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Herein, an efficient, facile, scalable production of graphene dispersions via exfoliation of graphite in an environment-friendly PVA/H2O solvent system is reported. To warrant the impact of processing parameters on exfoliation efficiency, a systematic investigation is carried out using UV–visible spectroscopy. Under the optimal shearing parameters (1 h, 10 k rpm) with the PVA-to-fed graphite mass ratio of 10, a high concentration graphene dispersion (3.36 mg mL−1) is achieved. The estimated graphene yield is found to be 33% that further increases to 90% after sediment recycling. With the aim of detailed quality analysis, centrifugal cascading is adopted to predominately sort the graphene flakes from the upper end of the distribution. Through various characterization techniques, it is confirmed that the resulting dispersion comprises high-quality graphene flakes (1–5 layers) having thickness up to 1.48 nm, lateral dimension ranging from 0.3 to 4 µm, and quite a low level of defects (ID/IG = 0.1). The statistical distribution histogram reveals that most flakes are single-layer (41%), including some bi-layer (21%) and tri-layer (28%), while the remaining can be said five or multi-layer graphene. Meanwhile, the efficacy of the PVA/H2O solvent system is also demonstrated using ultrasonic exfoliation, providing a high concentration of graphene (1.1 mg mL−1) in a relatively short time (8 h). Furthermore, the applicability of the PVA-stabilized graphene dispersion is addressed by fabricating various graphene products such as graphene paper electrodes, graphene composites, and graphene thin films. Impressively, the graphene paper electrode imparts an exceptionally high specific capacitance of 199.63 F g−1 in a potential window range of 0 to 2 V, and hence could be a promising alternative to traditional electrodes in supercapacitors. Conclusively, the exfoliation of graphite in a green polymer–solvent system offers to produce highly concentrated graphene dispersions at a minimal cost that could be widely applicable in different research areas, thus holding the potential for commercial viability. [ABSTRACT FROM AUTHOR]

The present work is aimed at developing the Zn-ion-conducting solid polymer electrolyte (SPE) films based on PVdF-HFP/Zn(Tf)2 complex system via solution casting method. The structural and morphological characteristics of the as-prepared films are elucidated by X-ray diffraction and scanning electron microscopy. Further, impedance spectroscopy and cyclic voltammetry are performed to investigate their electrical and electrochemical properties. The structural analysis confirms that the PVdF-HFP is semi-crystalline and its amorphous domain increases with the addition of Zn(Tf)2 salt. The impedance results reveal that the ionic conductivity of the electrolyte film is raised up to a maximum value of 2.44 × 10–5 S cm−1 at room temperature when the mass ratio of Zn(Tf)2:PVdF-HFP is 0.4 (named as PE/Zn-4). However, further loading of salt degrades the overall properties of the film. Hence, the PE/Zn-4 system is regarded to be the optimal composition for efficient SPE films. Additionally, the PE/Zn-4 electrolyte exhibits sound thermal stability and mechanical properties. The electrochemical stability window of the PE/Zn-4 system is evaluated as approximately 3.45 V, being acceptable for energy storage applications. In addition, the present polymer electrolyte may well suppress the formation of Zn dendrites on Zn electrodes. Conclusively, the development of high-performance SPEs could be potentially very useful for the next-generation Zn-based devices. [ABSTRACT FROM AUTHOR]

Based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and lithium tetrafluoroborate (LiBF) salt along with blending plasticizers, ethylene carbonate (EC) and propylene carbonate (PC), high Li-ion-conducting gel polymer electrolyte films are developed. Their properties are characterized by various techniques. The ambient temperature ionic conductivity of the 85PVdF-HFP:15LiBF + 150(EC + PC) electrolyte film has a high value of 8.1 × 10 S cm. Its crystallinity, melting point, and electrochemical stability window are 9.5%, 115 °C, and 4.6 V, respectively. The mechanical testing shows that the Young's modulus, yield strength, and breaking strain of this electrolyte film are 36.8 MPa, 3.4 MPa, and 320%, respectively. Lithium-ion batteries based on the gel polymer electrolyte film exhibit remarkable charge-discharge and cycling performances. The initial discharge capacity of this battery is as high as 165.1 mAh g at 0.1 C and just shows a small capacity fading of 4.8% after 120 cycles, indicating that the 85PVdF-HFP:15LiBF + 150(EC + PC) system is an excellent electrolyte candidate for lithium-ion battery applications. The charge-discharge performance of the Li-ion cell fabricated with this gel polymer electrolyte film is apparently better than that of the previously reported Li-ion cells fabricated with other PVdF-HFP-based gel polymer electrolyte films. [ABSTRACT FROM AUTHOR]

Ionic liquid-doped biodegradable gel polymer electrolyte membranes are currently new opportunities for rechargeable magnesium-ion batteries. In this work, poly(vinyl alcohol)/magnesium trifluoromethanesulfonate/1-ethyl-3-methylimidazolium trifluoromethanesulfonate (PVA/Mg(Tf)/EMITf) membranes of different compositions are prepared by solution casting. The crystalline structure, morphology, ionic conductivity, electrochemical stability window, and thermal stability of the membranes are analyzed by various techniques. It is found that the pristine PVA membrane possesses a semi-crystalline structure and its degree of crystallinity declines with augmenting EMITf concentration. The room-temperature ion conductivity of the 85PVA:15Mg(Tf):15EMITf gel polymer electrolyte membrane exhibits a high value of 2.10 × 10 S cm. Meanwhile, this gel polymer electrolyte membrane shows a wide electrochemical stability window (~5 V) and the temperature dependence of ionic conductivity obeys the Arrhenius rule ( E = 0.25 eV). Additionally, the mechanical properties of the electrolyte membrane are sufficiently high for its applications, being the following values: Young's modulus = 33 MPa; breaking strain = 452%; yield strength = 4.8 MPa. This inexpensive and environment-friendly gel polymer electrolyte membrane could be a promising potential electrolyte material for Mg-ion battery applications. Highlights: [ABSTRACT FROM AUTHOR]

Biodegradable polymer electrolyte films based on poly(ε-caprolactone) (PCL) in conjunction with lithium tetrafluoroborate (LiBF) salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF) ionic liquid were prepared by solution cast technique. The structural, morphological, thermal, and electrical properties of these films were examined using X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), and impedance spectroscopy. The XRD and OM results reveal that the pure PCL possesses a semi-crystalline nature and its degree of crystallinity decreases with the addition of LiBF salt and EMIMBF ionic liquid. DSC analysis indicates that the melting temperature and enthalpy are apparently lower for the 40 wt% EMIMBF gel polymer electrolyte as compared with the others. The ambient temperature electrical conductivity increases with increasing EMIMBF concentration and reaches a high value of ∼2.83 × 10 S cm for the 85 PCL:15 LiBF + 40 wt% EMIMBF gel polymer electrolyte. The dielectric constant and ionic conductivity follow the same trend with increasing EMIMBF concentration. The dominant conducting species in the 40 wt% EMIMBF gel polymer electrolyte determined by Wagner's polarization technique are ions. The ionic conductivity of this polymer electrolyte (∼2.83 × 10 S cm) should be high enough for practical applications. [ABSTRACT FROM AUTHOR]

Lithium ion conducting biodegradable gel polymer electrolytes based on a poly (ε-caprolactone):lithium tetrafluoroborate (PCL:LiBF) system doped with various concentrations of 1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF) ionic liquid were prepared by solution cast technique. The gel polymer electrolyte was eco-friendly, flexible, transparent and free-standing. The conductivity and transference number measurements were carried out to investigate ionic conduction and charge transport in the gel polymer electrolytes. The frequency-dependent conductivity results revealed that the room-temperature electrical conductivity increased with increasing EMIMBF concentration. At room temperature, the gel polymer electrolyte with a composition of 85PCL:15LiBF + 40EMIMBF exhibited a high conductivity value of approximately 2.83 × 10 S cm, which was favored by the rich amorphous phase as confirmed with X-ray diffraction analysis. The lithium ion transport number and electrochemical stability of the 40 % EMIMBF gel polymer electrolyte were 0.43 and 3.7 V, respectively. These values are acceptable and quite enough for practical device applications. Consequently, the 40 wt% EMIMBF incorporated gel polymer electrolyte could be used to fabricate lithium ion batteries with a suitable selection of other components of the battery system. [ABSTRACT FROM AUTHOR]

A functionally graded material (FGM) of polyetheretherketone (PEEK)-hydroxyapatite (HA) with a symmetrical three-layer structure containing 8.7, 2.6 and 8.7 vol% HA, respectively, is successfully fabricated by hot pressing and evaluated by scanning electron microscopy and tensile testing. A good bonding between the HA particles and the PEEK matrix is achieved by virtue of an in situ method in fabricating each PEEK-HA composite layer. There are no apparent microcracks and microscopic interfaces within each layer of the FGM. The symmetrical PEEK-HA FGM does not fall apart or delaminate during loading with a tensile strength of 86.2 MPa, and its fracture energy is 56.5 kJ/m. Furthermore, in vivo bioactivity of the FGM sample is also evaluated, showing that it has sound biocompability and bioactivity. Accordingly, the FGM in the future may be a promising biomaterial to be used as replacement implant of human bone through a proper design to balance mechanical properties and bioactivity. [ABSTRACT FROM AUTHOR]

The elctropulsing treatment (EPT) has been successfully applied to the processing of a low carbon Q235 steel strip. Comparing with the conventional heat treatment (CHT), a proper EPT is capable of achieving the similar or even better effect on the mechanical properties of the steel strip. It was found that the optimum combination of the EPT parameters are 180 V in voltage and 500 Hz in frequency (180 V-500 Hz) leading to a combination of tensile strength-elongation of 371 MPa-47.5%. Optical microscopy analyses indicates that the EPT/180 V-500 Hz for Q235 steel strip can accelerate the formation of the completely recrystallized microstructure in which the grain size become relatively finer and more uniform compared to the elongated one formed in the cold-rolled sample. Such phenomenon is consistent with the improvement of the mechanical performance of the Q235 steel sample under the EPT. However, the EPT with inadequate frequency can only result in partial recrystallization of the grains, while the one with an exceed frequency may lead to the apparent grain growth within the sample. Both cases can not produce satisfactory combination of strength and ductility for the steel samples. [ABSTRACT FROM AUTHOR]

Microwave sintering has emerged in recent years as a new method for sintering a variety of materials that has shown significant advantages against conventional sintering procedures. Sr and Pb doped BaTiO ceramics has been prepared by the high energy ball milling followed by conventional and microwave sintering. The phase formation was confirmed by X-ray diffractometer followed by Scanning electron microscopy, atomic force microscopy and Transmission electron microscopy. Dielectric constant was measured on both the samples and it is observed that, in BaPbTiO (abbreviated as BPT), it increased more than one order of magnitude and in BaSrTiO (abbreviated as BST), it increased two orders of magnitudes at room temperature and Curie transition temperature by microwave sintering. Interestingly the Curie transition temperature of BPT value decreased from 224 to 210 °C, where as in BST ferroelectric ceramics, no variation of transition temperature by conventional sintering and microwave sintering respectively. This promising technique has distinguished characteristics of energy saving, rapid processing and uniform temperature distribution throughout the samples. [ABSTRACT FROM AUTHOR]

Composite phosphors SrAlSiO/SrAlSiO codoped with Eu and Dy were synthesized via a simple one-pot nitrate-gel process. The thermal decomposition process of the precursor is investigated by thermal analysis, X-ray diffraction and infrared spectroscopy, respectively. The as-prepared Eu/Dy codoped SrAlSiO/SrAlSiO phosphors could yield blue (436 nm), bluegreen (486 nm), yellow (583 nm), and red (617 nm) lights under near-UV 380 nm excitation from a composite matrix produced by spontaneous phase separation during heat treatment of the precursor. Moreover, the effects of Dy doping concentration on the structures, defect features, and luminescence properties of the composite phosphors were examined in detail. [ABSTRACT FROM AUTHOR]

Nano-hydroxyapatite (HA) particles were prepared by a sol-gel method and polyetheretherketone (PEEK) composite materials containing a various amount of lab-prepared HA fillers had been successfully synthesized via an in situ synthesis process. The materials structure was characterized by infrared spectroscopy, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy and the mechanical performance was investigated by a tensile strength test. The tensile strength of HA/PEEK composites reaches an optimal 108 MPa at 6.1% HA content. The composites with HA content below 17.4% exhibit a plastic break mode, while a brittle break mode above 17.4%. The results exhibit that the strong bonding between hydroxyapatite fillers and PEEK matrix has been achieved. And it was proved that this strong bonding may be mainly attributed to the physical factors, such as mechanical interlock between PEEK molecules and HA surface. The study clearly demonstrates that in situ synthesized HA/PEEK composite materials have the potential for use as an alternative material for hard tissue replacement. [ABSTRACT FROM AUTHOR]

modified theoretical model is proposed to predict the grain boundary segregation of impurity atoms during high temperature plastic deformation. The model is based on the supersaturated vacancy-impurity complex created by plastic deformation and involves quasi-thermodynamics and kinetics. Model predictions are made for phosphorus grain boundary segregation during plastic deformation in ferrite steel. The results reveal that phosphorus segregates at grain boundaries during plastic deformation. At a given temperature, under a certain strain rate the segregation increases with increasing deformation amount until reaching a steady value, and at the same deformation amount it increases with increasing strain rate. The predicted results are compared with the available experimental values, indicating that there is a reasonable agreement between the theoretical predictions and the experimental observations. [ABSTRACT FROM AUTHOR]

Finding the internal-friction peak of grain boundary anelastic relaxation was one of the important breakthroughs in the study of internal friction in the last century. But the micro-mechanism of grain boundary anelastic relaxations is still obscure. Based on the observations of the grain boundary segregation or depletion of solute induced by an applied stress, the following micro-mechanism was suggested: grain-boundaries will work as sources to emit vacancies when a compressive stress is exerted on them and as sinks to absorb vacancies when a tensile stress is exerted, inducing grain-boundary depletion or segregation of solute, respectively. The equations of vacancy and solute concentrations at grain boundaries were established under the equilibrium of grain-boundary anelastic relaxation. With these the kinetic equations were established for grain boundary segregation and depletion during the grain boundary relaxation progress. [ABSTRACT FROM AUTHOR]

The research progress of non-equilibrium grain-boundary segregation theories in the last 20 years is reviewed. Based on studies by the present authors, the critical time of non-equilibrium segregation and its impact on the development of non-equilibrium segregation theories are described. Quasi-thermo-dynamics and kinetics for thermal non-equilibrium grain boundary segregation are detailed along with a non-equilibrium grain boundary cosegregation model. The experimental validation of the theories and their application to the reversible temper embrittlement of steels and the intermediate temperature brittleness in metals and alloys are also addressed. [ABSTRACT FROM AUTHOR]

The combined effect of phosphorus grain boundary segregation and hardness on the ductile-to-brittle transition was examined for a P-doped 2.25Cr1Mo steel by using Auger electron spectroscopy in conjunction with hardness measurements, Charpy impact tests and scanning electron microscopy. With prolonging time at 540 °C after water quenching from 980 °C, the segregation of phosphorus increases and the hardness decreases. The DBTT (FATT) increases with increasing phosphorus segregation and decreases with decreasing hardness. The effect of phosphorus segregation is dominant until 100 h aging and after that the hardness effect becomes dominant. This effect makes the DBTT (FATT) decrease with further prolonging ageing time although the segregation of phosphorus still increases strongly. [ABSTRACT FROM AUTHOR]

The degradation of thermal barrier coatings (TBCs) due to thermal cycling up to 1150°C has been studied. During thermal cycling, the bond coat in the TBCs was oxidised to form an alumina and a mixed oxide layer between the top coat of yttria stabilised zirconia (YSZ) and the bond coat of MCrAlY alloy. The mixed oxide layer mainly consists of α-Cr2O3 and (Ni,Co)(Cr,Al)2O4 spinel phases, which are formed above the α-alumina layer. Interestingly, the alumina layer gradually disappeared during the oxidation while the content of chromium in the mixed oxide increased with increasing oxidation time. As the oxidation accelerated after the disappearance of the alumina layer, cracks initiated and propagated in the mixed oxide layer near the YSZ. Eventually, the crack propagation induced the spallation of some YSZ top coatings after the 2000 h oxidation. [ABSTRACT FROM AUTHOR]