FUNCTIONALLY GRADED ALUMINA/MULLITE COATINGS FOR PROTECTION OF SILICON CARBIDE CERAMIC COMPONENTS FROM CORROSION
The main objective of this research project is the formulation of processes that can be used to prepare compositionally graded alumina/mullite coatings for protection from corrosion of silicon carbide components (monolithic or composite) used or proposed to be used in coal utilization systems (e.g., combustion chamber liners, heat exchanger tubes, particulate removal filters, and turbine components) and other energy-related applications. Mullite will be employed as the inner (base) layer and the composition of the film will be continuously changed to a layer of pure alumina, which will function as the actual protective coating of the component. Chemical vapor deposition reactions of silica, alumina, and aluminosilicates (mullite) through hydrolysis of aluminum and silicon chlorides in the presence of CO{sub 2} and H{sub 2} will be employed to deposit compositionally graded films of mullite and alumina. Our studies will include the kinetic investigation of the silica, alumina, and aluminosilicate deposition processes, characterization of the composition, microstructure, surface morphology, and mechanical behavior of the prepared films, and modeling of the various deposition processes. During this six-month reporting period, we continued the work on the development and construction of the thermogravimetric chemical vapor deposition system that we intend to employ for studying the deposition of alumina, silica, and aluminosilicates (such as mullite) from mixtures of metal chlorides in H{sub 2} and CO{sub 2}. Specifically, we worked on the development of the tubular flow reactor that will be used for producing aluminum chloride for delivery to the chemical vapor deposition system and of the vapor and gas supply system. Various problems arising from condensation of aluminum chlorides in some sections of the supply line were resolved, and we expect to perform experiments using mixtures containing AlCl{sub 3} in the next reporting period. Preliminary experiments on the deposition of SiO{sub 2} from mixtures of methyltrichlorosilane (MTS) or tetrachlorosilane in H{sub 2} and CO{sub 2} were carried out, and the results showed that the deposition rates from MTS were much higher than those from SiCl{sub 4} and comparable to those reported in the literature for alumina deposition from AlC{sub 3}-H{sub 2}-CO{sub 2} mixtures of similar composition. It was thus decided to employ MTS as silicon source in our codeposition experiments, and a comprehensive investigation of thermodynamic equilibrium in the Al/Si/Cl/C/O/H system for compositions corresponding to MTS-AlCl{sub 3}-H{sub 2}-CO{sub 2} mixtures was conducted so as to identify the boundaries of the region of the space of operating parameters and conditions where preparation of functionally graded mullite/alumina coatings through CVD from metal chloride, CO{sub 2}, and H{sub 2} is feasible. The results showed that deposition of silica, alumina, mullite, and other aluminosilicates is feasible in a broad range of operating conditions from the equilibrated gas phase, but temperatures above 1148 K have to employed to obtain deposits of alumina and mullite if the solid phases are also at equilibrium with each other.
- Research Organization:
- Federal Energy Technology Center Morgantown (FETC-MGN), Morgantown, WV (United States); Federal Energy Technology Center Pittsburgh (FETC-PGH), Pittsburgh, PA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FG22-96PC96208
- OSTI ID:
- 8827
- Report Number(s):
- DE-FG22-96PC96208-02; TRN: AH200117%%262
- Resource Relation:
- Other Information: PBD: 1 Oct 1997
- Country of Publication:
- United States
- Language:
- English
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Functionally Graded Alumina/Mullite Coatings for Protection of Silicon Carbide Ceramic Components from Corrosion
FUNCTIONALY GRADED ALUMINA/MULLITE COATINGS FOR PROTECTION OF SILICON CARBIDE CERAMIC COMPONENTS FROM CORROSION