Preparation And Characterization Of MWCNTs Composites Modified With Strontium Ferrite And Nickel

It has been reported both at home and abroad that either single or compound microwave absorbing materials almost appear in high-frequency band (8²0GHz). To measure absorbing properties in the low-frequency (0⁶GHz), it has been prepared two kinds of MWCNTs composites in this work. One is Strontium Ferrite-MWCNTs composite, and the other is MWCNTs eletroless plating with nickel.(1) SrFe₁₂O₁₉-MWCNTs composites with different MWCNTs content were prepared by sol-gel method. The results of X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) analyses demonstrated that the SrFe₁₂O₁₉ nanoparticles were immobilized on the external surfaces of the MWCNTs. The schematic procedure of the preparation of SrFe₁₂O₁₉-MWCNTs nanocomposites was proposed according to the morphology and phase analysis.(2) Consideration of the effect of MWCNTs contents on the magnetic and microwave absorbing properties of SrFe₁₂O₁₉-MWCNTs composites, it has been found that 6wt%SrFe₁₂O₁₉-MWCNTs composite obtained the best magnetic properties with coercive force(Hc), 5916.13Oe, saturation magnetization(Ms), 59.45emu·g^-1, and remanent magnetization(Mr), 35.62emu·g^-1, respectively. Meanwhile, the reflection loss of 6wt%SrFe₁₂O₁₉-MWCNTs composite was the largest (-19.7dB). Finally, the connection between magnetic property and microwave absorbing property was proposed through the analysis of electromagnetic parameters of SrFe₁₂O₁₉-MWCNTs composites.(3) Based on the study of SrFe₁₂O₁₉-MWCNTs composites, lanthanum and zinc were doped into ferrite-MWCNTs composites in according with mole ratio of Sr_1-xLa_xFe_11.5Zn_0.5O₁₉ (x=0.05,0.1,0.15,0.2,0.3,0.4,0.5). When x value was 0.15, the composite possessed the best microwave absorbing property with a double-peak absorption, which makes wider absorbing bandwidths come true.(4) The MWCNTs pretreated method, mole ratio of Ni to P, temperature of the reaction solution and pH value were determined to prepare MWCNTs electroless plating with nickel. The optimum craft was as follow: MWCNTs was pretreated in a mixed acid solution of concentrated sulfuric, nitric acids and distilled water(5:3:2 by volume), the mole ratio of Ni to P was 1:4, the temperature of the reaction solution was 70℃, pH value was 8.(5) MWCNTs electroless plating composite with Nickel pretreated by mixed acid solution has the best microwave absorbing property: the largest absorbing peak appears at 4.1GHz with reflection loss reaching -22dB, and the peak width of R<-10dB and R<-5dB was 0.56GHz, 1.25GHz, respectively.