Effect Of Vacuum Conditions Research Articles

Comparative Study of the Dehydrothermal Crosslinking of Electrospun Collagen Nanofibers: The Effects of Vacuum Conditions and Subsequent Chemical Crosslinking.

Collagen nanofibrous materials have become integral to tissue engineering due to their exceptional properties and biocompatibility. Dehydrothermal crosslinking (DHT) enhances stability and maintains structural integrity without the formation of toxic residues. The study involved the crosslinking of electrospun collagen, applying DHT with access to air and under vacuum conditions. Various DHT exposure times of up to 72 h were applied to examine the time dependance of the DHT process. The DHT crosslinked collagen was subsequently chemically crosslinked using carbodiimides. The material crosslinked in this way evinced elevated Young's modulus values and ultimate tensile strength values, a lower swelling rate and lower shrinkage ratio during crosslinking, and a higher degree of resistance to degradation than the material crosslinked solely with DHT or carbodiimides. It was shown that the crosslinking mechanism using DHT occupies different binding sites than those using chemical crosslinking. Access to air for 12 h or less did not exert a significant impact on the material properties compared to DHT under vacuum conditions. However, concerning longer exposure times, it was determined that access to air results in the deterioration of the properties of the material and that reactions take place that occupy the free bonding sites, which subsequently reduces the effectiveness of chemical crosslinking using carbodiimides.

An Investigation into the Effect of Vacuum Conditions on the Filling Analysis of the Pressure Casting Process

An Investigation into the Effect of Vacuum Conditions on the Filling Analysis of the Pressure Casting Process

The effects of vacuum pyrolysis conditions on wood biochar monoliths for electrochemical capacitor electrodes

Vacuum pyrolysis is mostly employed to extract liquid biofuels from biomass in industry, but the potential application of its by-product (biochar) is seldom studied. The wood biochar monoliths were prepared by pyrolyzing cotton rose stem under vacuum conditions and a common nitrogen atmosphere, respectively. The effects of vacuum conditions on the physicochemical properties of biochar monoliths were investigated by various techniques, such as Raman, FTIR, XPS, TG, BET, CO2 adsorption and SEM methods. The results showed that the vacuum pyrolysis biochar, in comparison with nitrogen atmospheric pyrolysis biochar, features a higher degree of graphitization, a richer micro-porosity (57.2% vs. 33.9%), and a more reactive surface. The comparison of electrochemical performance suggested that the electrode prepared by vacuum pyrolysis overtakes that by nitrogen atmosphere pyrolysis with a specific capacitance of 161 F g−1 versus 133 F g−1 and an ease ion delivery capacity. Moreover, 125% of initial capacitance was retained over 10000 cycles at 50 mA cm−2. The vacuum conditions are more favorable for the preparation of biochar as well as the biochar derived activated carbon materials for application as electrodes.

Effect of vacuum conditions on stability and crystallization of cobalt based amorphous alloy

Abstract The aim of this work was to investigate the effects of moderate vacuum conditions (10 Pa, 1 × 103 Pa and 2 × 104 Pa) on glass forming ability, thermal stability and aging behavior of Co42Cu1Fe20Ta5:5B26:5Si5 amorphous samples in terms of size and distribution of crystalline precipitates. The thinnest parts (300 μm) of the wedge-shaped samples were amorphous for all vacuum conditions, and they had similar compositional, structural and thermal characteristics. However, they represented different microstructural features after heat treatments at 950 K and 1100 K. The same phases precipitated in all samples but the amount and the size of the precipitates increased as the pressure was raised to the normal atmospheric value. The differences in the glass forming ability and the microstructure due to aging are considered to originate from lower thermal characteristics, such as relaxation and reduced glass temperature as well as γ parameter, resulting from the poor vacuum pressure used in the production process. The differences in the microstructures and hardness values caused by heat treatments have been observed.

Effects of vacuum conditions on activation of high-alumina fly ash roasted using conventional and microwave heating

In this study, Na2CO3 was used as activator to roast and activate high-alumina fly ash (HAFA), and the vacuum roasting technology was used to enhance the activation process of HAFA. The effects of the vacuum conditions on the activation of HAFA roasted using conventional and microwave heating were investigated. It was determined that the reaction time was shortened and the activation effect of HAFA was improved under vacuum conditions; however, the effect of the vacuum conditions on the roasting temperature was negligible. The activation process of HAFA-Na2CO3 mixtures (HAFA/Na2CO3 mass ratio of 1:1) was promoted by conducting conventional and microwave heating experiments under vacuum (−0.04 MPa). The leaching rate of aluminium of 93.00% was reached at the roasting temperature of 900 °C after only 20 min when the HAFA-Na2CO3 mixture was subjected to conventional heating under vacuum, and after 60 min when conventional heating occurred under normal atmospheric pressure. Moreover, the leaching rate of aluminium of 96.00% was reached at the roasting temperature of 700 °C after only 20 min when the HAFA-Na2CO3 mixture underwent microwave heating under vacuum, and after 30 min when microwave heating occurred under normal atmospheric pressure.

Scalable and Physical Synthesis of 2D Silicon from Bulk Layered Alloy for Lithium-Ion Batteries and Lithium Metal Batteries.

Owing to its distinctive structure and properties, 2D silicon (2DSi) has been widely applied in hydrogen storage, sensors, electronic device, catalysis, electrochemical energy storage, etc. However, scalable and low-cost fabrication of high-quality 2DSi remains a great challenge. In this work, a physical vacuum distillation method is designed to obtain high-quality 2DSi from a bulk layered calcium-silicon alloy. With this method, the lower boiling point calcium metal is evaporated to construct 2DSi and can be further recycled. The effect of vacuum conditions on morphology, components, and electrochemical properties is further explored. As an anode for lithium-ion batteries, the 2DSi delivers a stable cyclability of 835 mAh g-1 after 3000 cycles at 5000 mA g-1 (0.003025% capacity decay per cycle). The electrochemical performance enhancing mechanism is also probed. In addition, a 2D/2D flexible and binder-free paper by combining 2DSi with 2D MXene is constructed. As a lithiophilic nuclear agent for lithium metal anodes, the 2DSi can efficiently suppress the Li dendrite growth and reduce nucleation barriers, achieving a high Coulombic efficiency (98% at 1 mA cm-2, 97% at 2 mA cm-2) around 600 cycles and a long lifespan of 1000 h. The crystal growth difference of lithium metal on Cu foil and 2DSi is studied. This work may provide a pathway for green, low-cost, and scalable synthesis of 2D materials.

Effect of vacuum conditions and plasma concentration on the chemical composition and adhesion of vacuum-plasma coatings

The paper reports on the chemical composition of titanium nitride (TiN) and silicon (Si) coatings deposited with a new technological vacuum plasma setup which comprises magnetron sputtering systems, arc evaporators, and an efficient plasma generator. It is shown that due to highly clean vacuum conditions and highly clean surface treatment in the gas discharge plasma, both the coating-substrate interface and the coatings as such are almost free from oxygen and carbon. It is found that the coating-substrate interface represents a layer of thickness ≥ 60 nm formed through vacuum plasma mixing of the coating and substrate materials. The TiN coatings obtained on the new equipment display a higher adhesion compared to brass coatings deposited by industrial technologies via intermediate titanium oxide layers. It is concluded that the designed vacuum plasma equipment allows efficient surface modification of materials and articles by vacuum plasma immersion processes.

Impurity-controlled Mo films as diffusion barriers for Cu metallization

Effects of vacuum conditions on the oxygen content and microstructure of Mo layers used with Cu gate lines as thin-film transistor-liquid crystal display diffusion barriers were investigated. Mo was deposited using ion-beam sputtering at 1.0 × 10−5 and 7.0 × 10−7 Torr. The Mo layer oxygen content and the microstructure and changes in chemical composition of the Cu/Mo/SiO2/Si layer during annealing were examined. The Mo layer microstructure was influenced by oxygen; increasing concentration increased the energy required for secondary grain growth. Growth was suppressed at high oxygen levels. Therefore, diffusion barrier performance is enhanced by finer Mo layer grain sizes.

Multiple-pulse laser dynamic forming of metallic thin films for microscale three dimensional shapes

Laser dynamic forming (LDF) is a novel high energy rate microfabrication technique, which makes use of the shock pressure induced by laser to generate dynamic high strain rate three dimensional (3D) forming of thin films. In LDF process, a high shock pressure accelerates the workpiece to a high velocity and deforms it into complex 3D shapes. The forming velocity of the workpiece imparted by a single laser pulse with high energy may exceed the critical forming velocity of the material, and thus causing it to fracture. This problem is more severe when 3D structure of large aspect ratio needs to be formed. To overcome this problem, multiple-pulse LDF is investigated in this study. The total laser energy is evenly distributed in different laser pulses to keep the forming velocity below the critical forming velocity of the material. The effects of the multiple-pulse LDF on the deformation behavior of ultrathin foils are investigated. The deformation depth and thickness variation distribution of the formed 3D features are characterized to reveal these effects. In addition, the effects of vacuum conditions on multiple-pulse LDF process are carried out. It is found that the bounce off of the foil can be effectively reduced by multiple-pulse LDF and the final shape could be controlled much more accurately. By extending single pulse LDF to multiple-pulse LDF, the forming capability of LDF is further enhanced, and thus enlarges the applicable range of this technique.

Effect of positive ions on the microwave generation in a low-voltage vircator

The effect of vacuum conditions on the characteristics of microwave generation in a nonrelativistic electron beam with a virtual cathode (VC) formed in a retarding field (low-voltage vircator) has been experimentally studied. The ionization of residual gases in the working chamber of a low-voltage vircator leads to displacement of the VC out of the interaction space, which results in breakdown of the microwave generation. The experimental data agree with the results of numerical simulations.

Effects of vacuum conditions on low frequency noise in silicon field emission devices

The effects of pressure on emission current noise have been studied. Field emission currents from 50×50 arrays and single emitter silicon devices were observed over a range of pressures. The current fluctuations were analyzed in both the time and frequency domain. Signal to noise ratios between 0.9 and 6.9 were observed and appear to be more dependent on operation time and current than on pressures. At higher pressures, emission currents are reduced and the current is cut off completely above a threshold pressure which is somewhere in the 10 s of Torr. Plasmas were observed in the mTorr range. The total current from a 50×50 tip array was measured to be only one order of magnitude greater than that for a single tip, suggesting that only 4–10 of the emitters in the array were functional. Spectral density coefficients of low frequency measurements range from 1.37 to 1.81. Some pressure dependence is suggested in the lower pressure ranges. The single emitter exhibited burst noise with a cutoff frequency of about 10 Hz.

The effects of vacuum conditions on epitaxial Al/GaAs contacts formed by molecular-beam epitaxy

The effects of the quality of the vacuum on the epitaxy of aluminum on (100) gallium arsenide have been investigated. It was found that leaving the ion gauge running during the cooling down of the GaAs prior to the deposition of the Al and the presence of a helium cryopump both affected the nature of the epitaxy and the height of the resulting Schottky barrier. Reproducible results were only obtained with the ion gauge off and the cryopump on. The Al film was found to take up the (100) orientation irrespective of the reconstruction of the GaAs surface [c(2×8), c(4×4), or (4×6)]. The height of the Schottky barrier on n-type GaAs was 0.77±0.01 eV, and was independent of the GaAs reconstruction. The I-V characteristics were the most nearly ideal that have been reported, a plot of log{I/[1−exp(−qV/kT)]} vs V being linear over the whole voltage range from +0.5 to −1.0 V, with an ideality factor of 1.01 which can be explained solely in terms of image-force lowering. The barrier height on p-type GaAs was 0.64±0.01 eV, also irrespective of the GaAs reconstruction, so that φbn+φbp is equal to the band gap within the experimental error.

Effect of vacuum conditions on breakdown voltage between electrodes in vacuum

The electrical breakdown in vacuum was studied in the configuration: wire —plane. Measurements were performed in two different experimental systems: with technical vacuum and with the clean one. It was found that the value of breakdown voltage decreases with increasing vacuum and that at the same pressure the insulating properties of electrodes are better in the technical vacuum than in the oilless one.