Application of copper corrosion inhibitors in mineral oil : Surface analytical studies and corrosion mitigation evaluations

Abstract: This doctoral thesis explores the copper corrosion inhibiting properties of a number of nitrogen containing hetero-organic compounds in refined mineral oil. Traditional organic corrosion inhibitors, as well as novel and bioorganic compounds have been studied.The Hansen solubility parameters were determined for the three commercial organic corrosion inhibitors; benzotriazole, tolyltriazole and Irgamet 39™, an N-(aminomethyl) substituted triazole. The determination was done using an indirect method utilizing the solubility of the inhibitors in various solvents. The calculated Hansen solubility parameters of the inhibitors were compared with the Hansen solubility parameters and solubility sphere of refined mineral oil. The obtained Hansen solubility parameters of benzotriazole indicate very low solubility in mineral oils, while the solubility of tolyltriazole was slightly higher due to the methyl substitution. The obtained Hansen solubility parameters of Irgamet 39™ indicate full miscibility with refined mineral oil. The adsorption kinetics of the inhibitors on copper surfaces in refined mineral oil was studied by means of in situ ellipsometry and related to the Hansen solubility parameters. A good correlation was seen; the compound with the highest solubility (Irgamet 39™) generated the thinnest film, while the greatest film thickness was seen for the molecule with the lowest solubility (benzotriazole).The issue of decomposition of the N-(aminomethyl) substituted Irgamet 39™ and Irgamet 30™ upon adsorption was addressed and analysed by using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The ToF-SIMS study revealed that both compounds appeared to lose their aminomethyl tails upon adsorption. No signals from the intact molecules were detected.The possibility of utilising bio-organic substances as organic corrosion inhibitors has been examined. The copper corrosion inhibiting effects of four bioorganic compounds; adenine, purine, cysteine and histidine were studied by in situ ellipsometry, copper dissolution, and a standardised industrial corrosion test developed by the International Electrotechnical Commission (IEC 62535). Adenine and purine were found to adequately mitigate copper corrosion, while cysteine and histidine were found to have low, or even accelerating, effects on the corrosion rate.The corrosion inhibiting properties of five benzo-fused azoles; benzotriazole, benzimidazol, indole, benzothiazole and benzothiadiazole in refined mineral oil were analysed by means of ellipsometry, ToF-SIMS, copper dissolution studies and the standardised industrial corrosion test (IEC 62535). It was demonstrated that copper corrosion was mitigated by the addition of benzotriazole and benzimidazole. However, addition of indole, benzothiazole and benzothiadiazole did not generate any significant corrosion mitigating effect. In general, the corrosion inhibition efficiency of the investigated molecules was found to decrease with increased polarizability of the molecule.