中国腐蚀与防护学报, 2017, 37(3): 216-220
doi: 10.11902/1005.4537.2016.043
薄层液膜下空间电场对碳酸环己胺缓蚀性能的影响

Effect of External Electric Field on Inhibition Behavior of Cyclohexylamine Carbonate for Carbon Steel N80 Beneath Adsorbed Thin Electrolyte Layers
朱紫晶1, 魏莉莎1, 陈振宇1,2,, 邱于兵2, 郭兴蓬1,2

摘要:

研究了薄层液膜下空间电场对碳酸环己胺 (CHC) 缓蚀性能的影响。结果表明,CHC主要抑制碳钢腐蚀反应的阳极过程,对碳钢腐蚀具有显著的缓蚀效果,但施加垂直方向的电场后CHC缓蚀效果显著下降。扫描电镜和X射线光电子能谱分析表明,电场作用导致碳钢表面的腐蚀形貌出现明显变化,CHC在碳钢表面的吸附量显著减少。CHC分子的偶极距 (µ)、最高占据轨道能 (EHOMO)、最低空余轨道能 (ELUMO) 以及能隙 (∆E=ELUMO-EHOMO) 在不同的电场条件下的变化规律表明,电场会削弱CHC的反应活性和吸附能力,从而降低其缓蚀效率。

关键词: 气相缓蚀剂 ; 薄层液膜 ; 外电场 ; 量子化学

Abstract:

Effect of external electric field on the inhibition efficiency of cyclohexylamine carbonate (CHC) for carbon steel N80 beneath adsorbed thin electrolyte layers (ATEL) was investigated by means of electrochemical measurement, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results illustrated that CHC mainly suppresses the anodic corrosion reaction and has strong inhibition effect on the carbon steel corrosion. When an electric field vertical to the steel was applied, the inhibition efficiency of CHC decreased greatly and the adsorption of CHC on the carbon steel surface decreased significantly, so that the surface morphology varied quite obviously after corrosion test.The relevant quantum chemical parameters related to the corrosion inhibition efficiency of CHC were calculated by materials studio software. The acquired parameters such as dipole moment (µ), EHOMO, ELUMO and ∆E all implied that the reactivity and adsorption ability of CHC were reduced significantly after applying external electric field, which affects the inhibition efficiency of CHC.

Key words: vapor phase inhibitor ; thin electrolyte film ; external electric field ; quantum chemical

气相缓蚀剂 (VPI) 是一种在常温下能自动挥发并抑制金属大气腐蚀的物质[1]。VPI无需与金属表面直接接触便能发挥作用,且同时具有防锈效果好、操作简便、成本较低等优点,使其十分适合结构复杂的金属制品与构件的非涂装性保护[2]。脂环胺及其衍生物是一种重要的商业型VPI,其中碳酸环己胺 (CHC,C7H15NO3) 是环己胺 (C6H13N) 的一种衍生物,几十年前就被发现对碳钢保护十分有效[3]

研究[4,5]表明,缓蚀剂分子的缓蚀效果与其分子结构及电子的状态密切相关,而分子及其电子性质又会受到外加电场的影响。近年来,关于外加电场影响分子结构和电子状态的研究层出不穷。Taleb等[6]研究不同介质中溶解酵素在外电场下的迁移情况时认为,外部电场通过影响蛋白质浓度,从而在电极之间形成溶解酵素浓度梯度。谭莹等[7]通过研究发现,在电场作用下,配合物存在明显的结构变化和电子转移现象,并呈现出类似导电过程中电子定向运动的变化规律。研究[8,9]表明,垂直方向的电场能有效调节吸附分子与MoS2之间的电子转移,同时也发现电场对分子线的电荷分布有重要的影响,而电荷分布决定了分子轨道的扩展情况,从而直接影响着电子在分子线内的输运过程。除此之外,电场也被证明可以调节ZnONT和甲醛的吸附能,而且随着电场强度增强,调节作用也明显增加。以上研究表明,电场会改变分子的结构与电荷分布,而缓蚀剂的缓蚀效果已被证明与分子的电子结构有关[10],因此电场可能对缓蚀剂的缓蚀性能产生影响,但相关方面的研究目前还未见报道。

本论文利用电化学方法及表面分析手段,研究了空间电场对CHC分子活性的影响,并进一步探究了其与缓蚀性能之间的关系。

1 实验方法

实验材质为N80碳钢,其主要化学成分 (质量分数,%) 为:C 0.3407,Si 0.2923,Mn 1.3898,P 0.0152,S 0.0132,Cr 0.45,Ni 0.0282,Mo 0.3,Fe余量。将碳钢切割成尺寸为3.0 mm×5.0 mm×7.0 mm的块体,用环氧树脂封装一对平行电极,并保持平行电极的间距为0.5 mm,暴露面积为3.0 mm×5.0 mm。三电极设计如下:两块平行碳钢分别作为工作电极和辅助电极;在距离工作电极和辅助电极0.5 mm的位置打一个小孔,孔内灌入琼脂作为盐桥,连通U型装置中的饱和KCl溶液,而溶液的另一端则与作为参比电极的饱和甘汞电极相连。切割尺寸为5 mm×5 mm×1 mm的试片用作表面分析测试。试片表面均用1200#的金相砂纸打磨,然后使用1.5 μm的抛光膏及0.3 μm的抛光粉依次抛光,超声清洗,去离子水冲洗,乙醇除油及N2干燥。

可施加电场的电化学测试装置如图1所示,两块间距为10 cm的平行金属板与直流电源 (DW-P503-1ACF7) 相连。放入装置前,预先在电极表面滴100 µL 0.1 mol/L的NaCl溶液。用控温装置控制实验温度,甘油水溶液调控密闭容器内的相对湿度。当达到所需的温度和湿度后,金属表面便形成吸附薄层液膜 (ATEL)。实验过程中施加的电压值为15 kV,即电场强度为1.5×105 V/m。

电极在湿度为RH 98%,温度为55 ℃的密闭容器内放置,待开路电位稳定后进行电化学测试。电化学阻抗测量频率范围105~10-3 Hz,采用幅值为5 mV的正旋波作为扰动信号,极化曲线的扫描速率为0.5 mV/s。用于表面分析的试样放入温度为55 ℃,湿度为98%RH的密闭容器中,3 d后取出进行扫描电镜 (SEM,Nova NanoSEM 450) 测试及X射线光电子能谱 (XPS,AXIS-ULTRA DLD-600W) 分析。

利用密度泛函理论计算相关量子化学参数,使用软件Materials Studio 6.0 (AccelrysInc) 中DMol3模块的Geometry Optimization和Dynamics功能进行结构优化和计算。计算采用广义梯度近似 (GGA) 功能,基组选择双数值轨道基组 (DNP)。通过输入命令electric_field X Y Z,即可给分子施加电场,X,YZ为电场强度值。设置的场强为1.5×105 V/m。主要计算的参数有偶极距 (μ)、最高占据轨道能 (EHOMO)、最低空余轨道能 (ELUMO)、能隙 (∆E=ELUMO-EHOMO) 及Mulliken布居电子。

图1 可施加电场的电化学测试装置图

Fig.1 Schematic diagram of the experimental setup for electrochemical measurements in the electrical field

2 结果与讨论
2.1 极化曲线测试

图2是碳钢在不同条件下的极化曲线,表1为相关电化学参数。表中,Ecorr为自腐蚀电位,Icorr为腐蚀电流密度,babc分别为阳极与阴极Tafel斜率,η为通过式 (1) 计算获得的缓蚀效率[11]

η = 1 - I corr I corr × 100 % (1)

其中,IcorrI 'corr分别为添加缓蚀剂前后电极的自腐蚀电流密度。

图2 薄层液膜下N80碳钢在不同条件下的极化曲线

Fig.2 Potentiodynamic polarization curves of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃

表1 薄层液膜下N80碳钢在不同条件下的电化学参数
Table 1 Characteristic parameters obtained from polarization curves of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃
Test condition Ecorr / mV (vs SCE) Icorr / Acm-2 ba / mVdec-1 bc / mVdec-1 η
Blank -724 1.92×10-4 329 -167 ---
1.5×105 V/m -724 1.98×10-4 185 -174 ---
CHC -520 1.37×10-5 294 -133 92.8%
1.5×105 V/m+CHC -605 1.56×10-4 255 -138 18.8%

表1 薄层液膜下N80碳钢在不同条件下的电化学参数

Table 1 Characteristic parameters obtained from polarization curves of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃

极化曲线测试结果表明,单纯施加电场时,碳钢的腐蚀行为没有发生显著改变;单纯添加CHC后,电极的自腐蚀电位显著正移,腐蚀电流密度明显降低,说明CHC是一种阳极型缓蚀剂。但是添加CHC的同时再施加电场后,CHC的缓蚀性能显著下降。

2.2 EIS测试

图3是薄层液膜下碳钢在不同实验条件下的Nyquist图,图4为相应的等效电路。其中,Rs为溶液电阻,Qf为腐蚀产物等效电容,Rf为腐蚀产物等效电阻,Qdl代表双电层电容的常相位角元件,Rct为电荷传递电阻。电化学阻抗拟合结果见表2。其中,碳钢表面CHC的覆盖率 (θ) 由下式计算:

θ = 1 - R ct R ct × 100 % (2)

其中,RctR'ct分别为空白条件和添加CHC后的电荷传递电阻。电化学阻抗谱及拟合结果表明,空白条件下和仅施加电场条件的阻抗谱及拟合参数值并没有显著改变,表明单纯施加电场时,碳钢的腐蚀行为基本不受影响;添加CHC后,RfRct值均显著增大,CHC覆盖率达到91.7%,表明CHC较为完整地覆盖在电极表面,降低了碳钢的腐蚀反应;在添加CHC基础上,施加空间电场后,CHC在碳钢表面的覆盖度显著降低,电场明显降低了CHC的缓蚀性能。

图3 薄层液膜下N80碳钢在不同条件下的Nyquist图

Fig.3 Nyquist plots of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃

图4 N80碳钢试样在薄层液膜 (ATEL) 下的等效电路图

Fig.4 Equivalent circuit for N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃

2.3 SEM和XPS分析

N80碳钢表面的腐蚀形貌见图5。其中,图5a~d分别对应空白、仅施加垂直电场、添加CHC和添加CHC并施加垂直方向电场情况下的测试试样。

图5a可见,在没有添加CHC时,碳钢表面覆盖有大面积疏松的腐蚀产物,这种现象也出现在图5b中;而有CHC保护后,样品的表面十分光滑,腐蚀产物明显减少 (图5c)。而添加CHC并施加空间电场后,样品表面出现了枝状产物,且表面产物疏松、多孔 (图5d),表明空间电场减弱了CHC的缓蚀性能。SEM观察结果与电化学测试结果相吻合。

表 2 薄层液膜下碳钢在不同条件下电化学阻抗谱拟合参数
Table 2 Fitting parameters of EIS of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃
Test condition Rct / Ωcm2 Qdl / SnΩ-1cm-2 Rf / Ωcm2 Qf / SnΩ-1cm-2 θ
Blank 442 5.73×10-3 15.4 2.3×10-3 ---
1.5×105 V/m 421 1.18×10-3 12.3 3.4×10-3 ---
CHC 5350 4.14×10-3 41.97 2.45×10-3 91.7%
1.5×105 V/m+CHC 521 2.31×10-3 11.5 2.38×10-4 15.2%

表 2 薄层液膜下碳钢在不同条件下电化学阻抗谱拟合参数

Table 2 Fitting parameters of EIS of N80 steel under NaCl-containing ATEL at RH 98% and 55 ℃

为了进一步分析外加电场的作用,本文对CHC保护下,未施加电场与施加电场后的碳钢样品表面进行了XPS分析 (图6)。XPS测试结果表明,施加电场后,表面O含量显著增加,N含量显著下降 (由4.42%降为0.76%),说明施加电场后,CHC在电极表面的吸附量显著降低,Fe的腐蚀产物显著增加。

图5 薄层液膜下碳钢在不同条件下的SEM像

Fig.5 SEM images of N80 steel after corrosion for 3 d under NaCl-containing ATEL at RH 98% and 55 ℃: (a) blank, (b) 1.5×105 V/m, (c) CHC, (d) 1.5×105 V/m+CHC

图6 薄层液膜下碳钢的XPS谱

Fig.6 XPS spectra of N80 steel after corrosion for 3 d under ATEL

2.4 理论计算

分子模型和前线轨道理论可用于研究缓蚀剂的分子结构及电子分布与缓蚀效率的关系。金属与缓蚀剂的相互作用可以用几个相关的参数来表示,即EHOMO,ELUMO,∆E(ELUMO-EHOMO),和µEHOMO值越高,缓蚀剂则越易向金属的空余d轨道提供电子,即与金属原子的成键作用越好[12,13]。同样,ELUMO的值越低,缓蚀剂越容易接受来自金属处的电子即更难失去电子。∆E预示着抑制剂分子在金属表面的吸附能力的大小。∆E增加会降低缓蚀剂分子的活性,阻碍吸附,从而减低缓蚀效率。由于µ与分子的疏水性能有关,µ值越低,越有助于缓蚀剂分子在金属表面的累积[14,15]

表3是不同强度的电场下CHC的量子化学参数。数据表明,随着电场强度的增加,EHOMO值减小,能隙增加,偶极矩增加,N原子负电荷绝对值降低,说明电场不利于CHC的聚集,使得CHC在碳钢表面的吸附变得困难,降低了CHC的缓蚀作用。

表3 不同电场强度下的量子化学参数
Table 3 Quantum chemical parameters in the electric fields with different intensities
F / Vm-1 µ / debye EHOMO / eV ELUMO / eV |ELUMO-EHOMO| / eV Negative charge on N
0 0.7922 -4.521 -4.191 0.330 -0.174
0.5×105 0.8136 -5.256 -4.810 0.446 -0.172
1.0×105 0.8233 -5.276 -4.797 0.479 -0.149
1.5×105 0.8272 -5.911 -5.334 0.577 -0.147

表3 不同电场强度下的量子化学参数

Table 3 Quantum chemical parameters in the electric fields with different intensities

3 结论

(1) 碳酸环己胺 (CHC) 对薄层液膜下N80碳钢具有显著的缓蚀作用,且主要抑制了碳钢腐蚀的阳极过程。

(2) 空间电场使得CHC的最高占据轨道能减小,能隙增加,偶极矩增加,N原子负电荷绝对值降低。空间电场不利于CHC在碳钢表面的吸附,显著降低了CHC的缓蚀性能。

The authors have declared that no competing interests exist.

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(谭莹, 黄晓, 许旋. 电场对Ni3(dpa)4Cl2金属串配合物结构影响的理论研究[J]. 高等学校化学学报, 2012, 33: 1278)
正首个金属串配合物Ni3(dpa)4Cl2早在1968年就被合成并报导[1],但是它的晶体结构在1991年才得到[2]。金属串配合物Ni3(dpa)4Cl2中Ni-Ni-Ni成直线排列,四个桥联配体dpa-螺旋盘绕金属轴,两个轴向配体Cl与金属原子共线。作为潜在的分子导线,Ni3(dpa)4Cl2配合
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Using first-principles calculations, we investigate the adsorption of various gas molecules (H-2, O-2, H2O, NH3, NO, NO2, and CO) on monolayer MoS2. The most stable adsorption configuration, adsorption energy, and charge transfer are obtained. It is shown that all the molecules are weakly adsorbed on the monolayer MoS2 surface and act as charge acceptors for the monolayer, except NH3 which is found to be a charge donor. Furthermore, we show that charge transfer between the adsorbed molecule and MoS2 can be significantly modulated by a perpendicular electric field. Our theoretical results are consistent with the recent experiments and suggest MoS2 as a potential material for gas sensing application.
DOI:10.1186/1556-276X-8-425      PMID:24134512      URL     [本文引用:1]
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(李英德. 电场对分子线电荷密度的影响[J]. 低温物理学报, 2008, 30: 182)
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MNDO and AM1 theories on PCMODEL-optimized geometries are used to calculate the pK a-values of some 190 phenols and aromatic and aliphatic carboxylic acids. Heats of formation and the anion HOMO energies satisfactorily correlate with experimental (condensed-phase) acidity (correlation coefficients .952 and .953, respectively, for phenols, and .748 and .886 for all compounds). The correlation is improved by multiregression analysis, additional factors taken into account being calculated atomic charge densities. The best correlation employing four descriptors and encompassing all compounds has an r-value of .949. Hard- and software requirements are discussed as are the merits of the quantum-mechanical model especially with respect to the traditional LFER method.
DOI:10.1016/0045-6535(89)90503-1      URL     [本文引用:1]
[11] Zhang C, Duan H B, Zhao J M.Synergistic inhibition effect of imidazoline derivative and L-cysteine on carbon steel corrosion in a CO2-saturated brine solution[J]. Corros. Sci., 2016, 112: 160
The corrosion inhibition performance of imidazoline derivative (IM) andl-cysteine (CYS) on carbon steel in CO2-saturated brine solution was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss, contact angle and X-ray photoelectron spectroscopy (XPS) measurements. The results show that the inhibition performance of individual IM is slight for CO2induced corrosion, and can be strengthened greatly by combined use with Cys. The synergistic inhibition effect of IM and CYS is observed. An adsorption model involving the initial adsorption of CYS on carbon steel surface followed by IM was proposed to elucidate the synergistic mechanism.
DOI:10.1016/j.corsci.2016.07.018      URL     [本文引用:1]
[12] Hu Q S, Hu J C, Yu J H, et al.Quantitative structure-activity relationship studies on corrosion inhibition of benzimidazole and its derivatives[J]. J. Chin. Soc. Corros. Prot., 2010, 30: 354
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(胡松青, 胡建春, 郁金华. 苯并咪唑及其衍生物缓蚀性能的定量构效关系研究[J]. 中国腐蚀与防护学报, 2010, 30: 354)
用量子化学密度泛函理论(DFT)中的B3LYP方法,在6-31C(上标 *)基组水平上计算了20种苯并咪唑类缓蚀剂的6种量子化学参数,取其中16种缓蚀剂分子作为样本集对其缓蚀性能迸行定量构效关系(QSAR)研究,通过回归分析筛选出影响缓蚀剂缓蚀性能的主要因素,建立了QSAR模型,并通过”Jackknife”法中的逐一抽取法检验模型。结果表明,最高占有轨道能员E(下标 HOMO)、总的负电荷TNC及疏水参数LogP对苯并咪唑类缓蚀剂的缓蚀性能有很大的贡献,经自由度校正的回归系数R(下标 adj,)=0.977,所得模型具有较高的稳定性。用4个预测集缓蚀剂分子对该模型的预测能力进行验证,结果显示该模型其有很好的预测能力。
URL    
[13] Zhang D Q, Gao L X, Zhou G D.Molecular design and synergistic effect of morpholinium type volatile corrosion inhibitor[J]. J. Chin. Soc. Corros. Prot., 2006, 26: 120
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(张大全, 高立新, 周国定. 吗啉衍生物气相缓蚀剂的分子设计和缓蚀协同作用研究[J]. 中国腐蚀与防护学报, 2006, 26: 120)
采用Pcmodel分子力学程序和PM3半经验量子化学计算法,对新型吗啉衍生物气相缓蚀的分子设计过程进行了讨论.结果表明:通过分子内的亚甲基链把吗啉和二环己胺分子连接起来,合成吗啉Mannish碱衍生物N,N-二环己基胺甲基吗啉,可以在碳钢表面形成多中心的吸附,具有较高的EHOMO和较低的ELUMO,提高了N,N-二环己基胺甲基吗啉在金属表面的覆盖程度以及与金属的键合强度.当向N,N-二环己基胺甲基吗啉引入苯甲酸根阴离子后,整个体系的EHOMO进一步升高,ELUMO进一步降低,该复配体系和钢铁成键更稳定,从而使其气相缓蚀能力得到进一步的增强.
[14] Li Y, Guo Y, Cai H, et al.Quantum chemistry study of the structure-activity relationship of corrosion inhibitor[J]. Corros. Prot.,2007, 28: 392
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(李酽, 郭英, 才华. 缓蚀剂构效关系的量子化学研究[J]. 腐蚀与防护, 2007, 28: 392)
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[15] Khalil N.Quantum chemical approach of corrosion inhibition[J]. Electrochim. Acta, 2003, 48: 2635
An examination of quantum chemical and corrosion inhibition studies were made to see if any clear links exist between the two. The results of quantum chemical calculations and experimental efficiencies of inhibitors were subjected to correlation analysis. A composite index of some of the key quantum chemical parameters was constructed in order to characterize the inhibition performance of the tested molecules.
DOI:10.1016/S0013-4686(03)00307-4      URL     [本文引用:1]
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关键词(key words)
气相缓蚀剂
薄层液膜
外电场
量子化学

vapor phase inhibitor
thin electrolyte film
external electric field
quantum chemical

作者
朱紫晶
魏莉莎
陈振宇
邱于兵
郭兴蓬

ZHU Zijing
WEI Lisha
CHEN Zhenyu
QIU Yubing
GUO Xingpeng