The Effects Of The Electrode Area On Electrochemical Noise

Electrochemical Noise (EN) refers to spontaneous interface between electrode and solution. EN technique is simple and convenient, and doesn't bring extra disturbance to the corrosion system. The unique features of EN measurement make it an important role in the field of corrosion study.In this paper, neutral 0.5mol/L NaCl, NaHCO₃+NaCl and NaNO₂+NaCl solutions were selected as the studied media and the effects of the Q235 (A3) electrode area on EN were studied by EN measurements and other traditional electrochemical techniques. The main results are shown as follows:(1) In neutral 0.5mol/L NaCl, the relationship between the standard deviation of the current noise(σ_i), potentional noise (σ_v), electrochemical noise resistance (Rn) and electrode area (S) were obtained as: lgσ_i= 0.465lgS-6.421; lgσ_v= -0.225lgS-3.373; lg Rn = -0.686lgS+2.925. Rn could be comparable to the polarization resistance (Rp) and the charge transfer resistance (Rt) obtained from LPR and EIS respectively. Between Rn, Rp, Rt and S, there is a log-log linear relationship. As S increasing, the relative energy of the potentional noise has a tendency toward increasing firstly and then decreasing from high frequency crystal to low frequency crystal. And the minimum relative energy of crystal series would change from high frequency to medial frequency domain.(2) In NaHCO3+NaCl solution, the relationship betweenσ_i,σ_v, Rn and S were obtained as: lgσ_i= 1.948lgS-8.604; lgσv= 0.246lgS-3.264; lg Rn = -1.591lgS+5.272. The electrode area has a great influence on the passivation degree and probability of pitting. The relative energy of the potentional noise tends to be symmetrical from high frequency crystal to low frequency crystal.(3) In NaHCO3+NaCl solution, the asymmetric probe was used for EN measurements. Generally, the electrode with larger area often suffers pitting and acts as anode. There is not disciplinary conclusion by using the traditional method. So further researches should be needed in this system.(4) In the corrosion inhibiting system, Rn could be consistent with Rp, Rt. The evaluation results of the inhibitor efficiency obtained by the three different methods are identical. So Rn can be used to evaluate the inhibition performance and realize continuously in-situ monitoring of inhibition performance. And the smaller electrode is oxidized easily into the steady passive film by NaNO₂, thus inhibitor efficiency of the small electrode is better than the large electrode.In a word, the proper electrode area should be utilized in EN measurements.