查看更多>>摘要：A facile and well-known eco-friendly strategy has been used to synthesize colloidal silver nanoparticles (AgNPs) and applied for the catalytic reduction of azo dyes. Herein, AgNPs were produced using silver nitrate (AgNO3) as a metal precursor and sodium hyaluronate (SH) as both reducing and stabilizing agents without the assistance of any other toxic reagents. The different characterizations were employed to investigate the morphology, crystallinity, surface plasmon resonance (SPR), particle size/distributions, and composition of particles. The investigation revealed that the AgNPs were mostly spherical oval shape with an average size of 13.3 +/- 4.7 nm, highly crystalline with a d-spacing of 0.233 - 0.257 nm, and coated with SH-macromolecules layer of cladding. In application of wastewater treatment, the AgNPs showed an excellent catalytic reduction (more than 99% rate of degradation) of two carcinogenic pollutants, i.e., reactive red 195 (RR195) and reactive yellow 145 (RY145) azo-dyes, with the support of sodium borohydride. The azo-dye catalysis has followed the model of pseudo-first-order kinetics reactions, with a kinetic constant (k) of 0.0948 min(-1) (r(2) = 0.9889) and 0.0222 min(-1) (r(2) = 0.9877) for RR195 and RY145, respectively. The present study not only provides a facile synthesis of AgNPs without toxic chemicals but also can be a potential candidate to meet the actual demand for textile wastewater treatment. (C) 2021 Elsevier B.V. All rights reserved.
Cherif, H. SadokBentouaf, A.Bouyakoub, Z. A.Rached, H....
15页
查看更多>>摘要：The aim of this paper is the prediction of the structural, electro-magnetic and mechanical properties of the Co(2)HfZ (Z = Al, Ga, Si and Sn) full Heusler compounds using a full-potential linearized augmented-plane wave method (FP-LAPW) based on the Wien2k program. For the structural and mechanical properties, we used the Perdew-Burke-Ernzerhof Generalized Gradient Approximation (PBE-GGA) and modified Becke and Johnson (mBJ) schemes to compute the fundamental parameters. The latter was employed for the electromagnetic properties, to calculate the band structures (BS) and density of states (DOS) of these compounds. Our results showed the half-metallicity of Co(2)HfZ (Z = Al, Ga, Si and Sn). The obtained energy revealed that these alloys were thermodynamically stable and could be hence elaborated experimentally. The mechanical properties indicated that our compounds were anisotropic ductile materials. Our findings greatly support that these compounds are highly attractive potential candidates for electro-spintronic applications. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：A bulk fine-grained W35Ta35Mo10Nb10V10 (at%) high-density high-entropy alloy (HEA) was successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) with varying parameters. Microstructure evolution and mechanical behavior of the HEA samples in various processing conditions were investigated. The alloying effect in the mixed high-purity powders becomes more significant as the increase of ball milling time during MA. Upon SPS at various temperatures ranging from 1600 to 1800 degrees C, a supersaturated body-centered-cubic (BCC) matrix prevails with the precipitation of Ta2VO6 oxides. After SPS at 1700 degrees C for 10 min, the average mass density, ultimate compressive strength and microhardness of the bulk HEA at room temperature are 14.65 g cm(-3), 2519 MPa and 6.50 GPa, respectively. The mechanisms responsible for the high strength and hardness include massive substitutional solid solution strengthening by the alloying of multiple principal elements, grain boundary strengthening, precipitation strengthening by Ta2VO6 particles, and interstitial solid solution strengthening by interstitials (e.g., tramp 0 from processing) in the matrix. The systematic information on the relationships among processing parameters, alloy densities, microstructure characteristics (e.g., grain sizes, volume fractions and sizes of precipitated oxides) and mechanical properties provide useful insights for the development of novel high-density and high-strength materials. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：A series of tellurite glasses having the composition(70)TeO(2)-20ZnO-(10-x)Nb2O5 (in mol%) doped with Er3+ ion (x = 0.5, 1.0, 1.5, 2.5, 3, 3.5 and 4 mol% respectively) was synthesized using the melt quenching route. Based on the Raman analysis and Differential Scanning Calorimetry, the produced glasses exhibited low phonon (772 cm(-1)) energy and good thermal stability (147 degrees C), respectively. The X-ray (XR) diffraction proved the amorphous state of the synthesized glasses, which highlights the high quality of the obtained glass materials. The impact of Er2O3 content on the local structure around erbium ions was investigated via Judd-Ofelt theory. Various radiative parameters such as the quality factors (chi), the branching ratios (beta), the quantum efficiencies (eta) and radiative lifetimes (Tau R) have been reported and discussed. The Down -conversion (DC) energy-process in the Er3+ ions was analyzed using an excitation wavelength of 488 nm and the different mechanisms involved in the 1.53 mu m emission are discussed. The effect of erbium content on the measured lifetime of the I-4(13/2) state was analyzed according the M. Inokuti and F. Hirayama (I-H) model. For high concentrations of Er2O3 oxide, the obtained results showed an efficient energy transfer between Er3+ ions, which may cause the luminescence quenching and the reduction in radiative parameters of the I-4(13/2) -> I-4(15/2) transition at 1.53 mu m. While the addition of Er2O3 oxide at low content up to a concentration of 4.211020 cm(-3) showed that this glass possessed high quantum efficiency (91%), large emission cross section of about 9.1 10-21 cm(2) and effective bandwidth exceeding 100 nm attributed to the 1.53 mu m emission, which makes the proposed tellurite glass highly promising in many photonic applications, especially for the design of luminescent solar concentrators (LSC) for bandgap solar cells in the range of 0.7-0.9 eV. (C) 2021 Elsevier B.V. All rights reserved.
Sterkhova, I., VKamaeva, L., VChtchelkatchev, N. M.Lad'yanov, V., I...
10页
查看更多>>摘要：The Fe-Cr-C alloys are promising hard facing materials with excellent wear resistance to address extreme technological environments which is provided by the presence of carbide chemical bonds stipulating high hardness. In this research, we study the influence of the carbon concentration from 10 to 17 at% on phase equilibria during heating, as well as crystallization processes of Fe-Cr-C alloys at 15 at% Cr and their relationship with the structure of the undercooled liquid state. The concentration dependence of undercoolability of Fe85-xCr15Cx (x = 10-17) melts revealed the minimum value in the region of the equilibrium eutectic near 14 at%C. Crystallization of Fe-Cr-C melts under cooling at a rate of 100 degrees C/min proceeds according to a nonequilibrium mechanism with the formation at the first stage of a solid solution based on fcc-Fe. Structure analysis of the undercooled Fe85-xCr15Cx melts (x = 10-17) showed that the nonequilibrium crystallization is related to peculiarities of interatomic interaction. Moreover, there is formation of structures with microhardness decreasing with growing carbon concentration in the alloy. (c) 2021 Elsevier B.V. All rights reserved.
Taghvaei, Amir HosseinNickjeh, Hasan ShakerRamasamy, ParthibanEckert, Juergen...
12页
查看更多>>摘要：In this study, novel glassy Co-Fe-Ta-Si-C alloys were prepared by mechanical alloying, (MA) and the influence of annealing treatment and substitution of Fe for Co on glass-forming ability (GFA), thermal stability and magnetic properties were investigated. Quantitative X-ray diffraction (XRD) analysis by the Rietveld method showed that the new Co50Fe25Ta5Si5C15 powders have an enhanced glass formation rate, especially during the early milling stages compared to the Fe-free Co75Ta5Si5C15 alloy. In good agreement with the XRD measurements, the calculated PHSS thermodynamic parameter revealed that the GFA is notably increased for the new powder. Thermal analysis demonstrated a high thermal stability and a rather wide supercooled liquid region (SLR) of 51 K for the Co75Fe25Ta5Si5C15 glassy alloy. The milling process and subsequent annealing treatment remarkably improved the soft magnetic behavior of the Co75Fe25Ta5Si5C15 powder. The results indicated that the Co75Fe25Ta5Si5C15 glass exhibits a slightly higher coercivity (H-c) and a notably larger saturation magnetization (M-s) than the Co75Ta5Si5C15 alloy in the as-milled state. Furthermore, in the relaxed state, the new alloy possesses a markedly lower H-c of 0.96 kA/m and a higher M-s of 108 Am-2/kg than Co75Ta5Si5C15 and large number of ssoft magnetic glasy powders prepared before. The influence of milling time and annealing temperature on the evolution of the magnetic properties were discussed in detail. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：LiMnPO4 has gained much attention due to its higher electrode potential than that of the commercial LiFePO4. However, it suffers from worse electrode kinetics related to the extremely low electrical conductivity and Li+ ion diffusion rate. Reducing crystal size can shorten diffusion distance of Li+ ions, and suppress the negative effect of defect zones on Li+ ion diffusion during cycling, thereby improving the electrode activity. In this study, the effect of crystallite size and carbon coating of LiMnPO4 on the electrochemical behavior is systemically investigated. By facile acetic acid-assisted solvothermal synthesis method, the crystallite size of LiMnPO4 nanosheets (ca. 10-20 nm in thickness) is remarkably reduced to below 50 nm in length and width. The shortened Li+ ion diffusion distance, increased specific surface area, and improved electrical conduction via carbon layer coating lead to the excellent electrochemical performance. The resulting LiMnPO4/C cathode shows the good charge/discharge reversibility and high discharge specific capacities of 148.8 mAh g-1 and 96.4 mAh g-1 at 1 C and 20 C respectively. This work would greatly promote the development of high-performance Li-ion batteries balancing the energy density and safety. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：In this work, alkali-earth metal elements (Mg, Ca, Sr, Ba) doped Li13.9Sr0.1Zn(GeO4+delta)(4) electrolyte is prepared by sol-gel method. The influence of alkali-earth metal doping on the phase structure, morphology, Li+/H+ ion exchange and electrical conduction behavior of Li13.9Sr0.1Zn(GeO4+delta)(4)(LSZG) electrolyte is characterized by X-ray diffraction, scanning electron microscopy,thermal gravimetric analyzer and electrochemical impedance spectroscopy. The powders of Mg, Ba and Sr doped Li13.9Sr0.1Zn(GeO4+delta)(4) electrolyte are found to possess the same phase structure as LSZG powders. The grain size and density of Mg, Ba and Sr doped LSZG samples increase significantly after sintering at 1050 degrees C. Ca is partially doped into the LSZG lattice, and some is precipitated in the form of CaGeO3 second phase. The doping elements can promote the ion exchange of Li+/H+ in LSZG electrolyte. With the increase of ion radius of doping elements, the Li+/H+ ion exchange rate of samples gradually decreases. The proton conductivity of all doped samples is significantly higher than that of pure LSZG electrolyte pellets. Mg is considered to be the best doping element. In 5% H-2-Ar humid atmosphere, the proton conductivity of Li13.8Mg0.1Sr0.1Zn(GeO4+delta)(4)(LMSZG) electrolyte at 0.9 V bias voltage is about 0.053 S/cm at 600 degrees C. The proton conductivity of LMSZG sample with BaZr0.4Ce0.4Y0.1Ni0.1O3 (BZCYN) barrier layer is about 0.049 S/cm at 600 degrees C. (C) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：]Manganese oxides (delta-MnO2) with pompon-like microspheres and non-spherical shaped particles were hydrothermally grown on Ni foam substrates in the presence and absence of a structure-directing agent (ammonium fluoride), respectively. The intercalated K+ ions in the layer-structured MnO2 were exchanged by the dissolved nickel ions from Ni foam during hydrothermal synthesis, leading to the formation of MnO2 with embedded nickel ions (labeled as Ni foam@Ni-MnO2). The dominated oxidation state of nickel ions in MnO2 was found to be trivalent (Ni3+), making Ni foam@Ni-MnO2 a promising catalyst electrode for direct and indirect urea oxidation reactions (UORs). Ni foam@Ni-MnO2 exhibited large electroactive surface area and high oxidation state of nickel-ion catalyst for adsorption of urea molecule and the successive cleavage of urea. Pompon-like microspheres with ultrathin nanosheets offered abundant pore channels to facilitate the spread of urea molecules and products in the UOR process. Electrochemical impedance spectroscopy revealed that Ni foam@Ni-MnO2 with pompon-like microspheres has lower direct UOR impedance and indirect UOR impedance in the regeneration of active Ni3+ catalyst than Ni foam. Thus, Ni foam@Ni-MnO2 displayed greater current density and smaller onset potential than bare Ni foam in catalyzing UOR. (c) 2021 Elsevier B.V. All rights reserved.
查看更多>>摘要：A near alpha titanium alloy Ti-3Al-2Zr-2Mo (wt%) was prepared by vacuum sintering of TiH2-based powder compact and multiple directional hot forging. beta-transformed (beta(t)) domains were imported into lamellar structures in order to break the strength-ductility trade-off dilemma of high-oxygen PM titanium alloys. It was revealed that beta(t) domains were harder than alpha laths in bi-lamellar microstructure prepared by annealing at 880 degrees C, and the alpha/beta(t) interfaces contributed to activation of abundant basal and non-basal slip systems in a laths, which brought about strong strain hardening and resulted in simultaneously enhanced strength and ductility. The bi-lamellar microstructure renders a high ultimate tensile strength (UTS) of 881 MPa and an elongation-to-fracture (EI) of 15.0%. By contrast, basket-weave microstructure produced via annealing at 950 degrees C exhibited the highest UTS up to 975 MPa, mainly because that its predominant alpha laths become inversely harder than adjacent beta(t) domains. Correspondingly, strain hardening got much weakened, stress concentration at colony boundaries led to a premature fracture and a low ductility. A new insight of beta(t) domains and their effect on mechanical properties of PM near alpha titanium alloy is proposed. (C) 2021 Elsevier B.V. All rights reserved.
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