Herein, we demonstrate a facile approach in the fabrication of one-dimensional ZnO nanowires (NWs) from the vacuum die-casting method in assistance with anodic aluminum oxide (AAO) template. The ...casting method enables molten Zn to embed uniformly over the AAO nanomould under high pressure and temperature of 500 °C. Besides, the significant influence of the oxidation time and temperature stimulates the ZnO NWs growth inside the AAO nanochannels. The oxidation in the nanochannels was profoundly controlled by the inward diffusion of oxygen atoms and the ZnO grows perpendicular towards the surface which obeys the parabolic law. The TEM and XRD results revealed the ZnO wurtzite crystalline structure with preferential orientation along the c-axis. The relationship between ZnO geometry and function of oxidation parameters is demonstrated by microscopic and spectroscopic analysis. The obtained NWs from the chemical etching process resulted in high crystalline, homogeneous, and high-aspect ratio ZnO NWs in relationship with the AAO pore dimension. Further, the as-prepared ZnO NWs electrical properties were measured in a four-electrode system through the single nanowire device fabricated by FIB. The obtained current-voltage characteristic curves exhibited hysterias loop in consequence with the space charge limited current effect of ZnO NW, which confirms its potential to be used in practical electronic applications.
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•A facile synthesis of ZnO nanowires using vacuum die-casting method in assistance with anodic aluminum oxide (AAO) template.•Fabrication of single ZnO NW device through Focused ion Beam for electrical property determination.•The proposed ZnO NWs reveals the high purity and homogeneity to be used for potential electronic applications.
Herein, a systematic study was carried out to investigate the effect of wall thickness (2, 4, 6, 8 mm) and intensification pressure (65, 80, 95 MPa) on the microstructures and mechanical properties ...of AlSi7-SiC composites fabricated by the vacuum-assisted high-pressure die casting process. The results revealed that the pore's number initially decreased with the increase of wall thickness, followed by a gradual increase, and the pore's type changed from gas pore to shrinkage pore and concentrated in the central region of the sample. When the intensification pressure increased, the distribution of SiC particles and eutectic Si became more uniform, and the porosities of samples with different wall thicknesses decreased significantly. Furthermore, the change in tensile strength remained consistent with the porosity's variation, while samples' elongation increased with the increase of wall thickness. The sample with a wall thickness of 4 mm under an intensification pressure of 95 MPa obtained the maximum tensile strength of 298 MPa, increased by 52.8% compared with AlSi7-SiC composites fabricated by squeeze casting.
Graphene oxide (GO) has been a prized material for fabricating separation membranes due to its immense potential and unique chemistry. Despite the academic focus on GO, the adoption of GO membranes ...in industry remains elusive. One of the challenges at hand for commercializing GO membranes lies with large-scale production techniques. Fortunately, emerging studies have acknowledged this issue, where many have aimed to deliver insights into scalable approaches showing potential to be employed in the commercial domain. The current review highlights eight physical methods for GO membrane fabrication. Based on batch-unit or continuous fabrication, we have further classified the techniques into five small-scale (vacuum filtration, pressure-assisted filtration, spin coating, dip coating, drop-casting) and three large-scale (spray coating, bar/doctor blade coating, slot die coating) approaches. The continuous nature of the large-scale approach implies that the GO membranes prepared by this method are less restricted by the equipment's dimensions but rather the availability of the material, whereas membranes yielded by small-scale methods are predominately limited by the size of the fabrication device. The current review aims to serve as an initial reference to provide a technical overview of preparing GO membranes. We further aim to shift the focus of the audience towards scalable processes and their prospect, which will facilitate the commercialization of GO membranes.
Forming complex geometries using the casting process is a big challenge for bulk metallic glasses (BMGs), because of a lack of time of the window for shaping under the required high cooling rate. In ...this work, we open an approach named the "entire process vacuum high pressure die casting" (EPV-HPDC), which delivers the ability to fill die with molten metal in milliseconds, and create solidification under high pressure. Based on this process, various Zr-based BMGs were prepared by using industrial grade raw material. The results indicate that the EPV-HPDC process is feasible to produce a glassy structure for most Zr-based BMGs, with a size of 3 mm × 10 mm and with a high strength. In addition, it has been found that EPV-HPDC process allows complex industrial BMG parts, some of which are hard to be formed by any other metal processes, to be net shaped precisely. The BMG components prepared by the EVP-HPDC process possess the advantages of dimensional accuracy, efficiency, and cost compared with the ones formed by other methods. The EVP-HPDC process paves the way for the large-scale application of BMGs.
The microstructure and tensile properties of a vacuum-assist high-pressure die casting (HPDC) Mg-3.0Nd-0.3Zn-0.6 Zr alloy and the effect of runner design on the externally solidified crystals (ESCs) ...were investigated. The microstructure of the alloy mainly comprised ESCs (large primary α-Mg grains) formed in the chamber, small primary α-Mg grains crystalized in the cavity, divorced eutectic Mg12Nd and a small amount of Mg12(NdxZn1-x) or Mg12(NdxZnyZr1-x-y) phases in the region near the shrinkage. The average ESCs grain size decreased as the distance from the center increased remarkably. The employment of ESCs collector contributed to the depression of ESCs grain size, particularly in center region. On the contrary, the grain size of small primary α-Mg has overall slightly downward trend from center to skin region, and the size difference was small. The employment of an ESCs collector effectively decreased the number and size of the ESCs, and accordingly both strength and elongation of the alloy were improved. This specially design ESCs collector improve the runner system and optimize the mold design. The elongation of the alloy approached 10%.
The absolute pressure strongly affects the porosity and mechanical properties of castings produced by vacuum high-pressure die casting (V-HPDC) technology. The pore size, quantity and distribution of ...AlSi9Cu3 samples under three absolute pressures were evaluated by X-ray tomography and optical and electron microscopy. The paper presents an elaboration the stress concentration mechanism of pores affecting the tensile properties. According to a mathematical analysis of a sample under uniaxial stress, the greater the radius of the pore, the higher the stress value is at the pore perimeter. When the absolute pressure drops from 1013 mbar to 100 mbar, the porosity decreases from 6.8% to 2.8%, and the pore number and mean size decreases. In tensile tests, the pore sizes of the fracture surface decrease with decreasing absolute pressure, and the pore distribution becomes uniform. The tensile properties and extensibility of the sample are improved, and the microscopic fracture surface of the sample changes from cleavage fracture to quasi-cleavage fracture. The number, size and distribution of pores in die casting collectively affect the properties of the sample. Large-size or complex pores or pores with concentrated distributions produce large stress concentrations, decreasing the strength of the metal.
High pressure die casting copper is used to produce rotors for induction motors to improve efficiency. Experiments were carried out for a special “step-shape” casting with different step thicknesses. ...Based on the measured temperature inside the die, the interfacial heat transfer coefficient (IHTC) at the metal/die interface during vacuum die casting was evaluated by solving the inverse problem. The IHTC peak value was 4.5×10
3
–11×10
3
W·m
−2
·K
−1
under the basic operation condition. The influences of casting pressure, fast shot speed, pouring temperature and initial die surface temperature on the IHTC peak values were investigated. Results show that a greater casting pressure and faster shot speed could only increase the IHTC peak values at the location close to the ingate. An increase of pouring temperature and/or initial die surface temperature significantly increases the IHTC peak values.
With an inherent lowest density and distinct solubility with enhanced mechanical behavior reason, the magnesium alloy composite is extensively used in the auto and aero sectors. The processing of ...magnesium alloy found micro‐cracks and voids between the oxidation spot, which fails properties. Through the sulfur hexafluoride (SF6) atmosphere, the AZ91D alloy hybrid nanocomposites are synthesized with 10 wt% alumina (Al2O3) and 0, 3, 6, and 9 wt% of silicon carbide (SiC) nanoparticles via a liquid state process with 400 rpm stir speed followed by vacuum die casting. The effect of SiC actions on physical behavior, microstructural formation, and mechanical properties of AZ91D/10 wt%Al2O3, AZ91D/10 wt%Al2O3/3 wt% SiC, AZ91D/10 wt% Al2O3/6 wt% SiC, and AZ91D/10 wt% Al2O3/9 wt% SiC composites are studied and its results compared with cast AZ91D alloy. Due to the actions of SiC in AZ91D/10 wt%Al2O3, the composite density conforms to the rule of mixture, and the void and micro‐cracks are limited (less than 1%) by the impact of the casting process, as evidenced in the microstructural illustration. An effect of 10 wt% Al2O3 and 9 wt% SiC contents in AZ91D facilitates maximum tensile strength of 181 MPa, improved elongation percentage of 2.2%, optimum hardness of 85HV, and superior impact toughness of 21.8 J/mm2, which is higher than the all other compositions.
In order to reduce distortion after heat treatment, we investigated high vacuum die casting samples of Al-Si-Mn-Mg-Cr-Cu alloy after T6 tempering by solutionizing at low temperature. The distortion ...caused by water quenching (W. Q.) was larger than that by air quenching (A. Q.), and decreased with decreasing solutionizing temperature. We successfully reduced distortion by attaching a stainless steel tool to the die cast sample. In this report, the distortion of the sample after T6 tempering was the smallest when solutionizing (440℃-3 hour) was carried out in A. Q. and when the tool for reducing distortion was used. The elongation and the 0.2% yield strength of this sample were 16.4% and 139MPa. The microstructure of the sample at low temperature indicated that eutectic Si phase was spheroidized and the elongation of the sample was greater than the as cast sample. The quantitative analysis results of the α Al phase of the sample showed that most of the Mg in the alloy had solidified into the α Al phase. Si precipitation was also seen in low temperature solutionizing. The iron compounds of the samples were composed of Al, Si, Fe, Mn, Cr and Cu. Comparison of the 5 mm thickness sample with 3 mm thickness sample indicated that the 0.2% yield strength difference was less when T6 tempering was carried out by solutionizing at a low temperature compared to when as cast.
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