Self-Organized Hierarchically Rough Ceramic Coatings

世界范围内已有相当多的研究致力于了解固体表面的水扩散或排斥性质(润湿性)。纺织品和矿物加工的早期研究发现，表面粗糙度和化学成分是影响润湿行为的唯一变量，自那以后，人们尝试了大量的加工策略来生产亲水性和疏水性表面、涂层和复合材料，用于固相和液态相互作用的应用。在已探索的制造技术和材料中，极少数(如果有的话)是广泛存在的、商业上可行的、稳定的或耐用的。在实现稳定性和耐久性方面缺乏成功是由于主要使用聚合物；聚合物柔软、耐磨、在中低温度和压力下容易发生形态变化，并且不完全耐化学或耐光。本项目将通过在金属衬底上涂覆陶瓷材料(如氧化物、硫化物、氮化物和碳化物)来解决当前材料策略的缺点，应用范围从防腐、蒸汽产生和强化沸腾换热的涂层。*这项建议将调查并侧重于金属基材上陶瓷涂层的材料设计、涂层结构、加工和表征。通过适当的制造，如氧化合成(在实验室空气中加热金属)，陶瓷涂层有可能变得更硬、更惰性、更稳定和更耐用。该项目的长期工程愿景是发现一种工艺，在这种工艺中，陶瓷涂层可以以自组织的方式在金属表面就地制造，并具有通过良好识别和控制的工艺变量调节其润湿性的固有能力。*研究小组(HQP)将接受培训，学习、产生和传播与在金属基材上制造陶瓷涂层相关的基础材料科学和工程挑战方面的知识。计划的三个主要目标是：*1)设计、制造和评估亲水和疏水响应的分级粗糙结构(孔结构和相对体积及互连性、材料选择、涂层方法、表面化学、羟基含量、碳污染、电荷分布)。在这个阶段将研究各种材料和涂层系统，以选择热力学稳定性和兼容性；*2)适合于材料和涂层性能的建模和预测的陶瓷组件系统的表征、物相鉴定、动力学和热力学分析(结晶学，在不同相对湿度和温度下的表面润湿性)；*3)使材料体系适应高温和潮湿环境，以通过材料、加工和涂层体系设计，评估和防止任何导致拓扑或表面化学变化的有害结构演变，或改变润湿性(显微镜、粗糙度变化、污染、相分离及相关的表观接触角变化)。*可以控制表面形貌和化学成分的涂层技术将被研究：1)氧化合成，通过与气体环境反应生长涂层，生成粗糙的微晶；2)Sol-Gel工艺，即氧化合成的粗糙涂层将被涂上具有低极性表面自由能的陶瓷(稀土氧化物)，这也将是粗糙的；以及3)调幅分解，陶瓷涂层将分解，产生粗糙的涂层。影响将是广泛的，从腐蚀控制到能源生产的许多行业都可以看到。

A considerable worldwide research effort has been devoted to understanding the water spreading or repelling nature of solid surfaces (wettability). Early research in textiles and mineral processing identified surface roughness and chemistry as the only variables responsible for wetting behavior, and a plethora of processing strategies have since been attempted to produce hydrophilic and hydrophobic surfaces, coatings, and composites for applications where solid and liquid phases interact. Of the explored manufacturing techniques and materials an extreme minority, if any, are widespread, commercially viable, stable, or durable. The lack of success in achieving stability and durability has been due to the predominant use of polymers; polymers are soft, wear intolerant, susceptible to morphological changes under low to moderate heat and stress, and are not entirely chemically or light resistant. The shortcomings of current materials strategies will be addressed in this project through the coating of metallic substrates with ceramic materials (e.g., oxides, sulfides, nitrides, and carbides) for applications ranging from corrosion protection, steam generation and coatings for enhanced boiling heat transfer. * This proposal will investigate and focus on the materials design, coating architecture, processing, and characterization of ceramic coatings on metallic substrates. Ceramic coatings have the potential to be harder, inert, stable, and durable with an appropriate manufacturing such as oxidation synthesis (heating a metal in laboratory air). The long-term engineering vision for this project is to discover a process whereby ceramic coatings can be manufactured in situ on a metallic surface in a self-organized fashion with inherent capability to tune their wettability through well-identified and controlled process variables. * The research team (HQP) will be trained in and study, generation and dissemination of knowledge concerning the fundamental materials science and engineering challenges associated with creating ceramic coatings on metallic substrates. The three main program objectives are: *1) design, fabricate, and assess hierarchical roughness architectures for hydrophilic and hydrophobic response (pore structure and relative volume and interconnectedness, material selection, coating method, surface chemistry, hydroxyl content, C contamination, charge distribution). A variety of materials and coating systems will be investigated at this stage chosen by thermodynamic stability and compatibility; *2) characterization, phase identification, kinetics and thermodynamics analysis of ceramic component systems suitable for modeling and prediction of materials and coating performance (crystallography, surface wettability under varying relative humidity and temperature); *3) subject materials system to high temperature and moist environments to assess and prevent, through materials, processing, and coating architecture design, any deleterious structural evolution leading to topological, or surface chemistry changes alter wettability (microscopy, roughness changes, contamination, phase separation, and associated apparent contact angle changes). * Coating techniques which can control both surface topography and chemistry will be investigated: 1) Oxidation Synthesis whereby coatings will be grown through reaction with gaseous environments to produce rough crystallites; 2) Sol-Gel Processing whereby a rough coating from oxidation synthesis will be coated with a ceramic of low polar surface free energy (rare earth oxides) which will also be rough; and 3) Spinodal Decomposition whereby ceramic coatings will decompose to produce rough coatings. Impact will be widespread and seen in many industries from corrosion control to energy production.