A perspective on electromagnetic interference shielding materials comprising exfoliated graphite

Carbon materials in the graphite allotrope family are attractive for electromagnetic interference (EMI) shielding in the microwave/radio-wave regime, due to their electrical conductivity, low density and corrosion resistance. This is the first review of shielding materials comprising exfoliated graphite (EG), which is graphite with a degree of separation of some of the carbon layers. The EG differs from other carbons in the graphite allotrope family in its cellular structure and the consequent ability to interconnect three-dimensionally through mechanical interlocking without a binder. The connectivity, cellular structure and carbon-layer preferred orientation result in resiliency perpendicular to the plane of preferred orientation. The resiliency is beneficial to EMI gasketing. Therefore, SE is above that of most carbons. The SE of EG-containing materials reaches values in the vicinity of 130 dB, which is around the highest value that can be measured. Such high values were first reported by Luo and Chung in 1996, specifically SE 129 dB (thickness 3.1 mm). Recent progress has resulted in EG film that exhibits SE 108 dB (thickness 0.125 mm) and carbon foam that exhibits SE 137 dB (thickness 2.8 mm). The EG polymer-matrix composites include the incorporation of magnetic constituents (e.g., ferrite and nickel, including nickel in the form of a coating on EG), dielectric constituents (e.g., BaSrTiO3), conductive polymer matrices (e.g., polyaniline) and CNT-EG co-fillers (for forming 3D structures). However, the composites exhibit SE values that are mostly significantly below the abovementioned high values attained without a matrix. However, the composites are attractive for their moldability.