In order to clarify the rate and mechanism of the formation of Sm-Fe intermetallic compounds by the reduction-diffusion (R-D) process, three kinds of experiments were carried out:(1) the reduction of pellets of Sm₂0₃ powder mixed with CaH₂, (2) the R-D reaction for the pellets which were composed of Sm₂O₃, CaH₂ and Fe (powder or wire) at 1, 300, 1, 400 and 1, 500K, and (3) diffusion experiment by using Sm-Fe diffusion couples with Mo wire as a marker at 963K.
The reduction of Sm₂O₃ uniformly proceeded in the pellets; more than 90% of Sm₂O₃ was reduced at 1, 400 and 1, 500K in a reaction time less than 1 ks, though about 80% at 1, 300 K at a reaction time of 1 ks. During the R-D reaction, an Sm₂Fe₁₇ layer was formed on the Fe surface. The thickness of the Sm₂Fe₁₇ layer grew according to a parabolic rate law at 1, 300K. At 1, 400 and 1, 500K, however, the Fe dissolved in a liquid Sm or Sm-Ca melt, since the reduction rate of Sm₂O₃ was high. The experiment with the diffusion couple revealed that Fe diffused faster than Sm in the SmFe₂ layer.

View full abstract

Aiming at the development of less energy-consumptive process for producing hydrogen storage materials, an experimental study was carried out on absorption-desorption characteristics of hydrogen for the RmNi₅ compounds which were produced from various mischmetal oxides (Rm₂O₃) by the reduction-diffusion (R-D) method. In the R-D process, a mischmetal oxide was reduced by metallic calcium in the presence of nickel particles and the reduced mischmetal elements diffused into the nickel particles to directly form a RmNi₅ compound.The hydrogen pressure-composition isotherms (PCT) were determined by a Sievert's apparatus for hydrides of (a) lanthanum-base RmNi₅, (b) cerium-base RmNi₅, (c) cerium-base RmNi_4.5 Coos, RmNi_4.5 Al_0.3 and RmNi_4.5 Mn_0.5, and (d) cerium-base RmNi_3.55 Co_0.75 Mn_0.5 Al_0.3. The hydride of the lanthanum-base RmNi₅ presented a plateau region extending up to nH (=H/M) of about 1, where the equilibrium PH₂ in the desorption isotherm was 4.5 atm at 20°C. On the other hand, a small hydrogen absorbability was shown for the cerium-base RmNi₅ and no plateau region was observed in the PCT diagram. The hydrogen absorbability increased significantly by replacing some nickel sites of lattice of the cerium-base RmNi5 by cobalt, aluminium or manganese and forming RmNi_4.5 Co_0.5, RmNi_4.5 Al_0.5 or RmNi_4.5 Mn_0.5. The cerium-base RmNi_{3.5 5} Co_0.75 Mn_0.4 Al_0.3 cornpound also showed favourable characteristics amenable to the use for a hydrogen storage material. It absorbed hydrogen at ambient temperatures so fast that there seemed to be no need of an activation procedure for the hydrogen absorption.

View full abstract

The direct thermal decomposition of molybdenite concentration (MoS2=92.3 mass%, SiO₂=3.2mass%, Fe=0.65 mass%) in molten state has been carried out under Ar plasma-arc heating to produce the molybdenum metal product. The product was then refined to pure molybdenum metal above 99.9 mass% by H₂-Ar plasma-arc melting method.
Sulfur was removed rapidly as small bubbles from the molybdenite melt under Ar plasma-arc heating. The products above 98 mass% Mo containing 0.6-0.7 mass% S, 0.1-0.2 mass% O 0.05-0.1 mass% C, were obtained by thermal decomposition for 12 minutes. Oxygen and carbon in the products are probably due to the content of oil and SiO2 in the concentration. For metallic impurities, silicon can be separated as a slag and eliminated as a SiO-vapor from the molybdenite melt. Then the silicon content in the products was reduced to below 0.05 mass%. However, over 60% of iron contained in the concentration was retained in the products, so that the iron content reached to 0.7-0.8 mass%.
On H₂ -Ar plasma-arc melting of thermally decomposed molybdenum products, it is found that non-metallic and iron impurities can be removed quickly to the low level. Therefore, the sum of non-metallic impurities, such as (S+O+C+N) and the iron content of the molybdenum products after 10 minutes of melting decreased to below 150 mass ppm and 50 mass ppm, respectively. These excellent refining progresses are considered to be mainly caused by dissociated and activated hydrogen atoms in a H₂-Ar arc plasma.

View full abstract

Extraction rate of Fe (III) with D2EHPA was investigated in the presence of alkyl phosphoric acids to elucidate the extraction mechanism and rate determining step. Butyl phosphoric acid and 2-ethyloctyl phosphoric acid were used for the investigation.
The extraction rate of Fe (III) is extremely accelerated by addition of alkyl phosphoric acids. In the presence of 2-ethyloctyl phosphoric acid, the rate equation is expressed as,
-d [Fe³⁺] _aq/dt=k_f*[Fe³⁺] _aq [H₂A] _org [H⁺] _aqⁿ-k_b*[Fe³⁺] _org [RH] _org-1 [H₂A] _org^-1 [H⁺] _aq² (-1≤n≤0)
where k_f* and k_b* are forward and backward rate constants, and [HR] _org and [H₂A] org denote D2EHPA concentration and 2-ethyloctyl phosphoric acid concentration in the organic phase. Dependency of forward reaction on hydrogen ion concentration changes from -1 to 0, which is connected with the dissociation of mono-ester. The rate equation is interpreted by the idea that rate determining step is replacement reaction of water molecule in aquo Fe (III) ion with mono-ester molecule or ion. Value of kf/kf0, which is the rate constant in the presence of mono-esters devided by the rate constant in the absence of mono-esters, is a useful and quantitative measure to indicate the effect of mono-esters on the extraction.

View full abstract

Green algae (microspora) in the acidic mine drainage and blue-green algae (phormidium) in the alkaline hot spring stream were collected and used as biosorbents of metal ions. The results were as follows,
1. Algae which were washed by an aqueous hydrochloric acid and then dried, adsorbed the precious metals in aqueous solutions of tetrachloroaurate, silver nitrate and palladium chloride better than the living state of algae. For example, 1kg of washed phormidium adsorbed approximately 0.3kg of gold and the adsorbed gold on algae changed to metallic state. However, as for the adsorption of gold complex in thiourea solution by those algae, the adsorption was observed only in its dilute solution.
2. Washed algae could not adsorb base metal ions, such as Fe²⁺, Cu²⁺ or Co²⁺, however, unwashed dried phormidium adsorbed them fairly well. The adsorption of base metal ions on the phormidium was proved to be related to the cation exchange of Ca²⁺ in algae with chemical and EDS analyses.
3. As living algae could adsorb both precious metal and base metal ions, they could be used to recover or remove heavy metal ions from the waste water and so on by growing them in those water.

View full abstract

Some kinds of phospholipids have been detected as extracellular substance during the culture of Thiobacillus thiooxidans and Thiobacillus ferrooxidans, and during the pyrite leaching by Thiobacillus ferrooxidans. In this paper, the function of phospholipid in bacterial leaching of chalcopyrite concentrate by Thiobacillus ferrooxidans was investigated, using phosphatidylglycerol as a phospholipid.
Phosphatidylglycerol was observed to be adsorbed on chalcopyrite surface. As ferric ions would be inhibited to react with the chalcopyrite due to the adsorbed layer of phosphatidylglycerol, the amount of copper chemically leached with ferric sulfate become small with increasing phosphatidylglycerol addition. In the medium containing ferrous sulfate as substrate, growth of Thiobacillus ferrooxidans and iron oxidation from ferrous to ferric by the microorganisms were delayed with phosphatidylglycerol addition. On bacterial leaching, copper extraction was decreased with increasing phosphatidylglycerol addition. The leaching results were interpreted in terms of the functions of phosphatidylglycerol, which influenced the main reaction of indirect leaching mechanism.

View full abstract

Impact penetration test is important to observe the behaviour of rock undergoing very rapid loading which can not be realized by a testing machine. A force-penetration relationship is considered to be closely related to performance of percussive rock fragmentation process.
A lot of experimental studies have been carried out and it was found that the slope of force-penetration curve in impact penetration test is steeper than that in static penetration test. However, qualitatively much difference exists from author to author.
A system of impact penetration test developed in this study comprises a hammer and a cylindrical bar with a bit at one end. Stress wave is measured by a pair of semi-conductor strain gauges, and penetration is calculated by the measured stress wave.
Nine rocks were tested and force-penetration curves in impact and static tests were obtained together with uniaxial compressive strength, indirect tensile strength, Young's modulus, Poison's ratio, rebound hardness by Schmidt hammer and Shore hardness. Good correlation was found between force-penetration curves in impact and static tests, and slope by impact test, Kd can be expressed by slope in static test, Ks as Kd=1.2Ks
The difference between Kd and Ks is not so much as expected, just 20%.

View full abstract

On the basis of laboratory creep test of rocks under uniaxial compressive load, it is revealed that the strain rate of rock sample is inversely proportional to the residual failure life in the tertiary creep region. The residual failure life is defined as the time remained from an arbitrary time up to the time when creep failure occurs. Hence, the residual failure life is independent of the starting point of either time measurement or loading. The strain rate is also independent of the starting point of time measurement according to the definition.
It means that if the strain rate is observed from an arbitrary time in the tertiary creep region, then the residual failure life could be estimated.
This law of tertiary creep strain rate is applied to estimate the residual failure life of pillar which is loaded by approximately uniaxial compressive load.
Firstly, the estimation procedure of residual failure life of pillar is proposed and discussed by means of an example which is taken out from results of laboratory creep test of a rock. Secondly, the accuracy of estimation of residual failure life is discussed on the basis of theory of mathematical statistics.
It is revealed that
(1) the effect of sample number on the accuracy of estimation is not remarkable;
(2) as increases the term of observation, remarkably decreases the error of estimation. However, from the technical point of view, it is recommended to estimate the residual failure life as early as possible by several data taken in short term of observation, at the cost of accuracy, in order to ensure sufficient time for possible remedies.

View full abstract

Agglomerates formation and growth were investigated in terms of compaction process. Agglomeration experiments were carried out using BaSO₄ as model particles, sodium oleate (NaOI) as surface active reagent and kerosene as bridging liquid. Products of agglomeration experiments varied with saturation degree (volume of bridging liquid divided by voids volume of agglomerates) which is a function of compaction degree. Flocs were formed with saturation less than 0.45, discrete agglomerates were observed at saturation levels between 0.45 and 0.80, above 0.80 either amalgam or paste was formed. There was a drastic decrease in the number of agglomerates when the saturation degree approached the range of 0.70 to 0.75. Fast compaction rate means fast agglomerates formation and growth.
Compaction process of agglomerates was represented by modified Kawakita Equation. The constants a and b stand for final porosity of the agglomerates and ease of compaction, respectively. The constant b changes with the agglomeration conditions and the tendency of change of this constant can be used to predict the agglomerates formation and growth.
Based on theoretical considerations and experimental results the relationship between the time needed to start the second rapid growth stage t_c, the normalized bridging liquid volume ψB/ψBC and the normalized impeller speed N_I/_NIC was elucidated. Using similar approach, the relationship between the time needed to form agglomerates ta, the normalized bridging liquid volume ψB/ψBC' and the normalized impeller speed INIC was investigated. From the above results it is possible to predict the agglomerates formation and growth.

View full abstract