高濃度食塩水中における軟鋼および鋳鉄に対する各種防食剤の効果

電解加工における鉄の腐食に関する研究

抄録

Corrosion rates of mild steel and cast iron in concentrated sodium chloride solutions with and without addition of various inhibitors were determined from anodic and cathodic polarization curves.
In absence of inhibitor the corrosion rate of mild steel and cast iron increased within the concentration range of 10 to 50g/l. Within the range of about pH 5 to 11 the corrosion rate was almost independent of pH, but in the more acid range it increased rapidly as pH decreased and in the more alkaline range it decreased. In the neutral pH range corrosion was strongly accelerated by dissolved oxygen.
As an inhibitor for mild steel in sodium chloride solution, water glass was found to be most effective; the addition of 50g/l water glass plus 10g/l sodium hydroxide reduced the corrosion rate to about 1/140 of that in non-inhibited solution. The combination of 100g/l sodium nitrite and 1g/l sodium benzoate was second in effectiveness, reducing the corrosion rate to about 1/80. Among other inhibitors examined, sodium sulfite was effective and the corrosion rate decreased to about 1/30 by its addition.
For cast iron the best inhibition was obtained by sodium nitrite, and the addition of 100g/l reduced the corrosion rate to about 1/23. Sodium sulfite was second best; its addition of 1g/l reduced the rate to about 1/13. Among other inhibitors, water glass and Res-Cor W-711 were effective, which reduced the corrosion rate to about 1/7 and 1/4, respectively.
Generally the presence of passivating inhibitors deteriorates the electro-machinability. Since the passivating nature of inhibitors can be examined by determining polarization behaviors, a certain degree of estimation is possible as to the deteriorating effect of an inhibitor on the machinability.