SYNOPSISElectrical and magnetic properties of composite materials prepared by incorporating various nickel-based fillers of different shapes into polyethylene were investigated. The fillers used were nickel powders, nickel filamentary powders, nickel flakes, and nickel-coated graphite fibers. The particle-size distributions of the fillers were determined both before and after the processing of the composite samples. A wide range of filler volume fractions were used. In some cases, the volume fraction approached the maximum packing fraction of the solid phase to significantly exceed the percolation threshold. The composite samples were characterized in terms of their volume resistivity, dielectric constant, and magnetic permeability values. Filler particles of asymmetric shapes were very effective in terms of altering the electrical properties of the composite samples. At the highest loading levels of the nickel fillers, the volume resistivity values of the composites decreased by more than 17 orders of magnitude. At such high filler concentrations, the dielectric constant values of the composite samples increased considerably, to values that were greater than 1000. The permeability values of the samples increased linearly with the volume fraction of the nickel filler and were insensitive to the shape of the fillers. The highest relative permeability value measured was 5.8 for composites with 67% by volume of nickel powder. 0
ABSTRACT:Composites with high relative magnetic permeability values can be used in many industrial applications, especially if they can be shaped using conventional polymer-processing technologies. In this study, various hybrid composite systems ( i.e., particles with differing aspect ratio, size, and magnetic permeability embedded into a polymeric binder) were prepared in an attempt to reach high relative permeability values without the use of high pressures or sintering. It was determined that an interaction effect between the different types of fillers exists and enhances the relative magnetic permeability value of the composite in relation to the use of single type of magnetic filler. Relative magnetic permeability values of over 100 were achieved. Such relative magnetic permeability values represent a significant increase in the magnetic permeability over available magnetic composites prepared using similar processing techniques. The significant gains in magnetic permeability were realized by altering the maximum packing fraction, and ultimately the percolation threshold of the composite, by using low and high aspect ratio particles simultaneously in the formulation of the magnetic composites.
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