Gas-assisted Process Research Articles

A fast and efficient Al-5Ti-1B grain refiner prepared by gas-assisted continuous casting and extrusion process

The feasibility of preparing Al-Ti-B alloy wires based on a novel technology of gas-assisted continuous casting and extrusion (GAC) was investigated. Results show that Al-5Ti-1B alloy wire with fine and uniform distribution of the second phase can be prepared by combining the fluoride salt method and the GAC process. When the wire was added into an industrial pure aluminum at 730 °C with an addition of 0.2 wt%, the pure aluminum grains could be refined into equiaxed crystals with an average size of about 140 μm by contacting time of 60 s, which showed the characteristics of rapidity and high efficiency.

Study on the Melt Rheological Characterization of Micro-Tube Gas-Assisted Extrusion Based on the Cross-Scale Viscoelastic Model.

In the micro-tube gas-assisted extrusion process, flow theories ignoring cross-scale viscoelastic variations fail to effectively characterize the rheological state of the melt. To investigate the impact of cross-scale viscoelastic variation on the quality of the micro-tube gas-assisted extrusion, a 3D multiphase flow extrusion model incorporating a double gas-assisted layer was developed. Subsequently, we modified the DCPP constitutive equations based on the cross-scale factor model. Both the traditional and gas-assisted extrusions were simulated under macroscale and cross-scale models using the Ansys Polyflow. Finally, using the established gas-assisted extrusion platform, extrusion experiments were conducted. The results indicate that, owing to the reduced melt viscosity under the cross-scale model, the deformation behavior of the melt is more pronounced than in the macroscale model. The cross-scale model's numerical results more closely match the experimental outcomes under the same parameters, thereby confirming the feasibility of the theoretical analysis and numerical simulation. Moreover, the predictive capability of the cross-scale model for the micro-tube gas-assisted extrusion is further validated through numerical and experimental analyses with varying parameters. It is demonstrated that the cross-scale viscoelastic variation is a critical factor that cannot be overlooked in the gas-assisted extrusion.

Cooling rate calculation of pure aluminum solidified during a novel gas-assisted continuous casting and extrusion process

Gas-assisted continuous casting and extrusion (GAC) process is a novel technique for the continuous preparation of non-equilibrium solidified materials. To evaluate the solidification rate of the melt during GAC, the cooling rate of pure aluminum melt solidified in the wheel groove is calculated, based on the Newtonian heat transfer model and the one-dimensional Fourier heat transfer model. Results show that the cooling rate of the melt during GAC mainly depends on the conduction heat transfer in the wheel groove and the melt thickness. When the thickness of the pure aluminum melt is between 1 and 2.5 mm, the cooling rate can reach 103–104 K s−1, which is much higher than that in CAXTEX (~10 K s−1). It means that GAC is a very effective process in the preparation of non-equilibrium solidification alloys.

Numerical and experimental studies on the influence of gas pressure on particle size during gas-assisted extrusion of tubes with embedded antibacterial particles

Abstract During the gas-assisted extrusion process of plastic tubes embedded with antibacterial particles, the particles tend to agglomerate. The dispersion effect of these agglomerates using the nozzle-pressure-difference method is significantly influenced by the gas flow state. Therefore, this study establishes the nozzle dispersion model. The gas flow state near the nozzle is simulated and analyzed by using Ansys Fluent software. Gas-assisted extrusion experiments are conducted with different nozzle inlet pressures, and the size distribution of antibacterial particles is observed by using electron microscopy. The simulation results indicate that increasing the nozzle inlet pressure enhances the dispersion effect and expands the effective dispersion area. The experimental results demonstrate that using the nozzle disperses the agglomerates into particles with a diameter of approximately 100 nm. Furthermore, the nanoparticles diameter size decreases with the increase of the inlet pressure, validating the accuracy of the numerical analysis results.

Effect of Refresh Time on XeF2 Gas-assisted FIB Milling of GaAs

Focused ion beam (FIB) machining can be used to fabricate gallium arsenide-based devices, which have a surface finish of several nanometers, and the FIB machining speed and surface finish can be greatly improved using xenon difluoride (XeF2) gas-assisted etching. Although the refresh time is one of the most important parameters in the gas-assisted etching process, its effect on the machining quality of the surface finish has rarely been studied. Therefore, in this work, we investigated the effect of the refresh time on the etching process, including the dissociation process of XeF2, the refresh time dependency of the sputter in yield under different incident angles, and the surface finish under different refresh times. The results revealed that a selective etching mechanism occurred at different refresh times. At an incidence angle of 0°, the sputtering yield increased with the refresh time and reached its maximum value at 500 ms; at an incidence angle of 30°, the sputtering yield reached its minimum value at a refresh time of 500 ms. For surface roughness, the incident angle played a more important role than the refresh time. The surface finish was slightly better at an incidence angle of 30° than at 0°. In addition, both F and Xe elements were detected in the processed area: Xe elements were evenly distributed throughout the processing area, while F elements tended to accumulate in the whole processing area. The results suggest that the optimum surface can be obtained when a larger refresh time is employed.

Numerical and Experimental Studies on the Improvement of Gas Chamber Structure during Gas-Assisted Extrusion.

In the gas-assisted extrusion process, the melt inside the die is in a low-viscosity molten state, so the flow field of the gas cushion layer has a great effect on the cross-sectional shape of the micro-tube. Therefore, this study establishes the gas distribution chamber model of the gas-assisted die. Ansys Fluent software was used to simulate the gas flow field of the gas distribution chamber. The effect of the gas chamber structure on the size of the micro-tube was analyzed by the extrusion experiment. The research shows that the velocity unevenness coefficient of the gas outlet of the single gas chamber die is 11.8%, which is higher than that of the double gas chamber die. The use of a double gas chamber die can improve the stability of the gas cushion layer and the wall thickness non-uniformity of the micro-tube, which verifies the simulation results.

Research on the wood processing method of helium-assisted laser process

In order to promote the development of environmental protection, and the usage rate of green energy utilization, a progressive, innovative laser process method employing helium assisted is proposed, which optimizes the joint cutting process under the same energy consumption. This method provides a new idea for the wood process industry. The uniqueness of this paper establishes a mathematical model to address the diffusion of helium injection and the heat transfer of the laser beam on the processed surface. From the results, it can be exhibited that the oxygen concentration reduces when the helium is injected on the processed surface. The helium could destroy the combustion-supporting conditions and decrease the combustion zone of the processed joint cutting. Thus, the carbonized area of the processed surface is reduced, which could effectively enhance the processing quality of joint cutting. Notably, the helium with injection speed forms a sweeping effect on the processed surface, which could remove parts of the carbonized particles and residues on the processed surface, as well as improve the processing quality. Comparing the traditional laser process and helium-assisted laser process, the gas-assisted laser process owns higher process quality than that of traditional laser processing and cutting. In detail, it features the advantages of smaller joint cutting width, lower surface roughness and smoother surface. Eventually, a mathematical model based on the response surface method with the evaluation criteria of the kerf width, kerf depth, and surface roughness is established to analyze the interaction of laser power, cutting speed and inert gas pressure on the response factors. Comparing the error between the predicted and experimental measurement value, and the optimized process parameters could be acquired. In this paper, the helium-assisted laser process method proposed is meaningful and encouraging, which not only obtains better processing quality, but also provides a guide for developing green industry.

Effects of gas-assisted technology on polymer micro coextrusion

Abstract In this paper, a three-dimensional viscoelastic flow model of double-layer micro coextrusion with circular cross-section was established. The simulations were carried out by the finite element method and the influence of wall slip coefficient on micro coextrusion was studied. The results show that gas-assisted technology is suitable for polymer micro coextrusion forming. The differences between the gas-assisted and conventional micro coextrusion process were compared by analyzing the distribution of melts velocity, pressure, shear rate and first normal stress difference. The research results show that in the conventional micro coextrusion process there are pressure drop, shear rate, first normal stress difference and secondary flow. And there is a gradient distribution of melts velocity. The die swell and deformation vary with the forming process parameters, and it is difficult to control the product quality. But in the gas-assisted micro coextrusion process, there is no pressure drop, shear rate, first normal stress difference and secondary flow. The velocity of polymer melts is evenly distributed and the melts are extruded in a plunger shape. The melts do not swell and deform and it is independent of forming process parameters. It is easy to ensure the products quality and the inherent problems of polymer conventional micro coextrusion are well solved.

Tailoring Mesopores and Nitrogen Groups of Carbon Nanofibers for Polysulfide Entrapment in Lithium-Sulfur Batteries.

In the current work, we combined different physical and chemical modifications of carbon nanofibers through the creation of micro-, meso-, and macro-pores as well as the incorporation of nitrogen groups in cyclic polyacrylonitrile (CPAN) using gas-assisted electrospinning and air-controlled electrospray processes. We incorporated them into electrode and interlayer in Li–Sulfur batteries. First, we controlled pore size and distributions in mesoporous carbon fibers (mpCNF) via adding polymethyl methacrylate as a sacrificial polymer to the polyacrylonitrile carbon precursor, followed by varying activation conditions. Secondly, nitrogen groups were introduced via cyclization of PAN on mesoporous carbon nanofibers (mpCPAN). We compared the synergistic effects of all these features in cathode substrate and interlayer on the performance Li–Sulfur batteries and used various characterization tools to understand them. Our results revealed that coating CPAN on both mesoporous carbon cathode and interlayer greatly enhanced the rate capability and capacity retention, leading to the capacity of 1000 mAh/g at 2 C and 1200 mAh/g at 0.5 C with the capability retention of 88% after 100 cycles. The presence of nitrogen groups and mesopores in both cathodes and interlayers resulted in more effective polysulfide confinement and also show more promise for higher loading systems.

Study on the mass and heat transfer characteristics of the drying process of spent nuclear fuel cladding with nitrogen assisted

The spent nuclear fuel cladding needs to be cooled in water for a long time before being compressed. The water attached to the solid must be dried before compressing the spent nuclear fuel cladding. In this paper, based on the heat and mass transfer process inside the porous medium, a coupled heat and mass transfer model for the nitrogen-assisted drying of the waste cladding porous medium is established. The influence of nitrogen flow rate, temperature and inlet position on the heat and mass transfer characteristics of the porous medium in the nitrogen-assisted drying of waste cladding is analyzed. The results show that the calculated results of the model are in good agreement with the experimental results. According to the temperature change on the surface of the waste cladding, the gas-assisted drying process can be divided into three stages: the initial stage of drying, the accelerated drying stage and the latter stage of drying. In addition, the nitrogen flow rate has the greatest impact on the accelerated drying stage in the drying process, and the change of the nitrogen flow rate only changes the heat transfer rate between the liquid and solid phases. Nitrogen temperature affects the drying time by changing the heat transfer coefficient between the gas and liquid phases during the drying process. The inlet position of nitrogen affects the drying time by changing the convection effect between the gas and liquid phases in the drying process. The above research provides reference for the study of the heat and mass transfer characteristics and the mechanism of the drying process in the process of nuclear fuel solid waste treatment. It can also provide an important reference for the application research of key equipment in the reprocessing of spent fuel in nuclear power plants.

Design and Integration of the Single-Lens Curved Multi-Focusing Compound Eye Camera.

Compared with a traditional optical system, the single-lens curved compound eye imaging system has superior optical performance, such as a large field of view (FOV), small size, and high portability. However, defocus and low resolution hinder the further development of single-lens curved compound eye imaging systems. In this study, the design of a nonuniform curved compound eye with multiple focal lengths was used to solve the defocus problem. A two-step gas-assisted process, which was combined with photolithography, soft photolithography, and ultraviolet curing, was proposed for fabricating the ommatidia with a large numerical aperture precisely. Ommatidia with high resolution were fabricated and arranged in five rings. Based on the imaging experimental results, it was demonstrated that the high-resolution and small-volume single-lens curved compound eye imaging system has significant advantages in large-field imaging and rapid recognition.

Computer modeling of the gas assisted injection molding process - computer simulations vs. practice

Modern computer programs for simulation of polymer processing allow to conduct numerical calculations on the movement of the injected material, not only in the classical injection molding process. It is possible to simulate non-standard injection methods, e.g. gas assisted injection process. The paper presents the results of computer simulations and real gas-assisted injection. These results were compared and the compliance of numerical calculations with the results of practical tests was assessed. It has been shown that advanced algorithms of computer simulation programs enable modeling of phenomena specific to the injection method under consideration. The ability to conduct simulations of polymer processing processes (including gas-assisted injection) allows to shorten the time of implementation of molds for production, eliminate construction errors and expanding knowledge about the course of the actual process. The work focuses on the gas-assisted injection process by filling the forming cavity entirely in the melt filling phase. Particular attention was paid to the gas channel formation process and the parameters that determine its shape and dimensions.

Non-Metal Single-Phosphorus-Atom Catalysis of Hydrogen Evolution.

Non-metal-based single-atom catalysts (SACs) offer low cost, simple synthesis methods, and effective regulation for substrates. Herein, we developed a simplified pressurized gas-assisted process, and report the first non-metal single-atom phosphorus with atomic-level dispersion on unique single-crystal Mo2 C hexagonal nanosheet arrays with a (001) plane supported by carbon sheet (SAP-Mo2 C-CS). The SAP-Mo2 C-CS is structurally stable and shows exceptional electrocatalytic activity for the hydrogen evolution reaction (HER). A so-called high-active "window" based on the active sites of P atoms and their adjacent Mo atoms gives a ΔGH* close to zero for hydrogen evolution, which is the most ideal ΔGH* reported so far. Meanwhile, the moderate d-band center value of SAP-Mo2 C-CS can be also used as an ideal standard value to evaluate the HER performance in non-metal-based SACs.

Pulse gas-assisted multi-needle electrospinning of nanofibers

Multi-needle electrospinning is an effective method to increase the productivity of nanofibers. In this paper, the number of single-needle jets was increased to further improve the production efficiency. As the traditional method for increasing the number of single-needle jets has poor controllability and persistence, we proposed a gas-assisted method to increase the yield of nanofibers. A coaxial gas auxiliary needle was designed with an intermediate shaft supplied gas and the outer shaft supplied solution. Innovatively using pulse gas to produce continuous and stable bubbles which are ruptured on the needle. The liquid film is continuously disturbed, which generates jets in the electric field, thereby increasing the number of jets of a single needle. After optimization of the single-needle gas-assisted electrospinning process, the stable spraying process of 16-pin multi-needle electrospinning has been realized. The gas-assisted electrospinning productivity was 4.7 times higher than that of without gas assistance. It provided a new idea for improving the stable production of the multi-needle electrospinning.

Reconstructing focused ion beam current density profile by iterative simulation methodology

The authors present a simulation-based methodology for reconstructing the focused ion beam current density profile using sputtering and implantation information available from transmission electron microscopy images of single beam-width lines created using a Ga+ beam on SiO2 substrate. A bi-Gaussian distribution for the ion beam was assumed. Ga+ implantation in fused silica substrate was iteratively simulated sweeping through beams of varying parameters using srim monte carlo software. The resulting lateral distribution and density of the implanted Ga were visualized and compared to the experimental implanted Ga distribution on the cross-section of a physically sputtered line. Beam simulation parameters resulting in a close match between simulated and experimental Ga+ implantation were accepted as describing the primary ion beam. The authors apply the current density distribution of reconstructed beam profile to analyze single beam-width line profiles etched with XeF2 precursor and deposited with W(CO)6 precursor. Results indicate that XeF2 gas assisted etching and W(CO)6 deposition processes were enhanced in the peripheral regions of the Ga+ ion beam which are characterized by low current densities on the order of 1.0 ×10−4 pA/nm2. A similar simulation methodology as presented here can presumably be applied to reconstruct beam current density profiles and applied to characterize gas-assisted processes for arbitrary combinations of primary ion species and gaseous precursors with suitable substrates. This methodology is directly applicable to development of industrial processes using focused ion beams for modification of semiconductor, microelectromechanical systems, microfluidic, and photonics devices.

Laser-Assisted Focused He+ Ion Beam Induced Etching with and without XeF2 Gas Assist.

Focused helium ion (He+) milling has been demonstrated as a high-resolution nanopatterning technique; however, it can be limited by its low sputter yield as well as the introduction of undesired subsurface damage. Here, we introduce pulsed laser- and gas-assisted processes to enhance the material removal rate and patterning fidelity. A pulsed laser-assisted He+ milling process is shown to enable high-resolution milling of titanium while reducing subsurface damage in situ. Gas-assisted focused ion beam induced etching (FIBIE) of Ti is also demonstrated in which the XeF2 precursor provides a chemical assist for enhanced material removal rate. Finally, a pulsed laser-assisted and gas-assisted FIBIE process is shown to increase the etch yield by ∼9× relative to the pure He+ sputtering process. These He+ induced nanopatterning techniques improve material removal rate, in comparison to standard He+ sputtering, while simultaneously decreasing subsurface damage, thus extending the applicability of the He+ probe as a nanopattering tool.

Surface Defects Control for ZnO Nanorods Synthesized Through a Gas-Assisted Hydrothermal Process

Oxygen vacancies in crystal have an important impact on the electronic properties of zinc oxide (ZnO). In this paper, ZnO nanorods with rich oxygen vacancies were prepared through a novel gas-assisted hydrothermal growth process. X-ray diffraction data showed that single-phase ZnO with the wurtzite crystal structure was obtained and the crystallite size decreased as the reaction atmosphere pressure increased. The oxygen vacancies of ZnO were confirmed using x-ray photoelectron spectroscopy and photoluminescence spectroscopy. The results showed that the concentration of oxygen vacancies could be regulated by both the atmosphere pressure and the atmosphere properties. The oxygen vacancies in ZnO samples were reduced when the pressure increase in the hydrogen reaction environment (reducing atmosphere) and the oxygen vacancies in ZnO samples were increased when the pressure increased in the oxygen reaction environment (oxidizing atmosphere).

Determination of Optimum Process Parameters in Gas-Assisted Injection Molding

With finite element analysis software Moldflow, numerical simulation and studies about FM truck roof handle were conducted on gas-assisted injection molding process. The influences of melt pre-injection shot, gas pressure, delay time and melt temperature were observed by using multi-factor orthogonal experimental method. According to the analysis of the factors' impact on evaluation index, the optimized parameter combination is obtained. Therefore the optimization design of technological parameters is done. The results show that during the gas-assisted injection molding, optimum pre-injection shot is 94%,gas pressure is 15MPa,delay time is 0.5s,melt temperature is 240 oC. This study provided a more practical approach for the gas-assisted injection molding process optimization.

Aluminum Nanocomposites via Gas Assisted Processing

Aluminum nitride (AlN) possesses superior thermal and electrical properties and is an ideal candidate for high-temperature, as well as for packaging and optoelectronic applications. Aluminum based composites reinforced with AlN have been manufactured via an in situ gas-assisted process, where nitrogen gas is injected in the molten aluminum at 1273-1323 K. The process is carried out in an inert atmosphere in order to avoid oxygen contamination. Addition of Mg lowered the oxygen content in the melt by forming MgO and thus favoring the nitridation reaction. The reinforcement phase has been detected throughout the casting in two morphologies: pockets of powders and embedded in the microstructure. Particle size formed in the matrix varied from 1- 3 µm to sub-micron scale.

Processing of Lightweight Metal Matrix Composites via <i>In Situ</i> Gas/Liquid Reaction

Aluminum nitride (AlN) possesses superior thermal and electrical properties and is an ideal candidate for high-temperature, as well as for packaging and optoelectronic applications. Aluminum based composites reinforced with AlN have been manufactured via an in situ gas-assisted process, where a nitrogen-bearing gas is injected in the molten aluminum at 1273-1323 K. The process is carried out in an inert atmosphere in order to avoid oxygen contamination. Addition of Mg lowered the oxygen content in the melt by forming MgO and thus favoring the nitridation reaction. Particle size formed in the matrix varied from 1- 3 μm to sub-micron scale depending on the gas injection time. Longer bubbling times give rise to improved reinforcement dispersion. Addition of Si is detrimental for the synthesis of AlN; Mg2Si phase precipitates, replacing the formation of MgO and hindering the nitridation reaction. The challenges of controlling the kinetics are discussed.