THE INHIBITION ACTION OF ETHYL-2-PHENYL HYDROZONO-3-OXOBUTYRATE ON THE CORROSION OF 6061 Al ALLOY/SiCp COMPOSITE IN HYDROCHLORIC ACID MEDIUM

Abstract

The inhibition behavior of ethyl-2-phenyl hydrozono-3-oxobutyrate on the corrosion of 6061 Al alloy/SiCp composite in 0.1, 0.5 and 1 N hydrochloric acid solution at four different temperatures (30-60 °C) has been investigated using potentiostatic polarization techniques and weight loss method. The results indicated that the corrosion inhibition efficiency and the extent of surface coverage were increased with the increase in inhibitor concentration up to a critical concentration. The adsorption of the inhibitor compound on the composite surface was found to obey Temkins' and Langmuir adsorption isotherms. The potentiostatic polarization results have revealed that oxobutyrate acts as an efficient cathodic inhibitor for the corrosion of 6061 Al alloy/SiCp composite in HCl medium. The thermodynamic parameters for the corrosion and adsorption processes were determined. . Generally aluminium alloys and composites are highly resistant to corrosion owing to the formation of a protective oxide layer on their surface 2 . Corrosion does take place when this protective Al2O3-3H2O layer is either unstable or defective. Corrosion in Al alloys and composites takes one of the two forms - pitting or inter- granular corrosion. Pitting takes place in environments where the protective Al2O3-3H2O film is partially stable. In these cases, corrosion usually originates adjacent to the flaws in the microstructure of the film 3 . Inter-granular corrosion results in selective corrosion at the grain boundaries or any precipitate free zones that might be found adjacent to them, with the remainder of the matrix undergoing very little corrosion. Inter-granular corrosion occurs because of the formation of precipitates along the grain boundaries, which are more anodic with respect to the interior of the grains. As a result preferential dissolution occurs at these sites where these precipitates or precipitate free zones undergo anodic reactions 4 . Hydrochloric acid solutions are used for pickling, chemical and electrochemical etching and in various chemical process industries wherein aluminium alloy composites are used. In such cases it becomes very important to use corrosion inhibitors so as to protect the material against excessive corrosion 5, 6 . The effect of any particular organic compound on the corrosion behavior of metals in acid system depends on the type of metal and its interaction with the surface of the metal. The inhibiting action of organic compounds has been mainly attributed to adsorption of the compound on the surface of the material. This adsorption affects the electrochemical behavior involved in the corrosion process of metals/alloys/composites 7-9 . The inhibition effect of 3 - methyl - 4 - amino - 5 - mercapto - 1,2,4 - triazole on the corrosion behavior of 6061 Al alloy/SiCp composite has been reported 10 . This triazole compound was found to act as an anodic inhibitor with a maximum efficiency of 58 % at 30 °C. Allyl thiourea was used as an inhibitor for the corrosion of Al alloy/SiCp composite in HCl medium and showed a maximum efficiency of 70% in the temperature range of 30 - 50 °C 11 . In the present work, inhibitive action of ethyl-2-phenyl hydrozono-3- oxobutyrate on the corrosion behavior of 6061 Al alloy/SiCp composite in 0.1, 0.5 and 1 N hydrochloric acid medium at four different temperatures (30-60 °C) has been investigated using potentiostatic polarization techniques. The results obtained were cross checked by the weight loss method.