| Carbon steel and aluminum alloy are the most widely used metal materials in modern industrial production. Pickling process is usually used to remove the oxide scale and dirt from their surface. In many cases, however, metal substrate are also eroded due to the highly aggressive of acid. This phenomenon is called "excessive corrosion" which not only causes the environment polluted, but also brings huge economic losses. Using corrosion inhibitor during the pickling process is an effective way to deal with "excessive corrosion". In recent decades, many researchers have found that some clinical organic drugs which are usually used in medical field exhibit excellent corrosion performance in acidic medium. These organic drugs have many advantages such as wide source and non-toxic so that they are expected to become a new generation of environmentally friendly and novel inhibitor. Therefore, it is of significant importance to study their inhibition performance and inhibition mechanism on carbon steel and aluminum alloy in acid medium.In this thesis, weight loss method, potentiodynamic polarization, electrochemical impedance spectroscopy(EIS) combined with scanning electron microscopy(SEM) methods were used to investigate the inhibition performance of cefotaxime sodium(CEF) on Q235 carbon steel and aluminum alloy 2024-T3(AA2024-T3) in HCl solution, respectively. The inhibition performance of kanamycin sulfate(KANA) on Q235 carbon steel in HC1 solution was also studied. Meanwhile, adsorption behavior of these two organic drugs on metal surface were investigated by calculating adsorption thermodynamic parameters. Adsorption mechanism and adsorption type of CEF and KANA were determinted through X-ray photoelectron spectroscopy(XPS). The main conclusions are as follows:(1) Cefotaxime sodium(CEF) was a very good inhibitor for Q235 carbon steel in 0.1 mol·L-1,0.3 mol·L-1,0.5 mol·L-1 and 1.0 mol·L-1 HC1 solution and the inhibition efficiency could reach to 99%. CEF was also a good inhibitor for AA2024-T3 in 0.3 mol·L-1,0.5 mol·L-1 and 1.0 mol·L-1 HCl solution and the highest inhibition efficiency was up to 91%. Kanamycin sulfate(KANA) exhibited good corrosion resistance to Q235 carbon steel in 0.3 mol·L-1,0.5 mol·L-1 and 1.0 mol·L-1 HCl solution and the inhibition efficiency changed at the range of 65%-80%. However, KANA greatly accelerated the corrosion of Q235 carbon steel in 0.1 mol·L-1 HCl solution. The inhibition efficiency of CEF and KANA decreased with temperature.(2) The electrochemical tests results showed that CEF and KANA reduced the corrosion current density, indicating that they could effectively restrained the corrosion of Q235 carbon steel and AA2024-T3 in HC1 solution. The decrease of double layer capacitor and the increase of charge transfer resistance in metal/solution interface were attributed to the formation of a protective layer on metal surface by adsorption. The SEM results showed that the metal surface corrosion morphology became relatively smooth, indicating that CEF and KANA could mitigate the corrosion of metal.(3) CEF and KANA were both mixed type inhibitors. The adsorption model of CEF and KANA on metal surface were all followed the Langmuir isotherm adsorption. The adsorption type contained both of physical adsorption and chemical adsorption. The coordination bonds formed by organic drugs molecules and metal atoms have been found on the corroded metal surface through XPS tests when CEF and KANA were added in HCl solution.(4) Physical adsorption mechanism of CEF and KANA could be explained as follows:the amino(-NH2) in CEF and KANA molecules was positively charged due to the protonation in HC1 solution. Hence, the -H3+ would adsorb to Cl" which was attracted on metal surface because of electrostatic attraction. In this condition, the [metal-Cl--+NH3] double adsorption layer structure was formed. The chemical adsorption of CEF and KANA could be attributed to the coordination bond between the lone pair of N atom in -NH2 and metal atoms. The forming of insoluble complexes on metal surface effectively protected metal from corrosion so as to achieve the purpose of corrosion inhibition. |
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