Abstract
The aqueous extract of milk thistle (Silybum marianum) leaves as a green corrosion inhibitor for AA7051 aluminum alloy in sodium hydroxide solution was investigated at a range of temperatures. Potentiodynamic polarization findings exhibit a mixed–type inhibitor with directly increased inhibition efficiency with the concentration of inhibitor. The adsorption of the inhibitor on aluminum alloy obeys Langmuir isotherm and the kinetic as well as thermodynamic parameters were measured and discussed.
Highlights
In the late 19th century, demand for aluminum was increased in the manufacturing of boats and cars, while the real revolution began in the early 20th century when it was used in aviation industry
The corrosion parameters were calculated from Tafel plot by MLabSci software associated with the potentiostat and by Excel using the following equations [12,13]: IE% =
The findings indicate that the rates of the 7051 aluminum alloy corrosion, in non-inhibited and inhibited alkaline solutions, rose linearly with temperature due to the increase in passive film dissolution [20]
Summary
In the late 19th century, demand for aluminum was increased in the manufacturing of boats and cars, while the real revolution began in the early 20th century when it was used in aviation industry. Aluminum applications in the second half of 20th century were not limited to its light weight but rather to corrosion resistance, electrical conductivity, thermal conductivity, easy fabrication, variable strength, and comparably cheap prices. The applications of aluminum in packaging, architecture, petroleum, and transportation were increased dramatically [1]. The contact of aluminum and aluminum alloy parts with alkaline solutions causes dissolution of the oxide layer that is naturally formed on aluminum surface and decreases corrosion resistance [2]. The corrosion can be eliminated be one of the following techniques: (i) development of new alloys that have more corrosion resistance in alkaline media; (ii) coating the aluminum with organic or inorganic coatings; (iii) inhibiting the corrosion with organic or inorganic inhibitors.
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