On Mechanical Properties And Piezoresistance Performance Of Anisotropic Silicon Rubber Filled Iron Particles

In this paper, silicon rubber (SR) filled with micro-carbonyl iron powder composites (SR-Fe) was prepared, SEM/EDS, XRD techniques were used to characterize the microstructure and phase of composites, the mechanical properties and piezoresistivity were measured and analyzed, and the concerned mechanisms were probed. The following inclusions were derived:Imposing external magnetic field during the vulcanizing of liquid silicon rubber usher will induce directed microstructures consisting of aligned iron powders in silicon rubber. In the alternating magnetic field, magnetization direction alters at a specific frequency, so iron particles are easier to fill the vacancy and get rise to more perfect directed microstructures.Tensile tests on SR composite samples show the strain depends linearly on the displacement, observes as in typical rubbers, there is none of yield in tensile curves. The tensile properties, such as tensile strength and breaking elongation, of aligned directed composites exhibit clearly anisotropic in aligned (longitudinal) and perpendicular directions and the values in both directions are found higher than those obtained in random composites. Moreover, the positive effect of AC magnetic field on the tensile properties is greater than that of DC magnetic field, which is ascribed to the former can produce more perfect aligned microstructure than the latter.Electrical measurements show that the resistivity of aligned composites experience a sharp transition at a lower loading fraction of 5wt%, compared with a higher value of 20wt% of random composites. The dependence of resistivity on loading fraction obeys classical percolation theory, and the fitted value of scaling factor t ranges from 1.6 to 2.0. The higher values of t are obtained when magnetic field is applied during preparation of SR composites, in which due to alignment of microstructures a more correlation length of percolation network is induced. Piezoresistance measurements show when the composite samples are subjected to a loaded pressure, their resistivity decreases exponentially at low pressure loading and reach a steady value at a critical pressure of about 0.05~0.1Mpa, the corresponding extent of drop is about a magnitude of 1~2 orders. It is found that piezoresistance phenomena above can be described according to Ruschau's model, which implies the microcosmic conducting of iron powders agrees to quantum tunnel model. According to circle tests, the composite system developed in present study exhibits very steady piezoresistance, the difference in resistance under pressure loading through 100 turns is less than 5%.