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Corrosion Studies on Pure Aluminum in Aqueous Neutral Sodium Chloride Solutions

Author: CaiChao
Tutor: GaoZuoNing
School: Ningxia University
Course: Analytical Chemistry
Keywords: Pitting Pure aluminum Electrochemical noise Electrochemical impedance spectroscopy Wavelet Analysis
CLC: TG174
Type: Master's thesis
Year: 2005
Downloads: 419
Quote: 6
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Abstract


This thesis is divided into two parts, the first part of the electrochemical impedance spectroscopy (electrochemical impedance spectroscopy, EIS) technology combined with scanning tunneling microscopy (STM), scanning electron microscopy (SEM) and other modern means of testing pure aluminum in neutral sodium chloride solution the corrosion mechanism. The EIS results showed that: in the corrosion reaction of the first test phase, the polarization resistance (R_p) obtained in the low-frequency domain (10 MHz) and the capacitance of the electric double layer (C_dl) while increasing the line purity aluminum corrosion of the initial oxide film formation process is characterized . With the continuation of the time, the electrode potential and R_p reach the maximum Description: erosion halogen ion in the process of continuous growth of the surface oxide film has started to attack the surface of pure aluminum and gradually reach its substrate by diffusion. Meanwhile, in the whole of the process of corrosion, the performance of the system the two time constants, representative of the time constant of the high-frequency region including the oxide film and the reaction product, including the protective layer, the time constant of the low-frequency region is representative of the corrosion process in the diffusion and corrosion rapid reaction process. The experimental results show good correspondence between the morphology of the EIS characteristics and metal samples in the corrosion process performance, verify the the local anode area around the self-accelerating process of pitting corrosion and corrosion process in the reaction been protection. The second part of the paper through the use of fast Fourier transform (FFT), wavelet analysis (Wavelet) nonlinear data processing methods and combined SEM testing means pure aluminum in neutral NaCl solution electrochemical noise (electrochemical noise, EN ) signal. FFT analysis results show that: the one hand, electrochemical noise frequency domain curve PSD (power density spectrum), three characteristic parameters (W, f_c, k) alone can not correct the description of materials faces eclipse intensity and trends. On the other hand, based on the basic principles of dimensional analysis method and material corrosion processes influencing factors analysis found: feature parameters derived from the electrochemical noise frequency domain curve PSD correct characterization of materials strength and the trend of the two faces eclipse the parameters S_E and S_G, S_E pitting strength better regularity. The S_G in this stage work can only determine its value range between 5-20 of regularity in further research. The EN signal wavelet analysis results show that: good correspondence between the energy distribution of the different stages of the corrosion morphology. For the generation of the non-steady-state corrosion points, we can use the D grade series of smaller levels of energy corresponding to them. Similarly, the intermediate level and high level, respectively corresponding to the growth of corrosion pitting and repassivation process. At the same time, aluminum corrosion samples 3.0wt% NaCl solution, the corrosion morphology of EDP (energy distribution spectrum) better.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection
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