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Graphene materials have become one of the materials widely studied and applied in many fields for their excellent thermal, electrical, and mechanical properties. As the cause of deep space exploration continues to develop, the study of the performance of materials in low-temperature and even ultra-low-temperature environments is becoming increasingly important. In this paper, graphene paper was studied and analyzed in the temperature interval of 290 K~20 K using the transient electrical heating technique, and the effect of high temperature heating by electric current on the thermal conductivity of graphene paper was investigated. The thermal diffusion coefficient, thermal conductivity and volumetric specific heat capacity of graphene paper gradually decrease with decreasing temperature, and the resistance gradually increases with decreasing temperature, exhibiting strong non-metallic properties. After the structure of graphene paper is optimized by high temperature heating by electric current, the thermal conductivity of sample 1 increased from 2.31 W/(m ⋅ K) to 5.47 W/(m ⋅ K) and the thermal conductivity of sample 2 increased from 6.09 W/(m ⋅ K) to 22.21 W/(m ⋅ K) at 290 K. The thermal conductivity mechanism of phonon scattering from graphene paper was analyzed, and the Debye temperature and phonon mean free range of graphene paper were calculated using the thermal reffusivity model. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO), as a derivative of graphene (G), has excellent mechanical properties and thermal conductivity similar to graphene, and its hydrophilic functional groups make it easier to disperse in water and combine with cement-based materials. A large number of studies have shown that adding GO into cement matrix can not only enhance the mechanical properties and durability of cement matrix, but also enhance the electromagnetic shielding properties and thermal conductivity of cement matrix, which provides the possibility for the development of multifunctional and intelligent concrete. Focusing on the application of GO mixed with other functional fiber materials in cement-based materials, this paper briefly describes the performance characteristics and structural characteristics of GO, thus indicating the breadth and scope of its application in cementbased materials, emphatically summarizes the research on the dispersion of GO and the working performance, hydration process, mechanical properties, durability and functional properties of GO mixed with fiber cementbased materials, and looks forward to the future research direction of GO mixed with fiber cement-based materials. [ABSTRACT FROM AUTHOR]

Tn recent years, graphene/polyurethane nanocomposites have attracted much attention due to their superior comprehensive properties. Incorporating graphene or its derivatives into I〉U matrix could significantly improve the physical mechanical, thermal, electromagnetic and other properties, which meets the special requirements of high-performance and multi-functional polymer composites. Tn this paper, the functional modification methods of graphene nanosheets, including covalent modification and non-covalent modification were first introduced. Furthermore, the fabrication processes of graphene/poly urethane nanocomposites, including in-situ polymerization, solution blending, melt blending, aqueous (latex) blending, etc., were briefly introduced. The recent research progress of graphene/poly urethane composites in mechanical, electrical, dielectric, thermal, gas barrier, flame retardant, electromagnetic interference shielding and corrosion resistant properties were all reviewed in detail. The future challenges and development prospects of high-performance graphene/poly urethane nanocomposites were also prospected. [ABSTRACT FROM AUTHOR]

Boron nitride（BN） ceramics have excellent properties such as high aspect ratio, high temperature resistance, high thermal conductivity and electrical insulation, widely used in electronic information, aerospace, metallurgy, machinery and other fields. 3D printing technology has low cost and time-saving compared with traditional processing methods, and is an important molding technology for the preparation of ceramic parts with complex three-dimensional structure. To this end, in this paper, based on the self-developed pneumatic new direct-write 3D printing material forming platform, ceramic slurries with different BN contents were prepared using BN and polyvinyl alcohol（PVA） as raw materials and binder, and ceramic preforms with different 3D structures were designed and prepared using the layer-by-layer stacking principle. By changing the rheological properties of the slurries, the BN 2D nanosheets were realized in the printing process under the shear. By changing the rheological properties of the slurry, the orientation of BN 2D nanosheets under the action of shear force was achieved during the printing process, and ceramic materials with high interplanar thermal conductivity were obtained. The effect of BN content on the molding quality of the ceramic parts was investigated, and the structure and microscopic morphology of the printed ceramic materials were characterized by XRD and SEM. The results show that the BN/PVA 85 slurry has good shear thinning and viscoelastic properties, and the yield stress in the linear viscoelastic region reaches 240 Pa, which is suitable for direct-writing 3D printing technology. the increased horizontal orientation of BN inside the part contributes to the enhanced interfacial thermal conductivity of the ceramic material, where the interfacial thermal conductivity of the BN/PVA 85 ceramic part is about 4.3 W/（m·K）. [ABSTRACT FROM AUTHOR]

Polyimide（PI） material has become a hot precursor for the preparation of graphite cooling film in recent years because of its six-membered ring molecular structure and high carbon content. As a transition metal element, nickel is often used as the substrate for graphene catalytic growth. Doping nickel in the polyimide substrate can effectively improve its carbonization and graphitization degree and improve its thermal conductivity. However, pure nickel metal particles will deposit in the precursor of PI, polyamide acid（PAA）, which makes it difficult to disperse uniformly. In this work, the PI composite film was prepared by adding a metal complex soluble in organic solvent, nickel acetylacetone（Ni（acac）2）, into the PI matrix and graphitized at 2 700 ℃ to obtain a graphite film. The nickel obtained from the decomposition of Ni（acac）2 at high temperature can promote the carbonization of polyimide, and its solubility in organic solvent also significantly improves the dispersion of nickel in the PI matrix. Finally, the polyimide carbon film with a flat surface was prepared, and its thermal conductivity can reach 782 W/（m·K）, which is 30 times higher than that of the carbon film prepared by pure PI. The purpose of this paper is to analyze the carbonization process of polyimide catalyzed by metal complex Ni（acac）2 and the final carbon film structure, and explore the possibility of finally preparing high thermal conductivity graphite film.  [ABSTRACT FROM AUTHOR]

In this paper, boron nitride nanosheets (BNNS) were prepared by liquid phase mechanical stripping method and the double modified boron nitride nanosheets (KDBNNS) were prepared by silane coupling agent covalent modification and dopamine non-covalent modification. The reaction induced phase separation was used to distribute KDBNNS at the interface of epoxy resin (EP) and polyether sulfone (PES) to form a thermal conductive pathway. KDBNNS/PES/EP composites were prepared and characterized by Fourier transform infrared spectroscopy analysis, differential scanning calorimetry analysis (DSC), thermal weight loss analysis (TGA), and confocal scanning microscopy. It is observed that BNNS constructs a three-dimensional thermal conductive path in the ternary composite. Studies have shown that when the mass ratio of BNNS is only 3%, the thermal conductivity of the composite reaches 0.394 W/ (m·K), which is 103% higher than pure epoxy 0.194 W/ (m·K) [ABSTRACT FROM AUTHOR]

Aerogel materials have broad application prospects in the market of building thermal insulation materials because of their high porosity, strong compression resistance and low thermal conductivity. In this paper, Al2O3-SiO2 aerogel composite thermal insulation materials with different SiO2 content were prepared by sol-gel method using tetraethyl orthosilicate and sec butanol aluminum as raw materials. The effects of SiO2 doping amount on the crystal structure, micro morphology, mechanical properties and thermal conductivity of composite aerogels were studied. The results showed that Al2O3-SiO2 aerogel was mainly composed of polycrystalline boehmite. SiO2 doping inhibited the formation of γ-Al2O3 phase and hindered the occurrence of hydroxyl condensation reaction. H in AlO—H group was replaced by Si, forming a more stable Al—O—Si bond. Al2O3-SiO2 aerogel showed an open porous structure, and the doping of SiO2 improved the pore orientation of the aerogel, reducing the pore size and distributing evenly. With the increase of SiO2 doping, the compressive strength and specific surface area of Al2O3-SiO2 aerogel first increased and then slightly decreased, and the thermal conductivity first decreased and then increased. When the doping amount of SiO2 was 9 mol %, the maximum compressive strength of the aerogel was 40.92 MPa, which was 58.97% higher than that of the undoped aerogel. The maximum specific surface area was 257.33 m²/g, the lowest thermal conductivity was 0.022 W/（m·K）, and the thermal insulation performance was the best. In summary, the optimal doping amount of SiO2 was 9 mol%. [ABSTRACT FROM AUTHOR]

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GeTe based materials have great potential in thermoelectric applications,thus have become a research focus of middle temperature thermoelectric materials. In this paper, the crystal structure and phase transformation process of GeTe are introduced firstly. Then the research progresses of GeTe system are systematically introduced based on the thermoelectric properties enhancement technique in pervious reports, including:(1) Aiming at the enhancement of the power factor, by optimizing the hole carrier concentration and increasing the vacancy energy of Ge;(2) Energy band engineering strategy to optimize the energy band structure;(3) Reducing the thermal conductivity by introducing nano-sized defects(point defects, stacking defects and nanocrystalline precipitation) etc. In general, the research and development of GeTe-based thermoelectric materials have great significances to physics, chemistry and materials science and engineering. [ABSTRACT FROM AUTHOR]

In this paper, graphene from inexpensive sucrose is prepared by in-situ growth directly on the Cu flakes, and Cu matrix materials(Cu-MMs) with various in-situ graphene content is fabricated by hot-press sintering. The effect of sucrose content on the phase composition, microstructure and thermal properties of bulk Cu-MMs is studied by XRD, SEM, thermal conductivity (TC) and coefficient of thermal expansion (CTE). Results obtained indicate that after the heat treatment at 800 ℃ for 15 min under the H2/Ar gas flow, the in-situ growth of graphene on the surface of Cu flakes occurs. The graphene exhibits good attachment to Cu matrix and homogenous dispersion, which is beneficial for thermal properties of Cu-MMs. With 0.73 vol% grapheme, the TC of Cu-MMs reaches 339 W/(m·K), which is higher by 19.3% than that of Cu, and meanwhile CTE is far lower than that of Cu from 50 ℃ to 300 ℃. [ABSTRACT FROM AUTHOR]

Tn this experiment, the thermal conductivity of polyimide fibers at different temperatures is obtained by using transient electrothermal technology in order to explore the rule and cause of the variation of the thermal conductivity of polyimide fibers with temperature. The experimental results show that when the temperature is in the range of 1 0-290 K, with the decrease of temperature, the thermal diffusion coefficient of polyimide fiber increases gradually, and the thermal conductivity decreases gradually. Tn this paper, we start from the lattice vibration (phonon) thermal conductivity, and study the relationship between temperature and lattice vibration, phonon concentration, phonon mean free path and other experimental parameters. After excluding the influence of macroscopic defects such as pores, it is concluded that the crystallization rate is the main factor affecting the thermal conductivity of polyimide fibers near the glass transition temperature while the lattice vibration is the main factor affecting the thermal conductivity of polyimide fibers near the Debye temperature. Therefore, polyimide fibers can be prepared by changing the crystallization rate and improving process conditions to meet the needs of different life, production and scientific research. [ABSTRACT FROM AUTHOR]

Due to its high graphitization degree, high crystallinity and purity, flake graphite has high thermal conductivity in its base plane and becomes an important raw material for the preparation of oriented high thermal conductivity composites. The graphite flakes/aluminum composites have excellent comprehensive thermal properties, which has more significant application advantages in the fields of electronic communication and aerospace. In this paper, the main preparation technologies and thermal conductivity of graphite flakes/aluminum composites are introduced. Based on the wettability and interfacial reaction between carbon and aluminum phases, the surface modification methods of flake graphite and its influence on the interfacial microstructure and thermal conductivity of the composites are summarized. Finally, the research direction and development trend of graphite flakes/aluminum composites in the future are prospected. [ABSTRACT FROM AUTHOR]

With the development of electronics？ spaceflight and aviation, the integrated circuit develops rapidly, but it is often accompanied by the problem of heat dissipation ？ which affects the efficiency and the life of instruments. Considering the weight, corrosion resistance？ processing technology and cost？ polymer composites are the most promising materials for thermal conductivity. However, the inherent thermal conductivity of polymers is very low, so improving the thermal conductivity of polymers is very important for their applications in these fields ？ which has become a very important research topic in the past two decades. Tn this review paper, the following two aspects were mainly introduced. The micro thermal conductivity mechanism of polymers was analyzed and summarized from three aspects of molecular chain morphology ？ chain structure and inter-chain coupling. The main research progress in the thermal conductivity of graphene-filled polymer nanocomposites in recent years and the research challenges in the future were highlighted. [ABSTRACT FROM AUTHOR]

In this paper, a method for preparing starch expanded graphite phase change composites using emulsification mechanism was described. Starch expanded graphite phase change composites were prepared by using paraffin, expanded graphite (EG) and starch as raw materials, and their properties were studied. The infrared spectrum showed that there was a physical bond among paraffin, EG and starch, and no new substances formed. The heat storage capacity of the composite phase change material decreased as the phase change material decreased. When the EG content was less than 8.4 ms%, the phase change heat gradually decreased, and when the EG amount was more than 8.4 ms%, the phase change heat sharply decreased. The thermal conductivity of the phase change composite increased with the increase of EG. When the EG content was less than 8.4 ms%, the thermal conductivity gradually increased. When the EG content was more than 8.4 ms%, the thermal conductivity increased less. When the amount of EG were 8.4 ms% and 11 ms%, scanning electron microscopy showed that the starch expanded graphite phase change composite consisted of many tiny capsule particles. The phase change material was stably encapsulated in the niicrocapsules to prevent leakage during the phase change. Considering its heat storage, thermal conductivity and stability, the optimum amount of EG in the composite phase change material was 8.4 ms%. [ABSTRACT FROM AUTHOR]

Carbon nanotube aerogel is a kind of carbon nanotube with dispersed properties. In this paper, carbon nanotube aerogels were prepared by independent research and development. The carbon nanotube aerogels/natural rubber composites were prepared by traditional crafts. The mechanical properties and thermal conductivity of the as-prepared composites were studied. The results suggest that the tensile strength, tear strength and thermal conductivity of the composites are 47%, 52% and 49.9%, respectively higher than those of the carbon black/natural rubber composites, and reveal the good dispersion characteristics and broad application prospects of the carbon nanotube aerogels. [ABSTRACT FROM AUTHOR]