Studies on the production of fine palladium powders for thick film application were carried out by reducing the acid solution and the ammoniacal solution of the aqueous chloro-palladate in a hydrogen gas bubbling batch reactor in a range of temperatures from 293 to 353K and hydrogen partial pressures from 0.5×10⁵ to 1.0×10⁵ Pa. The palladium powders reduced in the acid solution were agglomerated and irregular in shape. The conditions of the reduction temperatures, the hydrogen partial pressures, the palladium concentrations and the stirrings did not effect on the agglomeration and the irregularity in shape.
However, the palladium powder reduced in ammoniacal solution was highly dispersed and granular particle of 2-5μm in diameter. The spherical fine particles with the smooth surface, the diameter of 0.5-1.0μm and the specific surface area under 1.0×10³ m² kg^-3 were obtained by adding a surfactant in an ammoniacal solution. Furthermore, the mean diameter, the smoothness of the surface and the specific surface area were controlled by the additional amount of the surfactant.

View full abstract

In-situ measurement were carried out in an experimental tunnel of Matsumine mine. Displacements in rock around the experimental tunnel were measured by five extensometers at a location, and convergences of the experimental tunnel were measured at two locations.
Displacement in rock around the tunnel increases rapidly with face advance at first, and these rates decrease gradually with face advance. And the face advance affect the displacement especially when the distance to face is less than one tunnel width. But it is interesting that the displacement continuously increases with time after the face advance was stopped, and that the displacement does not show a trend to level off at a certain value and increase continuously following the logarithmic law after quite long time has passed. Similar trend can be obtained by the result of convergence of tunnel.
Through the measurement of such displacement and convergence behaviors, it became clear that the rock mass around the experimental tunnel in Matsumine mine behaved as a visco-elastic body; a great part of the deformation is due to viscous or time-dependent bahavior.

View full abstract

Factors determining the magnitude of critical current density, at which Zn began to deposit from impurityfree electrowinning bath, were studied on the basis of extra-overpotentials peculiar to hydrogen evolution. Electrochemical condition, which permitted codeposition of electrochemically less noble Zn with more noble hydrogen, revealed a kinetic requirement that the deposition overpotential, nH, for hydrogen should be generated at the critical current density to polarize the cathode to reach the equilibrium potential of Zn. The nH was not caused by the diffusion overpotential but by the extra-overpotential, ηH, appearing due to the inhibitory Zn hydroxide adsorbed on the cathode in addition to the inherent hydrogen overpotential, ηH, on the substrate. The dependence of ηInhH on the total current density revealed that the critical current density, which was observed at various metalel ectrodes, should be identical to the hydrogen evolution rate to genarate necessary magnitude of ηInhH to satisfy above requirement.Therefore, the magnitude of the critical current density depends essentially on the η0H and any other factors affecting the depletion rate of hydrogen ions in the cathode layer. The theory predicts that the critical current density is unequivocally dependent on the riH in the bath of fixed composition while it depends on the buffer capacity of the baths when the electrode material is specified. These predictions were in good agreement with experimental results.

View full abstract

Uniaxial and indirect tensile strength of Sanjome andesite was obtained under air-dried and water-saturated conditions. It was found that the strength increases with loading rate in both conditions.
The difference in loading-rate dependency can not be observed between uniaxial and indirect tensile tests. And also the amount of strength increase with ten fold increase of loading rate shows no difference between air-dried and watersaturated conditions.
The experimental results were compared with previous results of uniaxial compressive strength. And, it was found that all results can be approximated by an equation where S is strength when loading time upto strength failure is tF, S₀ is strength when loading time is 500s, S₀ DRY is S₀, in air-dried condition, δ' is a constant.

View full abstract

Hydrolysis of acidic ferric sulphate solutions of various concentrations has been investigated in an autoclave at temperatures of 150°, 170°, and 220°.
The results obtained were as follows:
1. When hydrolysis of ferric sulphate solutions was at equilibrium, the concentration of ferric ion increased with an increase in the sulphuric acid concentration in solutions, while at the same sulphuric acid concentration, the concentration of ferric ion decreased considerably with an increase in temperature.
2. In hydrolysis of ferric sulphate solutions, ferric oxide, Fe₂0₃, was precipitated at lower concentrations of sulphuric acid, and ferric basic sulphate, Fe (OH) SO₄, was precipitated at higher concentrations of sulphuric acid.
3. At a temperature of 150°, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 53.4g/l, and above 53.4g/l, ferric basic sulphate was precipitated. Empirical formulas of the ferric ion concentration and the sulphuric acid concentration in solutions were as follows. up to the sulphuric acid concentration of 53.4g/l, log [Fe³⁺ (g/l)]=3.24log [H₂SO₄ (g/l)]-4.44 above 53.4g/l, log [Fe³⁺ (g/l)]=0.45 log [H₂SO₄ (g/l)] +0.45
4. At a temperature of 170°C, hydrolysis and precipitation of ferric oxide occurred up to the sulphuric acid concentration of 54.8g/l, and above 54.8g/l, ferric basic sulphate was precipitated. Empirical formulas of the ferric ion concentration and the sulphuric acid concentration in solutions were as follows. up to the sulphuric acid concentration of 54.8g/l, log[Fe³⁺ (g/l)]=4.07log[H₂SO₄(g/l)]-6.32 above 54.8g/l, log [Fe³⁺ (g/l)] =1.24log [H₂SO₄ (g/l)]-1.42
5. At a temperature of 220°C, hydrolysis and precipitations of ferric oxide and ferric basic sulphate occurred in wider concentration of sulphuric acid between 58.2g/l and 67.1g/l. Therefore the sulphuric acid concentration which allowed single precipitation of ferric oxide or ferric basic sulphate was not determined exactly. The sulphuric acid concentration, 67.5g/l, was determined from the point of intersection of the curved line of stable region of ferric oxide and that of ferric basic sulphate. up to the sulphuric acid concentration of 67.5g/l, log [Fe³⁺ (g/l)]=3.31 log [H₂SO₄ (g/l)]-5.91 above 67.5g/l, log [Fe³⁺ (g/l)]=1.43 log [H₂SO₄ (g/l)]-2.33
6.Equilibrium diagrams in the system, Fe₂O₃-SO₃-H₂O, at the temperatures of 150, 170, and 220°C were established from the experimental data.

View full abstract

Dental material waste from dental clinics, which contains the grinding dust of dental casting gold-silverpalladium alloy and gold, is treated by dissolution with nitric acid and aqua regia to recover precious metals.
In order to minimize the consumption of these reagents, the recovery of dental precious metal dust from dental material waste has been investigated by flotation. The X-ray diffraction analysis of the waste used in this study showed the patterns of aluminum oxide, gypsum, carbon silicate and cristobalite.The dental waste was screened into 6 size fractions;-4, 760+297, -297+210, -210+149, -149+105, -105+74, and-74μm. The gold and palladium grades of them except for the coarsest size fraction were from 0.15% to 1.25%. The grinding precious metal dust was floated selectively in acid pH range using amyl xanthate as a collector. At the size fractions finer than 149 pm, more than 80% of gold and palladium in the waste were recovered, and flotation recoveries were less than 30%. The waste volume to be treated in acidic solutions could be reduced by flotation preceding the dissolution process.
Carbon silicate was floated together with precious metal dust, but the additions of quebracho and corn starch depressed its floatability.

View full abstract

Recently, shortage of labor force has become a serious problem in mining industry, civil engineering and construction industry and so on. This is because of hard work load and its complication. Therefore, robotized machines have been required to improve labor-saving, safety and production in mining and construction works. Microcomputers have become very powerful in terms of communication capabilities and computing power. All that's at a lower cost. As a result of the availability of these powerful, low cost microcomputers, it is now possible to integrate them into oil hydraulic machines.
In this paper, a vibration technique is employed to the oil hydraulic cylinder, which has multiple function. An apparatus of the experiment is an oil hydraulic controlled system with the two single-rod cylinders, proportional solenoid controlled valve and high speed on-off solenoid valve. First, the system is identified by mean of an expended least square method, and its pulse transfer function is determined. Next, the experiment is made with variation of the supply pressure and the frequency and the bias voltage under some levels of the constant load. As a results, the quantitative properties, namely, the vibration amplitude, the feed speed, the frequency, the maximum pushing force and the acceleration, are obtained.

View full abstract

Adhesion behavior of CaCO₃ particles (size 10-20μm) to kerosene oil droplets in aqueous solutions, with or without surfactants, have been studied.
When mixed with sufficient volume of oil, CaCO₃ particles in surfactant-free solutions easily adhered to and floated with oil droplets at and above the natural pH (9.7) of the CaCO₃ aqueous suspension. The adhesion mechanisms of hydrophilic CaCO₃ particles and oil droplets at different pHs were discussed, based on the electrokinetic data of CaCO₃ particles and oil droplets and on the three-phase contactangles at calcite cleavage surfaces.
Effects of two surfactants, sodium dodecylbenzenesulfonate and sodium oleate on particle-droplet adhesion behavior were examined. The difference in adhesion behavior by these surfactant was discussed, in terms of stability of the oil droplets and hydrophobicity of the solid surface.

View full abstract

It is considered that land deformation caused by open-cut mining influences on wind system around the quarry. Two case studies were conducted to investigate the change of wind system around the quarry.
The results are summarized as follows:(1) Land deformations caused by open-cut mining were simulated with three dimensional computer graphics, and it became possible to forecast the changes of wind direction visually.(2) By use of quantitative formula that showed the relationship between lay of land and wind direction frequency, it became possible to forecast the changes of prevailing wind direction and wind direction frequency quantitatively.(3) It became clear that deforestation according to open-cut mining influenced on increase of wind speed around the quarry.(4) In case A, the ridge of the quarry will be mined, it was forecasted that change of wind system affected on living environment a little.(5) In case B, all over the mountain will be mined-out, it was forecasted that wind system around the quarry was changed widely.

View full abstract

An experimental study was carried out on the preparation for activated carbon from bark wastes in wood industry. This study involved an activation test with the phosphoric acid at temperatures in the range of 400 to 900°C, after the bark materials being dried, ground and sorted for sizes smaller than 4 mm.
The Parameters, such as internal surface area, pore size distribution and pore volume of the activated product, were measured, and the adsorption capacity with the methylene blue and benzene was tested separately. It was found that for activation longer than 5 minutes, the methylene blue adsorption capacity was increased with an increase in temperature of the above range, while the internal surface area and the benzene adsorption capacity were decreased at the temperatures above 600°C. Besides both trichloroethylene and tetrachloroethylene adsorption tests have shown that activated products of higher adsorption capacity could be obtained with this phosphoric acid activation process as compared with the commercial activated carbon.

View full abstract

The aqueous suspensions of precipitated silica exhibit anomalous stability due to the structural forces not considered in the classical DLVO theory. The magnitudes of the structural energies have been estimated using an extended DLVO theory, in which the structural energy is expressed as a double-exponential function. The result shows that the structural force decreases with increasing NaCl concentration as opposed to the structural forces observed in rutile and mica. It is believed that an inherent water structure exists on silica surfaces and develops a steric repulsion, while the water structures on rutile and mica are gradually formed as hydrated cations adsorb onto each solid surface. In this regard, the hydration force observed with silica can be referred to as “primary hydration force”, while those observed with rutile and mica can be referred to as “secondary hydration force”. By incorporating the concept of cation bridging in silica coagulation, it has been shown that the opposite effect of cations on the structural forces in silica and rutile can be explained consistently.

View full abstract

It is well known that moisture has a varying effect on the physical properties of rocks. For example, it is reported that the compressive strength of shale and sandstone under water saturated conditions decreases to about 50% of that under dry conditions. However, time-dependent behaviour such as creep at high humidity levels is still open to discussion.
In this study, 102 uniaxial creep tests under air-dried conditions and 174 creep tests submerged in water have been carried out. The most important result is that the life time is given by a function of (δF-oδc) where δF and δc denote the uniaxial compressive strength and the creep stress. This is true through air-dried and water saturated conditions. Also it was found that the creep curve of e vst*(elapsed time over life time) under water saturated conditions coincides very well with that under air-dried conditions without regard to creep stress.

View full abstract