Some triphosphates as corrosion inhibitors for mild steel in 3% NaCl solution

Abstract

Inhibition of mild steel corrosion in 3% sodium chloride solution by sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and adenosine triphosphate (ATP) in presence of 200 ppm zinc acetate has been investigated using weight loss, electrochemical polarisation and scanning electron microscopy techniques. Various corrosion parameters such as Tafel slopes, corrosion current density, heat of adsorption and activation energy value have been calculated to understand the inhibition mechanism. Inhibition efficiency increased with increase in concentration for STPP and SHMP whereas it decreased for ATP. However, inhibition efficiency decreased for all the three phosphates with increase in temperature. All the three phosphates acted as mixed inhibitors though anodic reactions are suppressed more in comparison to the cathodic reactions. STPP acted through chemisorption whereas SHMP and ATP are physically adsorbed over the surface of mild steel.