Evaluation of Coated Al Alloy Using the Breakpoint Frequency Method

Abstract

Electrochemical Impedance Spectroscopy (EIS) was used to study coated Al alloys during long-term exposure in 5 wt% NaCl solution. The breakpoint frequency extracted from Bode plots allows the determination of the electrochemically active area of the sample. It shifts from low to high frequency with increasing exposure time due to the enlargement of the active area. The appearance of a high breakpoint frequency f h , usually in the range of 10 2 to 10 3 Hz, occurred after a certain exposure time associated with a sharp drop of open circuit potential and low frequency impedance, and was accompanied by the visual initiation of corrosion under the coating. The incubation time before f h appears can be used as a criterion to evaluate the performance of chromate primer combined with different surface pretreatments. Optical profilometry analysis was conducted to determine the corroded area of coated sample after longterm exposure. The corroded area of one coating system was very close to, but that of another coating system was much higher than, the electrochemically active area estimated by the breakpoint frequency method, due to the different extent of attack. This indicates that the breakpoint frequency may be only valid for the determination of defect area during the initiation of attack, but probably not for the propagation to large regions of attack.

Harmonic analysis based method for linearity assessment and noise quantification in electrochemical impedance spectroscopy measurements: Theoretical formulation and experimental validation for Tafelian systems

“…This feature makes the technique suitable for a large range of applications. This explains why it has been widely used in electrochemical related fields as fuel cells [6][7][8][9][10][11][12], batteries [13][14][15][16][17][18], corrosion [19][20][21][22][23], coatings [24][25][26], electrochemical sensors [27][28] and supercapacitors [29][30][31][32]. This electrochemical technique has also been used in fields that are not traditionally related to electrochemistry as biochemical assays [33][34][35][36], oncology [37][38][39] and immunology [40][41], amongst others.…”

Impact of inhibitor loaded mesoporous silica nanoparticles on waterborne coating performance in various corrosive environments

“…[34] The values shown correspond to those in phase plots where the phase angle is crossing 45 . [35] The decrease in breakpoint frequency for HOBT samples after 24 hr immersion time clearly indicates the shift to capacitor behavior of the coating, respectively indicating the active impact of the inhibitor. For Oxine samples, it is evident that the breakpoint frequency increases after 24 hr, which means that active impact is absent during this period or is not effective enough.…”

Design of Corrosion Protective and Antistatic Hybrid Sol-Gel Coatings on 6XXX AlMgSi Alloys for Aerospace Application

“…The impedance modulus at low frequencies reached~2 × 10 6 ,~1 × 10 7 and~1 × 10 8 ohm•cm 2 for A 15 -, AC 15 -and B 15 -coatings, respectively. The boundary where the capacitive region transforms in a resistive region at phase angle about 45 • is known as breakpoint at low frequency and it can be used to evaluate and rank the performance of coatings [22]. It is related with the defect area, which is lower as breakpoint emerges at lower frequencies.…”