Fabrication of bulk magnetic composite materials consisting of controlled nano-structures

为了开发高饱和磁化密度和高磁导率的高频电用块状磁性材料，尝试在Fe-Ni晶粒（直径~ 5μm）外包裹一层厚度~ 0.3μm的MgFe_2O_4薄层，制备了Fe-Ni /Fe-Ni合金块状纳米复合材料，前者具有较高的饱和磁化密度，后者具有较高的电阻率。第一阶段，研究了MgFe_2O_4的最佳化学组成。采用常规固相反应和溶胶-凝胶法制备了Mg(Fe_<1-x>Mn_x)_2O_4固溶体铁氧体，并对其磁性能进行了精确测定；X =0.2的组合给出了最好的数据。第二阶段，在1200 ~ 1350℃的空气中，评价了Mg(Fe_<1-x>Mn_x)_2O_4铁氧体的塑性变形。最后采用高压烧结两种粉末：复合粉末I和复合粉末II制备了MgFe_2O_4/Fe-Ni合金体状复合材料。前者的准备如下：在600°和700℃的不同氧分压下，对MgO颗粒包覆的Fe-Ni粉末进行热处理。后者是细小的MgO+a-Fe_2O_3混合粉末颗粒包覆Fe-Ni粉末。对于复合粉末，试验了两种烧结工艺；即脉冲电流压力烧结PECPS（800℃/30MPa/3min）或HIP（950°-1250℃/196MPa/2h）。XRD和SEM相鉴定表明，复合粉末ⅱ、PECPS和再氧化处理可获得由尖晶石MgFe_2O_4和Fe-Ni合金两相组成的致密微观结构。而在烧结过程中，由于气氛的高度还原，除了Fe-Ni外，还形成了Mg_<1-x>Fe_xO和FeO的Wusteit相。结果表明，两相复合材料在室温下具有良好的磁性能：饱和磁化密度B_s为1.20 T， 1 MHz时磁导率μ ~ 15 ~ 30，居里点在460℃以上。少

With aiming at developing new bulk magnetic materials having both high saturation magnetization density and high magnetic permeability for high-frequency electric applications, fabrication of MgFe_2O_4/Fe-Ni alloy bulk nano-composites, in which Fe-Ni grains (〜5μm in diameter) are fully surrounded with thin MgFe_2O_4layer (〜0.3μm in thick), has been tried: the former metal grains have high saturation magnetization density and the latter has high electric resistivity.The first stage, the best chemical compositions of MgFe_2O_4 have been investigated. Mg(Fe_<1-x>Mn_x)_2O_4 solid solution ferrites were prepared using both conventional solid reactions and sol-gel process, and their magnetic properties were measured precisely ; x=0.2 composition gave the best data. The second stage, plastic deformation of Mg(Fe_<1-x>Mn_x)_2O_4 ferrites were evaluated at temperature 1200 to 1350℃ in air.Finally MgFe_2O_4/Fe-Ni alloy bulk composites has been tried by adopting high-pressure sintering two powder … More s: Composite Powder I and Composite Powder II . The former was prepared as follows; fine MgO particle-coated Fe-Ni powders were heat-treated under various oxygen partial pressures at 600°and 700℃. The latter was fine MgO+a-Fe_2O_3 mixed powder particles-coated Fe-Ni powders. For the composite powders, two sintering processes were tried; i.e., pulsed-electric current pressure sintering PECPS (800℃/30MPa/3min) or HIP (950°-1250℃/196MPa/2h). Phase identification by XRD and SEM observation revealed that dense microstructure consisting of two phases (spinel MgFe_2O_4 and Fe-Ni alloy) was attained from the combination of composite powders II, PECPS and a re-oxidation process. However, other process resulted in formation of Wusteit phase of Mg_<1-x>Fe_xO and FeO in addition to Fe-Ni due to highly reductive atmosphere during the sintering. Thus obtained composite materials consisting two phases showed good magnetic properties at room temperature as expected from their compositions and microstructures: saturation magnetization density B_s of 1.20 T, and permeabilityμ〜15-30 at 1 MHz, and a Curie point above 460℃. Less