Effect of Acidified Aerosols on Initial Corrosion Behavior of Q235 Carbon Steel

doi:10.1007/s40195-018-0853-y

Abstract

Abstract:

The effect of simulated acidified marine aerosols on the corrosion morphology of carbon steel was studied using an in situ optical stereomicroscope and scanning electron microscope equipped with an energy-dispersive spectrometer and a white-light interferometer. The morphologies of the carbon steel were identified under marine aerosols with different droplet diameters, pH, and acidifications. The results showed that corrosion was initiated in tens of seconds under aerosol droplets acidified by HCl or H₂SO₄. Despite the differences in the acidifier and diameter, corrosion for acidified droplets with pH?>?2 was general corrosion. For acidified droplets with pH?2SO₄. The segregation of Cl^- was believed to be the main factor for the formation of the corrosion morphology under acidified droplets with pH?4^2- in the droplets had some effect on the segregation of Cl^- ions when pH?

Key words: Atmospheric corrosion, Aerosol, Acidification, Carbon steel, pH, Corrosion morphology

Miao-Ran Liu, Xiao Lu, Qi Yin, Chen Pan, Chuan Wang, Zhen-Yao Wang. Effect of Acidified Aerosols on Initial Corrosion Behavior of Q235 Carbon Steel[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(8): 995-1006.

Figures/Tables 14

Table 1 Chemical compositions of Q235 (wt%)

Steel	C	Si	Mn	P	S	Fe
Q235	0.14	0.01	0.33	0.011	0.02	Bal.

Table 2 Solution used in the experiment with different pH and concentrations of SO42- (\(C_{{{\text{Cl}}^{ - } }}\): concentration of Cl-; \(C_{{{\text{SO}}_{ 4}^{{ 2 { - }}} }}\): concentration of SO42-)

Base solution	Acidifier	\(C_{{{\text{Cl}}^{ - } }}\) (mol/L)	pH	\(C_{{{\text{SO}}_{ 4}^{{ 2 { - }}} }}\) (mol/L)
NaCl	-	0.6	5.5-6.0	-
NaCl	HCl	0.6	1/2/3	-
NaCl	H₂SO₄	0.6	1/2/3	5?×?10^-2/5?×?10^-3/5?×?10^-4
NaCl	Na₂SO₄?+?HCl	0.6	1/2/3	5?×?10^-2/5?×?10^-3/5?×?10^-4
NaCl	Na₂SO₄?+?HCl	0.6	1	5?×?10^-2/5?×?10^-3/5?×?10^-4
NaCl	Na₂SO₄?+?HCl	0.6	2	5?×?10^-2, 0.6
NaCl	Na₂SO₄?+?HCl	0.6	3	5?×?10^-2, 0.6

Fig. 1 Schematic diagram of in situ observation experimental setup

Fig. 2 Morphologies of corrosion products under droplets acidified by HCl with: a pH?=?1; b pH?=?2; c pH?=?3; d pH?=?5-6 (not acidified)

Fig. 3 Morphologies of corrosion products under droplets acidified by H2SO4 with: a pH?=?1; b pH?=?2; c pH?=?3

Fig. 4 Effects of pH on morphologies of corrosion products under droplets with 0.05 mol/L SO42-: a pH?=?1; b pH?=?2; c pH?=?3

Fig. 5 Effects of pH on morphologies of corrosion products under droplets with 0.6 mol/L SO42-: a pH?=?1; b pH?=?2; c pH?=?3

Fig. 6 Effects of SO42- concentration on morphologies of corrosion products under droplets with pH?=?1: a 0.05 mol/L; b 0.005 mol/L; c 0.0005 mol/L

Fig. 7 Morphologies of corrosion pits after removal of corrosion products under droplets: a acidified by H2SO4 with pH?=?1; b acidified by H2SO4 with pH?=?2; c acidified by HCl with pH?=?1; d acidified by HCl with pH?=?2

Fig. 8 Initial corrosion morphologies varied with time under droplets acidified by H2SO4 with pH?=?1

Fig. 9 Corrosion morphologies varied with time under droplets acidified by H2SO4 with pH?=?1

Fig. 10 EDS mapping of corrosion products under droplet acidified by H2SO4 with pH?=?1 for 30 min

Fig. 11 Corrosion morphologies and element composition under acidified droplet with pH?=?1: a H2SO4; b HCl

Fig. 12 Schematic diagram of formation process of ridge-like morphology under droplet acidified by H2SO4: a anode and cathode formed under droplet. Na+ and Fen+ migrated to the cathode area; Cl- and SO42- moved toward the anode area; b radial segregation of Cl- in the periphery of the droplet. The segregation area acted as local anode and corrosion products deposited on the accumulation area firstly; c a raised irregular corrosion products ring formed in the end of radial corrosion products. The raised corrosion products will absorb more water and Cl-; d one or several weak points in raised corrosion products acted as anode forming a severe corrosion point

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