Characteristics of high fracture strength and high fracture toughness of zirconia in yttria doped tetragonal zirconia polycrystal (Y-TZP), Y-TZP/Al₂O₃ composites and ceria doped tetragonal zirconia polycrystal (Ce-TZP) are described in this paper. The maximum fracture strength of Y-TZP/Al₂O₃ composites is 2, 400MPa at 30°C The maximum fracture toughness of Ce-TZP is 20 MPam^1/2
It is found that hot isostatic pressing is effective to eliminate fracture origins such as pore. From the results of thermal shock behavior of Y-TZP with various grain sizes by the water quenching method and the tetragonal to monoclinic phase transformation by using Raman microprobe spectroscopy, it is found that the critical quenching temperature different of Y-TZP increases from 250°C to 425°C with increasing grain size from 0.4 to 3.0μm.

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This paper describes moisture movement in unsaturated sandstone and tuff, whose porosities are 13% and 29% respectively. For each rock three cylindrical specimens are prepared: dry (not perfectly) and saturated intact specimens, and one dry specimen including a tensile fracture parallel to the cylindrical axis. The side surface is sealed with silicon sealant to allow one dimensional movement of moisture. The 1cm lower part of the specimen is submerged in water, and the top surface is open to the room air. In this condition, water is infiltrated into the dry specimen upwards while the top surface of the initially saturated specimen becomes dry with time. During the experiments, relative humidity at two different heights above the top surface is monitored as well as total weight of the specimen. An evaporation rate is calculated from the difference between the two values of relative humidity, based on a molecular diffusion theory. In addition, water absorption at the top surface is measured using an infrared optical moisture meter. The experiments show that a steady state is not reached even in 70 days after the beginning of infiltration into the intact specimen. However, the changes of weight can be predicted with the data for the first 10 days, by a hyperbolic function which has two parameters giving a infiltration rate at the beginning of the experiment and weight at the steady state. The evaporation rate and the infiltration rate of intact sandstone are different from those of intact tuff, but each difference is not so large as that of the porosities. Distributions of saturation in the specimens are obtained from the results of the changes of weight and moisture at the top surfaces, which present increasing degrees of saturation with depth. When a two layer model composed of dry and capillary zones is used to estimate the evaporation rate in a drying process, the estimated value may include about a 50% error.

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In this study the special tests of gas permeability of coal have been conducted in order to make clear the effect of internal crack pressure and external stresses on gas permeability of coal. Practically, gas permeation rate has been measured by changing the differential pressure as a parameter under a constant mean pressure and a constant hydrostatic stress.
As the results of these tests, the relation between the gas permeation rate and the differential pressure had the linearity determined from Darcy's law. The gas permeability of coal decreased almost exponentially in response of an increase of the internal mean pressure and the external hydrostatic stress. From these considerations it became clear that the gas permeable cracks closed corresponding to the effective stress. Particularly, hydrostatic stress closed the permeable cracks irreversibly.

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The robots introduced in the excavation fields need to have the ability torecognize the environment around the robots and to move and work autonomously. In order to achieve this ability, the vision system is required in the robots. In this study, the vision system to estimate the self movement trajectory was investigated. At first, a simple method to judge the movement modes and to estimate the movement length and rotation angle was developed. The estimation is based on the location of two laser spots and single view image. Then, the experiments were carried out to confirm this method. By comparing the real trajectories and estimated ones by using images and laser spots, the agreement was observed to be good. This method could be applied to the natural environment including rocks and rock piles.

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Artificial diamond used as raw material for tool implements is mostly synthesized by the flux method. The final products of the synthetic reaction contain various kinds of impurities, such as ceramic brick, unreacted graphite and fluxes of Ni and Fe. In operation plants, the impurities are removed by chemical means. Residual fluxes are removed by dissolving with aqua regia, unreacted graphite with perchloric acid, and ceramic brick by sodium hydroxide fusing. As such methods for removing impurities are expensive and harmful to the environment, it is essential to establish more economical, safer and more efficient methods; froth flotation being one example of such attempts.
As part of the studies on the applicability of flotation to the removal of the impurities from the synthesized diamond products, flotation behaviors of unreacted graphite and synthesized diamond in the presence of depressants were investigated. Firstly, a series of flotation tests was conducted on raw synthesized diamond in order to determine the optimum conditions for removing unreacted graphite using sodium silicate, sodium hexametaphosphate and sodium pyrophosphate as depressants. When kerosene or Aerofloat #25 was used as a collector, both sodium silicate and sodium pyrophosphate were effective to depress the floatability of the synthesized diamond, but the depressing effect of sodium hexametaphosphate was more inferior than the above two because of less hydrolysis. Secondly, to assess the efficacy of separation flotation of the 1 to 1 mixture of the unreacted graphite and synthesized diamond, a series of flotation tests was carried out using sodium pyrophosphate and sodium hexametaphosphate as depressants and kerosene as a collector. It was found that these depressants were effective in separating the unreacted graphite from the synthesized diamond in an alkaline region of around pH 9.

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Desulfurization experiments were carried out with molten copper alloys by using a Na₂CO₃ flux in a 2 kg high freqency melting furnace to investigate the effects of alloying elements, melting atmosphere and melting temperature on the desulfurizing behavior of the flux. Sulfur distribution and desulfurization rate are affected by the contribution of alloying elements to the activity of sulfur in melts, the basicity of flux and the solidification temperature of alloys. The melting atomosphere has a large effect on sulfur re. moval: covering melt with charcoals or using a carbon crucible accelerates the desulfurizing ability of Na₂CO₃. The maximum desulfurizing ability was obserbed at 1, 473 K in the temperature range from 1, 423 to 1, 573 K. The reason is as follows: the sulfur removal is decreased at lower temperatures according to the temperature dependency of desulfurization equilibrium, and at higher temperatures by the vaporization of Na due to the reaction between Na₂CO₃ and carbon.

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Iron-group metals hardly precipitate in Zn sulfate solutions by cementation with Zn dust, although the less noble Cd than iron-group metals can precipitate easily. The partial polarization curves of irongroup metals indicated that the potential, at which an appreciable deposition of iron-group metals began, was polarized apparently in Zn sulfate solution nearly to reach the equilibrium potential of Zn. This fact was directly responsible for their extremely small deposition rate. According to the hydroxide suppression mechanism proposed for anomalous codeposition of iron-group metals with Zn, the minimum overpotential necessary to initiate iron-group metal deposition was composed of an inherent deposition overpotential, η°, and an extra-overpotential, η^Inh, appearing due to inhibitory Zn hydroxide adsorbed on the cathode. Consequently, it was predicted that any countermeasurs to reduce either η° or η^Inh might promote the precipitation rate of iron-group metals. This prediction was confirmed ernpirically by the precipitation behavior of iron-group metals in Zn ion-free sulfate solution, in Zn sulfate solution at elevated temperature or in Zn sulfate solutions containing catalytic chloride or thiocyanate ions. Further the mechanism, which permited the high removal rate of iron-group metals in conventional cementation by Zn dust with arsenous oxide in the presence of cupuric ions, was briefly discussed.

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Solvent extraction of lanthanum (III), samarium (III), and dysprosium (III) by kerosene solutions of phosphoric acid esters has been investigated to elucidate the structure effect of the phosphates on the extraction behaviors of these elements. As a result, it is found that the position of alkyl side chain in the organic groups of the phosphoric acid esters plays an important role in the extraction phenomena of the rare earths, and that the shorter the distance between the substituent and PO (OH) group, the greater the dependence of the extractability of rare earth on the pH of the aqueous phase is. It is also indicated that the separation factors between the elements are affected by the steric hindrance of the organic group of the phosphates. The factors of the substituent effect on the extraction phenomena are examined by using CNDO (Complete Neglect of Differential Overlap method) molecular orbital calculations.

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Solvent extraction of rare earths with phosphoric acid esters has been carried out to elucidate the structural effect of the phosphates on the extraction behaviors of thirteen rare earth elements. The results indicate that the position of the side chain in the alkyl group of the phosphates is important to control the extraction behaviors, and the alkyl side chain in the vicinity of PO (OH) group increases the separation factors of the elements. It is also suggested that the effect of the side chain on the extraction is related to dimerization of the phosphates. In the case of mixed phosphate systems, a heterodimer consisting of two different phosphates forms to afford the synergistic enhancement of the extraction. The formation of the heterodimer was assessed by use of fast atom bombardment mass spectrometry

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The extraction of molybdenum (VI) and tungsten (VI) from sodium hydroxide solutions by trioctylmethylammonium compounds (R₃R' NCl and R₃R'NOH) in benzene has been investigated under different conditions. As a result, it is found that although the extraction efficiency of quaternary ammonium compounds for molybdenum (VI) is larger than that for tungsten (VI), both metals are extracted from alkaline solutions through anion exchange reactions by the following equation: MO₄^2- (aq)+2R₃-R'NOH (org)⇔(R₃R'N) 2MO4 (org)+2 OH-(aq) where M=Mo or W. In addition, when the extraction of molybdenum (VI) and tungsten (VI) has been also examined by using trioctylmethylammonium salts, replaced by various anions such as NO^3-, SCN^-, HSO^4- and ClO^4-, in comparison with the results by R₃-R'NCl and R₃R'NOH, the extraction efficiency of quaternary ammonium salts for molybdenum (VI) and tungsten (VI) is in the order OH-Cl-HSO₄NO_3-SCN^-ClO_4-, depending on the anionexchange capacity of the salts. The formation of the species, (R₃R'N) 2MO₄, is supported by the fact that the characteristic vibrations of moiety appear in the infrared spectra of organic extracts.

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It is a purpose of this study to make the mechanism for the reduction of an aqueous silver nitrate solution clear. At each run 1.50×10^-4 m³ of the solution was loaded into a reducing gas bubbling batchreactor. The experiments were conducted for a range of temperatures from 333 to 353 K, SO₂ partial pressures from 0.05 to 0.01 MPa, gas flow rates from 0.83 to 1.67×10^-6 m³·s-1 and Ag concentrations from 0.01 to 0.05mol·m^-3.
At a temperature of 353 K, no product was obtained when pH=1.0 regardless of the reaction time. In the pH range from 5.0 to 7.0, the yields of Ag and Ag₂SO₃ at 0.3 ks were 0 and 95 %, respectively, while the yields of Ag were 10 % at 1.8 ks for both pH's. On the other hand, the yields of Ag at pH=9.0 were higher than those when pH=5.0 and 7.0. Based on these experimental findings, a reaction model was assumed to be expressed as a consecutive reaction. Results of the calculated changes with time in the concentrations of reactant and products agreed well with the experimental results, in particular when pH=9.0.
In contrast to the above, when pH=11.0, only Ag was formed at 353 K, while Ag and Ag₂SO₃ were formed at 343 and 333 K. Apparent reaction rates showed 1 st order dependency upon Ag concentration. These experimental results were explained by a simplified model simlar to the above. In this case the calculated changes with time in concentrations of reactant and products agreed well with those observed. Activation energies for the individual reaction steps were 84, 349 kJ·mol^-1. Consequently, the ratedetermining step of each reaction step was presumed to be controlled by the chemical reaction.

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