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

• TiN/SiO 2 double-layer coating owns the excellent oxidation resistance. • Durability is evaluated from three aspects: surface roughness, bonding force and coking inhibition performance. • TiN/SiO 2 coating maintains great reusability and anti-coking ratio being up to 92% during repeated use. • The superiority of TiN/SiO 2 coating results from the isolation of outer layer and the buffering of inner layer. 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/SiO 2 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/SiO 2 coatings. The outer amorphous SiO 2 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 SiO 2 . Therefore, excellent oxidation resistance, with a bearable temperature of 1000 °C, can be obtained for the TiN/SiO 2 coatings. In addition, during the coking-decoking cycles, the roughness of TiN/SiO 2 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%).