Study Of The Fabricating Technology Of Graphene Film For The Application Of Electromagnetic Shielding

The three-dimensional layered material assembled from graphene nanosheets in space is called graphene film.Among them,the graphene film material used for electromagnetic shielding combines excellent properties such as light weight,softness and foldability,and plays an important role in avoiding the radiation effects of electronic devices on the human body and other precision devices.Therefore,designing graphene films with excellent performance,rapid preparation,and low cost has become the top priority for large-scale applications of graphene films in the field of electromagnetic shielding.At present,graphene oxide is used as a precursor to reduce and treat the film at high temperature,which is a widely used method for preparing graphene film.This method has disadvantages such as high cost,complicated preparation,serious damage to the environment,etc.,and the performance of the obtained film is average.Among the many preparation methods,the one-step chemical method is to exfoliate natural graphite into graphene under the synergistic effect of concentrated sulfuric acid and oxidizing agent.This method has simple preparation steps,low environmental pollution,and can obtain graphene of large size and few layers,standing out among many methods.This paper proposes a method for the rapid preparation of highly conductive graphene nanoplatelets and graphene films,which have excellent electromagnetic shielding performance.In this thesis,two methods for preparing highly conductive graphene are designed,and the above two types of graphene are used to prepare high-performance graphene films at the same time.（1）Using 50 mesh natural graphite,BH₈Na O₇ and concentrated sulfuric acid as raw material,oxidizing agent and intercalating agent,respectively.In particularly,using concentrated H₂SO₄ to pre-soak the natural graphite to improve the exfoliation efficiency,in which BH₈Na O₇ was used as the oxidant at the first time.According to the different pre-soaking time,the exfoliation process can be divided into two experimental systems:non-soaking and pre-soaking.The results show that the graphene obtained by pre-soaking experimental system is of higher quality.The average areal sizes of the graphene sheets are reach 260μm²,and the oxygen content of which was only 2.62%.The graphene conductive film was prepared by the vacuum filtration self-assembly method by the obtain graphene.The obtained graphene film shows excellent electrical conductivity of 1.53×10⁶S/m.More importantly,it also exhibits an ultrahigh EMI SE of 68 d B at a frequency of 8.2–12.4 GHz,which can block 99.99999%of incident radiation.（2）（NH₄）₂SO₄ is inexpensive as an oxidant and is widely used in chemical exfoliation methods.In order to verify the universality of the pre-soaking procedure,this operation was applied to the chemical stripping system of（NH₄）₂SO₄ and concentrated sulfuric acid.Using 50 mesh natural graphite,（NH₄）₂SO₄ and concentrated sulfuric acid as raw material,oxidizing agent and intercalating agent,respectively,graphene is chemically exfoliated off.The results show that the graphene obtained by pre-soaking experimental system is of higher quality,and the oxygen content of which was only 1.92%.The graphene conductive film was prepared by the vacuum filtration self-assembly method by the obtain graphene.The obtained graphene film shows excellent electrical conductivity of 7.3×10⁵S/m.Besides,it also has an EMI SE of 73 d B at a frequency of 8.2–12.4 GHz.（3）Using the graphene film obtained from the ammonium persulfate/concentrated sulfuric acid system as the object,a high-quality graphene film was obtained after simple heat treatment operation.The results show that the strength of the graphene film obtained at a heat treatment operation of 400°C reaches 39MPa,and the electromagnetic shielding performance can reach 76d B.As the heat treatment temperature increases,the mechanical properties of the graphene film show a tendency of increase and then decrease.The heat treatment effectively improves the mechanical properties of the graphene film without affecting the electromagnetic shielding performance of the film.