High temperature oxidation study of iron-chromium-aluminum-yttrium fibers and sol gel surface coats for protection and catalytic supports.

摘要

For the first time, a systematic study is presented to study the high temperature oxidation behavior of Fe-Cr-Al-Y fibers with diameter varying from 12 to 38 μm, which are designed for hot gas filtration.; It was found that aluminum content is critical in determining the lifetime of FeCr-Al-Y fibers at high temperatures. At temperatures less than 1000°C, Fe-Cr-Al-Y fibers suffer from fast meta-stable phases growth characteristic of intensive whisker formation, which depletes the limited aluminum reservoir in fine fibers and shortens the lifetime. Fiber size affects the alumina phase evolution behavior on the fibers. Smaller size fibers tend to form α-alumina more quickly.; Sol gel TiO₂ coating was found to be a better choice than pre-oxidation to inhibit the intensive growth of meta-stable alumina phases on the fibers at 850°C and 915°C. Whisker formation was observed to disappear completely on fibers. The scale formed on fibers was flat and much thinner with no cracks, spallation or interfacial voids. Thus, the lifetime of fibers is greatly prolonged. On the contrary, a sol gel zirconia layer was found to facilitate and retain fine whisker formation on the fibers.; A novel concept was proposed and demonstrated to use Fe-Cr-Al-Y fibers as substrate with sol gel Pd/alumina deposited by dip coating for automobile catalyst converters and diesel particulate filters. Prior to deposition, the fibers were oxidized in air in advance to get an α-alumina scale as a buffer layer. It was observed that the dip coating behavior on fibers is far different from that on normal flat substrate. Alcohol based alumina sol is more suitable than water based sol for coating Fe-Cr-Al-Y fibers. However, it is hard to make thick Pd/alumina coating on a flat scale and spallation resistance of the pre-oxidized scale is weak.; Thus, another method was employed to pre-treat the fibers. A whiskered scale was achieved by using zirconia coating followed by heat-treatment. Finer and longer whiskers were formed on the surface. Therefore, the Pd/alumina coating thickness was significantly improved and the coating adherence was also strengthened remarkably.