Abstract
Coating metals with anti-coking materials inhibit their catalytic coking and are especially beneficial in the pyrolysis of hydrocarbon fuels. It is believed that growth characteristics and properties may play a pivotal role in the anti-coking performance of chemical vapor deposition (CVD) coatings. In this study, TiN and TiO2 coatings were obtained by CVD using TiCl4–N2–H2 and TiCl4–H2–CO2 systems, respectively. The effects of deposition time, residence time, and partial pressure were examined, and the coating microstructure was characterized by scanning electron microscopy (SEM). The results reveal that the effect of deposition parameters on the growth characteristics of TiN and TiO2 coatings is very different. The growth of the TiN coating shows characteristics of the island growth model, while the TiO2 coating follows the layer model. In general, the growth rate of the star-shaped TiN crystals is higher than that of crystals of other shapes. For the TiO2 coating, the layer mode growth characteristics indicate that the morphology of the TiO2 coating does not change significantly with the experimental conditions. Coking tests showed that the morphology of non-catalytic cokes is not only affected by the temperature, pressure, and coking precursor, but is also closely related to the surface state of the coatings. Both TiN and TiO2 coatings can effectively prevent catalytic coking and eliminate filamentous cokes. In some cases, however, the N or O atoms in the TiN and TiO2 coatings may affect common carbon deposits formed by non-catalytic coking, such as formation of needle-like and flaky carbon deposits.
Highlights
The results reveal that the effect of deposition parameters on the growth characteristics of TiN and TiO2 coatings is very different
The formation of cokes on metallic surfaces from thermal decomposition of hydrocarbon fuels pyrolysis is a major concern in the development of hypersonic aircraft, in which the fuel serves as the propellant, and the ideal coolants to resolve the problem of thermal management by removing the waste heat from aircrafts with the physical and chemical heat sink [1,2,3]
The coating method has been used to inhibit the catalytic coking of metal, and this has been especially beneficial during the pyrolysis of hydrocarbon fuels
Summary
The formation of cokes on metallic surfaces from thermal decomposition of hydrocarbon fuels pyrolysis is a major concern in the development of hypersonic aircraft, in which the fuel serves as the propellant, and the ideal coolants to resolve the problem of thermal management by removing the waste heat from aircrafts with the physical and chemical heat sink (sensible heat-absorbing and cracking heat-absorbing) [1,2,3]. Liu et al [9] investigated a series of alumina coatings with different thicknesses (318–1280 nm) in SS321 tubes (2 mm i.d.) obtained by MOCVD using aluminum trisecondary butoxide and evaluated their anti-coking performance during the thermal cracking of Chinese RP-3 jet fuel under supercritical conditions (inlet temperature, 575 ◦ C; outlet temperature, 650 ◦ C; pressure, 5 MPa). Their results indicated that the anti-coking performance increased from 37% to 69% as the thickness of alumina coatings increased from 318 to. TiO2 anti-coking coatings, and provide guidance for designing better anti-coking coatings
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