Toshihide Takenaka

Electrode reactions in dc electroslag remelting of steel rod

Abstract The non-metallic inclusion content increased significantly when a steel rod of Fe-Ni was remelted by dc electroslag remelting. The silicon content increased slightly. The manganese and sulphur contents did not change. The total aluminium content in the ingot was max. 0·7%, while that in the electrode was only 10 ppm. The aluminium cations Al3+ in the slag are reduced to metallic aluminium at the slag/electrode interface, while O2 - anions are oxidised to dissolved O in the metal pool. This Al and O subsequently recombine to form alumina inclusions in the metal pool. The inclusion content was dependent on the alumina content in the slag. When a rod of plain carbon steel was remelted, however, the increase in nonmetallic inclusion content was as little as one-tenth of that for the remelted Fe-Ni rod. The non-metallic inclusion content was independent of the polarity of the electrode.

High Temperature Electrolysis of Ti and its Alloys with a DC-ESR Unit

Direct electrolysis of Ti and its alloys has been attempted by the process using a DC-ESR unit. The concept of the process is explained in detail, and the expected key issues are commented. Liquid Ti metal was obtained in a CaF2-CaO-TiO2 bath, and electrolysis by using a new type of the electrolytic cell was also tried. Ti-Al alloy was successfully deposited in a CaF2-CaO-TiO2-Al2O3 bath, whereas Ti-Si alloy was not obtained in a CaF2-CaO-TiO2-SiO2 bath yet. Ti-Fe alloy was extracted in CaF2-CaO-TiO2-FeO bath of a particular composition. A common correlation between the cathodic current efficiency and the average consumed electric power seen in the Ti, Ti-Al and Ti-Fe electrolysis suggested the importance of sufficient temperature in the process. The bath composition also affected the temperature through the change in the electric conductivity of the bath.

Influence of Bath Composition on Ti Electrolysis in CaF2-CaO-TiO2 Melt

Ti electrolysis by using a DC-ESR unit was performed in a CaF2-CaO-TiO2 bath, and the influence of the bath composition was discussed. Ti metal in liquid was electrodeposited though some impurity elements were contained. The cathodic current efficiency strongly depended on the bath composition, and reached about 25% in the bath where the molar ratio of CaO to TiO2 was 1.5. The consumed electric power was also affected by the bath composition so that the close relationship between the cathodic current efficiency and the electric power was seen. The influence of the bath composition was considered due to the change in the species in the bath, and Ca3Ti2O7 seemed suitable for Ti deposition.

Electrochemical behavior of impurity elements in magnesium electrolysis

Electrochemical behavior of some metallic elements in molten salt systems has been investigated as a fundamental study for purification of Mg metal. A mixture of MgCl 2 , CaCl 2 and NaCI was mainly used as an electrolytic bath, and a eutectic mixture of LiCl and KCl including MgCl 2 was also used. The electrochemical behavior of Li, Cr, Fe and Ni was examined by voltammetry, and their cathodic reactions were discussed. The results indicated that the electrochemical separation of the elements from Mg metal was possible in the molten salt systems. Potentio-static electrolysis was carried out below the melting point of Mg metal, and Mg metal was obtained. However, the deposit consisted of small Mg metal particle, and the surface of the particle was oxidized during rinsing with water.

Chloride Pyrometallurgy of Uranium Ore, (I) Chlorination of Phosphate Ore Using Solid or Gas Chlorinating Agent and Carbon

A thermodynamical and pyrometallurgical study to recover uranium from the phosphate ores was undertaken using the chloride volatilization method. Iron was chlorinated with solid chlorinating agents such as NaCl and CaCl2 in combination with activated carbon, which will be used for removing this element from the ore, but uranium was not. On the other hand, the chlorination using Cl2 gas and activated carbon gave a good result at 1,223K. Not only uranium but also iron, phosphorus, aluminum and silicon were found to form volatile chlorides which vaporized out of the ore, while calcium remained in the ore as non-volatile CaCl2. The chlorination condition was studied as functions of temperature, reaction time and carbon content. The volatilization ratio of uranium around 95% was obtained by heating the mixture of the ore and activated carbon (35 wt%) in a mixed gas flow of Cl2 (200 ml/min) and N2 (200 ml/min) at 1,223 K for 120 min.A thermodynamical and pyrometallurgical study to recover uranium from the phosphate ores was undertaken using the chloride volatilization method. Iron was chlorinated with solid chlorinating agents such as NaCl and CaCl 2 in combination with activated carbon, which will be used for removing this element from the ore, but uranium was not. On the other hand, the chlorination using Cl 2 gas and activated carbon gave a good result at 1,223 K. Not only uranium but also iron, phosphorus, aluminum and silicon were found to form volatile chlorides which vaporized out of the ore, while calcium remained in the ore as non-volatile CaCl 2 . The chlorination condition was studied as functions of temperature, reaction time and carbon content. The volatilization ratio of uranium around 95% was obtained by heating the mixture of the ore and activated carbon (35wt%) in a mixed gas flow of Cl 2 (200 ml/min) and N 2 (200 ml/min) at 1,223 K for 120 min.

Influence of Conversion Coating Conditions with Rare Earth Elements on Corrosion Resistance of Mg Alloys

Influence of the conversion coating with some rare-earth elements, such as La, Y, Sm, Nd and Ce, on corrosion resistance of Mg alloy has been studied. Effect of pretreatment, such as the alkaline degrease, acid pickling and surface activation, has been also investigated. The surface of Mg alloy was covered with the so-called dry mad structure by the coating. The coating layer was a thin oxide film containing Mg, Al and rare earth element. F and P were detected in the coating with the pretreatment in addition. The corrosion resistance of Mg alloy against salt water was significantly improved by the conversion coating by immersion in the solution including both Mg(NO3)2 and rare earth nitrate. The corrosion resistance was improved by applying the pretreatment, further.

Reaction kinetics of some carbonaceous materials with oxidizing gas

In order to get a highly reactive carbonaceous material at low temperature, the reaction kinetics of various carbonaceous materials with different structure was investigated. The reaction rate was the largest for Bintyo char and bamboo char on unit mass base, but it was the largest for graphite on unit area base. The rate had a positive relation with the amount of CO adsorption, showing that the rate determining step would be the desorption of CO from the active site on the surface. The rate independent of surface area was derived from the data of the rate and amount of CO adsorption per unit area.

Chloride pyrometallurgy of uranium ore, (II) : Selective extraction of uranium using the mixed gas of chlorine and oxygen in the presence of activated carbon

A thermodynamical and pyrometallurgical study to recover uranium from the phosphate ores was undertaken using the chloride volatilization method. Iron was chlorinated with solid chlorinating agents such as NaCl and CaCl2 in combination with activated carbon, which will be used for removing this element from the ore, but uranium was not. On the other hand, the chlorination using Cl2 gas and activated carbon gave a good result at 1,223K. Not only uranium but also iron, phosphorus, aluminum and silicon were found to form volatile chlorides which vaporized out of the ore, while calcium remained in the ore as non-volatile CaCl2. The chlorination condition was studied as functions of temperature, reaction time and carbon content. The volatilization ratio of uranium around 95% was obtained by heating the mixture of the ore and activated carbon (35 wt%) in a mixed gas flow of Cl2 (200 ml/min) and N2 (200 ml/min) at 1,223 K for 120 min.