113 research outputs found
Control of Thermal Expansion in TaVO5 by Double Chemical Substitution
No full textThe control of thermal expansion is an important andchallengingissue. Focusing attention on the class of AMO(5) negativethermal expansion (NTE) materials, an approach to control their thermalexpansion is still missing. In this work, the thermal expansion ofTaVO(5) has been controlled from strong negative to zeroto positive by double chemical substitution, i.e., Ti and Mo replaceTa and V elements, respectively. A joint study of temperature-dependentX-ray diffraction, X-ray photoelectron spectroscopy, and first-principlescalculations has been performed to investigate the thermal expansionmechanism. With the increasing substitution of Ti and Mo atoms, thevalence state always remains balanced, and the volume decreases togetherwith a lattice distortion, which leads to the suppression of the NTE.Lattice dynamics calculations confirm that the negative Gru''neisenparameters of the low-frequency modes weaken and the thermal vibrationsof the polyhedral units diminish after the substitution of Ti andMo atoms. The present work successfully achieves a tailored thermalexpansion in TaVO5 and draws a possible way to controlthe thermal expansion of other NTE materials.We adopt the double-element chemicalsubstitution to realizethe control of thermal expansion from strong negative to zero to positivein a TaVO5 system, which causes more lattice distortionby simultaneously part replacing the A site (octahedron) and M site(tetrahedron)
3-Dimensional hollow graphene balls for voltammetric sensing of levodopa in the presence of uric acid
No full textThe development of novel nanomaterials brings new opportunity and challenge for high sensing detection of biomolecules. The authors describe the preparation of 3-dimentional hollow graphene balls (3D HGBs) using nickel nanoparticles (Ni-NPs) as the template. The Ni-NPs were synthesized by chemical reduction of nickel chloride and then graphene was coated onto their surface via carburization and carbonization. After etching Ni-NPs, 3D HGBs with few layers and a typical size of 100 nm were obtained. They were sprayed onto indium tin oxide glass to obtain a working electrode for electrochemical determination of levodopa in the presence of uric acid. Due to the unique hollow porous structure of the 3D HGBs, the electrode exhibits a sensitivity of 0.69 mu A.mu M-1.cm(-2) and a 1 mu M limit of detection. It is selective, reproducible and stable. It was applied to the determination of levodopa in spiked human plasma samples and it is of potential use in clinical research.
Goniozus omanensis (Hymenoptera: Bethylidae) an important parasitoid of the lesser date moth Batrachedra amydraula Meyrick (Lepidoptera: Batrachedridae) in Oman
No full textA new species of bethylid parasitoid wasp, Goniozus omanensis Polaszek sp. n., is described based on morphology and DNA sequence data. The species is currently known only from the lesser date moth Batrachedra amydraula, a pest of economic importance, but can be reared on two factitious host species. G. omanensis is compared with G. swirskiana, known from the same host in Israel. We summarise current knowledge of G. omanensis life-history, and its potential as an agent of biological pest control.Copyright: © 2019 Polaszek et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article.NHM Repositor
Physical modeling of spent-nuclear-fuel container
No full textA new physical simulation model was developed to simulate the casting process of the ductile iron heavy section spent-nuclear-fuel container. In this physical simulation model, a heating unit with DR24 Fe-Cr-Al heating wires was used to compensate the heat loss across the non-natural surfaces of the sample, and a precise and reliable casting temperature controlling/monitoring system was employed to ensure the thermal behavior of the simulated casting to be similar to the actual casting. Also, a mould system was designed, in which changeable mould materials can be used for both the outside and inside moulds for different applications. The casting test was carried out with the designed mould and the cooling curves of central and edge points at different isothermal planes of the casting were obtained. Results show that for most isothermal planes, the temperature control system can keep the temperature differences within 6 ℃ between the edge points and the corresponding center points, indicating that this new physical simulation model has high simulation accuracy, and the mould developed can be used for optimization of casting parameters of spent-nuclear-fuel container, such as composition of ductile iron, the pouring temperature, the selection of mould material and design of cooling system. In addition, to maintain the spheroidalization of the ductile iron, the force-chilling should be used for the current physical simulation to ensure the solidification of casting in less than 2 h
Effect of residual Al content on microstructure and mechanical properties of Grade B+Steel for castings for locomotives
No full textThe bogie made of Grade B+ steel is one of the most important parts of heavy haul trains. Some accidents were found to be the result of fracture failure of the bogies. It is very important to find the reason why the fracture failure occurred. Because Al was added for the final deoxidation during the smelting process of the Grade B+Steel, residual Al existed to some extent in the castings. High residual Al content in the bogie casting was presumed to be the reason for the fracture. In this work, the influence of residual Al content in the range of 0.015wt.% to 0.3wt.% on the microstructure and mechanical properties of the Grade B+ Steel was studied. The experimental results showed that when the residual Al content is between 0.02wt.% and 0.20wt.%, the mechanical properties of the steel meet the requirements of technical specification for heavy haul train parts, and the fracture is typical plastic fractures. If the residual Al content is less than 0.02wt.%, the microstructures are coarse, and the mechanical properties can not meet the demand of bogie steel castings. When the residual Al content is more than 0.2wt.%, the elongation, reduction of area, and low-temperature impact energy markedly deteriorate. The fracture mode then changes from plastic fracture to cleavage brittle fracture. Therefore, the amount of Al addition for the final deoxidation during the smelting process must be strictly controlled. The optimum addition amount needs to be controlled within the range of 0.02wt.% to 0.20wt.% for the Grade B+Steel
Influences of different degassing processes on refining effect and properties of 4004 Al alloy
No full textIn order to improve the plasticity of 4004 Al alloy and subsequently the productivity of 4004 Al foil, the research studied in detail the influence of the rotary impeller degassing process on the refining effect of 4004 Al alloy, in which the impacts of four major parameters: gas flow, rotational speed, refining time, and stewing time, on degassing rate of 4004 Al alloy was systematically studied by using an orthogonal experiment methodology. Results show that the rotational speed has the greatest impact on the degassing of 4004 Al alloy, followed by gas flow and refining time; stewing time has the least impact. The optimum purification parameters obtained by current orthogonal analysis were: rotor speed of 500 r·min-1, inert gas flow of 0.4 mL·h-1, refining time of 15 min, and stewing time of 6 min. Degassing rate using the optimum parameters reaches 68%. In addition, the comparison experiments among C2Cl6 refining, rotary impeller degassing, and combined treatment of C2Cl6 refining and rotary impeller degassing for 4004 Al alloy were performed. The experimental data indicated that the combined treatment of C2Cl6 refining and rotary impeller degassing has the best degassing effect. Degassing rate of C2Cl6 refining, rotary impeller degassing and combined refining treatment is 39%, 69.1% and 76.9%, respectively. The mechanical properties of the specimen refined by rotary impeller degassing were higher than those by C2Cl6 refining, but lower than those by combined refining treatment
Matter + Spirit
No full textMatter + Spirit: January 23 - May 12, 2023
Opening Reception: January 25, 2023 4-7pm
Lauren Schiller, Artist Talk: January 25, 2023 3-4pm
“What is the place of spirit in contemporary life, particularly in highly materialistic and increasingly secular societies like those of the United States and China?” This is the central theme of Matter + Spirit which brings together a cohort of artists from China and the United States working
to address the role of spirituality in contemporary society. In bringing these artists and artworks into proximity, curator Rachel Smith orchestrates an overview of what is at stake in a post-Christian, post-modern, post-human - and most recently what has been dubbed a trans-human age - where technological systems have overtaken the direction of how we live. This fundamental shift has indelibly influenced and altered the shape of human existence and society. Matter + Spirit is a catalyst for conversation and reflection on what it means to be human right here, right now.
Works by: Yefu Bai, Ying Cao, Yuanming Cao, Shin-hee Chin, Wantain Cui, DaoZi, Wei Ding, Scott Fisk, Brenton Good, Xin Guo, Chunye He, Liang Jiang, Suki Kwon, Leah Samuelson, Lauren Schiller, Justin Sorensen, Kenneth Steinback, Laura Stevenson, Meagan Stirling, Ziyun Tong, JoAnn VanReeuwyk, Yongliang Wang, Yong You, Erjun Zhao, Jiuyang Zhu
Curated by Rachel Hostetter Smithhttps://scholarship.shu.edu/past-exhibits-2023/1000/thumbnail.jp
Effect of Bi on graphite morphology and mechanical properties of heavy section ductile cast iron
No full textTo improve the mechanical properties of heavy section ductile cast iron, bismuth (Bi) was introduced into the iron. Five castings with different Bi content from 0 to 0.014 wt.% were prepared; and four positions in the casting from the edge to the center, with different solidification cooling rates, were chosen for microstructure observation and mechanical properties test. The effect of the Bi content on the graphite morphology and mechanical properties of heavy section ductile cast iron were investigated. Results show that the tensile strength, elongation and impact toughness at different positions in the five castings decrease with a decrease in cooling rate. With an increase in Bi content, the graphite morphology and the mechanical properties at the same position are improved, and the improvement of mechanical properties is obvious when the Bi content is no higher than 0.011wt.%. But when the Bi content is further increased to 0.014wt.%, the improvement of mechanical properties is not obvious due to the increase of chunky graphite number and the aggregation of chunky graphite. With an increase in Bi content, the tensile fracture mechanism is changed from brittle to mixture ductile-brittle fracture
Enhanced Age Strengthening of Mg-Nd-Zn-Zr Alloy via Pre-Stretching
No full textPre-stretching was carried out to modify the microstructure of Mg-Nd-Zn-Zr alloy to enhance its age strengthening. The results indicated that more heterogeneous nucleation sites can be provided by the high density of dislocations caused by the plastic pre-stretching deformation, as well as speeding up the growth rate of precipitates. Comparison of microstructure in non-pre-stretched specimens after artificial aging showed that pre-stretched specimens exhibited a higher number density of precipitates. The fine and coarse plate-shaped precipitates were found in the matrix. Due to an increase in the number density of precipitates, the dislocation slipping during the deformation process is effectively hindered, and the matrix is strengthened. The yield strength stabilizes at 4% pre-stretching condition, and then the evolution is stable within the error bars. The 8% pre-stretched specimens can achieve an ultimate tensile strength of 297 MPa. However, further pre-stretching strains after 8% cannot supply any increase in strength. Tensile fracture surfaces of specimens subjected to pre-stretching strain mainly exhibit a trans-granular cleavage fracture. This work indicated that a small amount of pre-stretching strain can further increase strength of alloy and also effectively enhance the formation of precipitates, which can expand the application fields of this alloy
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