Design of next-generation automotive corrosion protective coatings by improving inhibitor transport properties

防护涂料行业目前面临着数十亿英镑的挑战，要找到成功的材料替代有毒的六价铬防腐剂，通常作为难溶的盐颜料加入有机涂料中。欧盟已将铬(VI)的使用指定为2019年的“日落”日期，之后将被禁止。因此，迫切需要确定新的环境防腐技术，即使不是更好的保护能力，也是同等的保护能力。该项目提供了一个绝佳的机会，可以与世界领先的汽车涂料市场公司巴斯夫汽车公司合作，开发新的无铬(VI)缓蚀技术，从而更有效地提供腐蚀保护。目前涉及磷酸盐技术的技术状态仍然有限，因为活性缓蚀剂释放到涂层缺陷区域没有得到很好的控制。因此，现在人们对开发智能释放颜料的特性非常感兴趣，在智能释放颜料中，缓蚀剂被存储在其中，并仅在具有侵蚀性的腐蚀诱导剂存在的情况下按需释放。此外，还需要改进缓蚀剂物种从涂层主体到需要它们的区域的传输(例如，暴露在底层金属的缺陷)。目前，只有来自缺陷附近涂层的有限数量的缓蚀剂可用于保护暴露的金属。通过在涂层内引入远程渗流网络，希望通过加强缓蚀剂向缺陷区域的传输，可以在暴露的金属上产生更有效的缓蚀效果。项目目标：1.研究目前最先进的磷酸盐颜料和含有各种缓蚀剂的新型智能释放离子交换颜料对渗入性涂层缺陷的缓蚀效率。对上述颜料的不同包埋量进行详细的研究，以评价其对缓蚀剂释放速度的影响。评估新型缓蚀剂输送系统，如纳米管储罐、离子交换树脂和矿物，导电聚合物网络作为在保护有机涂层中引入远程渗流颜料网络的手段。评估来自优化系统的缓蚀剂的长距离传输对涂层失效的机理有多大影响，涂层失效的机制源于腐蚀驱动的阳极和/或阴极在穿透性缺陷附近的剥离。这项工作的主要目的将是为具有重要技术意义的轻合金表面开发下一代保护涂层，通常是铝和可能的镁汽车合金等级，尽管性能最好的技术也可能应用于钢的保护。该工作计划将利用世界领先的先进电化学扫描技术的专业知识，结合高通量方法来量化腐蚀保护效率，并从机理上了解缓蚀机理。调查将在斯旺西大学腐蚀研究小组的实验室使用扫描开尔文探头(SKP)、扫描振动电极技术(SVET)以及动电位和电化学阻抗谱方法进行全面的现场和非现场电化学表征。将使用一套世界级的仪器进行表面化学和结构表征，包括X射线光电子能谱(XPS)、掠角X射线衍射仪(X射线衍射仪)和场发射枪扫描电子显微镜(FEG-SEM)，这些仪器可在工程学院材料研究中心获得。

The protective coatings industry is currently facing a multi-billion pound challenge to find successful materials substitution for toxic hexavalent chromium-based anti-corrosion agents, typically incorporated as sparingly soluble salt pigments within an organic coating. Cr(VI) use has been assigned a "sunset" date of 2019 by the European union, after which it will be banned. As such there is an urgent need to identify new, environmentally corrosion inhibitive technologies showing equivalent, if not better protective capability. This project provides an excellent opportunity to work with a world leading company involved in the automotive coatings market, namely BASF Automotive, to develop new Cr(vi)-free corrosion inhibitive technologies which will deliver corrosion protection more effectively. The current state of the art, involving phosphate based technology, remains limited since release of active corrosion inhibitive agents into coating defect regions is not well controlled. As a result, there is now significant interest in exploiting the properties of intelligent-release pigments, in which corrosion inhibitive species are stored and only released "on-demand" in the presence of aggressive corrosion-inducing agents. Furthermore, there is also a need to improve the transport of inhibitor species from the bulk of the coating to the areas where they are required (e.g. defects where the underlying metal is exposed). Currently, only a finite quantity of inhibitor originating from the coating in the immediate vicinity of the defect may available to protect exposed metal. By introducing long-range percolation networks within the coating, it is hoped that enhanced transport of inhibitor to defect regions can produce significantly more effective corrosion inhibition at the exposed metal.Project aims:1. To investigate the efficiency of inhibition at penetrative coating defects using current state of the art phosphate based pigments and novel smart-release ion-exchange pigments containing various corrosion inhibitive species.2. To carry out detailed studies with varying in-coating loadings of the above mentioned pigments to evaluate the effect on speed of inhibitor release.3. To assess novel inhibitor delivery systems such as nanotube reservoirs, ion exchange resins and minerals, conducting polymer networks as a means of introducing a long-range percolation pigment network within the protective organic coating.4. To evaluate how long range transport of inhibitor from an optimised system influences the mechanism of coating failure due to de-adhesion originating from corrosion-driven anodic and/or cathodic disbondment in the vicinity of a penetrative defect.The main thrust of the work will be to develop next-generation protective coatings for technologically important light alloy surfaces, typically aluminium and possibly magnesium automotive alloy grades, although the best performing technologies may also be applied to the protection of steel. The program of work will exploit world-leading expertise in advanced electrochemical scanning techniques, coupled with high throughput methodologies to quantify corrosion protection efficiency and provide mechanistic understanding of inhibition mechanisms.The investigation will be carried out using comprehensive in-situ and ex-situ electrochemical characterization by means of scanning Kelvin Probe (SKP), Scanning Vibrating electrode technique (SVET), alongside potentiodynamic and electrochemical impedance spectroscopy methods in the laboratories of the Swansea University corrosion research group. Surface chemical and structural characterization will be carried using a world class suite of instrumentation including X-ray-photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (XRD), and field emission gun scanning electron microscopy (FEG-SEM), available in the Materials Research Centre at the College of Engineering.