Synthesis, Characterization and Corrosion Inhibition Investigation of substituted triazines on aluminium and mild steel in 1M HCl: Experimental and Theoretical approach

Corrosion is the natural process through which refined metals are gradually converted to more chemically stable forms such as oxides, hydroxides, or sulphides. This process occurs because metals tend to return to their natural states. Proper selection and use of corrosion inhibitors can greatly extend the lifespan of metal components and reduce maintenance costs. This current study investigates the synthesized substituted triazines, namely 4,6-dichloro-2-morpholine-1,3,5-triazine (DMT), 4.6-dichloro-2-anilino-1,3,5-triazine (DPT), and 4,6-dichloro-N-methylanilino-1,3,5-triazine (DNT) as corrosion inhibitor on aluminium (Al) and mild steel (MS) in 1M hydrochloric acid (HCl). The substituted triazines were successfully synthesized and characterized using Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FT-IR) spectroscopy, and liquid chromatography-mass spectrometry (LCMS). Thermogravimetric analysis (TGA) was performed on the DMT, DPT, and DNT inhibitors to determine the degradation temperature. It was observed that the mass loss of DMT, DPT, and DNT begins when the temperature reaches 85.91˚C, 181.007˚C, and 253.82˚C, respectively. Their anti-corrosive effect on Al and MS in 1M HCl was studied at a lower temperature using gravimetric analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve (PDP), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX), and density functional theory approach (DFT). The weight loss measurement was carried out at different temperatures (303 to 323 K) and concentrations from 0.001M to 0.005M of the DMT, DPT, and DNT. The results obtained from the weight loss analysis revealed that the %IE of all the inhibitors is directly proportional to concentration on Al and MS. The highest inhibition efficiency of DMT, DPT, and DNT was observed at a concentration of 0.005M. On Al surface, the %IE of DMT and DPT decreased with increasing temperature, reaching 83.02% and 82.39% at 303 K, respectively. In contrast, DNT showed improved performance with rising temperature, achieving a maximum %IE of 95.02% at 313 K, making it the most effective inhibitor for Al under these conditions. On the MS surface, all three inhibitors exhibited a decrease in %IE with increasing temperature, with values of 93.87% (DMT), 90.20% (DPT), and 87.95% (DNT) at 303 K. The inhibitor adsorption on the Al and MS surface for all the inhibitors obeyed the Langmuir adsorption isotherm. The adsorption isotherm indicates the reaction is spontaneous, and inhibitor molecules adsorb onto Al and MS surface through weak force (Physisorption) and chemical bond (Chemisorption). viii | P a g e Based on EIS results, the Al impedance spectra consist of capacitive loops at a higher frequency and inductive loops at a lower frequency. In contrast, MS consists of a high-frequency capacitive loop. The capacitive loops represent the charge transfer resistance of the corrosion process and double layer. The inductive loops are attributed to the relaxation process in the oxide film covered on the metal surface. The PDP results revealed an increase in Ecorr (a less negative value) was observed with a sustained rise in the DMT, DPT, and DNT concentration. For Al, all inhibitors are either anodic or cathodic inhibitors according to changes in Ecorr and mild steel PDP, revealed that all the inhibitors are mixed typer inhibitors, implying that DMT, DPT, and DNT interfere with both the dissolution of the metal (anodic reaction) and the reduction of oxygen (cathodic reaction). The SEM/EDX confirms that DMT, DPT, and DNT inhibitors formed a protective film on the Al and MS surfaces, protecting them from a corrosive environment. From a water contact angle, the hydrophobicity of the Al and MS surfaces is enhanced in the presence of DMT, DPT, and DNT. The effect of graphene oxide (GO) into DMT, DPT, and DNT inhibitor in 1M HCl solution on MS as corrosion inhibitor was done using EIS and PDP. The modification of GO indicates an increase in the diameter of the Nyquist plot semi-circle and a shift in Ecorr to more negative on the Tafel plot. DFT using the perdew-burke-ernzehof (PBE) in the DMol3 program was used to perform inhibitorAl interactions to estimate the binding energies of the inhibitors on the Al(111) surface. The calculated binding energies value indicates that all inhibitor molecules physically bind on the Al(111) metal surface. For MS, the Perdew–Wang exchange (PW91) was used to perform inhibitorFe interaction. The binding energy calculation values indicate that all inhibitor molecules are chemically adsorbed onto the Fe(100) surface.

Author dc:creator

• Tshikhudo, Fulufhelo

Advisors dc:contributor.advisor

• Murulana, L. C.
• Fernandez, C.
• Mnyakeni-Moleele, S. S.
• Kabanda, M. M.

• UCTD

Statement dc:rights

• University of Venda

Language dc:language.iso

en

Repository record dc:identifier.uri

https://univendspace.univen.ac.za/handle/11602/2925

OAI identifier oai:identifier

oai:univendspace.univen.ac.za:11602/2925