Fly ash cenospheres coatings by EPD-microwave sintering process for SiC corrosion resistance

摘要

Fly ash cenospheres coatings are a promising material in improving the oxidation and corrosion resistance of SiC. In this work, fly ash cenospheres coatings were deposited on SiC substrates by electrophoretic deposition process at 500 V during 30 seconds, 1, 2 and 3 minutes. These coatings were characterized by SEM to observe the surface morphology. The coatings were sintered at 1000, 1100 and 1200°C during 3 hours by microwave heating. After sintering, the coatings were characterized by XRD. Cross sections of the substrate/coating samples were analyzed by SEM/EDS. The coatings with the best deposition and sintering conditions were evaluated by oxidation and hot corrosion resistance tests. The oxidation test was performed in air at temperatures from 1000 to 1300°C during 100 hours. In addition, fly ash cenospheres coatings on SiC and uncoated SiC substrates were subjected to a hot corrosion test at 1000°C during 100 hours in Na_2SO_4. The coatings showed good adhesion after sintering; the main phases of the coating were mullite and SiO_2. The uncoated substrates were found to gain weight due to the formation of SiO_2 at the surface. In contrast, SiC samples coated with fly ash cenospheres showed no weight gain and exhibited no signs of cracking or spallation following the oxidation tests. After the high temperature corrosion test in Na_2SO_4, the uncoated SiC showed signs of oxidation and corrosion while the coated remained unreacted in the presence of molten Na_2SO_4, indicating that the electrophoretic deposition fly ash cenospheres acted as a hot corrosion barrier for SiC substrates.