| Research Abstract |
The purpose of the present research project is to develop the direct ingot making process of titanium by electro-winning of titanium, where the metal pool of titanium is used as the cathode. By using ESR unit, the thermo-analysis of process, electrode reaction mechanism and contamination mechanism were examined.
At first, the electrical conductivity of CaO-CaF_2-TiO_2 slag was measured. The effect of TiO_2 addition was so small that the electronic conduction could be neglected. Thus, the addition of TiO_2 to the slag was possible at relatively large amount.
By operating ESR unit with steel rod, the relation between shape of metal pool and current-voltage condition was clarified. In the case of ESR, the metal pool could not be obtained at far higher temperature than the melting point of pure titanium. It was seen that the melting point of titanium rose by the absorption of oxygen. Thus, the atmosphere of the whole apparatus, especially, cathode part, must be innert.
In the single cell oper
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ation with CaO-CaF_2-TiO_2 slag, the maximum cathodic current efficiency was 12%, and the anodic current efficiency was far less than 100%. The reasons must be 1) formation of metal fog of Ca and its re-oxidation at the anode, 2) formation of Ti^<2+> by the reaction of Ti with Ti^<4+> and its re-oxidation at the anode, and 3) formation of Ti^<2+> by the insufficient amount of Ca and its re-oxidation at the anode. Thus, it is important to control the electrodes distance properly and to control the TiO_2 content properly.
On the contrary, by the addition of Al_2O_3 to the slag, c.a. 70 g of electro-deposit and c.a. 60% of cathodic current efficiency were obtained. The reasons must be that the temperature of molten slag should be kept higher temperature by the addition, and that the Al deposit should act as the reductant of Ti^<4+> in the slag. This process is good for producing Ti-Al alloy, but not good for producing pure Ti, because the electro-deposit contained much Al.
On the base on the above results, the new apparatus was designed. It consists of twin cell, one of which is anode cell and the other, cathode cell, connected with molten salt bridge. By this apparatus, the distance between cathode and anode can be kept long, resulting in the larger current efficiency and better quality of electro-deposit. The apparatus was successfully operated. Thus, the proposed process is very promising. The above results are published in 6 papers. Less
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