Effect Of Oxygen Impurities Research Articles

Simultaneous effect of oxygen impurity and flow rate of purge gas on adsorption capacity of and heel buildup on activated carbon during cyclic adsorption-desorption of VOC

Irreversible adsorption, or heel buildup, negatively impacts activated carbon performance and shortens its lifetime. This study elucidates the interconnections between flow rate and the oxygen impurity of desorption purge gas with heel buildup on beaded activated carbon (BAC). Nine thermal desorption scenarios were explored, varying nitrogen purge gas oxygen impurity levels (<5 ppmv, 10,000 ppmv, 210,000 ppm (21 %)) and flow rates (0.1, 1, 10 SLPM or 1 %, 10 %, 100 % of adsorption flow rate) during thermal desorption. Results reveal that increasing purge gas flow rate improves adsorption capacity recovery and mitigates adverse effects of purge gas oxygen impurity. Cumulative heel increased with higher purge gas oxygen impurity and lower flow rates. In the least effective regeneration scenario (0.1 SLPM N2, 21 % O2), a 32.8 wt% cumulative heel formed on BAC after five cycles, while the best-case scenario (10 SLPM N2, <5 ppmv O2) resulted in only 0.3 wt%. Comparing the pore size distributions of virgin and used BAC shows that heel initially forms in narrow micropores (<8.5Å) and later engages mesopores. Thermogravimetric analysis (TGA) showed that oxygen impurity creates high boiling point and/or strongly bound heel species. TGA confirmed that higher purge gas flow rates reduce heel amounts but encourage chemisorbed heel formation in oxygen's presence. These findings can guide optimization of regeneration conditions, enhancing activated carbon's long-term performance in cyclic adsorption processes.

Balancing thermal conductivity and strength of hot-pressed AlN ceramics via pre-sintering and annealing process

The heat dissipation requirements of the new generation of semiconductors are placing higher demands on the overall performance of aluminum nitride (AlN) ceramics. This has led to an increasing emphasis on AlN ceramics that combine thermal conductivity and strength. AlN ceramics are often strengthened by hot-press sintering, but their thermal conductivity is typically modest. In this study, pre-sintering and annealing processes are introduced to optimize the thermal conductivity of hot-pressed AlN ceramics to avoid the detrimental effects of oxygen impurities in the AlN lattice. The effect of the oxide layer on the surface of commercial AlN particles is investigated, including density, phase composition, microstructure, and fracture behavior. The effect of annealing on the improvement of thermal conductivity and flexural strength is also verified. Electron paramagnetic resonance (EPR) analysis is performed to examine the concentration of intercrystalline defects under various conditions. Finally, AlN ceramics with a thermal conductivity of 204 W m−1 K−1 and a flexural strength of 376 MPa are obtained.

Fabrication of CZTS Films through a Combined Electrodeposition and Solution Process: An Experimental and First‐Principles Study

AbstractSulfurization has a critical role in preparation of CZTS films since the main drawback of CZTS is due to the presence of S‐based impurities. In general, sulfurization could be performed during or following annealing, or the entire CZTS structure could be prepared through sol‐gel. However, toxic gases are used for the former, and the latter takes prolonged times. Alternatively, a combined electrodeposition and solution process was proposed in the present work to prepare CZTS. Briefly, we electrodeposited CZT layers on a metal substrate, and then immersed the as‐prepared coating in a S containing solution for the sulfurization. The effects of electrodeposition time, electrodeposition order, current density, electrolyte compositions, sulfurization time, and annealing pressure were studied. Overall, the results show that S content of the films varied between 27 and 52 % depending on process parameters, thus, suggesting the effectiveness of the proposed approach regarding sulfurization. However, various secondary phases were also detected as well as considerable amount of oxygen impurity. Accordingly, we opted for a computational approach to elucidate the effect of oxygen impurities, and report that the band gap of the films varied between 0.59 and 0.05 eV depending on the presence and which sites oxygen atoms occupy.

Influence of Oxygen Impurity on Nitrogen Atmospheric-Pressure Plasma Jet

This study discussed the effect of oxygen impurity in the inlet gas of a nitrogen atmospheric pressure plasma jet (APPJ). A numerical model that takes into account the fluid dynamics, heat transfer, mass transfer, diffusion, and chemical reactions was developed to simulate the nitrogen APPJ. Further, a DC nitrogen APPJ experiment was performed to verify the plasma temperature characteristics on the treated surface. The plasma temperature decreased with an increase in the oxygen impurity. Moreover, the oxygen impurity influenced the related excited and neutral species. Specifically, with added oxygen impurity, N-related species decreased whereas O- and NOx-related species increased. Because the excited state species constitutes the most important reactant in APPJ treatment, this study could serve as a reference for the adjustment of a nitrogen APPJ.

Effect of oxygen impurity on corrosion behavior of a Zr-based bulk metallic glass in 0.5 M H2SO4 and 0.5 M NaOH solutions

• Effect of oxygen impurity on corrosion of a Zr-based BMG in H 2 SO 4 and NaOH is studied. • Oxygen impurity has no effects on the corrosion in 0.5 M H 2 SO 4 . • Oxygen impurity can improve the corrosion resistance in 0.5 M NaOH. • Oxygen-induced annihilation of free volume may account for the inhibited corrosion. Effects of unavoidable oxygen impurity in industrial-grade Zr-based bulk metallic glasses (BMGs) on their properties are the issues that must be considered. The studies on oxygen-related corrosion behaviors of Zr-based BMGs are rarely reported. This paper aims to clarify the effects of oxygen impurity on corrosion of the as-cast Zr 61 Ti 2 Cu 25 Al 12 BMGs in 0.5 M H 2 SO 4 and 0.5 M NaOH solutions. The results show that oxygen impurity has no effects on the corrosion in 0.5 M H 2 SO 4 , but is unexpectedly beneficial for improving the corrosion resistance in 0.5 M NaOH by inhibiting the cathodic reaction. The latter phenomenon could be correlated with the oxygen-induced annihilation of free volume. The finding herein further confirms that oxygen impurity is not harmful, even beneficial, for corrosion resistance of industrial-grade Zr 61 Ti 2 Cu 25 Al 12 BMGs.

Effect of oxygen defects on microstructure, optical and vibrational properties of ScN films deposited on MgO substrate from experiment and first principles

We report on the effects of oxygen impurities on the microstructure, surface morphology, optical absorption, and vibrational properties of scandium nitride thin films deposited onto magnesium oxide substrate by reactive magnetron sputtering and under ultrahigh vacuum conditions. Two distinct deposition temperatures of 700°C and 800°C were applied to adjust the level of oxygen contamination. The ScN/MgO(001) thin films have been characterized by various spectroscopic methods, including X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, Raman spectroscopy, and optical microscopy. The ScN films deposited at the lower temperature of the MgO substrate show higher content of defects, stronger disorientation, a larger concentration of twin domains, and suppressed adatom mobility as compared to layers deposited at the higher temperature. An increase by 2% in the amount of accommodated oxygen results in the increase in the direct energy gap of the ScN films by about 0.13 eV, which follows from the increased concentration of the n-type charge carriers incorporated by oxygen impurities. The observed increase in the absorption edge, i.e., enlargement of the optical band gap can be accounted for the Burstein–Moss effect. Experimental Raman spectra reveal coupling between longitudinal optic phonons and electronic states, which can be described by the Fano-type function with the asymmetry parameter increasing with increased content of oxygen defects. The ab initio Raman spectra of ScN with concentrations of oxygen impurities corresponding to the respective experimental values, obtained within density functional theory, demonstrate that incorporated impurities affect significantly the phonon dynamics via modified force constants, including those at atoms beyond the nearest neighbors of defects. The simulated Raman spectra reflect major features of the experimentally determined spectral patterns enabling better insight into the origin of changes experienced by the oxygen-modified ScN/MgO(001) films.

Influence of sputtered AlN buffer on GaN epilayer grown by MOCVD

The ex situ sputtered AlN buffer and GaN epilayer grown on top of it by metalorganic chemical vapor deposition were studied comprehensively by a variety of techniques including atomic force microscope, high resolution x-ray diffraction, Raman and x-ray photoelectron spectroscopy characterizations. It exhibited that the AlN buffer deposited by using sputtering technique could be oxidized with exposure in atmosphere. Such oxidation phenomenon significantly influences the characteristics of GaN epilayer, for example leading to poor surface morphology, high dislocation density, and large compressive stress. This study demonstrated the effect of oxygen impurities on GaN growth and has an important guiding significance for the growth of high-quality III-nitride related materials.

Effect of oxygen impurities on a caesium-covered Mo(0 0 1) surface

The interaction dynamics of atomic and molecular oxygen with a caesium-covered molybdenum surface is studied within a semiclassical collision method in conjunction with a Potential Energy Surface derived by DFT-D calculations. The surface exposed to a flux of oxygen atoms is immediately covered, as the only occurring process is the adsorption one, independently of impinging energy value. On the other hand, the incidence of molecules gives rise to three different competitive surface processes according to the molecule’s collisional energy: molecular adsorption, inelastic molecular scattering, inelastic atomic scattering. The interaction mechanism is highlighted and related to potential anisotropy. O2 molecules, initially in the ground roto-vibrational state, are mostly inelastically scattered in the same vibrational level, while the final rotational distributions extend to the complete rotational ladder. Vibrationally excited molecules can attenuate the oxygen adsorption detrimental effect because they trigger energy exchanges that favour molecular scattering.

The effect of oxygen impurities on the stability and structural properties of vacancy-ordered and -disordered ZrC x.

Theoretical calculations predict several long-range ordered sub-stoichiometric zirconium carbide phases to be stable at low temperature, rather than a random (disordered solution) distribution of vacancies. However, experimental synthesis of vacancy-ordered phases is extremely challenging and not all predicted phases have been experimentally observed. It has been hypothesised that the inevitable oxygen contamination in experimental samples may affect the vacancy ordering. In this work, the stability and structural properties of the vacancy-ordered and vacancy-disordered phases are investigated as a function of oxygen defect concentration using first-principles calculations. The observed trends are explained in terms of changes to the local bonding in the presence of varying amounts of oxygen and vacancies. It is found that the relative stability of the ordered phases (compared to the disordered phase at the same composition) decreases as oxygen concentration increases, and some vacancy-ordered phases are destabilised by the level of oxygen impurities found in experimental samples. This suggests that oxygen contamination is a contributing factor to the challenge of synthesising ordered zirconium carbides, and gives insight that may assist fabrication in the future. The volume of all ZrCx (x ≤ 1) phases was found to decrease with increasing oxygen concentration, which can be attributed to the different ionocovalent nature of the C–Zr and O–Zr bonds. The volume of the vacancy-ordered phases within the expected oxygen solubility limit is greater than the disordered phase of the same composition, which is explained in terms of the relative bond strengths surrounding different vacancy distributions.

Effects of oxides on optical absorption and homogeneity of GeS2-­Sb2S3-based glass

ABSTRACT We investigated the effects of oxygen impurities on the optical absorption, glass structure, and homogeneity of a sulfide glass that is a potential candidate for use as an infrared-transmitting material. We prepared glasses based on the pseudo-binary GeS2-Sb2S3 system by a conventional method using metals and sulfur as raw materials in an evacuated silica glass ampoule. The oxygen impurity content according to oxygen analysis was 0.034 mass% (340 ppm) for 20GeS2·80SbS3/2 glass. The oxygen impurities were distributed as oxides bonded to Ge and Sb with a distribution constant, although most of the oxygen was bonded to Ge. In addition, oxysulfide glasses were prepared by substituting GeO2 or Sb2O3 for the corresponding sulfides. In this case, the oxygen of the added oxides bonded mainly to Ge in the glasses. When more than 2 mol% of the oxides was substituted for the corresponding sulfides in the 20GeS2·80SbS3/2 glass, the glass became translucent or opaque. Microscopy observation revealed that droplet phases with diameters of 2 to 4 µm were precipitated. These phases were rich in germanium and oxygen. The inhomogeneity is induced by the addition of oxides to the glasses, particularly, in those with a large fraction of Sb2S3 in the composition.

Effect of Oxygen Impurity on Thermal Conduction Rate of Polycrystalline Si3N4

Heat transfer with homogeneous structures of Si3N4 system and the effects of oxygen defects in the Si3N4 grains are reported by Jung Woo Lee and co-workers in article number 2100566. The oxygen defects in the grains are moving to the surface of the grains and effectively captured by oxygen getter. The inhibition of the Si3N4 grain oxidization improves a spontaneous dissipation of thermal energy.

Oxygen impurity improving corrosion resistance of a Zr-based bulk metallic glass in 3.5 wt% NaCl solution

The effect of oxygen impurity on corrosion behavior of as-cast Zr61Ti2Cu25Al12 bulk metallic glasses (BMGs) is clarified using electrochemical measurements, microstructure characterization and surface analyses. We find unexpectedly that oxygen impurity (≤1200 ppm) improves pitting corrosion resistance when a fully amorphous structure is attained. The oxygen-induced annihilation of free volume enhances passive film protectiveness and hence accounts for the improved corrosion property. In contrast, adding more oxygen impurity (1800 ppm) deteriorates pitting corrosion resistance by assisting the formation of highly-reactive crystalline phases. The finding herein provides an avenue for designing new low-cost Zr-based BMGs with superior properties by oxygen microalloying.

Effect of oxygen impurities on the electronic and mechanical properties of penta-graphene sheet

The electronic and mechanical properties of a penta-graphene monolayer (PGM) in attendance and nonattendance of oxygen impurities were investigated using the SIESTA computational code, based on density functional theory calculations. The results of the first-principles (ab-initio) calculations show that PGM in the nonattendance of oxygen atoms is a semiconductor with indirect band gap. By adding the oxygen, the bandgap size of PGM changes. Analyzing the results indicates that oxygen absorption increases the stability of the structure. The results display that, the addition of oxygen atoms affects the electrical and mechanical properties of penta-graphene, such as converting the band structure from semiconductor to insulating, reducing Young’s modulus, and changing the Poisson’s coefficient sign. Penta-graphene has received a lot of attention from researchers as a mechanical metamaterial or auxetic material due to its negative Poisson coefficient.

Effect of Oxygen Impurity on Thermal Conduction Rate of Polycrystalline Si3N4

Herein, the thermophysical properties and microstructures of the densified Si3N4, which are prepared by using MgO, Y2O3, and oxygen getter as sintering additives via conventional hot‐pressing sintering and followed by postheat treatment, are reported. Herein, it is found out that the sample using 5 mol.% of MgO, 2 mol.% of Y2O3, and 1.5 mol.% of Nb has the optimized thermal conductivity of 108 W m−1·K. Furthermore, increased rate of thermal conduction in the range of 10–15% is mainly originated from the decrease in the lattice oxygen contents of the grains in Si3N4 based on electron spin resonance (ESR) analysis.

Effects of oxygen impurity and desorption temperature on heel build-up in activated carbon

Oxygen’s presence during thermal desorption of volatile organic compounds from activated carbon can promote heel build-up and loss of adsorption capacity. This study investigated the simultaneous effect of desorption temperature (200 °C and 288 °C) and oxygen concentration (≤5, 10,000, and 21,000 ppmv) on heel build-up. For this purpose, 5-cycle adsorption/desorption tests of 1,2,4-trimethylbenzene on a microporous activated carbon were completed. At low oxygen concentration (≤5 ppmv), desorption at 288 °C resulted in lower cumulative heel compared to at 200 °C; however, at high oxygen concentration (10,000 and 21,000 ppmv), desorption at 288 °C resulted in higher cumulative heel compared to 200 °C. Thermal gravimetric analysis (TGA) was used to assess the thermal stability of the heels formed on the samples. At high oxygen concentrations, the heel associated with desorption at 288 °C was more thermally stable than the heel formed at 200 °C, which can be attributed to thermal oxidation reactions of the adsorbate in the activated carbon pores.

Modeling of tip kinetics of undercooled Ti dendrites with consideration of forced flow and oxygen impurity effects

Tip velocities of undercooled dendrites in electromagnetically levitated melt droplets of pure Ti were modeled using a theory on three-dimensional dendritic growth with fluid flow and a dilute solute. The modeling shows that a forced flow due to electromagnetic stirring depresses tip velocities of the dendrites at low undercoolings and that its effect becomes negligible at high undercoolings. In contrast, an oxygen impurity dissolved in liquid Ti depresses tip velocities of the dendrites over a broad range of undercooling while it coarsens tip radii. Such modeling results allowed for reconciliation of discrepancies in literature data by considering an oxygen impurity effect. The modeling also predicts that the effect of the oxygen impurity becomes insignificant when its concentration is reduced below 50 ppm in atomic fraction.

Mapping the mechanical properties in nitride coatings at the nanometer scale

We report on a multilayered structure comprising of rock-salt (rs) structured CrN layers of constant thickness and AlN layers of varying thicknesses, which surprisingly enables the growth of metastable zinc-blende (zb) AlN layers for certain layer-thickness combinations. The multilayer exhibits an atomic and electronic structure gradient as revealed using advanced electron microscopy and electron spectroscopy. Gradient structures are also accompanied by a modulation of the chemical compositions. A combined experimental analysis based on valence electrons and inner shell electrons allowed mapping the mechanical properties of the multilayer at the nanometer scale and further unveiled the effect of oxygen impurities on the bulk modulus. We found that the presence of oxygen impurities causes a remarkable reduction of the bulk modulus of rs-CrN while having no significant effect on the bulk modulus of the stable wurtzite structure wz-AlN layers. The findings are unambiguously validated by theoretical calculations using density functional theory.

Effect of Acid Etching Time and Concentration on Oxygen Content of Powder on the Microstructure and Elastic Properties of Silicon Carbide Densified by SPS

In this current paper, oxygen content of a fine particle size SiC (H. C. Starck UF 25 Silicon Carbide) and coarser particle size SiC (Saint Gobain Silicon Carbide) were modified by using different concentrations of HF for etching. Fully dense silicon carbide ceramics (>99% th. density) were produced by the spark plasma sintering technique at 1950 °C under an applied pressure of 50 MPa for 5 min hold with boron carbide and carbon addition. Archimedes method, scanning electron microscopy, and the ultrasound analysis were used to examined density, microstructure, elastic (E), shear (G), and bulk (K) moduli of dense silicon carbide ceramics to investigate the effect of oxygen impurities on the densification and the properties of silicon carbide. The results showed that high oxygen content is detrimental to the final density of SPS silicon carbide. When the oxygen content increased from 0.60 to 5.92 wt.%, the relative density decreased from 99.99% to 96%. For both SiC powders, by increasing the etching time, the grain size of SiC decreased. It means that the high oxygen caused grain growth. Ultrasound analysis results showed that the high oxygen content affected the elastic properties. SiC samples with the high oxygen content had a lower elastic moduli, shear moduli and bulk moduli. It was clear that increasing the oxygen content decreased the elastic properties.

Effect of oxygen content on the sintering behaviour and mechanical properties of SiC ceramics

In the current work, SiC powders with various levels of oxygen content were obtained by two ways: acid leaching and heat treatment; and these SiC powders were densified by a pressureless sintering technique with boron carbide and carbon additives. The techniques of X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, transmission electron microscope, and mechanical testing were combined to examine the effects of oxygen impurities on the densification process of SiC ceramics. The experimental analyses indicated that high oxygen content is detrimental to the final sintering and mechanical properties of SiC ceramics. As the oxygen content increases from 0.55 to 2.10 wt%, the relative density and the hardness both decrease: the relative density drops from 98.53% to 70.55% (a 28% decrease), and the hardness drops from 27.1 ± 0.7 GPa to 6.7 ± 1.1 GPa (a 75% decrease). Furthermore, oxygen impurities can accelerate the abnormal growth and coarsening of SiC grains during sintering. In order to impede abnormal grain growth and achieve high densities of SiC ceramics, it is proposed that the oxygen content of the powders should be limited to less than 1.30 wt%.

Oxygen impurity effects on the mechanical properties of SiC studied by first principles calculations

First principle calculations are performed to study the oxygen doping effects on the mechanical properties of SiC. Both interstitial and substitutional oxygen atoms decrease the shear and tensile modulus and strength of SiC. The substitutional oxygen atoms decrease the shear and tensile modulus and strength more than the interstitial oxygen atoms do. Local distortions around the oxygen doping atoms are found in both of tensile and shear stress strain curve calculations in the elastic region. The shear strength of SiC decreases linearly with the increase of the oxygen concentration. The tensile strength of SiC also decreases with the oxygen concentration and it drops dramatically at low concentration region.