查看更多>>摘要：Investigating on the effect of sodium formate mediated double regulation in TiO_2 photocatalytic reduction of cadmium is firstly reported. Multiple characterized methods were used to characterize and confirmed the successful reduction of Cd~(2+) to the form of metal elements by sodium formate-P25 system. The metal elements were attached to the surface of the composite photocatalyst were directly observed by SEM. The removal efficiency of Cd~(2+) for the composite photocatalyst was tested. When the addition of sodium formate was 1 g/L, the maximum removal rate of Cd~(2+) was 94.8% within 10 min. Further experiments showed the mechanism and activity of the combined catalysis of sodium formate and photocatalysis and the role of composite photocatalyst in photocatalytic activity. This is mainly due to the bidentate chelation between sodium formate and TiO_2 which makes it possible to adsorb heavy metal ions and the transfer of photo-generated electrons on the bidentate complex, which improves the survival time of the electrons and reduces the metal ions.
查看更多>>摘要：In additive manufacturing especially in directed energy deposition, it is hard to control crystal growth pattern due to the high temperature gradient in AM. Essentially, the crystal grows epitaxially from the substrate and columnar crystals with strong texture are exhibited in AM components. Here, small spot diameter was used for DED-L of Ni-based alloys and various crystal growth patterns were obtained by changing power density. Samples processed under low power density were shown to exhibit wide and shallow spindle-like melt pool, along with apparently hierarchical planar-columnar-equiaxed micro-structure. While samples prepared under relatively high power density were shown to exhibit narrower and deeper melt pool with two sharp turning points, exhibiting inclined columnar grains and several discontinuous central axial columnar crystals. When highest power density and small spot diameter were applied, crystal growth with weak texture was achieved. Under this deep and narrow melt pool, the crystal growth can be separated into four regions: nearly-equiaxed grains with random grain orientations; horizontally symmetrically grown crystal grains; axial columnar in the center; columnar grains grew approximately vertical to the boundary of melt pool. Correlations were investigated between melt pool shape, solidification parameters and microstructure. The transformation of melt pool morphology was mainly attributed to the change of power density. Solidification parameters were shown to be different under different melt pool morphology. Diverse crystal growth patterns were achieved under different melt pool morphology controlled by power density, showing the feasibility of site-specific of microstructure control in DED-L according to the required mechanical properties.
查看更多>>摘要：Here, we report a robust method for fabricating ZnO nanorod arrays with arbitrary patterns on glass substrate for device integration applications. Photolithography patterned non-transparent Zn film is used as growth sites for ZnO nanorods in the hydrothermal reactions for facile and reproducible fabrication. Patterns including lines, dots, texts, and logos have been demonstrated and the dimension of ZnO nanorods are tunable. The semi-transparent ZnO nanorod/glass shows increased light transmission when immersed in water, which is an advantage when integrate into devices requiring optical imaging and sensing. For proof-of-concept purpose, surface-enhanced Raman scattering sensors based on Ag coated ZnO nanorods with back observation configuration are demonstrated and show high sensitivity.
查看更多>>摘要：Study of the magnetic properties of the FeTiF_6 - 6 H_2O single crystal has shown that this compound is a two-dimensional antiferromagnet with a N e el temperature of T_N = 8 K and its magnetic moment anisotropy attains 7000% at a temperature of T = 4.2 K. The Mossbauer spectroscopy data unambiguously indicate the paramagnetic state of iron cations in the temperature range of 4.2-300 K. However, a sharp change in the difference between the quadrupole doublet linewidths at 10 K has been observed, which is consistent with the temperature of magnetic ordering. It has been suggested that the long-range magnetic order is established in the crystal through the formation of the exchange coupling revealed by the electron spin resonance measurements on the oriented single crystals.
查看更多>>摘要：Metal oxide supports have attracted much attention for improving the performance and durability of polymer electrolyte fuel cells. In this study, niobium-doped tin oxide (NTO) nanoparticles with a network structure were synthesized and Pt catalysts deposited on them using a flame aerosol technology. Because the flame method involves a variety of particle formation processes, which depend on the type of raw material and combustion method used, the effect of these processes on the particle structure, of the flame-made Pt/NTO was evaluated. When Pt/NTO nanoparticles were prepared by flame-assisted spray pyrolysis (FASP) using an inorganic raw material (metal chloride) with lower combustion enthalpy, the precursor liquid burned incompletely and Pt aggregation was observed. However, when flame spray pyrolysis (FSP) using a combustible precursor solution was used, the precursor rapidly evaporated in spray flames, and NTO with uniformly dispersed Pt was synthesized through gas-to-particle conversion. The electrochemical surface area and mass activity values of 5.44 wt% Pt-loaded NTO particles prepared by FSP were 48.2 m~2 g~(-1) Pt and 338 mA mg~(-1) Pt, respectively. Flame aerosol synthesis of supported metal catalysts can be widely used as a dry one-step process that does not involve any complicated post-treatment. The two types of noble metal loading processes revealed in this study provide important insights for determining particle design guidelines for in-situ production of supported metal catalysts in flames.
查看更多>>摘要：Carbonate materials have been increasingly favoured in terms of the development of flame retardants because of the eternal subject of inorganic carbon sequestration. In this regard, anhydrous zinc carbonate (ZnCO_3) has been deemed as suitable candidate thanks to its excellent flame retardancy compared to traditional hydroxid flame retardant. However, the single crystals growth, accurate characterizations of structural and thermal properties are still not entirely clear from previous studies. With this in mind, ZnCO_3 single crystals were synthesized under high-pressure-temperature conditions (high P-T; 3 GPa and 973 K). The crystal structure of impurity-free ZnCO_3 was determined by means of single crystal X-ray diffraction (XRD). The symmetry was identified as R3c, while the unit cell parameters were a= 4.6463(3) A and c= 15.0015(11) A with a final R value of 0.0229. The quantitative analyses of Raman spectrum and infrared absorption indicate that the as-synthesized ZnCO_3 is anhydrous phase. Using Thermogravimetric (TG) / Differential Scanning Calorimeter (DSC) measurements, ZnCO_3 was decomposed in the temperature range of 593-773 K, whereas the heat capacity and the endothermic peak were determined. According to the single crystal XRD from 150 K to 383 K, the thermal expansion coefficients were quantified as α_a= 7.90 × 10~(-6) K~(-1) and α_c=22.8×10~6 K~(-1) as well as aVunit ceii=38.8× 10~(-6) K~(-1). These findings provide a precise characterisation and obtain important thermal parameters for the evaluation of its flame retardant properties.
查看更多>>摘要：(l-x)Ca_(0.8)Sr_(0.2)TiO_3-xSmAlO_3 (abbreviated as (l-x)CST-xSA) perovskite ceramics were synthesized through the conventional solid-state reaction process. The effects of SmAlO_3 on the microstructure, low-frequency dielectric performances, and microwave dielectric properties for (l-x)CST-xSA ceramics were investigated systematically. All compositions exhibited an orthorhombic perovskite structure with dense surface morphology. With increasing the content of SmAlO_3) the order of B-site cation revealed a trend of increase first and then slowly decreased. The presence of oxygen vacancies in the (l-x)CST-xSA ceramics was detected by using x-ray photoelectron spectroscopy. Excellent temperature stability of dielectric permittivity and low dielectric loss (tan<5 lower than 0.005) were observed for (l-x)CST-xSA ceramics at low frequencies. For x = 0.35 composition, the temperature coefficient of the resonant frequency approached zero. In addition, the dielectric permittivity of 42.0, the quality factor of 39,120 GHz, and the temperature coefficient of resonant frequency of - 6.4 ppm/°C were obtained for 0.65CST-0.35SA ceramics. It is suggested that (l-x)CST-xSA ceramics can be used as a candidate material for various microwave communication components.
查看更多>>摘要：Biotemplating technique using hard templates is an effective strategy to prepare visible light-activated TiO_2 inherited macrostructural morphologies and self-doping elements from templates. However, conventional hard biotemplating method for preparing TiO_2 focused only on replicating the macrostructural morphology of templates via the sol-gel method, and neglected the effect of microstructural building units for artificial macrostructure assembly. Generally, the microstructural building units of the final macrostructural morphology are tightly packed nanoparticles. This paper presents a newly designed solvothermal method to replace the microstructural building units from tightly packed nanoparticles to convex nanowires or concave pores. This strategy can achieve the leap of conventional hard biotemplating method from macro-structure replication to microstructural building units design. The hard-biotemplated TiO_2 with designed microstructure exhibited significantly further enhanced visible-light photocatalytic efficiency in tetracycline degradation due to the increase of active sites, high separation efficiency of photo-generated electrons and reducing the charge-transfer resistance. Biotemplated TiO_2 with concave porous micro-structural building units is 22.0, 5.5 and 4.4 times higher than those of pure TiO_2 and the two biotemplated TiO_2 samples prepared via conventional sol-gel method and solvothermal method without glycerol or HF added, respectively. The enhanced visible-light photocatalytic efficiency by microstructure design was also demonstrated by using ciprofloxacin.
查看更多>>摘要：High-entropy alloys (HEAs) have been extensively investigated primarily because of their wide range of properties (mechanical, thermal, corrosion, etc.) that enable their application in countless applications. One of the most promising families is the Al_xCoCrFeNi based HEA, which tends to form simple phases and exhibit simple phase evolution with temperature. In this system, the complexity of the phase evolution tends to increase with decreasing temperatures, which complicates the collection and analysis of experimental thermodynamic data. Therefore, most of the work done in this system regarding phase transitions has been at high temperatures (T > 1000 °C). AlcsCoCrFeNi has promising mechanical properties due to its duplex nature. It has an FCC dendrite core (DC) region at low temperatures, which occupies about 90 vol%: the reminder is a B2/BCC mixture inter-dendritic (ID) region. Each region has a different chemical composition, which leads to different phase evolution at intermediate temperatures (400 ≤ T ≤ 900 °C). The phase composition and evolution were studied using high-sensitivity calorimetry followed by electron microscopy and XRD characterization. The DC region exhibits a simpler phase evolution with ordered FCC (Ll_2) nano-precipitation at 508 °C that transitions to B2 precipitation at 778 °C. The Ll_2 → B2 transition is associated with a large exothermic event caused by the release of 'symmetry-breaking' strain and significant shrinkage. The ID region exhibits a more complicated phase evolution that starts with precipitation of a Co-Cr rich HCP phase at 626 °C and continues with the precipitation of Cr-Fe rich sigma (a) phase along the boundaries between the regions at 699 °C, followed by the transition of the BCC precipitation into FCC at 733 °C. All these transitions in the ID region are associated with non-linear expansion. The experimental findings were compared with the thermodynamic evolution made using the ThermoCalc software and two thermodynamic databases.
查看更多>>摘要：The CO gas sensing characteristics of polar GaN (P-GaN) and non-polar GaN (NP-GaN) thin-films grown by RF-plasma assisted molecular beam epitaxy on c-Al_2O_3 and r-Al_2O_3 substrate is analyzed. The temperature-dependent (27-300 °C) current-voltage (I-V) measurements were performed for both (P-GaN & NP-GaN) Schottky barrier diodes having identical device dimensions with Au as the metal contact. The Schottky barrier height increases with the increment in temperature, while vice versa was perceived for the ideality factor and series resistance. The I-V characteristics dictated that the terminal current for P-GaN is 25 times that of NP-GaN, further corroborated by simulation results. The I-V curve fitting suggests the initial emission of charge carrier from a trapped state to a continuum of electronic state, following the Frenkel-Poole emission model for P-GaN. The NP-GaN demonstrated a higher surface-to-volume ratio and native (shallow and deep level) defects corresponding to V_(Ga) and O_N as compared to the P-GaN. The sensing response obtained for the NP-GaN for 100 ppm CO gas at 300 °C is ~ 33%, which is about seven times the response in the case of P-GaN. The role of native defects and the potentiality of the fabricated NP-GaN over P-GaN films in providing a better sensing characteristic by reducing the current conduction paths are elaborated.
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Elsevier