Yttrium Aluminum Garnet Fibers from Metalloorganic Precursors

Richard Laine

Y Liu, Z.F. Zhang, J. Halloran, and RM Laine (1998)

Journal of the American Ceramic Society, 81:629-45.

Mixtures of yttrium acetate hydrate (Y(O2CCH3)34H2O) and aluminum formate hydrate (Al(O2CH)33H2O in H2O) or yttrium isobutyrate (Y[O2CCH(CH3)2]3) and aluminum isobutyrate (Al[O2CCH(CH3)2]3) in tetrahydrofuran were used as precursors to process yttrium aluminum garnet (YAG, Al5Y3O12) fibers. The pyrolytic decomposition patterns of Al(O2CH)33H2O, Y(O2CCH3)34H2O, and a [3Y(O2CCH3)34H2O/5Al(O2CH)33H2O] YAG stoichiometry mixture were assessed by heating samples to selected temperatures and characterizing the products by thermogravimetric analysis, differential thermal analysis, X‐ray diffractometry, and Fourier transform infrared spectroscopy. The YAG acetate/formate precursor decomposes to an amorphous intermediate at temperatures >400°C and crystallizes (at ∼800°C) to phase‐pure YAG with a ceramic yield of 40% at 1000°C. YAG isobutyrate precursor fibers were extruded or hand drawn. YAG acetate/formate precursor fibers were formed using a commercial extruder. The pyrolysis behavior of both precursor fibers was studied to identify the best pyrolysis conditions for producing dense, defect‐free ceramic fibers. Only thin (diameter of <30 μm) precursor fibers could be processed to dense, defect‐free, thin YAG fibers (diameter of <20 μm). For the YAG isobutyrate precursor, crack‐free crystalline YAG fibers (diameter of ∼7 μm) were obtained at 1000°C. For YAG acetate/formate precursor fibers, dwell times of 2 h at temperatures of 400° and 900°C were necessary to process fully dense, defect‐free ceramic fibers. Heating the resulting 900°C fibers (at a rate of 30°C/min) to 1570°‐1650°C gave dense fibers with grain sizes of 0.7‐3.2 μm and bend strengths of up to 1.7 ± 0.2 GPa (for fibers that had a diameter of ∼10 μm and had undergone sintering at 1600°C).

Yttrium Aluminum Garnet Fibers