离子液体中取向性AlPO-n分子筛膜的原位电化学可控合成及其防腐性能研究

For more than 100 years, hexavalent chromium (Cr6+)compounds, mainly chromates, have been widely used as a corrosion inhibitor to protect the metals or alloys. Unfortunately, chromate has become stringently regulated because it is highly toxic and carcinogenic. Hence, much effort has been dedicated to identify and develop environmentally friendly, Cr-free coatings with equivalent or superior corrosion perfermance as a viable replacement. zeolite films as corrosion resistant materials have attracted intense interest due to their intrinsic non-toxicity and excellent stability, and have the potential to become an environmentally begign alternative for Cr coatings.It is found that zeolite films with pore channels paralel to the substrate surface are suitable for corrosion protection application because such an oriented pore channel can be an impremeable barrier for most corrosive gases and liquids and limit access of corrosive chemicals. Obviously,the orientation of the pore channel of zeolite films is of particlular interest for the synthesis of corrosion-resistant zeolite coatings. In order to in-situ prepare defect-free and desirably oriented zeolite films, herein, we present a project that, by taking full advantage of negligible vapor pressure and wide electrochemical window of ionic liquids, as well as their preferred orientation as a function of applied potential,a one-step in-situ electrochemical method using Al elecctrode as an Al source to synthesize a highly oriented AlPO4-n film in ionic liquid are proposed for the first time. In detail, using a three-electrode cell in which two identical Al substrates are fixed vertically inside the synthesis solution containing ionic liquid as cathode and anode, respectively, we will carry out the detail investigation about the in-situ preparation of AlPO4-n film with high orientation on the surface of Al electrode by changing applied potential or current、the type of ionic liquid、and the concentration of synthetic solution, etc.. In the course of this project, we will focus our attention on the effect of the preferred orientation adsorption of imidazolium ring on the structure、morphology and orientation of AlPO4-n films synthesized by electrochemical method. And it is our task to explore the growth mechanism of AlPO4-n films under different electrochemcial parameters and ionic liquid environment, and develop a better understanding about the relationship between corrosion resistance and anti-corrosive stability of AlPO4-11 film and its orientation. we hope that ambient pressure procedure and controllable electrochemical parameters can offer an uprecedented opportunity to explore the growth mechanism of zeolite films, and the simple and in-situ synthesis system will be widely adopted by the surface fininshing industry for anti-corrosion applications.

防腐涂层广泛应用于国民经济各个领域。目前，实际应用最为广泛的是铬防腐涂层，但铬的高毒性和高致癌性使世界各国都在积极寻找其替代材料。分子筛膜无毒，且在酸、碱、海水等腐蚀环境中均显示出很好的防腐性能，是一种新型绿色环保涂层。为了进一步提高分子筛膜的防腐蚀性能，本课题充分利用离子液体蒸汽压低，电化学窗口宽的特性，特别是离子液体阳离子模板剂在电极表面特有的优先取向性吸附这一优势，首次提出了离子液体中电化学法原位合成取向可控磷铝分子筛膜的新方法和新观念。通过改变电化学参数和化学参数详细研究离子液体阳离子模板剂在电极表面的优先取向吸附对分子筛膜取向、结构、形貌、致密性的影响；加深对电化学原位合成过程中离子液体模板剂的结构导向作用的认识；研究离子液体中电化学条件下取向分子筛膜的原位生长机理；探索分子筛膜的防腐性能与其形貌及晶体取向性之间的关联；为高性能防腐分子筛膜的合成提供有价值的理论参考依据。

分子筛膜在催化、分离以及功能涂层等方面有着非常广泛的应用价值。而这些应用中，所追求的高性能通常要求分子筛膜具有高度的择优取向和致密性。如何采用简便的方法制备出高度取向的致密分子筛膜，是膜领域研究中一个重要的挑战。针对该挑战，本项目充分利用离子液体电化学窗口宽、蒸汽压低和热力学稳定性高的优势，将外加电场引入到离子热合成体系中，开发了离子液体中电化学合成取向分子筛膜的新方法。重要研究结果如下：.1、Al电极即作为基底也作为铝源，首次在离子液体中通过施加恒定的负电压，在Al工作电极表面原位合成出高度面内取向的AlPO4-11分子筛膜，提出了离子液体中电化学作用下高度面内取向分子筛膜的生成机理，发现电化学合成方法可以确保所合成的分子筛膜无缺陷。腐蚀研究发现，高度面内取向、无缺陷分子筛膜具有优异的防腐蚀性能。.2、在电化学离子热合成高度面内取向分子筛膜基础上，采用低温致密晶核层-高温晶体取向生长的取向膜合成策略，在离子液体中采用电化学合成方法合成出高度面外取向的分子筛膜，提出了离子液体中电化学作用下高度面外取向分子筛膜的生成机理。.3、在电化学离子热合成分子筛膜过程中，发现纳安级电流下，工作电极和对电极表面均生成致密分子筛膜，这与mA级电流下的分子筛膜生成现象和机理是完全不同的。鉴于此，提出了离子热合成条件下，非法拉第电化学效应合成分子筛膜机理。