N2 Protection Research Articles

Revealing the evolution of microstructure and mechanical properties with deposition energy and shielding gas to achieve phase-balanced directed energy deposition of 2205 duplex stainless steel

Directed energy deposition-arc (DED-arc) manufactured duplex stainless steel (DSS) has shown great potential for use in marine propellers. However, challenges remain in achieving phase-balanced DSS deposits through the DED-arc process. To overcome this, we conducted a study that involved regulating the deposition energy and shielding gas with the use of ER2205 wire. The results show that the austenite content in DSS deposits increases with the increase of deposition energy, and the content in the Ar+2%N2-protected deposits is significantly higher than that of Ar+2%CO2-protected deposits. Ultimately, DSS deposits with balanced phase content (austenite content of ∼48.4 %) are obtained at a line energy of 600 J/mm for DED-arc under Ar+2%N2 protection. Unlike the N loss in Ar+2%CO2-protected samples, more nitrogen elements are introduced into the DSS samples by Ar+2%N2 shielding gas. Ar+2%N2-protected samples contain more austenite and exhibit a more homogeneous microstructure, which results in the solid solution strengthening and a significant reduction in the anisotropy of the tensile properties. Furthermore, a more systematic evolution of the microstructure and tensile properties of DSS deposits under the influence of deposition energy and shielding gas is revealed. This study preliminarily obtains the relationship between the DED-arc parameters, microstructure, and tensile properties of DED-arc-fabricated DSS, which will provide an important reference for tailoring microstructure and properties in additive-manufactured DSS.

Structure adjustment on Fe-based electrocatalyst to regulate oxygen reduction reaction selectivity for Zn-air battery and H2O2 production

Fe-based materials are famous electrocatalysts in oxygen reduction reaction (ORR), but their selectivity towards four- or two-electron ORR still requires further research in detail. Herein, two Fe-based ORR electrocatalysts are synthesized from MIL-101, a metal–organic framework (MOF). After calcined with dicyandiamide (DCDA) under N2 protection, Fe3O4@NCNTs (NCNTs = N-doped carbon nanotubes) is synthesized, in which small Fe3O4 particles reside in NCNTs homogeneously. It is a typical four-electron electrocatalyst in both alkaline and neutral electrolyte. Without DCDA, Fe2O3 forms and it acts as two-electron electrocatalyst in ORR. Theoretical calculation suggests the discrepancy in ORR selectivity between Fe3O4@NCNTs and Fe2O3 roots from their different interactions with OOH*. If Fe3O4@NCNTs serves as cathode material, peak power density of Zn-air battery reaches 125.1 mW·cm−2 in alkaline electrolyte. When discharge at 10 mA·cm−2, the specific capacitance and energy density reach 799.7 mAh·g−1 and 839.7 Wh·kg−1. The performance of Fe3O4@NCNTs is also well kept in neutral Zn-air battery. We expect this work elucidates the effect of structure on ORR selectivity for Fe-based electrocatalysts.

Copper tungstates directly derived from polyoxotungstate-MOF as counter electrodes for dye-sensitized solar cells

The strategically selection of different selection of reaction temperature directly affects the performance of the target catalyst. Herein, copper tungstate species catalysts were directly derived from polyoxotungstate-based metal–organic frameworks ([Cu2(BTC)4/3(H2O)2]6[H3PW12O40], PW12-MOF) as sacrificial template by in-situ pyrolysis at temperatures of 600, 700, 800, 900, 1000 °C under the protection of N2, and further served as counter electrodes (CEs) to assemble dye-sensitized solar cells (DSSCs). The corresponding characterization of XRD, XPS, SEM and N2 adsorption/desorption revealed that PW12-MOF can be converted into copper tungstate, and the ligand groups can be carbonized into graphitic C to embedded in CuWO4, thus forming CuWO4@C composite at 800 °C. The significant effect of different pyrolysis temperatures on the electrocatalytic performance of the prepared CuWO4-based catalysts were identified with cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization. Furthermore, five different CuWO4-based catalysts were applied to regenerate I3−/I− shuttles in DSSCs, and then achieved power conversion efficiencies (PCE) of 5.79, 6.39, 7.01, 6.15 and 5.40% by photocurrent-voltage measurement, respectively, which was caused by the enhancement of electrical conductivity and the increase of catalytic active sites by the synergistic effect between CuWO4 and C, illustrating an excellent alternative to Pt CEs in the encapsulated DSSCs.

DNA-Conjugated Cyclopropane Derivatives Constructed from Sulfonium Ylides with α,β-Unsaturated Ketones.

Here, we report a DNA-compatible reaction for the generation of cyclopropane derivatives using thiolides with α,β-unsaturated ketones in the absence of transition metal and N2 protection, which is convenient for DNA encoded library (DEL) construction. This approach allows the rapid and efficient production of a series of DEL libraries of potentially biologically active cyclopropanes and spirocyclopropyl oxindole derivatives.

Single box dyeing of denim yarns under nitrogen protection with high indigo concentration

In the era of “double carbon,” green short process preparation of denim textiles will become more and more popular, and dyeing is an essential step in this process. In order to improve dye utilization and energy efficiency, a high-concentration indigo single box dyeing method based on nitrogen (N2) protection has been studied. The optimal dyeing conditions were obtained. The dyeing mechanism was revealed by evaluating the stability of the dyeing solution and dye distribution in the dyed yarns. Various dyeing properties, chemicals, energy consumption, and dyeing wastewater were measured and compared with conventional slasher dyeing. It has been shown that N2 protection effectively avoids the oxidation of soluble leuco-indigo and improves the stability of the leuco dyeing bath. In addition, the dyes diffused more deeply into the fiber in the dyeing box under a micro-positive pressure environment, enhancing the dyeing efficiency and depth. The proposed technique exhibited better dye utilization and excellent color fastness. Dyeing wastewater was more chemical and biodegradable, relieving wastewater treatment. Generally, cleaner dyeing not only reduces the consumption of energy, water, and chemicals, but also saves 46.8% of the economic cost compared with traditional slasher dyeing, indicating that the proposed technology is interesting for industrial application.

Co-CoO-Co3O4 Realizes ultra highly sensitive detection of 4-nitrochlorobenzene based on synergistic effect of adsorption and catalysis

Accurate determination of 4-nitrochlorobenzene (4-NCB) concentrations in water environment always keeps its challenge due to the high toxicity and redox inertness of organic pollutants. Herein, cobalt-based oxide nanomaterials with different oxidation states were prepared by annealing ZIF-67 under N2 protection and subsequent oxidation in air. The products obtained from non-oxidation, oxidation for 4 and 8 h were named Co, Co-CoO-Co3O4 and Co3O4, respectively. Compared with Co and Co3O4, incompletely oxidized Co-CoO-Co3O4 exhibited the best detection performance for the electroanalytical behavior of 4-NCB, with a high sensitivity of 2.29 μA μM−1 in the concentration range of 0.5–4 μM. The results show that the Co-CoO-Co3O4 composite obtained by Co oxidation for 4 h has a slight decrease in the adsorption capacity of 4-NCB, but its catalytic reduction performance is improved by about 4 times, and the improvement of catalytic ability makes it have more excellent electrochemical detection performance. It is confirmed that the synergistic effect of adsorption and catalysis affects the electrochemical detection performance of organic pollutants, and the catalytic behavior of the material is a more critical factor affecting electrochemical detection.

Deacetylated nimbin analog N2 fortifies alloxan-induced pancreatic β-cell damage in insulin-resistant zebrafish larvae by upregulating phosphoenolpyruvate carboxykinase (PEPCK) and insulin levels

This study aims to evaluate the protective behaviour of N2, a semi-natural analog of nimbin, for its anti-diabetic efficacy against alloxan-induced oxidative damage and β-cell dysfunction in in-vivo zebrafish larvae. A 500 μM of alloxan was exposed to zebrafish larvae for 24 h to induce oxidative stress in the pancreatic β-cells and co-exposed with N2 to study the protection of N2 by inhibiting ROS by DCFH-DA, DHE and NDA staining along with Cellular damage, apoptosis and lipid peroxidation. The zebrafish was further exposed to 500 μM alloxan for 72 h to induce β-cell destruction along with depleted glucose uptake and co-exposed to N2 to study the protective mechanism. Glucose levels were estimated, and PCR was used to verify the mRNA expression of phosphoenolpyruvate carboxykinase (PEPCK) and insulin. Alloxan induced (24 h) oxidative stress in the pancreatic β-cells in which N2's co-exposure inhibited ROS by eliminating O−₂ radicals and restoring the glutathione levels, thus preventing cellular damage and lipid peroxidation. The zebrafish exposed to 500 μM alloxan for 72 h was observed with β-cell destruction along with depleted glucose uptake when stained with 2NBDG, wherein N2 was able to protect the pancreatic β-cells from oxidative damage, promoted high glucose uptake and reduced glucose levels. N2 stimulated insulin production and downregulated PEPCK by inhibiting gluconeogenesis, attenuating post-prandial hyperglycemia. N2 may contribute to anti-oxidant protection against alloxan-induced β-cell damage and anti-hyperglycemic activity, restoring insulin function and suppressing PEPCK expression.

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Anion Modification and Theoretical Understanding for Improving Annealing-Free Electrochemistry Deposition of Perovskites under an Ambient Atmosphere

Organometallic halide perovskites have drawn tremendous attention for their remarkable photovoltaic properties. We report anion modification for improving annealing-free electrochemical deposition of perovskites under an ambient atmosphere and extending the applications. Relevant theoretical simulation based on the Butler–Volmer functions reveals the mechanism behind: introduced anions raise the exchange current and electrolyte conductivity, which promotes the deposition rate and current efficiency simultaneously. The crystallization and morphology of perovskites is conveniently and controllably improved by this strategy without additional annealing or N2 protection process. We extend this method onto fully textured silicon heterojunction solar cells, which optimizes the shape-preserving deposition of perovskites. Our article suggests a promising way toward low-cost perovskite/silicon monolithic tandem solar cells.

Enhanced thermal energy storage performance of hydrous salt phase change material via defective graphene

Structural modification of two-dimensional materials has a significant influence on performance. In this work, a novel preparation method is presented to get defective graphene and the as-obtained defective graphene shows great benefits for the thermal energy storage performance of phase change material (PCM). Based on the experimental results, we found the structure of few-layer graphene becomes weak at high temperatures (1200 °C) under the protection of N2, and then some micro-defects could be formated in the surface of graphene at a suitable thermal treatment schedule in air atmosphere. Owing to the unique nature of defective graphene, the PCM/defective graphene composite showed a higher thermal conductivity than barium hydroxide octahydrate (Ba(OH)2·8H2O) as the pure PCM. Scanning electron microscopy (SEM) and thermal cycling tests revealed that the defective graphene can be acted as the nucleating agent, which reduced the supercooling degree of Ba(OH)2·8H2O. Furthermore, thermal cycle stability tests showed the composite PCM had outstanding thermal cycling stability, and the defective graphene can also be acted as a kind of stabilizer. We showed the excellent application values of defective graphene in the PCM field for energy storage. This work is beneficial to the development of graphene and PCM composites.

Tribological and mechanical properties of wood dowel rotation welding with different additives

Wood friction welding is a green and pollution-free wood processing technology. Research on wood friction welding mainly focuses on the influence of wood type, welding process, and welding interface additives on welding interface strength. However, studies on the tribological properties of wood friction welded interface and its effect on the strength of the welded interface are few. In this article, chemical additives in wood were added to the interface. The frictional force, normal force, microstructure, and chemical composition of the welding interface, and their effects on the strength of the welding interface were studied. In the rotating friction welding of wood, frictional force increased gradually with friction welding. Approximately 2 s after welding, the frictional force achieved a stable state. Normal force increased and then gradually decreased. No considerable changes in frictional force and interface strength were observed and interface strength increased with normal force. The interface strength of glucose and rosin increased, whereas that of N2 protection showed little change. The interface strength of tung oil, cellulose, and guaiac decreased. This study provides a basic reference for the further industrial application of wood friction welding technology.

Coating of diamond by thermal explosion reaction

By using Cr/Al/B/diamond mixed powder as raw material, a CrB-AlN based multi-component composite coating was formed on a diamond surface by thermal explosion synthesis technology. The effects of protective atmosphere (N2 or Ar), Al content of the phase composition, and microstructure of the binder and coating were studied. X-ray diffraction and scanning electron microscopy were used to analyze the phase composition and microstructure of the samples. The results showed that under the protection of Ar, the raw material did not undergo a thermal explosion reaction. A loose and porous bulk structure can be obtained through thermal explosion reaction under the protection of N2. The coating on the diamond surface was mainly composed of CrB and AlN and contained other by-products, such as Cr5Al8 and Cr2AlB2.

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

Rare-Earth Doping Graphitic Carbon Nitride Endows Distinctive Multiple Emissions with Large Stokes Shifts

External Photocatalyst-Free Visible Light-Promoted 1,3-Addition of Perfluoroalkyl Iodides to Vinyldiazoacetates

External Photocatalyst-Free Visible Light-Promoted 1,3-Addition of Perfluoroalkyl Iodides to Vinyldiazoacetates

An important improvement of strength and ductility on a new type of CoCr2.5FeNi2TiW0.5 high entropy alloys under two different protective gases by selective laser melting

High entropy alloys (HEAs) have excellent mechanical properties for wide application range and market demand. However, low ductility is a persistent problem with such alloys. With two different protective gases (Argon and Nitrogen), a new type of high entropy alloy CoCr2.5FeNi2TiW0.5 has been prepared by selective laser melting (SLM) technology for additive manufacturing with discussion and analysis on the influence of microstructure and mechanical properties in this paper. Under the protection of argon (Ar), the HEA forms a single-phase solid solution. Meanwhile, the second phase TiN is formed when nitrogen (N2) is used as protective gas, which eventually becomes the matrix body-centered cubic (BCC) with precipitates TiN. The average microhardness values of samples under the protection of Ar and N2 were 436.7HV and 499.2HV, respectively. Along the scanning direction, the SLM sample (N2 protection) shows higher properties on the average yield strength (YS), ultimate tensile strength (UTS), and average elongation of samples (581 MPa, 893 MPa, and 9.9%, respectively.), compared with those obtained under Ar atmosphere. This method could effectively refine grain structure and offer theoretical guidance to manufacture fine grain materials with high strength and ductility of new HEA components.

MOFs-derived magnetic C@Cu–Ni bimetal particles: An efficient peroxymonosulfate activator for 2,4,6-trichlorophenol degradation

In this study, magnetic Cu and Ni bimetallic particles embedded carbon sheets, namely as C@Cu–Ni, was derived via calcining a mixture of Cu-MOFs and Ni-MOFs (mass ratio = 4:6) under N2 protection and served as a catalyst for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by peroxymonosulfate (PMS). The results showed that more than 98.5% of 2,4,6-TCP (10 mg L−1) was rapidly decomposed at initial pH = 5, PMS = 1 mM and catalyst dosage = 0.1 g L−1 within 30 min, accompanied by 42.47% removal of total organic carbon (TOC). This fully confirmed that C@Cu–Ni possessed excellent catalytic performance for PMS activation. The radical quenching experiments and electron paramagnetic resonance (EPR) investigation testified that the reactive oxygen species (ROS) included SO4•−, •OH, O2•− radicals and singlet oxygen (1O2), which were responsible for the rapid degradation of 2,4,6-TCP. Among them, O2•−and 1O2 played a decisive role. Cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) revealed that C@Cu–Ni material possessed superior electrical conductivity and electron transfer, improving its catalytic activity. What is more, C@Cu–Ni displayed excellent stability and could be consecutively used for five times without any decline of catalytic performance. The main intermediates of the 2,4,6-TCP degradation were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) and possible pathways of 2,4,6-TCP degradation were further proposed. The extraordinary stability and superior catalytic activity of C@Cu–Ni coupled with its easy separation from wastewater due to magnetism suggest that the newly synthesized material may offer a promising alternative approach to efficiently degrade organic pollutants by PMS.

Toward the Highly Ordered Lamellar Hybrid Membrane for Molecular Sieving by One-Pot Self-Assembly of Hybrid Hyperbranched Polymer

Ordered lamellar hybrid membranes are of great interest, due to their application as functional materials, including molecular sieving, biosensors, optical devices, and drug, as well as gene delive...

"On-Water" Synthesis of Quinazolinones and Dihydroquinazolinones Starting from o-Bromobenzonitrile.

A versatile and practical “on-water” protocol was newly developed to synthesize quinazolinones using o-bromobenzonitrile as a novel starting material. Studies have found that air as well as water plays an important role in synthesis of quinazolinones. Further investigation indicated that dihydroquinazolinones can be prepared with this protocol under the protection of N2. The protocol can be extended to other substrates and various quinazolinones and dihydroquinazolinones were obtained. o-Bromobenzamide, o-aminobenzonitrile, and o-aminobenzamide were also evaluated as starting materials, and the results further proved the versatility of this protocol, especially towards dihydroquinazolinones.

Preparation and characterization of t-BN coatings on the surface of carbon fibers

ABSTRACTTurbostratic boron nitride (t-BN) coatings were successfully synthesized on the surface of carbon fibers by dip-coating method. Boric acid and urea were used as boron source and nitrogen source separately and the nitridation process was carried out at 850°C for 4h under the protection of N2. Dipping times were considered as variables to find out optimum amounts. The structure, chemical composition, phase and properties of BN coated carbon fibers were characterized. Results showed that continuous and uniform coatings were prepared after three times dipping and adhered well with carbon fibers. The coatings were mainly composed of the phase of t-BN. The oxidation property and high temperature resistant performance of the BN modified carbon fibers were greatly improved.

Online deposition measurement and slag bubble behavior in the reduction zone of pulverized coal staged combustion

An online thermogravimetric measurement method of ash deposition was developed. Ash deposition and slag bubble in the reductive zone of pulverized coal staged combustion were investigated. Firstly, a steady pulverized coal staged combustion was achieved in an electrically heated down-fired furnace. Additionally, gas species, coal conversion, and particle size distribution were quantitatively measured. Secondly, real-time ash deposition rates at different temperatures (1100–1400 °C) were measured, and deposition samples were carefully collected with an N2 protection method. The morphologies of collected samples were investigated through a scanning electron microscope. It was found that the deposited ash transformed from a porous layer composed of loosely bound particles to a solid layer formed by molten slag. Different behaviors of the slag bubble were observed, and bubble sizes were significantly affected by the deposition temperature. A deposition and bubble formation mechanism was proposed and used for modeling. Results showed that the proposed model well predicted the observed ash deposition and bubble formation process.