Processes of extractive metallurgy include both heterogeneous and homogeneous reactions. Mass transfer rate to reaction interfaces, for example, an interface between an electrode and an aqueous solution in electrorefining processes, controlled the overall reaction rate of processes. Although the diffusion coefficient of solute is a fundamental parameter for mass transfer, available data are still limited at present. Therefore, it is often necessary to measure the values of diffusion coefficient under the conditions concerned. In this review paper, some techniques for determining diffusion coefficients of electrolytes in aqueous solutions are described with discussion on several points to be careful in the experiments, which includes the methods using a porous diaphragm cell, optical instruments and electrochemical devices.
Understanding strength characteristics of frozen rocks is important for stability assessment of rock slopes in cold region. In this study, uniaxial compression tests and Brazilian tests were carried out on frozen rock specimens of Noboribetsu welded tuff under temperatures of between -5°C and -20°C. Effects of temperature and loading rate on strength and failure process were examined. Main results are as follows. 1) Both temperature and loading rate affected strength of wet rock specimens, while no significant effect was observed for dry rock specimens. Their effects on uniaxial compressive strength are different from those on indirect tensile strength. Uniaxial compressive strength discontinuously increased as temperature decreases from -10°C to -15°C, but indirect tensile strength gradually increased with decrease in temperature. Rate of increase in indirect tensile strength with increase in loading rate was larger than that in uniaxial compressive strength. 2) No apparent difference in failure process was observed with varying temperature and loading rate in uniaxial compression test under dry condition. However, stress level at fracture initiation increased at -15°C temperature or with increase in loading rate under wet condition. The increase in such stress level is thought to result in increase in strength. 3) Effects of temperature and loading rate were considered with an inclusion model assuming that Young's modulus of frozen pore water varied with temperature or loading rate. The model succeeded to qualitatively predict the observed phenomena. The increase in strength was thought to result from reduction of stress concentration in rock matrix around pores with increase in Young's modulus of frozen pore water.
Rock around an underground opening may be damaged with excavation. Recently, it was pointed out that damaged zone or fractured rock might be compacted and recovered in strength under a proper condition. Strength recovery will, however, not contribute to long-term stability of an underground structure if time-dependency of the strength-recovered zone is so large and deformation of the region is increasing with elapsed time. As a first step to understand time-dependent behavior of a strength-recovered or compacted specimen, in this study, loading-rate dependency of the specimen in uniaxial compression was investigated. A rock specimen was, at first, completely fractured and then compacted in a steel cylinder. After pushed out of the cylinder, the compacted rock sample was loaded at alternating loading-rates to obtain loading-rate dependency accurately. Strength recovery was remarkable for Tage tuff, Kimachi sandstone and Kawazu tuff, but poor for Sanjome andesite. In the alternating loading-rate test, stress fluctuated clearly corresponding to up and down of the loading-rate in both pre- and post-failure regions. For the four rocks, loading-rate dependency of uniaxial compressive strength (peak strength) was found to be similar to the ordinary rock specimens. The result indicated that damaged zone or fractured rock around an underground opening might show time-dependency similar to the surrounding rock mass.
In order to develop the “Bio-filter”, silicon nitride porous bodies with complex pore structure were fabricated using the tape casting process. Macro-pores with diameters about 100 micron were introduced through the bulk silicon nitride porous bodies with micro-pores with diameters about 1 micron by stacking polyethylene meshes between the green sheets of silicon nitride, and being followed by burning out them in air. By optimizing the fabricating conditions, silicon nitride porous bodies with sufficiently high strength for the filter application were successfully obtained. By introducing the macro-pores, the strengths of silicon nitride porous bodies significantly decreased from about 200 MPa to less than 50 MPa, which was found to be due merely to the increase of porosity.
This study aims to elucidate the alteration mechanism of mortar surface reacted with seawater and the relationship between characteristics of secondary products on the surface and salt concentration of seawater. The experiment was carried out in closed system using two kinds of mortars which were made from high-early-strength portland cement (HES) or alumina cement (AL) and silica sand, and two kind of artificial seawater with quarter or twice the salt concentrations. Tablet type specimen (3.5-cm diameter, 1.0-cm height) was treated with seawater of 200.0 mL at room temperature during 91 days. Results of the experiment showed that secondary products were formed on the surface of altered tablet. These were characterized by SEM-EDS and XRD as brucite, Mg (OH)2, and aragonite, CaCO3, under low salt concentration of seawater. Production of brucite was remarkable at HES, while that of aragonite was remarkable at AL. Under high salt concentration of seawater the production of aragonite was promoted. Besides, analysis of cross section of altered tablet illustrated that the thin layer of brucite was formed at first, and then columnar or needle-shaped aragonite was formed on the layer.
Elution property of lead from granulated copper slag and synthesized slag was investigated. The conditions obtained from slag test were applied to the fly ash from waste incinerator in order to minimize the elution of lead. The results obtained are follows. 1. Elution concentration of lead from copper slag has no relation with lead content in the slag, and it has strong relation with silica content in the slag. Elution concentration of lead decreased with increasing silica content in the slag, even though, elution concentration of lead was relatively high from the slag containing lime in high concentration. 2. Elution concentration of lead from synthesized slag also has strong relation with silica content in the slag. Elution concentration of lead decreased with increasing silica content in the slag, and it clear the Japanese environment standard (0.01 ppm) at the silica content over 40 wt%. Elution of lead from slag may be attributed to the network structure of silica. Heat treatment of slag decreased elution of lead extremely attributed to crystallization. 3. Melting treatment of incinerator fly ash is not always decreasing elution of lead from the material. Although, melting incinerator fly ash with additional silica decreased elution of lead. Elution of lead from incinerator fly ash slag decreased extremely by heat treatment.