Inhibition of Galvanic Corrosion In Sodium Chloride Solutions

Zainab Ali Zgyli
Prof. Dr. Q. J. M.Slaiman

Because of the importance of galvanic corrosion the need arises to study the effect of corrosion inhibitors, area ratio of cathode to anode (Ac/A), on galvanic corrosion of several industrially important metals and also to follow the a behavior of corrosion rate of each member of the couple.  In the present experiments at the first stage, the corrosion potential with time was measured for four types of metals in solution of four pH values. The purpose of this stage is to find out the cathode metal from the anode. The weight loss technique is used as an indicator for determining the efficiency of the inhibition  process  using four types of metals carbon steel,stainless steel, cadmium,and tin,four values of solution pH 0,1,2, &3 and four concentrations of inhibitor 177.2,  354.4, 531.6, &708.8 ppm .Corrosion cell has been used to measure current and potential versus time for the metals coupled. Galvanic corrosion and inhibitor performance have been tested for four important factors that affect the process:Two values of solution pH (0 &1) in 0.1N NaCl ,three types of metals:carbon steel ,stainless steel ,and cadmium,four area ratios 1,0.75,0.5,&0.25,one concentration of dimethalaminoethanol inhibitor (708.8) ppm in air-saturated 0.1N NaCl solution at T= 40oC, & t=120min .It is found in this study the corrosion rate decreases with increasing inhibitor concentration under single and coupled conditions.  Efficiency of inhibitor reaches about 98% for cadmium in solution of pH=3 and in the presence of 708.8 ppm inhibitor concentration.Current and potential were measured for the couples cadmium/carbon steel,carbon teel/stainless steel, and cadmium/stainless.The value of galvanic current decreases with increasing inhibitor concentration and the galvanic potential difference decreases, i.e., approaching each other, especially  at pH(0).But this is not for all metals, area ratios and PH values.Galvanic dissolution current density was calculated for the two members of each couple obtained experimentally under zero resistance conditions. The results show that the two members of the couple corrode. This would verify that the galvanic corrosion systems are composed of two corroding metal members with the more noble metal being partially protected.