Graphite blocks with high thermal conductivity derived from natural graphite flake

In this work, natural graphite flake (NG) and mesophase pitch were used as precursor carbons to prepare the graphite blocks, which were doped with Si and Ti powders. After hot-pressed at 2700 °C, we investigated the effect of mean size of NG on properties and microstructure of the graphite blocks. Results showed that both thermal conductivity and flexural strength of the graphite blocks were improved as mean size of NG in raw material increased from 50 to 246 μm. However, a decrease of thermal conductivity was observed when mean size of NG was higher than 246 μm. The density and open porosity were respectively 2.26 g/cm³ and 5.82% when mean size of NG in raw material was 246 μm. The thermal conductivity was enhanced, however, the flexural strength was reduced as hot-pressing temperature increased from 2300 to 3000 °C. The thermal conductivity and flexural strength of the graphite block were respectively 704 W/m K and 21.1 MPa when hot-pressing temperature was 3000 °C. Phase analysis demonstrated there were diffraction peaks of graphite, TiC and α-SiC crystals in the graphite block as the hot-pressing temperature was less than 2500 °C. No SiC crystals were evident when the hot-pressing temperature was 2700 °C or above.     

Expanded graphite/polydimethylsiloxane composites with high thermal conductivity

Expanded graphite (EG)/polydimethylsiloxane (PDMS) composites with high thermal conductivity and high flexibility are prepared in this work. EG derived from natural graphite flake is infiltrated in PDMS prepolymer solution and then hot pressed in a steel mould at 80 °C for 2 h. Optical microscope and scanning electron microscope investigation reveals the interpenetrating network structures in the EG/PDMS composites. When mass fraction of EG increases to 10.0 wt %, the thermal conductivity of EG/PDMS reaches to 4.70 W/m K which should be attributed to the conductive path of graphite platelets. Meanwhile, the composites have excellent flexibility (the compressive modulus is 0.68 Mpa) because of its continuous PDMS network. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44843.     

Low temperature electrochemical preparation of carbon with a high surface area from polytetrafluoroethylene

A mixture of carbon and lithium fluoride dispersed on a molecular scale was prepared at a temperature of 100°C by corrosion of polytetrafluoroethylene using lithium amalgam. The corrosion mechanism was found to be electrochemical. Very highly dispersed amorphous carbon having a specific surface area of 3.5?4.0 × 10³m²/g could be isolated from the mixture by melting the lithium fluoride particles or dissolving them in water. The surface of the carbon particles is hydrophilic. Adsorption of Ar on them obeys an isotherm of the Langmuir type. No capillary condensation occurred during the adsorption.     

剥离石墨及功能石墨片材的低碳环保制备

剥离石墨(EG)是一种很有前途的吸油剂,也是制备柔性石墨薄膜(FGFs)的中间产品.传统的乙二醇生产技术已成为节能减排的重要挑战.提出了一种简单有效的制备剥离石墨的方法,探讨了制备过程中H2SO4和H2O2的用量、室温剥离石墨(RTEG)的制备温度等影响因素.与高温剥离法(HTEG)相比,室温剥离石墨结构均匀,体积和表...     

高碳石墨生产中废酸制备聚合氯化铝铁的研究

研究了利用“碱熔-水洗-酸浸”法提纯石墨过程中含Fe”废酸制备聚合氯化铝铁(PAFC)的工艺条件,结果表明直接用回收酸制备高效混凝剂PAFC切实可行,所制备的PAFC具有适用范围宽,混凝效果优的特点。     

A graphite nanoplatelet/epoxy composite with high dielectric constant and high thermal conductivity

A simple strategy for the preparation of composites with high dielectric constant and thermal conductivity was developed through a typical interface design. Graphite nanoplatelets (GNPs) with a thickness of 20–50 nm are fabricated and homogeneously dispersed in the epoxy matrix. A high dielectric constant of more than 230 and a high thermal conductivity of 0.54 W/mK (a 157% increase over that of pure epoxy) could be obtained for the composites with a lower filler content of 1.892 vol.%. The dielectric constant still remains at more than 100 even in the frequency range of 10⁵–10⁶ Hz. When loaded at 2.703 vol.%, GNP/epoxy composites have a dielectric constant higher than 140 in the frequency range of 10²–10⁴ Hz and a high thermal conductivity of 0.72 W/mK, which is a 240% increase over that of pure epoxy. The high dielectric constant and low loss tangent are observed in the composite with the GNPs content of 0.949 vol.% around 10⁴ Hz. It is believed that high aspect ratio of GNPs and oxygen functional groups on their basal planes are critical issues of the constitution of a special interface region between the GNPs and epoxy matrix and the high performance of the composites.     

Modeling the in-plane thermal conductivity of a graphite/polymer composite sheet with a very high content of natural flake graphite

Natural flake graphite/polymer composite sheets were prepared using tape casting method. The in-plane thermal conductivities, i.e. the thermal conductivities along the tape casting plane, of the composites were measured and the results compared to the predictions by the Maxwell and Agari models. The comparison indicated that both models cannot predict the thermal conductivity of the natural flake graphite/polymer composite at a very high graphite concentration where the flakes were shown from scanning electron microscopy (SEM) images to have a good orientation parallel to the tape casting direction. The SEM images also illustrated that the well oriented flakes formed a continuous graphite–graphite network. Based on the observed structure, a new thermal conductivity model was constructed. The new model applies well to the composites at a large content of highly oriented graphite flakes. The model was also validated by the experimental results from samples with the same graphite content but with different degrees of graphite flake orientation.     

Sustainable nitrogen-doped carbon latexes with high electrical and thermal conductivity

Nitrogen-doped carbon particles were produced using the hydrothermal carbonization of a nitrogen-containing carbohydrate, namely glucosamine, under mild temperature conditions (180 °C) followed by further calcination under a stream of inert gas at 750 °C. The resulting materials contain significant amounts of nitrogen doping within their structure, mainly as quaternary N involved in an aromatized/graphitized carbon structure according to X-ray photoelectron spectroscopy. This nitrogen-doped material was dispersed with nanolatexes having a high affinity for carbon. The resulting hybrid dispersions could be conveniently cast into dense and stable films for thermal and electrical conductivity measurements. The conductivities were commensurate with technical carbon nanotube latex-based films. A morphological analysis of the dispersing mechanism suggests that the potential for high performance materials realized in this contribution is very competitive, but still far from being fully exploited.     

Development of mesophase pitch derived high thermal conductivity graphite foam using a template method

A simple and inexpensive method is described for preparing high thermal conductivity graphite foam by impregnating a coal tar pitch based mesophase pitch into a substrate polyurethane foam template. Mesophase pitch impregnated polyurethane foam was converted into graphite foam by several heat treatments in air as well as in an inert atmosphere. Scanning electron microscope images show the retention of an excellent open pore structure despite volume shrinkage of over 50%. The graphite foam prepared by this sacrificial template method is found to possess a thermal conductivity of 60 W/m K with a compressive strength in the range of 3.0–5.0 MPa. The X-ray diffraction pattern shows an interlayer spacing (d₀₀₂) of 0.3388 nm at a heat treatment temperature of 2400 °C. Different concentrations of slurries of mesophase pitch in water were used in combination with substrate foams of different densities to prepare graphite foams of density in the range 0.23–0.58 g cm⁻³. The specific thermal conductivity of the carbon foam with a low density of 0.58 g cm⁻³ is found to be higher than that of copper metal traditionally used in thermal management applications.     

Shear-induced anisotropy in thermal conductivity of a polyethylene melt

A rotating concentric-cylinder thermal conductivity cell for polymer liquids is described. Thermal conductivity can be measured at temperatures approaching 200°C and at strain rates up to 400 s^?1, The transient heat flux probe (with inner cylinder as heat source and temperature probe) method is used to permit the separation of the viscous heating effect from the probe heating effect. A polyethylene melt was studied and showed that at 50 s^?1, a 2 percent increase in thermal conductivity occurs, followed by a gradual decrease until a value 10 percent less than the no-shear thermal conductivity was found at 400 s^?1. This effect is due to molecular orientation.     

Sublimation from a porous solid of high thermal conductivity

Theory is developed for sublimation from a porous solid of high thermal conductivity.The porous solid, which contains the material to be sublimed, is initially at a temperature T₀ and is submerged in a gas stream at temperature T_∞. The theory includes realistic expressions for the vapour pressure and the heat and mass transfer coefficients and assumes that the transfer occurs in a quasi-steady state.Numerical integration of the system of equations yields simultaneously the temperature of the solid and the fraction sublimed as a function of time. The predictions show good agreement with experimental results for the sublimation of D-camphor from a porous bronze bar.The experimental study includes the independent measurement of the coefficients for external heat transfer, the binary diffusion coefficient of D-camphor in air and of the tortuosity factor of the plate, thus not having any adjustable parameters. The error in the prediction of the time for sublimation is better than 10 per cent.A new unsteady method is proposed and employed for the determination of effective diffusivities (or tortuosity factors) taking into account open and closed pores.     

Steppingstone-inspired construction of high vertical thermal conductivity material with low carbon fiber content

Thermal interface materials (TIMs) with good thermal conductivity are paramount in mitigating the heat concentration challenges encountered during the operation of highly integrated components in sophisticated electronic devices. To optimize the comprehensive performance of TIMs, a balance must be struck: minimizing the filler concentration to attenuate materials hardness while maximizing filler content to bolster the thermal conduction pathway. Drawing inspiration from the orientation of tree branches passing through steppingstones in river, a method was proposed in this study. This method exploits the shear effect of carbon fiber (CF), owing to viscosity variances during diameter extrusion, and the differential flow velocity between CF and alumina to induce a significant degree of orientation. Combined with subsequent flipping and bonding, a TIM with vertically oriented CF was prepared. The TIM was obtained with a mere 12.1 wt% CF incorporation, the composite exhibits a through-plane thermal conductivity of 21.29 W/(m·K), representing an enhancement of two orders of magnitude relative to pristine silicone rubber, while retaining its flexibility and deformability. The orientation degree and high efficiency orientation effect of CF have been characterized via scanning electron microscopy (SEM), thermal conductivity test and light-emitting diode (LED) temperature rise test.     

Thermal conductivity of high density polyethylene filled with graphite

The effect of the grade, the content, and the particle diameter on the thermal conductivity of high‐density polyethylene (HDPE) filled with graphite were studied. The results show an increase of thermal conductivity of the HDPE/graphite composite with increase of graphite content. The thermal conductivity of the HDPE filled with the expanded graphite was larger than that of the HDPE filled with the colloid graphite system. At the same volume content (7%), the thermal conductivity of the former was twice that of the latter one. The particle diameter of the graphite also affected the thermal conductivity of HDPE composites. With increase of the particle diameter of the colloid graphite, the thermal conductivity of the HDPE/graphite increased. However, when the particle diameter of colloid graphite was larger than 15 μm, the increase of thermal conductivity of HDPE/graphite changed by inches. Some models proposed to predict thermal conductivity of a composite in a two‐phase system could not be applied to HDPE filled graphite powder composites, such as Maxwell‐Eucken, Cheng and Vachon, Zieblend, Lewis and Nielsen, Agari and Uno equations. But, according to the increase of thermal conductivity of HDPE composites filled with the colloid graphite, we find that Ziebland equation is suitable except of some constant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3806–3810, 2006     

Continuous SiC skeleton reinforced highly oriented graphite flake composites with high strength and specific thermal conductivity

Highly oriented graphite-based composites have attracted great attention because of their high thermal conductivity (TC),but the low mechanical properties caused by the inhomogeneous distribution and discontinuity of reinforcements restrict the wide applications.Herein,continuous SiC ceramic skeleton reinforced highly oriented graphite flake (SiC/GF) composites were successfully prepared by combining vacuum filtration and spark plasma sintering.The effect of SiC concentration on the microstructu...     

用激光导热仪测定炭黑填充橡胶的导热系数

用激光导热仪测定了5种填充不同量炭黑N 220的胶料在30～140℃时的导热系数,分析了导热系数随温度和炭黑填充量变化的关系,发现胶料的导热系数均随着温度的升高呈线性增大趋势,随炭黑填充量的增加也逐渐增大.将导热系数与温度和炭黑填充量进行了关联,得到了线性回归方程式,进而确立了适合于计算不同温度和不同炭黑N 220填充量胶料导热系数的关联方程A=0.133 77 2.008 74×10-4t 0.001 64 X.将用该方程计算的结果与实验值进行比较,60个数据点的平均相对误差仪为0.93%.     

低黏度高导热绝缘硅脂的制备与性能研究

以PMX-561(聚二甲基硅氧烷)为基体、JHN311(甲基三甲氧基硅烷)为处理氧化铝(Al)2O_3)、氧化锌(Zn O)粉体表面的硅烷偶联剂,制备了低黏度高导热绝缘硅脂。研究结果表明:当w(JHN311)=1.3%(相对于粉体质量而言)时,其对Al)2O_3的表面处理效果相对最优;当不同类型的Al)2O_3质量分数相同时,无规Al)2O_3填充硅脂的热导率和黏度相对更高,但无规(Al)2O_3难以达到高填充量的要求;对大粒径和小粒径Al)2O_3填充硅脂而言,前者的黏度小于后者,但前者的热导率大于后者;当w(粒径分布适宜的复配填料)=92%(相对于硅脂总质量而言)时,所得低黏度高导热的绝缘硅脂之热导率为3.98 W/(m·K)、黏度为20 000 m Pa·s和体积电阻率为9.13×10~(16)Ω·cm。     

Low sintering shrinkage porous mullite ceramics with high strength and low thermal conductivity via foam-gelcasting

Excessive sintering shrinkage leads to severe deformation and cracking, affecting the microstructure and properties of porous ceramics. Therefore, reducing sintering shrinkage and achieving near-net-size forming is one of the effective ways to prepare high-performance porous ceramics. Herein, low-shrinkage porous mullite ceramics were prepared by foam-gelcasting using kyanite as raw material and aluminum fluoride (AlF₃) as additive, through volume expansion from phase transition and gas generated from the reaction. The effects of AlF₃ content on the shrinkage, porosity, compressive strength, and thermal conductivity of mullite-based porous ceramics were investigated. The results showed that with the increase of content, the sintering shrinkage decreased, the porosity increased, and mullite whiskers were produced. Porous mullite ceramics with 30 wt% AlF₃ content exhibited a whisker structure with the lowest shrinkage of 3.5%, porosity of 85.2%, compressive strength of 3.06 ± 0.51 MPa, and thermal conductivity of 0.23 W/(m·K) at room temperature. The temperature difference between the front and back sides of the sample reached 710°C under high temperature fire resistance test. The low sintering shrinkage preparation process effectively reduces the subsequent processing cost, which is significant for the preparation of high-performance porous ceramics.