Study on Molecular Dynamics of the Adsorption and Film Formation of Octadecylamine on Carbon Steel Surface
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摘要: 华龙一号机组主给水系统大量使用P280GH碳钢管道，并应用十八胺（ODA）在管道内壁吸附形成缓蚀膜，ODA可高效抑制腐蚀，避免管道失效和蒸汽发生器（SG）严重结垢。但ODA在碳钢表面的吸附和成膜机理目前仍不明确，严重制约了ODA的性能优化和推广应用，针对该问题，采用分子动力学（MD）模拟开展研究。结果表明，ODA分子头部的氮原子与碳钢表面铁原子形成配位键，促使ODA分子吸附“锚定”。所形成缓蚀膜的微观构型与ODA浓度相关。浓度较低时，缓蚀膜呈ODA分子尾链间交织较差的单层构型，随着浓度增加，缓蚀膜逐渐演变为ODA分子尾链间紧密交织的复杂双层构型。在ODA浓度超过一定阈值后，缓蚀膜的构型不再显著变化，未吸附成膜的ODA分子最终积聚形成胶体微团。
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关键词:
- 十八胺（ODA） /
- 分子动力学（MD）模拟 /
- P280GH碳钢 /
- 缓蚀膜 /
- 蒸汽发生器（SG）
Abstract: P280GH carbon steel pipe is widely used in the main feedwater system of Hualong One unit, and octadecylamine (ODA) is applied to form a corrosion inhibition film by adsorption on the inner wall of the pipe. ODA can effectively inhibit corrosion and avoid pipe failure and serious scaling of steam generator (SG). However, the mechanism of adsorption and film formation of ODA on carbon steel surface is still unclear, which seriously restricts the performance optimization, optimization and application of ODA. In order to solve this problem, molecular dynamics (MD) simulation method is used to carry out the study. The results show that the nitrogen atoms at the head of the ODA molecule form coordination bonds with the iron atoms on the carbon steel surface, which promotes the adsorption and anchoring of the ODA molecule. The microscopic configuration of the corrosion inhibition film formed is dependent on the concentration of ODA. At low concentration, the corrosion inhibition film has a poorly interwoven single-layer configuration between ODA molecular tail chains, and as the concentration increases, the corrosion inhibition film evolves into a tightly interwoven complex bilayer configuration between ODA molecular tail chains. After the concentration of ODA exceeds a certain threshold, the configuration of the corrosion inhibition film no longer changes significantly, and the ODA molecules that are not adsorbed to form the film eventually accumulate to form colloidal micelles. -
图 1 单ODA分子吸附模型的初始结构和模拟结果
Figure 1. Initial Structure and Simulation Result of Single ODA Molecular Adsorption Model
图 2 多ODA分子成膜模型的初始结构（含27个ODA分子）
Figure 2. Initial Structure of the Film Forming Model for Multiple ODA Molecules (Containing 27 ODA Molecules)
图 4 ODA分子在液相和真空环境中的吸附轨迹
区域B—液相中氮原子平衡吸附位置；区域C—真空中氮原子平衡吸附位置；红点—出发点；红色箭头—初始运动方向；徘徊区—氮原子寻找吸附点位区域；x—原子在 x 方向的坐标；位置A—拐点位置
Figure 4. Adsorption Trajectories of ODA Molecules in Liquid Phase and Vacuum Environments
图 5 ODA分子数分别为9、18、27和36时平衡吸附构型
俯视图e~h为显示清晰，整个ODA分子用黄色表示；侧视图a~d中ODA分子颜色仍与前文一致
Figure 5. Equilibrium Adsorption Configurations When the Numbers of ODA Molecules are 9, 18, 27 and 36 Respectively
图 6 41个ODA分子在Fe(001)晶面吸附成膜构型
Figure 6. Configuration of Film Formed by Adsorption of 41 ODA Molecules on the Crystal Surface of Fe(001)
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