Chromium Carbide Growth by Direct Liquid Injection Chemical Vapor Deposition in Long and Narrow Tubes, Experiments, Modeling and Simulation

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 N 2 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 CrC x 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 × 10 2 to 7 × 10 3 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 Cr 7 C 3 and Cr 3 C 2. The model was 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.

Evidence for a Cr metastable phase as a tracer in DLI-MOCVD chromium hard coatings usable in high temperature environment

“…Numerical modeling (not reported here) showed for our DLI-MOCVD reactor that when the temperature of the furnace is set to 723 K, the substrate temperature was approximately 50 K lower, i.e. around 673 K. This temperature decrease comes from of the presence of a cold finger at the entrance of the reactor over several centimeters in the axial direction [33]. This is due to the lower temperature of the reactive gas phase (approximately 473 K) coming from the flash vaporization chamber which enters the reactor.…”

Chromium carbide growth at low temperature by a highly efficient DLI-MOCVD process in effluent recycling mode

“…modeling and simulation of the process. It is based on site competition reactions [31]. The lower concentration of recycled BEBC solutions would induce a lower supersaturation of BEBC near the growing surface.…”

“…They were placed on a planar horizontal sample-holder in the isothermal zone. More details are reported elsewhere [31]. The total pressure was automatically monitored and kept constant at 6.7 kPa and deposition temperature was set at 723 K.…”

“…Our greater knowledge of the growth mechanisms of Cr-based coatings [24,29], thermodynamic modeling without [29] and with direct liquid injection (DLI) to feed the reactor [30], the determination of a kinetic model and the simulation of the CVD process [31] led us to study the effect of direct recycling of effluents on the quality of chromium carbide (Cr x C y ) coatings grown by DLICVD using bis(ethylbenzene)chromium(0) as representative of this family. The results are compared with those obtained using a non-recycled solution of precursor.…”

Scale up of a DLI-MOCVD process for the internal treatment of a batch of 16 nuclear fuel cladding segments with a CrCx protective coating

“…In fact, simulating the coating deposition guides us towards several potential solutions for these last two points. Indeed, we were able to demonstrate the possibility in two steps to successively and alternatively inject the reactive gas phase at each end of the cladding segment to achieve a good compromise be tween both thickness uniformity and average thickness of coatings grown at 673 K [30]. However, for an industrial development, the op timization of the deposition conditions in only one step is preferred to simplify the process, which is precisely the aim of this paper.…”