溶融錫メッキ板の腐食と転位分布

抄録

Hot dipped tin plate is lustrous and very corrosion-resistive, and therefore, widely used for food cans which need corrosion resistance. But, when the plate is used for such a purpose, it is often observed that the cans become discolored purple or black in time. This phenomenon causes not only poor look of the cans but also spoiling of their contents, and seems to be one of serious problems in can manufacturing industry and in can packing industry. To prevent it, the plate is usually coated with special lacquers or is electrochemically treated.
Extent of the discoloration depends largely on the state of the microstructure of the tin plate surface, which is divided into two different types: one is susceptible to discoloration and the other is not.
Many investigations have been reported on the mechanism of the tin plate corrosion. But, we can't obtain any knowledge on the microstructure of tin plate surface from the majority of them, which can only provide electrochemical data. The present investigation was carried in order to clarify the relation between metallographical factors and corrosion, by measuring corrosion rate in acid solution, oxidation rate in the atmosphere and observation of surface microstructure by means of an optical microscope.
It was concluded that the surface which is susceptible to discoloration corresponds to rapid dissolution rate, rapid oxidation rate and large density of dislocations.