Displacement Discontinuity Method (DDM) is one of useful means for analyzing the stress state and the deformation of the discontinuous body. However, it is well known that the accuracy of DDM analysis using the conventional scheme is not satisfactory for solving the crack problem.
In this paper, the improvement of the accuracy of DDM analysis on the crack problem and the applicability of DDM to the stress analysis of the jointed rock are discussed. Firstly, the analytical error of the DDM on the crack problem is discussed and a new scheme for numerical modeling of the crack is presented. Secondly, some numerical results of crack problems are shown and it is confirmed that the stress and the displacement fields can be analyzed sufficiently and accurately by DDM based on the proposed scheme. Finally, the mechanical behavior of elastic body which contains many cracks is analyzed and it is made clear that the deformability of the elastic body is strongly affected by not only the density and orientations of cracks but also geometrical distribution of them.
It is concluded that the DDM based on the proposed scheme make a promise, to analyze the stress state and deformation of the discontinuous material like jointed rock.

View full abstract

In this paper, a general equation of modified Froude-number for limit deposit velocity was derived based on a dimensional analysis of forces acting on a deposit bed. Results predicted by this equation were compared with experiments obtained by other researchers.
The conclusions obtained in this study were summarized as follows:
1) The coefficient and exponents in the general equation could be estimated with experimental results using two different small diameter pipes. It was confirmed that this equation provided sufficiently accurate predictions of the limit deposit velocity for full scale pipes.
2) The general equation was also used to scale up the limit deposit velocity of different particle sizes if the coefficient and exponents in the general equation were determined by experiments using two kinds of particle sizes.
3) In the case that fine particles were dispersed in the carried fluid, the fluid viscosity had to be modified according to concentrations of fine particles. By using the modified fluid viscosity, the general equation obtained in this study could be used for the scale-up of limit deposit velocity.

View full abstract

In order to study the influence of particle shape on grindability, a crushing test was performed using a simple drop weight method. The samples used were quartz and limestone. The number of specimens prepared were 10, 000 pieces of 5-6 mesh quartz and 5, 000 pieces of 4-6 mesh limestone. The shape index defined by (diameter of a circumcircle/thickness) was measured by slide caliper and classified by value of shape index into five groups respectively. Assuming that the potential energy of a ball was the energy input to a specimen, the relationships between probability of fracture and dropping height of a ball or specific energy input to specimens were obtained experimentally. As a result, it was found that the probability of fracture increased with increase in shape index.

View full abstract

The reduction of hexavalent chromium (Cr⁶⁺) by sulfur-oxidizing bacteria was investigated using elemental sulfur as the substrate for bacteria in 9K medium (without FeSO₄). The test bacteria were collected from a neutralization plant at the abandoned Matsuo mine and cultured in iron-free 9K medium with elemental sulfur. The bacteria oxidized elemental sulfur to sulfate, and main strains of them must be Thiobacillus ferrooxidans and Thiobacillus thiooxidans.
The results obtained are summarized as follows.
1) Cr⁶⁺was reduced when the bacteria were cultured on elemental sulfur. It could be due to sulfurous acid formed as a intermediate during the oxidation of elemental sulfur to sulfate by the bacteria.
2) Cr⁶⁺inhibited the sulfur-oxidizing ability of the bacteria, but the oxidation rate of elemental sulfur increased remarkably after the reduction of Cr⁶⁺.
3) The rate of Cr⁶⁺reduction increased with the inoculum size and the concentration of elemental sulfur, and the optimum initial pH was 2.0.

View full abstract

In order to analyze the reduction rates for the mixture of iron oxide and zinc oxide, and ZnFe₂O₄with CO-CO₂gas mixtures, reduction experiments were carried out in the temperature range from 973 to 1173 K. Experimental data for both the reductions were analyzed in terms of the mixed control kinetics based on the isothermal two-interface model, in which activities of ZnO and FeO were taken into account. The results are summarized as follows:
(1) The calculated reduction curves by using the rate parameters based on the unreacted core model and activities of ZnO and FeO are in satisfactory agreement with the experimental data for both the reductions, except the reduction curve of zinc oxide on the experimental condition of 1173 K, 92.0%CO on which the experimental data of zinc oxide exhibited delay as compared with the calculated reduction curves.
(2) It was found from experimental results and calculations based on the isothermal two-interface model that the most suitable condition for the first reduction stage of the iron-reduction distillation process was the rather low temperature such as about 973 K.
(3) The difference in the experimental results between the mixture of oxides and ZnFe₂O₄was not found, and the calculated reduction curves based on the same isothermal two-interface model are finely in agreement with the experimental data for both the reductions. Then the formation of ZnFe₂O₄in the iron-reduction distillation process is out of the question.

View full abstract

Commercial-grade purity Pr and Nd metal rods were repeatedly melted in a 10kW EB-furnace to grasp the features of EB-melting of rare earth metals and the properties of the EB-melted rare earth metals. Initial amount of the melting samples was about 40g, and the beam current added was 0.22A and net melting time was 25X2min every double-melting for both metals.
(1) The average weight-loss of Pr and Nd metals were respectively 7% and 25% every double-melting, suggesting about 350°C and 250°C higher temperatures of the melting pools than each melting point of Pr and Nd, respectively.
(2) The significant decrease of the pressure inside the furnace after the melting of Nd rods reveals that the vapour of the metal can act as a strong getter of oxygen and nitrogen.
(3) Among the gaseous impurity elements (C, H, O, N) with a total amount of 5000 wt.ppm and the metallic ones with each amount of several wt. ppm, only H in Pr was effectively removed from 76 to 4 wt. ppm. EPMA images showed the presence of a large amount of inclusion-like deposits for oxygen, but not for nigrogen.
(4) Vickers hardness of Pr and Nd metals lowered from 58 to 32 and 50 to 36, respectively, while the grain size increased from 60 to 120μm in both metals.
(5) Initiation temperature of oxidation detected by weight increase was 450°C for Pr metal and above 900°C for Nd metal. But the oxidation of the former before EB melting proceeded rapidly owing to the formation of cracks and the collapse of specimen.

View full abstract

The behaviour of lead in anode during electrolysis was investigated in terms of impurity level in anode and concentration of dissolved oxygen and H₂SO₄ in electrolyte.
The metallic granular forms of lead were found in the anode at the lower lead level of less than 5, 000 ppm. However, the higher lead level anode exhibited a mesh-like shape in copper matrix. The anode potential-time curves show discontinuous steps based on the falling of slime from anode surface during electrolysis, and then the passivation were not observed. The slimes obtained in this work were falling and adhering slimes. The adhering slimes were dark-brown color mostly consisted of PbSO₄and copper powder. The ratio of PbSO₄to copper powder in the adhering slimes increased with increasing lead level in anode, and it ranged 50-80 wt%. The PbSO₄characteristically deposited around the undissolved metallic lead. This is because the lead was dissolved in the electrolyte and immediately reacted with SO₄ions in electrolyte to form PbSO₄.
On the electrolysis with the Cu-As-Pb-O anode composition of slime obtained was mainly shown to be PbSO₄and Cu₃As. Trace amount of As₂0₃and PbO were detected in the slime. Undissolved lead was also present in it.

View full abstract