Chemical Vapor Deposition of Aluminosilicates from Mixtures of SiCl[sub 4], AlCl[sub 3], CO[sub 2], and H[sub 2]

Abstract

A comprehensive study of the chemical vapor codeposition of silica, alumina, and aluminosilicates from SiCl 4 -AlCl 3 -H 2 -CO 2 mixtures is presented. A hot-wall reactor, coupled to an electronic microbalance, is used to investigate the dependence of the deposition rate on temperature, pressure, composition, and total flow rate over a broad range of operating conditions. The experimental observations are discussed in the context of the results obtained in independent deposition experiments of silica and alumina from mixtures of SiCl 4 -H 2 -CO 2 and AlCl 3 -H 2 -CO 2 , respectively, in the same apparatus. The results show that the deposition of silica proceeds at very low rates that are by more than an order of magnitude lower than those of alumina deposition at the same temperature, pressure, total flow rate, and carbon dioxide and chloride mole fractions in the feed. When both chlorides (SiCl 4 and AlCl 3 ) are fed to the reactor, that is, in the codeposition process, the rate of SiO 2 deposition is much higher than that seen in the single species deposition experiments, while the opposite behavior is observed for the rate of deposition of Al 2 O 3 . The results of deposition experiments conducted on refractory wires, in order to obtain information on the effect of the substrate position in the reactor, show that manipulation of residence time offers a way to control the composition of the codeposited films in alumina and silica. The experimental results are compared with those obtained in a past study using methyltrichlorosilane as silicon source.

Functionally Graded Alumina/Mullite Coatings for Protection of Silicon Carbide Ceramic Components From Corrosion

“…A region of rather weak variation of the deposition rate precedes the maximum in the case of MTS, and therefore, it may be possible to have a situation where the deposition rate does not change significantly over the length of the reactor. As we will see in the following section, the differences in the rates of silica deposition from MTS and SiCl 4 are in agreement with the experimental results [1,66].…”

“…A hot wall, tubular chemical vapor deposition reactor has been used in our laboratory to obtain the experimental data [1,58] that we will use to validate the predictions of the kinetic model that we formulated in the preceding sections. The diameter of this reactor is much smaller than its length, and thus, a plug-flow reactor [59] will be used to model it.…”

“…Some of these results were presented in [1,66], and information is provided there on the experimental arrangement and the procedures used in the experiments. Experiments were carried out using SiCl 4 or MTS in the feed, and deposition rate data were measured by using gravimetric monitoring of the deposition rate on small substrates or by determining the deposition rate profile on thin refractory wires traversing the axis of the tubular reactor.…”

Deposition of Compositionally Graded Mullite/Alumina Coatings from Mixtures of SiCl4, AlCl3, CO2 and H2

“…[18] Further studies revealed that manipulation of the temperature and pressure, and of the residence time of the mixture in the reactor, offered a way of controlling the composition of Al 2 O 3 and SiO 2 in the codeposited films, and shifting the composition towards alumina. [19] The content of the Al 2 O 3 in the deposit was found to increase with decreasing system pressure, increasing temperature, and operation at locations close to the entrance of the reactor.…”

“…A hot-wall CVD reactor of tubular configuration was used for the preparation of the coatings. The results of previous experimental studies on the preparation of aluminosilicate and mullite coatings [18,19] were employed to identify operating conditions under which the deposition of coatings with an Al 2 O 3 content equal to or greater than that corresponding to stoichiometric mullite had proved to be feasible. The development of the graded coatings exploits a key finding of our previous study, [19] viz., a decrease in residence time of the reactive mixture in the reactor has a positive effect on the incorporation of Al 2 O 3 in the deposit.…”