Combustion CVD of magnesium spinel and nickel spinel

Combustion chemical vapor deposition (combustion CVD) is being developed to deposit magnesium spinel, MgAl2O3, and nickel spinel, NiAl2O4, onto silica substrates. A possible use of the magnesium spinel is as an overlayer on thermal barrier coatings (TBCs) used in the hot sections of gas turbines. The deposition of nickel spinel is being developed to explore its role in the thermomechanical spallation of TBCs. Combustion CVD uses a flame to provide the heat for I:he chemical reactions and the medium for the deposition of the ceramic film. Combustion CVD is performed in the open atmosphere and requires relatively little capital investment compared to conventional CVD processes. Precursors of Mg naphthenate and Al acetylacetonate dissolved in toluene were used to successfully deposit MgAl2O4 with the face centered cubic spinel crystal lattice. Ni acetylacetonate and Al acetylacetonase, dissolved in toluene, were used to deposit NiAl2O4, with the face centered cubic spinel crystal lattice. Total metal ion concentrations in the flammable solutions ranged from 0.002 to 0.004 M. Flame temperatures at the surface of the substrate during deposition were approximately 1100 degrees C. Dense, nodular films up to 1 mu m thick were produced at deposition rates of 1.2 to 2.0 mu m/h. Transmission electron microscopy (TEM) dark-field imaging indicates that projected grain sizes range from 8 nm to 88 nm. Electron diffraction performed with TEM verifies the spinel crystal structure and quantitative EDS shows weight percents of the constituent elements close to the stoichiometric values. (C) 1997 Elsevier Science S.A.