Combustion Synthesized Porous Body of Fe_3O_4/Al System by Controlled Microwave Heating and Heating Behavior of the Products

Microwave-induced substitutional combustion reaction was utilized to fabricate porous ceramic composite from Fe_3O_4/Al powder mixtures.The porous composite body was obtained by controlling the combustion reaction progress in a 2.45 GHz single mode applicator.Prior to the fabrication of the porous body,heating behavior of the powder mixtures were studied in the separated electric(E)and magnetic(H)fields.In addition,heating ability of the microwave fabricated porous product was also investigated.Fe_3O_4 powder can be heated up easily in both maximum H and E field, but a better heating was observed in the maximum H field.Regardless of the mixtures ratio(mixing compositions), maximum H field shows better heating characteristics.In E-field heating,temperature of the Fe_3O_4 samples decreased sharply when Al powder was added.However,the same phenomenon was not observed in the maximum H field heating. Thus,fabrication of the porous composite body was carrying out in maximum H field.Through an adequate control of the reaction progress,products with a porous structure consisting of well-distributed metal particles in the alumina and/or hercynite matrix were obtained.Consequently,heating of the fabricated porous composite body was also been successfully carried out in the maximum H field.Product phases and microstructure were the main factors influencing the heating ability of the porous composite body.

Improvement of Heat Generation Ability in AC Magnetic Field and Magnetic Properties for Spinel Type MgFe_2O_4 Ferrite by Cu Substitution and Beads Milling

Mg_(1-X)Cu_XFe_2O_4 type spinel ferrite was prepared by solid reaction method in order to discuss the heat generation ability in AC magnetic field.The cubic type ferrite structure was obtained for X=0-0.6 samples calcined at 1200℃,and the mixture phase of cubic and tetragonal structures were obtained for X=0.7,0.8 samples from XRD result. The highest lattice parameter and highest hysteresis loss value were also shown at X=0.6 sample,the crystal distortion was increased with increase the Cu^(2+)substitution in cubic type ferrite structure.The sized nano Mg_(0.4)Cu_(0.6)Fe_2O_4 powder was prepared by physical milling method using beads milling.The highest heat generation in the AC magnetic field was obtained for the 6 h milled samples using 0.1mm beads.The Cu^(2+)substitution for MgFe_2O_4 ferrite and the beads milling were very effective for the improvement of their heat generation ability in AC magnetic field.

Direct TEM Observation of Phase Separation and Crystallization in Cu_(45)Zr_(45)Ag_(10)Metallic Glass

The structural evolution of Cu_（45）Zr_（45）Ag_（10） metallic glass was investigated by in situ transmission electron microscopy heating experiments. The relationship between phase separation and crystallization was elucidated. Nucleation and growth-controlled nanoscale phase separation at early stage were seen to impede nanocrystallization, while a coarser phase separation via aggregation of Ag-rich nanospheres was found to promote the precipitation of Cu-rich nanocrystals.Coupling of composition and dynamics heterogeneities was supposed to play a key role during phase separation preceding crystallization.