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A Study on Corrosion and Corrosion Inhibition of 6061 Al alloy-15 vol. % SiC(p) Composite in Hydrochloric Acid Medium

Kini, Achutha U (2011) A Study on Corrosion and Corrosion Inhibition of 6061 Al alloy-15 vol. % SiC(p) Composite in Hydrochloric Acid Medium. Phd. Thesis thesis, Manipal Institute of Technology, Manipal.

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Corrosion can be defined as the degradation of a material due to its reaction with the environment. Metals corrode because we use them in environments where they are chemically unstable. Corrosion occurs with metals except with the least active noble metals such as gold, platinum and palladium. Corrosion problems are found in all aspects of technology resulting in high costs. It is a global calamity and costs several million dollars all over the world. Corrosion costs studies carried out by several countries reveal that the annual corrosion costs range from approximately 1 to 5 percent of the GNP. The damage due to corrosion is observed in almost all industries. The economic losses due to corrosion could be direct or indirect. The economic factor is the prime objective behind most of the research in corrosion. Aluminium matrix composites are among the most promising materials for wear and structural applications due to their low cost, light weight and the ease of fabrication. One of the main drawbacks of aluminium matrix composites is that they are less resistant to corrosion compared to the Al base alloys for which a protective oxide surface film imparts greater corrosion resistance. The presence of reinforcing phase in the composite material can lead to inhomogeneties and cause discontinuities in the surface film, increasing the number of active sites available for corrosion to take place. Hydrochloric acid solutions are used for pickling, chemical and electrochemical etching and in various chemical process industries wherein Al alloy composites are used. In such cases, it becomes very important to use corrosion inhibitors so as to protect the material against excessive corrosion. Acid corrosion inhibitors find wide application in the industrial field as components in acid pickling, acid cleaning, oil and gas well acidizing, acid de-scaling etc. In the present work, an attempt has been made to study the inhibiting effect of a series of organic compounds namely, ethyl-2-phenyl hydrozono-3-oxobutyrate (EPHO), 2-chloro-1-benzothiophene-3-carbohydrazide (CBTC), 5-[(2-methylphenoxy) methyl]-4-{[(1E)-(3-phenyl-1H-pyrazol-4-yl) methylene] amino}-4,5-dihydro-1H-1,2,4-triazole-3-thiol (MMATT), ethyl (2E)-2-[2-(4-chlorophenyl)hydrazinylidene]-3-oxobutanoate (ECHO), propanoyl(1Z)-N-(2,6-dimethylphenyl)-2-oxopropanehydrazonoate (PDOH), propanoyl(1Z)-N-(2-hydoxyphenyl)-2-oxopropanehydrazonoate (PHOH), propanoyl(1E)-N-(2-acetylphenyl)-2-oxopropanehydrazonoate (PAOH) and N – naphthyl – N′ – phenyl thiourea (NPTU) on the corrosion of 6061 Al alloy–15 vol. % SiC(p) composite in 0.1, 0.5 and 1 M HCl solutions at 30, 40, 50 and 60 °C temperatures and at five levels of inhibitor concentrations using potentio-static polarization techniques and weight loss method. The polarization data have shown that all the compounds are mixed inhibitors for 6061 Al alloy–15 vol. % SiC(p) composite in hydrochloric acid medium with reasonably good inhibition efficiency (85.53 - 96.79 %). Adsorption of all the compounds on the composite surface is found to obey Temkin’s and Langmuir adsorption isotherms. The corrosion rate for 6061 Al alloy–15 vol. % SiC(p) composite increases with increasing concentration of acid medium and temperature in the absence of inhibitors. The corrosion rate decreases drastically in the presence of the inhibitors. This is mainly due to the adsorption of inhibitor molecules on the composite surface. The compounds are most likely adsorbed through the sulphur, nitrogen or oxygen atoms, forming donor - acceptor bond between unpaired electrons of these atoms and the positive active centers of the metal surface. The decrease in inhibition efficiency (% IE) of the compounds with increase in temperature is probably because of the weaker adsorption forces exist from decreased electron density. The thermodynamic parameters of adsorption reveal a strong interaction and spontaneous adsorption of the inhibitor compounds on the composite surface. The inhibition is governed predominantly by physical adsorption along with weak chemical bonding (mixed adsorption mechanism). The results of the investigation show that all the compounds can be recommended as good corrosion inhibitors for acid pickling and acid cleaning of 6061 Al alloy–15 vol. % SiC(p) composite in hydrochloric acid medium.

Item Type: Thesis (Phd. Thesis)
Subjects: Engineering > MIT Manipal > Mechanical and Manufacturing
Depositing User: MIT Library
Date Deposited: 17 Mar 2016 09:06
Last Modified: 17 Mar 2016 09:06

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