Preprint
|
|
|
Materials Science, General Materials Science; ionic liquids; ionic liquid-assisted solvothermal reaction; reaction time; titanium dioxide; heterogeneous photocatalysis; visible light
Online: 15 May 2018 (09:10:42 CEST)
|
|
Share this article with
×
Spherical microparticles of TiO2 were synthesized by the ionic liquid-assisted solvothermal method at different reaction time (3, 6, 12 and 24h). The properties of the prepared photocatalysts were investigated by means of UV-vis diffuse-reflectance spectroscopy (DRS), BET surface area measurements, scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicated that the efficiency of phenol degradation was related with a time of the solvothermal synthesis as determined for TiO2_EAN(1:1)_24h sample. Microparticles of TiO2_EAN(1:1)_3h formed during the only 3h of synthesis time revealed really high photoactivity under visible irradiation – 75%. This value increased to 80% and 82% after 12h and 24h, respectively. The photoactivity increase was accompanied by the increase of the specific surface area thus pores size, as well as ability to absorb UV-vis irradiation. The high efficiency of phenol degradation of IL-TiO2 photocatalysts was ascribed to the interaction between the surface of TiO2 and ionic liquid components (carbon and nitrogen).
Preprint
|
|
|
Materials Science, General Materials Science; ultrasound; TiO2 nanoparticles; oxygen vacancy; photocatalytic activity; visible light
Online: 18 April 2018 (09:45:18 CEST)
|
|
Share this article with
×
TiO2 nanoparticles were successfully synthesized using a facile and scalable sol-gel method followed by calcination in air. The structural and optical properties, along with the photocatalytic performance of the nanoparticles were analyzed using X-ray diffraction, infrared spectroscopy, transmission electron microscopy, energy dispersive spectroscopy, UV-vis spectroscopy, photoluminescence spectroscopy, and degradation of anionic azo dye (methyl orange (MO)) under visible light irradiation. The prepared TiO2 nanoparticles crystallize in the anatase structure with a highly crystalline order. The results showed a band gap energy of 3.59, 3.79 and 3.54 eV, respectively, which suggests a better photocatalytic activity for sample calcined at 450 °C compared to other samples’ thermal treatments. The synthesis route employed for the preparation of the TiO2 nano-photocatalyst resulted to be efficient for degradation reactions MO of dyes.
Preprint
|
|
|
Materials Science, General Materials Science; fly ash; nanocomposite; environmental pollution; volatile organic compounds; heavy metal
Online: 16 April 2018 (16:15:22 CEST)
|
|
Share this article with
×
Air pollutants such as volatile organic compounds (VOCs), nitrogen oxides (NOx), sulfur dioxide (SO2), as well as water pollutants including heavy metal, are harmful to human and environment. Effective control and reduction of their pollution is therefore an important topic for today’s scientists. Fly ash (FA) is a type of industrial waste that can cause multiple environmental problems if discharged into the air. On the other hand, because of its high porosity, large specific surface area, and other unique characteristics, the FA can also be used as a low-cost and high efficient adsorbent with some simple modifications. This paper reviews the effects of FA on treatment of the above air and water pollution based on our research experience over many years, including to the current status of global FA utilization, physicochemical properties, principle of adsorption, and the application direction of FA in the future. It focuses on the use of nanocomposite technology to fabricate functional FA fibrous membranes to adsorb VOCs from air, and treat heavy metal wastewater. This present review first describes the fabrication technology of FA nanocomposites and their mechanism of adsorption VOCs from air. Utilization of nanofiber technology to fabricate multi-functional FA emerging composite materials to mitigate air and water pollution has great potential in the future, especially use of pollutant material to control other pollutants.
Preprint
|
|
|
Materials Science, General Materials Science; : carbon; atomic structure; atomic behavior; atomic binding; force-energy behaviors; glassy carbon
Online: 16 April 2018 (05:55:12 CEST)
|
|
Share this article with
×
Many studies deal synthesis of carbon-based materials because of the versatility of carbon element where lack the arresting of understanding at convincing and compelling levels. A non-conservative energy is required to transfer occupied state electron to nearby unfilled state along both left and right sides of the gas state carbon atom to convert it into its graphitic state where exerting forces of relevant poles of transferring electrons remain neutral at the instant of tracking the arc-like trajectory to go into unfilled state. Changing the position of two electrons in each state carbon atom results into originate its new physical behavior. Different state carbon atoms were obtained under confined inter-state electron-dynamics under the involvement of non-conservative energies where engaging the non-conservative forces instead of conservative were engaged. Structure evolution for graphitic, nanotube, and fullerene states atoms mainly engages the surface format forces where involved arc-shape energies enable execution of confined inter-state electron-dynamics binding to amalgamating atoms in one quadrant, two quadrants and four quadrants to develop structure of one-dimension, two-dimension and four-dimension, respectively. However, a graphite structure is evolved under the application of electron-dynamics of attaining graphitic state atoms as well as under their attained dynamics, only. Evolution of structure in diamond and lonsdaleite state atoms are under the joint application of surface format force and grounded format force where electrons of binding atom deal another clamping of energy knots belonging to unfilled states of deposited atoms while visualizing the force of south to their bottom tips through them. Structural evolution of graphene engages both surface format and space format forces to work neutral at the instant of binding atom through its four electrons dealing another clamping of energy knots belonging to unfilled states of deposited atoms while visualizing the force of north to their top-sides through them. Growth of diamond is south to ground but binding of atoms is ground to south, so it is tetra-double-clamped energy knot ground to south topological structure. Same is the case for lonsdaleite state atoms except it is bi-double-clamped energy knot ground to south topological structure. Growth of graphene is north to ground but binding of atoms is ground to north, so it is tetra-double-clamped energy knot ground to north structure. Glassy carbon is related to a wholly layered-topological structure where tri-layers of gas carbon atoms, graphitic state atoms and lonsdaleite state atoms order in repetition manner. In glassy carbon, forces of space format, surface format and grounded format work as neutral while binding atoms of successive tri-layers. Due to maintenance of electrons at above ground surface in gas state carbon atoms, they do not attain the favorable point for binding. Hardness of carbon-based materials as per identified in literature is sketched under the exploration of different force-energy behaviors exerting at electron level is described. A carbon atom is a best model to explain binding mechanism in atoms of various elements and in fullerene state, it is a best model to understand the working forces at ground surface.
Preprint
|
|
|
Materials Science, General Materials Science; magnesium alloy; EV31A; MAGMASoft; simulation; casting; foundry
Online: 9 April 2018 (11:06:49 CEST)
|
|
Share this article with
×
Carrying out technological tests and research is indispensably connected with high costs and elongation of implementation time of new casting technologies and their modifications in industry. Hence, the application of specialised computer software, enabling the simulation and analysis of metallurgical and casting processes in modern foundry industry is of special interest. The present work presents an experimental application of MAGMASoft software in casting process of EV31A magnesium alloy structural element of helicopter engine. The results of computer simulation have been compared with industrial cast of the simulated element, fabricated in the same conditions. It has been revealed that the computer simulation provides a complex information on the analysed process, leading to reduction of costs and time, connected with technological tests in implementation of new casting technologies.
Preprint
|
|
|
Materials Science, General Materials Science; photocatalyst; flower-like SnS2; nanocomposites; visible light; methylene blue
Online: 3 April 2018 (10:53:52 CEST)
|
|
Share this article with
×
Semiconductor materials have been shown to have better photocatalytic behavior and can be utilized for the photodegradation of organic pollutants. In this work, three-dimensional flower-like SnS2 were synthesized by a facile hydrothermal method. Core-shell structured SiO2@α-Fe2O3 nanocomposites were then deposited on the top of the SnS2 flowers. The as-synthesized nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) and photoluminescence spectroscopy (PL). The photocatalytic behavior of the SnS2-SiO2@α-Fe2O3 nanocomposites was observed by observing the degradation of methylene blue (MB). The results show an effective enhancement of photocatalytic activity for the degradation of MB especially for the 15 wt. % SiO2@α-Fe2O3 nanocomposites on SnS2 flowers.
Preprint
|
|
|
Materials Science, General Materials Science; Cholesteric Blue Phase III; nonlinear viscoelasticity; disclination network; fracture
Online: 29 March 2018 (12:00:13 CEST)
|
|
Share this article with
×
Nonlinear rheological properties of chiral crystal cholesteryl oleyl carbonate (COC) in blue phase III are investigated under different shear deformations; large amplitude oscillatory shear, step shear deformation, and continuous shear flow. Rheology of the liquid crystal is significantly affected by structural rearrangement of defects under shear flow. One of the examples on the defect-mediated rheology is the blue phase rheology. Blue phase is characterized by three dimensional network structure of the disclination lines. It has been numerically studied that the rheological behavior of the blue phase is dominated by destruction and creation of the disclination networks. In this study, we find that the nonlinear viscoelasticity of BPIII is characterized by the fracture of the disclination networks. Depending on the degree of the fracture, the nonlinear viscoelasticity is divided into two regimes; the weak nonlinear regime where the disclination network locally fractures but still show elastic response, and the strong nonlinear regime where the shear deformation breaks up the networks, which results in a loss of the elasticity. Continuous shear deformation reveals that a series of the fracture process delays with shear rate. The shear rate dependence suggests that force balance between the elastic force acting on the disclination lines and the viscous force determines the fracture behavior.
Preprint
|
|
|
Materials Science, General Materials Science; Fe-6.5wt.% Si alloy; hot bar rolling; microstructure; texture; mechanical property
Online: 29 March 2018 (06:15:08 CEST)
|
|
Share this article with
×
Cylindrical Fe-6.5wt.% Si bars with 7.5 mm in diameter were successfully fabricated from as cast ingot through three rolling stages within 10 passes: rough rolling at 850–900 °C and 8–10 m/min, medium rolling at 800–850 °C and 10–15 m/min, and finish rolling at 800–850 °C and 12–18 m/min. The evolution of microstructure, texture and ordered structure, and the mechanical property are investigated. The results showed that the grains were refined by the hot bar rolling. Area fractions of the {100}<011> oriented grains and the {011}<100> oriented grains decreased to 0 during the hot bar rolling. Whereas, the {100}<001> component, the {011}<211> component and the {112}<110> component increased, and γ fiber with {111}<110> component was dominant. DO3 ordered phase were suppressed, and B2 ordered domains were refined after the hot bar rolling. Ductility of the as rolled bar was higher than that of the rotary swaged bar, due to the absence of the DO3 ordered phase and the fine grains in the rolled bar. Hence, the hot bar rolling technology is an excellent process to fabricate the Fe-6.5wt.% Si bars.
Preprint
|
|
|
Materials Science, General Materials Science; photocatalyst; titanium dioxide; multi-walled carbon nanotubes; methyl orange; degradation
Online: 14 March 2018 (06:43:53 CET)
|
|
Share this article with
×
In this study, functionalized-MWCNTs with 3-aminopropyltriethoxysilane (APTES) loaded titania nanoparticles (MWCNTs-APTES-TiO2) were prepared to investigate their physicochemical properties and photocatalytic activity for methyl orange (MO) degradation. The TiO2 nanoparticles, functionalized-MNCNT and composite powders were characterized by XRD, raman, and TEM. The results obtained proved that titania (TiO2) nanoparticles was successfully loaded on APTES-MWCNTs. The best photocatalytic degradation of methyl orange solution under UV light irradiation was recorded over MWCNTs-APTES-TiO2 (1:2), with 87% after 180 min. Kinetic analysis indicated that photocatalytic degradation of MO solution by MWCNTs-APTES-TiO2 obeyed second-order kinetic model (R2 > 0.95), supported by half-life equations and graph. The presence of carbon nanotubes accelerated the degradation of methyl orange due to inhibition of electron-hole recombination, the formation of additional hydroxyl radicals and functional groups of the latter had an inhibitory effect on the degradation of methyl orange. This study shows that the MWCNTs-APTES-TiO2 nanocomposites exhibit promising photocatalytic degradation against methyl orange.
Preprint
|
|
|
Materials Science, General Materials Science; water purification, oligodynamic metal, moringa oleifera seed, copper
Online: 12 March 2018 (15:20:37 CET)
|
|
Share this article with
×
A simple, efficient and stand-alone method for purification of river water using moringa seed powder and copper is discussed. Coagulant property of the seed powder clears turbid raw water and the oligodynamic activity of copper completely destroys E.coli bacteria. Both raw and treated water samples were tested for contaminants to verify the efficacy of the system. Treated water has turbidity in the range 3 NTU - 5 NTU and non-detected (< 1 MPN/100 mL) E.coli count making it suitable for drinking. The technique is very cost effective and can be practiced anywhere using locally available materials. It does not require a power source or any technical assistance. Being a stand-alone system the technique exceptionally useful in providing drinking water as an immediate solution in disaster areas affected by cyclone or floods.
Preprint
|
|
|
Materials Science, General Materials Science; bismuth vanadate, molten salt synthesis, platelet morphology, multi-foil shape, Wulff shape, Ostwald ripening
Online: 12 March 2018 (06:46:50 CET)
|
|
Share this article with
×
10% copper substituted (BiCUVOX/Bi2V0.9Cu0.1O5.5−δ) and 5% copper/titanium double-substituted bismuth vanadate (BiCUTIVOX/Bi2V0.9(Cu0.05Ti0.05)O5.5−δ) platelets were formed by molten salt synthesis (MSS) using a eutectic KCl/NaCl salt mixture. The product was phase pure within the limits of X-ray diffraction. The size and form of the platelets could be controlled by changing the heating temperature and time. The crystallite growth rate at a synthesis temperature of 650 °C, and activation energy for grain growth were determined for BICUTIVOX, which experienced inhibited growth compared to BICUVOX. Quasi-equilibrium, multi-foil shapes consisting of lobes around the perimeter of the platelets were observed and explained in the context of relative two-dimensional nucleation and edge growth rates.
Preprint
|
|
|
Materials Science, General Materials Science; Fe–6.5 wt.% Si; ribbon; melt spinning; ac iron loss prediction; magnetic properties
Online: 9 March 2018 (05:07:06 CET)
|
|
Share this article with
×
Ultra-thin Fe–6.5wt.%Si ribbons with 35 μm in thickness were prepared by melt-spinning. The magnetic properties were investigated before and after annealing 1000 ºC. DC properties and low-frequency (400 Hz ~ 10 kHz) iron losses have significantly improved after heat treatment. A simplified formula based on Steinmetz law which can be used to predict the AC iron loss is presented. According to the results of some iron losses data, a simplified formula has been determined, and the extent of AC iron losses can be predicted. The results obtained from the formula predict AC iron loss to a good degree. The method developed in this work could be extended to other magnetic materials for predicting AC iron loss with greater ease.
Preprint
|
|
|
Materials Science, General Materials Science; lithium-ion batteries, water-based binders; styrene-butadiene rubber (SBR); carboxymethyl cellulose (CMC); silicon; graphite; anode
Online: 27 February 2018 (11:07:11 CET)
|
|
Share this article with
×
Cycling reliability is crucial for Si-based materials due to severe volume change during cycles that results in the fast capacity fading. Though the binder only occupies a very low amount of the total mass of anodes, it is proved to perform a key parameter to improve the cycle performance of Si-based anodes. Because they are eco-friendly and cost saving, water-based binders styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are regarded as the better binder to substitute Poly (vinylidene difluoride) (PVDF) as the binder for Si-based anode. In this study, the anodes are fabricated by simply mixing the active materials (naso Si, graphite and conductive additive) together and using the mixture of SBR and CMC as a binder. The results showed that the retention capacities of the anodes are more than 440 mAh/g after 400 cycles. It indicates that it is an easy and simple way to make high performance anodes.
Preprint
|
|
|
Materials Science, General Materials Science; TiAl alloys; dislocation; twinning; nanoindentation; ECCI
Online: 12 February 2018 (17:07:45 CET)
|
|
Share this article with
×
In this work, plastic deformation was locally introduced at room temperature by nanoindentation on a γ-TiAl based alloy. Comprehensive analyzes of microstructures were performed before and after deformation. In particular, the Burgers vectors, the line directions and the mechanical twinning systems were studied via accurate electron channeling contrast imaging. Accommodation of the deformation are reported and a scenario is proposed. All features help to explain the poor ductility of the TiAl based alloys at room temperature.
Preprint
|
|
|
Materials Science, General Materials Science; Fe-6.5wt.%Si alloy; hot compression; processing map; microstructure; optimized processing parameter
Online: 11 February 2018 (11:20:10 CET)
|
|
Share this article with
×
The flow behavior of Fe-6.5wt.%Si alloys during hot compression was investigated at temperatures 650–950 °C and strain rates 0.01–10 s-1. The results showed that the flow stress depended distinctly on the deformation temperatures and strain rates. The flow stress and work hardening rate increased with the decrease of temperature and the increase of strain rate. The activation energy under all the deformation conditions was calculated to be 410 kJ/mol. The constitutive equation with hyperbolic sine function and Zener–Hollomon parameter was developed. The peak stress, critical stress, and steady-state stress could be represented as σ=A+Bln(Z/A). Dynamic recrystallization occurred under the deformation conditions where the values of Z were lower than 1020. Processing maps were established to optimize the processing parameters. The power dissipation efficiency decreased in the high temperature and low strain rate region, increased in the high temperature and high strain rate region, and remained unchanged in other regions with the increase of true strain. Furthermore, the unstable area expanded. The true strain of 0.7 was the optimum reduction according to the processing map. Based on the analysis of surface quality, microstructures, and ordered structures, the optimized processing parameters for the Fe-6.5wt.%Si alloys were the temperature and strain rate of higher than 900 °C and 0.01–10 s-1, respectively, or 800–900 °C and lower than 0.4 s-1, respectively.
Preprint
|
|
|
Materials Science, General Materials Science; surface energy, interfacial energy, surface tension, wetting model, wetting thermodynamics, sessile drop shape, microgravity
Online: 2 February 2018 (13:05:40 CET)
|
|
Share this article with
×
In this study, the values of the interfacial energies of seven different polymer-water systems obtained by Sessile Drop Accelerometry (SDACC) are compared with the values obtained by the Young’s-equation-based Owens-Wendt method. The SDACC laboratory instrument –a combination of a drop shape analyzer with high-speed camera and a microgravity tower- and the evaluation algorithms, are designed to measure the interfacial energies as a function of the geometrical changes of a sessile droplet shape due to the effect of “switching off” gravity during the experiment. The method bases on Thermodynamics of Interfaces and differs from the conventional aproach of the two hundred-years-old Young’s equation in that it assumes a thermodynamic equilibrium between interfaces, rather than a balance of forces on a point of the solid-liquid-gas contour line. A comparison of the mathematical model that supports the SDACC method with the widely accepted Young`s equation is discussed in detail in this study.
Preprint
|
|
|
Materials Science, General Materials Science; nanocrystalline ceramics; ionic transport; mechanochemsitry; NMR; conductivity spectroscopy; fluorides
Online: 25 January 2018 (04:46:39 CET)
|
|
Share this article with
×
Nanostructured materials have already become an integral part of our daily life. In many applications ion mobility decisively affects the performance of, e.g., batteries and sensors. Nanocrystalline ceramics often exhibit enhanced transport properties due to their heterogeneous structure showing crystalline (defect-rich) grains and disordered interfacial regions. In particular, anion conductivity in nonstructural binary fluorides easily exceeds that of their coarse-grained counterparts. To further increase ion dynamics aliovalent substitution is a practical method to influence the number of (i) defect sites and (ii) the charge carrier density. Here, we used high energy-ball milling to incorporate Y3+ ions into the cubic structure of SrF2. As compared to pure nanocrystalline SrF2 the ionic conductivity of Sr1-xYxF2+x with x = 0.3 increased by 4 orders of magnitude reaching 0.8 x 10 -5 S/cm-1 at 450 K. We discuss the effect of YF3 incorporation on conductivities isotherms determined by both activation energies and Arrhenius pre-factors. The enhancement seen is explained by size mismatch of the cations involved, which are forced to form a cubic crystal structure with extra F anions if x is kept smaller than 0.5
Preprint
|
|
|
Materials Science, General Materials Science; carbon clathrates; hybrid carbon-silicon clathrates; hybrid carbon-nitrogen clathrates; electrode materials; hydrogen storage materials; energy storage materials; hard materials
Online: 18 January 2018 (05:08:03 CET)
|
|
Share this article with
×
Hybrid carbon-silicon, carbon-nitrogen, and carbon-boron clathrates are new classes of Type I carbon-based clathrates that have been identified by first-principles computational methods by substituting atoms on the carbon clathrate framework with Si, N, and/or B atoms. The hybrid framework is further stabilized by embedding appropriate guest atoms within the cavities of the cage structure. Series of hybrid carbon-silicon, carbon-boron, carbon-nitrogen, and carbon-silicon-nitrogen clathrates have been shown to exhibit small positive values of the energy of formation, indicating that they may be metastable compounds and amenable to fabrication. In this overview article, the energy of formation, elastic properties, and electronic properties of selected hybrid carbon-based clathrates are summarized. Theoretical calculations that explore the potential applications of hybrid carbon-based clathrates as energy storage materials, electronic materials, or hard materials are presented. The computational results identify compositions of hybrid carbon-silicon and carbon-nitrogen clathrates that may be considered candidate materials for use as either electrode materials for Li-ion batteries or as hydrogen storage materials. Prior processing routes for fabricating selected hybrid carbon-based clathrates are highlighted and difficulties encountered are discussed.
Preprint
|
|
|
Materials Science, General Materials Science; elastic; three-dimensional, liquid crystals; graphene sponge
Online: 16 January 2018 (17:03:06 CET)
|
|
|
Share this article with
×
Three-dimensional graphene (3DG) sponge has attracted increasing attention because it combines the unique properties of cellular materials and the excellent performance of graphene. The preparation of 3DG sponge depends mainly on the self-assembly of graphene oxide sheets. Here, we demonstrate facile fabrication of 3DG sponge with a large-scale and ordered porous structure, exploiting the liquid crystals of large graphene oxide (LGO) and ultralarge graphene oxide (ULGO) sheets. The resulting materials exhibit a low density, high porosity and elasticity. Our work explores a new strategy for organizing the ordered alignment of controlled large GO sheets and exploring the relationship between the microstructures and mechanical properties of 3DG sponge.
Preprint
|
|
|
Materials Science, General Materials Science; intermediate heat treatment; boron; fabrication process
Online: 8 January 2018 (09:36:45 CET)
|
|
Share this article with
×
In this study, we evaluated the cold drawing workability of two kinds of modified 9Cr-2W steel containing different contents of boron and nitrogen, depending on the temperature and time of normalizing and tempering treatments. Using ring compression tests at room temperature, the effect of intermediate heat treatment condition on workability was investigated. It was found that the prior austenite grain size can be changed by the austenite transformation, and the grain size increases with increasing temperature during normalizing heat treatment. Alloy B and Alloy N showed different patterns after normalizing heat treatment. Alloy N had higher stress than Alloy B, and the reduction in alloy N increased, while the reduction in alloy B decreased. Alloy B showed a larger number of initially formed cracks and a larger average crack length than Alloy N. Crack length and number increased proportionally in Alloy B as the stress increased. Alloy B had lower crack resistance than Alloy N due to boron segregation.
Preprint
|
|
|
Materials Science, General Materials Science; heat energy; photon energy; fundamental forces; nanoscale phenomenon; atomic scale phenomenon; electron scale phenomenon
Online: 8 December 2017 (03:46:45 CET)
|
|
Share this article with
×
Technology is in the way to reach in its climax but the basic understanding of science in many phenomena is still awaited even though the nature witnesses it. Scientific research reveals strong analogy between photon and electron. When an atom deals neutral state, it levitates electron of outer ring from the back surface while placing the bit-energy at front surface. Gravitation behavior of that electron starts at the centre of relaxation point by including the force of side pole where the pulling force of nearby unfilled state of that atom from the front surface results into depict forcing energy shape like Gaussian distribution symbol with both ends turned called unit photon. The inertia is being involved at each stage of changing direction of that electron by introducing the disappearances of forces of two poles against the appearances of forces of two opposite poles during rest to motion and motion to rest in the first half-cycle. The same is the case in the second half-cycle of that electron during rest to motion and motion to rest but it is under different introduction of the disappearances of forces against appearances of forces. However, at stage of levitating or gravitating period of electron, only one force is being involved at one time where the opposite force is disappeared. The uninterrupted confined inter-state electron-dynamics of atom under the availability of several bits of bit-energy results into generate forcing energy shape like a wave. Two bits of bit-energy where shape of bit for first half-cycle is like integral symbol and second half-cycle is like opposite integral symbol which are being placed along the configuring trajectory of inter-state electron-dynamics during forward-direction cycle and two bits of bit-energy shape in opposite order are being placed along the trajectory of inter-state electron-dynamics during back-direction cycle. Generating forcing energy of unit photon in each cycle is pushing to the rear side by remaining connected till the electron is not restoring the state of rest. Silicon atom is considered as a model system under neutral state. Uninterrupted confined inter-state electron-dynamics result into generate forcing energy that can travel immeasurable length and unavailability of necessitating bit-energy at any interrupted stage result into generate an overt photon. Inter-state electron-dynamics for at least two cycles generate an overt photon –a photon length twice to unit photon. Under certain interaction of unit photon, it divides equally into two bits of bit-energy instead of dividing into tits and bits of heat. The mechanism of generating photon characteristic current by the electron of neutral state atom validates that atoms are four-dimensional discs at centre of dealing no force. An isolated electron is being grounded under directed forcing energy to impinge a neutral state atom where the gained instantaneous velocity under merged energy resulting into distort atom at that point. Matter changes the role of energy and force under various sorts of interactions. Here, heat energy and photon energy explore matter at atomic and electron levels, thus, devise basis of science to describe.
Preprint
|
|
|
Materials Science, General Materials Science; municipal waterworks sludge; waste; recycling; valorization; floor tiles
Online: 25 December 2017 (07:40:01 CET)
|
|
Share this article with
×
In municipal waterworks large amounts of waste in the form of sludge have to be discarded. This investigation focuses on the processing of ceramic floor tiles incorporated with a municipal waterworks sludge. Four floor tile formulations containing up to 10 wt. % of the municipal waterworks sludge in replacement of kaolin were prepared. The floor tile processing route consisted of dry powder granulation, uniaxial pressing, and firing between 1190 and 1250 °C using a fast-firing cycle (<60 min). The densification behavior and technological properties of the floor tile pieces as function of the sludge addition and firing temperature were determined. The development of the microstructure was followed by XRD and SEM/EDS. The results show that the replacement of kaolin with municipal waterworks sludge, in the range up to 10 wt. %, allows the production of ceramic floor tiles (group BIb and group BIIa, ISO 13006 Standard) at lower firing temperatures. These results suggest a new possibility for valorization of municipal waterworks sludge with many economical and environmental benefits.
Preprint
|
|
|
Materials Science, General Materials Science; equal-channel angular pressing; ECAP; shear band; matrix band; kinematic hardening; FEM; strain localization
Online: 20 December 2017 (10:01:31 CET)
|
|
Share this article with
×
Equal-Channel Angular Pressing (ECAP) is a method used to introduce severe plastic deformation into a metallic billet without changing its geometry. In special cases strain localization occurs and a pattern consisting of regions with high and low deformation (so-called shear and matrix bands) can emerge. This paper studies this phenomenon numerically adopting two-dimensional finite element simulations of one ECAP pass. The mechanical behavior of aluminum is modeled using phenomenological plasticity theory with isotropic or kinematic hardening. The effects of the two different strain hardening types are investigated numerically by systematic parameter studies: While isotropic hardening only causes minor fluctuations in the plastic strain fields, a material with high initial hardening rate and sufficient strain hardening capacity can exhibit pronounced localized deformation after ECAP. The corresponding finite element simulation results show a regular pattern of shear and matrix bands. This result is confirmed experimentally by ECAP-processing of AA6060 material in a severely cold worked condition, where microstructural analysis also reveals the formation of shear and matrix bands. Excellent agreement is found between the experimental and numerical results in terms of shear and matrix band width and length scale. The simulations provide additional insights regarding the evolution of the strain and stress states in shear and matrix bands.
Preprint
|
|
|
Materials Science, General Materials Science; BiS2-based superconductor; Flux growth; Layered structure; Superconducting Properties; Magnetic susceptibility measurement; Electrical resistivity measurement
Online: 18 December 2017 (13:38:47 CET)
|
|
Share this article with
×
Antimony (Sb) Substitution less than 10 % is examined on a single crystal of a layered superconductor NdO0.7F0.3BiS2. Superconducting transition temperature of the substituted samples decreases with increasing Sb concentration. A lattice constant along the c axis showed a large decrease compared with that along the a axis. Since in-plane chemical pressure monotonically decreases with increasing Sb concentration, the suppression of the superconductivity is well described in terms of the decrease in in-plane chemical pressure.
Preprint
|
|
|
Materials Science, General Materials Science; rotating photocatalytic reactor; TiO2 /Ag catalysts; water treatment
Online: 1 November 2017 (04:44:39 CET)
|
|
Share this article with
×
A four stage semi-pilot scale RFR reactor with ceramic disks as support for TiO2 modified with silver particles was developed for the removal of organic pollutants. The design presented in this article is an adaptation of the rotating biological reactors (RBR) and its coupling with the modified catalyst provides additional advantages to designs where a catalyst in suspension is used. The optimal parameter of rotation was 54 rpm and the submerged surface of the disks offer a total contact area of 387 M2. The modified solid showed a decrease in the value of its bandgap compared to commercial titanium. The system has a semi-automatic operation with a maximum reaction time of 50 h. Photo-activity tests show high conversion rates at low concentrations. The results conform to the Langmuir heterogeneous catalysis model.
Preprint
|
|
|
Materials Science, General Materials Science; surface energy; interfacial energy; surface tension; wetting model; wetting thermodynamics; sessile drop shape; microgravity
Online: 26 October 2017 (10:20:58 CEST)
|
|
Share this article with
×
A new method, the sessile drop accelerometry (SDACC) for the study and measurement of the interfacial energies of solid-liquid-gas systems, is tested and discussed in this study. The laboratory instrument and technique –a combination of a drop shape analyzer with high-speed camera and a laboratory drop tower- and the evaluation algorithms, were designed to calculate the interfacial energies as a function of the geometrical changes of a sessile droplet shape due to the effect of “switching off” gravity during the experiment. The method bases on the thermodynamic equilibrium of the system interfaces and not on the balance of bi-dimensional tensions on the solid-liquid-gas contour line. A comparison of the mathematical model that supports the method with the widely accepted Young`s equation is discussed in this study.
Preprint
|
|
|
Materials Science, General Materials Science; Multiferroicity; LiCuVO4; Spin-driven improper ferroelectricity; Hysteresis in magnetic fields, Multiferroic Hysteresis Loop
Online: 19 October 2017 (17:42:26 CEST)
|
|
Share this article with
×
Multiferroics, showing both ferroelectric and magnetic order, are promising candidates for future electronic devices. Especially, the fundamental understanding of ferroelectric switching is of key relevance for further improvements, which however is rarely reported in literature. On a prime example for a spin-driven multiferroic, LiCuVO4, we present an extensive study of the ferroelectric order and the switching behavior as function of external electric and magnetic fields. From frequency-dependent polarization switching and using the Ishibashi-Orihara theory, we deduce the existence of ferroelectric domains and domain-walls. These have to be related to counterclockwise and clockwise spin-spirals leading to the formation of multiferroic domains. A novel measurement – multiferroic hysteresis loop – is established to analyze the electrical polarization simultaneously as a function of electrical and magnetic fields. This technique allows characterizing the complex coupling between ferroelectric and magnetic order in multiferroic LiCuVO4.
Preprint
|
|
|
Materials Science, General Materials Science; austempered ductile iron; austempering parameters; microstructure; mechanical properties; salt bath agitation
Online: 13 October 2017 (15:44:58 CEST)
|
|
Share this article with
×
In this paper the influence of austempering temperature and salt bath agitation on the final microstructure and mechanical properties of the ferritic ductile iron were studied. 17 samples had been subjected to different heat treatment parameters. Different microstructures were recorded upon the completion of the tests. From the obtained micro images, it is obvious that both the austempering temperature and salt bath agitation affect the final microstructure of the austempered ductile iron. Lower austempering temperatures and salt bath agitation produce more ausferrite in the microstructure, hence the harder and tougher phases are present. This was confirmed with hardness and toughness test of the 17 heat-treated samples. Lower austempering temperatures give more ausferrite phase and therefore higher hardness, but hardness decreases with increasing austempering temperatures. Toughness rises with rising austempering temperatures, but drops significantly with temperatures above 395°C because of the final microstructure.
Preprint
|
|
|
Materials Science, General Materials Science; selective laser sintering (SLS); porous ceramic; carbon additive; laser absorptivity
Online: 1 October 2017 (06:20:03 CEST)
|
|
Share this article with
×
The aim of this study was to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitation of high melting point, brittleness and low thermal shock resistance from instinct ceramic material properties, the key hurdle lies on very poor absorptivity of oxide ceramics to fiber laser which is widely installed in the commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions was presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser will be discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.
Preprint
|
|
|
Materials Science, General Materials Science; copper mine tailings; mechanical activation; thermal activation; alkaline roasting; alkali leaching
Online: 25 September 2017 (08:41:24 CEST)
|
|
Share this article with
×
Copper mine tailings are the residual products after the purification of precious copper from copper ores, and their storage can create numerous environmental problems. Many researchers have used copper mine tailings for preparation of geopolymer. This paper studies the enhancement of the cementitious activity of copper mine tailings in geopolymer system. First, copper mine tailings are activated through a mechanical grinding activation. Afterward, the mechanically activated copper mine tailings are further processed through thermal activation and alkaline roasting activating. The cementitious activity index of copper mine tailings is characterized through the degree of concentration of alkali leaching silicon and aluminum. It was observed that the Si and Al alkali leaching concentration of mechanical activated tailings was increased by 26.03% and 93.33%, respectively. The concentration of Si and Al was increased by 54.19% and 119.92%, respectively. For alkaline roasting activating, roasting time, temperature and (C/N ratio) were evaluated through the orthogonal test, and the best condition was activation for 120 min at 600℃ with C/N ratio is 5:1. In this study, the SEM, XRD and IR analysis show that mechanically activation, thermal activation and alkaline roasting activating can improve the cementitious activity index of copper mine tailings.
Preprint
|
|
|
Materials Science, General Materials Science; thermal barrier coatings; 8 %YSZ; thermal conductivity; microstructure
Online: 20 September 2017 (08:28:21 CEST)
|
|
Share this article with
×
In this paper, the effect of microstructure on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) is investigated. Nine freestanding samples deposited on aluminum-base superalloy are studied. Cross-section morphology such as pores, cracks, m-phase content, grain boundary density of the coated samples are examined by scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Multiple linear regressions are used to develop quantitative models which describe the relationship between the particle parameters, m-phase content and the microstructure such as porosity, crack-porosity, the length density of small-angle-crack and the length density of big-angle-crack. Moreover, the relationship between microstructure and thermal conductivity is investigated. Results reveal that the thermal conductivity of the coating is mainly determined by the microstructure and grain boundary density at room temperature (25 ℃) and by the length density of big-angle-crack, monoclinic phase content and grain boundary density at high temperature (1200 ℃).
Preprint
|
|
|
Materials Science, General Materials Science; titania; kaolin; carbon; sintering temperatures; phases developed; sintered ceramic composite
Online: 4 September 2017 (06:37:14 CEST)
|
|
Share this article with
×
The effects of the additives (silicon carbide and titania) and sintering temperatures on the phases developed, physical and mechanical properties of sintered mullite-carbon ceramic composite produced from kaolin and graphite was investigated. The kaolin and graphite of known mineralogical composition were thoroughly blended with 5 and 3 (vol.) % silicon carbide and titania respectively. From the homogeneous mixture of kaolin, graphite and titania, standard samples were prepared via uniaxial compaction. The test samples produced were subjected to firing (sintering) at 1300˚C, 1400˚C and 1500˚C. The sintered samples were characterized for the developed phases using x‐ray diffractometry analysis, microstructural morphology using ultra‐high resolution field emission scanning electron microscope (UHRFEGSEM). Various physical and mechanical properties were determined. It was observed that the addition of SiC/TiO2 additives to the samples made them to possess very low oxidation indices .This also resulted in improvement in the bulk densities and cold crushing strength of the sample when compared with those without additives. It was concluded that the addition of SiC/TiO2 additives improves on the high temperature oxidation resistance of the mullite-carbon ceramic composite sample.
Preprint
|
|
|
Materials Science, General Materials Science; binary liquid alloy; chemical ordering; sodium; theoretical study; Warren-Cowley parameter
Online: 9 May 2017 (11:28:07 CEST)
|
|
Share this article with
×
A simple model has been used to investigate the nature of chemical order in Na-Pb and Na-Hg liquid binary alloy at 700K and 673K respectively. The energy parameter obtained from the model was used to calculate the concentration dependent mixing properties such as Gibb’s free energy of mixing, Concentration fluctuations in the long wavelength limit and the Warren-Cowley chemical short range order parameter. Results obtained showed that both alloys are hetero-coordinated throughout the entire concentration and there is tendency for segregation and demixing to take place in the liquid alloys. We observed that Na-Hg liquid alloy is more strongly interacting binary alloy and chemically ordered than Na-Pb liquid alloy.
Preprint
|
|
|
Materials Science, General Materials Science; Thermoelectric Materials; Energy Harvesting; CoSb3/ZT
Online: 8 May 2017 (18:44:39 CEST)
|
|
Share this article with
×
Thermoelectric materials may be used in devices as thermoelectric “air conditioner” in a smart house for improved energy efficiency. Energy harvesting uses ambient energy to generate electricity. It provides potentially low-cost, maintenance-free, long-life equipment by reducing the need for batteries or power chords. Energy harvesting (EH) is also known as power harvesting or energy scavenging. EH is considered to give benefits related to environmental friendliness, safety, security, convenience and affordability. EH can be used for brand enhancing. Technically, it can be used to make new things possible depending on visionary engineering. The variety of thermoelectric (TE) materials that can be used in energy harvesting is quite large, and the optimal material for a given application depends mainly on the temperature range in which the material is to be used. In this work we study the development and characterization of thermoelectric materials which were prepared by two different method, which were: a) ball-milling followed by sintering and b) ball-milling, microwave synthesis, high energy planetary ball milling, and sintering. Finally, we study the thermoelectric properties, calculate the band gaps and the ZT for the thermoelectric materials.
Preprint
|
|
|
Materials Science, General Materials Science; Pb(Zn1/3Nb2/3) O3-9%PbTiO3; relaxor ferroelectric crystals; structure phase transition; electromechanical coupling factor
Online: 1 May 2017 (10:35:10 CEST)
|
|
Share this article with
×
Piezoelectric properties are of significant importance to medical ultrasound, actuators, sensor, and countless other device applications. The mechanism of piezoelectric properties can be deeply understood from structure evolutions. In this paper, we report a diagram of structure evolutions of the Pb(Zn1/3Nb2/3)0.91Ti0.09O3 (PZN-9PT) single crystal with excellent piezoelectric properties among the orthorhombic, tetragonal, and cubic phases with temperature increasing from room temperature to 220 C. Through fitting the temperature dependence XRD curves with Gauss and Lorenz functions, we obtained the evolutions of the content ratio of three kinds of phases (orthorhombic, tetragonal and cubic) and the lattice parameters of the PZN-9PT system with the changes of temperature. The XRD fitting results together with Raman and dielectric spectrums show that the phase transitions of PZN-9PT are a typical continuous evolution process, very similar to the phase transition of paraffin from solid to liquid. Additionally, resonance and anti-resonance spectrum show excellent piezoelectric properties of the crystals, which probably originate from the nano twin domains, as demonstrated by the TEM images. Of particular attention is that the thickness electromechanical coupling factor kt is up to 72%.
Preprint
|
|
|
Materials Science, General Materials Science; ZnO; ceramic nanopowders; Segmented Flow Tubular Reactor (SFTR); Spark Plasma Sintering (SPS)
Online: 14 April 2017 (12:11:50 CEST)
|
|
Share this article with
×
Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulate their development: sufficient low-cost high throughput synthesis methods leading to a production with well-defined and reproducible properties, and for ceramics, conservation of their nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv50 ~ 60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a “scale-out” concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 °C and 1100 °C, and Spark Plasma Sintering (SPS) at 900 °C. The performances of the synthesized nanopowder were compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 minutes at 900 °C, while limiting the grain growth and thus leading to a nanostructured material.
Preprint
|
|
|
Materials Science, General Materials Science; copper resources; demand forecasting; system dynamics model; sustainability development
Online: 31 March 2017 (10:50:56 CEST)
|
|
Share this article with
×
Copper demand for a country's copper industry has a greater pull effect. China's copper consumption in 2015 has accounted for 50% of the world. The scientific forecast of China's copper demands trend is also an important basis for analyzing its future environmental impact. This paper assumes that China's economy will be developing high, medium and low scenarios, and forecasts economic and social indicators such as total GDP, population and per capita GDP in China from 2016 to 2030. Then, predicted the demand of copper resources in China from 2016 to 2030 by the combination of system dynamics model, vector autoregressive moving average model and inverted U-type empirical model. The results show that: (1) in 2020, 2025 and 2030, China's refined copper demand will be 13 Mt, 15 Mt and 15.5 Mt. (2) China's copper demand growth slowed down significantly from 2016-2030. (3) 2025-2030, China's copper resource demand is stable, into the platform of demand growth, the highest peak value in 2027 will be 15.5 Mt. (4) 2030 years later, China's copper resource demand will enter a slow decline.
Preprint
|
|
|
Materials Science, General Materials Science; mesoporous TiO2; reduced graphene oxide; Ag nanoparticles; photocatalytic activity; visible light irradiation
Online: 27 March 2017 (12:01:25 CEST)
|
|
Share this article with
×
Mesoporous TiO2/reduced graphene oxide/Ag (TiO2/RGO/Ag) ternary nanocomposite with effective electrons transfer pathway is obtained by an electrostatic self-assembly method and photo-assisted treatment. Compared with bare mesoporous TiO2 (MT) and mesoporous TiO2/RGO (MTG), the ternary mesoporous TiO2/RGO/Ag (MTGA) nanocomposite exhibited superior photocatalytic performance for the degradation of MB under visible light, and the degradation rate reached 0.017 min-1, which was 3.4 times higher than that of MTG. It is proposed that Ag nanoparticles can form the local surface plasmon resonance (LSPR) to absorb the visible light and distract the electrons into MT, and RGO can accept the electrons from MT to accelerate the separation efficiency of carriers. The establishment of MTGA ternary nanocomposite make the three components act synergistic effect to enhance the photocatalytic performance.
Preprint
|
|
|
Materials Science, General Materials Science; perfect metamaterial absorber; terahertz; six-band; cave-cross patch resonator
Online: 3 March 2017 (08:48:31 CET)
|
|
Share this article with
×
A simple design of an ultrathin six-band polarization-insensitive terahertz perfect metamaterial absorber (PMMA) composed of a metal cross-cave-patch resonator (CCPR) placed over a ground plane was proposed and investigated numerically. The numerical simulation results demonstrate that the average absorption peaks are up to 95% at six resonance frequencies with high quality-factors (>65). In addition, the absorption properties can be kept stability for both normal incident transverse magnetic (TM) and transverse electric (TE) waves. The physical mechanism behind the observed high level absorption is illustrated by the electric and power loss density distributions. The different absorption mainly originates from the higher order multipolar and multipolar plasmon resonance of the structure, which are sharp different to the most previous studies of the PMMAs. Furthermore, the resonance absorption of the PMMA can be tunable by varying the geometric parameters of the unit cell.
Preprint
|
|
|
Materials Science, General Materials Science; laser wavelength; polysilicon; laser damage; thermal shock
Online: 27 February 2017 (06:56:01 CET)
|
|
Share this article with
×
Based on PVDF (piezoelectric sensing techniques), this paper attempts to study the propagation law of shock waves in brittle materials during the process of three-wavelength laser irradiation of polysilicon, and discusses the formation mechanism of thermal shock failure. The experimental results show that the vapor pressure effect and the plasma pressure effect in the process of pulsed laser irradiation lead to the splashing of high temperature and high density melt. With the decrease of the laser wavelength, the laser breakdown threshold decreases and the shock wave is weakened. Because of pressure effect of the laser shock, the brittle fracture zone is at the edge of the irradiated area. The surface tension gradient and surface shear wave caused by the surface wave are the result of coherent coupling between optical and thermodynamics. The average propagation velocity of laser shock wave in polysilicon is 8.47×103m/s, and the experiment has reached the conclusion that the laser shock wave pressure peak exponentially distributes attenuation in the polysilicon.
Preprint
|
|
|
Materials Science, General Materials Science; high volume fly ash, high fluidity concrete, early strength, field application
Online: 13 February 2017 (11:44:54 CET)
|
|
Share this article with
×
In the recent concrete industry, high fluidity concrete is being widely used for the pouring of dense reinforced concrete. Normally, in the case of high fluidity concrete, it includes high binder contents, so it is necessary to replace part of the cement through admixtures such as fly ash to procure economic feasibility and durability. This study shows the mechanical properties and field applicability of high fluidity concrete that using mass of fly ash as alternative materials of cement. The high fluidity concrete mixed with 50% fly ash was measured to manufacture concrete that applies low water/binder ratio to measure the mechanical characteristics as compressive strength and elastic modulus. Also, in order to evaluate the field applicability, high fluidity concrete containing high volume fly ash was evaluated that fluidity, compressive strength, heat of hydration and drying shrinkage of concrete.
Preprint
|
|
|
Materials Science, General Materials Science; HfB4; structure prediction; superhard material; anisotropic properties
Online: 12 January 2017 (10:57:03 CET)
|
|
Share this article with
×
By using the particle swarm optimization algorithm for crystal structure prediction, we reveal a newly orthorhombic Cmcm structure of HfB4, which is more energetically superior to the previously proposed YB4-, ReP4-, FeB4-, CrB4-, and MnB4-type structures in the considered pressure range. The phonon dispersion and elastic constants calculations confirm that the new phase is dynamically and mechanically stable. The calculated large shear modulus (240 GPa) and high hardness (45.7 GPa) imply that the predicted Cmcm-HfB4 is a potential superhard material. Meanwhile, the directional dependences of the Young's modulus, bulk modulus, and shear modulus for HfB4 are systematically investigated. Further analyses of the density of states and electronic localization function indicate that the strong B-B and B-Hf covalent bonds greatly contribute to its high hardness and stability.
Preprint
|
|
|
Materials Science, General Materials Science; spin crossover; density functional calculations; Hubbard model; solid state; Slichter-Drickamer model; Monte Carlo simulation; Ising model
Online: 11 January 2017 (09:17:46 CET)
|
|
Share this article with
×
The total enthalpies of the 16 different spin configurations that can be realized in the unit cell of the archetype spin crossover complex [Fe(phen)2(NCS)2] (phen=1,2-phenanthroline) were calculated applying periodic density functional theory combined with the Hubbard model and the Grimme-D2 dispersion correction (DFT+U/D2). The obtained enthalpy differences between the individual spin configurations were used to determine spin couplings of an Ising-like model and subsequent Monte Carlo simulations for this model allowed to estimate the phenomenological interaction parameter Г of the Slichter-Drickamer model, which is commonly used to describe the cooperativity of the spin transition. The calculational procedure described here, which led to an estimate of about 3 kJ/mol−1 for Г, in good agreement with experiment, may be used to predict from first principles how modifications of spin crossover complexes can change the character of the spin transition from gradual to abrupt and vice versa.
Preprint
|
|
|
Materials Science, General Materials Science; high-entropy alloys; Al-Ni-Co-Fe-Cr alloys; microstructure; precipitation morphology; mechanical property
Online: 4 January 2017 (10:30:17 CET)
|
|
Share this article with
×
The present work investigates primarily the morphology evolution of the body-centered-cubic (BCC)/B2 phases in AlxNiCoFeCr high-entropy alloys (HEAs) with increasing Al content, which has been neglected so far. There exist two types of microscopic morphologies of BCC and B2 phases in this HEA series: one is the weave-like morphology induced by the spinodal decomposition, and the other is the microstructure of a spherical disordered BCC precipitation on the ordered B2 matrix that appears in HEAs with a much higher Al content. The shape of coherent precipitates is found to be closely related to the lattice misfit between BCC and B2 phases, which is sensitive to Al. The mechanical properties, including the compressive yielding strength and microhardness of the AlxNiCoFeCr HEAs, are also discussed in light of the concept of the valence electron concentration (VEC).
Preprint
|
|
|
Materials Science, General Materials Science; crystal structure; Hume-Rothery phases; structure stability
Online: 2 January 2017 (10:42:19 CET)
|
|
Share this article with
×
Crystal structures of simple metals and binary alloy phases based on the face-centered cubic (fcc) structure are analyzed within the model of Fermi sphere – Brillouin zone interactions to understand the stability of original cubic structure and derivative structures with distortions, superlattices and vacancies. Examination of the Brillouin-Jones configuration in relation to the nearly-free electron Fermi sphere for several representative phases reveals significance of the electron energy contribution to the phase stability. Representation of complex structures in the reciprocal space clarifies their relationship to the basic cubic cell.
Preprint
|
|
|
Materials Science, General Materials Science; MoS2; carbon nanofibers; electrospinning; anode material
Online: 28 December 2016 (10:49:33 CET)
|
|
|
Share this article with
×
The one-dimensional MoS2/carbon nanofibers (1D MoS2/CNFs) are synthesized by electrospinning using exfoliated MoS2 nanosheets and polyacrylonitrile as raw materials. The exfoliated MoS2 nanosheets with size of about 150 nm are encapsulated in carbon nanofibers, and the free-standing MoS2/CNFs can be easily cut into flexible tablet and directly used as binder-free anode for lithium storage. The resultant 1D MoS2/CNFs exhibit a very high reversible capacity of 700 mAh g-1 at 100 mA g-1 after 50 cycles, high rate capacity (450 mAh g-1 at 1000 mA g-1 after 200 cycles) and good cycle stability.
Preprint
|
|
|
Materials Science, General Materials Science; discrete element method; hypervelocity impact; debris cloud; fragmentation; space debris; multiscale modeling; computer simulation; high performance computing
Online: 23 December 2016 (10:21:21 CET)
|
|
|
Share this article with
×
In this paper we introduce a computational model for the simulation of hypervelocity impact (HVI) phenomena which is based on the Discrete Element Method (DEM). Our paper constitutes the first application of DEM to the modeling and simulating of impact events for velocities beyond 5 kms−1. We present here the results of a systematic numerical study on HVI of solids. For modeling the solids, we use discrete spherical particles that interact with each other via potentials. In our numerical investigations we are particularly interested in the dynamics of material fragmentation upon impact. We model a typical HVI experiment configuration where a sphere strikes a thin plate and investigate the properties of the resulting debris cloud. We provide a quantitative computational analysis of the resulting debris cloud caused by impact and a comprehensive parameter study by varying key parameters of our model. We compare our findings from the simulations with recent HVI experiments performed at our institute. Our findings are that the DEM method leads to very stable, energy–conserving simulations of HVI scenarios that map the experimental setup where a sphere strikes a thin plate at hypervelocity speed. Our chosen interaction model works particularly well in the velocity range where the local stresses caused by impact shock waves markedly exceed the ultimate material strength.
Preprint
|
|
|
Materials Science, General Materials Science; A. Ceramics; A. Oxides; C. X-ray diffraction; D. Crystal structure; D. Microstructure
Online: 28 October 2016 (08:09:48 CEST)
|
|
Share this article with
×
The aim of this work is to compare two softwares (MAUD and TOPAS) based on the Rietveld algorithm and to test the concept of tolerance factor using the dissolution at high temperature of yttrium into BaTiO3. In general, both softwares give up different values of the crystalline parameters however the trends are similar in most cases but the analysis of the strain and crystallite size in the BaTiO3 crystals suggests that, in this particular case, MAUD offered results more consistent with the expected behavior. Using the crystalline parameters calculated by Rietveld, the tolerance factor values were obtained and these data suggest even better stability in the crystalline structure than that expected using theoretical parameters. Tolerance factor concept also indicates that Ti4+ should be preferred.
Preprint
|
|
|
Materials Science, General Materials Science; Moiré patterns; MoS2; Graphene; WS2; WSe2; HRTEM
Online: 24 October 2016 (05:03:50 CEST)
|
|
Share this article with
×
We present a series of computer-assisted high resolution transmission electron (HRTEM) simulations to determine Moiré patters by induced twisting effects between slabs at rotational angles of 3°, 5°, 8°, and 16°, for molybdenum disulfide, graphene, tungsten disulfide, and tungsten selenide layered materials. In order to investigate the electronic structure, a series of numerical simulations using DFT methods was completed using CASTEP with a generalized gradient approximation to determine both band structure and density of states on honeycomb like new superlattices. Our results indicate metallic transitions when rotation approaches 8° with respect to each other for most of the two-dimensional systems that were analyzed.
Preprint
|
|
|
Materials Science, General Materials Science; neutron absorber; Mo-based composites; ball milling; microstructure; thulium oxide
Online: 27 September 2016 (10:45:47 CEST)
|
|
Share this article with
×
The microstructural evolution, thermodynamics and kinetics of Mo-21%Tm2O3 (mass fraction, %) powder mixtures during ball milling were investigated using X-ray diffraction and transmission electron microscopy. Ball milling induced Tm2O3 to be decomposed and then dissolved into Mo crystal. The supersaturated nanocrystalline solid solution of Mo (Tm, O) was obtained after 96 h of ball milling. The elements of Mo, Tm and O were distributed uniformly in the ball-milled particles. Based on the semi-experimental theory of Miedema, a thermodynamic model was developed to calculate the driving force of phase evolution. There was no chemical driving force to form a crystal solid solution of Tm atoms in Mo crystal or an amorphous phase because the Gibbs free energy for both processes was higher than zero. For Mo-21%Tm2O3, it was mechanical work, not negative heat of mixing, that provided the driving force to form supersaturated nanocrystalline Mo (Tm, O) solid solution.
Preprint
|
|
|
Materials Science, General Materials Science; polymer nanocomposites; thermal conductivity; finite element analysis; ABAQUS
Online: 27 August 2016 (09:57:54 CEST)
|
|
Share this article with
×
Polymer nanocomposites are composed of polymer materials reinforced with nano fillers. In the present study the effective thermal conductivity of the composites filled with nanofillers has been investigated using commercially available finite element software ABAQUS 6.11. The nanofillers used were alumina particles and multi-walled carbon nanotubes (MWNTs) and the matrix was considered to be made of epoxy. For the analysis 2D and 3D Representative Volume Elements (RVEs) were generated using Random Sequential Adsorption (RSA) algorithm using MATLAB and Python scripts. Thermal conductivity was found out for 2D and 3D RVEs for different area and weight fractions respectively. Two different shapes of the alumina nanoparticles were considered: spherical (circular) and ellipsoidal (elliptical) for 3D (2D) analysis. It was found that the thermal conductivity was increased with the addition of nanofillers. The increase in thermal conductivity was approximately same for both types of inclusions at corresponding area or weight fractions in 2D or 3D analysis. The results showed that addition of MWNTs to the composites lead to a significant increase in thermal conductivity than spherical or ellipsoidal inclusions.