The Processing And Application Of Graphene Materials With High Conductivity

Graphite has good electrical conductivity,thermal conductivity,chemical stability and many other excellent properties.Nano-graphite sheets,expanded graphite and graphene can be obtained by graphite processing.How to prepare graphite mineral materials with excellent stability,high conductivity and easy processing is a research hotspot nowadays.Graphene has good application prospects in the field of conductive materials,duo to the high specific surface area,high conductivity,excellent chemical stability,high thermal conductivity and many other excellent properties.For how to prepare graphene materials with high conductivity,thermal conductivity at low cost and high yield and improving industrial applications of graphene materials,graphene materials with excellent conductivity were prepared from flake graphite by liquid-phase ball-milling method,low-redox method and molecular intercalation stripping method.The processing technology of graphene materials with large sheet diameter and low defect was studied for industrial application.High conductive materials with different performances were obtained through the study of different graphene processing technology,and the practical application ability of graphene was improved.The preparation technology of conductive coating and heat conduction coating was studied to meet the relevant industry requirements.Graphite was peeling by liquid phase ball method.The yield of nano-graphite（NG）sheet is 6.26%under the conditions of solid-liquid ratio 2.75 and ball-to-material ratio 12.5.NG with transparent cicada wings,diameter of several hundred nanometers to several micrometers and a thickness of less than 50 nanometers,and with perfect crystal structure and no oxygen-containing functional groups were obtained,under the experimental conditions of 400 rpm speed and 20 h grinding time.NG have good conductivity,the conductivity of BGT-20,BMS-400 and BR-12.5 were 1.647×10⁴ S/m,1.692×10⁴ S/m and 1.719×10⁴ S/m,respectively.Reduced graphene oxide（RGO）was prepared by low-redox method.The larger the particle size of graphite,the less sufficient the oxidation,and the more graphite structure was retained with the same oxidation conditions.With the increase of KMnO₄ content,the graphite structure gradually changed into graphite oxide（GO）structure.The value of d increases first and then decreases with the increase of GO structure.The interlayer spacing of GO-1.5 sample is the largest（9.4981?）.With the increase of oxidation degree,the diameter of graphene oxide（GOs）obtained by peeling increases gradually.When the oxidation degree is low,only the edge of the particles is oxidized.And the oxidation part is peeled off during the ultrasonic process,while the graphite structure inside the particles is not peeled off.When the amount of KMnO₄ was added twice as much as that of graphite,most of the particles were oxidized,and the diameter of GOs obtained by peeling could reach 5¹5μm.Slight stacking will occur and an ordered structure will be formed,during the drying process of GOs.Adding proper amount of CTAB can weaken the orderly stacking of GOs,reduce the orderliness of structure layer after GOs stacking,and greatly shorten the preparation time of GOs.Graphene obtained by thermal reduction treatment of GOs is a black light flocculent powder with smooth surface,transparent cicada wings and thin lamellae with a thickness not exceeding 5 nm.With the increase of KMnO₄ dosage（0.5→2.0）,the conductivity of RGO decreases gradually（9.091×10² S/m→1.013×10² S/m）.In addition,the higher the thermal reduction temperature is,the higher the conductivity is and the better the conductivity is（41.841 S/m→5.128×10² S/m）.Graphene was prepared by intercalation stripping method.It was found that the expanded graphite（EG）obtained had the best expansion effect,when the concentration of concentrated H₂SO₄ was 6 mL and H₂O₂ was 1.25 mL.The particles showed a long worm shape and the expansion volume could reach 180 mL/g.The process of intercalation expansion of graphite particles is gradual from the edge to the interior.With the decrease of particle size,the expansion volume of the sample decreases gradually.When the particle size is greater than150 micron,the expansion capacity of the sample is larger（216 mL/g）;when the particle size is less than 75 micron,the expansion effect of the sample begins to decrease;when the particle size is less than 45 micron,the expansion volume of the sample decreases sharply（10 mL/g）.The sample obtained by ultrasound has nanometer scale and smooth surface.The graphene sheet with transparent cicada wing shape can be seen in each sample.The diameter of the sheet can reach 10μm.The conductivity of the sample with expanded intercalation is better than that of the original sample,and the maximum is 8.403×10⁴ S/m.The maximum yield of graphene obtained by centrifugal dispersions is 2.19%.The study of conductive coatings found that the conductivity of different resin coatings（polyacrylic resin,polyurethane）showed an upward trend with the increase of NG content.The conductivity began to increase sharply（NG/PAA-20:1.426×10³ S/m;NG/PU-20:1.386×10³ S/m）,when adding 20%NG.With the increase of purified reduced graphene oxide（P-RGO）,the conductivity of PRGO/resin coatings increased.The percolation threshold of PRGO in polyacrylic resin is 18%,and its conductivity is 9.069×10² S/m.The percolation threshold of PRGO in polyurethane is 22%,and its conductivity is 1.016×10³ S/m.The conductivity of CNT/resin coating is poor,and the conductivity is only 142.857 S/m,when the CNT content reaches 50%.When the ratio of CNT to PRGO is 1:2,the sample with carbon content of 25%has better conductivity,and the conductivity is 1.429×10⁴ S/m.The study of thermal conductive films found that the thermal conductivity of P-RGO film is better than that of RGO film（The X-direction thermal conductivity of P-RGO films is393.7280 W/m.K,Z-direction thermal conductivity is 393.6226 W/m.K;the X-direction thermal conductivity of RGO films is 2.3561 W/m.K,and Z-direction thermal conductivity is2.5358 W/m.K）.When P-RGO:CNT=3:1,the thermal conductivity of the two films with carbon content of 30%and 40%of polyacrylic resin is good（The thermal conductivity of films with 30%carbon content are 102.4805 W/m.K and 102.5156 W/m.K in X-direction and Z-direction respectively.The thermal conductivity of the films with 40%carbon content are127.8125 W/m.K and 128.5343 W/m.K in X-direction and Z-direction respectively）.Good dispersibility are showed in mixed materials（P-RGO:CNT=3:1）of organic coatings,and their thermal conductivity archieved the conductivity requirements of thermal conductive materials.