TiN-SiO2 double layer composite coating with enhanced oxidation resistance and reusability in anti-coking applications

Abstract

The passivation coating has been the main solution to the coking problem in the field of active cooling technology and ethylene cracking furnace. The need for repeated use and essential decoking process poses a great challenge to the single-layer coating. Herein, a new TiN/SiO2 double-layer coating suitable for internal channels has been prepared and characterized, whose results are compared with single-layer TiN coating. The oxidation resistance was revealed by HT-XRD and TGA. The reusability was analyzed from surface roughness, bonding force and coking inhibition performance in the repeated use of the coking-decoking cycle (RP-3 supercritical pyrolysis, on-line decoking technology). Results reveal the synergistic effect of the inner and outer layers of TiN/SiO2 coatings. The outer amorphous SiO2 with high crystallization temperature plays the role of isolating O and C atoms from penetrating, and the inner TiN acts to reduce the mismatch of thermal expansion coefficient between substrate and SiO2. Therefore, excellent oxidation resistance, with a bearable temperature of 1000 °C, can be obtained for the TiN/SiO2 coatings. In addition, during the coking-decoking cycles, the roughness of TiN/SiO2 coatings has been maintained at a low level; the coating has been tightly adhered to the substrate throughout the process; and the coking resistance has not been weakened with an average anti-coking ratio of 93%, higher than that of TiN (31–67%).