The inhibition effect of sodium tetraborate on the corrosion of steel in KOH media

• G.S. Öz and S. Bilgiç

Department of Chemistry, Faculty of Science, Ankara University, Ankara, Turkey

Abstract: In this study, the inhibition effect of sodium tetraborate (Na2B4O7·10H2O) on the corrosion of steel has been investigated in 3% and 5% KOH media. Corrosion parameters have been determined using Tafel extrapolation and impedance spectroscopy methods by the addition of 1% – 7% Na2B4O7 into two concentrations of KOH solutions. It has been found that the inhibition efficiency of Na2B4O7 in both KOH media increases in 1% – 4% concentration range whereas it decreases in 5% – 7% concentration range. However, corrosion rates are less than when the corrosion media does not contain the inhibitor. The effect of temperature on the corrosion rate of steel and the inhibition effect of Na2B4O7 concentration have also been investigated by carrying out each experiment at four different temperatures, i.e., 25°C, 40°C, 55°C and 70°C. Corrosion rates have been observed to increase with temperature and KOH concentration both in 3% and 5% media. Na2B4O7 is an effective inhibitor at low temperature for steel. According to scanning electron micrograph (SEM) images obtained by adding 4% Na2B4O7 into both KOH media for bare steel and steel, pitting corrosion occurs on the metal surface. Experimental results support SEM images. H2 flows in 3% and 5% KOH media have been investigated using gasometric measurement depending on the concentration of Na2B4O7 by a flowmeter and it has been observed that H2 flow rate decreases in 1% – 4% inhibitor concentration range for both KOH whereas it remains fixed in 5% – 7% concentration range especially in 5% KOH solution. This finding is consistent with the values found by determining corrosion rates and inhibition efficiencies.

Keywords: corrosion, inhibitor, steel, sodium tetraborate

Int. J. Corros. Scale Inhib., 2018, 7, no. 3, 390-408 PDF (1 266 K)
doi: 10.17675/2305-6894-2018-7-3-9

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