Guangyi Chen

Mechanical properties, crystallization and melting behaviors of carbon fiber-reinforced PA6 composites

Polyamide-6 (PA6)/carbon fiber (CF) composites were prepared by melt-extrusion via continuous fiber fed during extruding. The mechanical, thermal properties, and crystallization behavior of PA6/CF composites were investigated. It was found that the tensile modulus and strength of the composites were increased with the addition of CF, while their elongations at break were decreased. Scanning electron microscopy observation on the fracture surfaces showed the fine dispersion of CF and strong interfacial adhesion between fibers and matrix. Dynamic mechanical analysis results showed that the storage modulus of PA6/CF composites was improved with the addition of CF. Non-isothermal crystallization analysis showed that the CF plays a role as nucleating agent in PA6 matrix, and the α-form crystalline structure was favorable in the PA6/CF composites, as confirmed from the X-ray diffraction analysis. A trans-crystallization layer around CF could be observed by polarizing optical microscopy, which proved the nucleation effect of carbon fiber surface on the crystallization of PA6. The thermal stability of PA6/CF composites was also enhanced.

Synthesis of porous Cu7.2S4 sub-microspheres by an ion exchange method for high-performance supercapacitors

The porous Cu7.2S4 sub-microspheres were synthesized by ion exchange reaction using Cu2O as a precursor. The morphology and structure of the obtained samples were characterized by XRD, SEM, and TEM analysis in detail and the formation mechanism was studied. The pseudo-capacitive properties were evaluated by CV and galvanostatic charge–discharge tests in 6 M KOH solution. The as-prepared porous Cu7.2S4 sub-microspheres electrode has a specific capacitance of 491.5 F g−1 at 1 A g−1 and exhibits good electrochemical performance as an electrode material for supercapacitors.

Nonisothermal crystallization and morphology of poly(butylene succinate)/layered double hydroxide nanocomposites

Biodegradable poly(butylene succinate) (PBS) and layered double hydroxide (LDH) nanocomposites were prepared via melt blending in a twin-screw extruder. The morphology and dispersion of LDH nanoparticles within PBS matrix were characterized by transmission electron microscopy (TEM), which showed that LDH nanoparticles were found to be well distributed at the nanometer level. The nonisothermal crystallization behavior of nanocomposites was extensively studied using differential scanning calorimetry (DSC) technique at various cooling rates. The crystallization rate of PBS was accelerated by the addition of LDH due to its heterogeneous nucleation effect; however, the crystallization mechanism and crystal structure of PBS remained almost unchanged. In kinetics analysis of nonisothermal crystallization, the Ozawa approach failed to describe the crystallization behavior of PBS/LDH nanocomposites, whereas both the modified Avrami model and the Mo method well represented the crystallization behavior of nanocomposites. The effective activation energy was estimated as a function of the relative degree of crystallinity using the isoconversional analysis. The subsequent melting behavior of PBS and PBS/LDH nanocomposites was observed to be dependent on the cooling rate. The POM showed that the small and less perfect crystals were formed in nanocomposites.

A comparative study of the crystalline structure and mechanical properties of carbon fiber/polyamide 6 composites enhanced with/without silane treatment

Carbon fiber (CF) reinforced polyamide 6 (PA6) composites were manufactured by extrusion compounding and injection molding. The carbon fiber was considered in two forms including untreated and treated with silane coupling agent. The main focus of this study was to investigate the effects of the silane treatment on the mechanical properties and crystalline structure of the composites. Mechanical test results showed that the tensile, impact and flexural strength were significantly increased by incorporation of silane-treated carbon fiber. In particular, the specific tensile, impact and flexural strength of silane-treated CF composites with 20% fibre mass fraction are, respectively, 42%, 51.6% and 30% higher than those of untreated CF composites. Scanning electron microscopy examination showed that the tensile fracture surface of silane-treated CF composites failed in a fiber breakage pattern while the untreated CF composites fractured via a fiber pull-out pattern, suggesting an enhanced interfacial adhesion with the matrix. In addition, the incorporation of silane-treated CF increased the degree of crystallinity, promoted the formation of the thermodynamic crystalline form and induced the specific transcrystalline structure, as indicated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and polarizing optical microscopy (POM) analysis. Moreover, the mechanism of silane-treated CF reinforced PA6 composites with improved mechanical properties was discussed.

Mechanical properties and crystallization behavior of poly(butylene succinate) composites reinforced with basalt fiber

Biodegradable poly(butylene succinate) (PBS)/basalt fiber (BF) composites were prepared by melt blending method using twin-screw extruder followed by injection molding. Mechanical properties, crystallization and melting behavior, morphology, crystal structure and thermal stability of PBS/BF composites with various BF contents were investigated by different techniques. The tensile and impact properties of the composites were improved markedly with the addition of BF, due to the efficient interfacial adhesion between fibers and PBS matrix. Crystallization and melting behavior of PBS in its composites kept almost unchanged, indicating that the nucleation effect of BF was minimal and, meanwhile, it played a role in hindrance of chain motion. TG analysis showed that the thermal stability of PBS/BF composites was enhanced by the addition of BF. The crystal structure of PBS was not affected by the incorporation of BF, while the nucleation density increased gradually and the spherulite size reduced remarkably with the increase in BF. No transcrystallization phenomenon on the surface of BF was observed maybe as a result of without surface treatment.

Synthesis of Cu and Ni chalcogenides and evaluation of their properties for electromagnetic wave absorption

Cu and Ni chalcogenides were synthesized by hydrothermal methods and characterized by XRD and SEM. Their properties on electromagnetic (EM) wave absorption were evaluated by a vector network analyzer with a coaxial measurement. For the Cu7.2S4 and Cu2Se–paraffin systems, the peak for minimum reflection loss (RL) shifted from high frequency to low frequency as the thickness increases. At a thickness of 1.6 mm, the Cu7.2S4–paraffin composite could achieve a RL value of −36.60 dB at the absorption peak frequency (APF) of 17.2 GHz with a bandwidth of 6 GHz for RL < −10 dB. For the Cu2Se–paraffin composite, the RL value, APF, and bandwidth were −27.5 dB, 11.76 GHz, and 3 GHz, respectively, at a thickness of 1.5 mm. For the NiO, NiS, and NiSe–paraffin composite systems, the APF for minimal RL moved from high to low frequency as the thickness increases, too. The NiO–paraffin had a RL of −12.68 dB at the APF of 12.8 GHz when the thickness of the sample was 2 mm. For the NiS–paraffin composite, the RL value, APF, and bandwidth were −31.93 dB, 7.52 GHz, and 2 GHz, respectively, with a thickness of 3 mm, while the NiSe–paraffin composite had a RL value, APF, and bandwidth of −41.22 dB, 8.24 GHz, and 1.6 GHz, respectively, with a thickness of 2.2 mm. All Cu and Ni chalcogenides had excellent EM reflection loss, enabling them to be excellent microwave absorbing materials. And most importantly, our results were the first to report superior EM absorption properties for selenides.

Cobalt nanoparticles encapsulated in N-doped graphene nanoshells as an efficient cathode electrocatalyst for a mechanical rechargeable zinc–air battery

Air-cathodes with properties of efficiency, durability and low cost are essential for high performance metal–air batteries and fuel cells for practical applications. In this study, non-precious metal ORR electrocatalysts derived by the encapsulation of Co nanoparticles in N-doped graphene nanoshells were synthesized by a typical one-step pyrolysis process. Compared with commercial Pt/C catalysts, the prepared Co-30@N-G hybrid electrocatalyst showed a high ORR activity at the same level in an alkaline medium. Subsequently, the Co-30@N-G hybrid electrocatalyst has been used as a cathode of Zn–air batteries, which displays equivalent performance to the systems derived using a commercial Pt/C catalyst. The Co-30@N-G derived mechanical rechargeable Zn–air battery showed a persistent flat discharge curve with minimum voltage loss at a high discharge rate of 40 mA cm−2. The robustness of the Co-30@N-G ORR catalyst can allow the batteries to work constantly by periodically replacing the Zn anode and electrolyte, presenting an efficient and economical cathode for Zn–air flow batteries or Zn–air fuel cells.

In-situ synthesis of hierarchical Mn-decorated NiCo 2 S 4 nanosheet arrays on Ni foam as binder-free electrodes for high-performance supercapacitors

In this paper, novel hierarchical Mn-decorated NiCo2S4 nanosheet arrays on Ni foam have been synthesized by a facile multi-step hydrothermal method and directly used as binder-free electrodes for supercapacitors. The vertically aligned NiCo2S4 nanosheet arrays on Ni foam act as not only a good pseudocapacitive material but also a conductive scaffold that can be uniformly decorated by ultrathin and interconnected chiffon-like nanoflakes of MnS2. This unique architecture with a highly specific surface area and fast transfer channels for electron and ion can employ many independent nanospaces to participate in electrochemical reaction. The optimized Mn-decorated NiCo2S4 nanosheet arrays electrode represents an impressive areal capacitance of 4.6xa0Fxa0cm−2 at 2xa0mAxa0cm−2 and good cycling stability (87.3% of the areal capacitance can be maintained after 2000 cycles at 10xa0mAxa0cm−2), indicating the great potential of this hybrid hierarchical nanostructure as a promising candidate for high-performance supercapacitors.

Direct growth of bundle-like cobalt selenide nanotube arrays on Ni foam as binder-free electrode for high-performance supercapacitors

Freestanding bundle-like Co0.85Se nanotube arrays on nickle foam were prepared through a facile ion-exchange reaction and directly used as electrodes for supercapacitors. The morphology and structure of the obtained Co0.85Se nanotube arrays were studied by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). The electrochemical properties of the obtained Co0.85Se electrodes were studied by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS) in a three-electrode system. The Co0.85Se nanotube array/Ni foam electrode exhibited remarkable pseudocapacitive performance with high specific capacitance (1394xa0F g−1 at 4xa0Axa0g−1) as well as good cycling performance and rate capability. The good electrochemical properties were due to the hollow nanostructure of the bundle-like Co0.85Se nanotube arrays and the three-dimensional (3D) conductive Ni foam, which can increase the contact between electrode and electrolyte and improve the conductivity of the whole electrode.

CoSb3 alloy nanoparticles wrapped with N-doped carbon layers as a highly active bifunctional electrocatalyst for zinc–air batteries

Rational design and successful synthesis of highly efficient, long-term stable and low-cost bifunctional electro-catalysts are vital for commercialized application of rechargeable zinc–air batteries. Herein, a series of composite catalysts of different contents of CoSb3 alloy nanoparticles wrapped with N-doped carbon layers (CoSb3@NCL) have been synthesized by a simple one-step pyrolytic process. The optimized catalyst (CoSb3@NCL-30) exhibits excellent catalytic activities for both the ORR and OER in alkaline medium, which can be competitive with the Pt/C catalyst (20%). More importantly, a real rechargeable zinc–air battery with the CoSb3@NCL-30 catalyst serving as an air cathode exhibits outstanding electrochemical properties and excellent cycling stability (the overall increment of the voltage gap was only 0.1 V after 60 hours), making it possible to replace expensive noble metal-based catalysts for actual application in rechargeable zinc–air batteries.