In this paper, atmospheric pressure N2/O2 plasma jets with homogeneous shielding gas excited by nanosecond pulse are obtained to generate simplex reactive nitrogen species (RNS) and reactive oxygen ...species (ROS), respectively, for the purpose of studying the simplex RNS and ROS to induce the myeloma cell apoptosis with the same discharge power. The results reveal that the cell death rate by the N2 plasma jet with N2 shielding gas is about two times that of the O2 plasma jet with O2 shielding gas for the equivalent treatment time. By diagnosing the reactive species of ONOO−, H2O2, OH and O2− in medium, our findings suggest the cell death rate after plasma jets treatment has a positive correlation with the concentration of ONOO−. Therefore, the ONOO− in medium is thought to play an important role in the process of inducing myeloma cell apoptosis.
High nitrogen stainless steel with nitrogen content of 0.75% was welded by gas metal arc welding with Ar–N2-O2 ternary shielding gas. The effect of the ternary shielding gas on the retention and ...improvement of nitrogen content in the weld was identified. Surfacing test was conducted first to compare the ability of O2 and CO2 in prompting nitrogen dissolution. The nitrogen content of the surfacing metal with O2 is slightly higher than CO2. And then Ar–N2-O2 shielding gas was applied to weld high nitrogen stainless steel. After using N2-containing shielding gas, the nitrogen content of the weld was improved by 0.1 wt%. As N2 continued to increase, the increment of nitrogen content was not obvious, but the ferrite decreased from the top to the bottom. When the proportion of N2 reached 20%, a full austenitic weld was obtained and the tensile strength was improved by 8.7%. Combined with the results of surfacing test and welding test, it is concluded that the main effect of N2 is to inhibit the escape of nitrogen and suppress the nitrogen diffusion from bottom to the top in the molten pool.
•Exploring the inhibition of moisture intrusion and the protection of perovskite solar cells in a CO2 and N2 sealed environment.•Established the model of moisture intrusion under the environment of ...N2, CO2 and SF6, and simulated the degree of moisture intrusion under the three gas environments.•In the practical application of perovskite solar cells, on the premise of considering sealing and cost, it provides guidance for the selection of shielding gas.
The stability and reliability of perovskite solar cells (PSCs) are severely affected by moisture. Therefore, it is very meaningful to study the barrier effect of gases with different compositions on moisture in a sealed environment. In this work, the stability of PSCs in a sealed environment filled with N2, CO2 with an external environment of 45 °C and 85% RH was investigated. After 240 h treatment, the PCE of the PSCs in the CO2 sealed environment decayed to 71.1% of the initial value. The PCE of the PSCs in the N2 sealed environment decayed to 51.8% of the initial value, while in the air environment as a control, the PCE decayed to 36.3% of the initial value. Through SEM, XRD film characterization and finite element simulation, it is found that both CO2 and N2 can be used as shielding gases to inhibit moisture intrusion, thereby slowing down the decay rate of perovskite solar cells. And CO2 is more effective than N2 in inhibiting moisture intrusion. On the one hand, CO2 molecules are larger than N2 molecules. When tiny gaps appear in the sealed environment, N2 molecules can escape, but CO2 cannot escape, which will lead to less moisture intrusion in the CO2 sealed environment. On the other hand, when there are large gaps in the sealed environment, both N2 and CO2 can escape, because the diffusion coefficient of moisture in the N2 sealed environment is larger, resulting in more moisture intrusion in the N2 sealed environment.
High nitrogen stainless steel has extensive applied foreground in industries. But the weldability limits the use of the steel. The weld without nitrogen can become the weakness of the joint in ...corrosion resistance and strength. In this study, response surface methodology was applied to optimize the Ar-N2-CO2 ternary shielding gas for a nitrogen-containing filler metal in high nitrogen stainless welding. The influence of the proportion of N2 and CO2 on the nitrogen content, the impact energy and the tensile strength were investigated by the statistical regression models. The results show that the tensile strength, nitrogen content and impact energy increase and then decrease with the increasing of CO2, which indicates that CO2 content should not be too high. N2 addition can increase the nitrogen content of the weld obviously. But the impact energy decreases when N2 content exceeds about 7%. Integrating the mathematic models of the three performances, the optimal shielding gas compositions were determined to be 87 %Ar-6.5 %N2-6.5 %CO2. With this optimal shielding gas, the tensile strength and impact energy reached 956.7 MPa and 166.8 J, respectively. The deviation between the experimental value and the predicted value was below 2%.
The influences of N2 content in shielding gas on microstructure and impact toughness of different zones in cold metal transfer and pulse (CMT-P) hybrid welded joint of duplex stainless steel (DSS) ...were systematically studied. The results showed that the N2-supplemented in shielding gas significantly facilitated austenite formation (weld root: 39.9%→41.2%, weld filler: 40.5%→43.7%, and heat affected zone (HAZ): 36.4%→39.6%). However, when the N2 content in the shielding gas exceeded 4%, there was no significant change in austenite content because of reaching the solubility limit of N atoms. In addition, γ2 precipitated both in the weld root and HAZ but not in the weld filler, which cannot be inhibited by N2 addition in the shielding gas. Besides, a great number of Cr2N and dislocations in addition to γ2 formed in the HAZ, and the content of Cr2N and dislocation significantly increased with the increase of N2 content in the shielding gas. Furthermore, the HAZ exhibited the lowest toughness in comparison with other zones. In addition, with the increase of N2 content in the shielding gas from 0% to 6%, the toughness increased first and then decreased, and reached the maximum when 4% N2 added to the shielding gas as (weld root: 122.0 J/cm2, weld filler: 135.0 J/cm2, and HAZ: 91.8 J/cm2). According to detailed microstructure analysis and toughness level, Ar+4% N2 was recommended as the shielding gas to join DSS by using CMT-P welding technique.
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•There was a solubility limit of N in weld pool with N2 addition in shielding gas.•Reheating from subsequent weld-pass was a prerequisite for γ2 formation.•N2 addition in shielding gas cannot inhibit γ2 precipitation in weld root and HAZ.•Cr2N and dislocation in HAZ increased with N2 addition in shielding gas.•N2 content in shielding gas had obvious influence on toughness of welded joint.
Abstract A novel DC arc plasma torch is designed in this paper in order to reduce the electrode erosion, and a series of experiments are carried out to investigate how to improve the lifetime and ...performance of the nitrogen DC arc plasma torch. The analysis of voltage characteristics of the plasma torch indicates that the interelectrode insert can increase the average arc voltage and the sudden expansion structure can reduce the voltage fluctuation, which is helpful to improve the working stability to some extent. The spectrum characteristics at the plasma torch outlet and the cold flow simulations show that the dual shielding gas mainly act near the anode and can effectively cover the entire anode wall. Combining the shielding gas distribution with anode heat transfer processes in argon and nitrogen plasma torch, it is inferred that argon shielding gas plays an important role on reducing the anode heat transfer processes in nitrogen plasma torch, which can effectively suppress the anode erosion. The life testing experimental results find that there is no significant erosion of the cathode, anode, and interelectrode insert after cumulative working time exceeding 20 h. The maximum nitrogen plasma jet length can reach ∼35 mm with the outlet jet temperature of about 20 000 K at the current of 100 A and nitrogen gas flow rate of 10 slm. The maximum average specific enthalpy and thermal efficiency are respectively about 14 MJ kg −1 and 75% in the nitrogen plasma torch. Therefore, this newly designed DC arc plasma torch not only can suppress the electrode erosion but also has good working performance, which is expected to have excellent application prospects.
Abstract
The effect of ambient air as an unavoidable problem for atmospheric pressure plasma jet (APPJ) applications has attracted a lot of interest, especially when the specific scenarios are highly ...sensitive to ambient species such as the biomedical process. The coaxial double-tube device is a promising method for controlling the ambient species into the jet effluent and thus the chemical properties of the jet effluent. In this work, the discharge characteristics and plasma chemistry of the coaxial double-tube helium APPJ at different shielding gas (SG) flow rates are studied numerically. An experiment on optical images of the discharge is conducted to illustratively validate the variation of the (main) discharge channel widths in the model as the SG flow rate varies. The results illustrate that the discharge is enhanced at the high flow rate, while it shows the weaker discharge behavior at the low flow rate as well as that without SG. The analysis of the dielectric plate surface indicates that the species fluxes to the dielectric plate significantly increase with the increases in the flow rate, which can be attributed to the wider (main) discharge channel. Moreover, to further explore the impact of the SG on the effluent chemistry, the ions fluxes on the surfaces of the main discharge channel and the discharge channel are distinguished and discussed. The analysis shows the great difference in the ions fluxes affected by the flow rate between the two discharge channels. In summary, advancing the knowledge that the flow rate of the SG has an impact on the discharge behavior, this study further reveals that different discharge positions greatly influence the production of nitrogen/oxygen species. This work enables the previously elusive account of the effect of SG and may open new opportunities for the further application of coaxial double-tube APPJ.
A two-dimensional (r, z) numerical simulation of the discharge characteristics of an atmospheric pressure plasma jet (APPJ), with coaxial shielding gas, was performed. The helium working gas flowed ...in a central capillary tube, engulfing a needle electrode powered by 13.7 MHz radio frequency sinusoidal voltage. The N2 shielding gas flowed in the annular space of a coaxial tube. These gases emerged, in laminar flow, in a 78%N2-21%O2-1%Ar dry air ambient. The characteristics of the APPJ with shielding gas were compared to those of the APPJ without shielding gas. The nitrogen shielding gas hindered the diffusion of oxygen and argon from the ambient air into the helium jet. With the shielding gas present, more nitrogen penetrated into the helium core, causing a shorter plasma 'plume'. The flow rates of the working and shielding gas, critically affected the gas temperature, and in turn the discharge characteristics. For a He flow of 2 standard liters per minute (slm), switching on the nitrogen shielding gas flow (at 4.5 slm) reduced the on-axis O2 and Ar mole fractions from 3.9×10−4 to 6.8×10−5 and from 1.9×10−5 to 3.3×10−6, respectively, at an axial distance of 3 mm downstream of the nozzle. The radial profiles of the mole fractions of the ambient gases were monotonically and strongly decreasing towards the system axis, for short axial distances from the nozzle (∼1 mm), but became progressively flatter at longer distances from the nozzle (3 mm and 5 mm). Simulation predictions captured the salient features of experimental data of ambient species mole fractions in the plasma jet, and the 706 nm optical emission intensity profiles of the He 33S excited state.
Wire arc additive manufacturing (WAAM) has been considered as a promising technology for the production of large metallic structures with high deposition rates and low cost. Stainless steels are ...widely applied due to good mechanical properties and excellent corrosion resistance. This paper reviews the current status of stainless steel WAAM, covering the microstructure, mechanical properties, and defects related to different stainless steels and process parameters. Residual stress and distortion of the WAAM manufactured components are discussed. Specific WAAM techniques, material compositions, process parameters, shielding gas composition, post heat treatments, microstructure, and defects can significantly influence the mechanical properties of WAAM stainless steels. To achieve high quality WAAM stainless steel parts, there is still a strong need to further study the underlying physical metallurgy mechanisms of the WAAM process and post heat treatments to optimize the WAAM and heat treatment parameters and thus control the microstructure. WAAM samples often show considerable anisotropy both in microstructure and mechanical properties. The new in-situ rolling + WAAM process is very effective in reducing the anisotropy, which also can reduce the residual stress and distortion. For future industrial applications, fatigue properties, and corrosion behaviors of WAAMed stainless steels need to be deeply studied in the future. Additionally, further efforts should be made to improve the WAAM process to achieve faster deposition rates and better-quality control.
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