镁合金表面无铬双重自修复功效防腐涂层耐蚀机理

This project proposes the hybrid pretreatment coating and boron nitride-poly(urea-urethane) elastomeric protective nanocomposite coating, which are successively deposited on magnesium alloys for aerospace applications. The coating systems provide the reliable protection for magnesium alloy through dual synergistic self-healing functions, facilitating them better deal with the complex working environments. First of all, the hybrid pretreatment coating is constructed by doping smart nanocontainers possessing Mg2+/OH-/corrosion potential triple stimuli-responsive controlled release characteristics into bottom part of sol-gel coating with the aid of external magnetic field. Once the local corrosion initiates, smart nanocontainers can simultaneously respond to the different environmental stimuli occurring on corrosive micro-anodic regions, micro-cathodic regions and the regions between them and quickly release entrapped corrosion inhibitors, forming the molecular films on damaged surface of magnesium alloy via spontaneous adsorption and accomplishing self-healing process. The rational distribution of smart nanocontainers and the unique triple-stimuli responsive controlled release features enhances the effectiveness of self-healing. Secondly, boron nitride-poly(urea-urethane) elastomeric composite coating achieve intrinsic self-healing function at room temperature by cleavage-recombination of supramolecular hydrogen bonds on damaged interfaces. The introduction of functionalized boron nitride nanosheets dramatically enhances the mechanical strength and toughness, which make the nanocomposite coating meets the requirements of practical applications. In addition, functionalized boron nitride nanosheets, acting as barrier fillers, can also increase the resistance to penetration of aggressive species and improve the weakness of moisture-sensitivity for supramolecular hydrogen polymers.

项目提出在航空航天用镁合金表面依次涂覆杂化预处理涂层和氮化硼-聚脲弹性体复合涂层体系，通过双重协同自修作用为镁合金提供可靠的耐蚀防腐体系，以便其更好应对复杂的工作环境。首先，利用外磁场将具有Mg2+/OH-/腐蚀电位三重刺激响应释放功能的智能纳米容器掺入溶胶凝胶涂层底部形成杂化预处理涂层。一旦局部腐蚀开始，智能纳米容器可以同时敏锐响应腐蚀微阴极区、微阳极区和两区之间区域内不同环境因素变化，迅速释放缓蚀剂在局部腐蚀区域吸附成膜完成自修复。合理排布智能纳米容器和其三重刺激响应释放特性提升了自修复效率。其次，氮化硼-聚脲弹性体复合涂层依靠超分子氢键在涂层破损界面的断裂—重组过程实现室温本征自修复功能。改性氮化硼纳米片的并入大大增强了聚脲弹性体涂层的机械强度和韧性，满足对复合涂层基本力学性能的要求。改性氮化硼纳米片作为阻隔型填料还可增强涂层抗腐蚀介质渗透以及改善超分子氢键型聚合物的水汽敏感性弱点。

项目提出在航空航天用镁合金表面依次涂覆杂化预处理涂层和氮化硼-聚脲弹性体复合涂层体系，通过双重协同自修复作用为镁合金提供可靠的耐蚀防腐体系。项目中杂化预处理涂层基于“主体”—“客体”刺激反馈化学转化膜层的结构，其中“客体”为智能纳米容器，其可对镁合金腐蚀微区环境因素的刺激进行反馈，迅速释放缓蚀剂吸附在裸露镁合金表面成膜，形成致密的保护性分子膜层，有效抑制局部腐蚀。本项目中，基于超分子纳米阀门成功制备了酸/碱/Mg2+/腐蚀电位四重刺激响应智能纳米容器，其在镁合金腐蚀微区可以灵敏响应腐蚀微区的离子强度和腐蚀电位，自主打开超分子纳米阀门或者解离超分子纳米阀门实现缓蚀剂在腐蚀微区的快速释放。另外，项目还基于层状双氢氧化物材料，通过离子交换过程负载阴离子型缓蚀剂。一旦腐蚀性阴离子渗透到达智能纳米容器附近，可以轻易置换出存贮的阴离子型缓蚀剂，形成沉淀膜阻止腐蚀介质的进一步扩散。化学、电化学以及微区电化学实验综合证明，掺杂“主体”溶胶凝胶涂层内的智能纳米容器可以在镁合金表面腐蚀微区发挥自修复功效，快速抑制腐蚀微区电流，并可以作为阻隔性填料协同“主体”膜层实现长效防腐。项目中制备的氮化硼-聚脲弹性体复合涂层依靠可逆、动态的超分子氢键在涂层断裂界面上的断裂—重组过程，实现了涂层材料的室温本征自修复功能。改性氮化硼纳米片的添入非常关键，它的作用主要包括：(1)改性氮化硼纳米片和聚合物分子链间产生界面间氢键作用，氮化硼纳米片作为非共价交联中心，使得室温本征自修复聚氨酯材料增强增韧，解决了室温本征自修复材料机械性能偏弱的问题；(2)改性氮化硼纳米片加入聚合物网络，没有明显地抑制聚合物链段的流动，复合材料玻璃化转变温度仍然远远小于室温，这保证了涂层材料在室温下的自主修复；(3)改性氮化硼纳米片具有类石墨烯的“迷宫效应”，其随意分散在聚合物网络内，可以有效阻隔腐蚀介质（尤其是水和腐蚀性离子）的渗透，提升了涂层的综合防腐性能。