Ppm Oxygen Research Articles

UV-enhanced O2 sensing using β-Ga2O3 nanowires at room temperature

Oxygen sensors based on β-Ga2O3 nanowires were prepared by a chemical vapor deposition method and investigated in detail. β-Ga2O3 nanowires grew on sapphire substrate at 1100 °C with Au as a catalyst. The polycrystalline structure was confirmed according to the X-ray diffraction (XRD) patterns. Scanning electron microscope (SEM) images revealed the average diameter of the nanowires was 150 nm. The ratio of Ga to O was 0.765 according to energy dispersive spectroscopy (EDS) results. Photoluminescence emissions at 445 and 484 nm originated from oxygen vacancies and gallium-oxygen vacancy pairs. Both EDS results and photoluminescence revealed intrinsic oxygen vacancies in β-Ga2O3 nanowires. We coated the β-Ga2O3 nanowires on an interdigitated electrode to fabricated an oxygen sensor. Under ultraviolet light irradiation, at room temperature, the sensor’s response rise time and recovery time were 1034 s and 1283 s to 600 ppm oxygen, those were 1290 s and 1709 s to 1200 ppm oxygen. The mechanism of oxygen sensing was discussed.

Influence of powder surface chemistry on the defect formation in AlSi10Mg alloy processed via laser powder bed fusion additive manufacturing

In laser powder bed fusion(LPBF) additive manufacturing(AM) of Al alloys, surface chemistry and dissolved gas composition(oxygen/oxides/hydroxides, hydrogen and moisture) of AM powders is a major influencing factor for porosity formation. Therefore, in the present investigation, this aspect is addressed using two sets of virgin AM AlSi10Mg powders, namely, Hi-Ox (2770 ppm oxygen) and Lo-Ox (660 ppm oxygen), to assess the printability under various processing parameters and defect formation in printed parts. Comprehensive and in-depth metallurgical analysis of both powders utilizing multiple characterisation techniques established the presence of various types of oxides/hydroxides with different complex chemistries on the powders’ surface. Enhanced spherical gas porosity and oxide inclusions were witnessed in Hi-Ox print coupons in contrast to the least defects in Lo-Ox coupons rationalized due to surface chemistry difference between the virgin powders. Consequently, the mechanical properties of the Hi-Ox print coupons, even with minimum defect density, are significantly inferior to Lo-Ox specimens. These observations suggest a competing influence of surface chemistry/dissolved gas composition and laser parameters for the processing of both powders. Overall, by correlating the microstructures with processing conditions and oxide concentration, defects morphology, the probable melt pool formation mechanism in LPBF of AlSi10Mg alloy (for high and low oxygen concentration) is elucidated.

Understanding the mechanism of propane dehydrogenation over coordinatively unsaturated Co-O acid-base pairs and the inhibition effect of trace oxygen

High temperature and a reducing atmosphere are characteristic of propane dehydrogenation (PDH) reaction. Under such condition, the real surface structure of catalysts often differs from that in the ambient environment, particularly for CoOx species with multiple valence states and coordination. Here, a combination of in situ/operando Raman spectroscopy, in situ UV–Vis diffuse reflectance spectroscopy (DRS), and density functional theory (DFT) calculations reveal that coordinatively unsaturated Co-O (Cocu-O) acid-base pairs via lattice oxygen consumption are the PDH active sites of CoOx/Al2O3 catalysts. This highly dispersed Cocu-O species exhibit a C3H6 formation rate and C3H6 selectivity as high as 2 mmol‧gcat−1‧min−1 and 95 %, respectively, which is comparable to most state-of-the-art CoOx-based catalysts. However, industrial C3H8 raw gases typically contain 10–1000 ppm oxygen gas, and the complete eliminating oxygen increases costs. PDH catalytic performance of CoOx/Al2O3 catalysts is sensitive to the extremely low concentration of oxygen gas and is significantly inhibited by it. The fundamental reason is that the concentration of Cocu active sites is determined by the competitive reaction between the filling of trace oxygen on oxygen vacancies and lattice oxygen consumption. The reaction rate of the former is significantly higher than that of the latter. The higher reducibility of CoOx species leads to relatively weaken inhibition of trace oxygen for PDH activity. The oxygen content in the propane feed gas is a non-negligible factor in the development of new Co-based PDH catalysts, especially for their industrial applications.

Loss-of-Life Analyses Based on Modified Arrhenius and Relative Aging Rate for Non-Thermally Upgraded Paper in Oil-Immersed Transformer

This study evaluates the Loss-of-Life (LOL) based on the modified relative aging rate of an Oil Natural Air Natural (ONAN) transformer with voltage and power ratings of 132/33 kV and 60 MVA. The study’s methodology included the determination of the Hotspot Temperature (HST) based on the differential equation in IEC 60076-7. The loading and ambient temperature profiles for HST determination are forecasted based on the Seasonal Autoregressive Integrated Moving Average (SARIMA). Next, a new relative aging rate was developed based on the Arrhenius equation, considering the pre-exponential factors governed by oxygen, moisture in paper, and acids at different content levels. The LOL was computed based on the new relative aging rate. The study’s main aim is to examine the impact of pre-exponential factors on the LOL based on modified Arrhenius and relative aging rate. The results indicate that the LOLs for different conditions increase as the oxygen, moisture, low molecular weight acid (LMA), and high molecular weight acid (HMA) increase. The LOLs are 46 days, 1,354 days, and 2,662 days in the presence of 12,000 ppm, 21,000 ppm, and 30,000 ppm of oxygen. In 1%, 3%, and 5% moisture, the LOLs are 477 days, 2,799 days, and 7,315 days. At 1% moisture, the LOL is 1,418 days for LMA, while for HMA, it is 122 days. The LMA has the highest impact on the LOL compared to other aging acceleration factors.

Inert-Atmosphere Microfabrication Technology for 2D Materials and Heterostructures.

Most 2D materials are unstable under ambient conditions. Assembly of van der Waals heterostructures in the inert atmosphere of the glove box with ex situ lithography partially solves the problem of device fabrication out of unstable materials. In our paper, we demonstrate an approach to the next-generation inert-atmosphere (nitrogen, <20 ppm oxygen content) fabrication setup, including optical contact mask lithography with a 2 μm resolution, metal evaporation, lift-off and placement of the sample to the cryostat for electric measurements in the same inert atmosphere environment. We consider basic construction principles, budget considerations, and showcase the fabrication and subsequent degradation of black-phosphorous-based structures within weeks. The proposed solutions are surprisingly compact and inexpensive, making them feasible for implementation in numerous 2D materials laboratories.

Tellurium Corrosion of Type 304/304L Stainless Steel, Iron, Chromium, and Nickel in High-Temperature Liquid Sodium.

Investigating tellurium (Te) corrosion on structural materials is crucial for sodium-cooled fast reactors (SFRs) due to radionuclide presence and knowledge gaps. In this study, Type 304/304L stainless steel (SS304), chromium (Cr), iron (Fe), and nickel (Ni) samples were immersed in low-oxygen environments with Te in liquid sodium at 773 K for 30 days. At 10 ppm oxygen, SS304 showed multiple oxide layers, including a compact NaCrO2 interlayer and porous Na-Fe-Ni-O outer layers. Tellurium penetrated through the porous layers but was hindered by the NaCrO2 interlayer. At 0.01 ppm oxygen, Cr had no oxide layer, while Fe and Ni had unstable ones. Tellurium-induced pitting was deeper in Fe and Ni compared to Cr. Oxygen levels and Cr composition are critical factors affecting stable oxide compound layer formation and mitigating Te-induced pitting.

Oxygen content effect on mechanical properties and microstructure of TZM alloy

A series of molybdenum‑titanium‑zirconium (TZM) alloys with continuous oxygen content gradients were fabricated by powder metallurgy and the correlation between microstructure and properties was investigated. By controlling the carbon source, TZM-like alloys with an oxygen content of 2000 ppm, 1000 ppm, and TZM alloy with an oxygen content of 300 ppm (±100) were obtained, followed by rolling and heat treatment, and the effect of oxygen on the development of the microstructure and the mechanical properties of the alloy was studied. The results show that the changing of the oxygen content has a significant impact on the mechanical properties and microstructure of the alloy. With the increase in oxygen content, titanium and zirconium are more inclined to combine with oxygen to form oxide particles of titanium and zirconium (TiO2, ZrO2), the secondary phase particles increase significantly, and the alloy strengthening mode changes from solid solution strengthening to secondary phase dispersion strengthening. Owing to the inhibition of grain boundary migration by the secondary phase, the grain size of the alloy decreases as its oxygen content rises, which causes an increase in hardness of around 10 HV0.1 for every 1000 ppm increase in oxygen content. According to the Hall-Petch relationship, the yield strength of the annealed alloy increased from 336 MPa (300 ppm) to 556 MPa (2000 ppm) with smaller grain size. Kernal Average Misorientation (KAM) is used to characterize the dislocation density of the alloy, and the results show that the value of KAM is negatively correlated with the toughness of the alloy. The KAM value of the alloy is the lowest at 1000 ppm and its greatest elongation reaching 16.8%. Dislocation cells formed in the long-striped grains with an oxygen content of 300 ppm, greatly enhancing the strength of the material and maintain good plasticity. TZM alloy with 300 ppm oxygen has the highest tensile strength of 866 MPa and has an elongation of 15%, which is the leading performance compared with ASTM-specification B386/B386M.

Injectable Antioxidant and Oxygen-Releasing Lignin Composites to Promote Wound Healing

The application of engineered biomaterials for wound healing has been pursued since the beginning of tissue engineering. Here, we attempt to apply functionalized lignin to confer antioxidation to the extracellular microenvironments of wounds and to deliver oxygen from the dissociation of calcium peroxide for enhanced vascularization and healing responses without eliciting inflammatory responses. Elemental analysis showed 17 times higher quantity of calcium in the oxygen-releasing nanoparticles. Lignin composites including the oxygen-generating nanoparticles released around 700 ppm oxygen per day at least for 7 days. By modulating the concentration of the methacrylated gelatin, we were able to maintain the injectability of lignin composite precursors and the stiffness of lignin composites suitable for wound healing after photo-cross-linking. In situ formation of lignin composites with the oxygen-releasing nanoparticles enhanced the rate of tissue granulation, the formation of blood vessels, and the infiltration of α-smooth muscle actin+ fibroblasts into the wounds over 7 days. At 28 days after surgery, the lignin composite with oxygen-generating nanoparticles remodeled the collagen architecture, resembling the basket-weave pattern of unwounded collagen with minimal scar formation. Thus, our study shows the potential of functionalized lignin for wound-healing applications requiring balanced antioxidation and controlled release of oxygen for enhanced tissue granulation, vascularization, and maturation of collagen.

Effects of pulse rise time on electron dynamics properties in nitrogen–oxygen mixture under repetitive nanosecond pulses

The effects of pulse rise time on the temporal evolution of electron energy and density under repetitive nanosecond pulses in atmospheric nitrogen with 100 ppm oxygen impurities are investigated in this paper by a two-dimensional particle-in-cell/Monte Carlo collision model. It is found that the peak value of mean electron energy increases with decreasing pulse rise time in the single pulsed discharge. However, in the repetitive pulsed discharge approximated by pre-ionization, the peak value of mean electron energy no longer varies with the pulse rise time, showing a saturation trend with decreasing pulse rise time. Whether or not pre-ionization is present, the time required for the mean electron energy to reach its peak is approximately equal to the pulse rise time. It is worth noting that the presence of pre-ionization enhances the tracking ability of the mean electron energy to the pulse waveform during the pulse rise edge. Although after the peak of the pulse, the mean electron energy terminates the tracking process to pulse waveform due to the formation of high-density avalanches and even streamers, its energy decay rate gradually decreases with the increase in the pre-ionization density. Therefore, when the pulse repetitive frequency is greatly increased or the pre-ionization density is increased by other means, it is possible to achieve the complete control of the mean electron energy by pulse waveform modulation.

Directed-energy deposition of Ti-6Al-4V alloy using fresh and recycled feedstock powders under reactive atmosphere

This research studies the directed-energy deposition of Ti-6Al-4V (wt%) in an argon atmosphere containing 9–9500 ppm oxygen (from air), using both fresh and recycled feedstock powders. For fresh powder builds, when exposed to a 3500 ppm oxygen-containing atmosphere, a yield strength (YS) of 1061 ± 0.6 MPa and an elongation-to-fracture (ETF) of 10.5 ± 1.6 % are obtained. The oxygen pickup in the build deposit tends to plateau at 1000 ppm beyond 3500 ppm oxygen exposure. Conversely, the nitrogen pickup shows an increasing trend, reaching 1000 ppm for the air exposure range investigated. Recycled powder builds are stronger but less ductile than equivalent fresh powder builds made under comparable atmospheres. A higher degree of interstitial element pickup with no apparent saturation is identified for builds made from recycled powders, due to their smaller average particle size and a correspondingly larger specific surface area. The resulting microstructure for all samples made with air exposure comprises full lamellar α + β, formed through the in-situ decomposition of martensite at a temperature close to 600 °C. This conclusion is supported by the β volume fraction at 600°C as predicted by Thermo-Calc agreeing with image analysis data. The α lath thickness is found to increase with air exposure level. The increased β-transus temperature and martensite start temperature, and the accelerated diffusion-driven phase transformation due to the presence of elevated interstitial element contents accounts for the α lath thickening behaviour. YS and ultimate tensile strength (UTS) are found to increase linearly with oxygen equivalent. Solid solution strengthening from nitrogen and oxygen pickup is responsible for this increase. YS and UTS models based on oxygen equivalent are proposed. Nitrogen and oxygen in the builds dictate the ETF, with nitrogen content being the more potent factor.

Influence of long term Sodium Exposure on the Corrosion and Tensile Properties of AISI Type 316LN stainless steel and modified 9Cr-1Mo steel

AISI Type 316LN stainless steel (SS) and modified 9Cr-1Mo (P91) steel are used in the intermediate heat exchanger and steam generator (SG), respectively of prototype fast breeder reactor (PFBR). This paper presents the effect of long-term sodium exposure (50000 h) on the corrosion and tensile properties of 316LN SS and P91 steel. The results showed that the prolonged sodium exposure of 316LN SS can lead to selective leaching of alloying elements (depletion of Cr, Ni, and Mo), enrichment of Fe, formation of ferrite layer and carburized zones with increased hardness at the surface (272 HV), and a reduction in ductility by nearly 40 %. Double-loop electrochemical potentiokinetic reactivation (DLEPR) results of sodium exposed 316LN SS showed a 25% higher degree of sensitization (DOS) as compared to thermally aged one. The microstructural examination of sodium exposed 316LN SS revealed a ditch structure near the surface and carbide precipitates along the grain boundaries indicating the diffusion of carbon through grain boundaries and surface carburization. XRD studies of sodium exposed 316LN SS revealed predominant phases of ferrite and Cr23C6 phases, which further corroborated the results of DLEPR, microstructure, and hardness data. The sodium exposed P91 steel showed no significant microstructural, microchemical changes and tensile properties after sodium exposure. The carbon depth profiles carried out using SIMS in sodium exposed 316LN SS and P91 steel showed a surface carbon concentration of 0.85 and 0.32 wt.%, respectively. Fractography of sodium exposed 316LN SS showed intergranular fractures whereas the fractographs of P91steel showed fibrous dimple and cleavage type of fractures indicating the growth of carbides. The present results confirm that P91 steel can sustain the reactor life in flowing sodium containing 25 ppm carbon and less than 2 ppm oxygen.

Effects of oxygen content on microstructure and mechanical properties of 18Ni300 maraging steel manufactured by laser directed energy deposition

Compared to conventional material processing technologies, laser directed energy deposition (LDED) belonging to additive manufacturing (AM) has many advantages and enormous commercial potential. However, the effect of external factors on the deposition process has not been completely revealed such as the oxygen content in the manufacturing environment. 18Ni300 as maraging steel has excellent mechanical performance, but oxidation inside parts could induce metallurgical defects like inclusion or cracks and impair the service life of parts. Therefore, this paper focuses on the microstructure and mechanical properties of 18Ni300 maraging steel fabricated by LDED under different oxygen contents. The control of oxygen content in the environment was achieved by changing the argon content. Experimental results indicated that the forming accuracy of specimens and process stability were effectively improved at both 500 ppm and 50 ppm oxygen contents. The width of equiaxed grain region, grain growth orientation and primary dendritic arm spacing were significantly affected by gaseous environment. In the low oxygen content group, higher microhardness values were obtained due to the effect that similar to heat treatment. The ultimate tensile strength of samples reached to 908 MPa under 50 ppm oxygen content, which exceeded the tensile strength of wrought components.

Ppm-level oxygen detection system based on deep-ultraviolet-absorption spectroscopy.

Oxygen is a gas essential to human life and industrial processes. Here, we developed a highly sensitive oxygen gas sensor based on deep ultraviolet absorption spectroscopy between 180 and 200 nm. The implemented method relies on differential absorption spectra extracted from the obtained high-resolution absorption spectra. The detection capability was greatly improved (six-fold) by eliminating air from the open optical path, achieved by purging the entire system with pure nitrogen. A linear relationship was obtained between the optical parameter and the oxygen concentration with a slope of 0.107 and determination coefficient of 0.999. A detection limit of 24 ppm per meter was determined with a response time of 25 s. Good repeatability (standarddeviation=16ppm) and stability were confirmed. We demonstrated that this system can detect ppm oxygen levels with high sensitivity and low uncertainty.

Short-time heat treatments in oxygen strengthened Ti-Zr α titanium alloys: A simple approach for optimized strength-ductility trade-off

The influence of short-time heat treatments on Ti-4.5Zr alloys (wt%) with respectively low (2000 ppm) and high (6000 ppm) oxygen contents is investigated with the aim of optimizing their strength/ductility trade-off. Starting from a cold-rolled state (85% of total thickness reduction), a high level of ductility is restored in both systems thanks to the recovery process while the resistance drop is limited, thus proving the effectiveness of the approach. This work highlights the potential of reaching a recovered microstructure to obtain optimized mechanical properties in Ti-Zr system.

Mechanisms of heat treatment and ductility improvement of high-oxygen Ti–6Al–4V alloy fabricated by metal injection molding

Ti–6Al–4V alloy samples with 4000 ppm oxygen are fabricated by metal injection molding. The samples are subjected to a heat-treatment, in which the samples are solution-treated below the β transus and subsequently water-quenched. The tensile tests on the samples indicate that the plastic elongation of the alloy is successfully improved from 1.0 to 3.2% by the heat-treatment. Investigation on the microstructural evolution in the heat-treatment shows that an acicular α phase, existing in the β lamellar structure of the as-sintered samples and harmful for its ductility, is suppressed by quenching and effectively eliminated from the heat-treated samples. Moreover, in the solution treatment, the alloy splits into a primary α phase and a β phase. In the water quenching, the β phase is transformed into a lamellar structure of secondary α phase and β phase with improved ductility. As a result, the improved ductility of the heat-treated samples derives from the plastic deformation of the ductile lamellar structures and the synergic displacement of the rigid primary α phase.

Influence of Storage Conditions on Powder Surface State and Hot Deformation Behavior of a Powder Metallurgy Nickel‐Based Superalloy

Powder metallurgy (PM) FGH96 superalloy powders are stored under vacuum, argon, ambient air, and oxygen atmospheres for as long as 500 days. The surface analysis results demonstrate that the chemical state of Ni, Ti, Cr, Co, O, and C remain unchanged after 90 days storage. However, the oxygen content and NiO/Ni(OH)2 layer thickness increase from initial values (∼120 ppm and ∼3.8 nm) to stabilized values (∼200 ppm and ∼10 nm) after a short time storage (7–15 days), and remain basically unchanged with the extension of storage time. Powders stored in oxygen atmosphere possess the highest oxygen content (maximum 213 ppm) while the lowest in vacuum, the gap can reach to 25 ppm. The hot isostatic‐pressed (HIPed) parts that consolidated from original and stored powders are isothermally compressed at different conditions. The results indicate that HIPed parts with more oxygen will cause higher activation energy and narrower processing window due to a lower degree of dynamic recrystallization (DRX). Discontinuous DRX (DDRX) dominates the DRX nucleation mechanism of HIPed FGH96 superalloys with ∼120–200 ppm oxygen content, while continuous DRX (CDRX) is the auxiliary mechanism. The increased oxygen content and surface NiO/Ni(OH)2 layer thickness of superalloy powders generate higher oxygen content of corresponding HIPed parts, thus decreasing the hot workability.

Superior protective performance of Ni Cr coating on stainless steel 316L in pure, oxygenated and chlorinated supercritical water

The protective effect of Ni Cr coating in supercritical water (SCW) was studied in this work. Ni Cr coated 316 L stainless steel showed an excellent microstructure and performance stability in SCW. The corrosion weight gains of as-received 316L were 2–3.6 times of that of Ni Cr coated sample in SCW with 5000 ppm oxygen content. The coating greatly reduced the corrosion weight gain of 316L in a SCW environment after 144 h exposure. The surface of Ni Cr coating was composed of the outermost hydration layer (Ni(OH) 2 ), oxide layer (NiO, NiCr 2 O 4 and Cr 2 O 3 ) and metallic layer (Ni 0 ) mixed in oxides. NiO on the surface of the Ni Cr coating decomposed with the addition of oxygen or chloride ions in SCW. • The corrosion weight gains of as-received 316L were 2–3.6 times of that of the two coated samples. • The coating greatly reduced the corrosion weight gain of 316L in SCW environment after 144 h exposure. • Small amount of Fe diffused to the coating surface along surface defects on the Ni-Cr coating. • Ni-Cr coating contains the outermost hydration layer, oxide layer and metal elementary layer.

Effects of oxygen on thermal behavior and magnetic properties of FePC amorphous alloy

Effects of oxygen on thermal behavior and magnetic properties of Fe80P13C7 amorphous alloy were investigated in detail. Microstructures and thermal analysis revealed that crystallization behavior of oxygen-contained alloy was more sensitive to the temperature. With oxygen increasing, the saturation magnetization (Bs) of alloy increased firstly and then dropped, and the maximum value of 1.62 T was achieved with 241 ppm oxygen. The X-ray photoelectron spectroscopy result combined with atomic reconstruction model unveiled that oxygen only occupied one side of the C-centered clusters, and with oxygen doping, the breakage of Fe-C bonds triggered the more Fe-Fe and Fe-O bonds formed, and the competitive dominance of Fe-Fe supported an enhanced Bs of oxygen-contained alloy. Moreover, the domain patterns were analyzed to disclose the coercivity changes of relaxed alloy. This work has important theoretical significance for re-understanding the role of oxygen in the amorphous alloy and its influence on performance.

Measuring oxygen solubility in Ni grains and boundaries after oxidation using atom probe tomography

Poor oxidation resistance is a key contributor to material failure within extreme environments. Understanding oxygen solubility is important for computation aided design of new high strength, high-temperature oxidation resistant alloys. Oxygen solubility within pure metals, such as Ni, has been studied using a multitude of techniques, but Atom Probe Tomography (APT) has not been used for such a measurement to date. APT is the only technique offering both a high chemical sensitivity (<10 ppm) and resolution (<1 nm) allowing for a composition measurement within nms of the oxide/metal interface. APT was employed to measure the oxygen content at different depths from the oxide/metal interface as well as grain boundaries for a high and low purity Ni sample oxidized at 1000 °C for 48 h. The results reveal <10 s of ppm oxygen solubility within Ni metal at all depths and 100 s of ppm oxygen within GBs.

Selective laser melting of Al and AlSi10Mg: parameter study and creep experiments

Selective laser melted (SLM) aluminum alloys are widely used for many technical applications. However, the application is limited to low temperatures due to their relatively poor creep resistance. The creep resistance and strength could be enhanced by oxide dispersion-strengthening. A hypothesis is that oxygen intake during selective laser melting can lead to formation of fine aluminum oxides and thus strengthen the SLMed part. To elucidate this in more detail, selective laser melted AlSi10Mg was tested in creep experiments at temperatures of 300 °C. Although, in other studies at lower temperatures, a relatively large stress exponent for creep was found, the high temperatures in this work led to a creep exponent of just 7 to 8, indicating no significant dispersion strengthening. Furthermore, for future research, it was necessary to investigate the feasibility of SLM with pure aluminum. For this purpose, a parameter study was carried out and an optimum parameter set for pure aluminum was found. Dense samples with a porosity below 0.2% were produced. Selective laser melting was carried out with a varying oxygen content in the inert-gas atmosphere to elucidate the hypothetic strengthening effects by oxygen intake. However, even at 800 ppm oxygen in the atmosphere, no effect on hardness and microstructure could be observed.