1,721,053 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Properties and thermal stabilization of Nanocrystalline copper via solute additions of niobium
Get PDFNanocrystalline materials, those with grain size <100 nm, were found to have superior mechanical properties compared to their coarse-grained (CG) counterparts. However, these materials are not thermally stable because of having a high density of grain boundaries which increases their Gibbs free energy. Consequently, the nano-grains grow back to their original size in order to release this energy, which results in losing their exceptional properties. Hence, finding ways to stabilize these nano-grains is an utmost importance. Introducing solute to such systems was found to solve the instability issue. Two approaches can describe the mechanism in which the solute atoms prevent or minimize the grain growth, Kinetic Approach which is concerned with reducing the mobility of the grain boundaries by pinning them; and Thermodynamic Approach that works on reducing the energy of the system, hence eliminating the need for the grains to grow.
Nanocrystalline (nc) Cu and Cu-1 at.% Nb are prepared via mechanical ball milling under argon. The microstructure and the properties of the as-milled and the annealed samples are characterized using XRD, TEM, Vickers Microhardness, Tensile tests, SEM, and Four-Point Probe technique. Only one atomic percent of Nb is found to enough to thermally stabilize the nanostructure of copper up to 1073 K, which represents 80% of its melting point. Solute drag and Zener pinning are found to be the main kinetic stabilization mechanisms that succeeded to keep the grain size in the nanoscale. In addition, the solute atoms substantially enhanced the strength and hardness of the nc Cu, along with maintaining a better ductility. Moreover, such small amount of Nb did not sacrifice the excellent electrical conductivity of copper. This approach of synthesizing and improving the thermal stability of nc materials is not necessarily limited to Cu and could be applied to other metals and alloys. This shall make a leap forward in the production of thermally-stable and ultra-tough nanocrystalline materials for many industrial applications, without affecting their inherent properties
Thermoelectric Behavior of Nanocrystalline Tin Selenide Nanocomposites
Get PDFThermoelectric technology converts thermal energy to electricity. Many studies were conducted on thermoelectric materials such as Bismuth Telluride and Lead Telluride. And the goal was to achieve an average ZT >2 which is required for waste heat recovery applications. Recently Tin Selenide (SnSe) showed a promising performance with a ZT of nearly 2.6 at 923 K for its single crystal structure at the b-axis. However, single crystal SnSe is very fragile and the production of single crystal SnSe structure is a complicated and costly process. Therefore, great interest was given to polycrystalline SnSe.
In this work, the thermoelectric performance of polycrystalline SnSe was enhanced through nanostructuring and nano-composting with graphene via a cost-effective methodology. Nanocrystalline SnSe composites were successfully prepared by high energy ball milling and SPS techniques, and the structural characterization by X-ray Diffraction and Transmission Electron Microscopy revealed that the average grain size of both pristine SnSe and SnSe with Graphene was approximately (~ 10 nm). The mechanical properties were evaluated and showed an enhancement with high hardness values. The nanostructuring contributed in the enhancement of Seebeck coefficient and the highest reported value so far was obtained for pristine SnSe with 1032 μV/K at 873K. A significant improvement in ZT value was observed for the pristine nanostructured SnSe with a value of 0.9 at 873 K, and the addition of Graphene increased the ZT to 1.2 at 873 K due to the increased power factor and the lower thermal conductivity. Graphene was detected to be mainly present around the grain boundaries and this finding represents the first ever reported evidence to identify the location of graphene in a nanocrystalline TE material
EFFECT OF ALUMINUM CONCENTRATION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF NICRCONB HIGH ENTROPY ALLOYS
No full textThe debate between growing economies and increased environmental burdens forces countries to make excessive efforts to reduce their energy consumption. The reduction of weight in structural materials, such as Al-based and Ni-based alloys that are utilized in everyday aspects, has a great potential for reducing the consumption of energy and minimizing the burden on the environment. High entropy alloys (HEAs) are a new class of multi-component alloy systems in which the design of the alloys is based not on adding solutes to a single "base" element, but rather on choosing elements that will form solid solutions when mixed with specific concentrations. In this work, we studied the effect of aluminum content on novel NiCrCoNb HEAs and produced low-cost and low-density HEAs with superior unprecedented mechanical properties through simple thermomechanical treatments
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
THE EFFECT OF HEAT TREATMENT AND MICROSTRUCTURES ON THE CORROSION PROPERTIES OF ALCOCRFENI HIGH ENTROPY ALLOYS
No full textHigh-entropy alloys have emerged as promising materials in NaCl environment operations due to their superior strength, ductility, and corrosion resistance. This paper investigates the microstructure, mechanical properties, and corrosion behavior of an AlCoCrFeNi HEA alloy after annealing. treatment at 1000 °C and 1200 °C . The alloy was produced via arc melting in an argon environment and underwent 48 hours of annealing in a high-temperature tube furnace to achieve uniform heat distribution. Results showed that higher annealing temperatures led to a greater degree of microstructural refinement and uniformity achieved by the reduced Ni3Al phase fraction as well as enhanced phase stability. The HEA with 1200 °C exhibited exceptional mechanical properties, having an average yield strength of 947 MPa and an average ultimate tensile strength of 1263 MPa, which surpasses Inconel 718 while maintaining considerable levels of ductility. Due to the highly stable Cr2O3 passive film, the 1200 °C annealed HEA was found to outperform SS316 L and 1000 °C HEA in corrosion resistance. The 1200 °C HEA was also observed to provide lower cost than Inconel 718 and lower reliability than SS316L for offshore environments when compared to conventional materials due to better performance in strength-to-corrosion ratio and economic efficiency
Optimization and Stabilization of P-Type BISBTE/GRAPHENE Nanocomposites for Efficient Thermoelectric Energy Conversion
Get PDFThe state-of-the-art Bismuth Antimony Telluride (BiSbTe) alloys have a
promising potential to advance thermoelectric applications in energy harvesting for
efficient power generation and active refrigeration. In this thesis, the combination of
High-Energy Ball Milling and FAST/SPS Sintering Press showed a reliable and cost
effective synthesis approach for artifact-free nanostructured bulk BiSbTe/Graphene
nanocomposites. The results show successfulness in synthesizing homogenous
elemental distribution and stable single phase of Bi0.4Sb1.6Te3 either in the pristine
nanopowder or the multicomponent nanocomposites. It also confirms the crucial rule
of graphene addition time on its structure, as well as, the morphology, mechanical
behavior, and thermoelectric performance of the synthesized nanocomposites. The
5mins nanocomposite showed an ultrahigh micro-hardness of 1.78GPa, the highest
power factor of 1.73mW/m.K2 at 323K, and the lowest thermal conductivity of
0.723W/m.K at 323K. This has resulted in its optimum Figure-of-Merit of 0.70 at 323K
with 25% of improvements compared to the pristine BiSbTe
THE EFFECT OF SINGLE WALLED CARBON NANOTUBES ON THE THERMOELECTRIC PROPERTIES OF BISMUTH TELLURIDE
Get PDFModern new technologies, including carbon nanomaterials, polymers performed electronically, and their nanocomposites enhance the performance of thermoelectric materials. Thermoelectrical responses can be improved by simultaneously tuning different properties within the material, such as nano structuring, nanocomposites, and doping. The purpose of this work is to determine the effect of single walled carbon nanotubes (SWCNT) on the thermoelectric properties of an n-type bismuth telluride alloy. Mechanical alloying and compaction sintering techniques are used to prepare SWCNT/Bi2Te2.55Se0.45 composites. Experiments are conducted with different concentrations (0.01, 0.025, 0.1 and 0.5 weight percent) and duration times of 20 hours. The results of the thermoelectric characteristics of SWCNT indicates that ball milling technique influences both its structure and agglomeration. The CNT filler is added during the step of mechanical milling, as this preserves SWCNT structure and increases its electrical conductivity. Additionally, it is demonstrated that SWCNT milling technique improves the Seebeck coefficient. While an increase in thermal conductivity is expected as a result of the high electrical conductivity due to increased scattering at the new interfaces, a significant drop in the lattice thermal conductivity is attained. The figure-of-merit for the optimal sample with 0.1 percent SWCNT added in 20 milling hours has improved by 13% at room temperature indicating a value of 0.3, and by 32% at 156.9°C indicating the highest ZT value of 0.6
THE EFFECT OF NIOBIUM ON THE PHASE STABILITY AND MECHANICAL PROPERTIES OF NICKEL-BASED HIGH ENTROPY ALLOYS
No full textA fundamental understanding of the mechanisms of phase stability of high entropy alloys (HEAs) and the influence of refractory elements is a recent topic of active research. This study investigates the effect of Niobium (Nb), as a refractory element, on the phase stability and mechanical properties of NiCoCrAlNb HEAs. In this thesis, Ni0.55CoCrAlNbx (x= 0, 0.01, 0.03, 0.05) high entropy alloys are prepared by using a vacuum arc melting technique. X-ray diffraction results demonstrate a single solid solution phase FCC in all samples. The addition of Nb content is studied through thermomechanical assessments and microstructure processing. Remarkable tensile properties were achieved for the HEA with 5% Nb content. The thermomechanical treatments were optimized, and the best combination of mechanical properties was obtained at an aging temperature of 950°C for one hour. Significant improvements are detected in tensile properties as the Nb content is increased. The yield and ultimate strength values of the optimized sample were found to be 1050 MPa and 1534 MPa, respectively. All the specimens aged at 950°C had a good tensile ductility of 34%. This thesis indicates that the properties of HEAs could be well tailored using thermomechanical and microstructure management for a high-performance HEA in industrial engineering applications
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