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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70, 下载量60

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63, 下载量54

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58, 下载量50

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537, 下载量358

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301, 下载量174

7. chinaXiv:201705.00218 [pdf]

Development of Energy Finite Element Analysis in Vibration Analysis of Composite Laminate Plate Structures

Yang, Y [Yang, Yang][ 1 ]; Chen, XL [Chen, Xiliang][ 1 ]; Zhang, WW [Zhang, Wenwu][ 1 ]
分类: 材料科学 >> 材料科学(综合)

The high frequency vibration analysis of a composite laminate plate structure subjected to impact loads was investigated by using method of energy finite element analysis (EFEA). The time and space averaged energy density was used as the primary variable to form the governing differential equations. The multilayer laminate plate is simplified to be equivalent isotropic plate using the average concept, such as the average damping loss factor and the average group speed. The global system of EFEA equations can be solved numerically and the energy density distribution within the whole system can then be obtained. The EFEA numerical results for composite laminate plate structure are validated through comparison with those of very dense conventional finite element analysis (FEA).

提交时间: 2017-05-09 点击量1424, 下载量199

8. chinaXiv:201705.00215 [pdf]

Role of cis-1,4-cyclohexanedicarboxylic acid in the regulation of the structure and properties of a poly[butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate] copolymer

Liu, F [Liu, Fei][ 1 ]; Qiu, J [Qiu, Jia][ 1 ]; Wang, JG [Wang, Jinggang][ 1 ]; Zhang, JW [Zhang, Junwu][ 1 ]; Na, HN [Na, Haining][ 1 ]; Zhu, J [Zhu, Jin][ 1 ]
分类: 材料科学 >> 材料科学(综合)

A unique non-planar ring structure 1,4-cyclohexanedicarboxylic acid (CHDA) is introduced to synthesize a poly(butylene adipate-co-butylene 1,4-cyclohexanedicarboxylate) (PBAC) copolyester. The impact of the stereochemistry of CHDA on the structure and properties of PBAC, especially the role of cis-CHDA in tuning the thermal, tensile and elastic properties of PBAC is explored in depth. Instead of considering PBAC as a diblock random copolymer consisting of poly(butylene adipate) (PBA) and poly(butylene 1,4- cyclohexanedicarboxylate) (PBC), our results reveal that PBAC can be considered as a random copolymer consisting of actually three blocks, namely PBA, a PBC unit with only trans-CHDA (trans- PBC), and PBC unit with only cis-CHDA (cis-PBC). The role of cis-CHDA is found to be rigid which initiates a high modulus and strength, and soft which results in a decreased melting temperature and increased elongation at break and elasticity.

提交时间: 2017-05-09 点击量1293, 下载量185

9. chinaXiv:201705.00242 [pdf]

Improving thermal and mechanical properties of epoxy composites by using functionalized graphene

Pan, LL [Pan, Lulu][ 1 ]; Ban, JF [Ban, Jianfeng][ 3 ]; Lu, SR [Lu, Shaorong][ 1 ]; Chen, GX [Chen, Guoxin][ 2 ]; Yang, J [Yang, Jin][ 1 ]; Luo, QY [Luo, Qiyun][ 1 ]; Wu, LY [Wu, Linyan][ 1 ]; Yu, JH [Yu, Jinhong][ 1,2 ]
分类: 材料科学 >> 材料科学(综合)

Perylene tetracarboxylic anhydride (PTCDA) was reacted with 6-aminocaproic acid to form the corresponding perylene bisimide (PBI). PBI was used as the foundation for oligomerisation of glycidol in a ring-opening reaction of glycidol leading to a hyper branched, water-soluble glycidol derivative of perylene (PBI-HPG). PBI-HPG was bound to the reduced graphene oxide via p–p stacking resulting in a compound termed PBI-HPG/RGO. The structure and morphology of PBI-HPG/RGO were investigated by infrared spectroscopy (FT-IR), wide angle X-ray diffractometry (WAXD), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). PBI- HPG/RGO was blended at different loadings in order to improve the thermal and mechanical properties of epoxy composites. The maximum Tg of the epoxy composites was about 20 C and the decomposition temperature (Td) was 26 C higher than that of neat epoxy. The incorporation of PBI- HPG/RGO yields a material with an impact strength of 39.6 kJ m 2 and a tensile strength at 0.7 wt%. It increased by 50.8% and 62.3%, respectively, compared to the neat epoxy.

提交时间: 2017-05-09 点击量1939, 下载量542

10. chinaXiv:201705.00256 [pdf]

Excellent tribological and anti-corrosion performance of polyurethane composite coatings reinforced with functionalized graphene and graphene oxide nanosheets

Mo, MT [Mo, Mengting][ 1,2 ]; Zhao, WJ [Zhao, Wenjie][ 1 ]; Chen, ZF [Chen, Zifei][ 1,2 ]; Yu, QX [Yu, Quanyao][ 1,2 ]; Zeng, ZD [Zeng, Zhixiang][ 1 ]; Wu, XJ [Wu, Xuedong][ 1 ]; Xue, Q [Xue, Qunji][ 1 ]
分类: 材料科学 >> 材料科学(综合)

In order to improve the mechanical durability, polyurethane (PU) needs to be modified to enhance the tribological and anti-corrosion properties. In this work, we fabricated a series of PU composite coatings reinforced with functionalized graphene (FG) and functionalized graphene oxide (FGO). The structural and morphological features of the composite coatings were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results showed that the dispersion and compatibility of graphene and graphene oxide were improved via chemical modification. Moreover, they effectively enhanced the tribological and anti-corrosion properties of PU composite coatings, whose optimized additive range was between 0.25 wt% and 0.5 wt%. The effect depends on the balance of lubrication and barrier of fillers and cracks generated by them. Finally, in comparison with FG/PU coatings, the FGO/PU coatings exhibited a better tribological property but worse anti-corrosion property owing to the abundant oxygenated groups of GO. They led to stronger interfacial interactions between FGO and the PU matrix, but destroyed the graphene lattice structure to some extent.

提交时间: 2017-05-09 点击量1456, 下载量190

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