Carbon black pastes as coatings for improving thermal gap-filling materials

Carbon black pastes were found to be effective as coatings for improving the performance of thermal gap-filling materials, including flexible graphite, aluminum and copper. The thermal contact conductance across copper mating surfaces was increased by up to 180%. A fluidic form of carbon black paste (based on polyethylene glycol) was more effective than a thixotropic form (based on polyol esters). The carbon black pastes were much more effective as coatings than a commercial silver paste. With a carbon black paste coating, aluminum foil (7 μm thick) was a superior gap-filling material compared to similarly coated flexible graphite (130 μm thick). However, without a coating, flexible graphite was superior to aluminum. Commercial silicone-based gap-filling materials were inferior to flexible graphite or aluminum (whether coated or not).     

Significant enhancement of thermal conductivity in graphite/polyester composite via interfacial π–π interaction

Interfacial thermal resistance between matrix and filler is one of the most serious factors hindering heat transfer in composites. Here, a type of liquid crystalline polyester (LCP) containing phenyl pendant groups was intended to blend with pristine graphite by interfacial interaction. The intensity at 26.6° of the wide angle X‐ray diffraction pattern which exceeded that of pristine graphite indicated the existence of a strong interfacial π–π interaction. Both DSC and XRD tests showed that the ordered structure of the LCP matrix is directly affected by the mass fraction of graphite, indicating the interfacial interaction between LCP and graphite. By increasing the content of graphite, the thermal diffusivity showed a sharp increment by 1004%. The maximum thermal conductivity of the composite reached 28.613 W m^?1 K^?1, which was seven times that of traditional thermoplastic blended with graphite. Compared with the data calculated using effective medium theory, interfacial interaction plays a significant role in enhancing the thermal conductivity of the composites. Furthermore, the maximum tensile strength of this series of composites reached 13.3 MPa and the maximum Young's modulus reached 1067 MPa, exhibiting a potential guideline for further applications in flexible electronics. © 2019 Society of Chemical Industry     

Thermal conductivity of exfoliated graphite nanoplatelet paper

Exfoliated graphite nanoplatelets (xGnP) were produced by acid intercalation followed by thermal exfoliation and a controlled size reduction to produce graphite nanoplatelets of 1–15 μm in lateral dimension and approximately 10 nm in thickness. These highly hydrophobic nanoparticles were dispersed and stabilized in a DI water/polyethyleneimine (PEI, a cationic polyelectrolyte) solution. A free standing, mechanically robust paper of xGnP was prepared by vacuum filtration. The effect of xGnP size, polyelectrolyte coating and paper porosity on thermal transport properties was investigated. It was found that the annealing process improves the thermal conductivity by decomposing the PEI molecule that is adsorbed on the xGnP particles while still maintaining the porosity of the paper. Mechanically compressing the sample effectively reduces the pore volumes within the paper and increases the contact area among individual platelet. The strong alignment effect and larger contact area was evidenced by a 80% increase in in-plane thermal conductivity (178 ± 12 W/mK) and a 10% reduction in through-plane conductivity (1.28 ± 0.12 W/mK). This flexible, lightweight, low-cost, paper material made of xGnP particles is a promising candidate for applications requiring 2D heat conduction.     

Synthesis of silica-coated graphite by enolization of polyvinylpyrrolidone and its thermal and electrical conductivity in polymer composites

Silica-coated graphite flakes, which have electrical insulating property and high thermal conductivity, were synthesized by a polyvinylpyrrolidone (PVP)-assisted sol–gel reaction. The critical role of keto-enol tautomerism of PVP in base-catalyzed silica sol–gel reaction was elucidated. The degree of silica coating on graphite was controlled by the amount of PVP and silica precursor, tetraethyl orthosilicate. The silica-coated graphite was used as a filler in thermoplastic polyester elastomer (TPEE). The in-plane (Λ) and through-plane (Λ_⊥) thermal conductivity values of silica-coated graphite/TPEE composites are 67.5% and 86.6% of those of raw graphite/TPEE at 80 phr loading. Even after a severe mixing process under high shear at elevated temperature, silica-coated graphite/TPEE composites retain the perfectly insulating surface resistivity of >10¹³ Ω/sq up to high filler contents.     

Flexible perfluoroalkoxy films filled with carbon nanotubes and their electric heating property

Carbon nanotubes (CNTs) filled perfluoroalkoxy (PFA) films with the thicknesses of about 10 μm have been prepared via blade coating. Both of the CNTs and PFA are aqueous dispersion, which are favorable for the uniform dispersion of fillers into the matrix. The morphology, direct current (DC) resistivity, electrothermal property, and thermal diffusivity of the composite films were studied. We find out that the fraction of CNTs played a vital role in the heating property and thermal transferring capacity of the composite films. Under the input voltage of 110 V, the temperature of PFA composite film with 15 wt % CNT reached to 200 °C, and the thermal diffusivity was about 3.3 mm²/s. We believe these CNTs/PFA films are promising alternatives to work as flexible electric heating devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44782.     

Effective thermal conductivity of a diamond coated heat spreader

Thin diamond coatings are often suggested to enhance thermal conductivity of some substrate. We measured the effective thermal conductivity of varying thicknesses of diamond on tape cast, polycrystalline silicon carbide. The effective thermal conductivity of 30 μm diamond on tape cast silicon carbide is 1.7 W/(cm K). The effective thermal conductivity can be increased to 2.2 W/(cm K) by increasing the diamond thickness to approximately 70 μm. With the measured effective thermal conductivity, the thicknesses of the diamond film and substrate, and knowledge of the thermal conductivity of the substrate material, the thermal conductivity of the diamond layer can be calculated from a simple formula. The thermal conductivity of the 30-μm and 69-μm diamond layers were found to be 3.9 W/(cm K) and 5.8 W/(cm K), respectively.     

Thermal conductivity and electrical resistivity of two types of ATJ-S graphite to 3500° K

Thermal conductivity and electrical resistivity in the with-grain direction of two types of ATJ-S graphite, from 300°K up to 3500°K are reported. Above 500°K, the thermal conductivity appears to follow a T^?1 type function, which is characteristic of Umklapp thermal resistivity processes. The results are analyzed in terms of relative first order contributions of the lattice and electronic components of the thermal conductivity. At high temperatures, our results are at variance with some literature that indicate a ‘strongly’ decreasing thermal conductivity or an essentially ‘temperature independent’ thermal conductivity.     

Ablation behavior of HfC coating with different thickness for carbon/carbon composites at ultra-high temperature

The thickness of the different HfC coatings from 20 μm to 50 μm were prepared on the surface of carbon/carbon (C/C) composites by low pressure chemical vapor deposition (LPCVD). The microstructure and thermal stress of the coatings after ablation were investigated, as well as the effect of thickness and thermal stress on the ablation resistance of the HfC coating was analyzed. After being ablated at a heat flux of 2.4 MW/m² for 60 s, the thermal stress gradually increased at first and then rapidly increased with the increasing thickness of coating. The results indicated that the moderate coating thickness can effectively release the thermal stress generated during the ablation process. The 40 μm-thick HfC coating showed the best ablation resistance with the mass ablation rate and line ablation rate were only 0.13 mg/s and 0.09 μm/s, respectively.     

金属基有机硅树脂涂层复合材料的导热性能

以锌粉为导热填充剂对环氧有机硅树脂进行改性,考察了改性环氧有机硅树脂涂层干膜中锌粉含量对涂层导热系数的影响,分析了涂层厚度对碳钢基材导热性能的影响. 结果表明,环氧有机硅树脂涂层的导热系数约为0.19 W/(m?K),其耐温能力在200℃以上,可保证涂层在中低温烟气余热回收换热器表层长期工作而不发生任何热反应;添加锌粉可改善环氧改性有机硅涂层的导热性能,涂层干膜锌粉25wt%时,涂层材料导热系数达0.35 W/(m?K),较未添加锌粉时增大了84%. 复合材料的导热系数随涂层厚度增加而下降,无涂层的碳钢导热系数为47.59 W/(m?K),涂层厚度为200 ?m时,导热系数降至34.33 W/(m?K).     

Efficient CVD diamond film/alumina composite substrate for high density electronic packaging application

Due to its extreme hardness, chemical and mechanical stability, large band gap, low dielectric constant and highest thermal conductivity, diamond film is expected to be an excellent electronic packaging material for high frequency and high power devices. Under an alcohol concentration of 0.8% and a substrate temperature of 850 °C, high quality diamond films deposited on alumina are obtained by hot filament chemical vapor deposition (HFCVD) method using the optimum parameters determined by an infrared spectroscopic ellipsometer. Prior to the deposition of diamond film, carbon ions are implanted into alumina wafers to release the residual stress between interfaces. The measurement results indicate that dielectric properties and the thermal conductivity of diamond film/alumina composites are improved further with the increase of diamond coating. When the thickness of diamond coating is up to 100 μm, dielectric constant and dielectric loss of diamond film/alumina composite are 6.5 and 1.1 × 10^− 3, respectively. However, a thermal conductivity of 3.98 W/cm·K is obtained.     

Dielectric and electrical conduction behavior of carbon paste electrochemical electrodes,with decoupling of carbon,electrolyte and interface contributions

The electrical conduction and dielectric (capacitive) properties of electrolyte-filled carbon paste electrochemical electrodes are reported, with the carbon, electrolyte (15% H₂SO₄), carbon–electrolyte interface and carbon–contact(metal) interface contributions fully decoupled for the first time. Without full decoupling and with the carbon contributions neglected, the carbon–electrolyte specific interfacial capacitance would be much over-estimated and the carbon–electrolyte interfacial resistivity would be much under-estimated. The carbons and electrolyte are comparable in both dielectric constant and resistivity. The specific contact capacitance is increased and the contact resistivity is decreased by adding the electrolyte to a carbon. The electrolyte is more effective than water in enhancing carbon–liquid and paste–contact interfaces. Conductivity is attractive for batteries and supercapacitors; strong dielectric properties are attractive for supercapacitors but not batteries. Exfoliated graphite provides handleability and excellent volumetric and interfacial conductivities. It gives low carbon dielectric constant, but contributes to the interfacial capacitances. Activated graphite nanoplatelet (GNP) gives high carbon and paste dielectric constants and high specific contact capacitance. Activated carbon gives poor volumetric and interfacial conductivities. Exfoliated graphite is even better than carbon black for batteries; GNP is even better than activated carbon for supercapacitors; an exfoliated-graphite/GNP mixture is suitable for both; natural graphite is not competitive for either.     

Solar reflectance,surface adhesion,and thermal conductivity of wood/natural rubber composite sheet with Tio2/polyurethane topcoat for roofing applications

Effects of titanium dioxide (TiO₂) dosage in polyurethane (PU) coating and PU coating thickness on solar reflectance, surface adhesion, crack resistance to bending, and thermal conductivity of wood/(natural rubber) (WNR) composite sheet were studied before and after prolonged UV aging. The TiO₂ powder content added to the PU coating was varied from 0 to 15 parts per hundred parts of PU. The average PU coating thickness on the WNR composite sheet was altered from 127 ± 10 to 315 ± 10 μm. The experimental results suggested that the solar reflectance slightly increased with increasing TiO₂ powder but did not change upon varying the PU coating thicknesses. The presence of TiO₂ in the PU coating caused a slight decrease in thermal conductivity because of porosities occurring due to the presence of voids, but increasing the TiO₂ powder content in the coating resulted in a progressive increase in thermal conductivity of the composite sheet. In a UV‐accelerated weathering tester (UVB 313 nm), the lightness of the PU coating slightly increased owing to PU discoloration, whereas the solar reflectance, PU/WNR layer adhesion, and crack resistance to bending remained unaffected with increasing UV aging time. J. VINYL ADDIT. TECHNOL., 18:184–191, 2012. © 2012 Society of Plastics Engineers     

Laser degradation of polymer coatings on reflective heat sinks

The 10.6 μm laser-induced degradation and volatilization of thin non-char forming organic polymer coatings on aluminum heat sinks has been investigated. Volatilization rates were determined from coating absorptivities measured as a function of irradiation time at 110 W/cm². First order volatilization rate constants (kJ^?1) were: poly(ethylene-co-ethyl acrylate) 0.30, polystyrene 0.85, poly(ethyl methacrylate) 1.6, poly(methyl methacrylate) 2.1, and nitrocellulose 3.1. Residual coating thicknesses at infinite irradiation time are reported. Degradation results from exposure to the thermal environment provided by the heat sink as well as by the direct absorption of laser radiation. Relative polymer thermal stabilities measured at this laser irradiance level and by conventional heating methods are in agreement.     

Magnetron sputter deposition of hafnium nitride coating on high density graphite and niobium substrates

Hafnium nitride (HfN) is a refractory compound considered to be a suitable material for reaction barriers. The present paper deals with the preparation of HfN thin films by reactive magnetron sputtering on high density (HD) graphite and niobium substrates. Deposition process parameters have been optimised with Si(100) substrate in order to get HfN coating of 3 μm thickness. The optimised parameters were used to deposit HfN on HD graphite and on niobium substrates. The results showed that HfN coating with a thickness of 2.8 μm was successfully deposited on HD graphite and niobium substrates. The presence of HfN was confirmed by glancing incidence X-ray diffraction (GIXRD) and X-ray photoelectron spectroscopy (XPS). XRD studies on HfN coating on Si(100), HD graphite and Nb substrates showed nanocrystalline grains of size 130, 55 and 46 Å, respectively. The surface morphology of HfN coating on HD graphite and niobium by atomic force microscope (AFM) and scanning electron microscope (SEM) showed that nanoparticles are getting agglomerated into clusters. The HfN coating on niobium substrate exhibited good adhesion compared to that on HD graphite as studied by microscratch test. The thermal stress generated in the sputter deposited HfN coating on HD graphite and niobium substrates were calculated by analytical formula for thermal stress. The tensile and highly compressive stresses observed in the HfN coating on niobium and HD graphite, respectively, indicated a lower adhesive strength of the coating on the later than that of the former.     

基于聚偏氟乙烯/石墨的换热板片材料的制备及导热性能研究

以聚偏氟乙烯（PVDF）为基体,石墨为填料,使用溶液共混法制备导热复合材料,研究了石墨填充量、混炼工艺等对复合材料导热性能的影响。结果表明,石墨填充量超过40 %（质量分数,下同）后,复合材料的热导率呈明显增大的趋势;当石墨填充量达到70 %时,PVDF/石墨复合材料的热导率达到2092 W/（m·K）,是纯PVDF热导率的110倍;270 μm：106 μm石墨含量比为1∶9时,热导率达到最大值;采用叠片式转子比腰鼓形转子可以制备出更高热导率的复合材料;转子转速和混炼时间对复合材料的热导率影响不大;设计并制备了板式换热器换热板片,实验验证了基于PVDF/石墨复合材料加工生产换热板片的可行性。     

Dense SiC Coatings as Barrier Layer on Graphite Heat Elements in Furnaces for Smelting Silicon in Photovoltaic Industry

This study puts forward an application of a dense SiC coating of graphite heat elements as a barrier layer to prevent the spoilage of the purity of photovoltaic Si elements by impurities of the graphite. The SiC barrier performance in high‐temperature vacuum environment has been analyzed measuring the mass loss of graphite with/without coating of 5, 20, 30 μm 1200, 1400, and 1600°C. A thickness of 20 μm showed to be the best choice and could reduce the weight loss by more than 90%. The adhesion strength of samples decreased with the increase in heat treatment temperature.     

Improving room-temperature electrochemical performance of solid-state lithium battery by using electrospun La2Zr2O7 fibers-filled composite solid electrolyte

Low ionic conductivity at room temperature and poor interfacial compatibility are the main obstacles to restrain the practical application of polymer solid electrolytes. In this work, lanthanum zirconate (LZO) fibers were prepared by electrospinning method and used for the first time as fillers in sandwich polypropylene carbonate (PPC)-based solid electrolyte. Meanwhile, a graphite coating was applied on one surface of the composite solid electrolyte (CSE) membrane. The results show that the LZO fibers significantly increases the room-temperature electrochemical performance of the CSE, and the graphite coating enhances the interfacial compatibility between electrolyte and lithium anode. Furthermore, an ultra-thin PPC-LZO CSE with a total thickness of 22 μm was prepared and used in NCM622/CSE/Li solid-state cell, which shows an initial discharge capacity of 165.6 mAh/g at the current density of 0.5C and a remaining capacity of 113.0 mAh/g after 250 cycles at room temperature. Rise to 1C, the cell shows an initial discharge capacity of 154.2 mAh/g with a remaining capacity of 95.6 mAh/g after 250 cycles. This ultra-thin CSE is expected to be widely applied in high energy-density solid-state battery with excellent room-temperature electrochemical performances.     

Thermal conductivity and electrical resistivity of poco grade AXF-Q1 graphite to 3300° K

Thermal conductivity and electrical resistivity of Poco Grade AXF-Q1 Graphite are presented from 110 to 3300°K. The temperature range was covered by two steady state techniques: (a) a comparative rod apparatus and (b) a radial inflow apparatus. Above 500°K the thermal conductivity data are represented quite well by a T^?1 type function, that is characteristic of Umklapp scattering processes which give rise to the thermal resistivity. We have further shown that the lattice conduction accounts for about 80 per cent of the heat transport even at 3300°K. For more highly graphitized graphite and other cokes, the results can be different. Our results are at variance with some literature that indicate a ‘strongly’ decreasing thermal conductivity above 3000°K or a ‘constant’ thermal conductivity with a ‘strong’ electronic conduction at up to 3300 °K.     

Improvement in thermal conductivity and mechanical properties of ethylene‐propylene–diene monomer rubber by expanded graphite

Thermally conductive fillers are usually employed in the preparation of rubber composites to enhance thermal conductivity. In this work, ethylene‐propylene‐diene monomer rubber (EPDM)/expanded graphite (EG) and EPDM/graphite composites with up to 100 phr filler loading were prepared. Compared to EPDM/graphite compounds with the same filler loading, stronger filler network was demonstrated for EPDM/EG compounds. Thermal conductivity and mechanical properties of EPDM/graphite and EPDM/EG composites were compared and systematically investigated as a function of the filler loading. The thermal conductivity of both EPDM/graphite and EPDM/EG composites increased with increasing volume fraction of fillers, and could be well fitted by Geometric Mean Model. The thermal conductivity as high as 0.910 W · m⁻¹ · K⁻¹ was achieved for the EPDM/EG composite with 25.8 vol% EG, which was ∼4.5 times that of unfilled EPDM. Compared to EPDM/graphite composites, EPDM/EG composites exhibited much more significant improvement in thermal conductivity and mechanical properties, which could be well correlated with the better filler‐matrix interfacial compatibility and denser structure in EPDM/EG composites, as revealed in the SEM images of tensile fracture surfaces. POLYM. COMPOS., 38:870–876, 2017. © 2015 Society of Plastics Engineers     

Thermal conductivity and electromagnetic shielding effectiveness of composites based on Ag‐plating carbon fiber and epoxy

Thermally conductive and electromagnetic interference shielding composites comprising low content of Ag‐plating carbon fiber (APCF) were fabricated as electronic packing materials. APCF as conductive filler consisting of carbon fiber (CF) employed as the structural component to reinforce the mechanical strength, and Ag enhancing electrical conductivity, was prepared by advanced electroless Ag‐plating processing on CF surfaces. Ag coating had a thickness of 450 nm without oxide phase detected. The incorporation of 4.5 wt % APCF into epoxy (EP) substrate yielded thermal conductivity of 2.33 W/m·K, which is approximately 2.6 times higher than CF–EP composite at the same loading. The APCF–EP composite performed electromagnetic shielding effectiveness of 38–35 dB at frequency ranging from 8.2 to 12.4 GHz in the X band, and electromagnetic reflection was the dominant shielding mechanism. At loading content of APCF up to 7 wt %, thermal conductivity of APCF–EP composites increased to 2.49 W/m·K. Volume resistivity and surface resistivity decreased to 9.5 × 10³ Ω·cm and 6.2 × 10² Ω, respectively, which approached a metal. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42306.