Preparation Of ?-Al₂O₃ Coating On FeCrAl Substrates

Monolithic catalysts are becoming widely used in industry in recent decades because of their advantages such as low pressure drop and efficient mass transfer. The preparation of the coating on monolithic structure is the key technology in terms of monolithic catalyst application. In the present work, with the method of high temperature oxidation, ?-Al₂O₃ coatings were deposited on the FeCrAl substrates by sol-gel method, slurry method and in situ growth method. The morphology, crystal structure, texture property of coatings as well as the adhesion of coatings to FeCrAl substrates were investigated by SEM, XRD, BET and ultrasonic vibration.?1? FeCrAl substrates were washed by acid and alkali and then pre-oxidized at 950? for 10 h. A large number of alumina whiskers were formed on the surfaces which increased specific surfaces area and surface roughness. The alumina whisker layer are beneficial for the adhesion of coatings to substrates.?2? The sol coatings are smooth, dense, uniform and crack-free when the loading is below 3 wt.%. The sol coatings have good adhesion to FeCrAl substrates even with the presence of cracks with the loading range of 3-8 wt.%. However, spallation from the substrate is observed on the sol coatings when the loading is higher than 8 wt.%. As a result, sol coatings are more suitable as a catalyst support in monolithic catalyst due to its higher specific surface area, pore volume and better adhesion to substrates when relatively low catalyst loading is required.?3? It is suggested that no crack-free slurry coatings can be deposited on the FeCrAl substrates. With an increase of the slurry loading, the cracks on the surfaces of coatings become stronger and the adhesion become weaker. However, no spallation from the substrate is observed on the slurry coatings when the loading is higher than 8 wt.%. So slurry coatings can be applicable as a catalyst support when higher catalyst loading is needed.?4? A highly opened cluster structure ?-Al₂O₃ layer with thickness of 9-10?m was successfully synthesized via a two-step solvothermal route. Furthermore the formation mechanism of ?-Al₂O₃ layers was proposed. The first step process is essential to form a dense, uniform and continuous layer. However, the adhesion of the layer to the substrate needs to be improved. The process sheds a new light on preparing alumina layer on the metal substrate.