Synthesis Of Nano Ferrite/graphene Composites And Their Application In Water Based Electromagnetic Shielding Coatings

As a kind of high-tech product, waterborne electromagnetic shielding coatings have good electromagnetic shielding function and are environmentally friendly. The ferrite/graphene composite materials might show unique electromagnetic properties owing to the combination of the excellent electrical conductivity of graphene and the outstanding magnetic properties of ferrite nanostructures.In this thesis, nano ferrite/graphene composite materials and ferrite nanorods/graphene composites were synthesized using a hydrothermal reaction and solvethermal method, respectively. The waterborne electromagnetic shielding coatings were prepared by adding ferrite/graphene composites to polyacrylate emulsions. The influence of filler kinds and contents on electromagnetic shielding properties of coatings was investigated.Firstly, ferrite nanoparticles/graphene composites were synthesized using a one-step hydrothermal method with Na2S2O3 as reductants. X-ray diffractometer(XRD), transmission electron microscopy(TEM), scanning electron microscopy(SEM), and vibrating sample magnetometer(VSM) were used to characterize the structures, morphologies and magnetic properties of as-obtained composites. The effects of reaction temperatures, times and ferrite loadings on structures, morphologies and properties of ferrite/graphene nanocomposites were studied. CoFe2O4 /graphene composites with 5-40 nm of spinel CoFe2O4 nanoparticles on the surface of graphene were prepared at 150 oC for 15 h. NiFe2O4/graphene nanocomposites with 10-60 nm of spinel NiFe2O4 nanoparticles were obtained at 150 oC for 15 h. A minimum reflection loss of CoFe2O4 nanoparticles/graphene composites was- 7.2 dB at 14.6 GHz with a thickness of 3 mm.Secondly, rod-like ferrite/graphene composites were synthesized by a solvothermal method followed by calcination. XRD, TEM, and SEM were used to characterize the structures and morphologies of as prepared composites. The influence of reaction temperatures, times, pH, ratio of solvents and ferrite loadings on structures, morphologies and properties of ferrite/graphene nanocomposites was investigated. Rod-like CoFe2O4/graphene composites with 50-600 nm diameter of spinel CoFe2O4 were obtained at 120 oC for 15 h. Rod-like NiFe2O4/graphene composites with 50-100 nm diameter of spinel NiFe2O4 were obtained with volume ratio of 2:1 for ethylene glycol to water at 120 oC for 14 h. A minimum reflection loss of rod-like CoFe2O4/graphene composites was-18.4 dB with a thickness of 2 mm at 16 GHz. However, a minimum reflection loss of rod-like NiFe2O4/graphene composites was-3.7 dB with a thickness of 1 mm at 15.6 GHz.Finally, the waterborne electromagnetic shielding coatings were prepared using CoFe2O4 nanoparticles/graphene composites and rod-like CoFe2O4/graphene composites as fillers in polyacrylate emulsion. The result showed that EMI shielding effectiveness of the coatings was increased and the electromagnetic shielding band was broadened with increasing the amount of the fillers and thickness of coating. The EMI shielding effectiveness of-4.54 dB was observed for the coating with 20 wt% of CoFe2O4 nanoparticles/graphene composites.