Microwave sintering of nanometer and micrometer ferrite powders

Two ferrite powders, one nanometre and one micrometre-sized, have been proc essed into small pellets using two different green forming routes, viz, die pressing and slip casting. Prior to forming using slip casting the powders were dispersed into water using a range of surfactants and then wet ground in an attempt to reduce the presence of agglomerates in the as-received po wder. The pellets were subsequently microwave sintered using a TE102 single mode applicator operating at 2.45 GHz. The die pressed samples produced fr om the nanometre-sized powder displayed microstructures that were increasin gly duplex in nature as the sintering temperature increased. This was belie ved to arise from the highly agglomerated nature of the as-received powder. When a wet grinding route was introduced followed by slip casting to preve nt reagglomeration of the powder, the number of agglomerates was very signi ficantly reduced and a largely submicron microstructure was achieved. Unfor tunately, most of the slip cast pellets suffered from cracking during the s intering process indicating the presence of stresses in the green bodies pr oduced. Nevertheless, the results achieved suggest that it is possible to m icrowave sinter nanometre powder compacts without suffering major grain gro wth provided the initial powder is not agglomerated.