Corrosion Inhibition of Sodium Silicate and Piperazine and Their Synergistic Effect on Carbon Steel in Soft Water Media

Abstract

The aim of this study is first to investigate piperazine behavior as an inorganic corrosion inhibitor for a ST-14 steel and then to explore synergistical effect of organic (sodium silicate) and inorganic (piperazine) corrosion inhibitors. Due to different corrosion inhibition behavior of these two chemicals, positive results are expected. The corrosion inhibition characteristics of sodium silicate (Na2SiO3) and nitrogen contained organic compound, piperazine (C4H10N2) as corrosion inhibitor for carbon steel was studied using weight loss, Tafel polarization, impedance and some spectrophotometric techniques. Also Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible spectroscopy (UV–Vis) and scanning electron microscope (SEM) tests were conducted in order to indicate the formation of a protective film on the surface of steel coupons. The obtained results indicated that the combination of these two inhibitors improve the corrosion behavior about 87 and 76% in accordance with potentiodynamic polarization tests and electrochemical impedance spectrometry, respectively. The corrosion inhibition efficiency has been increased using an optimum combination including 2 ppm piperazine (PIP) and 10–15 ppm sodium silicate. It should be noted that the corrosion inhibition action has been employed using remarkably low concentration of corrosion inhibitors. From the interaction between corrosion inhibitors molecules and iron oxide layer, it can be concluded that the physical adsorption has more effect compared to chemical adsorption in the film formation process for both sodium silicate and PIP inhibitors. It is proposed at least two mechanisms for synergism.