Microstructure, Mechanical Properties, and Pyroconductivity of NiFe_2O_4 Composite Reinforced with ZrO_2 Fibers

摘要

NiO-Fe_2O_3-ZrO_(2f) composites were fabricated by a two-step sintering process. No phase transformation for ZrO_(2f) was observed. The as-prepared NiO-Fe_2O_3-ZrO_(2f) ceramic showed excellent mechanical properties because of the introduction of ZrO_2 fiber. The values for both the bending strength and fracture strength of 3 wt.% ZrO_(2f)-reinforced NiFe_2O_4 samples reached the maximum values of ～89.0 MPa and ～4.67 MPa m~(1/2), respectively, The toughness mechanism is mainly attributed to fibers' fracture, crack deflection, fibers' pull-out, and fibers' debonding. The conductivity of ZrO_(2f)-reinforced NiFe_2O_4 is dependent on temperature and ZrO_(2f) content. When the electrolytic temperature is up to 950℃, the conductivity value of the sample reinforced with 4 wt.% ZrO_2 fibers is 0.63 S/cm, which has been improved by 37.8% compared with the conductivity value of 0.45 S/cm for the un-doped samples. The main conductive mechanisms of ZrO_2 fiber in the matrix are the one based on the substitution of Zr~(4+) ions to produce quasi-free electrons, and the other based on oxygen ionic conducting mechanism.