Abstract
Because calcined alpha alumina (α-Al2O3) inherits the morphology characteristic of milled precursors, it is expected that the α-Al2O3 morphology could be improved by controlling the precursor morphology through the use of different milling processes. The microstructure evolution of the boehmite precursor under different milling treatments (planetary ball milling [PBM] and high-energy ball milling [HEBM]) and its influence on the microstructure of as-synthesized α-Al2O3 were investigated. The experimental results indicate that HEBM has a stronger modification effect in crystallinity, particle size and dispersibility of the boehmite precursor than PBM, which is of great importance to inhibit the formation of the typical worm-like structure of α-Al2O3. The microstructure of α-Al2O3 was further improved by the introduction of NH4BF4, NH4F and NH4Cl as additives. In particular, polygon-like α-Al2O3 particles with a size of 0.5 μm and a good dispersibility were prepared by calcination of the precursor with 30 h of HEBM and 20 wt.% NH4BF4.
Experimental Measurement of Temperature Gradient during Bone Drilling in Cameroon, Sub-Sahara Africa
