Preparation And Piezoresistivity Study Of Conductive Silicon Rubber Composite Filled With Aligned Iron Powder

Conductive silicon rubber filled with dispersed conductive filler is an increasingly active branch in the field of conductive polymer composite. Conductive rubber based antistatic materials, electromagnetic shielding materials and conductive materials have been employed in electrics, aerospace and service industries etc to play an important role for promoting national economic growth. In this article, we used micron carbonyl iron powder (granular) and polycrystalline carbonyl iron fiber (fiber) as conductive filler, prepared two kinds of conductive silicone rubber composites, studied the electrical conducting and piezoresistive mechanism of these materials. The main conclusions are obtained as follows:A conductive silicon rubber composite with aligned micron carbonyl iron powder was prepared through the process of magnetic field assisted curing. The resistance dependence upon filler content and pressure was tested. The results showed the composite owned rich piezoresistive characteristics; the composite samples with resistance of more than 10¹⁰Ωexhibited negative piezoresistivity, while those with resistance of less than 10¹⁰Ωexhibited positive piezoresistivity; the silicon rubber filled with 10wt%⁵0wt% iron powder showed a sharp increase in resistance up to 3⁵ orders of magnitude close to 0.2 MPa, but the system with 50wt% filler obtained at 0.2T magnetic field exhibited a linear positive piezoresistivity. The underlying mechanism is correlated with the configuration diversity of aligned microstructure induced by magnetic field, and researched a new direction for new materials.Another composite filed with polycrystalline carbonyl iron fiber was prepared through a similar process. The test results showed the conductivity of this system is much more excellent than the former system, for example, the addition of only 1.0wt% iron fiber can produce a resistance less than 1Ω, and all systems showed the negative piezoresistivity. The study revealed the alignment of iron fiber reduced the resistance loss and increaced the rate of utilization of filler; moreover, conductive path was improved and resistance decreased with increase of magnetic field intensity continuously. Stduty suggest that through the process of magnetic field assisted curing the system piezoresistivity was mainly affected by iron shape which decreased electron flow resistance of conductive path.We compared the performance of composite filled with granular iron powder and iron fiber and studied the affect of iron powder shap on material microstructure and conductive properties. The results showed the percolation threshold of granular iron powder with magnetic field treatment was 5wt%, the lowest resistance was 10⁶Ω, while the percolation threshold of iron fiber with magnetic field treatment was just 0.2wt%, the lowest resistance was less than 1Ω; the former showed positive piezoresistivity and negative piezoresistivity near by 10¹⁰Ω, while the latter just show negative piezoresistivity. Study showed axial conductivity and deformation resistance of iron fiber with greater aspect ratio in conductive composite was better than granular iron powder, so it determined the difference conductivity of two kinds iron powder.