离子液体在甲醇/硫酸介质中对Q235钢表面的缓蚀性能

doi:10.11949/0438-1157.20191372

摘要/Abstract

摘要：

探究硫酸存在时Q235钢在甲醇中的腐蚀行为，以及离子液体1-丁基-3-甲基咪唑氯盐（[Bmim]Cl）对金属表面的缓蚀作用。通过静态失重法、电化学测试、扫描电子显微镜来测定[Bmim]Cl对Q235钢的缓蚀性能。并利用量子化学计算和分子动力学模拟分析[Bmim]Cl分子的缓蚀机理。在甲醇中随着硫酸含量的增加碳钢的腐蚀速率增加。含有59.51 ml 0.05 mol·L^-1 H₂SO₄的甲醇溶液作为腐蚀介质时，随着[Bmim]Cl浓度升高，缓蚀效率逐渐增大，当浓度为0.6 mol·L^-1时，缓蚀效率达到最佳值，为90.63%，且[Bmim]Cl是主要控制阳极反应的混合抑制剂，SEM分析表明在含有缓蚀剂溶液中浸泡后的Q235钢表面相对于未加缓蚀剂更加平整。前线轨道分析和Fukui指数都表明，离子液体在碳钢表面的吸附位点分布在咪唑环上，与Fe发生化学吸附。分子动力学模拟结果表明缓蚀剂分子以阳离子[Bmim]⁺平行吸附于金属表面，阴离子Cl^-扩散在溶液中的方式达到缓蚀的效果。理论计算结果与实验结果一致，即[Bmim]Cl在甲醇/硫酸水溶液中对Q235钢具有很好的缓蚀作用，为新型离子液体缓蚀剂研究应用奠定了基础。

关键词: 离子液体, 缓蚀剂, Q235钢, 电化学, 量子化学计算, 分子模拟

Abstract:

The corrosion behavior of Q235 steel in methanol medium in the presence of sulfuric acid and the inhibition properties of 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) for Q235 steel in methanol/sulfuric acid aqueous solutions were studied in the paper. The corrosion inhibition characteristics of [Bmim]Cl for Q235 steel were evaluated by static mass loss method, polarization curve method, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The corrosion inhibition mechanism of [Bmim]Cl was analyzed by quantum chemical calculation and molecular dynamics simulation. The corrosion rates of carbon steel increased with the increase of sulfuric acid in methanol. The results of experiments showed that the corrosion inhibition efficiency increased gradually with the increase of the concentration of [Bmim]Cl in methanol solution containing 59.51 ml 0.05 mol·L^-1 H₂SO₄ aqueous solutions. When the concentration was 0.6 mol·L^-1, the corrosion inhibition efficiency can reach the optimal, that is 90.63%. And [Bmim]Cl was a mixed inhibitor, which mainly controlled by the anodic reaction. Frontier orbitals analysis and Fukui function showed that the adsorption sites of ionic liquids on the surface of carbon steel were distributed on the imidazole ring and chemisorbed with Fe. The molecular dynamics simulation results showed that the inhibitor molecules were adsorbed parallel to the metal surface by cationic [Bmim]⁺, and the anion Cl^- diffuses in solution to achieve the inhibition effect. The theoretical calculation results are consistent with the experimental results, that is, [Bmim] Cl has a good corrosion inhibition effect on Q235 steel in a methanol / sulfuric acid aqueous solution, laying a foundation for the research and application of new ionic liquid corrosion inhibitors.

Key words: ionic liquids, corrosion inhibitor, Q235 steel, electrochemistry, quantum chemical calculations, molecular simulation

中图分类号:

TG 174.42

郑天宇, 王璐, 刘金彦, 王佳. 离子液体在甲醇/硫酸介质中对Q235钢表面的缓蚀性能[J]. 化工学报, 2020, 71(5): 2230-2239.

Tianyu ZHENG, Lu WANG, Jinyan LIU, Jia WANG. Corrosion inhibition of ionic liquids on the surface of Q235 steel in methanol/sulfuric acid medium[J]. CIESC Journal, 2020, 71(5): 2230-2239.

图/表 15

图1 [Bmim]Cl的结构式

Fig.1 Chemical structure of [Bmim]Cl

表1 加入不同体积的0.05 mol·L-1 H2SO4后对Q235钢在甲醇中的腐蚀速率

Table 1 Corrosion rate of Q235 steel in methanol after adding 0.05 mol·L-1 H2SO4

V_{sulphuric acid}/ml	C_methanol/(mol·L^-1)	v/(g·(m²·h)^-1)
0	24.69	—
19.03	20.00	0.76
39.27	15.00	0.91
59.51	10.00	1.30
79.76	5.00	1.59
100.00	0	3.29

表2 不同浓度[Bmim]Cl对Q235钢的静态失重数据

Table 2 Static mass-loss parameters of Q235 steel with different concentrations of [Bmim]Cl

C/(mol·L^-1)	W/g	v/(g·(m²·h)^-1)	η₁/%
blank	0.194	1.59	—
0.05	0.075	0.61	61.43
0.1	0.061	0.49	68.85
0.2	0.05	0.41	74.30
0.4	0.039	0.32	79.81
0.6	0.018	0.15	90.63
0.8	0.083	0.68	57.21

图2 不同浓度[Bmim]Cl对Q235钢的极化曲线

Fig.2 Polarization curves of Q235 steel with different concentrations of [Bmim]Cl

表3 Q235钢在不同[Bmim]Cl浓度下的极化曲线拟合参数

Table 3 Polarization parameters for Q235 steel with different concentrations of [Bmim]Cl

C/(mol·L^-1)	E_corr/mV	I_corr/(μA·cm^-2)	β_a/(mV·dec^-1)	β_c/(mV·dec^-1)	η₂/%
blank	-526.38	121.33	144.63	67.65	—
0.05	-523.97	50.58	154.86	132.37	58.31
0.1	-497.11	40.01	140.62	142.95	67.03
0.2	-491.24	37.71	106.49	102.88	68.90
0.4	-485.06	28.93	106.76	92.89	76.16
0.6	-472.23	18.13	82.87	90.58	85.06
0.8	-507.03	38.69	117.64	120.67	68.11

图3 不同浓度的[Bmim]Cl对Q235的Nyquist图(a)、Bode图(b)和相位角图(c)

Fig.3 Nyquist plots(a), Bode plots(b), and phase angle plots (c) for Q235 steel with different concentrations of [Bmim]Cl

表4 不同浓度的[Bmim]Cl对Q235钢的阻抗谱拟合参数

Table 4 EIS parameters for Q235 steel with different concentrations of [Bmim]Cl

C/ (mol·L^-1)	R_s/ (Ω·cm^-2)	R_p/ (Ω·cm^-2)	n	CPE/ (μF·cm^-2)	χ²	η₃/%
blank	28.35	157.41	0.80	222	4.65×10^-3	—
0.05	21.92	329.99	0.73	201	9.41×10^-3	52.30
0.1	18.64	564.60	0.75	186	2.13×10^-3	72.12
0.2	15.37	667.38	0.76	178	1.43×10^-3	76.41
0.4	11.89	737.54	0.71	159	7.17×10^-3	78.66
0.6	9.74	1052.90	0.76	143	2.24×10^-3	85.05
0.8	7.45	462.14	0.72	195	5.15×10^-3	65.94

图4 电化学等效电路图

Fig.4 Electrochemical equivalent circuit

图5 Q235钢的SEM形貌图

Fig.5 SEM micrographs of Q235 steel

图6 几何优化结构图

Fig.6 Optimized structure

图7 [Bmim]+的前线分子轨道分布

Fig.7 Frontier molecular orbital distribution of [Bmim]+

表5 [Bmim]+的量子化学计算参数

Table 5 Quantum chemical parameters for [Bmim]+

Molecule	E_HOMO/eV	E_LUMO/eV	?E^①/eV	?E₁^②/eV	?E₂^③/eV
[Bmim]⁺	-8.08	-3.18	4.90	4.63	7.83
Fe	-7.81	-0.25	—	—	—

表6 由Hirshfeld电荷分布计算得到[Bmim]+的Fukui指数

Table 6 Fukui index of [Bmim]+ calculated by Hirshfeld charge distribution

Atom	N(1)	C(2)	C(3)	C(4)	N(5)	C(6)	C(7)	C(8)	C(9)	C(10)
f(r)^-	0.092	0.187	0.079	0.082	0.092	0.032	0.019	0.006	0.008	0.008
f(r)⁺	0.046	0.144	0.158	0.170	0.045	0.023	0.017	0.007	0.011	0.009

图8 [Bmim]Cl在Fe(110)和Fe2O3(110)上动力学模拟吸附的最低能量构型

Fig.8 Lowest energy configuration for [Bmim]Cl adsorption on Fe (110) and Fe2O3(110)

表7 [Bmim]Cl在甲醇/硫酸水溶液中不同表面上的吸附能

Table 7 Adsorption energy of [Bmim]Cl on different surfaces in methanol/sulfuric acid aqueous solutions

System	E_total/(kcal·mol^-1)	E_{surface/solution}/(kcal·mol^-1)	E_{inhibitor/solution}/(kcal·mol^-1)	E_solution/(kcal·mol^-1)	E_adsorption/(kcal·mol^-1)
Fe(110)	-4368.342	-4156.534	-3720.335	-3617.749	-109.222
Fe₂O₃(110)	-3611.302	-3494.727	-3683.005	-3646.258	-79.828

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