Browsing by Subject "Materials science"

Now showing 1 - 3 of 3
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    Electrochemical behaviors of micro-arc oxidation coated magnesium alloy
    (2014) Liu, Jiayang; Zhang, Jing; Chen, Jie; Li, Jiliang; Na, Sungsoo
    In recent years, magnesium alloys, due to their high strength and biocompatibility, have attracted significant interest in medical applications, such as cardiovascular stents, orthopedic implants, and devices. To overcome the high corrosion rate of magnesium alloys, coatings have been developed on the alloy surface. Most coating methods, such as anodic oxidation, polymer coating and chemical conversion coating, cannot produce satisfactory coating to be used in human body environment. Recent studies demonstrate that micro-arc oxidation (MAO) technique can produce hard, dense, wear-resistant and well-adherent oxide coatings for light metals such as aluminum, magnesium, and titanium. Though there are many previous studies, the understanding of processing conditions on coating performance remains elusive. Moreover, previous tests were done in simulated body fluid. No test has been done in a cell culture medium, which is much closer to human body environment than simulated body fluid. In this study, the effect of MAO processing time (1 minute, 5 minutes, 15 minutes, and 20 minutes) on the electrochemical behaviors of the coating in both conventional simulated body fluid and a cell culture medium has been investigated. Additionally a new electrolyte (12 g/L Na2SiO3, 4 g/L NaF and 4 ml/L C3H8O3) has been used in the MAO coating process. Electrochemical behaviors were measured by performing potentiodynamic polarization and electrochemical impedance spectroscopy tests. In addition to the tests in simulated body fluid, the MAO-coated and uncoated samples were immersed in a cell culture medium to investigate the corrosion behaviors and compare the difference in these two kinds of media. The results show that in the immersion tests in conventional simulated body fluid, the 20-minute MAO coated sample has the best resistance to corrosion due to the largest coating thickness. In contrast, in the cell culture medium, all MAO coated samples demonstrate a similar high corrosion resistance behavior, independent of MAO processing time. This is probably due to the organic passive layers formed on the coating surfaces. Additionally, a preliminary finite element model has been developed to simulate the immersion test of magnesium alloy in simulated body fluid. Comparison between the predicted corrosion current density and experimental data is discussed.
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    Optical refrigeration on cadmium selenide/cadmium sulfide quantum dots
    (Springer Nature, 2025-04-17) Hua, Muchuan; Decca, Ricardo S.; Physics, School of Science
    Critical progress in perfecting semiconducting quantum dots' photoluminescence quantum yield has been made in the past few years. The production of quantum dots with nearly unitary quantum yield has significantly expanded their possible applications, as it is the case of optical refrigeration. We report for the first time optical refrigeration achieved in cadmium selenide/cadmium sulfide (core/shell) structure nanocrystals. Experiments were carried out in colloidal quantum dots suspension, where the excitonic non-radiative decay paths of the quantum dots are effectively suppressed by applying sub-band excitation, eliminating the possible states for energy down-conversion. The cooling effect comes from the significant energy up-conversion observed in the photoluminescence spectra of the samples under sub-band excitation. These results highlight the possibility of realizing temperature control on semiconducting quantum dots through optical approaches, which could provide power cooling mechanism for nano devices and cryogenic systems.
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    Thermoplastic polyurethane flexible capacitive proximity sensor reinforced by CNTs for applications in the creative industries
    (Springer Nature, 2021-01-13) Moheimani, Reza; Aliahmad, Nojan; Aliheidari, Nahal; Agarwal, Mangilal; Dalir, Hamid; Mechanical and Energy Engineering, School of Engineering and Technology
    Wearable sensing platforms have been rapidly advanced over recent years, thanks to numerous achievements in a variety of sensor fabrication techniques. However, the development of a flexible proximity sensor that can perform in a large range of object mobility remains a challenge. Here, a polymer-based sensor that utilizes a nanostructure composite as the sensing element has been presented for forthcoming usage in healthcare and automotive applications. Thermoplastic Polyurethane (TPU)/Carbon Nanotubes (CNTs) composites are capable of detecting presence of an external object in a wide range of distance. The proximity sensor exhibits an unprecedented detection distance of 120 mm with a resolution of 0.3%/mm. The architecture and manufacturing procedures of TPU/CNTs sensor are straightforward and performance of the proximity sensor shows robustness to reproducibility as well as excellent electrical and mechanical flexibility under different bending radii and over hundreds of bending cycles with variation of 4.7% and 4.2%, respectively. Tunneling and fringing effects are addressed as the sensing mechanism to explain significant capacitance changes. Percolation threshold analysis of different TPU/CNT contents indicated that nanocomposites having 2 wt% carbon nanotubes are exhibiting excellent sensing capabilities to achieve maximum detection accuracy and least noise among others. Fringing capacitance effect of the structure has been systematically analyzed by ANSYS Maxwell (Ansoft) simulation, as the experiments precisely supports the sensitivity trend in simulation. Our results introduce a new mainstream platform to realize an ultrasensitive perception of objects, presenting a promising prototype for application in wearable proximity sensors for motion analysis and artificial electronic skin.