Particle Size Comparison of Soft-Chemically Prepared Transition Metal (Co, Ni, Cu, Zn) Aluminate Spinels

Nanocrystalline MAl₂O₄ (M=Co, Ni, Cu, Zn) spinel powders are synthesized by pyrolysis of complex compounds of aluminum and transition metal (cobalt, nickel, copper, and zinc) with triethanolamine (TEA). The precursor materials are formed on complete dehydration of the soluble complexes of aluminum–TEA and transition metal–TEA (Co, Ni, Cu, Zn), maintaining the resulting pH of each of the solutions at 4–5. The precursors are heat treated at different temperatures to provide phase formations. Single-phase MAl₂O₄ spinel powders were obtained after heat treatment of the precursor material at 600°C, but for CuAl₂O₄, the precursor passed through an intermediate-phase CuO at a lower treatment temperature. The precursor and the heat-treated powders were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectrometry, thermal gravimetric and differential thermal analysis, and transmission electron microscopy (TEM); the surface area was measured by a Brunauer–Emmet–Teller (BET) adsorption isotherm. The average particle sizes that were obtained from XRD, TEM, and BET adsorption isotherm were compared.