Abstract
Chromium carbide layers were deposited using liquid-injection metal-organic chemical vapor deposition inside long (0.3 to 1 m) and narrow (8 to 24 mm in diameter) metallic tubes. The deposition was carried out using a molecular single-source, bis(benzene)chromium (BBC), as representative of the bis(arene)metal family diluted in toluene and injected with N2 as carrier gas. A multicomponent mass transport model for the simulation of the coupled fluid flow, heat transfer and chemistry was built. The kinetic mechanism of the growth of CrCx films was developed with the help of large-scale experiments to study the depletion of the precursors along the inner wall of the tube. The model fits well in the 400–550 !C temperature range and in the 1.3 ⇥ 102 to 7 ⇥ 103 Pa pressure range. The pressure is shown to have a pronounced effect on the deposition rate and thickness uniformity of the resulting coating. Below 525 !C the structure, composition and morphology of the films are not affected by changes of total pressure or deposition temperature. The coatings are amorphous and their Cr:C ratio is about 2:1, i.e., intermediate between Cr7C3 and Cr3C2. Themodelwas applied to the design of a long reactor (1 m), with a double injection successively and alternatively undertaken at each end to ensure the best uniformity with sufficient thickness. This innovative concept can be used to optimize industrial deposition processes inside long and narrow tubes and channels.
Highlights
During their working lifetime, tools and machinery components are subjected to intensive degradation due to the combination of abrasive wear, corrosion and oxidation
This paper presents the growth of CrCx thin films using a metalorganic chemical vapor deposition process (MOCVD) process coupled with direct-pulsed liquid injection (DLI) of the precursor [29]
The results presented provide robust kinetic and multicomponent transport models capable of predicting amorphous CrCx growth at a range of low temperature (400 to 550 °C) and pressures
Summary
Tools and machinery components are subjected to intensive degradation due to the combination of abrasive wear, corrosion and oxidation. BN [7,8] and W filaments with TaC [9], or for continuous deposition of functional layers on flexible substrates as Nb3 Ge [10] or more recently graphene [11] These continuous CVD processes in belt furnaces were extended to mass production of many others thin films as ZnO [12] and are even implemented for photovoltaic Si at an industrial level [13]. We have learned from the modeling and optimization of such processes that low pressure is required to improve uniformity in the axis of the tube This was demonstrated by the recent kinetic modeling of Ta CVD in long narrow channels with a high aspect ratio (AR = 500) [6]. The practical objectives are (i) to identify operating conditions leading to the growth of uniform films over the interior of long tubes and (ii) to predict the spatial distribution of gas-phase species along the tube, which is inherently difficult to probe by in situ non-intrusive techniques
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