Study On Cement Based Electromagnetic Shielding Composite Materials Of Modified Graphite

Graphite is one of the few non-metallic minerals which has electrical conductivity, magnetic effect, abundant source, low cost, stable chemical properties and good compatibility with cement. So cement based electromagnetic shielding composite materials priority to choose graphite as conductive medium. But the shielding effectiveness of ordinary graphite filling into cement based composite materials is not ideal, especially the shielding effectiveness in low frequency band is poor. Ordinary graphite must be modified with physical and chemical modification in order to improve the shielding effectiveness of the cement based electromagnetic shielding composite materials of graphite.This article focuses on the method of using flaky graphite preparation of expanded graphite, and instantaneous co-firing method and Citric acid sol-gel method are used to modify expanded graphite, so iron oxide magnetic expanded graphite, nickel ferrite magnetic expanded graphite and barium ferrite magnetic expanded graphite are prepared; using XRD、SEM to analyze and characterize the phase composition and microstructure of the modified graphite; using coaxial planar-spectrum analyze method to test the shielding effectiveness of the modified graphite; discussing the effect of modification of the process, the content of conductive medium, the double mixing of other medium to the mechanical properties and shielding effectiveness of cement-based composite materials.The results show that oxidation treatment on flaky graphite can prepare expanded graphite whose maximal expansion coefficient achieve245times; iron oxide magnetic expanded graphite, nickel ferrite magnetic expanded graphite and barium ferrite magnetic expanded graphite can be prepared by instantaneous co-firing method and Citric acid sol-gel method; testing different cement-based composite materials of graphites’s shielding effectiveness found that the shielding effectiveness of cement-based composite materials is only14.5dB when mixed with15wt%of flaky graphite; however, the shielding effectiveness of cement-based composite materials will not be improved after expansion of process on flaky graphite; but the shielding effectiveness will be improved after magnetism of process on expanded graphite. The shielding effectiveness of cement-based composite materials is24dB when mixed with15wt%of iron oxide magnetic expanded graphite and barium ferrite magnetic expanded graphite, however barium ferrite magnetic shielding effectiveness of expanded graphite is stable and better in most of frequency range compared with iron oxide magnetic expanded graphite; nickel ferrite magnetic expanded graphite is the best, the best shielding effectiveness is26.5dB when mixed with15wt%of nickel ferrite magnetic expanded graphite; nickel ferrite magnetic expanded graphite mixed with carbon fiber will improve the shielding effectiveness of cement-based composite materials which is33.5dB when mixed with0.9%of carbon fiber.