Electrical Spectrum And Fractal Characteristics Of Magnetic Particles/Zirconia Composites

Composites consisting of magnetic particles and structural ceramics are one member of the structure-function integrative materials and have broad application prospects in electromagnetic shielding,wave absorbing stealth,integrated circuit,stress fracture sensing,etc.In this work,3Y-TZP is selected as matrix with excellent mechanical properties,and two kinds of magnetic particles(strontium doped barium ferrite and nickel cobalt alloy)are mixed with 3Y-TZP,respectively to obtain two types of structure-function integrative ceramics.The two composite materials,'20%wt strontium doped barium ferrite/80%wt 3Y-TZP'and'10%wt nickel cobalt alloy/90%wt 3Y-TZP',are prepared by different methods under different processing conditions.Their fundamental properties including mechanical,electrical and magnetic properties are comprehensively studied.This work focuses particularly on the correlations among the fractal characteristics,electrical properties spectra,preparation methods and processing conditions of the two composites.The systematical investigations of these correlations have provided a simple and practical way,by means of which the microstructural information inside the composite materials can be analyzed by the easily obtained spectrum parameters of electrical properties.It also conveniently helps to judge the optimum process parameters and it is a new way to evaluate the properties of the composite materials.Firstly,the influences of the composition and preparation process on the mechanical and magnetic properties of the composite ceramics are studied to determine the optimal group of comprehensive performance.The experimental results show that for the strontium-doped barium ferrite/3Y-TZP series,the composite ceramic with the strontium ratio of 0.50 possesses the optimal properties when prepared by in situ method and sintered at 1300?.The bending strength,Vickers hardness,fracture toughness and saturation magnetization reach 800 MPa,12.6 GPa,11.3 MPam^1/2 and 86.17 emu g^-1,respectively;for the nickel cobalt alloy/3Y-TZP series,the composite ceramic with the cobalt ratio of 0.50 exhibits the best properties when sintered at 1400?.The bending strength,Vickers hardness,fracture toughness and saturation magnetization are 909 MPa,12.5 GPa,11.0 MPam^1/2 and 95.7 emu g^-1,respectively.Then,the influences of sintering temperature,preparation method and composition on the fractal dimension of the interface profile of two phases(magnetic particle phase and matrix phase)of the composites and the parameters of the equivalent circuit of the impedance spectrum are analyzed based on the comprehensive properties and microstructure of the both composites.The results obtained in this work show that the variation tendency between the index of CPE element and the fractal dimension is opposite under certain conditions.The composite materials sintered at the optimum temperature correspond to the smallest fractal dimension,while the index of CPE element for the equivalent circuit parameters is the largest;the composite materials prepared by the optimum method have the smallest fractal dimension,and the index of CPE element of the composite materials is the largest;the composite materials with the optimum composition have the smallest index of CPE element correspondingly.At last,dielectric spectra of the two composite ceramics are studied and analyzed in this work.On one hand,the effects of sintering temperature,preparation method and composition on the curve of the low-frequency dielectric spectrum are investigated.It is shown that the dielectric loss of the composite ceramic sintered at the optimum temperature is the largest.The frequency corresponding to the dielectric loss peak of the composite ceramic prepared by the optimal method is the highest,while the fractal dimension is the smallest correspondingly.The frequency corresponding to the dielectric loss peak of the composite ceramic with the optimum composition is the highest.On the other hand,the optical frequency permittivity of composite ceramics was explored,and the optical frequency permittivity of matrix phase composition(tetragonal zirconia,monoclinic zirconia and their interfaces)under atmospheric pressure are obtained by material calculation software.The relationship between state density and imaginary part of optical frequency permittivity is further analyzed.The results demonstrate that the components of matrix phase can be distinguished by comparing and analyzing the characteristics of peaks of imaginary part.