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EIS measurements of 4 coating samples

2024-09-19

EIS measurements of 4 coating samples
Aim: to evaluate the protection of coating(through different treatments) on the low carbon steel based on EIS measurements
Four types of samples:
#1: coating sample through oiling plate vitrification
#2: coating sample through oiling plate phosphating
#3: coating sample through Chromium-free passivation plate vitrification
#4: coating sample through Chromium-free passivation plate degreasing
Corrosion media: 3.5% NaCl solution
Experiment method: EIS- Frequency
Experiment Setup: CS350 potentiostat galvanostat, CS936 flat corrosion cell,(exposure WE area 1cm². The cell is put in a Faraday cage. )
Pt mesh (built-in in flat corrosion cell) as CE, CS900 saturated calomel electrodes as RE, Coating sample as WE.
Parameters setting: AC amplitude is 10mV during measurement, frequency range is 100kHz~0.01Hz, choose “logarithmic” scan, points/decade is “10”.

EIS plots of the four samples

2-1: EIS of #1coating sample through oiling plate vitrification

2-2 EIS of #2: coating sample through oiling plate phosphating

2-3 EIS of #3 coating sample through Chromium-free passivation plate vitrification

2-4 EIS of #4 coating sample through Chromium-free passivation platedegreasing

Impedance of sample #1 and #2

Table 1 coating impedance data

Test time/h	0.01Hz coating impedance /Ω•cm²
	#1 vitrification	#2: phosphating
24	1.11×10⁹	9.73×10⁸
72	2.99×10⁹	3.18×10⁹
240	6.40×10⁹	3.10×10⁹
480	4.65×10⁹	2.42×10⁹

Impedance of sample #3 and #4

Table 2 impedance data

Test time/h	0.01Hz coating impedance/Ω•cm²
Test time/h	Sample #3	Sample #4
24	1.08×10⁹	1.12×10⁹
72	2.89×10⁹	2.80×10⁹
240	3.01×10⁹	2.92×10⁹
480	2.59×10⁸	7.38×10⁸

3. Conclusion

(1)Under the same conditions, compared with the sample #2, the impedance of the coating #1 is bigger, indicating that the sample #1 has better anti-corrosion abilities.

(2) Under the same conditions, compared with the sample #4, the impedance of the coating #3 is bigger, indicating that the sample #3 has better anti-corrosion abilities.

Wuhan Corrtest Instruments Corp., Ltd.

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EIS measurements of 4 coating samples

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