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Electrochemical synthesis of Al–Al <sub/>2</sub> O <sub/>3</sub> composites for selective laser melting
摘要： Novel electrochemical method for obtaining Al–Al2O3 composites for selective laser melting technology has been studied. The electrochemical cell with the flexible cathode and the anode device has been developed. The initial aluminum powder was characterized: aluminum content was more than 99.8 wt %; the average particle diameter was ～40 μm. Oxidized aluminum powder was studied: γ–Al2O3 in the surface oxide layer form was detected; the increase in the particle diameter was 10–20 μm. Electrochemical oxidation technological parameters have been studied. At 0.1 A cm cathodic current density electrolysis duration was 220 min, 24 V voltage along with 80 ° C electrolyte temperature reached. The oxidation mechanism of aluminum particles has been developed. The increase in the surface oxide layer occurred, and this led to an increase in voltage. The 3D object from the oxidized aluminum powder was synthesized by selective laser melting method. The 3D object was perfectly sintered and did not crumble. Good reinforcements distribution in the volume of the synthesized 3D object has been achieved.
关键词： reinforcements,anodic oxidation,electrolysis,aluminum–alumina composites,selective laser melting
更新于2025-11-21 11:24:58
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Effect of thermal stress induced by femtosecond laser on fracture toughness of fine-grained alumina
摘要： The ultra-sharp V-notch with tip radius smaller than 0.5 μm was cut by femtosecond laser on the fine-grained alumina ceramic bars to measure the fracture toughness by single-edge V-notched beam (SEVNB) method. In order to relieve the effect of thermal stresses induced by laser on fracture toughness testing, the samples with V-notch were annealed before measurement. The morphologies of the notch tip were analyzed by SEM and micro-Raman spectra. Results reveal that the fracture toughness value of this fine-grained alumina with thermal stresses on the V-notch is equal to that after annealing, and the effect of thermal stresses induced by laser on the fracture toughness can be ignored.
关键词： SEVNB,Fracture toughness,Laser processing,Thermal stress,Alumina
更新于2025-11-21 11:18:25
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Cr3+ doped nanoporous anodic alumina: Facile microwave assisted doping to realize nanoporous ruby and phase dependent photoluminescence
摘要： Microwave-assisted solution technique (MAST) was used for the homogeneous doping of Cr3+ in nanoporous anodic alumina (NAA) which when heat-treated transforms into nanoporous ruby. The rise in annealing temperature led to the phase transition in the sequence: amorphous- δ- θ- α-alumina as evidenced by XRD. The dopant was homogenously distributed as seen from the elemental mapping and the Cr3+ content was 0.5 at%. Di?use re?ectance spectroscopy (DRS) displayed the characteristic blue and green absorption bands and the color-tone varied from light-green at 700 °C to the pink appearance at 1350 °C owing to the dopant di?usion. Two broad photoluminescence (PL) excitation bands centered at ～550 nm and ～400 nm were observed whose intensity increased with the annealing temperature. All the alumina phases exhibited characteristic phase dependent PL showing variation in the luminescence intensity and peak position. The characteristic R-line for α-phase was intense and observed at 694 nm with 4 m s lifetime in accordance with that expected for Ruby. Crystal ?eld parameters were obtained from the PL excitation spectra and Dq/B values were found to be higher than 2.3 for all the phases of NAA con?rming the presence of Cr3+ ions in the strong crystal ?eld. With annealing, the CIE coordinates moved towards the red region. The presented work shows a promising easy and inexpensive method for dopant incorporation into alumina and explores the understanding of phase-dependent emission of Cr3+ doped NAA for their potential applications in the areas of nano-optics and composite luminescent nanomaterials.
关键词： Nanoporous anodic alumina,Cr3+ doping,Photoluminescence,Phase transition
更新于2025-11-21 11:18:25
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Effect of counter-surface chemistry on defect-free material removal of monocrystalline silicon
摘要： To bring light on material removal remains fundamental for promoting the advancement of nanotechnology. In this study, nanoscratching test on silicon surface against Al2O3 microsphere was performed using an atomic force microscope, and the material removal by SiO2 microsphere sliding was taken as a comparison. It was found that nanochannels can be produced on silicon surface by Al2O3 microsphere scratching under much lower contact pressure than the yield limit for plastic deformation, which can be ascribed to water-participated tribochemical reactions. The tribochemical removal was verified by high resolution transmission electron microscope (HRTEM) detection. Further analysis indicates that the tribochemical reactions on silicon surface are strongly affected by the counter-surface chemistry. It is noted that counter-surface chemistry influences the tribochemical reactions via altering the activation energy barrier for forming bonding bridge, and has little influence on decreasing the activation energy barrier for the rupture of Si-Si backbonds in silicon substrate. Compared with SiO2 tip, Al2O3 tip has longer working life span, and the nanochannels fabricated by Al2O3 tip under the same processing conditions exhibit better uniformity even in KOH solution. The results provide useful knowledge for chemical mechanical polishing and tip-based nanomanufacturing processes, and shed new light for enriching the basic theory of nanotribology.
关键词： Tribochemical removal,Nanoscratching,Counter-surface chemistry,Alumina/silicon pair
更新于2025-11-14 17:03:37
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Stacked Nanoporous Anodic Alumina Gradient-Index Filters with Tunable Multispectral Photonic Stopbands as Sensing Platforms
摘要： This study presents the development and optical engineering of stacked nanoporous anodic alumina gradient-index (NAA-GIFs) filters with tunable multi-spectral photonic stopbands for sensing applications. The structure of these photonic crystal (PC) is formed by stacked layers of NAA produced with sinusoidally modified effective medium. The progressive modification of the sinusoidal period during the anodization process enables the generation and precise tuning of the characteristic photonic stopbands (PSB) (i.e. one per sinusoidal period in the anodization profile) of these PC structures. Four types of NAA-GIFs featuring three distinctive PSBs positioned within the visible spectral region are developed. The sensitivity of the effective medium of these NAA-GIFs is systematically assessed by measuring spectral shifts in the characteristic PSBs upon infiltration of their nanoporous structure with analytical solutions of D-glucose with several concentrations (0.025 – 1 M). This study provides new insights into the intrinsic relationship between the nanoporous architecture of these PCs and their optical properties, generating opportunities to fabricate advanced optical sensing systems for high-throughput and multiplexed detection of analytes in a single sensing platform.
关键词： nanoporous anodic alumina,sensing platforms,stacked,multispectral bands,photonic crystals,gradient index filters
更新于2025-09-23 15:23:52
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Fabrication of thin-film spherical anodic alumina oxide templates using a superimposed nano-micro structure
摘要： Compared to the single-scale planar anodic aluminum oxide (AAO) film, the multi-scale hierarchical AAO structures can have a better performance due to the larger surface area. The conventional multi-scale AAO structure on a micro-pattern surface was fabricated using time-consuming lithography and etching process at high cost. In this article, the 3D porous AAO films with nanopores of 35~45 nm in diameter have been achieved on the surface of silica micro beads of 2 μm in diameter. The superimposed nano-micro structure was fabricated using hybrid-pulse anodizing the sputtered Al film on beads with a period of negative potential to dissipate Joule heating at room temperature. The 3D AAO-on-beads structure provides a large-surface-area substrate for enhancing the sputtered TiO2 photocatalysis. The photocatalysis on the superimposed nano-micro structures can exhibit a high performance with the MB concentration of 30% after 15 hr photo-degradation.
关键词： AAO,nano-microstructures,anodic aluminum oxide,nanoporus alumina,micro bead
更新于2025-09-23 15:23:52
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Comparative investigation into effects of ZrO <sub/>2</sub> and Al <sub/>2</sub> O <sub/>3</sub> addition in fluorapatite laser-clad composite coatings on Ti6Al4V alloy
摘要： Composite coatings consisting of fluorapatite mixed with 20 wt% yttria (3 mol%) stabilized cubic phase zirconia (c-ZrO2, 3Y-TZP) or 20 wt% alumina (a-Al2O3) were deposited on Ti6Al4V substrates using a Nd:YAG laser cladding system. The interface morphology, phase composition, micro-hardness and biological properties of the two coatings were examined and compared. The results showed that the fluorapatite/Al2O3 specimen underwent a greater inter-diffusion at the interface between the coating layer and the transition layer than the fluorapatite/ZrO2 specimen. During the cladding process, the ZrO2 and Al2O3 components of the coating were completely decomposed or underwent phase transformation. In addition, the fluorapatite was partially decomposed. For both specimens, the coating layers contained fluorapatite, CaF2 and CaTiO3 phases. The coating layer of the fluorapatite/ZrO2 specimen additionally contained TTCP, CaO, CaZrO3 and m-ZrO2 (monoclinic phase), while that of the fluorapatite/Al2O3 specimen contained b-TCP, CaAl2O4 and u-Al2O3. The average micro-hardness of the fluorapatite/ZrO2 coating layer (1300 HV) was approximately 200 HV higher than that of the fluorapatite/Al2O3 coating layer (1100 HV). Both specimens generated dense bone-like apatite following immersion in simulated body fluid for 3 days. In other words, both specimens had a good in vitro bioactivity. However, the fluorapatite/ZrO2 specimen showed a better initial attachment and spread of osteoblast-like osteosarcoma MG63 cells than the fluorapatite/Al2O3 specimen in in vitro biocompatibility tests performed for 24 h.
关键词： Ti6Al4V,bioactivity,biocompatibility,alumina,laser cladding,Fluorapatite,zirconia
更新于2025-09-23 15:23:52
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Effect of nitrogen gas pressure during heat treatment on the morphology of silicon nitride fibers synthesized by carbothermal nitridation
摘要： The effects of N2 gas pressure on the diameter and morphology of Si3N4 fibers obtained via carbothermal nitridation were investigated. Sol–gel-derived precursors containing a silica and carbon mixture were placed in an Al2O3 crucible and heat-treated under various N2 pressures from 0.1 to 0.5 MPa at 1500oC. The heat-treated samples were characterized by X-ray diffraction (XRD), a scanning electron microscope (SEM) coupled with an energy dispersion X-ray (EDX) spectrometer, and transmission electron microscopy (TEM). Various nitride fibers with α- and β-phase Si3N4 were formed. The fiber diameter decreased with increases in N2 pressure, and nanometer-scale fibers of around 200 nm in diameter were obtained at a N2 pressure of 0.5 MPa. It was found that silicon oxynitride Si2N2O or its Al-doped form, O′-SiAlON, was produced due to high N2 pressure and doping with Al originating from the Al2O3 crucible. This oxynitride was considered to act as a template for Si3N4 fiber growth by the direct phase transformation mechanism. It was shown that the diameter of the Si3N4 fibers decreased for two reasons: decreased partial pressure of SiO gas due to high N2 pressure and increased formation of the silicon oxynitride templates.
关键词： carbothermal reduction,nanofibers,alumina,Silicon nitride
更新于2025-09-23 15:23:52
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On-chip sensor solution for hydrogen gas detection with the anodic niobium-oxide nanorod arrays
摘要： Two types of anodic niobium-oxide nanofilms were synthesized via anodization of an Al/Nb bilayer sputter-deposited onto a SiO2-coated Si wafer. Type I nanofilm was composed of a 200 nm thick NbO2 layer holding the upright-standing 650 nm long, 50 nm wide, and 70 nm spaced Nb2O5 nanorods, of 7·109 cm?2 density, whereas the Type II nanofilm had similarly long but bigger Nb2O5 nanorods, 100 nm wide, 220 nm spaced, and of 8·108 cm?2 density, aligned directly on a niobium metal without any buffering oxide layer, which was achieved for the first time. Each film was then incorporated in an advanced 3-D architecture and multilayer layout on a silicon chip comprising 33 microsensors, with variable sizes and tuned electrical characteristics, by combining the high-temperature vacuum or air annealing, sputter-deposition, and lift-off photolithography to form Pt/NiCr top electrodes and a multifunctional SiO2 interlayer, chemical etching, laser dicing, and ultrasonic wire-bonding. The proposed on-chip sensor solution allowed for a sensitive, fast, and highly selective (toward NH3 and CH4) detection of hydrogen gas. Comprehensive gas sensing tests performed for Type II nanofilm ultimately confirmed the presence of a Schottky-type sensing mechanism, the contribution, however, being substantially weaker than that due to reactions over the surface of the oxide nanorods, especially when the rods show a transition from fully to partially depleted states when interacting with H2 gas. The film formation and chip fabrication technologies may be transferable to other PAA-assisted 1-dimensional metal-oxide nanomaterials suitable for on-chip gas sensing.
关键词： niobium oxide nanorods,anodic alumina,hydrogen,Schottky barrier,anodizing,on-chip sensor
更新于2025-09-23 15:23:52
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Durability and purification performance of concrete impregnated with silicate and sprayed with photocatalytic TiO2
摘要： This paper proposes an integrated concrete surface treatment with surface enhancement via silicate impregnation and surface spraying with TiO2 (a photocatalyst). In this work, two types of silicate-based materials, sodium alumina silicate (SAS) and colloidal silica (COS) were used. Various tests were carried out to characterize the silicate properties and engineering performance of the impregnated concrete. In addition, the purification performance in concrete sprayed with TiO2 was investigated. Concrete impregnated with silicate and sprayed with TiO2 showed an improvement in the durability and mechanical performance because of the addition of the CSH gel and TiO2 barrier. After impregnation, the TiO2 applied by spraying retained good performance for the removal of acetaldehyde and methyl orange.
关键词： Sodium alumina silicate,Durability performance,Purification performance,Photocatalyst,Colloidal silica
更新于2025-09-23 15:22:29