無電解めっき浴中におけるステンレス鋼不働態皮膜の安定性(腐食防食小特集)

概要

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The stability of passivation films on SUS304 and SUS316 stainless steels used for the bath container of an electroless nickel plating bath was studied by immersion test and electrochemical polarization method. The stainless steel specimens which had been passivated in 32.5% HNO_3 for 3 h at 313K were simultaneously immersed in the plating bath with a SS41 steel specimen. The concentration of phosphonic acid that was formed by oxidation of phosphinic acid in the bath increased during the immersion with the metal turnover. When the concentration exceeded 2 mol・dm^<-3> in the bath, steady nickel deposition did not occur on SS41 steel. The anodic polarization curves of the stainless steels in 1N H_2SO_4 solution were measured by immersing them in the plating bath after passivation in 32.5% HNO_3. The passive current on the polarization curve increased with immersion time and the corrosion potential moved to the positive direction. After the immersion for 60 h the SUS304 specimen did not reveal any passivation on the polarization curve, but the SUS316 specimen did it even after the immersion for 144 h. This indicates that the passivation film formed on SUS316 in 32.5% HNO_3 is more stable than that on SUS304. The concentrations of phosphonic and phosphinic acids seem to be most influcncial on the stability and breakdown of passivation films on the stainless steels.
社団法人日本材料学会の論文
1994-11-15