Self-Organized Hierarchically Rough Ceramic Coatings

在了解固体表面的水扩散或排斥特性（润湿性）方面，世界范围内进行了大量的研究。纺织品和矿物加工的早期研究确定表面粗糙度和化学是负责润湿行为的唯一变量，并且已经尝试了大量的加工策略来生产亲水和疏水表面，涂层和复合材料，用于固相和液相相互作用的应用。在探索的制造技术和材料中，如果有的话，也只有极少数是广泛的、商业上可行的、稳定的或耐用的。由于主要使用聚合物，在实现稳定性和耐久性方面缺乏成功；聚合物是柔软的，不耐磨损的，在低到中等的热和应力下易受形态变化的影响，并且不完全耐化学或耐光。当前材料策略的缺点将在这个项目中通过用陶瓷材料（例如，氧化物，硫化物，氮化物和碳化物）涂层金属基板来解决，应用范围从防腐，蒸汽产生和涂层增强沸腾传热。

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.