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1. chinaXiv:201709.00081 [pdf]

Porous TiO2 nanowires derived from nanotubes synthesis, characterzation and their enhanced photocatalytic properties.doc

金震
分类: 材料科学 >> 材料科学(综合)

Anatase porous TiO2 nanowires were synthesized via simple in situ hydrothermal treatment of the amorphous anodic TiO2 nanotubes in urea aqueous solution at 70 ºC. The morphology transformation process was also analyzed so that hydroxide induced dissolution-recrystallization mechanism was proposed. Due to the coarse surface and porous structure, the porous TiO2 nanowires possess a large surface area of 267.56 m2g-1, which is almost 4 times higher than that of amorphous anodic TiO2 nanotubes. The photocatalytic properties of the porous TiO2 nanowires towards MB, phenol and Rhodamine 6G were investigated. The porous TiO2 nanowires display better photocatalytic activity than that of TiO2 nanotubes or Degussa P25. The enhanced photocatalytic activity is attributed to the porous structure and the large specific surface area. Such porous TiO2 nanowires maybe considered as an ideal photocatalyst for the rapid photodegradation of organic pollutant in water. Furthermore, this facile, low-cost and environmentally friendly method is highly expected to innovate the design and fabrication of highly photoactive porous TiO2 nanowires, which have potential applications in photocatalysis and solar energy conversion.

提交时间: 2017-09-19 点击量76, 下载量65

2. chinaXiv:201708.00302 [pdf]

Electronic origin of strain effects on solute stabilities in iron

刘伟
分类: 材料科学 >> 金属与冶金

Nonuniform strain fields might induce the segregation of alloying solutes and ultimately lead to the mechanical performance degradation of body-centered-cubic (bcc) Fe based steels serving in extreme environments, which is worthy of investigation. In this paper, two typical volume conserving strains, shear strain (SS) and normal strain (NS), are proposed to investigate the strain effects on solute stabilities in bcc iron by first-principles calculations. For solutes in each transition metal group, the calculated substitution energy change due to SS exhibits a linear dependence on the valence d radius of the solutes, and the slope decreases in an exponential manner as a function of the absolute difference between the Watson’s electronegativity of iron and the averaged value of each transition metal group. This regularity is attributed to the Pauli repulsion between the solutes and the nearest neighboring Fe ions modulated by the hybridization of valence d bands and concluded to be originated from the characteristics of valence d bonding between the transition-metal solutes and Fe ions under SS. For main-group and post transition-metal solutes, the considerable drop of substitution energy change due to NS is concluded to be originated from the low-energy side shift of the widened valence s and p bands of the solutes. Our results indicate that the stabilities of substitutional solutes in iron under volume-conserving strain directly correlate with the intrinsic properties of the alloying elements, such as the valence d radius and occupancy, having or not having valence s and p bands.

提交时间: 2017-08-23 点击量67, 下载量57

3. chinaXiv:201708.00301 [pdf]

Clustering and segregation of small vacancy clusters near tungsten (0 0 1) surface

李祥艳
分类: 材料科学 >> 材料科学(综合)

Nanoporous metals have been shown to exhibit radiation-tolerance due to the trapping of the defects by the surface. However, the behavior of vacancy clusters near the surface is not clear which involves the competition between the self-trapping and segregation of small vacancy clusters (Vn) nearby the surface. In this study, we investigated the energetic and kinetic properties of small vacancy clusters near tungsten (0 0 1) surface by combining molecular statics (MS) calculations and object Kinetic Monte Carlo (OKMC) simulations. Results show that vacancies could be clustered with the reduced formation energy and migration energy of the single vacancy around a cluster as the respective energetic and kinetic driving forces. The small cluster has a migration energy barrier comparable to that for the single vacancy; the migration energy barriers for V1–5 and V7 are 1.80, 1.94, 2.17, 2.78, 3.12 and 3.11 eV, respectively. Clusters and become unstable near surface (0 0 1) and tend to dissociate into the surface. At the operation temperature of 1000 K, the single vacancy, V2, V3 and V4 were observed to segregate to the surface within a time of one hour. Meanwhile, larger clusters survived near the surface, which could serve as nucleating center for voids near the surface. Our results suggest that under a low radiation dose, surface (0 0 1) could act as a sink for small vacancy clusters, alleviating defect accumulation in the material under a low radiation dose. We also obtained several empirical expressions for the vacancy cluster formation energy, binding energy, and influence radius as a function of the number of vacancies in the cluster.

提交时间: 2017-08-23 点击量63, 下载量53

4. chinaXiv:201708.00300 [pdf]

Surface-structure dependence of healing radiation-damage mechanism in nanoporous tungsten

李祥艳
分类: 材料科学 >> 金属与冶金

Under nuclear fusion environments, displacement damage in tungsten (W) is usually caused by neutrons irradiation through producing large quantities of vacancies (Vs) and interstitials (SIAs). These defects not only affect the mechanical properties of W, but also introduce trap sites for implanted hydrogen isotopes and helium. Nano-structured W with high fraction of free surfaces has been developed to mitigate the radiation damage. However, the mechanism of the surface reducing defects accumulation is not well understood. Using multiscale simulation methods, we investigated the interaction of the SIA and V with different surfaces at across length and time scales. We found that, at a typical operation temperature of 1000K, surface (110) preferentially heals radiation damage of W compared with surface (100) and boundary (310). On surface (110), the diffusion barrier for the SIA is only 0.68eV. The annihilation of the SIA-V happens via the coupled motion of the V segregation towards the surface from the bulk and the two dimensional diffusion of the SIA on the surface. Such mechanism makes the surface (110) owe better healing capability. On surface (100), the diffusion energy barrier for the SIA is 2.48eV, higher than the diffusion energy barrier of the V in bulk. The annihilation of the SIA-V occurs via the V segregation and recombination. The SIA was found to migrate one dimensionally along a boundary (310) with a barrier of 0.21eV, leading to a lower healing efficiency in the boundary. This study suggested that the on-surface process plays an important role in healing radiation damage of NP W in addition to surface-enhanced diffusion and annihilation near the surface. A certain surface structure renders nano-structured W more radiation-tolerant.

提交时间: 2017-08-23 点击量72, 下载量63

5. chinaXiv:201703.00903 [pdf]

Preparation and electrochemical properties of high purity mixed-acid electrolytes for high energy density vanadium redox flow battery

Fan, Chuanlin; Yang, Haitao; Zhu, Qingshan
分类: 材料科学 >> 材料化学

All-vanadium redox flow battery (VRFB) is a large-scale electrochemical energy storage technology with numerous potential applications because of its inherent safety and long service life. In previous years, a novel mixed-acid electrolyte system, vanadium electrolytes with mixture of sulfuric acid and hydrochloric acid, has been developed by the Pacific Northwest National Laboratory (PNNL) to increase vanadium solubility, which can effectively raise the electrolyte energy density from 25 Wh/L to 40 Wh/L. To further improve mixed-acid VRFBs, in present work, high purity mixed-acid electrolytes were prepared using a novel direct dissolution – electrochemical reduction process from high purity vanadium oxytrichloride (VOCl3). And the purity and electrochemical properties were investigated, comparing with common mixed-acid electrolytes and regular sulfate electrolytes prepared from metallurgical grade vanadium pentoxide. It was found that the novel process demonstrated a great potential for the low cost and high efficiency production of high purity electrolytes with excellent electrochemical properties for mixed-acid VRFBs. Comparing the traditional high purity electrolytes preparation process, the present novel method will dramatically cut the cost by more than 90 percent, which will considerably facilitate the commercial application of high performance and high density VRFBs.

提交时间: 2017-08-15 点击量576, 下载量368

6. chinaXiv:201705.00188 [pdf]

Magnetocaloric effect in high Gd content Gd-Fe-Al based amorphous/nanocrystalline systems with enhanced Curie temperature and refrigeration capacity

Zhang, LL [Zhang, Linlin][ 1,2 ]; Bao, MD [Bao, Mingdong][ 2 ]; Zheng, Q [Zheng, Qiang][ 2 ]; Tian, LH [Tian, Linhai][ 1 ]; Du, J [Du, Juan][ 3 ]
分类: 材料科学 >> 纳米科学和纳米技术

The Gd-Fe-Al amorphous/nanocrystalline composites were successfully designed and obtained with both high Curie temperature (Tc) and large magnetic entropy change (∆SM). The Tc can be tuned from 172 to 280 K and refrigeration capacity (RC) has a value between 690 and 867 J/kg under a eld change of 0–5 T by changing the Gd contents and the formation of Gd nanocrystallites. And, ∆SM in Gd-Fe-Al amorphous/nanocrystalline composites reached a value of 7.2 J kg−1 K−1 under a eld change of 0–5 T. The high RC in Gd-Fe-Al system were ascribed to the widening full width at half maximum (δFWHM) up to 240 K of the magnetic entropy change (∆SMmax) peak because of the combination contribution of amorphous matrix and the precipitated Gd-riched nanocrystalline. Our research would shed light on how to design attractive candidates for magnetic refrigeration materials with high perfor- manceatnearroomtemperature

提交时间: 2017-05-09 点击量302, 下载量175

7. chinaXiv:201705.00240 [pdf]

A feasible multilayer structure design for solid lubricant coatings in a lunar environment

Pu, JB [Pu, Jibin][ 1 ]; Ren, SM [Ren, Siming][ 1 ]; Lu, ZB [Lu, Zhibin][ 2 ]; Wang, LP [Wang, Liping][ 1 ]
分类: 材料科学 >> 材料科学(综合)

Solid lubricant coatings have received considerable research attention in space applications owing to their remarkably improved tribological characteristics. But their service life is seriously restricted by the harsh environment, such as high vacuum and abrasive wear. In this paper, a novel design of carbon-based multilayer (MoS2/DLC multilayer) coatings was reported to clarify the friction and wear behavior in high vacuum conditions with and without simulated lunar-dust (SLD). Compared with pure DLC or MoS2 coatings, the multilayer coating showed excellent tribological performance with a low friction coefficient of 0.02 and a wear rate of $6.5 10 6 mm3 N 1 m 1. What is particularly interesting is that the wear volume of MoS2/DLC multilayer coatings with the increase of time is in accordance with the Archard linear law, regardless of the condition with or without SLD. Moreover, the surface morphology and composition of wear tracks and scars reveal that the long life of carbon-based multilayer coatings cannot be explained solely by excellent mechanical performance, and is also attributed to the formation of ridge layers as third body reservoirs and a tribo-induced composite transfer layer containing SLD nanoparticles and coating materials.

提交时间: 2017-05-09 点击量1454, 下载量174

8. chinaXiv:201705.00246 [pdf]

Edge-enriched porous graphene nanoribbons for high energy density supercapacitors

Zheng, C [Zheng, C.][ 1 ]; Zhou, XF [Zhou, X. F.][ 1 ]; Cao, HL [Cao, H. L.][ 1 ]; Wang, GH [Wang, G. H.][ 1 ]; Liu, ZP [Liu, Z. P.][ 1 ]
分类: 材料科学 >> 材料科学(综合)

A simple solution-based oxidative process and subsequent chemical activation combination method has been developed to prepare edge-enriched porous graphene nanoribbons (GNRs) as a high-performance electrode material for supercapacitors. The precursor aligned carbon nanotubes are cut longitudinally and unzipped by a modified Brodie method to form tube-like GNRs with abundant edges. The intermediate GNRs were subsequently chemically activated using KOH to generate a suitable porosity and create more edge sites. These edge sites contribute a larger capacitance than the basal plane of graphene and the nanopores facilitate the fast immigration of ions. As a result, the edge-enriched GNRs exhibit a capacitance uptake per specific surface area almost two times higher than that of conventional activated graphene sheets, which gives rise to the high energy density of the porous GNR electrode. The highly efficient utilization of the edge planes and easy, low-cost scale-up production will make porous GNRs potentially applicable to high-performance supercapacitors.

提交时间: 2017-05-09 点击量1453, 下载量188

9. chinaXiv:201705.00245 [pdf]

Synthesis and characterization of novel 4-phenyl-pyridine unit based alkaline anion exchange membranes

Lu, D [Lu, Di][ 1,2 ]; Wen, LL [Wen, Lele][ 1,3 ]; Xue, LX [Xue, Lixin][ 1 ]
分类: 材料科学 >> 材料科学(综合)

For exploring more types of suitable polymeric membranes for application in alkaline fuel cells (AFCs), a series of 1,2-dimethylimidazolium functionalized poly(arylene ether sulfone)s containing 4-phenyl- pyridine units in the main chain (named as DIm-PPYPAES) were firstly synthesized as anion exchange membranes (AEMs) in this work. Proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy were employed to characterize and confirm the chemical structure of the synthesized copolymers and the derived membranes. The DIm-PPYPAES membranes with different ionized levels ranging from 1.15 meq. g 1 to 1.77 meq. g 1, exhibited good thermal stability, solubility behavior and a relatively high level of hydroxide conductivity. The highest hydroxide conductivity of 83.35 mS cm 1 at 80 C was achieved for the DIm-PPYPAES-4 membrane with a moderate IEC of 1.77 meq. g 1. Moreover, after 15 days of treatment with a 2 M NaOH solution at 60 C, the DIm-PPYPAES membrane still exhibited relatively high ionic conductivity even above 10 mS cm 1 at 30 C and retained their integrated shapes.

提交时间: 2017-05-09 点击量1451, 下载量177

10. chinaXiv:201705.00237 [pdf]

High adsorption capacity of heavy metals on two-dimensional MXenes: an ab initio study with molecular dynamics simulation

Guo, X [Guo, Xun][ 1 ]; Zhang, XT [Zhang, Xitong][ 1,2 ]; Zhao, SJ [Zhao, Shijun][ 1 ]; Huang, Q [Huang, Qing][ 3 ]; Xue, JM [Xue, Jianming][ 1,2 ]
分类: 材料科学 >> 材料科学(综合)

Density functional theory (DFT) calculation is employed to study the adsorption properties of Pb and Cu on recently synthesized two-dimensional materials MXenes, including Ti3C2, V2C1 and Ti2C1. The influence of surface decoration with functional groups such as H, OH and F have also been investigated. Most of these studied MXenes exhibit excellent capability to adsorb Pb and Cu, especially the adsorption capacity of Pb on Ti2C1 is as high as 2560 mg g 1. Both the binding energies and the adsorption capacities are sensitive to the functional groups attached to the MXenes’ surface. Ab initio molecular dynamics (ab-init MD) simulation confirms that Ti2C1 remains stable at room temperature after adsorbing Pb atoms. Our calculations imply that these newly emerging two-dimensional MXenes are promising candidates for wastewater treatment and ion separation.

提交时间: 2017-05-09 点击量1485, 下载量198

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