Search

BNT-6BT-based lead-free ceramics have gained significant attention due to their relatively large piezoelectric coefficients and tunable morphotropic phase boundary conditions. In this investigation, SrTiO 3 (ST) was added to BNT-6BT ceramics to fabricate the BNT-6BT- x ST (BNBT- x ST) composition. The impact of ST content on the phase structure and dielectric permittivity of the BNBT- x ST ceramics was studied. The XRD refinement data show that with increasing ST content, the crystal structure of BNBT- x ST ceramics was transformed from the morphotropic phase structure (coexisting tetragonal (P4/mmm) and pseudo-cubic (Pmm) phase) to the pseudo-cubic phase. The dielectric permittivity data of the BNBT-80ST showed that the T m (the maximum permittivity temperature) moved to −61.9 °C, which caused the room temperature to fall within the range of T m < T < T B (the Burns temperature). This makes the BNBT-80ST a superparaelectric state in relaxor ferroelectrics (RFE). Furthermore, the maximum energy density and the charge-discharge efficiency of the BNBT-80ST achieved 5.48 J/cm3 and 87% at 495 kV/cm, respectively. The energy density of the BNBT-80ST was improved by 2.97-fold and 49% compared with that of the BNBT-30ST and BNBT-70ST. This is mostly attributed to weakened ferroelectricity and improved paraelectricity in the BNBT-80ST. This investigation demonstrates that BNBT- x ST ceramics can be adjusted to a superparaelectric state with an ST content of 80%. This makes the material to possess both a large polarization and a high breakdown field. This material holds great promise for high energy density capacitor applications. [ABSTRACT FROM AUTHOR]

Lead-free (1− x )(K 0.37 Na 0.63 )NbO 3 - x Ca(Sc 0.5 Nb 0.5 )O 3 ( x =0.050, 0.070, 0.090, 0.095 and 0.100) transparent ferroelectric ceramics have been fabricated by pressureless sintering procedure. Transmittance of 0.91(K 0.37 Na 0.63 )NbO 3 -0.09Ca(Sc 0.5 Nb 0.5 )O 3 ceramics sintered in sealed alumina crucible was 15% higher than those sintered unsealed in air. By increasing the content of Ca(Sc 0.5 Nb 0.5 )O 3 , the phase structure of (K 0.37 Na 0.63 )NbO 3 ceramics transformed from orthorhombic to tetragonal symmetry first and then to pseudo cubic symmetry. The 0.91(K 0.37 Na 0.63 )NbO 3 -0.09Ca(Sc 0.5 Nb 0.5 )O 3 ceramics exhibited high density (98%), high transmittance (60%) in the near-IR region and relatively good electrical properties ( ε r =1914, tan δ =0.037, T c =147 °C, P r =6.88 μC/cm 2 , E c =8.49 kV/cm). Meanwhile, the introduction of Ca(Sc 0.5 Nb 0.5 )O 3 induced a composition fluctuation in the (K 0.37 Na 0.63 )NbO 3 lattice and made the ceramics more relaxor-like, which would lead to a further reduction of light scattering. These results demonstrated that 0.91(K 0.37 Na 0.63 )NbO 3 -0.09Ca(Sc 0.5 Nb 0.5 )O 3 could be promising lead-free transparent ferroelectric ceramics. [ABSTRACT FROM AUTHOR]

Abstract: WO3/AlPO4 catalysts were prepared by impregnation of AlPO4 with ammonium metatungstate. Powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and thermo gravimetric and differential thermal analysis (TG–DTA) demonstrated that the tungsten compound was incorporated into AlPO4 forming the catalyst with an enhanced acidity. When transesterification of soybean oil over the catalysts was performed, the catalyst with 30wt.% WO3 loading and calcined at 1073K, exhibited the best catalytic activity with a conversion of 72.5%. The transesterification was optimal at 453K for 5h with a methanol/oil ratio of 30:1 and catalyst dosage of 5wt.%. Free fatty acid (FFA) and water did not affect the catalytic activity. The catalyst proved to be stable over four transesterification cycles as it lost only 4% of its activity after being reused four times. The catalyst could be used for the transesterification of low-cost oils for biodiesel production. [Copyright &y& Elsevier]

Abstract: ZnO rod-assembled microspheres were successfully fabricated by using the microwave-assisted hydrothermal method in the existence of the poly ethylene glycol (PEG) with the molecular weight of 2000. The structure and morphology of as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The experimental results exhibit that the as-prepared ZnO microspheres with a diameter about 1.5–2.0μm were composed of many rods with the diameter of 300nm and the length of 1μm, respectively. Photoluminescene measurement shows a broad visible emission band centered at around 500–560nm. The improved catalytic activity may be attributed to structural difference, including morphology, surface orientation and surface defects. Furthermore, the possible growth and photodegradation mechanism of the as-prepared sample is also briefly discussed. [Copyright &y& Elsevier]

Abstract: Using CaCO3 as blowing agent and via melt foaming method, Mg foams with closed-cells have been fabricated successfully. It has been proved that the blowing gas to foam melted Mg is not CO2 but CO, which is released from the liquid–solid reaction between Mg and CaCO3. The releasing temperature of CO is more than 100°C lower than the decomposition temperature of CaCO3, which leads to melted Mg being foamed much more easily and the foaming process can be accomplished in a temperature range of 665–750°C. [Copyright &y& Elsevier]

A label-free liquid crystal (LC) biosensor based on orientation changes of LC molecules was reported for the detection of cecropin B. The homeotropic-to-tilted alignment transition of LC molecules, induced by the specific binding event between cecropin B and anti-cecropin B antibody immobilized via glutaraldehyde, could result in obvious change of the optical appearance from a dark to a bright response and as a result, the detection limit of cecropin B was as low as 50 ng/mL. The average gray-scale intensities (GIs) of optical appearances were calculated to quantitatively analyse cecropin B concentrations. This study offers a simple, highly sensitive and specific, lable-free method for cecropin B detection. [ABSTRACT FROM AUTHOR]

Local phase transformations of materials during mechanical machining influence the variation of surface integrity directly. The aim of this work is to investigate the relationship between cutting parameters and phase transformations during high speed machining (HSM) of Ti-6Al-4V. Rapid heating and cooling phase transformation models are firstly proposed based on phase transformation dynamics. Then, the proposed models are implemented into the Ti-6Al-4V cutting simulation model as a user subroutine of Abaqus/Explicit. The simulated results indicate that, in the chip formation process, β phase volume fraction increases from 8% to 90% in the serrated chips and the machined surface at the cutting speed range of 50–600 m/min. In the rapid cooling process, the ratio of the transformed α ” phase is about 4%. Finally, comparisons of the simulated results and high speed cutting experiments indicate that the developed models can precisely predict the phase transformations during HSM Ti-6Al-4V. The results help to get deeper insights into understanding the phase transformation mechanisms during HSM o Ti-6Al-4V. The research can also provide an instruction for optimizing the cutting parameters to control the surface integrity in machining of Ti-6Al-4V. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel "turn-on" fluorescent chemosensor for the detection of Al3+ was developed. • The probe exhibited anti-interference recognition and low detection limit of 22.0 nM. • The detection mechanism of the probe for Al3+ is the formation of Al-complex. • HL can be utilized as a film to detect Al3+ ions. Many Al3+ sensors have been reported in the literature, the lack of spectral features and poor coordination of Al3+ pose a significant challenge to detection. Herein, the design and synthesis of a Schiff's base (HL) sensor is reported, which exhibits a turn-on response to Al3+ in an aqueous solution, and the fluorescence color of HL from light green to cyan upon the addition of Al3+. The limit of detection (LOD) for Al3+ was determined to be 2.20 x 10−8 M. The mechanism for fluorescence sensing was revealed through the analysis of single-crystal X-ray diffraction, DFT, and UV–vis absorption spectra. HL gradually coordinated with Al3+ during the titration process, leading to the formation of HL-Al crystals. The outcome of this study resulted in the successful preparation and application of flexible and foldable films for visual detection of Al3+. [ABSTRACT FROM AUTHOR]

Abstract: Poly(N-isopropylacrylamide)-b-[poly(ethyl acrylate)-g-poly(2-(diethylamino)ethyl methacrylate)] (PNIPAM-b-(PEA-g-PDEAEMA)) double hydrophilic graft copolymers were employed to prepare stable colloidal gold nanoparticles in situ with controllable size in aqueous media without any external reducing agent. PDEAEMA side chains served as reduction agent and stabilizer and PNIPAM segment acted as a hydrated layer to enhance the stability of gold nanoparticles. These gold nanoparticles showed a remarkable colloidal stability without any observable flocculation or aggregation for at least 2 months and they were characterized by UV–vis, XRD, TEM and AFM in detail. The size of gold nanoparticles can be tuned by adjusting the length of PDEAEMA side chains and the molar ratio of [DEAEMA]/[AuCl4 −]. Both the increasing of the length of PDEAEMA side chains and the decreasing of [DEAEMA]/[AuCl4 −] molar ratio resulted in the fall of size. [Copyright &y& Elsevier]

This study investigated the interfacial bond performances between ordinary Portland cement concrete (OPCC) and self-compacting geopolymer concrete (SCGC). The studied factors include nano-SiO 2 , repair material type, curing time, casting direction, and interface pretreatment method. The interfacial bond performances were assessed by Bi-surface shear and drying shrinkage tests. The evolutions in elemental compositions, hydration products, and microstructure in the matrix and interface were verified by BSE/EDS, XRD, and FTIR tests, respectively. ANOVA analysis was conducted to quantitatively analyze the influences of each factor from a statistical approach. The results demonstrated that the bond strength of SCGC increased by 24.5% to 31.7% compared to conventional OPCC. Meanwhile, geopolymers exhibited more compact microstructures but higher drying shrinkage (ε sh,u =891 µε). While nanofillers significantly amplified the cracking potential of geopolymers, which was attributed to the higher early-stage autogenous shrinkage instead of drying shrinkage. The SCGC showed a high enrichment degree of calcium at the interface, indicating that more calcium-rich products were formed. In contrast, the use of nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions, which provided extra nucleation sites for the polymerization of (C, N)-A-S-H gels. The nano-SiO 2 enhanced the intensity of the hydroxide ion and Si-O-T band and promoted the formation of (C, N)-A-S-H gels. The ANOVA analysis proved that the repair material, nano-SiO 2 , and interface treatment were significant factors to affect the interfacial bond strength. In addition, geopolymer-based repair materials were less sensitive to the casting direction, which differed from the conventional self-compacting OPCC. [Display omitted] • Geopolymer concrete at the same strength grade has 25-30% higher bond strength than conventional OPCC. • Nanofillers amplified the cracking potential of geopolymers due to higher early-stage autogenous shrinkage. • nano-SiO 2 in SCGC caused the enrichment of Na, Al, and Si at the interfacial regions. • geopolymer-based repair materials were less sensitive to the casting direction. [ABSTRACT FROM AUTHOR]

Abstract: This paper concerns uniaxially stretched ultra-thin polyimide (PI) films containing ether and ketone moieties. The stretched PI films exhibited remarkable high modulus (4.9 GPa) and high strength (258 MPa) in the stretch direction compared with commercial polyimides because of their high degree of molecular orientation induced by uniaxial hot stretch. The tensile strength of the stretched PI films is about 2.4 times of that of undrawn films and the coefficients of thermal expansion decreased by as much as 84%. Studies of birefringence and wide-angle X-ray diffraction all proved a high degree of molecular orientation and crystallization induced during the drawing process. The thickness of stretched PI films was reduced at least 75% as compared to unstretched PI films and the thinnest film is only 7 μm. [Copyright &y& Elsevier]

Abstract: The alumina microfibers with mesoporous structure were synthesized by a facile hydrothermal and thermal decomposition route. The as-obtained products were well characterized by XRD, SEM, TEM (HRTEM), SAED and N2 adsorption–desorption measurement. It was shown that the length and diameter of these alumina microfibers are about 10μm and 300–500nm, respectively. All these alumina microfibers prepared by the PEG templates with different molecular weight have the different high surface area but nearly the same pore diameter about 3.5nm. The calcination experimental result shows that the mesoporosity of these alumina microfibers can be maintained even at 1373K. On the other hand, the higher selective catalytic reduction (SCR) of NO effectiveness present that the as-obtained mesoporous alumina have stronger adsorption property because of its high surface area. [Copyright &y& Elsevier]

Understanding the structure–property relationships of solid-state, solution luminescence and aggregation-induced emission (AIE) at the molecular level could greatly develop efficient organic light-emitting materials. However, intermolecular π···π interaction were always considered to quench fluorescence. By contrast, a diametrically opposed effect was recently found in a class of naphthalimide polymorphs. In this work, naphthalimide derivative ND showed solvatofluorochromic properties, which attributed to the interaction of ND with different solvents resulted in ND polymorphs directly and these polymorphs formed dimers in crystallization states. Apart from the different structural motifs, torsion angles, π···π, CH···π and other supramolecular interactions made a significant difference between these polymorphs. Also, these polymorphs displayed distinctly different luminescent color in solids under 365 nm UV light. Obvious AIE characteristics were observed in aqueous mixtures. The X-ray diffraction analysis suggested that the π···π stacking interaction was the critical element that determined the solid-state emission and AIE in aqueous solution and CH···π interaction governed solvatofluorochromism. In addition, the solvents-protomed polymorphs interconversion provided a new pathway for the colormetric and ratiometric sensing of dichloromethane and 1,4-dioxane. The X-ray diffraction analysis suggested that the π···π stacking interaction was the critical element that determined the solid-state emission and AIE in aqueous solution and CH···π interaction governed solvatofluorochromism. In addition, the solvents-protomed polymorphs interconversion provided a new pathway for the colormetric and ratiometric sensing of dichloromethane and 1,4-dioxane. Image 1 • Multiple naphthalimide dimers polymorphs was obtained. • The X-ray diffraction analysis suggested that the π···π stacking interaction was the critical element that determined the solid-state emission and AIE in aqueous solution and CH···π interaction governed solvatofluorochromism. • The solvents-promoted polymorphs interconversion provided a new pathway for the colormetric and ratiometric sensing of dichloromethane and 1,4-dioxane. [ABSTRACT FROM AUTHOR]