The Preparation of Blue CoAl₂O₄ Powders by the Malonate Method: The Effect of the Amount of Malonic Acid Used, the Formation Pathway of CoAl₂O₄ Crystallites and the Characteristics of the Prepared Powders

The Preparation of Blue CoAl₂O₄ Powders by the Malonate Method: The Effect of the Amount of Malonic Acid Used, the Formation Pathway of CoAl₂O₄ Crystallites and the Characteristics of the Prepared Powders

A pathway for the formation of normal $CoAl_2O_4$ particles is suggested. The optimal amount of malonic acid was determined, and the characteristics of the obtained powders were investigated. Normal $CoAl_2O_4$ powders were prepared using solutions of malonic acid and metal nitrates. X-ray diffraction, Brunauer-Emmett-Teller (BET) and scanning electron microscope (SEM) measurements, as well as Fourier transform infrared (FTIR) and ultraviolet/visible (UV-Vis) spectroscopy were carried out. Normal $CoAl_2O_4$ crystallites were formed by a solid state reaction between $CoAl_2O_4$ and amorphous aluminum oxide. The optimal molar ratio of malonic acid to the nitrate anions present in the initial solution was found to be 0.30~0.35. The particles were composed of agglomerates of primary particles. The primary particles were 40 nm in size. This size was relatively constant regardless of the preparation temperature. However, the size of the agglomerated particles increased to 220 nm with increasing temperature.