Effect of silica fume and colloidal graphite additions on the EMI shielding effectiveness of nickel fiber cement based composites

Utilization of silica fume and colloidal graphite in nickel fiber cement based composites as a mean of improving the dispersity of nickel fiber and the electromagnetic interference (EMI) shielding effectiveness (SE) of cement based composites. This study aimed of test the EMI SE of cement based composites in 1-1500 MHz of the frequency range by coaxial cable method. The conductivity of cement based composites was test by four-point probe meter. The uniformity distribution of nickel fiber, silica fume and colloidal graphite was characterized by scanning electron microscopy. The results obtained indicate the nickel fiber has great effects on the EMI SE of cement based composites. With the content of nickel fiber was increased, the EMI SE of the composites were gradually increasing. When the nickel fiber was doping by 9.0 vol.%, the average SE of cement composites was reached 21.78 dB, the maximum SE was 24.48 dB in 120 MHz. When 20 wt.% of silica fume and 9.0 vol.% of nickel fiber were added in a cement matrix, the shielding property of the composite was best, the average SE was reached 30.13 dB, the maximum SE was 35.50 dB in 30 MHz. The best EMI SE was achieved by the sample comprised of colloidal graphited 20 wt.% and nickel fiber 5.0 vol.%, as exhibiting the average SE was reached 45.0 dB, the largest SE was 51.19 dB at 1170 MHz, indicating a synergistic effect of colloidal graphite and nickel fiber.