Study On Inhibition Effect Of Domperidone On Brass In Two Chloridion Contained Solutions

Brass alloy which mainly consisted of copper and zinc was widely applied in modern industry due to its excellent mechanical and technological properties. However,the brass was corroded faster in the aqueous solution containing chloride ions. Therefore the study on environment-friendly corrosion inhibitor with excellent performance to brass in chlorine-containing solution was paid much attention. In this paper, methods including polarization curve, AC impedance, weight loss, scanning electron microscope and quantum chemical calculation were used to evaluate the corrosion inhibition of Domperidone on brass in 1mol/L HCl and 3.5%NaCl solution, respectively.The results showed that the corrosion rate of brass in 1mol / L HCl solution was greater than that in 3.5% NaCl solution. Domperidone had good inhibition effect on corrosion of brass alloy both in 1mol / L HCl solution and 3.5% NaCl solution. The inhibition effect in 1mol/LHCl solution was much more remarkable than that in 3.5% NaCl solution. In 1mol / L HCl solution, the inhibition efficiency on brass was increased with the addition of Domperidone firstly, and then reached the peak with the addition of Domperidone 150mg / L, but then the inhibition efficiency decreased with much higher addition of Domperidone. The highest inhibition efficiency was 91.5%. The inhibition efficiency of Domperidone on brass in 3.5% NaCl solution has the same tendency with that in 1mol / L HCl solution. The highest inhibition efficiency was 88.5% in 3.5% NaCl solution with 150mg / L Domperidone. It was assumed that there were imidazoline structure and nitrogen-containing six-member ring in Domperidone molecular that could supply lone pair electrons to bond with the lowest unoccupied molecule orbital (LUMO) of copper and absorb on the surface of brass. So Domperidone molecules and chloride ions, water molecules would compete to absorb on the surface of brass due to the nitrogen, oxygen, chlorine, nitrogen-containing six-member ring and benzene ring in Domperidone molecules which make it more easily adsorbed on the surface of brass to form absorbed film to inhibit the corrosion of brass. When the dose of Domperidone, the corrosion inhibitor was 150mg / L, the most perfect adsorbed film would be formed on the surface of brass so its efficiency of corrosion inhibition was greatest. With the inhibitor addition increased, the adsorbed film would become more and more completely. When the inhibitor dose was added to 150mg / L, there would be a layer of saturated adsorption film which results in the highest inhibition efficiency. When inhibitor concentration continues to increase, the forces between inhibitor molecules would cause the configuration of adsorbed molecules on the brass surface change, or the inhibitor molecules coordinate with the Cu2+ in solution, both above reasons might lead more fierce corrosion of brass, so inhibition efficiency decreases too. Results of weight loss and electrochemical method were consistent.Geometry optimization of Domperidone molecule was obtained by quantum chemical calculation, Fukui index indicates that the active adsorbed centers in Domperidone molecules are the imidazoline structure and nitrogen-containing six-member ring, in which nitrogen atoms, oxygen atoms and chlorine atoms are easier to provide electrons to interact with brass, more over, nitrogen-containing six-member ring would tend to accept the electrons from the brass.In order to study the adsorption behavior of Domperidone on brass, the data of inhibition efficiency of the impedance test was substituted into model of Temkin, Frumkin and Langmuir, respectively, and it was found that the absorbed behaviour was fit with the Langmuir adsorption isotherm model. Thermodynamic calculations show that the adsorption Gibbs free energy of Domperidone on brass in 1mol/LHCl solution with 150mg / L of Domperidone is -15.742kJ/mol, which is physical adsorption. While the adsorption Gibbs free energy in 3.5%NaCl solution is -21.057kJ/mol, a physical and chemical adsorption and dominated mainly by physical adsorption. Kinetic studies showed that the pre-exponential factor A and apparent activation energy Ea with inhibitor are much larger than that without inhibitor. Because the corrosion inhibitor molecules adsorbed on the surface of brass and covered those superficial corrosion activity centers, so the activation energy increased, and naturally the corrosion of brass in these both corrosion solutions was inhibited.