チタンの電解脱スケール技術の開発

概要

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A new descaling process for cold rolled and annealed titanium metal strip was developed in order to produce defectfree titanium plates efficiently. The process includes newly introduced electrolysis in certain electrolytes which promotes the descaling in cooperation with the preceding salt bath treatment (immersion in fused alkali-salt mixture) and the following pickling with nitric-hydrofluoric acid. Laboratory study by anodic electrolysis showed that HNO_3 or HNO_3-NaNO_3 solution was most effective electrolyte for promoting descaling, and NaOH-NaNO_3, HNO_3-H_2SO_4 or Na_2SO_4-NaNO_3 solution was also effective more or less, but H_2SO_4, HCl or NaOH solution was scarecely effective. It was also confirmed that intermittent alternate current electrolysis in HNO_3 solution promoted descaling without absorbing hydrogen and the current density on the electrolysis was desirable to be 15-20 A/dm^2. Chemical analysis of the electrolyte by ICP emission spectroscopy and surface analysis of the specimen by GDS proved that the titanium scale dissolved by the anodic electrolysis, and current measurement on the electrolysis suggested that the dissolution was made easy by the salt bath treatment. Finally, the effectiveness of the electrolysis was verified by a manufacturing test using titanium metal strip.
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