Preparation of homogeneous super-circular alumina microspheres in microchannels by controlling extraction and motion processes

The sol–gel technique combined with microfluidics is an effective approach for the preparation of microspheres. The formation and solidification of the sol can be influenced by the motion and extraction processes. The effects of extraction and motion were investigated using a real-time moisture content test, in situ observations, and CFD simulations. The microspheres retained their homogeneous internal structure with a narrow pore distribution when the extraction rate was less than 1 × 10 −4 ml/min·mm 2 , whereas extraction rates greater than 2 × 10 −4 ml/min·mm 2 resulted in clear hollows and stacking. A continuous phase devoid of extraction capability results in an internal hierarchy and bimodal pore size. Higher surface tension (greater than 4 mN/m) and lower fluid shear forces promoted high sphericity. These novel methods offer a promising approach for the preparation of alumina microspheres with a high spherical degree of 0.987 by matching the motion and extraction curing techniques.