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Effect of Laser Beam Conditioning on Fabrication of Micro-Channels in Al <sub/>2</sub> O <sub/>3</sub> Bio-ceramics Using Nd:YAG Laser
摘要： In the present study, laser micro-milling tests were carried out to fabricate micro-channels on Alumina bio-ceramics (Al2O3), using a Q-Switched 30W Nd:YAG pulsed laser. A systematic approach based on a full factorial Design of Experiment (DoE) has been successfully applied with the aim to detect which and how the key input laser process parameters affect the channel dimensional accuracy. The examined process parameters were the laser beam scanning speed, the pulse frequency and the pulse intensity. Optical microscope was used to analyze the channel geometries responses (i.e. channel's top width, bottom width, depth, and taper wall angle). Moreover, mathematical models for predicting the micro-channel geometries are successfully proposed for controlled micro-milling of micro-channels in Al2O3. Results reveal that, the change of scanning speed and laser intensity significantly affected the ablated channel’s geometries. Further it is observed that the channel depth and width increase linearly with increasing of laser intensity and decreasing of scanning speed and not much affected by changing of pulse frequency. Finally, the experimental results bear a good agreement with the proposed prediction models.
关键词： micro-channels,Nd:YAG laser,Al2O3 bio-ceramics,Design of Experiment,Laser micro-milling
更新于2025-09-23 15:21:01
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Preparation method and underlying mechanism of MWCNTs/Ti6Al4V nanocomposite powder for selective laser melting additive manufacturing
摘要： The fabrication of high-performance metal matrix nanocomposites is a new development direction in laser additive manufacturing (AM); however, the unique localized line-by-line and layer-by-layer forming process of AM has special requirements on the applicable powder materials for AM. The feedstock powder preparation is an important factor in laser AM, especially the CNTs/metal nanocomposite powder for selective laser melting (SLM) due to the agglomeration of the CNTs. This work focused on the preparation of multi-walled carbon nanotubes/Ti6Al4V (MWCNTs/TC4) nanocomposite powder for laser AM by a planetary ball-milling (PBM). The effect of ball-milling time on the characteristics of nanocomposite powder was studied and the underlying physical mechanism for powder preparation was disclosed. Three nanocomposite powders with milling time of 2 h, 4 h and 16 h were used for SLM processing to determine the optimal nanocomposite powders. The results showed that although the MWCNTs were dispersed uniformly in the matrix powder at increased milling time, severely plastic deformation of nanocomposite powder occurred with loss of its spherical shape. It was concluded that a ball-milling time of 4 h at a speed of 300 rpm was determined to achieve optimal nanocomposite powder for SLM. SLM processing of the nanocomposite powder demonstrated a smooth laser-powder interaction, yielding good metallurgical bonding of scanning tracks with previous tracks and relatively flat surface of samples. This work provided the significant reference to prepare high quality CNTs/metal nanocomposite powder for SLM, which has great potentials to fabricate high-performance metal matrix nanocomposite.
关键词： Planetary ball milling,Selective laser melting,Ti6Al4V (TC4) powder,Multi-walled carbon nanotubes (MWCNTs),Powder characteristics
更新于2025-09-23 15:19:57
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Investigating Various Permutations of Copper Iodide/FeCu Tandem Materials as Electrodes for Dye-Sensitized Solar Cells with a Natural Dye
摘要： This work presents the synthesis and deposition of CuI and FeCu materials on copper substrates for dye-sensitized solar cell applications. FeCu is a metastable alloy of iron and copper powders and possesses good optical and intrinsic magnetic properties. Coupled with copper iodide as tandem layers, the deposition of these two materials was permutated over a pure copper substrate, characterized and then tested within a solar cell. The cell was sensitized with a natural dye extracted from a local desert plant (Calotropis Gigantea) and operated with an iodine/triiodide electrolyte. The results show that the best layer arrangement was Cu/FeCu/CuI, which gave an efficiency of around 0.763% (compared to 0.196% from reported cells in the literature using a natural sensitizer).
关键词： natural sensitizers,copper iodine,FeCu alloys,dye-sensitized solar cells,Calotropis Gigantea,ball milling
更新于2025-09-23 15:19:57
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Effect of tungsten doping on structural and optical properties of rutile TiO2 and band gap narrowing
摘要： Pure and W doped nanocrystalline rutile TiO2 samples were synthesized using high energy ball milling process. Rietveld refinement results of X-ray diffraction data confirmed that pure sample exhibited rutile TiO2 phase whereas doped samples contained both rutile TiO2 and a secondary Ti0.54W0.46O2 phase. Different models of Williamson–Hall method were employed to evaluate crystallite size and strain in the samples. The crystallite size was found to decrease from 50 to 47 nm with increase in the dopant concentration. The pure TiO2 exhibited tensile microstrain which became compressive and increased upon doping. A blue shift in A1g Raman mode with doping of W also indicated the increase in the compressive strain. The HR-TEM images also confirmed the presence of higher strain in doped samples compared to un-doped sample. The observed decrease in band gap from 3 to 2.83 eV with dopant concentration, as calculated from UV–vis spectroscopy data, may be attributed to the increased strain. The decrease in the intensity of photoluminescence emission indicated the increase in number of defects and oxygen vacancies with increasing dopant concentration. This is further, supported by the rise in Urbach energy, a signature of increased number of defects in doped samples. This study shows that the dopant induced strain plays significant role in band gap narrowing.
关键词： Strain,Peak profile analysis,Band gap narrowing,Rutile TiO2 nanoparticles,High energy ball milling
更新于2025-09-19 17:15:36
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The mechanochemical synthesis of PbTe nanostructures: following the Ostwald ripening effect during milling
摘要： A fundamental understanding of the Ostwald ripening effect (ORE) during the mechanochemical synthesis of PbTe nanostructures is presented. The ripening process involves the coarsening of larger particles from those of smaller size; this phenomenon was systematically evaluated at different stages of milling by microscopy analyses (AFM, TEM, STEM and HRTEM). At the early stage of milling, smaller particles and quantum dots are eventually dissolved to lower the total energy associated with their surfaces. The ripening process – during milling – involves short-range mass transfer among particles. HRTEM analyses allowed us to identify that coarsening occurs by thermo-mechanically activated cooperative mechanisms. The detachment of the atoms from smaller particles to form bigger ones plays a major role in the particle coarsening. It was found that the coarsening process was not limited to crystalline nanostructures; so grain boundaries, edge dislocations and boundaries among crystalline and amorphous phases also play an important role to determine how species migration contributes to generate coarse particles. Those serve as sites for inducing coarsening in an equivalent way as surfaces do. Secondary ion mass spectrometry and elemental chemical mapping (EDX-STEM) revealed that both the purity and the chemical homogeneity of the PbTe nanostructures are prominent features of this material. Additionally, a direct band gap enhancement (780 nm) compared to bulk PbTe (3859 nm) was detected. It occurred due to the quantum confinement effect, lattice imperfections and even surface properties of the nanostructures. It is important to point out that the whole optical behaviour of the PbTe nanostructures was dependent upon the embedded nanoparticles and quantum dots in the clusters and coarse particles ranging from 15 nm to 35 nm.
关键词： PbTe nanostructures,microscopy analyses,quantum confinement effect,mechanochemical synthesis,Ostwald ripening effect,high-energy milling
更新于2025-09-19 17:15:36
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Efficient Luminescence of Sr2Si5N8:Eu2+ nanophosphor and its film applications to LED and Solar cell as a downconverter
摘要： Here we present the synthesis of the efficient nanophosphor Sr2Si5N8:Eu2+ (D50 = 144 nm) by a simple milling approach, its strong Rayleigh scattering, and its film applications to white LED and silicon solar cell as a downshifting medium. The final nanophosphor product showed the quantum efficiency comparable to the bulk phosphor which is, to our knowledge, the highest record of nitride nanophosphors. Especially the nanophosphor showed the more tail emission at the shorter-wavelength side of the emission spectrum and the faster thermal quenching with the more spectral broadening along with the temperature due to Rayleigh scattering. Also the lowering in the excitation spectrum was observed due to lower absorbance. Finally, the nanophosphor-dispersed polyvinyl alcohol (PVA) film was made, and its applications to white LED and silicon solar cell as a downshifting medium demonstrated that it gave the high color rendering property in white LED in spite of still lower luminous efficiency, and it caused the increase in efficiency of silicon solar cell.
关键词： nanophosphor,white LED,milling,downconverter,solar cell,Sr2Si5N8:Eu2+
更新于2025-09-19 17:13:59
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A Non-Isolated Buck-Boost DC-DC Converter with Continuous Input Current for Photovoltaic Applications
摘要： High-power grinding mills are used in the cement and mining industries to crush clinker or copper ore and grind these materials to fine powder. The multi-megawatt speed-controlled mill drives operate at a very low angular speed. Synchronous motors with a high number of pole pairs are used as the prime movers. They are traditionally fed by load-commutated thyristorized cycloconverters. These are prone to failure modes that can lead to excessive torque pulsations and high overcurrents. The huge stator, which was built as a separate ring-shaped structure around the tubular mill, may then get mechanically displaced, and the operation of the plant is interrupted. A novel and reliable direct drive uses a voltage source inverter that operates at the unity power factor for increased efficiency. Synchronous optimal pulsewidth modulation ensures a low harmonic current distortion and reduced switching losses at a very low switching frequency. The optimization of the pulse patterns takes the anisotropic magnetic properties of a separately excited synchronous motor into account. The implementation in a 23-MW semiautonomous grinding mill installed in a Zambian copper mine is intended.
关键词： Alternators,pulse width modulation inverters,gradient methods,ball milling,software algorithms,variable speed drives,Fourier transform
更新于2025-09-19 17:13:59
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Effects of Milling Time, Zirconia Addition, and Storage Environment on the Radiopacity Performance of Mechanically Milled Bi2O3/ZrO2 Composite Powders
摘要： Mineral trioxide aggregate (MTA) typically consists of Portland cement (75 wt.%), bismuth oxide (20 wt.%), and gypsum (5 wt.%) and is commonly used as endodontic cement. Bismuth oxide serving as the radiopacifying material reveals the canal filling effect after clinical treatment. In the present study, bismuth/zirconium oxide composite powder was prepared by high energy ball milling of (Bi2O3)100?x (ZrO2)x (x = 5, 10, 15, and 20 wt.%) powder mixture and used as the radiopacifiers within MTA. The crystalline phases of the as-milled powders were examined by the X-ray diffraction technique. The radiopacities of MTA-like cements prepared by using as-milled composite powders (at various milling stages or different amount of zirconia addition) were examined. In addition, the stability of the as-milled powders stored in an ambient environment, an electronic dry box, or a glove box was investigated. The experimental results show that the as-milled powder exhibited the starting powder phases of Bi2O3 and ZrO2 and the newly formed δ-Bi7.38Zr0.62O2.31 phase. The longer the milling time or the larger the amount of the zirconia addition, the higher the percentage of the δ-Bi7.38Zr0.62O2.31 phase in the composite powder. All the MTA-like cements prepared by the as-milled powder exhibited a radiopacity higher than 4 mmAl that is better than the 3 mmAl ISO standard requirement. The 30 min as-milled (Bi2O3)95(ZrO2)5 composite powder exhibited a radiopacity of 5.82 ± 0.33 mmAl and degraded significantly in the ambient environment. However, storing under an oxygen- and humidity-controlled glove box can prolong a high radiopacity performance. The radiopacity was 5.76 ± 0.08 mmAl after 28 days in a glove box that was statistically the same as the original composite powder.
关键词： mineral trioxide aggregates,radiopacity,bismuth oxide,mechanical milling,zirconia
更新于2025-09-19 17:13:59
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Size-controlled MoS<sub>2 </sub>nanosheet through ball milling exfoliation: parameter optimization, structural characterization and electrocatalytic application
摘要： Unique properties and potential applications of 2D materials draw much attention for mass production of thin-layer 2D materials. Ball milling exfoliation of 2D materials has been rarely used, in spite of a promising dry phase production method, because of the superficial information in the mechanism and the effect of the operating parameters on the yield, size and thickness. Here, we investigate systematically the ball milling operating parameters in the exfoliation of bulk MoS2 in the presence of sodium cholate (SC) as an exfoliant. The yield and dimensions of the exfoliated MoS2 nanosheet were monitored by changing the parameters such as the weight ratio of bulk MoS2 and SC (SC/MoS2), the filling ratio in the volume of milling ball and container (!), milling ball size (dB), milling revolution speed (nR), and initial mass of bulk MoS2 (mMoS2). The yield of exfoliation is found to be 95% at the optimum ball milling conditions (SC/MoS2 = 0.75, ! = 50%, mMoS2 = 0.20 g). In addition, yield and size of the exfoliated MoS2 were controlled by the conditions of the ball milling. As for the evaluation of size and thickness of the ball-milled MoS2 powder with less than 30% difference from those determined by the well-known absorption method. Finally, the size and thickness of the MoS2 nanosheets prepared by ball milling exfoliation were correlated with their electrocatalytic and photoelectrocatalytic activities.
关键词： electrocatalyst,sodium cholate,nanosheet,exfoliation,Ball milling,molybdenum disulfide,XRD
更新于2025-09-19 17:13:59
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Investigation on laser-induced oxidation assisted micro-milling of Inconel 718
摘要： Poor surface quality and rapid tool wear are the main problems in micro-cutting of Inconel 718. In this study, a novel hybrid machining method named laser-induced oxidation assisted micro-milling is proposed to solve the aforementioned problems. A loose oxide layer and a relatively flat sublayer are formed on the material after laser irradiation. Under optimized laser parameters with a scanning speed of 1 mm/s and an average laser power of 4.5 W, the thicknesses of the oxide layer and the sublayer are 24 and 18 mm, respectively. The influence of cutting parameters on milling force, surface roughness, surface quality, and top burr size is studied in detail. Cutting force and thrust force in the proposed hybrid machining process are lower than those in the conventional micro-milling. Results show that for the investigated range of parameters, the optimal feed per tooth and depth of cut in the hybrid process are 3 mm/z and 3 mm, respectively. When using the optimal parameters, the surface roughness of the machined slot bottom is 108.5 nm. The top burr size on the up-milling side and the down-milling side is 26.8 and 36.2 mm, respectively. In addition, the tool wear mechanism is coating delamination in hybrid process, whereas chipping, coating delamination, tool nose breakage, and adhesion are the main tool wear mechanism in the conventional micro-milling. For the same amount of material removal, the proposed hybrid process can decrease the tool wear and enhance the service life of the micro-end mill as compared to conventional micro-milling.
关键词： micro-milling,Inconel 718,surface quality,tool wear,laser-induced oxidation
更新于2025-09-19 17:13:59