Inhibition Action of Machilus yunnanensis Leaves Extract on Corrosion of Al-plate in HCl Medium
The inhibition action of Machilus yunnanensis leaves extract(MYLE)on Al-plate in 1.0 mol·L-1 HCl solution were studied by means of mass loss method,electrochemical tests,inductively coupled plasma optical emission spectrometer(ICP-OES),metallographic microscope,scanning electron microscope(SEM)and contact angle measurements.The results show that the maximum inhibition effi-ciency of 1000 mg·L-1 MYLE at 20℃ can reach as high as 93.5％.The inhibition efficiency increases with the increase of MYLE concentration,while the higher the temperature,the weaker the inhibition perfor-mance.The adsorption of MYLE on Al surface is mainly based on chemisorption,which conforms to Langmuir isotherm at lower temperatures and Freundlich isotherm at higher temperatures.The corrosion kinetic reaction of Al in HCl solutions without or with MYLE is in accordance with Arrhenius formula and transition state theory equation.In the presence of MYLE,the relevant apparent activation energy(Ea),pre-exponential factor(A),apparent activation enthalpy(ΔHa)and apparent activation entropy(ΔSa)are all increased.MYLE is a mixed inhibitor through"geometric blocking effect".Nyquist diagram is mainly composed of a capacitive reactance arc in high frequency region and an inductive reactance arc in low frequency region.With the increase of MYLE concentration,both the charge transfer resistance and in-ductance resistance increase.After the addition of MYLE,the concentration of Al3+in HCl solutions is sig-nificantly dropped,and SEM morphology further confirms that MYLE can efficiently slow down the corro-sion degree of Al-plate.
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