Synergistic Effect of Plant-Derived Compounds on Corrosion of cp-Ti in Artificial Oral Media: An Experimental and Theoretical DFT Approach

Abstract

This work studies corrosion behavior of the α-pinene (C₁₀H₁₆) and citric acid (1 × 10^–3 M CA, H₃C₆H₅O₇·2H₂O) compounds on commercial purity (cp-Ti) dental material investigated by electrochemical methods in artificial oral solutions (AOS, pH: 5.25, 37 ± 0.1°C) and density functional theory (DFT) study. The methods carried out by using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potential-current (Tafel) and linear polarization resistance (LPR) techniques in the AOS. In the previous study, α-pinene showed significant anti-corrosion capacity in CA medium by increasing the concentration of hydrogen ions. The aim of this research is to reveal the synergistic effect of the α-pinene and CA compounds on the material. Electrochemical results revealed that α-pinene played a role in the synergistic effect and acted as an excellent corrosion inhibitor. This effect shifted the pH of the solution from 5.20 to 5.60 on the basic side, also corrosion potential (E_corr) shifted by 158 mV from –0.412 to –0.254 V towards the anode. Therefore, corrosion resistance (R_p) significantly increased from 50 to 254 kΩ cm² (80%). Results indicated that TiO₂ layer formation supported by α-pinene in this conditions. ICP-MS analysis also confirmed the formation of this layer. DFT study carried out by using different methods on the Gaussian 09W with 6-311G (d, p) basis set for α-pinene on cp-Ti. The studies showed that PBE method gave the higher maximum wavelength (λ_max = 212.41 nm) than the other methods. The experimental results supported ICP-MS analysis by the DFT study.