Bulletin of Materials Science最新文献

Effect of dendritic and globular (rosette-like) morphology and its parameters on the hardness of Al–7.5% Si castings has been investigated. It was established that Brinell hardness demonstrates a slight increase with the rise of globules’ size and a slight decrease with the rise in dendrite parameter. In the first case, this is apparently due to isothermal holding in the process of obtaining castings, in the second case, with a decrease in the quenching rate of eutectics due to a decrease in the surface area of the dendrites because of coarsening.

Effective charge separation and use of hot charge carriers are considered to be the most essential factors affecting the activity of an excellent energy harvester. Herein, we have successfully decorated 3 nm of CdSe quantum dots (QDs) on the surface of reduced graphene oxide (rGO) using solvothermal method. Formation of CdSe–rGO nanocomposite (NC) has been confirmed by X-ray diffraction pattern, transmission electron microscopy and Raman analysis. Further, the emission spectrum of CdSe–rGO NC shows quenching of emission of CdSe QDs on the surface of rGO nanosheet. To elucidate this phenomenon, we have carried out time-correlated single-photon counting (TCSPC) measurements, which reveal efficient electron transfer, as the exciton lifetime of CdSe QDs in the NC is significantly reduced compared to bare CdSe QDs. Owing to the efficient electron transfer, this NC showed big boost in total shielding effectiveness (SE_T = 29 dB) when compared to graphene (SE_T = 23 dB) in electromagnetic interference shielding application.

Graphical abstract

Eu³⁺ red phosphors in new phosphomolybdates, La_0.8−xCa_xP_1−xMo_xO₄ were developed by high-temperature ceramic route. These phosphors show intense red emission under broad excitation of the charge transfer band (CTB) (345 nm), near UV (394 nm) and blue (464 nm) wavelengths. The incorporation of CaMoO₄ in LaPO₄ reduces CTB energy of MoO₄²⁻ tetrahedron, making it to overlap with Eu³⁺ excitations and also enhances the distortion of Eu³⁺ environment. These factors facilitate the effective energy transfer from the host to Eu³⁺ excitation levels leading to intense red emissions unlike orange emission in LaPO₄. The Commission International d'Eclairage colour coordinates of phosphors (0.66, 0.34), are very close to the standard red phosphor. Thus, the new phosphomolybdate red phosphors are a mode to enhance the Eu³⁺ absorptions making them promising candidates for white light-emitting diode applications.

This paper reports the synthesis, photoluminescence (PL) and spectroscopic ellipsometry (SE) studies of MnGa₂S₄ single crystal. Here, the study of photoluminescence properties of the compound in the visible and infrared regions and the calculation of colour coordinates were widely investigated. In the present work, previously observed optical transitions in various works were observed in PL spectra. A higher correlated colour temperature value of 4353 K suggests that this material is suitable for light-emitting diode applications. Ellipsometry measurements were performed on the samples using a variable angle spectroscopic ellipsometer in the spectral range of 1–6 eV. The ordinary refractive index has a peculiarity at ~3.469 eV and the extraordinary component at 3.751 eV. These peculiarities in the line shape resemble the critical point M0 for the 2D case. The values of these critical points correspond to the direct band gap value.

Friction stir processing (FSP) is considered as a prolific secondary processing method to enhance the properties of aluminium matrix composites (AMCs) by altering their microstructure. AA6061/(15 wt.%) Al₃Zr and AA6061/(15 wt.%) Al₃Ni AMCs were manufactured with the addition of zirconium (Zr) and nickel (Ni) powders to the molten AA6061 and followed by FSP. The change in microstructure of AMCs before and after FSP was analysed through optical and electron microscopies integrated with electron back-scattered diffraction. The cast AMCs exhibited clustered, sharp cornered particles with micropores near the particle–matrix interfaces and showed coarse-grained microstructure. Upon conducting FSP, the particle distribution was uniform along with the elimination of cast defects. The sharp cornered particles were fragmented into finely dispersed particles in the aluminium matrix. Significant grain refinement was observed on AMCs owing to the pinning effect of particles and severe deformation happened during FSP. FSP enhanced the accumulation of dislocations and resulted in modification microstructure, which favoured attaining a combination of ductility and tensile strength. The strength attained by the Al₃Ni AMC was higher than that of Al₃Zr AMC due to the existence of finely dispersed near round-shaped particles, which exhibited better load-bearing ability.

Preliminary findings on the fabrication of a bio-composite are presented. Polylactic acid was blended with Ulex europaeus particles, compression moulding was used to produce samples, and the mechanical properties of fabricated composites were tested. Polylactic acid reinforced with a 5% (wt) of U. europaeus attained the highest tensile strength (53.118 MPa), impact strength (1.3 kJ m⁻²) and flexural strength (101.235 MPa). Various defects, such as air bubbles and particle agglomeration, were found to be responsible for the decrease in mechanical properties. This issue should be contemplated in future studies.

Gadolinium aluminium garnet (Gd₃Al₅O₁₂) nanopowders, with 30 at% lutetium substitution have been successfully synthesized using the co-precipitation method. Several sources, such as aluminium nitrate or sulphate, have been used to develop the (Gd_0.7Lu_0.3)₃Al₅O₁₂ (GdLuAG) compound via normal and reverse add titration using ammonium hydrogen carbonate (AHC) as a precipitant. Different techniques such as X-ray diffraction, FTIR, Raman scattering, BET and SEM/EDS analysis were performed in this study. The X-ray results confirmed that the garnet compound crystallized in the cubic structure with group space Ia (bar{3}) d. The crystallite sizes of the powders were determined by using Rietveld refinement analyses. The FTIR results of vibrational characteristics exhibit the internal and external bonds of GdLuAG. The He–Ne laser 633 nm Raman spectra showed a response in the second phonon region exhibiting strong fluorescence in the near-infrared (NIR). The GdLuAG internal Raman active mode in the visible range and excited by a 785 nm diode laser were measured. The X-ray, BET and SEM results indicated that aluminium nitrate reverse titration compound calcined at 1150°C is the best homogeneous and uniform sample.

In this study, we have hydrothermally synthesized Nb₂O₅ nanorods of various dimensions at different reaction times. These synthesized samples were physio-chemically characterized by UV-visible, XRD, FESEM, HRTEM and XPS techniques. The absorbance spectrum has shown blue-shift than the bulk counterpart, whereas XRD and XPS confirm the formation of Nb₂O₅. FESEM and HRTEM reveal the formation of rod-like structures. The annealing temperature affects the surface porosity of the samples as the porous rod like Nb₂O₅ formed at higher annealing temperature. Further, the Nb₂O₅ was used as photoanode material in dye-sensitized solar cells and characterized by different photovoltaic characterization parameters (photocurrent density–voltage (J–V) curve, IPCE, FF and cell efficiency). The enhanced photovoltaic parameters were obtained for NB-2 with photocurrent value of 8.40 mA cm⁻² and efficiency (η) of 3.43%. This enhanced performance is the result of high surface roughness and porosity, which assisted in improving the efficiency, dye loading and better electronic conduction pathway. Electrochemical impedance spectroscopy (EIS) was studied to understand the charge transfer and recombination at Nb₂O₅|dye|electrolyte interfaces.

Electro-discharge layering (EDL) is a coating technique, used for fabricating wear and corrosion resistance layer on the parts used in automobile, biomedical and structural applications. Eventhough, selecting the suitable parameters and levels in EDL process is difficult to attain better coating characteristics. We have studied the prediction and effect of process parameters on EDL of magnesium alloy using response surface methodology (RSM)-assisted feed forward back propagation artificial neural network (ANN). In this work, WC–Cu composite coating was deposited on AZ31B magnesium alloy using EDL viz. compaction pressure (CP), discharge current (DC) and pulse on time (PT). Influence of process parameters on electrode deposition rate (EDR) and coating roughness (CR) during EDL of magnesium alloys is studied. It was revealed that the correlation between the experimental values of RSM and predicted values of ANN was 0.991, which is closely to the working limit. Therefore, it was agreed that the established ANN model is suitable for predicting the EDR and CR. Furthermore, effect of parameters on CR and EDR are studied with support of mean effect plots generated by RSM tool. It was studied that the CR and EDR will increase, as increase in DC and PT at processing with low compaction pressured electrode. Conversely, it decreases with increase in CP of the electrode. Mechanism of coating, such as craters and globules were identified in the surface coated with higher DC and PT, resulting in higher surface roughness values.

A solid-state refrigerator device has the potential to overcome the use of greenhouse effect-related gases or hazardous chemicals. Most of these devices work on the basis of magnetocaloric effect (MCE). Ce(Fe_0.975Cr_0.025)₂ is an engrossing material to study MCE originating from paramagnetic (PM)–ferromagnetic (FM; second-order) transition and FM–antiferromagnetic (first-order) transition. In the present work, the MCE of Ce(Fe_0.975Cr_0.025)₂ compound, prepared in Arc melting in an argon atmosphere, has been studied. Magnetic entropy change (∆_SM) and the relative cooling power have been calculated from the M–H curves to characterize the MCE. Direct and inverse MCE are found to be linked with two different magnetic transitions in this compound.