Metallic Corrosion in Molten Chloride

抄録

Many interesting electrochemical processes by the use of molten chloride have been proposed and developed, but there are some problems mainly because of the corrosion of the materials for industrial plants, and it seems very important to find a new material for an electrolytic cell. From these viewpoints, basic studies were carried out as follows. 1) In a LiCl-KCl melt, the corrosion rate estimated from the polarization characteristics and that directly measured by the chemical analysis are in very good agreement in the case of zinc and nickel. This strongly suggests the corrosion by a local cell mechanism. Iron shows somewhat peculiar behavior but the corrosion seems to proceed substantially by the formation of local cells. In all cases cathodic protection was found to be effective. 2) The suitability of some cell materials with ceramic coating was examined for a long term electrolysis in molten chloride system under severe conditions such as at high temperature and in an oxidizing atmosphere, Cl₂, and at least one effective combination of coating material and steel has been found. The cathodic protection of the coated material shows a significant effect supporting the local cell mechanism. 3) Practical cell using this combination was made and examined, and the possibility of a long term operation with this cell was confirmed. The safety operation for a longer time service can be expected with the cathodic protection.