Humid N2 Research Articles

Healable and Optically Transparent Polymeric Films Capable of Being Erased on Demand.

Different from living organisms, artificial materials can only undergo a limited number of damage/healing processes and cannot heal severe damage. As an alternative to solve this problem, we report in this study the fabrication of erasable, optically transparent and healable films by exponential layer-by-layer assembly of poly(acrylic acid) (PAA) and poly(ethylene oxide) (PEO). The hydrogen-bonded PAA/PEO films are highly transparent, capable of conveniently healing damages and being erased under external stimuli. The PAA/PEO films can heal damages such as scratches and deep cuts for multiple times in the same location by exposure to pH 2.5 water or humid N2 flow. The healability of the PAA/PEO films originates from the reversibility of the hydrogen bonding interaction between PAA and PEO, and the tendency of films to flow upon adsorption of water. When the damage exceeds the capability of the films to repair, the damaged films can be conveniently erased from substrates to facilitate the replacement of the damaged films with new ones. The combination of healability and erasibility provides a new way to the design of transparent films with enhanced reliability and extended service life.

Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

Influence of composition, structure and testing atmosphere on the tribological performance of W–S–N coatings

W–S–N coatings deposited by reactive magnetron sputtering offer the possibility of ultra-low friction in unlubricated sliding. In this work, W–S–N coatings of different composition and structure have been deposited, characterised and evaluated with respect to the tribological performance and tribofilm formation. The composition was varied by changing the flow of N2 into the deposition chamber, leading to N contents ranging from 0 to 47at.%. W–S–N coatings deposited without substrate heating are amorphous, while substrate heating results in coatings containing nanocrystalline tungsten sulphide (WSx) for low N contents, and nanocrystalline tungsten nitride (WyN) at a high N content. The coatings were tribologically tested against steel balls in four different atmospheres—dry N2, dry air, humid N2 and humid air—to study the effects of atmospheric O2 and H2O both separately and simultaneously. In dry N2, all coatings exhibited an excellent performance with very low friction (μ≈0.02) and wear. Notably, this included the N-richest and hardest coating, containing nanocrystalline WyN and only 13at.% of S. The friction and wear increased on changing the atmosphere, in the order of dry air–humid N2–humid air. In these three non-inert atmospheres, the friction and wear also increased with increasing N content of the coating. It is thus concluded that the presence of O2, the presence of H2O, and a high N content (i.e., low W and S contents) are three factors increasing the risk of high friction and wear, especially when occurring together. Raman spectroscopy mapping of the contact surfaces on the coatings and the balls showed that low friction and wear is connected to the presence of WS2 tribofilms in the contact, and that the three previously mentioned factors affect the formation and function of this tribofilm.

Dynamic CO2 adsorption performance of internally cooled silica‐supported poly(ethylenimine) hollow fiber sorbents

The dynamic adsorption behavior of CO2 under both nonisothermal and nearly isothermal conditions in silica supported poly(ethylenimine) (PEI) hollow fiber sorbents (Torlon®‐S‐PEI) is investigated in a rapid temperature swing adsorption (RTSA) process. A maximum CO2 breakthrough capacity of 1.33 mmol/g‐fiber (2.66 mmol/g‐silica) is observed when the fibers are actively cooled by flowing cooling water in the fiber bores. Under dry CO2 adsorption conditions, heat released from the CO2‐amine interaction increases the CO2 breakthrough capacity by reducing the severity of the diffusion resistance in the supported PEI. This internal resistance can also be alleviated by prehydrating the fiber sorbent with a humid N2 feed. The CO2 breakthrough capacity of prehydrated fibers is adversely affected by the release of the adsorption enthalpy (unlike the dry fibers); however, active cooling of the fiber results in a constant CO2 breakthrough capacity even at high CO2 delivery rates (i.e., high adsorption enthalpy delivery rates). In full RTSA cycles, a purity of 50% CO2 is achieved and the adsorption enthalpy recovery rate can reach ∼72%. Studies on the cyclic stability of uncooled fiber sorbents in the presence of SO2 and NO contaminants indicate that exposure to NO at 200 ppm over 120 cycles does not lead to a significant degradation of the sorbents, but SO2 exposure at a similar high concentration of 200 ppm causes 60% loss in CO2 breakthrough capacity after 120 cycles. A simple amine reinfusion technique is successfully demonstrated to recover the adsorption capacity in poisoned fiber sorbents after deactivation by exposure to impurities such SO2. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3878–3887, 2014

Testing Atmosphere Effect on Friction and Wear Behaviors of Duplex TiC/a-C(Al) Nanocomposite Carbon-Based Coating

Due to strongly tribological atmosphere sensitivity of carbon-based coatings, it is of extreme significance to investigate their friction and wear behaviors in different atmospheres. In this letter, duplex nc-TiC/a-C(Al) nanocomposite carbon-based coating coupled with high hardness, low internal stress and high adhesion strength was successfully fabricated using magnetron sputtering process. The friction and wear behaviors of as-fabricated coating were evaluated in dry N2, humid N2, air, dry O2, and humid O2 atmospheres, respectively. Results show that the as-fabricated coating possesses very high friction and wear due to the strong covalent bond interactions at the sliding interface caused by the free σ-bonds on the coating surface in dry N2 atmosphere. Whereas the free σ-bonds can be efficiently terminated and passivated by water and/or oxygen molecules to weaken the strong covalent bond interactions to result in low friction and wear of coating in humid N2, air, dry O2, and humid O2 atmospheres. The compact and homogeneous carbonaceous tribo-layer on the counterpart is mainly responsible for the lowest friction and wear of coating in humid N2 atmosphere. Whereas the tribo-layer can be restrained to a certain extent by the tribo-chemical reaction, especially it results in a nearly negligible carbonaceous tribo-layer on the counterpart in dry O2 atmosphere, which is mainly responsible for largely increased friction and wear of coating.

Understanding OH Yields in Electron Beam Irradiation of Humid N2

Recent experimental work by Hakoda et al. attempted to determine the G-value of OH radical in electron-beam irradiation of humid N2 using the conversion of CO to CO2 to titrate OH. Kinetic modeling is used to simulate the experiment of Hakoda et al. in an attempt to determine the validity of their assumptions and the reason the observed G-value was higher than expected. The model predicts CO2 production that is roughly 25% lower than observed and OH production about 10% higher than concluded from experimental data. This apparent contradiction is resolved by understanding the detailed chemistry of the OH + CO reaction and the fate of the thermalized HOCO intermediate. Analysis of the reactions producing OH indicate that the sources of OH are significantly different in humid air than in humid N2, and the G-value for OH is much higher in humid air than humid N2.

Determination of the Number of OH Radicals in EB-Irradiated Humid Gases Using Oxidation of CO

Electron beam (EB) technology has an advantage for treating dilute environmental pollutants in gases due to high-density population of active species such as radicals and atoms. In general, OH radicals play an important role of initiating the decomposition and removal of such pollutants. It is quite important to understand the behavior of OH radical production for the development of efficient decomposition/removal processes and the comparison with other purification methods. The number of OH radicals produced in humid N2 at doses of 2.0–10.0 kGy with dose rates of 0.17–2.55 kGy/s under 1-MeV EB irradiation was indirectly determined using an index of oxidation of CO to CO2, which has been used in atmospheric chemistry. An experiment under conditions where all OH radicals produced react with CO demonstrated that the concentration of CO2 increased linearly with doses of 0–10 kGy, and the G(OH) was estimated as 4.90.

Micro-fabricated membrane gas valves with a non-stiction coating deposited by C4F8/Ar plasma

Micro-fabricated gas valves with C4F8/Ar treatment at the sealing interface are designed, fabricated and characterized to passively control gases in a micro gas analysis system. The check valves form a seal between a polished Si/SiO2 substrate and a smooth polyimide (PI) membrane. The smooth PI membrane touches the SiO2 surface, giving rise to relatively strong van der Waals adhesion, and under humid conditions hydrogen-bonded stiction can occur at the interface between PI and SiO2. To prevent stiction from dominating adhesion, the valve-seat surface was treated with a hydrophobic CFn thin film, which was formed by exposing the surface to C4F8/Ar inductively coupled plasma (ICP) at low power. The valves without a non-stiction coating did not open with inlet pressures up to 210 kPa. With a non-stiction coating, the valves showed an average initial opening pressure of 59.25 kPa. In order to further reduce the opening pressure, 40% of the valve-seat area is reduced. After modification, the average opening pressure is reduced to 32.5 kPa. After the initial opening, the average in-use opening pressure was 16.9 kPa before area modification, and 13.1 kPa after the modification. The valve has been tested up to 10 000 open/close cycles under dry N2 gas flow, and an additional 3000 open/close cycles under humid N2 gas flow. The average forward flow conductance of the valves before modification was 1.1 sccm kPa−1, and the conductance after modification was 1.41 sccm kPa−1. The measured leakage is between 0.0003 and 0.004 sccm up to 35 kPa reverse pressure.

Effect of Contact Geometry on the Pull-Off Force Evaluated under High-Vacuum and Humid Atmospheric Conditions

The effect of condensed water on pull-off forces under high vacuum (HV) and 0 to 83% relative humidity (RH) N2 atmospheric conditions was evaluated for different contact geometries using atomic force microscopy (AFM). The pull-off force was measured using two types of contact geometry: contact between hemispherical asperities and a flat silicon probe on an AFM cantilever (called a spherical-flat contact) and between a flat silicon substrate and a flat nickel probe on an AFM cantilever (called a flat-flat contact). The hemispherical asperities were fabricated using a focused ion beam (FIB) system, and each peak had a radius of curvature of between 70 and 610 nm. The flat nickel probe was fabricated by friction-induced wear. Measurement results showed that for the spherical-flat contact the pull-off force was proportional to the radius of curvature of the asperity peak and was slightly lower in HV than in humid 14% RH N2. For the flat-flat contact in HV, with increasing contact time, the pull-off force increased in HV but decreased in humid 62 and 83% RH N2. The pull-off force in HV was lower than that in humid N2 when the contact time was less than 10 s but was higher when the contact time was longer than 30 s. The estimated adhesion force based on the Laplace pressure from the contact geometry agreed reasonably well with the measured pull-off force.

Theoretical study of influence of H2O on parameters of low-temperature plasmas in humid mixtures

Monte Carlo (MC) electron dynamic simulations in dry and humid N2, O2, CO2 and air were performed in order to obtain electron energy distribution functions (EEDFs), mean free path (λ), drift velocity (v d) and collision frequency of electrons (ν), their mean energy \((\bar \varepsilon )\) and rate coefficients of electron impact reactions, as functions of reduced electric field strength (E/N) and concentration of H2O. The aim was to test the latest compilation of cross-sections for H2O, the applicability of the MC method used, and the effect of the H2O concentration.

Tribochemical effects on the friction and wear behaviors of diamond-like carbon film under high relative humidity condition

Friction and wear behaviors of diamond-like carbon (DLC) film in humid N2 (RH-100%) sliding against different counterpart ball (Si3N4 ball, Al2O3 ball and steel ball) were investigated. It was found that the friction and wear behaviors of DLC film were dependent on the friction-induced tribochemical interactions in the presence of the DLC film, water molecules and counterpart balls. When sliding against Si3N4 ball, a tribochemical film that mainly consisted of silica gel was formed on the worn surface due to the oxidation and hydrolysis of the Si3N4 ball, and resulted in the lowest friction coefficient and wear rate of the DLC film. The degradation of the DLC film catalyzed by Al2O3 ball caused the highest wear rate of DLC film when sliding against Al2O3 ball, while the tribochemical reactions between DLC film and steel ball led to the highest friction coefficient when sliding against steel ball.

Kinetics of the Reaction of Ca(OH)2 with CO2 at Low Temperature

The kinetics of the reaction of Ca(OH)2 with CO2 in humid N2 has been studied at 60−90 °C by using a differential reactor. Ca(OH)2 reacted with CO2 to form CaCO3 only when the relative humidity exceeded 0.08. The reaction ceased before 1 h, and Ca(OH)2 was incompletely converted. The reaction rate and final conversion of Ca(OH)2 were significantly affected by relative humidity, were slightly dependent on temperature, and were zeroth order with respect to gas phase CO2 concentration. The carbonation of Ca(OH)2 was well described by the asymptotic equation which is obtained by assuming chemical reaction control and considering the surface coverage by product. The rate-controlling step might be the dissolution of Ca(OH)2 at the water-adsorbed surface. The reaction behavior of Ca(OH)2 with CO2 was similar to that with SO2. The model derived for the reaction with CO2 may be applied to that with SO2 with proper modifications. The results of this study are useful to the design and efficient operation of the processes using hydrated lime to remove SO2 from the flue gas, in which both SO2 and CO2 are present.

Influence of ultraviolet illumination on microdischarge behavior in dry and humid N2, O2, air, and Ar/O2: The Joshi effect

The influence of UV illumination on the behavior of silent electrical discharge streamers (microdischarges) in dry and humid gases (nitrogen, oxygen, air, and Ar/O2 mixtures) is presented. A commercial low-pressure mercury lamp, which was spectrally calibrated, provides UV light. The UV irradiance power coupled into the discharge cell is also calculated. The transferred charge per mean microdischarge (in a voltage half-cycle) was measured for a pin electrode assembly, configured to deliver either M−G+ transitions (electrons going from metal towards dielectric) or M+G− transitions (electrons going from dielectric to metal). The total transferred charge is recorded by monitoring a charge versus voltage plot (Lissajous figure). When illumination is restricted to the gas alone, both the total transferred charge and the individual-microdischarge transferred charge remain constant for either transition (M−G+ or M+G−). However, when the dielectric is illuminated, a marked decrease in the individual-microdischarge transferred charge is observed for M+G− transitions in some gases. For this case, a greater number of microdischarges must occur in a half-cycle to keep the total transferred charge constant, thereby creating more homogeneous discharge conditions.

Raman Spectroscopy Studies of Reactions Between Sulfur Dioxide and Microparticles of Hydroxides

AbstractGas-aerosol chemical reactions between dilute SO2 and alkali-metal hydroxides have been explored using elastic and inelastic (Raman) light scattering. Single charged particles of NaOH, KOH, and Ca(OH)2 were levitated electrodynamically in a reaction chamber and exposed to humid nitrogen. Particles that were not water soluble remained crystalline while water soluble compounds deliquesced into solution microdroplets. The resulting solids or solutions were reacted with dilute SO2 in humid N2. Elastic scattering measurements and Raman spectra were taken during the gas-aerosol reactions, and results indicate that reaction products and sorbent utilization are highly dependent on the water content of the particle.

Micromechanical Behaviour of Amorphous Hydrogenated Silicon Carbide Films

ABSTRACTAmorphous hydrogenated silicon carbide (a-Si1-xCx:H) films (x = 0.65 to 1) were deposited by radio frequency plasma assisted chemical vapour deposition (RF-PACVD). Their friction and wear properties were investigated by means of a conventional ball-on-disk apparatus. The results were correlated with film mechanical properties. It was found that adding silicon to a-C:H (also called diamond-like carbon (DLC)) films reduces the hardness, elastic modulus and internal stress values by 15 to 30 %. Scratch testing induces film spallation from stainless steel substrates at low loads (1 N). In the low normal load (1 N) ball-on-disk tests under humid N2 conditions, a-Si1-xCx:H films (0.7 < x < 0.9) combine a very low wear rate of both the film and the counterbody with a steady state low friction coefficient below 0.1. For higher loads (5 and 10 N), however, this low friction coefficient only lasts for a relatively short time. In this case, the harder diamond-like carbon films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficients between 0.15 and 0.35 in a humid ambient atmosphere. In a dry N2 atmosphere, pure DLC films perform tribologically better than a-S1-xCx:H films in all respects.

Acid-Base Balance during Emergence in the Freshwater Bivalve Corbicula fluminea

The Asian freshwater clam, Corbicula fluminea, was emersed at 23°C under three conditions: humid air, N₂ hypoxia, or air with valves clamped or bound shut. Under all conditions, clams became acidotic during emersion. In air, hemolymph pH declined from 790 to 7.14 in 72 h. Hypoxic clams displayed a similar decline in pH, but clams with valves clamped became acidotic more rapidly. Hemolymph CO₂ content (Cco₂) and Pco₂ rose with duration of aerial exposure in all treatment groups. However, hemolymph of bound clams had significantly higher Cco₂ and Pco₂ than that of either air- or N₂-exposed bivalves after 48 h emersion. Although hemolymph Po₂ declined with emersion time in all groups, there was no effect of exposure condition, suggesting that ventilatory behaviors did not affect hemolymph Po₂ or that the effects were masked by rapid utilization of inspired O₂. Hemolymph calcium and osmolality increased with emersion time and were greatest in clams with clamped valves. Presumably, shell calcium carbonate was ...

ChemInform Abstract: Study of Copper Contamination in Air or Nitrogen Containing Hydrogen Sulfide and Nitrogen Dioxide.

AbstractIt is shown that the rate of copper sulfidation is much greater in air containing 0.1 ppm H2S (925 Å of Cu2S after 72 h in dry air) than in dry or humid nitrogen containing 0.1 ppm H2S (116 Å after 72 h in humid N2; 70 Å in dry N2).