The Corrosion Protection of Steel Coated with the Cement Containing Metal Powders under Seawater Environment

Abstract

To protect steels from water-line attack in seawater, we examined to coat steel with cement containing metals powder of different grain sizes. Steel specimens coated with these cements were immersed in 3 mass% sodium chloride solution. The condition to prevent steels from corrosion was determined by measuring potentials and observing the surfaces of specimens.
The potentials of specimens coated with the cement containing aluminum or magnesium powder were about -400mV vs. SHE. The corrosion was observed. The cement containing more than 50 mass% zinc powder kept the potentials less than -700mV vs. SHE when steels were covered fully with the cement. In these conditions, no corrosion appeared, though the potential did not always stay at the immunity domain. The protection ability became less with the increasing grain size.
When the one side of specimen was coated with the cement containing more than 67 mass% zinc powder and the other side and edges were left bare, the potential of specimen stayed at less noble than -750mV vs. SHE for 60 days. In these conditions the uncoated areas of a specimen were protected. We concluded that the application of cement coating containing more than 67 mass% zinc powder would be effective for the prevention of water-line attack in a marine environment.