Effects of SnO_2, WO_3, and ZrO_2 addition on the magnetic and mechanical properties of NiCuZn ferrites

摘要

In this study, the effects of SnO_2, WO_3 and ZrO_2 addition at levels up to 5 wt% on the magnetic and mechanical properties of Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramics were investigated. Only Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramic with a SnO_2 addition of ≥ 3.5 wt% required a densification temperature of 1150 ℃, while the others reached maximum densification at 1075 ℃. All samples revealed a pure spinel phase and a uniform microstructure, except for the Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramic with the WO_3 addition, which showed an exaggerated grain growth accompanied with a small amount of needle-shaped Cu_(0.85)Zn_(0.15)WO4 second phase. The fracture mode in the pure Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramic revealed a transgranular phase, as the CuO second phase increased the grain boundary strength; the Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramics sintered with 5 wt% additives showed an intergranular phase. The Vickers hardness and the bending strength of the Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramic were 733.6 and 62.0 MPa, respectively. The Vickers hardness of the ferrite with added SnO_2 or ZrO_2 showed only a slight improvement, while an apparent change (832.7) was observed with the addition of 5.0 wt% WO_3. The bending strength of the ferrite was optimized at 75.7 MPa with 2.0 wt% SnO_2 and at 90.5 MPa with 3.5 wt% ZrO_2, while that of the ferrite sintered with WO_3 added dropped gradually from 62.0 to 47.7 MPa as the amount of WO_3 was increased from 0 to 5.0 wt% due to the non-uniform microstructure. The pure Ni_(0.5)Cu_(0.3)Zn_(0.2)Fe_2O_4 ceramic sintered at 1075 ℃ had an initial permeability of 356.9 and a quality factor of 71.2. The addition of ZrO_2 led to a significant increase in the initial permeability (588.4 at 5.0 wt% ZrO_2), but a slight decline in the quality factor (56.6 at 5.0 wt% ZrO_2).