Dry Air Environment Research Articles

Enhancing the response of NH3 graphene-sensors by using devices with different graphene-substrate distances

Graphene (G) is a two-dimensional material with exceptional sensing properties. In general, graphene gas sensors are produced in field effect transistor configuration on several substrates. The role of the substrates on the sensor characteristics has not yet been entirely established. To provide further insight on the interaction between ammonia molecules (NH3) and graphene devices, we report experimental and theoretical studies of NH3 graphene sensors with graphene supported on three substrates: SiO2, talc and hexagonal boron nitride (hBN). Our results indicate that the charge transfer from NH3 to graphene depends not only on extrinsic parameters like temperature and gas concentration, but also on the average distance between the graphene sheet and the substrate. We find that the average distance between graphene and hBN crystals is the smallest among the three substrates, and that graphene-ammonia gas sensors based on a G/hBN heterostructure exhibit the fastest recovery times for NH3 exposure and are slightly affected by wet or dry air environment. Moreover, the dependence of graphene-ammonia sensors on different substrates indicates that graphene sensors exhibit two different adsorption processes for NH3 molecules: one at the top of the graphene surface and another at its bottom side close to the substrate. Therefore, our findings show that substrate engineering is crucial to the development of graphene-based gas sensors and indicate additional routes for faster sensors.

Experimental study of laser irradiated graphite oxidation using IFTS

Graphite oxidation is investigated at varying porosity and laser irradiance, resulting in surface temperatures of 1500–3100 K. Samples are irradiated using a 1.07 µm fiber laser at irradiances of 1000 and 3600 W/cm2 in dry air environment (20% O2, < 1% H2O) at atmospheric pressure, producing a buoyant flow. Combustion plumes are analyzed using a midwave (MW) imaging Fourier transform spectrometer (IFTS) at 2 cm−1 spectral resolution, 0.5 mm/pixel spatial resolution, and data cube rates of 1 Hz. Spectral signatures from CO and CO2 are predominant in the 1800–2500 cm−1 spectral region. A radiative transfer model is used to infer species concentration and temperature from the hyperspectral data, resulting in 2D characterization of the reacting boundary layer. Plume temperatures of up to 2500 K are observed. CO and CO2 populations are correlated with surface temperature, with a general trend of [CO]/[CO2]=10exp(−5,200/Ts). A simplified model incorporating diffusion transport and surface kinetics is presented to assess the relative strengths of the S1) 2C+O2⇒2CO, S2) C+CO2⇒2CO, and S3) C+O2⇒CO2 surface oxidation mechanisms. The role of kinetic and transport mechanisms is discussed.

Compositionally gradient PVD CrAlSiN films: structural examination and oxidation resistance

The thermal stability and the resistance against oxidation of quaternary compositionally gradient CrAlSiN coatings deposited on steel substrate are investigated by examining their structural, morphological and chemical features before and after oxidation tests, as well as by quantitative thermal analysis. The as-deposited samples exhibit a columnar structure, with each column consisting of nanocrystals as fine as 20 nm. The as-deposited coating is mainly composed of CrxAl1−xN solid solution nanocrystals, which are embedded in an amorphous SiNx matrix. When exposed to high-temperature dry air environment the coated samples exhibit remarkable stability as they remained intact up to 800°C. Over 800°C, elements from the substrate outdiffused and modified the chemical content of the film, but still remain oxidation-resistant up to 900°C.

Low temperature growth of CuO nanowires through direct oxidation

CuO nanowires (NWs) are important for various applications, thus finding a low cost synthesis route is vital to best utilize this material. Herein, CuO NWs synthesized by direct oxidation of pure copper foil in a dry air environment at a low temperature regime between 100 and 400 °C were studied. Based on the results of our research, we have unprecedentedly identified (1) the threshold temperature and oxidation duration required to form CuO NWs; (2) an opposite trend in the NW lengths as function of temperature below 400 °C compared to that of above 400 °C; and (3) unambiguous evidences on the formation of Cu2O layer prior to the CuO NW formation. In particular, the threshold temperature and oxidation duration required to form CuO NWs are determined to be 250 °C and 2 h, respectively. The lengths and widths of the synthesized CuO NWs were found to be controllable with temperature (300 and 400 °C) and oxidation duration (1–3 h) ranging from 0.78 to 2.91 μm and 20 to 90 nm, respectively. The trend of the NW lengths was found to be increasing as the temperature increases and below 400 °C, which is opposite to that for oxidation temperature higher than 400 °C. Based on a combination of the Raman, X-ray diffraction, and scanning electron microscopy measurements, it was further concluded that a Cu2O layer is formed right before CuO NW growth.

MCO-Coated Interconnects: Stack Testing and Results

Coating development at Fuel Cell Energy is a continuous activity looking at optimizing chemistry, application process and features of the coating for longer life of the SOFC stack in high humidity level. Cathode interconnects surfaces are protected with manganese cobalt oxide (MCO) coatings to minimize chrome evaporation and poisoning of the fuel cell. Protecting the surface of cathode interconnects becomes necessary to extend the SOFC life. Two different coatings have been studied at FCE. MCO was either deposited as a perovskite by dip coating or formed in situ during stack operation. A direct comparison of the two methods was studied after hundreds of hours in SOFC stack testing both in dry and humid air environment. The stacks were tested in normal conditions with dry air in cathode and also in air with additional humidity. A significant improvement in degradation rate and cell stability have been observed and achieved with those stacks.

MCO-Coated Interconnects: Stack Testing and Results

Coating development at Fuel Cell Energy (FCE) is a continuous activity looking at optimizing chemistry, application process and features of the coating for longer life of the solid oxide fuel cell (SOFC) stack in high humidity environment. Cathode interconnects surfaces are protected with manganese cobalt oxide (MCO) coatings to minimize chrome evaporation and poisoning of the fuel cell. Protecting the surface of cathode interconnects becomes necessary to extend the SOFC life. Two different coatings have been studied at FCE. MCO was either deposited as a perovskite by dip coating or formed in situ during stack operation. A direct comparison of the two methods was studied after hundreds of hours in SOFC stack testing both in dry and humid air environment. The stacks were tested in normal conditions with dry air in cathode and also in air with additional humidity. A significant improvement in degradation rate and cell stability has been observed and achieved with those stacks.

Diagnosing Exercise Induced Bronchoconstriction

Eucapnic Voluntary Hyperpnoea (EVH) is a sensitive indirect airway challenge to assist in the diagnosis of Exercise Induced Bronchoconstriction (EIB). However, it has been previously reported that a positive EVH challenge may not necessarily predictive a positive exercise challenge (EX). EX have previously shown varying sensitivity due to differences in control over the inspired air water content, with studies being conducted in ambient lab conditions or using medical grade dry air. PURPOSE: To compare the EVH challenge with an EX in a controlled dry air environment, to see if a standardised EX can be used in the diagnosis or EIB. METHODS: Thirty-one healthy participants (10 female; 21 males, age 36 ± 10 yrs, exercising 7.7 ± 3.0 hrs per week) gave informed consent. Eight had a history of asthma but were not taking preventative medication. Participants completed an EVH and an EX on a cycle ergometer in a randomised order. The EVH required participants to breathe a gas mixture (5% CO2, 21% O2 and 74% N2, <2%RH) at a rate equivalent to 85% predicted MVV. The EX was conducted in an environmental chamber (16°c, 25%RH). Following a 4-min set warm up participants completed 6-mins of cycling at a work rate associated with 85% HRmax. Tests were deemed positive if there was a fall in FEV1 of ≥ 10% following the challenge. Results were analysed using paired t-tests and Pearson’s correlation and are presented as mean ± SD. RESULTS: Seven participants were positive to EVH. Of these, only two had a positive response to Ex. No differences in baseline FEV1 between EVH and EX were found (EVH:4.06 ± 0.79, EX: 4.06 ± 0.77 L, p = 0.746). There was a strong correlation between the % fall in FEV1 post EVH and EX (r = 0.520, p = 0.003). However, the % fall in FEV1 post EVH was significantly greater that post EX (EVH: -7.5 ± 5.4, EX: -2.0 ± 3.8 %, p < 0.001). The total amount of air expired was significantly higher in 6 mins EVH compared to 6 mins EX (EVH: 686.5 ± 141.7, EX: 617.9 ± 83.1 L, p = 0.002). CONCLUSION: A positive EVH challenge may not be predictive of a positive Exercise Challenge in a dry environment. EVH may have a greater sensitivity due to the lower water content of inspired air and a greater VE. This suggests that a mild positive EVH challenge (a fall in FEV1 of 10-15%), may not be predictive of EIB.

High temperature oxidation behaviour of CVD β-SiC seal coated SiC f /SiC composites in static dry air and combustion environment

Abstract A composite with SiC matrix and 40 vol% of SiC fibres with a β-SiC coating (SiC f /SiC) was prepared by the isothermal chemical vapour infiltration process. Oxidation of the SiC f /SiC composite was investigated at 1200 °C, 1300 °C and 1400 °C, for up to 100 h in static dry air, and for up to 24 h in combustion environment. In static dry air, the composite showed mass gain with nearly parabolic oxidation kinetics. The uniform oxide scale developed cracks as oxidation progressed. Oxidation in combustion environment was performed using an oxy-acetylene flame containing CO 2 and H 2 O gases. The chemical erosion by the reaction of H 2 O with oxide scale was the likely ablation mechanism. At 1200 °C and 1300 °C, the oxidation rate was higher than that of ablation and the composite showed a net mass gain. However, at 1400 °C, significant ablation was observed. Localised attack by the combustion gases caused pitting of the β-SiC seal coating. The present study shows that β-SiC seal coating remains intact at relatively lower temperatures (below 1300 °C) for a shorter period of time (~24 h) and is lost it at higher temperatures (~1400 °C) by ablation.

Radical Decomposition of Ether-Based Electrolytes for Li-S Batteries

In this work, the stability of ether-based electrolytes for Li-S batteries is investigated with particular regard to the effect of dissolved oxygen. Specifically, the performance of two different electrolyte solvents, i.e., 1,2-dimethoxyethane and its mixture with 1,3-dioxolane (DME:DOL, 1:1 v/v), is characterized in cells assembled in dry air environment, which would substantially lower production costs with respect to inert atmosphere (Ar). Although stability of all the components would suggest that Li-S batteries built in both the environments should behave similarly, it is found that cells containing the DME:DOL-based electrolyte are rather unstable in the presence of O2 in contrast to those employing DME-based electrolyte, which show a relatively good performance. The different sensitivity toward O2 of these electrolytes is associated to the ring-opening reaction of DOL, which happens to a greater extent when O2 is present, but occurs also in its absence. Based on these results a mechanism for electrolyte degradation in Li-S cells, and its reaction with dissolved polysulfides is proposed, which rationally explain for the first time the behavior already reported in literature for these kind of batteries. These findings are also relevant to the field of Li-O2 batteries, where these ether-based electrolytes are also used.

Humidity effects on tribochemical removal of GaAs surfaces

Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1–90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

NaCl induced corrosion of Ti-6Al-4V alloy at high temperature

This paper presents a study on the Ti-6Al-4V behaviour in presence of NaCl deposit under dry and moist air environments at 560°C. The results evidence a detrimental effect of the NaCl deposit with a synergistic effect in presence of moist air environment. Treatments under dry and moist air with NaCl deposit for 600h, lead respectively to weight gains per unit area 5 and 15 times higher than observed under classic oxidation in dry air. Enhancement of the corrosion phenomenon is attributed to the presence of gaseous metal chlorides, leading to the establishment of an active corrosion process.

극건조 환경에서 염화티오닐 동시 노출자의 자각증상 경험률

Objectives: An ultra dry air environment of nearly RH is often required in lithium battery factories. The objective of this study is to evaluate the subjective eye, pulmonary, nose, and skin symptoms of workers exposed to ultra-low relative humidity and thionyl chloride. Methods: We recruited 274 workers using a self-reported questionnaire in March 2014. Those who worked in ultra-low relative humidity and with thionyl chloride were identified and their prevalence of symptoms was compared with that of other workers. We excluded white collar workers, researchers and other workers who were exposed to various hazard factors, and finally included 164 workers. Results: There were significant differences in the rate of self-reported eye and skin symptoms between exposure group_1 and exposure group_2. Exposure group_2 experienced more frequent eye, and skin symptoms. Multinomial logistic regression analysis for experience of dry eye symptoms and skin symptoms in exposure group_2 showed that dry eye symptoms (odds ratio [OR], 6.33, 95% confidence interval [CI], 2.19-18.24, p

A modified model to depict corrosion fatigue crack growth behavior for evaluating residual lives of aluminum alloys

A modified Trantina–Johnson model was developed to characterize corrosion fatigue crack growth behavior. Crack growth accumulative methodology based on the Willenborg–Chang rule was used to evaluate the residual lifetimes of corrosion fatigue crack growth. Fatigue crack growth tests were performed on 2524-T3 and 7050-T7451 aluminum alloys subjected to constant amplitude and random spectra loading under the environments of dry air and 3.5% NaCl sodium chloride solution, and the load–environment interaction and load interaction mechanisms were deduced from fractographic analysis. The developed models showed good correlation with experimental results.

Studies on pulsed Nd:YAG laser cutting of thick stainless steel in dry air and underwater environment for dismantling applications

Abstract Dismantling of old equipments and structures is an important application in nuclear facilities and shipping industry. This paper presents a study on process optimization during pulsed Nd:YAG laser cutting of thick stainless steel (AISI SS304) sheets having a thickness in the range of 4–20 mm in dry air and underwater environment. Laser cutting experiments have been performed using a 500 W average power long pulse Nd:YAG laser system with fiber optic beam delivery. A water shielded laser cutting nozzle with coaxial gas jet was specifically developed to form a local dry cavity around the laser beam during the cutting experiments in underwater condition. It was found that for a given pulse energy, a higher cutting speed is possible with optimal value of pulse duration, spot overlapping, and assist gas pressure. Cutting speed of 20 mm thick SS sample was enhanced to about three times by means of increase in pulse duration from 14 ms to 20 ms and reduction in the required spot overlapping from a value of 80% to 40% using oxygen as the assist gas. A comparison of the cutting speed and heat affected zone in dry air and underwater environment has been performed. These results will be highly useful in laser based dismantling of old steel structures in radioactive and underwater environment to save time and minimize radiation dose consumption as compared to conventional dismantling methods.

Stabilizing MoS2 Nanosheets through SnO2 Nanocrystal Decoration for High-Performance Gas Sensing in Air.

The unique properties of MoS(2) nanosheets make them a promising candidate for high-performance room temperature sensing. However, the properties of pristine MoS(2) nanosheets are strongly influenced by the significant adsorption of oxygen in an air environment, which leads to instability of the MoS(2) sensing device, and all sensing results on MoS(2) reported to date were exclusively obtained in an inert atmosphere. This significantly limits the practical sensor application of MoS(2) in an air environment. Herein, a novel nanohybrid of SnO(2) nanocrystal (NC)-decorated crumpled MoS(2) nanosheet (MoS(2)/SnO(2)) and its exciting air-stable property for room temperature sensing of NO(2) are reported. Interestingly, the SnO(2) NCs serve as strong p-type dopants for MoS(2), leading to p-type channels in the MoS(2) nanosheets. The SnO(2) NCs also significantly enhance the stability of MoS(2) nanosheets in dry air. As a result, unlike other MoS(2) sensors operated in an inert gas (e.g. N(2)), the nanohybrids exhibit high sensitivity, excellent selectivity, and repeatability to NO(2) under a practical dry air environment. This work suggests that NC decoration significantly tunes the properties of MoS(2) nanosheets for various applications.

Gaseous Tribochemical Products of Hydrogenated DLC Film and Stainless Steel Pair in Air Detected by Mass Spectrometry

A technique for detecting gaseous products in an air atmosphere was achieved based on a quadrupole mass spectrometer and a space-minimized sliding unit settled in a vacuum chamber for the purpose of controlling the flow of sample gas and increasing the concentration of products. The test results showed that when a hydrogenated DLC film was rubbed in a dry air environment, carbons were oxidized to form CO2. However, in a humid air atmosphere, water molecules competitively reacted with carbons to form hydrocarbons, so the oxidization of carbons by oxygen was inhibited. The different tribochemistry is thought to play an important role in the tribological behaviors of DLC films.

Model of Oxidation‐Induced Fiber Fracture in SiC/SiC Composites

Stress rupture of SiC/SiC composites at intermediate temperatures in oxidizing environments is the result of a series of internal chemical and thermomechanical processes that lead to premature, localized fiber fracture. This article presents analytical models for two potentially critical steps in this process. The first involves the generation of tensile stresses in the fibers due to SiO2 scale formation (following removal of fiber coatings) and the associated reduction in the applied stress required for fiber fracture. The second occurs once the gaps produced by coating removal are filled with oxide and subsequent oxidation occurs subject to the constraints imposed by the matrix crack faces. In this domain, the failure model is couched in terms of the stress intensification within the fibers caused by constrained oxidation. The models incorporate the combined kinetic effects of oxide growth and viscous flow. The competing effects of increased oxidation rate and accelerated stress relaxation with increasing temperature on fiber stress feature prominently in the results. The results suggest that, in dry air environments, the highest risk of fiber fracture occurs at temperatures in the range 840°C–940°C. In this range, the oxide scales grow at appreciable rates yet the resulting growth stresses cannot be mitigated sufficiently rapidly by viscous flow.

A free energy model and availability analysis for onset of condensation on rigid and liquid surfaces in moist air

A thermodynamic model based on changes in Gibbs free energy and availability is developed for onset of heterogeneous condensation on subcooled rigid and liquid surfaces in moist air. Effects of wettability of the wall, subcooled wall temperature, relative humidity and dew point temperature of the surrounding air on critical radii for heterogeneous condensation on a rigid surface are investigated based on the change of Gibbs free energy. From the analysis of changes in availability, it is found that onset of droplet condensation is easier to occur on a hydrophilic surface than on a hydrophobic surface, in moist air than in a dry air environment, on a colder surface than a warmer surface, on a liquid surface than a rigid surface. It is also found that condensation droplet occurs earlier on oil surfaces with small surface tensions than on oil surfaces with large surface tensions.

Fundamental environmental reactivity testing and analysis of the hydrogen storage material 2LiBH4·MgH2

While the storage of hydrogen for portable and stationary applications is regarded as critical in bringing PEM fuel cells to commercial acceptance, little is known of the environmental exposure risks posed in utilizing condensed phase chemical storage options as in complex hydrides. It is thus important to understand the effect of environmental exposure of metal hydrides in the case of accident scenarios. Simulated tests were performed following the United Nations standards to test for flammability and water reactivity in air for a destabilized lithium borohydride and magnesium hydride system in a 2 to 1 molar ratio respectively. It was determined that the mixture acted similarly to the parent, lithium borohydride, but at slower rate of reaction seen in magnesium hydride. To quantify environmental exposure kinetics, isothermal calorimetry was utilized to measure the enthalpy of reaction as a function of exposure time to dry and humid air, and liquid water. The reaction with liquid water was found to increase the heat flow significantly during exposure compared to exposure in dry or humid air environments. Calorimetric results showed the maximum normalized heat flow of the fully charged material was 6 mW/mg under liquid phase hydrolysis; and 14 mW/mg for the fully discharged material also occurring under liquid phase hydrolysis conditions.

Surface and structural modifications of titanium induced by various pulse energies of a femtosecond laser in liquid and dry environment

The surface and structural modification of titanium (Ti) has been explored after the interaction of ultrashort laser pulses with the surface target. The targets were exposed by femtosecond Ti: Sapphire laser pulses in liquid (ethanol) and dry (air) environment. In order to explore the effect of pulse energy, the targets were exposed to 1,000 succeeding pulses for various pulse energies ranging from 200 to 500 μJ for pulse duration of 25 fs. SEM analyses were performed for central as well as the peripheral ablated areas of the target. It was found that in the case of ethanol (both for central and peripheral ablated areas) there is a grain growth along with nanoscale pores and dots when the target was irradiated for 200 μJ. For intermediate energies (300–400 μJ), grains of 1–2 μm with distinct boundaries are formed in the central ablated area. Whereas in the peripheral ablated area, laser-induced periodic surface structures (LIPSS) and globules are grown. For the highest pulse energy (500 μJ), distinct grains are observed for both regions. However, in the peripheral area the grains are of bigger size with cracks along the boundaries. In case of ablation in air, in the center of ablated areas, island-like structures with multiple ablative layer or LIPSS and nanoscale spheres are observed both for lower and intermediate pulse energies. For the highest pulse energy only nanoscale LIPSS could be observed. For ablation in air at the peripheral areas, well-defined, laser-induced periodic surface structures are observed for all pulse energies. Raman spectroscopy reveals that the liquid (ethanol) environment forms the carbonyl compounds with the metal and induces C–C stretching vibration, whereas in case of air, hydroxo complexes are formed. It has been found that surface treatment of Ti with ultrashort (25 fs) laser radiation in ethanol environment allows the growth of particular surface structures in the form of grains and simultaneously induces changes in its chemical composition.