The objective of this research was to prepare a clay film with electromagnetic shielding properties by making a clay film electrically conductive. To achieve this goal, we attempted to intercalate graphene into smectite clay and to prepare a graphene-smectite composite film with dimensions corresponding to those of A4 paper. The composite film was prepared by mixing graphene oxide and smectite in water, drying the solid, and annealing at 250℃ for 30 min in an air atmosphere. The film was characterized by X-ray diffraction analysis, Fourier transform infrared spectroscopy, thermogravimetry, differential thermal analysis, and scanning electron microscopy. Conductivity and electromagnetic shielding were measured with a linear, 4-pin electrode method and the KEC method, respectively. The characterizations indicated that the reduced graphene oxide compounded with the smectite clay at the nanometer scale. The obtained composite film contained 33 wt% carbon, and the sheet resistance was 1036 Ω・cm^<-2>. The shielding effectiveness of the composite film was 67% at electromagnetic frequencies less than 100 MHz. At frequencies less than 10 MHz, the shielding effectiveness of the film exceeded 97%. We have therefore succeeded in developing a clay film with electromagnetic shielding properties by addition of reduced graphene oxide to smectite clay.
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