Mechanochemical Synthesis Of Ultrafineα-Al₂O₃Particles

Alumina is an important ceramic material with many excellent properties, and it can be widely used in the fields of electronics, metallurgy, high temperature ceramics, cutting tool, composite materials and bio-medical material et al due to its high melting point, high hardness, high electrical resistivity, high corrosion-resistance, good biocompatibility and catalytic activity. Nanoceramic has recently received great attention due to their improved functional and mechanical properties. Ultrafine and monodispersed α-Al2O3particles must be synthesized in order to get alumina nanoceramic. Using cheap Fe2O3and Al as raw materials, ultrafine α-Al2O3nanopowders with good dispersivity were prepared by high energy ball milling. The influence of milling speed, milling time and the mole ratios of Fe2O3to Al on the particle size and agglomeration degree of αa-AlO3were investigated. Then, Fe serving as isolating phase was added to the as-milled products of Fe2O3and aluminum for20h. The influence of the volume ratios of α-AlO3to Fe on the particle size and agglomeration degree of α-Al2O3was studied.It is found that ultrafine α-Al2O3nanopowders with good dispersivity can be prepared when the stoichiometrical mixture of Fe2O3and Al milled at the revolution speed of300rpm for20h. The particle size and dispersivity of α-Al2O3can be controlled by changing milling speed, milling time and mole ratios of Fe2O3to Al. The reaction begins at70min and finishes at2h when milled at the revolution speed of250rpm. As the milling time increases from70min to4h, the average crystallite size of α-Al2O3reduces from125nm to30nm. When the milling time increases to10h, the average crystallite size of α-Al2O3reduces to22nm. However, the particle size distribution is wide and the agglomeration of the powders is serious. The influence of the mole ratios of Fe2O3to Al on experimental results was also studied. α-Al2O3and γ-Al2O3was prepared when Fe2O3is excess and the particle size of the α-Al2O3is large. Only α-Al2O3was prepared when Al is excess and the particle size of the α-Al2O3reduces. The average crystallite size of α-Al2O3reduces as the increasing of the milling speed. When the revolution speed increases to300rpm, the average crystallite size of α-Al2O3reduces to17nm and the average particle size reduces to16nm.When Fe was added to the samples milled at the revolution speed of250rpm for20h, the average crystallite size of α-Al2O3reduces to18nm. The particle size decreases first and then generates aggregates as the increasing of the volume faction of Fe. When the volume ratio of Fe to α-Al2O3is3:2, the average crystallite size of α-Al2O3with better dispersivity is14nm and the average particle size is16nm after the different centrifugation speeds. The average crystallite size of alumina ceramics plate sintered at1450℃for5h is280nm, and the crystallite size distribution is from60nm to500nm. The agglomeration of powders is serious when the volume ratio of Fe to α-Al2O3is3:2milled at the revolution speed of300rpm for20h.