Influence of the interface structure on the thermo-mechanical properties of Cu–X (X = Cr or B)/carbon fiber composites

This study focuses on the fabrication, for power electronics applications, of adaptive heat sink material using copper alloys/carbon fibers (CF) composites. In order to obtain composite material with good thermal conductivity and a coefficient of thermal expansion close to the ceramic substrate, it is necessary to have a strong matrix/reinforcement bond. Since there is no reaction between copper and carbon, a carbide element (chromium or boron) is added to the copper matrix to create a strong chemical bond. Composite materials (Cu–B/CF and Cu–Cr/CF) have been produced by a powder metallurgy process followed by an annealing treatment in order to create the carbide at the interphase. Chemical (Electron Probe Micro-Analysis, Auger Electron Spectroscopy) and microstructural (Scanning and Transmission Electron Microscopies) techniques were used to study the location of the alloying element and the carbide formation before and after diffusion. Finally, the thermo-mechanical properties have been measured and a promising composite material with a coefficient of thermal expansion 25% lower than a classic copper/carbon heat sink has been obtained.     

Measuring spectral transmission and refractive index of AgCl1−xBrx (0 ⩽ x ⩽ 1) and Ag1−xTlxBr1−xIx (0 ⩽ x ⩽ 0.05) at the wavelength of 10.6 μm

We measured the complex refractive index at the wavelength of 10.6 μm with the help of Fourier transform infrared spectroscopy for polycrystalline plates of the following compositions AgCl_1−xBr_x (0 ⩽ x ⩽ 1) and Ag_1−xTl_xBr_1−xI_x, where x varied from 0 to 0.05. In order to do it we chose a segment of the spectrum, which was recorded with a high resolution (0.5 cm⁻¹) using the HgCdTe detector and which had a set of 10 identical peaks. It is shown that the real part of the refractive index rises along with increasing the substituting component fraction in the solid solution from 1.99 to 2.17 for AgCl_1−xBr_x and from 2.17 to 2.24 within the range of TlI mole fraction up to 0.05 for Ag_1−xTl_xBr_1−xI_x. We considered errors introduced by the spectrometer resolution and the accuracy rating of the micrometer, which was used to measure sample thickness. It is seen in the spectra, recorded for the second system with a lower resolution and using a deuterated and l-alanine doped triglycine sulfate detector, that increasing the thallium monoiodide fraction results in widening the transmission range towards bigger wavelengths. We also plan to use the obtained refractive index values for simulating mid-infrared optical fibers, the polycrystalline structure of which is close to the structure of the plates under investigation.     

Effect of amino functionalized MWCNT on the crosslink density,fracture toughness of epoxy and mechanical properties of carbon–epoxy composites

Amino functionalized multiwalled carbon nanotubes (A-MWCNTs) reinforced two phase (A-MWNT–epoxy) and three phase (A-MWCNTs–carbon fiber–epoxy) nanocomposites were fabricated with 0.25 wt%, 0.5 wt% and 1.0 wt% loadings of A-MWCNTs. It is observed that, A-MWCNTs can improve the crosslink density of epoxy significantly. Fracture toughness of epoxy matrix is found to increase up to an optimum crosslink density improvement, indicating the role of crosslink density in imparting toughness to epoxy apart from the crack deflection contributions of A-MWCNTs. In addition to that, this study infers that, tensile, flexural properties of the three phase composites are strongly influenced by the fracture toughness changes of the matrices. This study, thus proposes additional mechanisms of toughness enhancements for two phase and mechanical properties enhancements for three phase composites imparted by A-MWCNTs.     

Morphology and fracture toughness of nanostructured epoxy thermosets containing macromolecular miktobrushes composed of poly(ε-caprolactone) and polydimethylsiloxane side chains

In this work, we investigated the nanostructures and mechanical properties of epoxy thermosets containing a macromolecular miktobrush composed of poly(ε-caprolactone) (PCL) and polydimethylsiloxane (PDMS) side chains. The novel macromolecular miktobrush was synthesized via the combination of reversible addition–fragmentation chain transfer and ring-opening polymerizations. In the brush-like copolymer the molar ratio of PCL to PDMS was controlled to be 1:1 and the length of PCL chains was controlled to be close to that of PDMS chains (i.e., L _PDMS = 1000). The densely grafted miktobrush copolymer was incorporated into epoxy and the nanostructured thermosets were obtained as evidenced by means of transmission electron microscopy and dynamic mechanical thermal analysis. The results of small-angle X-ray scattering showed that the formation of nanostructures in the thermosets followed a self-assembly mechanism. The measurement of critical stress intensity factor (K _1C) showed that the nanostructured thermosets displayed the improved fracture toughness owing to the formation of nanostructures.     

Microstructure and mechanical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites were prepared by isothermal chemical vapor infiltration. The phase compositions, microstructures and mechanical properties of the composites were investigated. The results show that the multilayered matrix consists of alternate layers of PyC and β-SiC deposited on carbon fibers. The flexural strength and toughness of C/(PyC–SiC)_n composites with a density of 1.43 g/cm³ are 204.4 MPa and 3028 kJ/m³ respectively, which are 63.4% and 133.3% higher than those of carbon/carbon composites with a density of 1.75 g/cm³. The enhanced mechanical properties of C/(PyC–SiC)_n composites are attributed to the presence of multilayered (PyC–SiC)_n matrix. Cracks deflect and propagate at both fiber/matrix and PyC–SiC interfaces resulting in a step-like fracture mode, which is conducive to fracture energy dissipation. These results demonstrate that the C/(PyC–SiC)_n composite is a promising structural material with low density and high flexural strength and toughness.     

Effects of multi-walled carbon nanotube (MWCNT) dispersion and compatibilizer on the electrical and rheological properties of polycarbonate/poly(acrylonitrile–butadiene–styrene)/MWCNT composites

In this study, the effects of multi-walled carbon nanotube (MWCNT) dispersion and poly(styrene-co-acrylonitrile)-g-maleic anhydride (SAN-g-MAH) as a compatibilizer on the electrical conductivity, electromagnetic interference shielding effectiveness (EMI SE), and rheological properties of polycarbonate (PC)/poly(acrylonitrile–butadiene–styrene) (ABS)/MWCNT composites were investigated. The morphological results from the scanning and transmission electron microscope images showed that the droplet size of the ABS decreased when the SAN-g-MAH (5 phr) was added to the PC/ABS (80/20) blend. This result suggests that the SAN-g-MAH acts as an effective compatibilizer in the PC/ABS blend. Also, the MWCNT appeared to be located more in the ABS phase (dispersed phase) than in the PC phase (continuous phase). The interfacial tension of the ABS/MWCNT composite was lower than that of the PC–MWCNT composite, and the lower value of interfacial tension of the ABS/MWCNT composite affected the preferred location of the MWCNT in the ABS phase more than in the PC phase. The electrical conductivities and EMI SE of the PC/ABS/MWCNT composite with the compatibilizer were higher than those of the composite without compatibilizer. The complex viscosity of the PC/ABS/MWCNT composite containing the SAN-g-MAH increased with the frequency compared to that of the composite without SAN-g-MAH. This result is possibly due to the increased degree of MWCNT dispersion. The result of rheological properties is consistent with the results of the morphology, electrical conductivity, and EMI SE of the PC/ABS/MWCNT composite.     

Processing and properties of poly(ε-caprolactone)/carbon nanofibre composite mats and films obtained by electrospinning and solvent casting

Composite materials based on poly(ε-caprolactone) (PCL) and carbon nanofibres (CNFs) were processed by solvent casting and electrospinning. The main objective was to investigate the effects of the CNFs on the microstructural, thermal and mechanical properties of the PCL matrix composites processed by two different routes. The hybrid materials obtained with different CNF content (1, 3 and 7 wt%) were analysed by electron microscopy (FESEM), differential scanning calorimeter (DSC), thermogravimetry (TGA) and mechanical testing. The composite films showed a good dispersion in the PCL matrix while electrospun samples were consisted of homogeneous and uniform fibres up to 3 wt% CNFs with average fibre diameter ranged between 0.5 and 1 μm. Composite films and mats revealed an increased crystallization temperature with respect to the neat PCL matrix. Mechanical properties of solvent cast films and electrospun mats were assessed by uniaxial tensile tests. A stiffness increase was achieved in PCL films depending on the CNF content, while mechanical properties of mats were only slightly affected by CNF introduction.     

Crystal structure and thermal expansion of LaCr1−xMgxO3, 0 < x ≤ 0.25

Solid solution LaCr_1?xMg_xO₃, 0 < х ≤ 0.25 was prepared by heating stoichiometric amounts of appropriate oxides in air at 1400 °C, 48 h. At room temperature it crystallizes in orthorhombically distorted GdFeO₃-type structure (a ≈ √2 × a_per; b ≈ √2 × a_pe; c ≈ 2 × a_per, where a_per – perovskite subcell parameter). High-temperature X-ray powder diffraction (HT XRPD) and dilatometry revealed first order phase transition to rhombohedral perovskite phase (R-3c, a ≈ √2 × a_per, c ≈ 2√3 × a_per) at 260–311 °C (OR phase transition). Crystal structures of room-temperature orthorhombic and high-temperature rhombohedral phases for LaCr_0.75Mg_0.25O₃ were refined using HT XRPD data. Temperature of OR phase transition increases gradually with increasing of magnesium content. Low-temperature orthorhombic phase exhibits TEC lower in comparison with high-temperature rhombohedral one (e.g. for LaCr_0.85Mg_0.15O₃ TEC(O) = 8.8 ppm K^?1; TEC(R) = 11.6 ppm K^?1). TEC for rhombohedral phase increases with increasing magnesium content from 10.4 ppm K^?1 for LaCr_0.95Mg_0.05O₃ to 12.1 ppm K^?1 for LaCr_0.75Mg_0.25O₃.     

Nylon 66/poly(vinyl pyrrolidone) reinforced composites:: 1. Interphase microstructure and evaluation of fiber–matrix adhesion

Nylon 66, an aliphatic semicrystalline polyamide, was reinforced with E-glass fibers or high-modulus (AS4) carbon fibers. As in many reinforced semicrystalline thermoplastics, an interphase composed of transcrystallinity developed owing to the high nucleation density of the polymer on the fiber surface. The influence of this region on the fiber–matrix adhesion was studied with a modified microdebond test. E-glass fibers were freshly prepared in our laboratory by traditional glass-forming techniques and embedded in a film of Nylon 66 or a Nylon 66/poly(vinyl pyrrolidone) (PVP) blend. Previous work has shown that PVP, an amorphous polar polyamide, has a dramatic influence on the morphology of Nylon 66. This phenomenon was utilized to manipulate the interphase formation in the Nylon 66 composite from one having a complete transcrystalline interphase to a composite with the absence of an interphase. PVP was introduced to the matrix by solution blending with Nylon 66 and/or to the fibers as a sizing prior to embedment. The resulting morphologies were studied by polarized hot-stage optical microscopy. From the microdebond and morphology results, it was shown that the fiber–matrix adhesion in this composite system is dependent upon interphase microstructure. Composites containing transcrystallinity have higher interfacial shear strength values than those that do not contain this interphase. This has profound implications for the bulk mechanical properties of the composite, which are addressed in Part 2 of this paper.     

Mechanical properties and fracture morphologies of poly(phenylene sulfide)/nylon66 blends—effect of nylon66 content and testing temperature

Poly(phenylene sulfide) (PPS) was melt blended with Nylon66 and the mechanical properties and corresponding fracture morphologies were investigated. The thermal distortion temperature (HDT) of PPS/Nylon 66 blend showed that the inherent thermal stability of pure PPS can be maintained up to 30 wt% Nylon66, but then it started to decrease linearly thereafter to that of pure Nylon66 based on the rule of mixtures relationship. Tensile tests of PPS/Nylon66 blends at testing temperatures of –30, 25, 75, and 150°C showed that the maximum stress decreased up to 30 wt% Nylon66, and started to increase thereafter. Strain at break showed little change at low nylon content regardless of testing temperature, however, a large strain at break increase could be observed at more than 30 wt% Nylon66 and at 150°C testing temperature. At the same testing temperatures, the impact strength of PPS/Nylon66 blends was investigated, and it was found that an impact strength increase at all testing temperatures could be observed at more than 30 wt% Nylon66.     

Synthesis and characterization of flower-like CuIn1−xGaxS2 (x = 0.3) microspheres

We report the formation and characterization of the flower-like CuIn_1?xGa_xS₂ (x = 0.3) microspheres using CuCl₂·2H₂O, GaCl₃, InCl₃ and l-cystine in the mixed solvent of ethylene glycol and distilled water (1:2, v/v) at 200 °C for 24 h. XRD results indicated that the CuIn_0.7Ga_0.3S₂ nanostructures have a (1 1 2) preferred orientation. The EDS and XPS analyses of the sample revealed that Cu, In, Ga and S were present in an atomic ratio of approximately 1:0.7:0.3:2. FESEM and TEM images showed that the product was microspheres, consisting of nanoplates with the thickness of about 20 nm. The optical properties were investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and Raman spectroscopy. UV–vis absorption spectrum indicated that the band gap of as-synthesized flower-like CuIn_0.7Ga_0.3S₂ microspheres was about 2.427 eV. Raman spectrum of the obtained CuIn_0.7Ga_0.3S₂ exhibited a high-intensity peak at 302 cm^?1 could be assigned as A1-mode.     

Thermal resistance and dynamic damping properties of poly (styrene–butadiene–styrene)/thermoplastic polyurethane composites elastomer material

We present the preparation of novel thermoplastic composites elastomer material based on poly (styrene–butadiene–styrene) (SBS), ester-type polyurethane (TPU-EX) and ether-type polyurethane (TPU-ER) materials via melt blending. A series of studies were conducted on the relationship between their morphology, thermal resistance, mechanical properties, and dynamic damping properties, given different compositions. An important feature of the SBS/TPU composites elastomer materials of all compositions is their uniform transparency, because the particles are very small with a narrow size distribution and the refractive indices of SBS and TPU are coincide. Additionally, the thermal resistance, dynamic damping properties and mechanical properties of SBS before and after thermal aging are improved as the amount of added TPU is increased, suggesting that blending SBS with TPU is consistent with the compound rule. In addition, the SBS/TPU composites elastomer materials have better dynamic damping properties at high frequency.     

Structural and electrical properties of high-quality 0.41 μm-thick InSb films grown on GaAs (1 0 0) substrate with InxAl1−xSb continuously graded buffer

High-quality InSb was grown on a GaAs (1 0 0) substrate with an InAlSb continuously graded buffer (CGB). The temperatures of In, Al K-cells and substrate were modified during the growth of InAlSb CGB. The cross-section TEM image reveals that the defects due to lattice-mismatch disappear near lateral structures in CGB. The measured electron mobility of 0.41 μm-thick InSb was 46,300 cm²/Vs at 300 K. These data surpass the electron mobility of state-of-the-art InSb grown by other methods with similar thickness of InSb.