Wentao Hu,Xi'an Fan,Zigui Luo,Fan Luo,Guangqiang Li,Jian Wang
In this work, Fe/ZnO soft magnetic composite (SMC) is prepared successfully by sol-gel method combined with a pyrolysis process. Formation mechanism and effect of annealing on magnetic properties for the Fe/ZnO SMCs are studied in detail. The results show that Fe/zinc acetate hydrogel mixture will be decomposed into the Fe/ZnO composites by heating above 340 °C. And ZnO is well coated on the surfaces of Fe particles. The Fe/ZnO composite compact has lower total core loss and better frequency stability of magnetic permeability compared with pure Fe compact. In addition, annealing treatment shows an enhanced effect on the magnetic properties for the Fe/ZnO composite compact such as reduced coercivity and increased permeability. The annealed Fe/ZnO SMCs can keep stable magnetic permeability (26) from 50 Hz to 10 kHz, high magnetic induction (1.65 T) and a relatively low core loss of 91.11 kW/m 3 measured under a magnetic flux density of 30 mT at 10 kHz. Therefore, the Fe/ZnO soft magnetic composites prepared by the above-mentioned method provide a great potential application in electromagnetic conversion equipment.
A simple and efficient method was developed to prepare a copper–carbon (Cu–C) catalyst with high oxygen reduction reaction (ORR) activity via direct pyrolysis of a mixture of metal salts (Cu(NO3)2·3H2O and Zn(CH3COO)2) and 1,3,5-benzenetricarbocylic acid at 1010 °C under a N2 stream. It is found that the Cu–C catalyst exhibits superior catalytic activity toward ORR with a half-wave potential of 0.81 V and a four-electron transfer pathway in 0.1 M KOH electrolyte. Generally, it is known that N plays an important role for the high ORR catalytic activities of nonprecious metal-doped carbon materials. Herein, we demonstrate that N is not required for the superior catalytic activity of Cu–C materials. Both the Cu particles and the embedded Cu atoms in the carbon substrate are suggested to provide the ORR active sites. In addition, despite the fact that the Zn is removed during the pyrolysis, the adding of Zn salt in the precursor is important for the enhanced catalytic activity. The evaporation of Zn during the pyrolysis results in the large surface area of the catalyst, which is beneficial to the mass transfer during the catalytic process. Moreover, a large number of carbon defects can be created via the removal of Zn atoms that facilitated the ORR.
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