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Effect of inhibitors on the corrosion behaviour of 6061ai•15 vol. Pet. Sic composites

Rao, Suma (2008) Effect of inhibitors on the corrosion behaviour of 6061ai•15 vol. Pet. Sic composites. Phd. Thesis thesis, Manipal Institute of Technology, Manipal.

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Abstract

Unintentional gradual deterioration or destruction of a material caused by chemicalor electrochemical reaction with environment is corrosion. Corrosion could be classified collectively as the greatest economic calamity known to humankind. The economiccosts of corrosion are obviously enormous. Annually about 4% of G.D.P in the case of developing nation has been suggested for the savings that could result if all economicallyuseful measures were taken to prevent or minimize corrosion. The damage due to corrosion is observed in practically all industrial and domestic fields, but predominantly in chemical and petrochemical plants, combustion motors, vehicles, turbines,hydraulic power aggregates, nuclear reactors and many other projects. It is thus evident that a comprehensive research and development programme in the field of corrosionwill result in the reduction of the corrosion damage and thus help to conserve nation's economic resources. Aluminium, being an industrially important metal, is subject to corrosion In service by various corrosive agents, of which the aqueous inorganic acids are the most dangerous. Extensive research on the mechanical properties have been carried out on Aluminium, Aluminium alloys and Aluminium matrix composites. But research studies leading to their corrosion properties are still at the development stage, particularly in the case of composites; but the outlook is very promising, as these materials are expected to overtake conventional materials such as Aluminium base alloys, since aerospace, military and automotive industries have been promoting the use of Aluminium composites which have good strength to weight and stiffness-to weight ratio. The present work involves study of the corrosion behaviour of 6061Al-15 voL pet. SiC composite material in mineral acid solutions and to control the corrosion rate by usingcertain organic compounds as inhibitors which have N, Sand 0 as hetero atoms. Corrosion rates of 6061 AI- 15 vol .pet. SiC composite material was determined by electrochemical polarization methods for three different acid concentrations (O.OIN, O.lN, IN) using ten inhibitors with four different concentrations of inhibitors (50,100,200,500 ppm) and at three different temperatures (303K 313K, 323K) and these results are compared with the corrosion rate of the composite under comparable conditions but without inhibitors. Inhibition efficiency and surface coverage were computed.Adsorption isotherm fitting with experimental data was identified to arrive at the mechanismof inhibition in each case of inhibitors All the ten compounds studied for their inhibitive action were found to function as moderate inhibitors for the corrosion of 6061AI-15 vol. pet. SiC composites in HCI environment. The inhibition efficiency increases with increase in inhibitor concentration for a given set of conditions for all the inhibitors. The minimum quantity is 0.05wt.pct. to get more than 60% efficiency. The percentage inhibition efficiency also increases with increase in temperature in all cases except in the case of Allyl thiourea addition. Temkin's model of adsorption is found to be valid indicating the type of adsorption is physisorption. The corrosion potential shifts to more positive values indicating the inhibitors are affecting the anodic metal dissolution process The interactions of the adsorbed inhibitors with surface metal atoms may prevent the metal atoms from participating in the anodic reaction of corrosion process. This simple blocking effect (surface coverage) is proportional to the inhibition efficiency. The bondingof adsorbed corrosion inhibitors on to metals, mainly responsible for inhibitive efficiency,has been attributed to electron densities at functional groups. The substituents increasefurther the electron densities due to nucleophilic effect or the polar character of electrophilicsubstituent. The physical adsorption of inhibitor molecules or the corrosion product (aluminum complex molecules) on the matrix brings down considerably the potential difference between the matrix and reinforcement and hence corrosion tendency. decreases

Item Type: Thesis (Phd. Thesis)
Subjects: Engineering > MIT Manipal > Chemistry
Depositing User: MIT Library
Date Deposited: 03 Dec 2014 09:17
Last Modified: 02 Aug 2016 10:21
URI: http://eprints.manipal.edu/id/eprint/141077

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