Effect of nano-TiO2 and nano-SiO2 addition on the morphological control of α-Al2O3 platelets via solid-state reaction

Controlling the morphology of α-Al2O3 plate-like powders is essential, asmulti-morphological α-Al2O3 platelets are needed in various applications. The α-Al2O3 platelets investigated in this work, were prepared via conventional solid-state reaction using gibbsite and pseudo-boehmite as the starting materials; nano-TiO2, nano-SiO2, silica gel, and the mixtures of nano-SiO2 and nano-TiO2 were used as morphology modifiers during the synthesis. The effect of the type and amount of modifiers used, on the morphology of the platelets was determined via scanning electron microscopy, X-ray diffraction, and measurements of the specific surface area. The results indicated that nano-TiO2 resulted in small and thick platelets. In fact, nano-TiO2 led to increased crystallinity and accelerated phase transformation to α-Al2O3, and additions of ≥2.00 wt% resulted in severe aggregation of the α-Al2O3 particles. Conversely, addition of nano-SiO2 led to significant increases in the diameter and reductions in the thickness of the α-Al2O3 platelets; for equal additions, liquid silica gel, which has excellent mobility, was more effective in controlling the morphology than solid SiO2. Additions of up to 1.00 wt% of the nano-SiO2 resulted in an incomplete α phase transformation, owing to SiO2 inhibition of the transformation to α-Al2O3. Moreover, simultaneous additions of nano-TiO2 and nano-SiO2 led to competing effects on the morphology of the α-Al2O3 particles, as evidenced by changes in the specific surface area.