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High Thermal Conductivity (high + thermal_conductivity)
Selected AbstractsCarbon Nanosheets for Polymeric Nanocomposites with High Thermal ConductivityADVANCED MATERIALS, Issue 20 2009L. Monica Veca Nanometer-thick 2D carbon structures ("carbon nanosheets") are processed from commercially available expanded graphite. These carbon nanosheets are then incorporated in various polymers to produce flexible nanocomposites that exhibit record-setting anisotropic thermal conductivities, which may prove highly valuable in many technological applications. [source] Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Microstructure Tailoring for High Thermal Conductivity of ,-Si3N4 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Hiroshi Yokota ,-Si3N4 ceramics sintered with Yb2O3 and ZrO2 were fabricated by gas-pressure sintering at 1950°C for 16 h changing the ratio of "fine" and "coarse" high-purity ,-Si3N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of "coarse" powder with a "fine" one, while maintaining high thermal conductivity (>140 W·(m·K),1). Thus, this work demonstrates that it is possible for ,-Si3N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder. [source] Boron Nanotube,Polymer Composites: Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as Fillers (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Mater. Composites formed through embedding of high-concentration boron nitride nanotubes in polymers are reported by C. Y. Zhi et al. on page 1857. The composites possess high thermal conductivity, high break-over voltage, low coefficient of thermal expansion, and other favorable properties. These polymeric composites are promising highly thermoconductive electrically insulating materials for a range of applications. [source] Towards Thermoconductive, Electrically Insulating Polymeric Composites with Boron Nitride Nanotubes as FillersADVANCED FUNCTIONAL MATERIALS, Issue 12 2009Chunyi Zhi Abstract Ultilizing boron nitride nanotubes (BNNTs) as fillers, composites are fabricated with poly(methyl methacrylate), polystyrene, poly(vinyl butyral), or poly(ethylene vinyl alcohol) as the matrix and their thermal, electrical, and mechanical properties are evaluated. More than 20-fold thermal conductivity improvement in BNNT-containing polymers is obtained, and such composites maintain good electrical insulation. The coefficient of thermal expansion (CTE) of the BNNT-loaded polymers is dramatically reduced because of interactions between the polymer chains and the nanotubes. Moreover, the composites possess good mechanical properties, as revealed by Vickers microhardness tests. This detailed study indicates that BNNTs are very promising nanofillers for polymeric composites, allowing the simultaneous achievement of high thermal conductivity, low CTE, and high electrical resistance, as required for novel and efficient heat-releasing materials. [source] Sintered Reaction-Bonded Silicon Nitride with High Thermal Conductivity and High StrengthINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 2 2008You Zhou Sintered reaction-bonded silicon nitride (SRBSN) materials were prepared from a high-purity Si powder doped with Y2O3 and MgO as sintering additives by nitriding at 1400°C for 8 h and subsequently postsintering at 1900°C for various times ranging from 3 to 24 h. Microstructures and phase compositions of the nitrided and the sintered compacts were characterized. The SRBSN materials sintered for 3, 6, 12, and 24 h had thermal conductivities of 100, 105, 117, and 133 W/m/K, and four-point bending strengths of 843, 736, 612, and 516 MPa, respectively. Simultaneously attaining thermal conductivity and bending strength at such a high level made the SRBSN materials superior over the high-thermal conductivity silicon nitride ceramics that were prepared by sintering of Si3N4 powder in our previous works. This study indicates that the SRBSN route is a promising way of fabricating silicon nitride materials with both high thermal conductivity and high strength. [source] Non-isothermal multi-phase modeling of PEM fuel cell cathodeINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2010Nada Zamel Abstract In this study, numerical simulation has been carried out for the heat transfer and temperature distribution in the cathode of polymer electrolyte membrane fuel cells along with the multi-phase and multi-species transport under the steady-state condition. The commercial software, COMSOL Multiphysics, is used to solve the conservation equations for momentum, mass, species, charge and energy numerically. The conservation equations are applied to the solid, liquid and vapor phases in the bipolar plate and gas diffusion (GDL) and catalyst layers of a two-dimensional cross section of the cathode. The catalyst layer is assumed to be a finite domain and the water production in the catalyst layer is considered to be in the liquid form. The temperature distribution in the cathode is simulated and then the effects of the relative humidity of the air stream, the permeability of the cathode and the flow channel shoulder to channel width ratio are investigated. It is shown that the highest temperature change, both in the in-plane and across-the-plane directions, occurs in the GDL, while the highest temperature is reached in the catalyst layer. The distribution of temperature in the bipolar plate is shown to be relatively uniform due to the high thermal conductivity of the plate. A decrease in the inlet relative humidity of the air stream results in the decrease of the maximum temperature due to the absorption of heat during the evaporation of liquid water in the GDL and catalyst layer. The non-uniformity of the temperature distribution, especially in the catalyst layer, is observed with the increase of the permeability of the cathode. Similarly, the decrease of the channel shoulder to channel width ratio leads to a non-uniform distribution of temperature especially under the channel areas. Copyright © 2009 John Wiley & Sons, Ltd. [source] Heat transfer enhancement of fatty acids when used as PCMs in thermal energy storageINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2008Muhsin Mazman Abstract Phase change materials (PCM) used in latent heat storage systems usually have very low thermal conductivities. This is a major drawback in maintaining the required heat exchange rate between PCM and heat transfer fluid. This paper investigates the enhancement of the heat transfer between PCM and heat transfer fluid, using high thermal conductivity as additives like stainless steel pieces, copper pieces and graphite,PCM composite material. In the experiments, palmitic,lauric acid (80:20) (PL) and stearic,myristic acid (80:20) (SM) were used as PCMs. Test results show that heat transfer enhancement of copper pieces was better at 0.05 Ls,1 flow rate compared to 0.025 Ls,1. Using copper as an additive increased the heat transfer rate 1.7 times for melting and 3.8 times for freezing when flow rate was 0.050 Ls,1. Decreasing the flow rate from 0.050 to 0.025 Ls,1, increased the melting times 1.3 times and freezing times 1.8 times, decreasing heat transfer rates accordingly. The best result of heat transfer enhancement was observed for the PCM,graphite composite. However, changing the flow rate did not affect the heat transfer rate when graphite was used as additive. Copyright © 2007 John Wiley & Sons, Ltd. [source] Degradation behavior of nanoreinforced epoxy systems under pulse laserJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2009M. Calhoun Abstract Nanocomposites using EPON 824 as their matrix were exposed to pulse laser at 532 nm for various time intervals. The developed nanomaterials used for this study were manufactured using EPON 824 with multiwalled carbon nanotubes (MWCNTs) at a loading rate of 0.15% by weight and nanoclays at a loading rate of 2% by weight as reinforcements. The effect of laser irradiation on polymer composites has been investigated. The degradation mechanism for the epoxy was of a laser induced burning nature. Of all specimens tested, the ultimate strength of the MWCNT-reinforced specimens decreased the most as a function of radiation time; the nanoclay-reinforced epoxy retained the most strength after 2 min of laser radiation. In addition, the threshold fluence for decomposition indicated that less energy was required to initiate decomposition in the MWCNT-reinforced epoxy than in the nanoclay-reinforced epoxy. This can be attributed to the high thermal conductivity of the carbon nanotubes. Measurement of surface damage in the material was observed via electron microscopy. Fourier transform infrared spectroscopy was used to investigate changes to the molecular structure as a function of exposure time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Thermal stability and ablation properties of silicone rubber compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Eung Soo Kim Abstract Effects of incorporation of clay and carbon fiber (CF) into a high temperature vulcanized (HTV) silicone rubber, i.e., poly(dimethylsiloxane) (PDMS) containing vinyl groups, on its thermal stability and ablation properties were explored through thermogravimetric analyses (TGA) and oxy-acetylene torch tests. Natural clay, sodium montmorillonite (MMT), was modified with a silane compound bearing tetra sulfide (TS) groups to prepare MMTS4: the TS groups may react with the vinyl groups of HTV and enhance the interfacial interaction between the clay and HTV. MMTS4 layers were better dispersed than MMT layers in the respective composites with exfoliated/intercalated coexisting morphology. According to TGA results and to the insulation index, the HTV/MMTS4 composite was more thermally stable than HTV/MMT. However, addition of CF to the composites lowered their thermal stability, because of the high thermal conductivity of CF. The time elapsed for the composite specimen, loaded with a constant weight, to break off after the oxy-acetylene flame bursts onto the surface of the specimen was employed as an index for an integrated assessment of the ablation properties, simultaneously taking into consideration the mechanical strength of the char and the rate of decomposition. The elapsed time increased in the order of: HTV < HTV/CF , HTV/MMTS4 < HTV/CF/MMTS4 , HTV/MMT < HTV/CF/MMT. This order was different from the increasing order of the thermal stability determined by TGA results and the insulation index. The decreased degree of crosslinking of the composites with MMTS4 compared with that of the composite with MMT may be unfavorable for the formation of a mechanically strong char and could lead to early rupture of the HTV/MMTS4 specimen. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Novel microfibrous-structured silver catalyst for high efficiency gas-phase oxidation of alcoholsAICHE JOURNAL, Issue 6 2010Jiping Mao Abstract Novel microfibrous-structured silver catalysts were developed for gas-phase selective oxidation of mono-/aromatic-/di-alcohols. Sinter-locked three-dimensional microfibrous networks consisting of 5 vol % 8-,m-Ni (or 12-,m-SS-316L) fibers and 95 vol % void volume were built up by the papermaking/sintering processes. Silver was then deposited onto the surface of the sinter-locked fibers by incipient wetness impregnation method. At relatively low temperatures (e.g., 380°C), the microfibrous-structured silver catalysts provided quite higher activity/selectivity compared to the electrolytic silver. The microfibrous Ag/Ni-fiber offered much better low-temperature activity than the Ag/SS-fiber. The interaction at Ag particles and Ni-fiber interface not only visibly increased the active/selective sites of Ag+ ions and Agn,+ clusters but also significantly promoted their low-temperature reducibility and ability for O2 activation. In addition, the microfibrous structure provided a unique combination of large void volume, entirely open structure, high thermal conductivity and high permeability. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Spark Plasma Sintered Silicon Nitride Ceramics with High Thermal Conductivity Using MgSiN2 as AdditivesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2009Gui-hua Peng Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°,1600°C for 3,12 min, using ,-Si3N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%,-Si3N4 phase left in the sintered material. ,-Si3N4 was completely transformed to ,-Si3N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K),1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate ,-Si3N4 ceramics with high thermal conductivity when appropriate additives are used. [source] Microstructure Tailoring for High Thermal Conductivity of ,-Si3N4 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003Hiroshi Yokota ,-Si3N4 ceramics sintered with Yb2O3 and ZrO2 were fabricated by gas-pressure sintering at 1950°C for 16 h changing the ratio of "fine" and "coarse" high-purity ,-Si3N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of "coarse" powder with a "fine" one, while maintaining high thermal conductivity (>140 W·(m·K),1). Thus, this work demonstrates that it is possible for ,-Si3N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder. [source] Evidence for late-Pleistocene permafrost in the New Jersey Pine Barrens (latitude 39°N), eastern USAPERMAFROST AND PERIGLACIAL PROCESSES, Issue 3 2003Hugh M. French Abstract Relict sand wedges, up to 2.5,m deep and 0.4,m wide, are present in the Pine Barrens of southern New Jersey. They indicate the previous existence of permafrost. The wedges are composed predominantly of sand that shows evidence of wind transport and abrasion. Optically-stimulated-luminescence dating of infill material indicates that thermal-contraction-cracking and emplacement of the sand infill must have occurred during two separate periods during the Late Pleistocene. The most recent was in Late Wisconsinan times,,15,18,ka. An earlier period of permafrost conditions is indicated by dates >55,65,ka. On both occasions, the Late-Pleistocene ice sheets would have advanced as far south as northern New Jersey and strong winds would have occurred in the lower mid-latitudes. The sandy soils of the Pine Barrens would have allowed the ice-marginal periglacial zone to extend southwards into southern New Jersey. The sparse tundra vegetation on the sandy substrate, with its relatively high thermal conductivity, would have permitted deep frost penetration because the ,thermal offset' would have been minimized. A mean annual air temperature of between ,3.0°C and ,4.0°C is inferred. Permafrost was probably discontinuous and less than 10,15,m in thickness. Episodes of permafrost thaw are indicated by the widespread occurrence of deformed sediments (,thermokarst involutions') and by various small-scale non-diastrophic structures associated with bog ironstone beds. The presence of soil (ground) wedges in southern New Jersey and adjacent Delaware also suggest conditions of deep seasonal frost, probably when the most recent permafrost degraded. Copyright © 2003 John Wiley & Sons, Ltd. [source] New composites with high thermal conductivity and low dielectric constant for microelectronic packagingPOLYMER COMPOSITES, Issue 2 2010Wei Ling Three composites based on cyanate (CE) resin, aluminum nitride (AlN), surface-treated aluminum nitride [AlN(KH560)], and silicon dioxide (SiO2) for microelectronic packaging, coded as AlN/CE, AlN(KH560)-SiO2(KH560)/CE, and AlN-SiO2/CE composite, respectively, were developed for the first time. The thermal conductivity and dielectric constant of all composites were investigated in detail. Results show that properties of fillers in composites have great influence on the thermal conductivity and dielectric constant of composites. Surface treatment of fillers is beneficial to increase the thermal conductivity or reduce dielectric constant of the composites. Comparing with binary composite, when the filler content is high, ternary composites possess lower thermal conductivity and dielectric constant. The reasons leading to these outcomes are discussed intensively. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] Thermal conductivity and mechanical properties of aluminum nitride filled linear low-density polyethylene compositesPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Junwei Gu To acquire polymer composites with high thermal conductivity and mechanical properties, the aluminum nitride (AlN) microparticles modified with titanate coupling reagent of isopropyltrioleictitanate (NDZ-105) were employed to blend linear low-density polyethylene (LLDPE) via powder mixing method. Thermal conductive coefficient of the AlN/LLDPE composites was measured using hot disk thermal analyzer, and the thermal stability characteristics of AlN/LLDPE composites were mainly investigated via thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC). The results indicated that the use of AlN particles modified by NDZ-105 significantly enhanced thermal conductivity and mechanical properties of AlN/LLDPE composites. The thermal conductivity coefficient , was 1.0842 W/mk with 30% volume fraction of AlN, about three times higher than that of native LLDPE. The tensile strength of composites was maximum (17.42 MPa) with 20% mass fraction of AlN. DSC analyses results indicated that AlN had an influence on the melting temperature and the crystallinity of LLDPE. Additionally, TGA analyses showed that the thermal stability of LLDPE was significantly increased with addition of AlN. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Thermal conductive PS/graphite compositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2009Haoming Tu Abstract Polystyrene (PS) was compounded with graphite that possesses high thermal conductivity and layer structures, and the PS/graphite thermal conductive nano-composites were prepared. Thermal conductivity of PS improved remarkably in the presence of the graphite, and a much higher thermal conductivity of 1.95,W/m,K can be achieved for the composite with 34,vol% of colloidal graphite. The Maxwell-Eucken model and the Agari model were used to evaluate the thermal conductivity of the composites. For the purpose of improving the interfacial compatibility of PS/graphite, realizing the exfoliation and nano-dispersion of graphite in the PS matrix, three intercalation methods, including rolling intercalation, solvent intercalation, and pan milling intercalation, were applied to prepare the composites, and the morphologies, thermal conductivities, and mechanical properties of the composites were investigated. It should be noted that the one prepared by pan milling intercalation not only had excellent thermal conductivity but also much higher mechanical properties, resulting from a high degree of layer exfoliation of the graphite, the formation of the chain structure agglomerates of the graphite, and the creation of more conductive paths under the strong shear stress of pan milling. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analytical Model for Predicting Thermal Bridge Effects due to Vacuum Insulation Panel Barrier Envelopes,BAUPHYSIK, Issue 1 2008Martin Tenpierik ir. arch. Because of a necessity for sustainability and thus for a reduction of the amount of primary energy generated with fossil fuels, vacuum insulation panels (VIP) have recently caught the attention of practitioners in the building industry. The reduction of layer thickness may be considered among the most promising features for large-scale application of VIPs in buildings. The high barrier laminate (or casing) with relatively high thermal conductivity envelops the core material, thus introducing a thermal bridge at the panel edges and corners. Especially for barrier laminates containing ,thick' metal foils, the thermal bridge effect needs to be considered thoughtfully. In this contribution analytical models are presented which on the one hand allow rapid estimation of the VIP's overall thermal performance and on the other hand show the influence of material and geometric parameters on this performance. The analytical models are validated through numerical simulations. Rechenmodell zur Vorhersage von Wärmebrückeneffekten an der Hülle aus Hochbarrierefolien von Vakuum-Isolations-Paneelen (VIP). Aufgrund der Notwendigkeit von nachhaltigem Bauen und Energieeinsparung wird zunehmend der Einsatz von Vakuum-Isolations-Paneelen (VIP) zur Wärmedämmung im Bauwesen erwogen, insbesondere ist damit die erhebliche Reduzierung der Wärmedämmschichtdicke möglich. Die Umhüllung aus Hochbarrierefolien erfordert allerdings die Berücksichtigung der Wärmebrückenwirkung. Der vorliegende Beitrag stellt Berechnungsmodelle vor, welche einerseits die schnelle Abschätzung des thermischen Verhaltens von VIP-Elementen ermöglichen und andererseits den Einfluss der Geometrie und Konstruktion der Elemente aufzeigen. Die Berechnungsmodelle wurden anhand von Simulationen validiert. [source] | |||||||||||||||||||||||||