The Effect of Immersion Time and Immersion Temperature on the Corrosion Behavior of Zinc Phosphate Conversion Coatings on Carbon Steel

Asadi, Vahid; Danaee, Iman; Eskandari, Hadi

doi:10.1590/1516-1439.343814

Vahid Asadi

Abadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan, Iran

Iman Danaee ^**e-mail: danaee@put.ac.ir

Abadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan, Iran

Hadi Eskandari

Abadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan, Iran

*e-mail: danaee@put.ac.ir

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Figure 1
Polarization curves of steel electrode with and without zinc phosphate conversion coatings. Conversion coatings were obtained by 20 min immersion time in phosphate solution in different temperatures: 1) uncoated, 2) 20 °C, 3) 45 °C, 4) 55 °C, 5) 65 °C, 6) 80 °C.

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Figure 2
The Nyquist plots of steel electrode with and without zinc phosphate conversion coatings. Conversion coatings were obtained by 20 min immersion time in phosphate solution in different temperatures: 1) uncoated, 2) 20 °C, 3) 45 °C, 4) 55 °C, 5) 65 °C, 6) 80 °C.

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Figure 3
Equivalent circuits compatible with the experimental impedance data in for corrosion of zinc phosphate coated steel electrode.

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Figure 4
Polarization curves of steel electrode with and without zinc phosphate conversion coatings. Conversion coatings were obtained at 45 °C in phosphate solution with different immersion times: 1) uncoated, 2) 5 min, 3) 10 min, 4) 15 min, 5) 20 min, 6) 30 min.

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Figure 5
The Nyquist plots of steel electrode with and without zinc phosphate conversion coatings. Conversion coatings were obtained at 45 °C in phosphate solution with different immersion times: 1) uncoated, 2) 5 min, 3) 10 min, 4) 15 min, 5) 20 min, 6) 30 min.

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Figure 6
SEM images of zinc phosphate conversion coatings obtained by 20 min immersion in phosphate solution in different coating temperatures: (a) 45 °C, (b) 65 °C and (c) 80 °C.

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Figure 7
SEM images of zinc phosphate conversion coatings obtained at 45 °C in phosphate solution with different immersion times: (a) 5 min and (b) 30 min.

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Figure 8
EDS spectra of the phosphate conversion layer obtained by 20 min immersion in phosphate solution at 45 °C.

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Figure 9
SEM images of zinc phosphate conversion coatings after polarization test obtained at 45 °C in phosphate solution with different immersion times: (a) 20 min and (b) 30 min.

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Table 1
Potentiodynamic polarization parameters of different operating temperature for the phosphate coatings in 3.5 wt. % NaCl solution. Coatings were prepared by 20 min immersion time in phosphate solution.

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Table 2
Impedance parameters of different operating temperature for the phosphate coatings in 3.5 wt. % NaCl solution. Coatings were prepared by 20 min immersion time in phosphate solution. The error obtained through fitting is presented for each element as (%).

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Table 3
Potentiodynamic polarization parameters of different immersion times for the phosphate coatings in 3.5 wt. % NaCl solution. Coatings were prepared by immersion in phosphate solution in 45 °C.

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Table 4
Impedance parameters of different immersion times for the phosphate coatings in 3.5 wt. % NaCl solution. Coatings were prepared by immersion in phosphate solution in 45 °C. The error obtained through fitting is presented for each element as (%).

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(1)

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(2)

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(3)

Phosphate coating	B_a (±10^–3) / V dec^–1	B_c (±10^–3) / V dec^–1	I_corr (±5×10^–7) / A cm^–2	E_corr (±10^–3) / V	R_p (±5) / ohm	Corr.rate (±10^–3) / mpy
uncoated	0.114	0.094	2.89×10^–5	–0.653	772.995	3.39×10^–1
20 °C, 20 min	0.2	0.15	2.78×10^–5	–0.585	1336.216	3.27×10^–1
45 °C, 20 min	0.137	0.110	6.49×10^–6	–0.620	4078.901	7.62×10^–2
55 °C, 20 min	0.205	0.136	1.04×10^–5	–0.592	3397.255	1.22×10^–1
65 °C, 20 min	0.188	0.066	8.68×10^–6	–0.600	2443.455	1.02×10^–1
80 °C, 20 min	0.195	0.042	7.59×10^–6	–0.595	2157.797	8.92×10^–2

Phosphate coating	R_ct (±10) / ohm	Q_dl (±10^–3) / Ω^–1cm^–2sⁿ	C_dl (±10^–3) / F	n (±10^–2)
uncoated	605 (2%)	0.015 (3%)	0.061	0.61 (2%)
20 °C, 20 min	1842(4%)	0.015 (2%)	0.105	0.63 (1%)
45 °C, 20 min	2566(5%)	0.012 (5%)	0.056	0.69 (6%)
55 °C, 20 min	1421(1%)	0.015 (1%)	0.137	0.58 (6%)
65 °C, 20 min	1632(2%)	0.019 (1%)	0.096	0.68 (2%)
80 °C, 20 min	1687(2%)	0.018 (1%)	0.083	0.69 (5%)

Phosphate coating	B_a (±10^–3) / V dec^–1	B_c (±10^–3) / V dec^–1	I_corr (±5×10^–7) / A cm^–2	E_corr (±10^–3) / V	R_p (±5) / ohm	Corr.rate (±10^–3) / mpy
uncoated	0.114	0.094	2.89×10^–5	–0.653	772.995	3.39×10^–1
45 °C, 5 min	0.104	0.132	3.80×10^–5	–0.666	664.513	4.45×10^–1
45 °C, 10 min	0.140	0.188	3.01×10^–5	–0.638	1155.662	3.54×10^–1
45 °C, 15 min	0.160	0.138	1.58×10^–5	–0.653	2032.394	1.85×10^–1
45 °C, 20 min	0.137	0.110	6.49×10^–6	–0.620	4078.901	7.62×10^–2
45 °C, 30 min	0.189	0.108	1.11×10^–5	–0.578	2676.457	1.30×10^-1

Phosphate coating	R_ct (±10) / ohm	Q (±10^–3) / Ω^–1cm^–2sⁿ	C_dl (±10^–3) / F	n (±10^–2)
uncoated	605 (2%)	0.015 (3%)	0.061	0.61 (2%)
45 °C, 10 min	685 (5%)	0.014 (5%)	0.067	0.59 (1%)
45 °C, 15 min	1043 (5%)	0.008 (2%)	0.073	0.49 (2%)
45 °C, 20 min	2566(5%)	0.012 (5%)	0.056	0.69 (6%)
45 °C, 30 min	1464 (4%)	0.003 (3%)	0.012	0.51 (7%)

[1] *e-mail: danaee@put.ac.ir

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The Effect of Immersion Time and Immersion Temperature on the Corrosion Behavior of Zinc Phosphate Conversion Coatings on Carbon Steel