Effect of nano-TiO 2 and nano-SiO 2 addition on the morphological control of α-Al 2 O 3 platelets via solid-state reaction

Controlling the morphology of α-Al 2 O 3 plate-like powders is essential, asmulti-morphological α-Al 2 O 3 platelets are needed in various applications. The α-Al 2 O 3 platelets investigated in this work, were prepared via conventional solid-state reaction using gibbsite and pseudo-boehmite as the starting materials; nano-TiO 2 , nano-SiO 2 , silica gel, and the mixtures of nano-SiO 2 and nano-TiO 2 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-TiO 2 resulted in small and thick platelets. In fact, nano-TiO 2 led to increased crystallinity and accelerated phase transformation to α-Al 2 O 3 , and additions of ≥2.00 wt% resulted in severe aggregation of the α-Al 2 O 3 particles. Conversely, addition of nano-SiO 2 led to significant increases in the diameter and reductions in the thickness of the α-Al 2 O 3 platelets; for equal additions, liquid silica gel, which has excellent mobility, was more effective in controlling the morphology than solid SiO 2 . Additions of up to 1.00 wt% of the nano-SiO 2 resulted in an incomplete α phase transformation, owing to SiO 2 inhibition of the transformation to α-Al 2 O 3 . Moreover, simultaneous additions of nano-TiO 2 and nano-SiO 2 led to competing effects on the morphology of the α-Al 2 O 3 particles, as evidenced by changes in the specific surface area.