基于植酸的功能性防腐蚀薄膜的构建技术与耐蚀性能调控的研究

Traditional hexavalent chromium passivation process and phosphating process will be phased out due to either the carcinogenicity or the environmental pollution caused by the discharge of waste solutions. Therefore, developing new environment-friendly technologies for the anti-corrosion surface treatment of steel and iron materials is a matter of great urgency. Phytic acid, as a natural and non-toxic inhibitor, is considered as a promising environment-friendly substance that can substitute hexavalent chromium passivation agents. However, at the present time, the studies concerning the anti-corrosion mechanisms of phytic acid films are seriously backward; in particular, the formation process of the passive films and possible passivation mechanism are purely speculative, which have restricted the wide application of phytic acid in the field of metal surface treatment. Accordingly, in this protect we plan to use EC-STM, AFM and spectroelecterchemistry to in situ characterize the adsorption modes of phytic acid and the possible orientations on the electrode surface, and further demonstrate that the phytic acid films are not traditional phosphating films or deposition films, but the self-assembled films closely related to complexation, with strong corrosion resistance. At the same time, we will study the corrosion properties of steel and iron materials under thin electrolyte layer to reveal the essential reasons why phytic acid can cause the surface passivation of these materials. Seeing that phytic acid films have obvious disadvantages in corrosion protective property and self-healing ability, we plan to use phytic acid as a starting material to synthesize multifunctional inhibitors, and moreover, fabricate the functional protective films with the stronger corrosion resistance and adjustable anti-corrosion properties. The research goal of the project is the development of phytic acid-based environment-friendly anti-corrosion technologies that can effectively protect the metal surface against corrosion.

传统的六价铬钝化和磷化处理或因自身的致癌性或因废液排放对环境的污染而逐渐被淘汰，因此发展环保型的钢铁材料表面防腐蚀处理新技术已迫在眉睫。植酸是一种天然无毒的缓蚀剂，被认为是很有希望代替六价铬钝化剂的环境友好型物质。目前关于植酸膜腐蚀防护机理的研究严重滞后，尤其是致钝原因和钝化机理多为推测，已经制约了植酸在金属表面处理领域的广泛应用。 为此，本项目提出利用EC-STM、AFM、光谱电化学原位表征植酸在电极表面的吸附方式与取向、成膜特点，结合传统电化学研究结果，证明植酸膜不是传统的磷化膜和沉积膜，而是与络合作用相关的自组装薄膜，有较强的耐腐蚀性能。同时，研究薄液膜层下钢铁材料的腐蚀特征，揭示植酸致钝作用的本质。针对植酸膜耐蚀性偏弱、缺乏自修复能力的缺陷，拟以植酸为起始原料合成多功能缓蚀剂，应用其构筑耐蚀性能更好的功能性防护膜，并对防腐性能进行调控，发展基于植酸的环境友好型金属表面防腐新技术。

植酸（肌醇六磷酸酯）是一种天然无毒的有机磷酸酯化合物，一度被认为是很有希望代替污染性六价铬钝化膜的环境友好型物质。然而目前关于植酸在钢铁表面的成膜和抗腐蚀机理依旧模糊不清，因此本项目致力于探究植酸在钢铁表面的成膜特征，并发展基于植酸的环境友好型防腐预处理新技术。. 本项目的主要研究内容可概括为：（1）研究了不同pH条件下植酸对铁腐蚀的缓蚀功能，阐明了单一植酸及其盐膜的抗腐蚀性能较差的原因，基于植酸分子的结构特点提出了在铁表面构筑植酸基复合保护膜的新方法并成功实现；（2）依据两亲性分子易于在水溶液/固体界面聚集的特点，建立了水相中在铁表面自发组装烷基磷酸酯缓蚀功能膜的实用型新方法。. 截止目前所获得的重要结果及其科学意义或应用价值阐述如下：（1）研究确认植酸在酸性条件下只显示混合型缓蚀剂的作用，而在中性或碱性条件下则充当成膜剂，尽管所形成的盐膜表现出钝化膜的某些特征，但耐腐蚀性能明显不如传统钝化膜。这些结果在一定程度上澄清了以往对植酸防腐蚀行为的模糊认识。（2）植酸与Zn2+或其它金属离子（如Ca2+、Co2+、Ni2+等）在水溶液中共存时所形成的螯合物可通过金属离子的桥联作用而被吸附沉积于铁基体表面，并以层层沉积的方式生长到10微米以上的厚度。这是一种环境友好型的成膜方法，基本满足了替代磷化成膜工艺的技术要求，具有广阔的应用前景。（3）利用植酸分子中磷酸酯基团上的羟基易于发生缩合反应的特点，制备了一种具有三维多孔结构的植酸/硅烷杂合材料的稀溶胶。该杂合材料可通过浸凃的方式在钢铁表面成膜，很适合充当涂装前处理化学转化膜。（4）研究发现磷酸酯基团对氧化的铁表面有很强的亲和力，因而将成膜物质拓宽到烷基磷酸酯化合物，并充分利用两亲性分子容易在固-液界面发生聚集的特性，在水溶液中直接在铁基体表面制备了烷基磷酸酯自组装薄膜。这一实用型自组装方法的建立为自组装分子膜的实际防腐蚀应用提供了理论依据。