关键词： Mechanical activation   Niobium-bearing mineralisation   KOH   Kinetics   Hydrothermal leaching  

摘要： The leaching kinetics of niobium-bearing mineralisation in KOH hydrothermal system was investigated. Particle size analyzer, XRD and SEM were used for studying the influences of mechanical activation on particle size, surface area, crystal structure and surface morphology of niobium-bearing mineralisation. The results showed that mechanical activation decreased the mineral particle size, increased the surface area and the degree of lattice distortion or disorder. Kinetics of alkali leaching of niobium is modeled and explained. The activation energy of niobium leaching from unactivated niobium-bearing mineralisation was 45.6 kJ/mol. When the mineralisation was activated for 10 min and 30 min, the activation energy decreased to 32.2 kJ/mol and 21.9 kJ/mol respectively. Compared with the non-mechanical activation method, mechanical activation greatly improved the activity of niobium-bearing mineralisation and decreased the activation energy, so that the reaction speed was accelerated remarkably.

关键词： In situ TEM   flexible electronics   core-shell nanowire  

摘要： Research on electromechanical properties of semiconducting nanowires, including plastic behavior of Si nanowires and superb carrier mobility of Ge and Ge/Si core-shell nanowires, has attracted increasing attention. However, to date, there have been no direct experimental studies on crystallography dynamics and its relation to electrical and mechanical properties of Ge/Si core shell nanowires. In this Letter, we in parallel investigated the crystallography changes and electrical and mechanical behaviors of Ge/Si core-shell nanowires under their deformation in a transmission electron microscope (TEM). The core-shell Ge/Si nanowires were bent and strained in tension to high limits. The nanowire Young's moduli were measured to be up to similar to 191 GPa, and tensile strength was in a range of 3-8 GPa. Using high-resolution imaging, we confirmed that under large bending strains, Si shells had irregularly changed to the polycrystalline/amorphous state, whereas Ge cores kept single crystal status with the local lattice strains on the compressed side. The nanowires revealed cyclically changed electronic properties and had decent mechanical robustness. Electron diffraction patterns obtained from in situ TEM, paired with theoretical simulations, implied that nonequilibrium phases of polycrystalline/amorphous Si and beta-Sn Ge appearing during the deformations may explain the regarded mechanical robustness and varying conductivities under straining. Finally, atomistic simulations of Ge/Si nanowires showed the pronounced changes in their electronic structure during bending and the appearance of a conductive channel in compressed regions which might also be responsible for the increased conductivity seen in bent nanowires.

关键词： mechanisms   oxidation   permanganate   poly(ethylene glycol)   ruthenium(III) catalyst  

摘要： The kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm(-3) has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo-first-order plots showed curves of inverted S-shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first-order dependence in [MnO4-], fractional first-order dependence in [H+], and fractional first-order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First-order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.

关键词： Epoxy coating   Solvent   Curing kinetics   Mechanical properties  

摘要： Commercial coatings based on epoxy and amine hardener and organic solvent were prepared to investigate the effect of organic solvent on coating properties, their mechanical property and curing kinetics were discussed in terms of different solvent content. The curing degree was characterized by FT-IR, the mechanical properties were studied by tensile and adhesion tests, the non-isothermal curing kinetics and glass transition temperature of epoxy coating were also investigated by differential scanning calorimetry (DSC). The results indicated that the presence of solvent could lower the curing degree thus affecting the cross-linked structure, the tensile strength and modulus of elasticity, while the flexibility was highly improved by adding more solvent into the system. Different adhesive failure modes were observed with the increasing amount of solvent in comparison with that of pure epoxy, it transformed from cohesive to adhesive failure. Furthermore the two parameter autocatalytic kinetic model Sestak- Berggren (m,n) was introduced to describe the curing process and it shows a good agreement with the experimental rates. The results also demonstrated that activation energy of curing reaction increased with rising conversion which revealed that curing process was considered to be diffusion controlled.

关键词： scale formation   coordinate measuring machine   mixing   fluids mechanics   macroinstabilities   computational fluid dynamics  

摘要： Accelerated growth of scale was studied in a baffled agitated reactor, which could be disassembled into nine sections, allowing quantitative determination of scale thickness. A coordinate measuring machine was used to determine the scale thickness on individual wall segments. The growth pattern of the scale was found to be nonuniform due to the variation of fluid velocity near the wall at various heights. Computational fluid dynamics (CFD) simulation showed that fluid flow is time-dependent and has two distinct flow zones, one involving recirculation through the impeller in the lower part of the vessel and the other involving lower velocities due to the flow separation at the wall in the upper part. CFD simulation also showed the presence of macroinstabilities, which manifest as asymmetrical and chaotic flow structures with relatively long-time scales. Scale growth is found to be prominent in regions where the fluid velocity and wall shear stresses are low. (C) 2018 American Institute of Chemical Engineers

关键词： Metallic glasses   Molecular dynamics simulation   Mechanical properties   2NN modified embedded-atom method (MEAM) potential  

摘要： This study uses molecular dynamics (MD) and the density functional theory (DFT) calculation to investigate the structural, mechanical, thermal, and electronic properties of Mg3Ca7, Mg5Ca5, Mg7Ca3 bulk metallic glasses. A fitting process for the Mg-Ca cross-element parameters of the second-nearest neighbor modified embedded-atom method (2NN MEAM) potential was performed via the particle swarm optimization (PSO) based on density functional theory (DFT) calculations with reference data present in ESI. Using these fitted potential prameters, the Mg3Ca7, Mg5Ca5, Mg7Ca3 structures were constructed with the simulated-annealing basin-hopping (SABH) method. X-ray diffraction results provided the angle distribution range, which indicates that the predicted Mg3Ca7, Mg5Ca5, Mg7Ca3 match those of Mg- and Ca- BMG5. This confirms that the fitted parameters of 2NN MEAM potential can indeed precisely represent the interactions of the Mg and Ca atoms in MgCa BMG. Results from the analysis of Honeycutt-Andersen (HA) index show the local icosahedral-like structures occupy 75.52%, 75.33%, 73.84% within Mg3Ca7, Mg5Ca5, Mg7Ca3. The chemical affinity indicated by Warren-Cowley chemical short-range-order (CSRO) parameters shows the Ca atom has a higher affinity to the Mg atoms while possessing less affinity to itself. The tensile simulation results indicate that the Young's moduli are about 9.77, 9.56, and 8.52 GPa, and the strengths are about 582, 552 and 507 MPa for Mg3Ca7,Mg5Ca5, and Mg7Ca3, respectively. For the thermal properties, the melting temperatures of Mg3Ca7, Mg5Ca5 , and Mg7Ca3 range from 750 to 810 K, which are located within the experimental melting temperatures of MgCa alloys. Einstein equation is utilized to calculate self-diffusion coefficients of Mg3Ca7 , Mg5Ca5, and Mg(7)Ca(3 )around melting temperatures, based on the MSD profiles at 500 ps time interval. Based on these diffusion coefficients, the diffusion barriers of Mg, Ca, and total atoms can be determined. The diffu

关键词： CARBON nanowires   GRAPHITIZATION   TENSILE strength   MOLECULAR dynamics   MOLECULAR physics  

摘要： T-carbon, a new carbon allotrope, was initially predicted to exist in a theoretical study [Phys. Rev. Lett. 106 (2011) 155703] and successfully fabricated in recent experiment [Nat. Commun. 8 (2017) 683]. This work investigates the mechanical behaviors and structural evolution of T-carbon nanowires under tensile loading by using molecular dynamics simulations. It is found that T-carbon nanowires exhibit mechanical anisotropy and excellent ductility. This is due to the fact that global graphitization (sp(3)-sp(2) transitions) of T-carbon nanowires can be induced by tensile loading, which has been rarely reported for other carbon materials. Occurrence of the global graphitization is due to the competition between the mechanical strengths of sp(3) and sp(2) networks that eventually determines the graphitization dependence on temperature and lattice direction of T-carbon. A phase diagram of T-carbon nanowires is finally drawn to unveil their graphitization under tensile loading, thus interpreting their mechanical behaviors. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： magnesium alloys   rare-earth metals   decomposition of solid solution   hardness   mechanical properties   structure  

摘要： The aging kinetics, the mechanical properties, and the structure of cast alloy IMV7-1 of theMg - Y - Gd - Zr system alloyed additionally with dysprosium are studied. It is shown that yttrium and gadolinium may be replaced partially with dysprosium without changes in the aging kinetics and lowering the hardening and the level of the mechanical properties of alloy IMV7-1.

关键词： Polymerization kinetics   DSC   Isoconversional methods   PEGMA   PEGMEMA  

摘要： Monomers composed of a polymerizable methacrylate moiety connected to a short poly(ethylene) glycol (PEG) chain are versatile building-blocks for the preparation of smart biorelevant materials. Hydrogels based on these PEG methacrylates are a very important class of biomaterials with several applications. The radical polymerization kinetics of two such oligomers, namely poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) was investigated. Experimental polymerization rate and monomer conversion data were measured using DSC operating under non-isothermal conditions, at several constant heating rates, or isothermal, at different constant reaction temperatures. Isoconversional techniques were employed to estimate the variation of the polymerization effective activation energy as a function of the extent of reaction. It was found that isothermal and non-isothermal experiments results in similar trends of the activation energy, whereas by comparison of differential to integral isoconversional methods it was postulated that in non-isothermal polymerization experiments integral methods should not be used. From comparison of the two oligomers employed in the polymerization experiments, it was clear that the presence of the terminal hydroxyl group in PEGMA compared to the methoxy group in PEGMEMA leads to different conversion time profiles and activation energies. In particular, monomer-monomer association through hydroxyl groups results in initially lower activation energy of PEGMA. As polymerization proceeds, the existence of aggregated hydroxyl structures ( OHOHOH ) in the PEGMA macromolecular chains result in higher activation energies and a more abrupt increase in the conversion time curve.

关键词： cardiogenic shock   mechanical circulatory support   temporary ventricular assist device   cardiac output   systemic response  

摘要： Emerging clinical evidence has suggested that short-term mechanical augmentation of cardiac output (CO) may not consistently improve mortality in patients with cardiogenic shock (CS), despite improvements in hemodynamics. Such failures could reflect the underlying complexity of the mechanisms that contribute to malperfusion and organ dysfunction in CS. Distinct molecular and physiologic shock endophenotypes likely exist among patients with CS, with hemodynamic aberrations as the inciting insult but not necessarily the primary drivers of clinical outcomes. We propose that building a framework that moves away from the current "hemodynamic model" in preference for a "mechanistic disease-modifying model" of CS may facilitate progress toward reducing the stagnant mortality rates in this population. Such a therapeutic paradigm shift in patients with chronic systolic heart failure the shift away from strategies that augment CO to those that modulate the systemic responses to low CO has been one of the single most important shifts in contemporary cardiovascular medicine. (C) 2018 International Society for Heart and Lung Transplantation. All rights reserved.