Characterization of CVD TiN coating at different deposition temperatures and its application in hydrocarbon pyrolysis

Abstract

In this study, titanium nitride (TiN) coatings at different deposition temperatures have been designed as anti-coking coatings during cyclohexane steam pyrolysis. The TiN coatings were deposited on 310S foils (10mm×10mm×0.9mm) between 750 and 950°C by a chemical vapor deposition (CVD) method. To evaluate the anti-coking property of TiN coatings, cyclohexane was employed for cracking in a tubular quartz reactor. The as-deposited and coked TiN coatings were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, Raman spectroscopy and X-ray diffraction. The results show that the deposition temperature has a great influence on the morphology and microstructure of CVD TiN coatings. The structures of TiN coatings with apparent differences tend to lie on (220) preferred orientation as the deposition temperature increases. When the deposition temperature is below 850°C, the TiN coatings cannot cover the substrate surface completely and some filamentous coke was observed. However, the anti-coking ratios of TiN coatings at different deposition temperatures are all above 90% during cyclohexane pyrolysis at 770°C for 1.5h. In summary, the TiN coatings at high deposition temperatures can completely cover the cracks and gaps on the rough surface of blank substrate, and thus provide a very good protective layer to prevent the substrate from metal dusting and severe coking. Moreover, the Raman spectra show that the dust-like coke on the surface of TiN coatings has a higher degree of graphitization than the filamentous coke on 310S substrate, which also proves the good anti-coking performance of TiN coatings.