Microstructural properties and grinding of γ-Al₂O₃ and coal for environmental applications

The amphoteric characteristics of some metal oxides complemented by their chemical microstructures form the basis for their use for environmental engineering applications, e.g., alumina as catalyst and abrasive agents. This paper describes the microstructural properties and grinding behavior of γ-Al₂O₃ and coal particles in a batch impact mill. By grinding γ-Al₂O₃ and Hunan coal separately in an impact mill, a grinding process model of two dimensionless groups Π_1* and Π₂ is developed using Buckingham Pi theorem to obtain the desired particle morphologies. The properties established in this grinding model as key determinants of the grinding behavior are particle hardness, particle density and milling speed. The milling results confirm that γ-Al₂O₃ of the HBW 5/100 hardness 247 show higher resistance to grinding than coal of HBW hardness 28, because the final ground particle diameters d_0.9 after 30 min milling were 136.6 and 33.4 µm for γ-Al₂O₃ and coal, respectively. This grinding model is pioneering as the particle hardness contained in the dimensionless group Π_1* embodies an intrinsic material property which controls grinding and is confirmed to be in agreement with the fragmentation pattern.