Tcmag clearly decreased with increasing x and reached a value of 83 K in the sample with composition of NdBa2Cu3Oy.
Spherical phenolic resin powders with two particle sizes, i.e. the average particle sizes of 25 and 9.1 μm, were treated in Ar-H2, Ar-N2, Ar-H2-CO2 and Ar-N2-CO2 RF thermal plasma under reduced pressures of 26.6 and 53.3 kPa. The plasma-treated powders were characterized by X-ray diffractometry, scanning electron microscopy and Raman spectroscopy. The BET surface area and the content of carbon, hydrogen, oxygen and nitrogen were also measured. The plasma-treated powders were heated in-flight and carbonized through thermal decomposition, and partially evaporated. For the powder of the smaller particle size, more amount of evaporation occurred and a lot of fine powders were formed. The larger particle powder had a higher degree of crystallinity than the small particle one as examined by the X ray diffraction patterns and Raman spectra. The plasma-treated powders have a non-uniform structure, which is composed of the graphitized and amorphous structures, and the phase content depended on the particle size. Electrochemical measurements as an anode of lithium rechargeable battery were performed in 1 M LiClO4/ (ethylene carbonate+diethyl carbonate). Some powder samples of the plasma-treated powders showed higher capacity than theoretical capacity of graphite, 372 mAh/g.
Colloidal processing of fine powders of zirconia, alumina and titania was conducted for obtaining fine-grained microstructures. Well-dispersed aqueous suspensions of the fine powders were prepared by adding appropriate amount of zirconium acetate. The suspensions were characterized by measuring particle size, zeta-potential and rheological properties. Dense green bodies of zirconia, alumina and titania were obtained by slip casting of the suspensions and further CIP treatment. Low-temperature densification was observed and dense and fine-grained sintered bodies were obtained.