Masahiro Kawakami

Anodic dissolution of chromium in acidic sulphate solutions

Active anodic dissolution of chromium in acidic sulphate solutions was investigated by using the rotating ring—disc electrode (rrde). Chromous ions dissolved from the chromium disc could be collected on the gold ring electrode by oxidation to chromic state. The empirical collection number was estimated to be 0.052, although the theoretical value was 0.24. The current of active anodic dissolution gave two Tafel regions with the Tafel slope of 0.03 and 0.12 V decade−1 in the lower and higher current density regions, respectively. The pH value of the solutions did not affect the dissolution current. The increase in sulphate anion concentration reduced the current in the higher cd region. In order to interpret the experimental results on the active dissolution of chromium, a new mechanism was proposed, which was similar to the Bockris mechanism in the case of the iron dissolution. Passivation of chromium was found to take place without relation to active dissolution. It was concluded that the passivation was attributable to the formation of the trivalent chromium oxide such as CrO(OH).

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.

Analysis of Waste Heat Recovery to Steel Scrap Preheating in an Enclosure Vessel

A method for preheating steel scraps using waste heat in a continuous casting process was proposed. Experiment and numerical analysis were carried out to examine the ability of scrap preheating and to determine the factors affecting the rise in scrap temperature. Coupled natural convection-radiation heat transfer was solved by three-dimensional FEM. The distance and the constant were found to influence the samples temperature rise greatly. The overall Nusset number can be obtained as Nu0=(-0.33α*D*0.8+7.08)Ra0.15t*-1- 32.4D*-0.99α*-1.98 *-1.98

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.

Preparation of fine particles of tin–M (M: silver, bismuth) alloys with ammonia splashing method

Abstract In this study, as a part of a series of fundamental studies on the production of fine metallic particles with the ammonia splashing method, tin–silver or tin–bismuth alloy on a graphite rod was induction-melted in an ammonia gas stream to investigate the production rate of particles, i.e. the rate of the splash, and the characteristics of the particles. Pure silver and bismuth were not splashed by ammonia gas, but pure tin was splashed. The rate of splash of the alloy decreased with increase of the content of the alloying element. According to the Arrhenius equation, the rate of splash increases with the temperature of the molten alloy. The rate of splash also increased with increase in the ammonia gas flow rate. The particles obtained were metallic and spherical. The size of the particles increased with temperature rise and with increasing ammonia gas flow rate. When alloying elements were added to the pure tin, the particle size decreased abruptly.

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.

Kinetics of Steel Scrap Melting in Molten Fe-C Bath

The melting phenomena of steel scrap in molten steel bath has been investigated by several workers. Their works are reviewed in the present paper. The phenomena are, in general, so complicated that both heat and mass transfer take place simultaneously. Many workers made small scale experiments in such condition that only mass transfer was taken into consideration. The results were summarized in the form of dimensionless correlation among Sh, Gr. Re, Sc and J D . Only one paper reported the experiment in which pure heat transfer was taken into consideration. The overall heat transfer coefficient was estimated by fitting numerical solution of heat transfer equations to the results of immersion experiments. The simultaneous heat and mass transfer were analyzed by mathematical model in relation to BOF converter operation. Some workers made experiments and numerical solution of mathematical model to obtain the heat and mass transfer coefficients in pilot plant converter and commercial converter.

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.

Densification During Spark Plasma Sintering of Ni Powder Containing Dispersed MgO Particles

It is known that metal powders containing dispersed oxide particles are difficult to sinter by the conventional process. Spark Plasma Sintering (SPS) method was tried for making the dense sinter tablets from Ni powders containing MgO. The high–temperature hardness of the sinter tablets were examined from room temperature to 1173 K. The results were summarized as the follows. The relative density of the tablets increased with an increase in sintering temperature. The relative density of more than 97 was obtained at higher temperature than 1273 K with MgO contents of 0, 2.5, 5 and 10. The Vickers hardness of the sinter tablets increased with an increase in MgO contents and an increase in sintering temperature. The maximum hardness of about 270 Hv, which corresponded to more than 2.5 times of pure Ni, was obtained with 10MgO at 1273 K sintering. These high relative density and hardness can be obtained by SPS method but not by the conventional sintering. The high–temperature hardness decreased with an increase in the temperature. Plotting the logarithm of hardness against the temperature, two straight lines were obtained. The reflection point which showed the change in deformation mode was shifted to high–temperature side by the dispersion of MgO particles. The high–temperature hardness straightly increased against a reciprocal of a space between MgO particles.