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1.
High loadings of fillers are usually needed to achieve high-thermal conductivity (TC) of polymer-based composites, which inevitably sacrifices processability and meanwhile causes high-cost. Therefore, it is of great significance to achieve high-TC composites under low-filler loading. Here, a novel p-phenylenediamine (PPD) modified expanded graphite (EG-PPD)/epoxy (EP) composite with high TC and low-filler content was successfully prepared via pre-dispersion and vacuum assisted mixing strategy. With the improved interfacial compatibility between EG and EP by PPD, the prepared EG-PPD/EP composite exhibited excellent thermal management performance, resulting in the TC of which reached 4.00 W·m−1·K−1 with only 10 wt% (5.59 vol%) of EG-PPD, which is approximately 19 times higher than that of pure EP. Meantime, the interface thermal resistance of EG-PPD/EP composite between EG-PPD and EP is reduced by 33% compared with EG/EP composite. This composite with excellent TC property is expected to be used in thermal management field.  相似文献   

2.
High-performance ceramics with low thermal conductivity, high mechanical properties, and idea thermal expansion coefficients have important applications in fields such as turbine blades and automotive engines. Currently, the thermal conductivity of ceramics has been significantly reduced by local doping/substitution or further high-entropy reconfiguration of the composition, but the mechanical properties, especially the fracture toughness, are insufficient and still need to be improved. In this work, based on the high-entropy titanate pyrochlore, TiO2 was introduced for composite toughening and the high-entropy (Ho0.2Y0.2Dy0.2Gd0.2Eu0.2)2Ti2O7-xTiO2 (x = 0, 0.2, 0.4, 1.0 and 2.0) composites with high hardness (16.17 GPa), Young's modulus (289.3 GPa) and fracture toughness (3.612 MPa·m0.5), low thermal conductivity (1.22 W·m−1·K−1), and thermal expansion coefficients close to the substrate material (9.5 ×10−6/K) were successfully prepared by the solidification method. The fracture toughness of the composite toughened sample is 2.25 times higher than that before toughening, which exceeds most of the current low-thermal conductivity ceramics.  相似文献   

3.
Thermally conductive epoxy nanocomposite with core–shell structured filler beads has been prepared. The core represents plasma-treated poly(methyl methacrylate) bead, and the shell, amine-functionalized reduced graphene oxide (frGO) sheets. The negatively charged core and the positively charged shell form core–shell unified structure through electrostatic attraction and the conductive bridges are formed among neighboring filler particles in the composite mass. The epoxy composite prepared with these core–shell structured filler shows a thermal conductivity of 0.72 W m−1 K−1 for an overall frGO concentration of as low as 0.96 wt %. Pal model has been applied to evaluate the effective thermal conductivity of frGO sheets that have been realized in the epoxy composition. Assuming the maximum possible volume packing fraction of the spherical beads for random jamming to be equal to 0.63, the effective thermal conductivity has been estimated as 280 W m−1 K−1. Evaluation of the effective thermal conductivity is a step forward to in-depth study of real contribution of the highly conductive fillers in the polymer composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47377.  相似文献   

4.
A composite was prepared by in-situ polymerization of liquid crystal epoxy (LCE4) with a low dielectric and high thermal conductivity boron nitride (BN) filler, which the filler (f-BN) was surface-functionalized by γ-glycidoxypropyltrimethoxysilane (KH560) and aminopropylisobutyl polyhedral oligomeric silsesquioxane (NH2-POSS). The surface-functionalized BN was more uniformly dispersed in LCE4, which improved the interfacial compatibility between inorganic and organic phases. Compared with pure LCE4, KH560, and NH2-POSS modified f-BN/LCE4 composites exhibited a higher glass transition temperature, better thermal stability, and higher thermal conductivity. For example, when the f-BN content reached 30 wt%, the energy storage modulus of the composite increased to 2580 MPa, and the glass transition temperature was 103°C. The thermal conductivity of this 30 wt% f-BN composite was 0.48 W m−1 K−1, 128.6% higher than that of pure LCE4. In addition, thermal stability, low hygroscopicity, and dielectric properties of the composites were characterized and analyzed to explore the application prospects of f-BN/LCE4 composites in electronic packaging and in high-performance microelectronic devices.  相似文献   

5.
To develop insulating materials with a high thermally conductive anisotropy, planarly aligned mesogenic epoxy (ME) resin film was fabricated by uniaxial coating on a hydrophobic polyethylene terephthalate substrate. Grazing incidence small-angle X-ray scattering (GISAXS) and transmission SAXS measurements exhibited that the films spontaneously formed uniaxially aligned monodomain-like smectic structures by curing on the hydrophobic substrate. Then, an in- and out-of-plane thermal conductivity of 10 and 0.048 W m−1 K−1 and outstanding thermal conductivity anisotropy of 208 have been confirmed, respectively. The ME resin films with high thermal conductivity can be applied as insulating materials for multiple-layer electrical and electronic devices.  相似文献   

6.
The lattice thermal conductivity of ZrC with different Hf contents was investigated theoretically. The density of states and electron density differences were calculated for ZrC and (Zr,Hf)C containing 3.125 or 6.25 at% Hf. It was found that the electronic structure did not change significantly with the Hf additions. Lattice thermal conductivities were calculated for all of the compositions by combining first-principles calculations with the Debye–Callaway model. The theoretical lattice thermal conductivity of ZrC was 68 W·m−1·K−1 at room temperature. When adding 3.125 and 6.25 at% Hf into ZrC, the lattice thermal conductivities decreased to 18 and 15 W·m−1·K−1, respectively. The mechanism for the decreased conductivity is that with the addition of Hf impurities, the frequency of the acoustic phonons decreased, which resulted in decreases in the Debye temperature and lattice thermal conductivity.  相似文献   

7.
《Ceramics International》2023,49(18):29808-29819
Phase change materials (PCMs) are prospective energy materials that are widely applied in building energy conservation, waste heat recovery, infrared stealth technology and solar dynamic power system. The enhancement of heat transfer and leak-proof performance are critical to PCMs. Although geopolymers have been applied in thermal energy storage, meanwhile, hierarchically porous geopolymers have already shown superb performance in various functional applications, to the authors’ knowledge, no report concerning the application of hierarchical porous ones have been issued. This paper concerns the preparation of a shape-stabilized composite PCMs, consisting of hierarchically porous kaolinite-based geopolymer (PKG) embedding polyethylene glycol 4000 (PEG4000), which shows promising prospects in thermal energy storage. Optimized porous geopolymer matrices feature high porosity (>83%), combined with high specific surface area (4.7 m2/g) and thermal conductivity (TC, 1.324 W·m−1·K−1). Furthermore, the shape-stabilized composite PCMs show excellent thermal energy storage properties: loading rate of 80.93 wt%, latent heat of 168.80 J g−1 and TC of ∼0.36 W·m−1·K−1 at 20–30 °C, which is 1.64 times of the TC of pure PEG4000. Finally, the photothermal conversion performances of the shape-stabilized composite PCMs were also simulated.  相似文献   

8.
Dense silicon carbide/graphene nanoplatelets (GNPs) and silicon carbide/graphene oxide (GO) composites with 1 vol.% equimolar Y2O3–Sc2O3 sintering additives were sintered at 2000 °C in nitrogen atmosphere by rapid hot-pressing technique. The sintered composites were further annealed in gas pressure sintering (GPS) furnace at 1800 °C for 6 h in overpressure of nitrogen (3 MPa). The effects of types and amount of graphene, orientation of graphene sheets, as well as the influence of annealing on microstructure and functional properties of prepared composites were investigated. SiC-graphene composite materials exhibit anisotropic electrical as well as thermal conductivity due to the alignment of graphene platelets as a consequence of applied high uniaxial pressure (50 MPa) during sintering. The electrical conductivity of annealed sample with 10 wt.% of GNPs oriented parallel to the measuring direction increased significantly up to 118 S·cm−1. Similarly, the thermal conductivity of composites was very sensitive to the orientation of GNPs. In direction perpendicular to the GNPs the thermal conductivity decreased with increasing amount of graphene from 180 W·m−1 K−1 to 70 W·m−1 K−1, mainly due to the scattering of phonons on the graphene – SiC interface. In parallel direction to GNPs the thermal conductivity varied from 130 W·m−1 K−1 up to 238 W·m−1 K−1 for composites with 1 wt.% of GO and 5 wt.% of GNPs after annealing. In this case both the microstructure and composition of SiC matrix and the good thermal conductivity of GNPs improved the thermal conductivity of composites.  相似文献   

9.
Low thermal conductivity of polypropylene (PP) is a key factor in limiting its use for the manufacture of solar heaters. To overcome this problem, in the present work, two different methods were tested to increase the thermal conductivity of a PP matrix by increasing the dispersion and compatibility between PP and carbon nanoparticles (CNPs). In the first method, CNPs modified superficially by plasma of propylene were used, and in the second, mixtures of CNPs (carbon nanofibers and graphene platelets in 9:1, 8:2, and 7:3 ratios) were used. Dispersion and compatibility between PP and CNPs were tested by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results show that both methodologies increase the dispersion and compatibility and, therefore, the thermal conductivity of the PP matrix (0.14 W m−1 K−1), which reached up 0.90 W m−1 K−1. It was also observed that dispersion is a key factor in high concentrations (5 wt/wt%) of CNPs to obtain high thermal conductivity and compatibility in low concentrations (1 wt/wt%). Finally, only a synergistic effect was observed at 1 wt/wt% when using surface-modified CNPs by plasma and at 5 wt/wt% when the CNPs were used without surface treatment.  相似文献   

10.
Aluminum nitride (AlN) ceramics with dense structure, high thermal conductivity, and exceptional mechanical properties were fabricated by pressureless sintering with a novel non-oxide sintering additive, samarium fluoride (SmF3). The results showed that the use of a moderate amount of SmF3 promoted significant densification of AlN and removed the oxygen impurity. This led to the formation of fine and isolated secondary phase that cleaned the grain boundaries and increased the contact between AlN grains, remarkably enhancing thermal conductivity. Furthermore, SmF3 also exhibited grain refinement and grain boundary strengthening effects similar to traditional sintering additive, samarium oxide (Sm2O3), leading to high mechanical properties in SmF3-doped AlN samples. The most optimal characteristics (thermal conductivity of 190.67 W·m−1·K−1, flexural strength of 403.86 ± 18.27 MPa, and fracture toughness of 3.71 ± 0.19 MPa·m1/2) were achieved in the AlN ceramic with 5 wt% SmF3.  相似文献   

11.
We developed a simple solution mixing and molding process for the incorporation of graphene nano-flakes (GNFs) in polymer films. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and poly(ethylene-co-methacrylic acid) (PEMAA) were used for preparation of the samples. The orientation and stacking of GNFs were confirmed using a scanning electron microscope. The thermal conductivity values for these composites were obtained using (1) laser flash method (commercially available) and (2) an optothermal Raman (OTR) technique (homemade device). The former measures the thermal diffusivity (α) and one needs to measure the density (ρ) and the heat capacity (Cp) of the composites in order to measure the in-plane thermal conductivity (κ = α.ρ.Cp), while the latter measures the in-plane thermal conductivity directly from the relation between the excitation power and the position of the Raman resonance. The data obtained from Raman spectroscopy were analyzed, assuming heat propagation in three and two dimensions. The Raman results obtained based on the two-dimensional model were very close to the results obtained using the laser flash method with less than 10% difference. The OTRspectroscopy was found to be a promising technique for measuring the in-plane thermal conductivity of carbon-based polymer composites. PVDF-HFP and PEMAA composite films with very high in-plane thermal conductivity (25 W m−1 K−1) were obtained through the incorporation of GNFs (20 wt % concentration). Considering a very low thermal conductivity of these polymers (<0.2 W m−1 K−1), this corresponds to a large enhancement of roughly 12 400%. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48927.  相似文献   

12.
《Ceramics International》2023,49(15):25063-25073
A core–shell structured spherical graphite (SG)@SiC attenuating agent with a tunable silicon carbide (SiC) shell thickness was synthesized via in-situ solid-liquid reaction of SG and Si. Then, fully dense 10 wt%SG@SiC/AlN microwave attenuating composite ceramics were prepared through hot-pressing sintering, and the morphology of SG@SiC particle was well maintained. By moderately modulating the thickness of the SiC shell with relatively low complex permittivity and thermal conductivity, an effectively inhibited solid solution of SiC into AlN, weakened dipole and electron polarization, enhanced conduction loss, and an improved impedance matching, thermal conductivity and microwave loss capacity were simultaneously achieved. Thus, the SG@SiC/AlN composite exhibit excellent and impressive thermal conductivity of 63.92 W m−1·K−1 and minimum reflection loss of −34.2 dB. The outstanding performance of SG@SiC/AlN composite indicates that the composite is promising microwave attenuating ceramic with excellent thermal conduction and microwave absorption ability. This work opens up a new core–shell structure strategy for designing and developing a high-efficiency attenuating agent and microwave attenuating ceramic.  相似文献   

13.
Among the various concepts of SiC-based accident-tolerant fuel cladding, duplex SiC cladding, consisting of an inner composite layer and an outer monolithic SiC layer, is considered an optimal design due to its low load failure probability. In this study, SiC nanowires (SiCnw) were introduced on the substrate graphite rod to decrease the diameter of architectural valley-regions of SiC fiber (SiCf) tubular preform. By avoiding the architectural valley-voids, a dense two-layer SiCnw tube consisting of an inner SiC fiber-reinforced SiC matrix (SiCf/SiC) composite layer deposited by chemical vapor infiltration with a smooth inner surface was obtained. The microstructure and thermal properties of as-obtained two-layer SiCnw tubes were studied. Results showed that the thermal conductivity of the whole tube was highly sensitive to variations in thermal conductivity of the inner composite layer. By improving the thermal conductivity of the inner composite layer, the two-layer SiCnw tube exhibited a thermal conductivity of 23.8 W m−1 K−1 at room temperature, which had an improvement of 71 % compared to the two-layer SiC tube (13.9 W m−1 K−1). Moreover, the thermal transport properties of the two-layer SiCnw tube were significantly improved by a reduction in roughness of the inner surface.  相似文献   

14.
In 5G era, integration and miniaturization of electronic components lead to increasing challenges in thermal management. Materials with high thermal conductivity and flexibility are strongly desired for dissipating heat locally generated in such devices. Due to its extraordinary thermal conducting performance, graphene has been exhibiting great potential in thermal management. In this work, composite films based on graphene oxide and poly-naphthylamine (gGO/PNA) with enhanced thermal conducting performance have been achieved by employing poly (naphthylamine) (PNA) as repairing additives to restore topological defects of graphene oxide (GO). Specifically, gGO/PNA films are prepared with a facile operation of vacuum filtration followed by an elevated temperature treatment. The optimal thermal conductivity (κ) of gGO/PNA reaches to 1016.03 W m−1 K−1, 31.3% enhancement over that of the pristine graphene one. The thermal conducting performance test demonstrates the film an efficient heat-dissipation ability from a heat-generating LED bulb. Furthermore, the film exhibits excellent flexibility, making it survival from a 1000-cycle bending test. This finding may promote the development of heat-spreading materials and their applications in thermal management of highly integrated electronics.  相似文献   

15.
Si3N4 whisker (Si3N4w) is selected as epoxy filler. The influence of filler content on the bulk density, porosity, bending strength, Young's modulus, critical stress intensity factor, work of failure, morphologies of fracture surface, and thermal conductivity of Si3N4w/epoxy is investigated. The bending strength is 82.63 MPa at a Si3N4w content of 5 vol% and increases to 25.29% more than that of neat epoxy. Compared with that of neat epoxy, the work of failure and thermal conductivity increase by 455% and 34.78% to 18 248.92 J·m−2 and 0.31 W·m−1·K−1, respectively, at a Si3N4w content of 7 vol%. However, Si3N4w/epoxy becomes sensitive to precrack due to a weak C N bond and residual tensile stress at the interface, thereby resulting in the decline of critical stress intensity factor. The coexistence of various energy dissipation mechanisms, namely, steps, craters or depressions, stress whitening, plastic flow, pull out of Si3N4w, and rough fracture surface, is observed in Si3N4w/epoxy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48721.  相似文献   

16.
Design and preparation of membranes with ultrahigh separation performance and antifouling property for oil-in-water (O/W) emulsions remains challenging. In this study, a high flux mullite/TiO2 ceramic composite membrane was prepared via multi-precipitation of TiO2 on a whisker mullite hollow fiber support synthesized by combining phase inversion and high-temperature sintering techniques. The results showed that the generated whisker mullite structure improved the permeation flux, and the micro-nano structured TiO2 functional layer endowed the membrane surface with superhydrophility and stability. The retention of the optimal composite membrane (M20T13) that was soaked in the titanium solution 20 times for 13 min each time for the O/W emulsions like n-hexane, toluene and engine oil maintained over 98 %, and the flux after 6 h filtration was 668.34 L·m−2·h−1, 487.25 L·m−2·h−1 and 258.66 L·m−2·h−1, respectively, much higher than that of the optimal substrate (F3A1, mass ratio of fly ash: Al2O3 = 3:1). Moreover, the flux recovery rate of M20T13 was much higher than that of F3A1 after chemical backwashing. This work manifests great potential in O/W treatment fields.  相似文献   

17.
In this paper, the i-MAX phase (Mo2/3Y1/3)2AlC ceramic with high purity of 98.29 wt% (1.13 wt% Y2O3 and 0.58 wt% Mo2C) and high relative density of 98.59% was successfully synthesized by spark plasma sintering (SPS) at 1500°C with the molar ratio of n(Mo):n(Y):n(Al):n(C) = 4:2:3.3:2.7. The positions of C atoms in the crystal of (Mo2/3Y1/3)2AlC were determined. Microstructure and physical and mechanical properties of (Mo2/3Y1/3)2AlC ceramic were systematically investigated. It was found that the obtained (Mo2/3Y1/3)2AlC ceramic had an average grain size of 32.1 ± 3.1 μm in length and 14.2 ± 1.7 μm in width. In terms of physical properties, the measured thermal expansion coefficient (TEC) of (Mo2/3Y1/3)2AlC was 8.99 × 10−6 K−1, and the thermal capacity and thermal conductivity at room temperature were 0.43 J·g−1·K−1 and 13.75 W·m−1·K−1, respectively. The room temperature electrical conductivity of (Mo2/3Y1/3)2AlC ceramic was measured to be 1.25 × 106 Ω−1·m−1. In terms of mechanical properties, Vickers hardness under 10 N load was measured as 10.54 ± 0.29 GPa, while flexural strength, fracture toughness, and compressive strength were determined as 260.08 ± 14.18 MPa, 4.51 ± 0.70 MPa·m1/2, and 855 ± 62 MPa, respectively, indicating the promising structural applications.  相似文献   

18.
《Ceramics International》2023,49(4):5707-5719
As one of the key components of electronic devices, thermal management materials (TMMs) with high thermal conductivity are essential to ensure their safety and long service life. For polymer-based TMMs, AlN is one of the preferred fillers, but it has some drawbacks such as high cost and easy hydrolysis. Herein, a controllable and continuously oriented three-dimensional AlN skeleton (3D-AlNNS) was in-situ transformed from a low-cost 3D Al-containing skeleton (3D-AlNS) by combining the ice-templating and nitriding reaction sintering. Subsequently, AlN/epoxy composites were obtained by a vacuum infiltration. The composite containing 39.69 vol% AlN had the highest thermal conductivity of 4.29 W m?1·K?1, which was 21.45 times higher than that of pure epoxy. The composite substrates showed excellent heat dissipation performance in practical applications due to their high thermal conductivity. The continuous directional alignment of AlN powders in the 3D skeleton and intersection of AlN whiskers between the skeleton walls produced in-situ contributed to the formation of effective multichannel heat transferring paths and improvement in thermal conductivity. This novel approach has the advantages of low-cost, short processing time, simple operation and repeatability, and provides a new idea for developing heat-conducting polymer composites, which can also be extended to the preparation of similar TMMs.  相似文献   

19.
SiC whisker (SiCw)-reinforced SiC composites were prepared by an oscillatory pressure sintering (OPS) process, and the effects of SiCw content on the microstructure and mechanical and tribological properties of such composites were investigated. The addition of SiCw could promote the formation of long columnar α-SiC, and the aspect ratio of α-SiC grains first increased and then decreased with the increase of SiCw content. When the SiCw content was 5.42 wt%, the relative density of the SiC–SiCw composite reached up to 99.45%. The SiC–5.42 wt% SiCw composite possessed the highest Vickers hardness, fracture toughness, and flexural strength of 30.68 GPa, 6.66 MPa·m1/2, and 733 MPa, respectively. In addition, the SiC–5.42 wt% SiCw composite exhibited the excellent wear resistance when rubbed with GCr15 steel balls, with a friction coefficient of .76 and a wear rate of 4.12 × 10−7 mm3·N−1·m−1. This could be ascribed to the improved mechanical properties of SiC–SiCw composites, which enhanced the ability to resist peeling and micro-cutting, thereby enhancing the tribological properties of the composites.  相似文献   

20.
《Ceramics International》2022,48(18):26651-26659
With rapid advances in electronic device miniaturization and increasing power density, high thermal conductivity polymer composites with excellent properties are becoming increasingly significant for the progress of next-generation electronic apparatuses. In this work, a new type of three-dimensional (3D) network silicon carbide (SiC) frame and core-shell SiC@SiO2 (SiC@SiO2) were successfully prepared. The effects of different filler forms (dispersed particle filler and three-dimensional continuous filler network) on the thermal conductivity of the composites were compared. The composites based on the three-dimensional filler network exhibited evidently better thermal conductivity improvement rates, compared to their traditional counterparts. The thermal conductivity of the epoxy/SiC@SiO2 composite having a total filler content of 17.0 vol% was 0.857 W/m/K, 328.5% higher than that of pure epoxy resin. Similarly, the thermal conductivity of the EP/3D-SiC composite having a total filler content of 13.8 vol% was 1.032 W/m/K, 416.0% higher than that of pure epoxy resin. The abovementioned stats were proven via molecular simulations. We estimated the interfacial thermal resistance (ITR) of the EP/3D-SiC composite to be 5.98 × 10?8 m2 K/W, which was an order of magnitude lower than that of the epoxy composites without a 3D network. Simultaneously, computerized molecular simulation technology was used to verify the feasibility of the experiment, which provided new ideas for the preparation of other highly thermally conductive materials.  相似文献   

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