Thermal properties of Cf/HfC and Cf/HfC-SiC composites prepared by precursor infiltration and pyrolysis

Ultra-high temperature ceramic infiltrated carbon-fibre composites were prepared by precursor infiltration and pyrolysis (PIP) using a laboratory synthesized precursor. Microstructures and thermal properties including thermal expansion, thermal diffusivity, specific heat capacity and oxidative stability are correlated. XRD reveals the presence of C_f-HfC and C_f-HfC-SiC phases without formation of oxides. The CTE observed at 1200?°C is slightly higher for C_f-HfC (3.36?×?10^?6?K^?1) compared to C_f-HfC-SiC (2.95?×?10^?6?K^?1) composites. Lower thermal diffusivity of the C_f-HfC-SiC compared to C_f-HfC composites is attributed to a thermal barrier effect and cracks in the composites which formed due to the CTE mismatch between carbon fibre and the matrix as well as CO generated during graphitization. The thermal conductivity of C_f-HfC (4.18?±?0.14?Wm^?1?K^?1) is higher than that of C_f-HfC-SiC composite (3.33?±?0.42?Wm^?1?K^?1). Composites microstructures were coarse with some protruding particles (5?μm) with a homogeneous dense (～70%) matrix (HfC and HfC-SiC) for both composites.     

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.     

Effect of Al2O3 addition on thermo‐electrical properties of polymer composites: An experimental investigation

To develop a new class of composites with adequately high thermal conductivity and suitably controlled dielectric constant for electronic packages and printed circuit board applications, polymer composites are prepared with microsized Al₂O₃ particle as filler having an average particle size of 80–100 μm. Epoxy and polypropylene (PP) are chosen as matrix materials for this study. Fabrication of epoxy‐based composite is done by hand lay‐up technique and its counterpart PP‐based composite are fabricated by compression molding technique with filler content ranging from 2.5–25 vol%. Effects of filler loading on various thermal properties like effective thermal conductivity (k_eff), glass transition temperature (T_g), coefficient of thermal expansion (CTE) and electrical property like dielectric constant (ε_c) of composites are investigated experimentally. In addition, physical properties like density and void fraction of the composites along with there morphological features are also studied. The experimental findings obtained under controlled laboratory conditions are interpreted using appropriate theoretical models. Results show that with addition of 25 vol% of Al₂O₃, k_eff of epoxy and PP improve by 482% and 498% respectively, T_g of epoxy increases from 98°C to 116°C and that of PP increases from −14.9°C to 3.4°C. For maximum filler loading of 25 vol% the CTE decreases by 14.8% and 26.4% for epoxy and PP respectively whereas the dielectric constants of the composites get suitably controlled simultaneously. POLYM. COMPOS., 36:102–112, 2015. © 2014 Society of Plastics Engineers     

Thermal properties of polytetrafluoroethylene/Sr2Ce2Ti5O16 polymer/ceramic composites

Polytetrafluoroethylene (PTFE) composites filled with Sr₂Ce₂Ti₅O₁₆ ceramic were prepared by a powder processing technique. The structures and microstructures of the composites were investigated by X‐ray diffraction and scanning electron microscopy techniques. Differential scanning calorimetry showed that the ceramic filler had no effect on the melting point of the PTFE. The effect of the Sr₂Ce₂Ti₅O₁₆ ceramic content [0–0.6 volume fraction (vf)] on the thermal conductivity, coefficient of thermal expansion (CTE), specific heat capacity, and thermal diffusivity were investigated. As the vf of the Sr₂Ce₂Ti₅O₁₆ ceramic increased, the thermal conductivity of the specimen increased, and the CTE decreased. The thermal conductivity and thermal expansion of the PTFE/Sr₂Ce₂Ti₅O₁₆ composites were improved to 1.7 W m^?1 °C^?1 and 34 ppm/°C, respectively for 0.6 vf of the ceramics. The experimental thermal conductivity and CTE were compared with different theoretical models. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and mechanical properties of tetra‐functional mesogenic type epoxy resin cured with aromatic amine

A novel tetra‐functional epoxy monomer with mesogenic groups was synthesized and characterized by ¹H‐NMR and FTIR. The synthesized epoxy monomer was cured with aromatic amine to improve the thermal property of epoxy/amine cured system. The glass transition temperature (T_g) and coefficient of thermal expansion (CTE) of the cured system were investigated by dynamic mechanical analysis and thermal mechanical analysis. The properties of the cured system were compared with the conventional bisphenol‐A type epoxy and mesogenic type epoxy system. The storage modulus of the tetra‐functional mesogenic epoxy cured systems showed the value of 0.96 GPa at 250 °C, and T_g‐less behavior was clearly observed. The cured system also showed a low CTE at temperatures above 150 °C without incorporation of inorganic components. These phenomena were achieved by suppression of the thermal motion of network chains by introduction of both mesogenic groups and branched structure to increase the cross linking density. The temperature dependency of the tensile property and thermal conductivity of the cured system was also investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46181.     

In-plane thermal expansion behavior of dense ceramic matrix composites containing SiBC matrix

In order to reveal the effect of matrix cracks resulted from thermal residual stresses (TRS) on the thermal expansion behavior of ceramic matrix composites, SiBC matrix was introduced into C_f/SiC and SiC_f/SiC by liquid silicon infiltration. The TRS in both two composites were enlarged with incorporating SiBC matrix which has higher coefficients of thermal expansion (CTEs) than SiC matrix. Due to the relatively high TRS, matrix cracks and fiber/matrix (f/m) debonding exist in C_f/SiC-SiBC, which would provide the space for the expansion of matrix with higher CTEs. For SiC_f/SiC, no matrix cracking and f/m debonding took place due to the close CTEs between fiber and matrix. Accordingly, with the incorporation of SiBC matrix, the in-plane CTE of C_f/SiC between room temperature to 1100 °C decreases from 3.65 × 10⁻⁶ to 3.19 × 10⁻⁶ K^-1, while the in-plane CTE of SiC_f/SiC between room temperature to 1100 °C increases slightly from 4.97 × 10⁻⁶ to 5.03 × 10⁻⁶ K^-1.     

Electrical and thermal conductivities of polyethylene composites filled with biaxial oriented short-cut carbon fibers

Polyethylene composites filled with various types of carbon fiber were prepared for electrical and thermal conductivity measurements. By estimation of the anisotropic parameter (Hermans' parameter), the fibers were confirmed to be significantly biaxially oriented in the composites. The critical volume fractions in the electrical conductivity of these composites for the two oriented directions (X and Y) were equal to each other and smaller than that for a direction (Z) vertical to the above. The electrical anisotropy, i.e., ratio of electrical conductivity of the composite for the Z direction to the X and Y directions varied drastically with increase in filler content. The longer the length of carbon fiber was, the higher became the electrical conductivity of the biaxially oriented carbon fiber composites for all directions. But, the thermal conductivity of the composite was almost unchanged for the Z direction, even if fiber length was sufficiently long. Our equation, previously proposed, proved adaptable to these thermal conductivities. The factors of C_p and C_f in the equation are kept unchanged, in spite of increasing fiber length. © 1994 John Wiley & Sons, Inc.     

Design and preparation of low-filled magnetic oriented BN@Fe3O4/EP insulating composite with improved thermal conductivity and thermal stability

As an excellent two-dimensional insulating material with high thermal conductivity, high temperature stability and high hardness, hexagonal boron nitride(h-BN) is widely applied in semiconductor manufacturing, aerospace, metallurgical manufacturing and other cutting-edge fields. However, the unique surface structure of h-BN leads to poor lubricity and easy agglomeration, which limits the application of h-BN especially in the field of electronic packaging. To address key issues boosted above, this study designed and prepared the BN@Fe₃O₄ magnetic insulating particles and doped it into the reduced viscosity epoxy resin to prepare the composites. By selecting appropriate external magnetic field strength and BN@Fe₃O₄ particles’ content, a novel 3D structure of fillers like dominoes in epoxy resin composite was successfully constructed. The microstructure of the BN@Fe₃O₄ particles and composites were analyzed, the thermal conductivity, the mechanical and the electrical properties of composites were simultaneously tested. Results manifested that the core-shell structures with BN as core and Fe₃O₄ as shell was successfully prepared, linking through the PDA middle layer between the BN core and Fe₃O₄ shell. Under the influence of magnetic orientation, the BN@Fe₃O₄ magnetic particles were preferred an out-of-plane oriented in the epoxy resin composites, resulted an enormously enhanced on thermal conductivity of composites. At a magnetic field strength of 60 mT and 25 vol% BN@Fe₃O₄ content, the thermal conductivity of BN@Fe₃O₄/EP composites is as lofty as 1.832 W/(m K), which is 1023.46% higher than that of pure epoxy resin. Meanwhile, the thermal stability has also been slightly improved, the elastic modulus and insulation performances remain at the same level.     

Thermal properties of diamond/Ag composites fabricated by eletroless silver plating

Thermal management in microelectronic technology has become an important issue due to the increase of device power and integration levels. Diamond and silver were selected for the fabrication of composites with high thermal conductivity and low coefficient of thermal expansion (CTE). Diamond reinforcement powders with varied types, shapes and sizes were electroless plated by silver. Then these powders were hot-pressed in air at 600 °C, 500 MPa for 30 min to produce bulk silver matrix composites. The thermal conductivity and the CTEs of the composite at 20 vol.% are 420 W/m K and 12 ppm/K, respectively. These diamond/Ag composites have potential applications for the high integration electronic devices.     

环氧树脂/镀银纳米石墨微片导热复合材料的制备与性能

以膨胀石墨为原料,采用超声分散法和化学镀法制得镀银纳米石墨微片,然后将其填充在环氧树脂基体中制备环氧树脂/镀银纳米石墨微片复合材料。结果表明,银粒子均匀镀覆在纳米石墨微片上,银层厚度为100 nm,有利于在环氧树脂基体中形成导热通路;与环氧树脂相比,环氧树脂/镀银纳米石墨微片复合材料的力学性能和热导率能都得到提高;当镀银纳米石墨微片含量为3 %时,复合材料的热导率为1.827 W/(m·K),比纯环氧树脂热导率提高了近5倍。     

Thermo-mechanical behaviors of epoxy resins reinforced with nano-Al2O3 particles

This study examined the thermo-mechanical behavior of epoxy resins/nano-Al₂O₃ composites including the curing behavior, thermal stability, dynamic mechanical properties and thermal mechanical properties. The DSC curve peak temperature of the composites was decreased by the addition of nano-Al₂O₃. The thermal stability of the composites was similar to that of the neat epoxy resins. Dynamic mechanical analysis (DMA) indicated the glass transition temperature of the composites to be approximately 11 °C higher than that of the neat epoxy resins. The coefficient of thermal expansion (CTE) of the composites decreased with increasing nano-Al₂O₃ content.     

Evaluation of the high temperature performance of HfB2 UHTC particulate filled Cf/C composites

Room and high temperature flexural strength and coefficient of thermal expansion (CTE) of HfB₂ ultra‐high temperature ceramic (UHTC) particulate filled C_f/C composites are determined along with UHT oxidation behavior. Both room and high temperature strength of the composites were found to be broadly comparable to those of other thermal protection system materials currently being investigated. The CTE of the composites was measured both along and perpendicular to the fiber direction up to 1700°C and the values were found to depend on fiber orientation by approximately a factor of 3. Arc‐jet testing of the UHTC composites highlighted the excellent ultra‐high temperature oxidation performance of these materials.     

Enhancing the thermal conductivities of SiO2/Epoxy composites by orientation

To improve the thermal conductivity of epoxy resin, tensile way was used to orient the molecular chain of epoxy resin with SiO₂ particles filled. In this article, SiO₂/Epoxy composites which had approximately one‐dimensional lattice structure were prepared. The heat generated by LED chip rapidly passed along the direction of the one‐dimensional orientation in SiO₂/Epoxy composites. The results showed that the thermal conductivity of oriented composites increased with the increase of silica concentration and draw ratio (If S is the cross‐sectional areas of composites at the mold outlet, S₀ is the cross‐sectional areas of composites after molding set, and draw ratio is S/S₀). With the addition of 50 wt% SiO₂ to the epoxy resin, the thermal conductivity of oriented SiO₂/Epoxy composites with the draw ratio of 4 was 0.873 W/m K, which was 2.55 times that of unoriented SiO₂/Epoxy composites. And a thermal conductivity, 5.97 times that of the epoxy resin, was obtained with 80 wt% SiO₂ and the draw ratio of 4. Nevertheless, the relative permittivities of epoxy composites which had 50 wt% SiO₂ with the draw ratio of 4 are stable with increasing frequency. POLYM. COMPOS., 37:818–823, 2016. © 2014 Society of Plastics Engineers     

Mechanically robust,electrically and thermally conductive graphene-based epoxy adhesives

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5?vol%; for example, Young’s modulus, fracture toughness (K_1C) and energy release rate (G_1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58?vol% and thermal conductivity of 2.13?W m^?1 K^?1 at 6?vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7?MPa for neat epoxy to 13.57?MPa at 0.375?vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives.     

Effect of the filler size and content on the thermomechanical properties of particulate aluminum nitride filled epoxy composites

Polymer matrix composites based on brominated epoxy as the matrix and aluminum nitride (AlN) particles as the filler were prepared. The influences of the size, content, and size distribution of AlN on the thermomechanical properties, including the glass‐transition temperature (T_g), coefficient of thermal expansion (CTE), dynamic storage modulus (E′), dynamic loss modulus (E″), and loss factor (tan δ), of the composites were investigated by thermomechanical analysis and dynamic mechanical analysis. There was a total change trend for T_g; that is, T_g of the composites containing nano‐aluminum nitride (nano‐AlN; 50 nm) was lower than that of the micro‐aluminum nitride (micro‐AlN; 2.3 μm) filled composites, especially at high nano‐AlN contents. The T_g depression of the composites containing nano‐AlN was related to the aggregation of nano‐AlN and voids in the composites. On the other hand, the crosslink density of the epoxy matrix decreased for nano‐AlN‐filled composites, which also resulted in a T_g depression. The results also show that E′ and E″ increased, whereas tan δ and CTE of the composites decreased, with increasing the AlN content or increasing nano‐AlN fraction at the same AlN content. These results indicate that increasing the interfacial areas between AlN and the epoxy matrix effectively enhanced the dynamic modulus and decreased CTE. In addition, at a fixed AlN content of 10 wt %, a low E′ of pre‐T_g (before T_g temperature) and high T_g were observed at the smaller weight ratio of nano‐AlN when combinations of nano‐AlN plus micro‐AlN were used as the filler. This may have been related to the best packing efficiency at that weight ratio when the bimodal filler was used. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Improved dispersion and interfacial interaction of SiO2@polydopamine fillers in polytetrafluoroethylene composites for reduced thermal expansion and suppressed dielectric deterioration

Copper-clad laminate (CCL) comprised of copper foil and polytetrafluoroethylene (PTFE) faces severe thermal expansion mismatch due to the discrepancy in coefficient of thermal expansion (CTE) between the two components. Incorporating inorganic fillers with low CTE into PTFE has been proved to be a promising way to achieve the goal. However, it is a challenge to achieve homogeneous distribution and good interfacial interaction of fillers in PTFE composites owing to the characteristics of PTFE emulsion. In this work, core@shell structured SiO₂@polydopamine fillers (SiO₂@PDA) were synthesized and incorporated into PTFE matrix to form SiO₂@PDA/PTFE composites. Due to the presence of PDA shell, SiO₂@PDA exhibited improved dispersion and interfacial interaction, contributing to the reduced CTE and suppressed dielectric deterioration of SiO₂@PDA/PTFE composites. With 40 vol% of filler, the CTE of SiO₂@PDA/PTFE composite was efficiently reduced (50%), coupled with a limited sacrifice of only 2% and 40% of increments for dielectric constant (D_k, 2.3) and dielectric loss (D_f, 2.4 × 10⁻³), respectively (@40 GHz), as compared with that of the corresponding SiO₂/PTFE composite. The fillers and composites were comprehensively characterized to verify the mechanism of CTE and dielectric properties of the composites.     

Additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic composites

A material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (C_f/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of C_f/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the C_f. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different C_f contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with C_f content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m^1/2) while the thermal conductivity of the samples with the C_f content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare C_f/SiC composites via MEX additive manufacturing and RMI.     

Mechanical,thermal, and hydrophobic properties of silica aerogel–epoxy composites

Epoxy composites were prepared with different contents of hydrophobic silica aerogel particles to investigate their mechanical, thermal, and hydrophobic properties. The composites, particularly the one containing 1 wt % silica aerogel, showed remarkable toughness and yielding behaviors compared to neat epoxy, with its brittle behavior. As the content of silica aerogel increased, the thermal properties of the composites (e.g., thermal conductivity and thermal stability) improved. This was due to the very low thermal conductivity and high thermal stability of the silica aerogel particles. Moreover, the use of the hydrophobic silica aerogel led to the development of composites with hydrophobic properties. To examine the hydrophobicity more deeply, a series of water‐uptake tests were performed, and the results show that the composite with 3 wt % silica aerogel absorbed 50% less water than the neat epoxy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45706.     

Medium dielectric constant and low-loss PTFE composites filled with MgO-LiF co-doped Li2TiO3 particles

In this work, we presented a simple strategy to fabricate medium dielectric constant and low-loss composites for microwave substrate applications. MgO-LiF co-doped Li₂TiO₃ (LT) powders were fabricated by the solid-state reaction route and modified by perfluorooctyltriethoxysilane (F8261). The LT/polytetrafluoroethylene (PTFE) composites were fabricated by cold pressing and hot treatment. The XPS and contact angle analysis indicated that the fluorinated group was introduced to LT particle successfully. The effects of modified LT powders content on the dielectric, thermal, and mechanical properties of composites were investigated. As the modified LT content increases, the dielectric constant, dielectric loss, and temperature coefficient of dielectric constant (τ_ε) increase while the bending strength and coefficient of thermal expansion (CTE) decrease, which is attributed to the higher dielectric constant of LT ceramic, more pores, stable τ_ε of LT ceramic, interface defects and low CTE of LT ceramic, respectively. The composites with 60 wt % LT exhibit the best microwave dielectric properties: ε_r = 6.8, tanδ = 0.001, τ_ε = −29.6 ppm °C⁻¹ at 8 GHz and acceptable coefficient of thermal expansion (28.3 ppm °C⁻¹). Therefore, modified LT powders filled PTFE composites are potential materials for high-frequency microwave substrate applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47980.     

Electroless silver plating on the PET fabrics modified with 3‐mercaptopropyltriethoxysilane

The feasibility of adherent silver layers onto PET fabrics by electroless plating was explored and its optimal technology for modification and electroless plating was investigated. Morphology, structure, and thermal stability of silver plating PET fabrics were characterized by scanning electric microscope (SEM), X‐ray diffraction (XRD) and thermogravitric (TG) analysis. As the silver weight on the modified fabric is 25 g/m², the electromagnetic shielding effectiveness (SE) of silver plating PET fabric is more than 30dB at the frequency ranging from 1MHz to 5000 MHz. The results show that the silver plating PET fabric has good electrical conductivity and electromagnetic shielding property. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012