The novel low temperature synthesis of nanocrystalline MgAl2O4 spinel using “gel” precursors

Nanocrystalline MgA12O4 was synthesized by pyrolysis of the homogeneous spinel precursor, Mg(C4H5O2)2·(H2O):Al2(OH)3(C3H3O2)3·(H2O)2:NH4(C3H3O2)·(H2O). The spinel precursor gel is composed of a mixture of magnesium and aluminum acrylate salts dissolved in an ammonium acrylate gel. The reaction of acrylic acid with magnesium hydroxide in water produced magnesium methacrylate, and a similar reaction of basic aluminum acetate produced the aluminum salt of acrylic acid. The reaction of acrylic acid with ammonium hydroxide produced the ammonium acrylate gel. Ammonium acrylate gel was found to absorb many times its own weight of water. Although similar properties have been identified in PMMA and in the polymer of sodium acrylate, only the ammonium acrylate gel exists as an unpolymerized monomer. The spinel precursor gel is a pre-ceramic material that yields an amorphous oxide phase at 425°C that begins to crystallize to the MgAl2O4 spinel at 600°C and is fully crysta1line at 1030°C with a uniform particle size of 7–100 nm. The spinel precursor gel and the nanocrystalline MgA12O4 spinel were characterized by XRD and TEM.