Abstract
The authors have investigated the galvanic corrosion of mild steel in contact with phosphorus bronze in Na2SO410H2O and Na2CO3 alkaline solutions at 30° and interpreted the relation between the potential difference of both metals, the specific resistance of solutions, the solubilities of corrosion products, the polarization and the galvanic corrosion loss ΔW of mild steel, by introducing the following equation:
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Furthermore the following items were cleared up.
(1) In stagnant state, the maximum point of ΔW is at pH=10.5 in Na2CO3 solution. At pH<10.5, ΔW is controlled mainly by V, γ and cathodic depolarization, but at pH>10.5, it is controlled mainly by decrease of V and anodic polarization. (2) In Na2CO3 solution, the decrease of ΔW of mild steel with increase of r.p.m. is based on the decrease of V and anodic polarization. The fact that the pH value at which the maximum point of ΔW is obtained shifts to smaller values by revolution seems to be caused by anodic polarization due to the increase of diffusion amount of OH−. (3) On the contrary, in Na2SO410H2O solution, ΔW increases by revolution and this is because anodic polarization is affected differently by the difference of anions (CO3−− or SO4−−) in the solutions.
