Browsing by Author "Kang, Min"

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    Alkali/steam corrosion resistance of commercial SiC products coated with sol-gel deposited Mg-doped Al₂TiO₅ and CMZP
    Kang, Min (Virginia Tech, 1994-05-05)
    The corrosion resistance of two commercially available SiC filter materials coated with Mg-doped Al₂ TiO₅ and (Ca 0.6.6' Mg0.52) Zr₄P₆O₂₄ (CMZP) was investigated in high-temperature high pressure (HTHP) alkali-steam environments. Coated specimen properties, including cold and hot compressive strengths, bulk density, apparent porosity, permeability, and weight change, detected after exposure to 92% air-S% steam 10 ppm Na at 8OO°C and 1.8 MPs for 500 h were compared with those of uncoated specimens. Procedures for applying homogeneous coatings of Mg-doped Al₂ TiO₅ and CMZP to porous SiC filters were established and coating of the materials was successfully accomplished. Efforts to stabilize the Al₂ TiO₅ coating composition at elevated temperature were successful. Coatings show promise for providing improved corrosion resistance of the materials in pressurized fluidized bed combustion (PFBC) environments as evidenced by higher compressive strengths exhibited by coated SiC specimens than by uncoated SiC specimens following HTHP alkali-steam exposure.
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    Magnesium doped .beta.-aluminum titanate thin film coating
    (United States Patent and Trademark Office, 1996-10-15)
    Mg.sub.x Al.sub.2-2x Ti.sub.1+x O.sub.5 (x.ltoreq.0.2) protective coatings have been developed for both dense and porous substrates, such as SiC and Si.sub.3 N.sub.4, using a chemical solution processing method involving the hydrolysis and condensation of magnesium, aluminum and titanium precursors. The solution viscosities, pH values, H.sub.2 O/alkoxide molar ratios, and dip coating withdrawal rates which are optimum for crack-free Mg.sub.x Al.sub.2-2x Ti.sub.1+x O.sub.5 (x.ltoreq.0.2) are 1.0 to 6.2 cP, pH 1-4.5, molar ratio 1.5-10, and withdrawal rate of 2.2-8.0 cm/min, respectively. Conversion of the amorphous coating to crystalline Mg.sub.x Al.sub.2-2x Ti.sub.1+x O.sub.5 (x.ltoreq.0.2) is achieved by a succession of calcination below 450.degree. C. and a final heat treatment above 1000.degree. C. for ten hours with controlled heating and cooling rates.