查看更多>>摘要：This work mainly deals with the synthesis of Al substituted copper ferrite infused reduced graphene oxide (rGO) as a microwave absorbing material in a frequency ranging from 8.2 to 12.4 GHz (X-band). Firstly, Al substituted copper ferrite (CAF) infused rGO was synthesized using the solvothermal method. Then it mixed in the epoxy media to fabricate lightweight nanocomposites for their potential uses as competent electromagnetic wave absorbers. The structural analysis using XRD validates the successful substitution of Al into copper ferrite lattice. TEM results showed that copper-Al-ferrite's spherical morphology with size ~20–30 nm is well infused on rGO in the as-synthesized nanohybrid. BET analysis confirmed numerous pore formations in the nanohybrid that created during CAF over rGO. Furthermore, the effect of rGO-loaded/and unloaded nanohybrid on the microwave absorption properties was also studied. Notably, it is seen that the strategy to infuse CAF on rGO was found more effective in enhancing the absorption capacity of pure CAF. Remarkably, the CAF-rGO/epoxy nanocomposite exhibited excellent microwave absorption capacity as the reflection loss (RL) value of ? 35.7 dB (99.973% absorption) is achieved with 3.55 GHz of broad ? 10 dB (90% absorption) bandwidths under the low filler content of 20 wt% and small matching thickness of 2.2 mm. Besides, the possible microwave absorption mechanisms in the nanohybrid composite are also disclosed. Therefore, our results could be helpful to manufacture the rGO based dielectric-magnetic hybrid nanocomposites for the highly efficient and lightweight microwave absorber exclusively for X band application, i.e., in the high gigahertz range.
查看更多>>摘要：Incorporating Ag-graphene oxide hybrid material (Ag-GO) on optical fiber offers a novel approach for flexible ultrasensitive detection in biomedical and environmental areas. In this work, Ag-GO surface-enhanced Raman scattering (SERS) optical fiber probe was synthesized by a SnCl2-sensitized solvothermal method and modified Hummer's method. After optimizing SERS test parameters, SERS performance of the fiber probes synthesized by different synthetic procedures of GO, Ag-GO hybrid structures and GO concentration are compared. The obtained GO shows superior ability to quench fluorescence by reducing the photobleaching of dyes. GO with high oxidation degree is preferred. Compared to Ag and hybrid structures including GO/Ag and GO/Ag/GO, Ag/GO fiber probe exhibits strongest enhancement due to π-π stacking and charge transfer process from lone pair of electrons on GO to the molecules. Ag/GO fiber probe with 5 mg/mL GO displays strongest SERS enhancement. Apart from chemical enhancement, it is worthwhile to note that GO is also found to selectively enhance specific vibrations regarding π bond or lone pair of electrons. The fiber probe shows high sensitivity (10?9 M R6G), good reproducibility (RSD of 3.5%) and good stability. Moreover, the enhanced area of Ag-GO fiber probe occurs in core area and cladding edge. The enhancement mechanism of Ag-GO fiber probe is that, as GO provides an additional route for excited dyes to decay through its Fermi level, photobleaching of dyes is reduced by charge transfer process. The enhancement is a synergic effect of chemical enhancement of GO, electromagnetic enhancement of silver and waveguide propagation of optical fiber.
查看更多>>摘要：The paper describes the synthesis of substrate for surface enhanced Raman spectroscopy (SERS) based on magnetic nickel nanotubes (Ni NTs). For the success application of Ni NTs in quantitative SERS analysis of organic molecules by the example of Rhodamine 6G (R6G), electroless deposition of gold (I) on Ni NTs in alkali media was performed. The purity and uniformity of the gold layer has been proven by methods of XRD, SEM-EDX, XPS and FTIR analysis. The magnetic properties of the obtained magnetic Ni-Au NTs measured by VMS did not change compared to the initial Ni nanotubes. The efficiency of substrates with Ni-Au NTs is determined by the optical properties of the substrate (the position of the plasmon resonance peak). The substrates with scattered nanotubes having a plasmon resonance position at 530 nm are the most effective for use in SERS when using a laser with a wavelength of 532 nm, as exemplified by the spectra of Radomin 6G. SERS analysis of R6G using Ni-Au NTs in concentration range from 10?3 to 10?8 led to average enhancement factor of 8?105.
查看更多>>摘要：Cadmium telluride (CdTe) is one of the well-explored semiconductors in the history of material science research, because of its innumerable benefits in all dimensional nanostructures. However, no endeavor has been dedicated as of now to understanding the size-dependent tuning of nonradiative emission efficiency and how it influences the sensitive detection of organic vapors (ethanol and acetone) through photoluminescence (PL) quenching mechanism. Herein, the aspect ratio of CdTe nanorods (NRs) is varied by changing its diameter while keeping the axial length constant through electrodeposition into lab made anodic aluminium oxide (AAO) membranes. The growth kinetics and thermodynamics involved while electrodeposition of CdTe NR in each distinct pore diameter of AAO membrane is studied and reasoned. The surface morphology of variable diameter AAO membranes and NRs, respectively fabricated under various electrochemical parameters are observed through a field emission scanning electron microscope. The relation between NRs dimension and structural parameters like d-spacing, crystallite size, band area ratio, and exciton-phonon ratio are extracted from X-ray diffraction and Resonance Raman spectroscopy. The strongly luminescent CdTe NRs, coupled with their chemical durability and organic molecule affinity displayed a sensitive response of ~12 and 6 ppm to ethanol and acetone vapors in the range of 10–100 ppm as a PL sensor. The carrier lifetime measurement through time-correlated single photon counting spectroscopy endorses the role of increased recombination density with a decrease in the diameter of NRs.
查看更多>>摘要：The thermal residual stresses and plastic deformation caused by the coefficient of thermal expansion (CTE) mismatch in the cooling process play an important role in the physical and mechanical properties of metal matrix composites (MMCs). In this study, the Cu/SiCp composites with and without cooling process are subjected to uniaxial tensile and compressive loadings through molecular dynamics (MD) simulation. We found that the cooling process leads to a decrease in strength and earlier yielding. The mechanical response depends on the temperature drop, and samples cooled from a higher temperature have a lower yield strength. The introduction of reinforcements and thermally induced defects reduce the tension/compression (C/T) asymmetry as compared with that of single crystal and defective Cu. These pre-existing defects can be the source for the initiation of plasticity in early stage of external loading, and the defect evolution shows a C/T asymmetry. For the density of two predominant dislocation types, the Shockley partial increases at the stress buildup stage, while the stair-rod dislocation decreases, regardless of tension and compression. The mechanisms for the dissociation of stair-rod dislocation and incomplete stacking fault tetrahedrons (ISFTs) at the stress buildup stage have been revealed. Our results provide an atomic-scale perspective to understand the influence of thermally residual stresses and defects on mechanical behavior of MMCs.
查看更多>>摘要：The FeCoNiCuAl high-entropy alloy (HEA) has good magnetic and –mechanical properties which can be finely tuned by the fraction, composition, and distribution of the BCC and FCC phases. In this paper, we report the magnetic properties, corrosion resistance, and microstructure of the FeCoNiCuAlCex (0 ≤ x ≤ 0.09) HEAs. The results show that Ce addition is beneficial to the remanence (Br), coercivity (Hc), and hysteresis losses (Pu), but detrimental to the maximum permeability (μm) and maximum flux density (Bm). When x = 0.09, the Br, Hc, and Pu of the HEAs are improved by about 91%, 64% and 91%, respectively. The FeCoNiCuAl HEA has good corrosion resistance, comparable to 304 stainless steels. The addition of Ce improved the Icorr of the HEAs. X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) results show that the FeCoNiCuAl HEAs are composed of a face-centered cubic (FCC) phase and a body-centered cubic (BCC) phase, with the Cu-rich nano-precipitates embedded in the BCC phase. With the addition of Ce, the nano-precipitates become even smaller and more uniform. Meanwhile, the FCC phase becomes Cu-rich and its magnetism changes from ferromagnetic to non-ferromagnetic. The electronic density of state (DOS) for the alloys calculated by density functional theory (DFT) is discussed.
查看更多>>摘要：In this study, the recycled Al-Mg-Mn-Fe alloys having different Fe levels (0.1%, 0.5%, and 0.8%) were successfully developed by applying squeeze casting without heat treatment. Optical and scanning electron microscopy, synchrotron X-ray tomography and radiography, X-ray diffraction, and tensile tests combined with thermodynamic calculations were used to study the correlation between the microstructural evolution and mechanical properties. The results showed that for the alloys with an applied pressure of 75 MPa, as the Fe increase from 0.1% to 0.8%, the yield strength (YS), and ultimate tensile strength (UTS) increased from 122 MPa and 244–146 MPa and 289 MPa, and elongation decreased from 34% to 12%. Even though Fe additions increased the volume fraction of Fe-rich intermetallic phases, it significantly increased the UTS and YS. The synchrotron X-ray tomography and deep-etched results both show that the 3D morphology changed from individual Chinese-script to interconnected plate-like. The 3D morphology of 0.8Fe alloy clearly demonstrate that the hole partially or whole penetrated the entire rectangle-shaped Al6(FeMn) phases, which is due to the close-packed plane growth. In-situ synchrotron X-ray radiography results showed the facet growth behaviour of Al6(FeMn) in 0.8Fe alloys during solidification with a long needle-like shape. The size of primary Al6(FeMn) phases decreases, whereas their number increases with increasing cooling rate. Moreover, the applied pressure was beneficial in refining the size of α-Al grains and Fe-rich phases and reducing the volume fraction of pores, thus contributing to the improvement of strength and elongation. The in-situ tensile test results indicated that the crack initiated in the Fe-rich phases and pores, and the slip lines were blocked by the Fe-rich phases resulting in the strengthening of the secondary phases.
查看更多>>摘要：The Mg-8Gd-4Y-1Zn-0.5Al (wt%) alloy prepared by metal type casting were homogenized, rolled or extruded-rolled to obtain sheets, and followed by aging treatment. The microstructures were analyzed by OM, SEM, TEM, EBSD and XRD, the hardness and tensile mechanical properties were tested. The results show that the optimal process is rolling at 793 K with the deformation of 70% for the homogenized sheet. The microstructure of the sheet is composed of fully dynamic recrystallized grains with a strong basal texture, and the aggregated 18R-LPSO structures randomly distribute in the matrix. After peak aging treatment, the yield strength (YS), ultimate tensile strength (UTS) and elongation to failure (EL) of the sheet are 343 MPa, 380 MPa and 7.5%, respectively. After the extruded sheets were rolled at 793 K with 50% deformation, the grains grew up. The texture changes from a silk type to the strong basal type. The 18R-LPSO structures reduce the torsion phenomena, but get together. After peak aging treatment, the YS, UTS and EL reach 391 MPa, 462 MPa and 5.5%, respectively. The 18R-LPSO structures with streamlined distribution along rolling direction increase the anisotropy of mechanical properties of the extruded-rolled sheet.
查看更多>>摘要：Sm2Co17 magnetic materials were synthesized using a combination of electrodeposition from an aqueous medium and a reduction-diffusion (R-D) process. The electrodeposition solution contained a complex agent (glycine) because of a significant reduction potential difference between Sm and Co. Co, Sm, O, and S were incorporated in the as-deposited Sm-Co alloy. The Sm compounds with O and S were difficult to reduce to metallic Sm without a reducing agent at high temperatures (>1000 ℃). Thus, a mixed sample of the as-deposited Sm-Co alloy, Ca granules, and NaCl was converted into Sm2Co17 at 800 ℃ during the R-D process. The annealing time was varied from 3 h to 12 h. X-ray diffraction analysis showed that the as-deposited Sm-Co alloy was amorphous. After the R-D process, the Sm-Co alloy was converted into a crystalline Sm2Co17 form. An increase in the Sm2Co17 phase transformation was observed in the morphology analysis of the cross-section. Based on these analyses, the mechanism involved in the formation of Sm2Co17 was elucidated. The changes in the magnetic properties, including saturation magnetization (Ms) and coercivity (Hci), were determined using a vibrating sample magnetometer.
查看更多>>摘要：Recently, color-changing glasses have been developed from a series of Ce-based metallic alloys. The functionality originates from fast and spontaneous surface oxidation. In most cases, single-color glasses have been obtained, but in a few cases, multicolor glasses that have spatially-dependent color contrast have been found. The natural color contrast mostly results from the interference effects on the oxide layer. The present work investigates factors that influence and control the variable oxidation rate observed at different locations on the surface, and what manufacturing steps and processing history lead to the rate variation. It is found that cooling rate, residual strain, and precipitation in melt-spun ribbons are the effects controlling the oxidation rate giving the enhanced color contrast. Therefore, the final surface color contrast reflects the non-uniform distribution of enthalpy (glassy state), microstructure, and chemistry of the metallic glass beneath the surface. The inspection of natural color contrast also represents technologically useful method for early surface flaw detection in color-changing metallic glasses.
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Elsevier