Effect Of Gas Atmosphere Research Articles

Effect of gas atmospheres and SiO2 content on preparation and properties of SiO2–Si3N4 composite ceramics via nitridation of diamond-wire saw silicon waste powder

Composite ceramics are applied widely nowadays by combining superior properties of different ceramic materials. In this study, SiO2–Si3N4 composite ceramics with higher mechanical properties and lower dielectric constant were successfully fabricated by nitriding diamond-wire saw silicon waste. The effect of gas atmospheres (N2, NH3, N2–H2) and SiO2 content (0%, 10%, 20%, 30%, 40%) on the microstructure and properties of composite ceramics were studied. It shows that the synthesis of SiO2–Si3N4 composite ceramics can be obtained in the NH3 atmosphere, and it is inevitable to form the Si2N2O phase in N2 and N2–H2 mixture atmospheres. Furthermore, the shrinkage rate and dielectric constant of the ceramics decreased as SiO2 content increased from 0% to 40%. As for the porosity of the sintered ceramics, it first decreased and then increased, with a minimum of 1.73% at the SiO2 content of 20%. However, the flexural strength of the sintered ceramics was the inverse of the porosity, with a maximum of 160.72 MPa at the SiO2 content of 30%. For the sintered ceramic with 30% SiO2, the shrinkage rate, dielectric constant, porosity and flexural strength are 0.3%, 4.62, 1.97% and 160.72 MPa respectively. Thus, this study provides an environment-friendly and value-added approach to recycling photovoltaic waste and reducing the cost of the reactive sintering SiO2–Si3N4 composite ceramics with excellent mechanical and dielectric properties.

Effect of Gas Atmosphere in Aluminobarothermal Synthesis on the Structure of Metal Matrix Composites Based on Fe – Cr – Mn – Mo Alloy

Effect of Gas Atmosphere in Aluminobarothermal Synthesis on the Structure of Metal Matrix Composites Based on Fe – Cr – Mn – Mo Alloy

Effect of gas atmospheres on the interactions between liquid silicon and coated graphite substrates

Interactions between the gas atmosphere, liquid silicon, Si 3 N 4 coating, and graphite are of great interest for photovoltaic silicon applications. However, previous studies focus more on the wetting of silicon on coated substrates rather than the coating stability and interaction with furnace atmosphere. Here we report on the coating deoxidation and the liquid silicon behavior at different compositions of nitrogen, carbon monoxide, and argon. In-situ melting experiments were performed with solar grade silicon samples in various gas compositions. The results showed a rapid reaction between molten silicon and carbon monoxide that led to the formation of a silicon carbide layer at the liquid free surface. This layer retains the silicon droplet at the early stage of wetting and prevents silicon infiltration and spreading. Furthermore, CO gas prohibits the self-reduction of SiO 2 in the coating and the reduction by graphite. On the other hand, nitrogen accelerates the wetting of silicon as it favors the formation of highly wetted silicon nitride compound at the triple line of the droplet. A slight increase in the decomposition rate of silica content in the coating was observed with the introduction of nitrogen to the furnace. The influence of the morphology and the growth of nitride and carbide layers on the wettability was elucidated in detail. The results were supported by Raman spectroscopy and thermodynamic calculations. • Effect of gas atmosphere on the wetting behavior. • Interactions at the liquid-coating interface and the coating-substrate interface. • Effect of gas atmosphere on the coating stability. • Kinetics and mechanism of the reactions between liquid silicon and gas phase.

The effect of gas atmosphere on the coating formation by electric arc surfacing with cermet SHS electrodes of the TiB2–Co2B composition

Due to their unique properties, metal-matrix composite materials, when used as a surfacing material for electric arc surfacing, provide high properties of the deposited layers. SHS-extrusion is a promising method for a wide range of surfacing metal-matrix electrodes. The gas environment of surfacing affects the quality of coatings formed by SHS electrodes, their microstructure and properties. In this paper, cermet SHS electrodes of the TiB2–Co2B composition obtained by SHS-extrusion were used to form protective coatings on a steel substrate by electric arc surfacing in an argon atmosphere and in a nitrogen atmosphere. The elemental and phase composition, as well as the microstructure of the deposited layers, were investigated. Based on the conducted studies, the influence of the gas atmosphere on the formation of the structure of cermet coatings was established. It is shown that, despite the similar phase composition, there are fundamental differences in the microstructures of the deposited coatings, which are caused by the partial fusion of the tungsten electrode and the transfer of the electrode material in the coating during surfacing in an argon atmosphere. The maximum values of the microhardness of coatings deposited in a nitrogen atmosphere exceed the maximum microhardness of coatings obtained by surfacing in an argon atmosphere by 200–450 HV.

Effect of gas atmosphere on hydrogen production in microbial electrolysis cells

Inert gas is often used in the deoxygenation of microbial electrolysis cells (MECs) to maintain growth and viability of anaerobes. However, the effects of the gas atmosphere on hydrogen production and microbial community of MECs are often neglected. Here, the performances and biofilm microbiomes of MECs pre-sparged with different gases were compared. MECs pre-sparged with argon gas (Ar) yielded more hydrogen (3.73 ± 0.13 mol-H2/mol-acetate) and a higher hydrogen production rate (2.99 ± 0.17 L-H2/L-reactor-day) than MECs pre-sparged with N2 (3.41 ± 0.13 mol-H2/mol-acetate and 2.27 ± 0.28 L-H2/L-reactor-day, respectively). Microbiome analysis indicated that the relative abundance of Geobacter increased from 59.25% to 77.79% when the gas atmosphere in MECs shifted from N2 to Ar. Hydrogen production may have been catalyzed by nitrogenase from Geobacter and photosynthetic bacteria in MECs pre-sparged with Ar. These findings suggested that the gas atmosphere substantially influences the microbiome of anode biofilms and Ar sparging is most effective for enhancing hydrogen production in MECs.

Effect of gas atmospheres on degradation of MgO thin film magnetic tunneling junctions by deionized water

The degradation of the MgO thin film barrier of magnetic tunneling junctions caused by the dissolution of the film in deionized water during manufacturing processes is critical to the performance of spintronic devices. In this work, the influence of gas atmospheres including oxygen (O2), nitrogen (N2) and carbon dioxide (CO2) on dissolution behavior of the film was investigated by using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic absorption spectroscopy (AAS). XPS depth profile results reveal that deionized water reacts with the film and infiltrates into the deeper layer of the film resulting in the chemical transformation of MgO to Mg(OH)2. AAS results confirm that the films dissolve because Mg2+ ions are released into deionized water. Consequently, Mg concentration in deionized water increases. It is found that the concentration of Mg2+ ions in deionized water is highest in the dissolution of CO2-saturated deionized water and lowest in those of N2-saturated deionized water. Simultaneously, the release of Mg2+ causes the development of the coral-like clusters over their surface and a decrease of the film thickness. XPS depth profile and SEM cross-sectional results demonstrate that the film thickness slightly decreases in sample N2 and decreases considerably in sample CO2. This is due to the fact that CO2 gas reacts with water, reducing its pH and thus increasing of the dissolution rate, while N2 gas has no reaction with water. Finally, this work proposes a qualitative model based on chemical reaction to explain the dissolution behavior of the film.

Genesis of micropores by thermal activation of Mg-Al layered double hydroxides possessing interlayer organic sulfonates under oxygen-free environments

Microporosity and basic-site density of mixed oxides formed from Mg-Al layered double hydroxides possessing interlayer isethionate (MgAl-Ise) were investigated to seek for a potential application of them to basic catalyst supports for natural gas conversion. The oxide samples were prepared by thermal activation of MgAl-Ise at 500 °C in air, 5% O2 in N2, N2, vacuum, H2 in helium with various concentrations, H2, and NH3 to investigate effects of gas atmosphere. The N2 adsorption data show that Mg-Al mixed oxides obtained by thermal activation of MgAl-Ise in H2, NH3, and N2 possess substantially larger micropore volumes characterized by N2 uptake at the relative pressure <10–3 than those obtained in oxygen-containing atmospheres. The data indicate that these accessible micropores originate from interlayer spaces and form upon removal of a majority of sulfonates under H2, NH3, and N2 treatments. Thermal activation of MgAl-Ise in H2 and NH3 enhances the concentration of basic sites probed by CO2 relative to that conducted in N2 by facilitating removal of sulfonate-derived species. Upon conversion of MgAl-Ise to mixed oxides with removal of interlayer sulfonates, the material catalyzes H2-D2 exchange reaction.

Effect of Gas Atmosphere on the Phase Chemistry in the CaO–FeO–Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;–SiO&lt;sub&gt;2&lt;/sub&gt; System Related to Iron Ore Sinter-making

Experimental phase equilibria studies have been carried out to investigate the phase chemistry in the CaO Fe2O3-SiO2 system related to the iron ore sinter making in 1 atm CO2 at 1 200-1 230 degrees C. The measurements have been performed using a modified experimental technique involving high temperature equilibration and rapid quenching followed by electron probe X-ray microanalysis (EPMA). In contrast to the equilibria in air, the experimental results show that no silico-ferrite of calcium (SFC solid solution) is formed in 1 atm CO2 within the temperature range investigated; that is, the SFC phase is not stable at liquidus temperatures. The liquidus for the iron -rich corner of the CaO Fe2O3-SiO2 system in CO2 atmosphere for the spinel (magnetite Fe3O4) and dicalcium silicate (C2S = Ca2SiO4) primary phase fields has been proposed.

Green synthesis of water dispersied graphene nanosheets using gamma radiation and natural capping agents

Clean and green reduction of graphene oxide (GO) to graphene (GR) nanosheets was achieved by gamma irradiation. The reduction efficiency was evaluated using UV–vis spectra. The effects of gas atmosphere, pH value of the dispersion medium, type of capping agent and absorbed dose on GR nanosheet formation were studied. Sodium carboxymethyl cellulose, ethyl hydroxyethyl cellulose, glucose and polyvinyl alcohol were investigated as capping agents. The presence of such one of them was proven to be crucial. The GR nanosheets obtained were characterized using AFM, TEM, FTIR, XRD, TGA and DSC. Effectiveness, simplicity, reproducibility, and low energy consumption are the merits of this technique.

Vpliv plinske atmosfere na nekovinske vključke v lasersko varjenem trip jeklu z dodatkom Al in Si

Vpliv plinske atmosfere na nekovinske vključke v lasersko varjenem trip jeklu z dodatkom Al in Si

The Potential of Na–Air Batteries

AbstractSodium–air batteries (SABs) have attracted wide attention in the chemistry society owing to their high energy density, abundant precursor sources, inexpensive materials and reduced manufacture costs, and environmental benignity. This review summarizes the research and progress of the rechargeable SABs based on nonaqueous and aqueous electrolytes. The effects of gas atmosphere, environmental pressure, catalysts, and architectures of the electrodes on the distribution and morphology of discharge products in SABs are also included. The complex and rich sodium electrochemistry of air electrodes is presented, and many electrochemical reaction mechanisms based on the structure design of air electrodes with various catalysts and electrolytes are also summarized. They involve the reversible formation/decomposition reactions of NaO2, Na2O2, Na2CO3, NaHCO3, Na2C2O4, and NaOH. It is a great challenge to seek for highly efficient electrocatalysts, and more stable and less volatile electrolytes to improve the cyclability of nonaqueous SABs. Internal resistance of the cell could be efficiently improved by developing solid electrolytes with high ion conductivity and optimizing the structures of the cells for the high power density of aqueous SABs. How to effectively control the growth and decomposition of discharged products at three‐phase boundary reaction zones by the integration of highly stable electrolytes and optimization of air electrodes is the next challenge urgently needing to be addressed; only then can we realize practical high performance nonaqueous SABs for daily use.

Pyridine and pyrrole oxidation under oxy-fuel conditions

ABSTRACTIn this article, a study on pyridine and pyrrole oxidation under oxy-fuel conditions has been carried out. The experimental results indicate that when the temperature is above 800°C, concentration of N2O in the offgas quickly destructs mainly into N2 with the increase of temperature. Both NO and N2O concentrations can be enlarged, obviously due to the increase of oxygen concentration. In addition, the effect of gas atmosphere on pyrrole oxidation is quite different from that on pyridine oxidation. Introduction of high content CO2 in oxy-fuel combustion can lead to a certain migration change of fuel nitrogen.

Effect of gas atmosphere on the formation of silicon by reaction of SiC and SiO2

The formation of silicon by reaction between quartz and SiC has been studied in the temperature range of 1600–1900 °C in argon and hydrogen atmospheres. The reaction process was monitored by an infrared gas analyzer, and the reaction products were characterized by LECO, XRD, and SEM. Quartz–SiC reactions with SiO2/SiC molar ratio of 1:1 and 1:2 were studied in a fixed bed reactor in a graphite furnace. The production of silicon from quartz and SiC was strongly affected by temperature, SiO2/SiC molar ratio, and gas atmosphere. The yield of silicon in the reaction at 1900 °C in argon from samples with SiO2/SiC molar ratios of 1:1 and 1:2 reached 32.7 and 44.5 %, respectively. SiO2–SiC reaction at 1900 °C in hydrogen with the SiO2/SiC molar ratio of 1:2 resulted in the silicon yield of 66.7 %. Higher silicon yield in hydrogen was attributed for the involvement of hydrogen in the direct reduction of silica to SiO.

Trace element deportment and particle formation behaviour during thermal processing of iron ore: technical reference for risk assessment of iron ore processing

Understanding the mechanisms of the formation and emission of pollutants during iron and steel manufacturing is significantly important for improved control, collection, and recycling of the trace element impurities and particle emissions. The aim of this study was to investigate the distribution of trace elements and particle size formation behaviour of products during the thermal processing of iron ores. The effects of gas atmosphere (inert, oxidizing, and reducing) and temperature (850 and 950 °C) on trace element distribution in solid and liquid products were studied in a circulating fluidized bed reactor. The particle size distribution of the solid products was also assessed to determine the proportion of particulate matter formed with a diameter less than 2.5 microns. The study revealed the influence and importance of the gas atmosphere and processing temperature on the particle formation behaviour and deportment of certain trace elements from the input iron ore to the product streams during thermal processing of iron ore. The increase in temperature resulted in further migration of the elements from the iron ore to the particles formed and emitted during the processing. The relative risk assessment from the individual trace elements suggested that manganese and sulphur are the most important elements with highest risk scores in the particles and, in case of sulphur, also in the condensed phase. This paper provides a reference for risk assessment of the trace elements and particle emissions from iron ore processing to facilitate the control, collection, and recycling of trace element impurities and particle emissions.

Effect of Gas Atmosphere on Graphitization of Carbon Powder

Effect of Gas Atmosphere on Graphitization of Carbon Powder

Effect of Gas Atmosphere on Ag-Embedded ZnO Nanofilms: Structural, Optical and Electrical Properties

The effects of gas atmosphere and sputter time for depositing silver (Ag) on the structural, optical and electrical properties of ZnO/Ag/ZnO transparent conducting oxide (TCO) films have been investigated with sputtering Ag target in Ar or N2. It was found that the properties of the Ag and ZnO/Ag/ZnO films are quite dependent on the gas environment and the sputter time. The optical transparency of ZnO/Ag/ZnO films was easily controllable when sputtering the Ag target in N2 rather than in Ar. With optimizing the sputter time and atmosphere for Ag adsorption, the ZnO-based TCO films where the Ag layer was embedded in N2 yielded low resistance of 6.1-9.1 omega/sq and high transmittance of 93-96% over the visible range of wavelengths.

Effects of gas atmospheres on poly(lactic acid) film in acrylic acid plasma treatment

Plasma polymerized acrylic acid (AA) coatings were deposited on poly(lactic acid) (PLA) films in various gas atmospheres during the pre-treatment of PLA and the deposition of AA, respectively. Therefore, this work was twofold: the argon pretreated PLA films followed by a deposition in argon were investigated against the mixture of argon and oxygen pretreated ones under the same deposition conditions; the plasma deposition of AA operating in different atmospheres (argon, oxygen and nitrogen) was employed to modify the pretreated PLA in oxygen. Chemical and physical changes on the plasma-treated surfaces were examined using contact angle, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and attenuated total reflection infrared (ATR-FTIR) analysis. The results showed that the discharge gas can have a significant influence on the chemical composition of the PLA surfaces: oxygen plasmas introduced oxygen-containing groups in company with surface etching in pretreatment and deposition, while argon discharges was able to achieve much better hydrophilic behavior and high retention ratio of poly(acrylic acid) (PAA) coating before and after washing in water.

Effect of Gas Atmosphere on Catalytic Behaviour of Zirconia, Ceria and Ceria–Zirconia Catalysts in Valeric Acid Ketonization

Ketonization of valeric acid, which can be obtained by lignocellulosic biomass conversion, was carried out in a fixed bed flow reactor over ZrO2, 5–20 % CeO2/ZrO2 and CeO2 both under hydrogen and nitrogen stream at 628 K and atmospheric pressure. Regardless gas-carrier 10 wt% CeO2/ZrO2 was found to show higher catalytic activity compared to zirconia per se as well as other ceria modified zirconia while ceria per se exhibited very low catalytic activity. All catalysts provided higher acid conversion in H2 than in N2 whereas selectivity to 5-nonanone was insensitive to gas atmosphere. XRD, FTIR, UV–Vis DRS, XPS, HRTEM methods were applied to characterize catalysts in reduced and unreduced states simulating corresponding reaction conditions during acid ketonization. XRD did not reveal any changes in zirconia and ceria/zirconia lattice parameters as well as crystalline phase depending on gas atmosphere while insertion of ceria in zirconia caused notable increase in lattice parameter indicating some distortion of crystalline structure. According to XPS, FTIR and UV–Vis methods, the carrier gas was found to affect catalyst surface composition leading to alteration in Lewis acid sites ratio. Appearance of Zr3+ cations was observed on the ZrO2 surface after hydrogen pretreatment whereas only Zr4+ cations were determined using nitrogen as a gas-carrier. These changes of catalyst’s surface cation composition affected corresponding activity in ketonization probably being crucial for reaction mechanism involving metal cations catalytic centers for acid adsorption and COO− stabilization at the initial step.

Oxy-fuel combustion of millimeter-sized coal char: Particle temperatures and NO formation

In this work, differences in particle temperature and NO yield during char oxidation in O2/N2 and O2/CO2 atmospheres, respectively, have been examined. A laboratory scale fixed bed reactor, operated isothermally at 1073K, was used for combustion of millimeter-sized lignite and bituminous coal char particles in 5–80vol.% O2. Experiments were carried out with both single particles of different sizes (1.3–543mg) and multiple particles (30–50mg). Particle temperatures and structural changes were recorded by a Charged Coupled Device (CCD) camera during the experiments. The particle surface temperatures increased with mass loading, by as much as 700K above the furnace set point. The formation of NO from lignite char was not influenced by the change from N2 to CO2 whereas the NO yield from bituminous coal char was considerably lower in O2/CO2 compared O2/N2. For both chars the conversion to NO decreased as the O2 concentration or the particle size increased. However, for the bituminous coal char, a peak in NO yield was observed at an intermediate particle size of 0.1–0.2g. The differences in the effect of gas atmosphere, O2 concentration, and particle mass on the NO yield from oxidation of bituminous coal char and lignite char, respectively, cannot be fully explained. Char/NO interactions appear to be quite complex, and mineral catalysis and release to the gas-phase of volatile N-species such as HCN, either from secondary pyrolysis or as a product of the char–N+O2 reaction, may play a role.

Effect of Gas Atmosphere on Carbothermal Reduction and Nitridation of Titanium Dioxide

This article examined the reduction/nitridation of rutile in the He-N2, Ar-N2, and He (Ar)-H2-N2 gas mixtures, as well as pure nitrogen, in the temperature-programmed and isothermal experiments in a fixed-bed reactor. The extents of reduction and nitridation were determined from the off gas composition and LECO analysis. The off-gas composition was monitored using the infrared sensor (CO, CO2, and CH4) and dew point analyzer (H2O). The phase composition of the reduced samples was analyzed using X-ray diffraction (XRD). The temperature and gas composition had a strong effect on the rutile reduction. The reduction was the fastest in the H2-N2 gas mixture, followed by a reduction in nitrogen; the rate of reduction/nitridation in the He-N2 gas mixture was marginally higher than in the Ar-N2 gas. The rate of titania reduction/nitridation in the He (Ar)-H2-N2 gas increased with the replacement of He (Ar) with hydrogen. The article also discusses the mechanisms of reduction/nitridation in different gas atmospheres.