Latest ArticlesA polyurethane-based nanocomposite with modified hexagonal boron nitride (h-BN) nanoparticle/graphene oxide (GO) was fabricated via effective dispersion of modified h-BN and GO into highly viscous polyurethane prepolymer in the presence of a polymer dispersant in a high energy-density stirred bead mill and subsequently crosslinking with a chain extender. The effects of h-BN and GO particles modified by a saline coupling agent, dispersion and h-BN and/or GO contents on the thermal transport capacity and mechanical properties were investigated, and the Kapitza thermal resistivity at the interface between h-BN nanoparticle or graphene oxide and polyurethane matrix was calculated based on the effect media approximation. The samples were characterized by thermal diffusivity measurement, wear rate analysis, Shore hardness measurement, scanning electron microscopy, infrared spectroscopy and infrared image. The results show that the nanoparticles modified by a saline coupling agent and dispersed with a polymer dispersant in the mill have a good compatibility with polyurethane matrix, thus enhancing the thermal conductivity of the nanocomposite, i.e., (0.671±0.033) W/(m·K), which is increased by 188 %, compared to neat polyurethane, i.e., 0.233 W/(m·K). This is possibly because the incorporation of modified h-BN nanoparticles or graphene oxide into polyurethane matrix can reduce the Kapitza thermal resistivity at their interface. Also, the Shore hardness of the polyurethane-based nanocomposite is 91, which is increased by 4.12%, and the wear rate is 2.03%, which is decreased by 26.63%, respectively, compared to those of neat polyurethane.
Tungsten (W)-doped vanadium dioxide (VO2) films were prepared by a polymer-assisted deposition (PAD) method. The morphology and phase transition of the doped VO2 films with different tungsten concentrations were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and Raman spectroscopy. The results indicate that tungsten atoms are incorporated into the VO2 films via the PAD method, and the fabricated VO2 films also show great crystallization characteristics. Based on the results by Raman spectroscopy, the M2 phase appears during the phase transition in the 1.0% (in mole) W-doped VO2 films. The results by electrical test indicate that the phase transition temperature of W-doped VO2 films is reduced by 10℃ as tungsten ions doped are increased by 0.3% (in mole), and the higher the doping concentration of tungsten is, the narrower the width of the phase transition thermal hysteresis loop will be.
MoS2 has attracted great attentions as a transition metal sulfide due to its excellent electrical, chemical, mechanical and thermal properties, which has the similar structure of graphite. However, the synthesis of high-quality MoS2 is still a challenge. MoS2 with specific morphology, a few layers, high active edges and single phase can be prepared by a space-confined method as a novel synthetic strategy. This review summarized the synthesis of MoS2 by different dimensional space-confined methods, In addition, research progress on lithium-ion batteries, supercapacitors, photoelectrocatalysis, etc. and future development were also prospected.
Na0.25K0.25Bi2.5-xHoxNb2O9 (NKBN-xHo3+, 0.000≤x≤0.030) bismuth layered ceramics were prepared by a conventional solid-state method. Effect of Ho3+ doping on the structural, electrical properties and up-conversion luminescence properties of NKBN ceramics was investigated. Based on the results by X-ray diffraction results, Ho3+ enters into the NKBN lattice and forms a solid solution. The grain size of NKBN samples decreases with the increased of Ho3+ doping. The optimum piezoelectric and ferroelectric properties of ceramic can be obtained as x=0.020, i.e., d33=21.8 pC/N, 2Pr=1.84 μC/cm2, where d33 is piezoelectric constant and Pr is remanent polarization. All the samples show little depolarization at 400 ℃, thus having a good thermal stability. Under the excitation of 980 nm laser, all the samples have the characteristics of up-conversion fluorescence luminescence, indicating that NKBN-xHo3+ ceramics can offer a potential application for optical-electrical multifunctional materials. The lattice structure symmetry of ceramic samples increases and the up-conversion fluorescence luminescence intensity reduces with the increase of polarization voltage.
A floating composite photocatalyst of hollow glass microspheres (HGM)/ZnIn2S4/α-Fe2O3 was prepared by a modified hydrothermal method. The HGM/ZnIn2S4 composite was firstly prepared with HGM as a carrier, and then further modified with nanorod-shaped α-Fe2O3 to obtain the floating composite photocatalysts of HGM/ZnIn2S4/α-Fe2O3. The effects of α-Fe2O3 content, photocatalysts addition and solution pH value on the photocatalytic activity of the composite photocatalysts for the degradation of hexavalent chromium (Cr6+) were investigated. The results show that α-Fe2O3 and hexagonal ZnIn2S4 heterogeneous structure are formed, and the composite photocatalyst is uniformly loaded on the surface of HGM. Compared to α-Fe2O3 powder and HGM/ZnIn2S4 composite microspheres, the photocatalytic performance of HGM/ZnIn2S4/α-Fe2O3 is improved. The prepared composite photocatalyst still has a good photocatalytic efficiency after several recycling. In addition, the synthesis mechanism of HGM/ZnIn2S4/α-Fe2O3 and its enhanced photocatalytic mechanism were also discussed.
The influences of sand ratio and paste aggregate ratio on fresh properties of high-fluidity concrete (HFC) were investigated. Two strength grades of HFC with different sand ratios and paste aggregate ratios were prepared. The fresh properties of HFC were investigated by rheological experiment, workability measurement and sliper test. The results show that the rheological properties and workability of HFC are related to the sand ratio and paste aggregate ratio. The yield stress and plastic viscosity of HFC and the lubrication layer initially firstly decrease and then increase with the increase of sand ratio. With the change of sand ratio of 6.38%, the variation range of yield stress of HFC can be up to about 27%, and the variation range of plastic viscosity can be up to about 78%. The yield stress and plastic viscosity of HFC and the lubrication layer gradually decrease with the increase of paste aggregate ratio. With the change of paste aggregate ratio of 16.07%, the variation range of yield stress of HFC can be up to about 331%, and the variation range of plastic viscosity can be up to about 204%. The varying tendency of workability of concrete is consistent with its rheological properties. A linear relationship between pumping pressure and quantity of flow for concrete predicted by sliper test shows the contribution of the lubrication layer to the process of pumping. The reliability of yield stress of the lubrication layer based on the sliper test is low.
R2O-CaO-SiO2-Al2O3-F (RCSAF) glass-ceramics were prepared via melting method. The nucleation and crystal growth kinetics of RCSAF glass-ceramics were analyzed by thermogravimetric analysis and X-ray diffraction. The nucleation and crystal growth kinetics of the glass-ceramics were obtained by Gaussian fitting. The temperature-time-transition (T-T-T) curve of R2O-CaO-SiO2-Al2O3-F glass-ceramics under non-isothermal heating conditions was obtained, and the Gaussian fitting of glass-ceramics and crystal growth kinetics were obtained. The crystallization kinetic parameters including the crystallization apparent activation energy (Ea) and the crystallization index (n) were also measured with Ozawa and JMA methods (i.e. Ea=357.74 kJ/mol, n=3.13). Effects of time, temperature and precipitated crystal phase on the crystallization rate curve of R2O-CaO-SiO2-Al2O3-F glass-ceramics were established. The CaF2 crystal particles precipitated from glass-ceramics were uniformly distributed in canasite and α-canasite. The crystal precipitation process of RCSAF glass-ceramics was further verified by typical crystal structure presented in scanning electron microscopic images.
A diatomite composite with a molecular sieve structure was prepared via acid hydrothermal treatment, and its adsorption performance was evaluated by a saturated adsorption rate of methylene blue in solution. The results show that a phase Variscite 10 with a molecular sieve structure can be formed by hydrothermal treatment. The saturated adsorption capacity of the composite with the specific surface area of 96.02 m2/g is 98.60 mg/g, which is 298.79 times greater than that of the raw diatomite. The size and crystallinity of the molecular sieve particles increase and the diatomite shell with tubular structure destroys as the reaction time increases, leading to the decrease of the adsorption performance of methylene blue. The optimum parameters for hydrothermal treatment are mixed acid of 10%(in mass fraction), reaction temperature of 180 ℃ and reaction time of 2 h.
The flake structure SAPO-34 was firstly synthesized via a hydrothermal method with co-template triethylamine and tetraethylammonium bromide as crystal seeds, and then the layered SAPO-34 molecular sieves with different thicknesses were synthesized via changing the template composition. The prepared samples were characterized by X-ray diffraction, scanning electronic microscopy and NH3-temperature programmed desorption. The methanol to olefins catalytic performance of the SAPO-34 was evaluated by a fixed-bed reactor. The results show that the crystallization time of SAPO-34 shortens by to 36 h and the SAPO-34 cannot be produced without template. The template has an influence on the thickness of layered SAPO-34. The lamellar SAPO-34 has better light olefins selectivity than the flake and cubic ones, but its catalytic stability is slightly inferior to that of the flake one.
Based on the study of ancient black glazed porcelains, high-fired glazes of SiO2-Al2O3-K2O-MgO-CaO-Fe2O3 system were designed and prepared. Different glaze decoration effects were achieved by changing the firing schedules to modify the crystallization behavior and microstructure of the glazes. The influence of thermal history on the crystal attribute and morphology, glaze appearance and coloring mechanism was investigated by using optical microscopy, field emission scanning electron microscopy, electron backscattered diffraction, X-ray diffraction and Raman spectroscopy, respectively. ε-Fe2O3 crystalline layer was prepared in a slight oxidation atmosphere at about 1 000-1 050 ℃. The results show that α-Fe2O3 crystals precipitated on the glaze surface have a good orientation and a variety of morphologies, which are related to the crystallization position and the direction of the crystallization plane. α-Fe2O3 crystals on the glaze surface show a silvery metallic luster, which belongs to a physical structural color.