查看更多>>摘要：The composition of nanoparticles obtained by a thermal plasma process was quantitatively investigated using a Ni-Cu isomorphous alloy system. Specifically, a Ni-Cu alloy nanopowder with an average particle diameter of ~ 70 nm was prepared by the thermal plasma process and the particle composition was investigated. As the lattice constant follows the Vegard's law, a nanopowder with an average composition equivalent to the predefined composition was successfully obtained. According to the EDS analysis obtained from each particle, the standard deviation of composition distribution was 7.7 at% as a powder. The computational study indicated that each particle has a homogeneous composition because of the nanoparticle formation via nanodroplet and that a composition distribution of 1.05 at% is estimated in the powder. Further, the spatial composition distribution of the alloy powder in the reaction chamber was experimentally studied by trapping the powder at a certain location, and the results indicated that the composition distribution of the powder varied spatially.
查看更多>>摘要：A series of Dy~(3+) activated Ba(YLu)_2Si_3010 samples were prepared by high temperature solid-phase method. The purity of the phase was determined and the structural changes were analyzed. Under excitation at 350 nm, the BaY_2Si_3O_(_10): Dy~(3+) phosphor shows two stronger luminescence peaks at 486 nm and 572 nm and weaker emission peak at 668 nm. In addition, with the continuous replacement of Y~(3+) in the matrix by Lu~(3+) ions, the chromaticity coordinates of samples in the system can be adjusted from the cold white region to the warm white region, and the luminescence performance of phosphors can be effectively improved. It was observed that the thermal stability of the phosphor was gradually enhanced with Lu~(3+) concentration increases, and the emission intensity of the BaLu_2Si_3O_(10): 0.04Dy~(3+) phosphor at 453 K could still maintain 83.78% of that at room temperature, which was discussed in conjunction with the Debye temperature and the rigid structure model to provide a reference for the improvement of the thermal stability performance. In addition, the increase of the concentration of Lu~(3+) ions doping will shorten the lifetime of phosphors due to the non-radiative energy transfer caused by the shortening of the ion distance in the lattice.
查看更多>>摘要：Tin oxide (SnO_2) is widely used in metal-oxide-semiconductor for gas-sensing materials due to its unique physical and chemical properties. The grain size is one of the major influencing factors that determine the gas-sensing characteristics. In this work, a facile hydrolysis-oxidation-hydrothermal method is used to prepare the size-controllable SnO_2 quantum dots (QDs) of 4.7-8.9 nm, and the gas-sensing characteristics of the SnO_2 QDs sensors are evaluated by C_4H_(10), H_2 and C_2H_5OH at room temperature. The experimental results show that the resistance has a negative correlation with hydrothermal time, and the maximum response is obtained when the grain radius is comparable to the depletion layer width. A comprehensive model is proposed by considering all gas-sensing procedures of the receptor function, the transducer function and the utility factor. The sensor properties are formulated as functions of grain size, depletion layer width, film thickness, oxygen vacancy density, gas concentration, pore size as well as operating temperature. The present model provides a comprehensive mathematical interpretation of the size effects of SnO_2 from partial depletion to volume depletion.
查看更多>>摘要：Electrically-assisted manufacturing (EAM) has been proved to be very efficient in homogenizing the alloy with heterogeneous grain distribution due to the local Joule heating effect, which completely differs from the common heat treatment. However, the interaction between pulsed current and texture evolution during deformation have been rarely investigated even though texture is critical for the plastic behaviour of anisotropic material. Here, the effect of pulsed current on texture evolution behaviour has been studied by comparing the evolution behaviours of a Ni-based superalloy under electrically-assisted and quasi-static tension. The result showed that the evolution of easy-to-deform texture into hard one was promoted by the pulsed current, but the further enhancement of the hard-to-deform texture's intensity was inhibited. This difference could be attributed to the more pronounced local Joule heating effect in the hard-to-deform grain due to larger lattice distance here, and then the softened hard-to-deform grain could rotate itself towards other orientations more easily. This is called "target effect" of pulsed current on the hard-to-deform texture in present work, which further indicates that EAM is effective in the control of homogeneous behaviour of anisotropic materials not only from the microstructure distribution but also from the mechanical property.
查看更多>>摘要：Molybdenum and vanadium mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) were synthesized by the modified sol-gel method. The phase formation and structure were investigated through X-ray powder diffraction (XRD) patterns. The optical absorption measurements show that the sample has an efficient light response covering the region UV-visible to near IR wavelength. The two Mo-V mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) show an indirect forbidden transition with band energies of 1.67 eV and 1.64 eV, respectively. The multivalent cations (V and Mo ions) were confirmed via X-ray photoelectron spectroscopy (XPS) measurements. The effective photocatalysis of the samples was conducted via the photodegradation of RhB under visible-light irradiation (λ ≥ 420 nm). The conductivity properties and lifetime of charge carriers were characterized via impedance spectra and luminescence decay curves respectively. It was suggested that intrinsic redox couples in these Mo-V mixed oxides lead to intervalence transfer between V~(5+/4+) and Mo~(6+/5+) couples, which can improve photocatalysis. This work offers a potential alternative material with rich intrinsic redox couples and defects toward high-performance photocatalyst.
查看更多>>摘要：Nowadays, it is still a big challenge to synthesize Mn~(4+)-doped fluoride red phosphors with high water resistance, luminescent intensity and thermal stability simultaneously. Therefore, KSF:M,N@GQ.Ds@KSF (K_2SiF_6:0.06Mn,0.10Na@GQPs (12 mg/mol)@K_2SiF_6 (0.2 wt) KSF: K_2SiF_6, GQDS: OH-contained graphene quantum dots) with high luminescent intensity, high luminescent thermal stability and water resistance have been synthesized via a combination of H_2O_2-free room temperature reaction method, hydrothermal coating method and room temperature surface coating process. Experimental results show that enhancement of negative thermal quenching (NTQ) effect and water resistance can be synergistically induced by double coating of GQPs and KSF. After being immersed in deionized water for 360 min, emission intensities of the KSF:M,N@GQDs and KSF:M,N@GQPs@KSF are decreased from 100% to 70.57% and 91.63%, respectively, indicating that water resistance of the latter is obviously improved by coating of KSF. The improved water resistance is attributed to preventing hydrolysis of [MnF_6]~(2-) on sample's surface by insoluble coating shell of KSF. A prototype WLEDs (white light-emitting diodes) emitted warm white light (CCT = 4546 K and Ra = 91.3, at a driving current of 20 mA) has been assembled by coating mixture of KSF:M,N@GQPs@KSF, yellow emitting phosphor (YAG:Ce~(3+)) and epoxy resin on blue light InGaN chips. The good performances of the WLEDs suggest that the KSF:M,N@GQPs@KSF has potential applications in blue-based warm WLEDs.
Claudio Shyinti KiminamiFrancisco Gil CouryDiego de Araujo Santana
11页
查看更多>>摘要：Medium/High Entropy Alloys (M/HEAs) exit over immense compositional fields, which represent a challenging opportunity for the development of alloys with optimized properties. To realize their potential, we need to be able to predict properties of interest from different compositions effectively. Precipitation strengthened alloys are of wide interest, but their yield strength modeling is not simple because many factors as precipitate type, size, fraction, and composition play important roles. The Cr_(29.7)Co_(29.7) Ni_(35.4)Al_(4.0)Ti_(1.2) (at%) alloy was designed to have a highly concentrated Cr-Co-Ni face centered cubic matrix with Ll_2 precipitates. In the present work, this alloy was aged at 850 °C for times up to 166 h and had its yield strength measured in the different aging conditions through tensile tests. A recently developed model to calculate the solid solution contribution in FCC multi-principal element alloys was coupled with classical grain-boundary strengthening and precipitation hardening models to predict the yield strength of the studied alloy. We show that the different strengthening contributions can be modeled independently with satisfactory accuracy. The results can be easily extrapolated to other alloys of the Cr-Co-Ni-Al-Ti system. An empirical relationship to estimate the room temperature lattice parameter of FCC alloys is also proposed. A promising route to explore the vast compositional space of M/HEA and design new precipitation hardening alloys with optimized mechanical properties is suggested.
查看更多>>摘要：A very rare set of glasses having chemical compositions of B_2O_3-TeO_2-Na_2O-PbO, doped with europium trioxide were obtained by the conventional melt quenching procedure. An X-ray diffractometer was run to confirm the non-crystalline nature of the structural studies. The AC conductivity and dielectric properties of glasses were studied in the temperature range 343-483 K with a 40 Hz to 6 MHz frequency range. The Almond-West model of power-law suggests, the well-fitting of found AC conductivity values and conductivity is due to translational motions of carriers. AC conductivity decreases with increasing concentration of Eu_2O_3. The non-Debye type of relaxations was predicted by AC conductivity plots. The dielectric constant and dielectric loss of complex permittivity was measured and obtained values suggested that the phenomenon of dielectric relaxation is mainly subjected to the frequency-dependent polarization mechanism. The obtained power-law exponent values indicate the AC conductivity mechanism and follow the CBH model.
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.
NSTL
Elsevier