Dry N2 Research Articles

Role of Electric Field on Sensing Mechanism of Carbon Nanotube Based Ammonia Gas Sensor

Multi-walled carbon nanotubes (MWCNTs) grown on SiO2/Si substrate, were investigated as resistive sensors for Ammonia (NH3 gas detection upto 100 ppm concentration in the presence of dry carrier gas N2. Sensitivity and recovery time are serious problem in case of NH3 sensing and these are related to the interaction mechanism between NH3 molecules and CNTs surface and the defect level of CNT. It was found that the chemisorption of NH3 molecules on the side-wall defect sites of CNTs enhances the sensitivity along with a poor recovery. We have demonstrated by an effective approach to get improved sensitivity and fast recovery. Best sensor performance and desorption of NH3 were done by tuning the DC excitation electric field applied across the sensor electrodes. Such stimulation process provides sufficient energy to the electrons to jump through defective sites due to Poole-Frenkel effect resulting in the desorption of gas.

Measurements of electron attachment by oxygen molecule in proportional counter

We present pulse height measurements for 5-keV Auger electrons from a radioactive 55Fe source mounted at the inner cathode surface of cylindrical proportional counter, which is operated with CH4 admixed dry air or N2. A clear shift of the pulse height has been observed by varying the amount of the admixtures; the number of electrons, created in the primary ionization by Auger electrons, is decreased by the electron attachment of the admixtures during their drift from the place near the source to the anode wire. The large gas amplification (typically 104) in the secondary ionization of proportional counter makes it possible to investigate a small change in the number of primary electrons. The electron attenuation cross-section of O2 has been evaluated by analyzing the shifts of the pulse height caused by the electron attachment to dry air and N2.

Impedance spectroscopy studies of bulk electrical conduction in A-site acceptor (K)-doped BaTiO3

BaTiO3 ceramics with different acceptor concentrations of potassium at A-site Ba1−x K x TiO3−x/2 (BKT) were prepared by solid-state processes. The solution limit of potassium in BKT is determined to be 1 mol%. Furthermore, electrical conduction behaviours were investigated in the temperature range of 300–800 °C by analysing impedance spectra and were found extremely depending on processing and measurement conditions. When annealed at 800 °C and measured in an atmosphere of dry N2, BKT is a mixed oxide ion/electron conductor and its ionic transference number decreases with increasing temperature. But when annealed at 800 °C and measured in an atmosphere of dry air and O2, BKT is a p-type semiconductor with a transition from a trapped holes’ conduction to activated holes’ conduction as temperature increases. On exposure of BKT to an atmosphere of wet N2, BKT is a proton conductor in the temperature of 300–550 °C; however, it reverts to a p-type semiconductor above 550 °C as water is lost from the sample.

Structural and environmental dependence of superlow friction in ion vapour-deposited a-C : H : Si films for solid lubrication application

Understanding the tribochemical interaction of water molecules in humid environment with carbonaceous film surfaces, especially hydrophilic surface, is fundamental for applications in tribology and solid lubrication. This paper highlights some experimental evidence to elucidate the structural and environmental dependence of ultralow or even superlow friction in ion vapour-deposited a-C : H : Si films. The results indicate that both surface density of silicon hydroxyl group (Si–OH) and humidity level (RH) determine the frictional performance of a-C : H : Si films. Ultralow friction coefficient μ (∼0.01–0.055) is feasible in a wide range of RH. The dissociative formation of hydrophilic Si–OH surface and the following nanostructure of interfacial water molecules under contact pressure are the origin of ultralow friction for a-C : H : Si films in humid environment. The correlation between contact pressure and friction coefficient derived from Hertzian contact model is not valid in the present case. Under this nanoscale boundary lubrication, the friction coefficient tends to increase as the contact pressure increases. There even exists a contact pressure threshold for the transition from ultralow to superlow friction (μ ∼ 0.007). In comparison, when tribotested in dry N2, the observed superlow friction (μ ∼ 0.004) in the absence of water is correlated with the formation of a low shear strength tribolayer by wear-induced phase transformation.

Synchronous ATR infrared and NIR-spectroscopy investigation of sepiolite upon drying

A new environmental cell allowing for the independent synchronous collection of the near- and mid-infrared spectra (12,000–600cm−1) in the diffuse reflection and attenuated total reflection (ATR) modes, respectively, is reported. The cell is employed to study in real time the dehydration of the phyllosilicate mineral sepiolite, Mg8Si12O30(OH)4(OH2)4·wH2O, in both its natural form and after in situ deuteration at ambient. The spectra are obtained under dynamic purging with dry N2 and compared to those of the same material conditioned over saturated salt solutions. Sepiolite is an important industrial mineral with a modulated structure of alternating tunnels and ribbons. Its mild drying is associated with pronounced vibrational spectral changes due to the removal of surface and zeolitic H2O and the concomitant structural relaxation of the ribbons. Detailed assignments are provided for the fundamental, combination and overtone spectrum of H2O confined in the tunnels of sepiolite, SiOH groups on the external surface of the particles, and Mg3OH groups in the 2:1 ribbons. The spectra are discussed in comparison to those of palygorskite (modulated phyllosilicate with narrower ribbons and tunnels), talc (trioctahedral magnesian phyllosilicate without modulation) and high-surface area silica. It is demonstrated that sepiolite exhibits three discrete states of zeolitic hydration at ambient temperature: Besides the previously known hydrated (w=7–8) and dry (w=0–1) states which dominate the spectra above 30% and below 3% relative humidity, respectively, a hitherto unknown intermediate (w=4–5) is found in the 3–10% range. The new state is most conveniently identified in the near-infrared by a ν02 Mg3O-H stretching mode at 7205cm−1 (ν01=3686cm−1, X=83.5cm−1) and a characteristic H2O combination band at 5271cm−1 (D2O: 3908cm−1).

SYMBIOTIC NITROGEN-FIXING ACTIVITY AND YIELD POTENTIAL OF INOCULATED HEDYSARUM CORONARIUM IN ISRAEL

ABSTRACT Hedysarum coronarium L. has recently been introduced into Israel for evaluation as a “new” winter forage crop. The lack of a native rhizobial population suitable for this legume and the need for inoculation were assessed. Field inoculation experiments with effective Rhizobium strains, previously selected under greenhouse conditions, proved the benefits of symbiotically fixed N2 to yield potential and forage quality of H. coronarium. Seasonal changes in nodulation, plant dry matter accumulation and N2 (C2 H2)-fixation activity under field conditions were followed. The effect of defoliation on root nodule development and nitrogen fixation rate during the vegetative regrowth period are briefly discussed.

Effects of polytetrafluoroethylene or polyimide coating on H2 sensing properties of anodized TiO2 films equipped with Pd–Pt electrodes

Diode-type H2 sensors based on anodically oxidized TiO2 thin films equipped with Pd–Pt electrodes (Pd–Pt/T-TiO2, T-TiO2 represents the TiO2 thin film fabricated by the anodization of the pre-oxidized Ti plate at 600°C for 1h in air) have been fabricated, and the effects of the polymer coating on the Pd–Pt/T-TiO2 sensor to humidity and oxygen partial pressure on the sensing properties to 500–8000ppm H2 under dry and wet atmospheres have been investigated in this study. The films tested were polytetrafluoroethylene (PTFE), polyimide (PI) film and heterogeneously laminated layers of these two polymer films, and the sensors fabricated were referred to as P-n/Pd–Pt/T-TiO2 or P1-n/P2-n/Pd–Pt/T-TiO2 (P, P1 and P2: PTFE or PI, n: polymer concentration of the coating solution (wt%)). The H2 response of almost all sensors in wet air was larger than that in dry air, while the PTFE-n/Pd–Pt/T-TiO2 and PI-n/PTFE-n/Pd–Pt/T-TiO2 sensors showed only a slight enhancement in the H2 response by introduction of moisture, in comparison with the Pd–Pt/T-TiO2 or PI-n/Pd–Pt/T-TiO2 sensors. On the other hand, the H2 response of all sensors in N2 was not affected by humidity. The PI-10/Pd–Pt/T-TiO2 sensor showed the largest H2 response in air at 250°C as well as N2 among the all sensors tested; the response of the sensors in dry air and dry N2 were ca. 3.1×10−4A and ca. 4.7×10−2A, respectively, where the sensor current in H2 atmosphere was regarded as sensor response, since that in the atmosphere without H2 was extremely small. In addition, the H2 response of the Pd–Pt/T-TiO2, PTFE-20/Pd–Pt/T-TiO2 and PI-20/Pd–Pt/T-TiO2 sensors were almost proportional to the H2 concentration in a lower concentration range (500–2000ppm) in both dry and wet air, while it tended to saturate at a higher concentration range, especially for the PI-20/Pd–Pt/T-TiO2 sensor in wet air. On the other hand, the sensor response to H2 is well proportional to the logarithm of H2 concentration in both dry and wet N2 in the whole concentration range. Thus, the direct coating of the PTFE-n film on the Pd–Pt/T-TiO2 sensors reduced the effect of humidity on the H2 response and the direct coating of the PI-n film on the Pd–Pt/T-TiO2 sensors was effective for enhancing the H2 response.

Evaluating the dynamic retention capacities of microfabricated vapor preconcentrators as a function of flow rate

Adsorbent-packed preconcentrators are essential elements of most microanalytical systems designed for monitoring airborne volatile organic compounds (VOC) at low concentrations. These devices also serve as thermally desorbed injectors that transfer focused bands of captured VOCs to downstream separation and/or detection modules. Despite their importance, the factors affecting the capture efficiency of such devices have not been extensively or systematically studied. In this study, the dynamic retention capacities of four deep-reactive-ion-etched Si micropreconcentrator-focusers (μPCF) packed with a commercial graphitized carbon, Carbopack X (C-X), were characterized for several VOCs and compared to those of a reference capillary preconcentrator-focuser (cPCF). Devices were challenged with ~100 parts-per-billion of benzene, 2-butanone, toluene, or n-heptane in dry N2 over a range of volumetric flow rates, Q. The relationships between the bed residence time, τ, and the 10% breakthrough volume and breakthrough time (Vb−10 and tb−10, respectively) were evaluated in the context of the modified Wheeler Model. Both Vb−10 and tb−10 decrease monotonically with decreasing τ, in accordance with the model. The performance of the largest μPCF, packed with 2.3mg of C-X, was comparable to that of the reference cPCF packed with a similar quantity of C-X. The critical flow rates, Qc−10, corresponding to immediate breakthrough, ranged from 70 to 290mL/min and varied directly with the affinity of the vapor for the adsorbent. As a practical operating guideline, it is recommended that flow rates be limited to <0.4Qc for reliable performance of any μPCF used for quantitative analysis. Estimated preconcentration factors range from 730 to 39,000. Challenges to predicting device performance via the modified Wheeler Model are illustrated.

RESPON DUA VARIETAS TANAMAN SELADA (Lactuca sativa L.) TERHADAP MACAM NUTRISI PADA SISTEM HIDROPONIK

Lettuce (Lactuca sativa L) is a common vegetables crops grown in the highland and lowlands. A sample hydroponic lettuce cultivation provides an sources an alternative for farmers who have a narrow area, so that can server as an adequate source of income. Providing nutrients to the two varienties of lettuce are expected to yield maximum production. This tudy aims to determine the effect of nutrients on two varieties of lettuce plants. The study was conducted in the greenhouse Agroekoteknologi Departement Faculty of Agriculture, University Trunojoyo Madurese from January to March 2011. The method used was a factorial experiment based on Completely Randomized Design (CRD) with three replicates consisting of two treatment factors, the first factor are two different varieties of lecctuce and the second factor are two differwnt kinds of nutrients. The results showed that the chief varieties of butter (V1) produces the number of leaves and dry biomass is higher than the varieties of cos (V2). Nutrition in V1 generate the number of leaves, wet biomass, dry biomass, and root length was higher than without the provision of (N0). V1 responses to nutrient hidrogroup (N1) resulted in higher leaf number than nutrition greentonik (N2), but the provision of dry biomass yield N2 higher than N1. Nutrition on V2 generate the number of leaves, wet biomass and dry biomass was higher than N0. V2 response to the provision of N1 and N2 produce the number of leaves, wet biomass, dry biomass, and root length are not significantly different. Key word : lettuce, varieties, nutrition, simple hydroponics

Vacuum-assisted drying of polymer electrolyte membrane fuel cell

Purging a polymer electrolyte membrane fuel cell (PEMFC) with dry N2 to remove water in the catalyst layer and the membrane during shutdown is necessary for ensuring successful startup and avoiding damages from the freeze/thaw cycling during cold-start. However, carrying N2 onboard may be impractical for mobile applications. Vacuum-assisted drying can accelerate and aid in water removal by reducing the boiling point of water, thus enhancing the evaporation and diffusion rate. This method is applied to a single cell PEMFC and compared to purging using dry N2. The drying process was monitored using electrochemical impedance spectroscopy (EIS), and the results were fitted to an equivalent circuit model. Our experimental results show the vacuum-assisted drying method may provide faster and more thorough water removal than N2 purging.

Effects of Surface Modification of Noble-Metal Electrodes with Au on the H2-Sensing Properties of Diode-Type Gas Sensors

Diode-type TiO2 film gas sensors equipped with noble-metal (Pd or Pt) electrodes (M/TiO2, M = Pd or Pt) have been fabricated, and the effects of surface modification of the electrodes with Au on their H2-sensing properties have been investigated at 250oC in both air and N2 under dry and wet atmospheres. H2 response of M/TiO2 sensors in dry N2 was much larger than that in dry air, but the surface modification of the Pd or Pt electrode with Au (Au/Pd or Au/Pt) improved the H2 response, especially in dry air. In addition, the sensor with the Au/Pt electrode showed large and O2-independent H2 response under wet atmosphere.

Adhesive and corrosive wear at microscales in different vapor environments

Abstract Adhesive and corrosive wear at microscales are quantitatively distinguished in lifetime tests of resonant bulk-fabricated silicon microelectromechanical systems (MEMS). By analyzing the oscillation decay characteristics in different vapor environments, we find that wear is dominated by asperity adhesion during the initial stages of rubbing in dry N2 or O2/N2 mixtures; in these situations the transient wear rate is inversely proportional to the wear depth. But in water or ethanol vapors, chemical reactions between the corrosive adsorbed layer and the silicon substrate limit the wear rate to a constant. These observations are consistent with atomic explanations. The differences between adhesive and corrosive wear explain the advantages offered by lubricating with alcohol vapors rather than using dry environments for tribo-MEMS devices. Compared to ethanol, the relatively poor anti-wear effect of water vapor is explained by aggressive and rapid tribo-reactions.

Pressurized Oxygen Blown Entrained-Flow Gasification of Wood Powder

In the present study, an oxygen blown pilot scale pressurized entrained-flow biomass gasification plant (PEBG, 1 MWth) was designed, constructed, and operated. This Article provides a detailed description of the pilot plant and results from gasification experiments with stem wood biomass made from pine and spruce. The focus was to evaluate the performance of the gasifier with respect to syngas quality and mass and energy balance. The gasifier was operated at an elevated pressure of 2 bar(a) and at an oxygen equivalence ratio (λ) between 0.43 and 0.50. The resulting process temperatures in the hot part of the gasifier were in the range of 1100–1300 °C during the experiments. As expected, a higher λ results in a higher process temperature. The syngas concentrations (dry and N2 free) during the experiments were 25–28 mol % for H2, 47–49 mol % for CO, 20–24 mol % for CO2, and 1–2 mol % for CH4. The dry syngas N2 content was varied between 18 and 25 mol % depending on the operating conditions of the gasifier. The syngas H2/CO ratio was 0.54–0.57. The gasifier cold gas efficiency (CGE) was approximately 70% for the experimental campaigns performed in this study. The synthesis gas produced by the PEBG has potential for further upgrading to renewable products, for example, chemicals or biofuels, because the performance of the gasifier is close to that of other relevant gasifiers.

How far does contamination help dry lubrication efficiency?

Space tribology implies lubricating not only in vacuum but also in air and in dry N2 environments. To decipher the influence of environment on dry lubrication, two MoS2-based coatings (MoS2 and MoS2+Ti) with antagonistic behaviours are studied under four different environments (high and moderate vacuum, dry N2, and air 50% HR). By coupling both mechanics and physico-chemistry measurements while conducting experiments on a macroscale level, localization of velocity accommodation is possible. Contrary to general opinion, a dry N2 environment is not neutral. More generally, contaminations and surface complexes help low friction and low wear by delocalizing accommodation from the 3rd body volume to its surface.

Highly selective sorption and unique packing geometries of unsaturated hydrocarbons and CO2 in a fluorine-substituted organic–inorganic ionic crystal

An ionic crystal [Cr3O(OOCCF3)6(H2O)3]3[α-PW12O40]·8CH3COCH3·8H2O·CHCl3 [Ia] was synthesized by the complexation of a fluorine-substituted macrocation with a phosphododecatungstate. Compound Ia possessed a layered structure with an interlayer distance of ca. 3.5 Å, and the inner surface of the layer was decorated with CF3 groups of the macrocations. The solvent molecules (acetone and chloroform) spontaneously desorbed and exchanged with water under an ambient atmosphere and a hydrated phase [Cr3O(OOCCF3)6(H2O)3]3[α-PW12O40]·25H2O [Ib] was formed. The water molecules were partially desorbed by the treatment of Ibin vacuo or under a dry N2 or He flow at 298-303 K, and [Cr3O(OOCCF3)6(H2O)3]3[α-PW12O40]·15H2O [Ic] was formed. The powder XRD pattern of Ic well agreed with that calculated for Ia, showing that the structure was maintained after the exchange and partial desorption of guests. Compound Ic sorbed CO2 and unsaturated hydrocarbons, while saturated hydrocarbons such as ethane and methane were almost excluded despite the similar kinetic diameters. Acetylene/methane, CO2/methane, and ethylene/ethane sorption ratios were 13, 15, and 4.9, respectively, at 198 K and 100 kPa. Typical Monte Carlo-based optimized geometries of acetylene and CO2 showed different alignments in the structure of Ic despite the similar amounts of sorption and molecular sizes. Acetylene and CO2 were aligned mainly parallel and perpendicular, respectively, to the layer, which is probably due to the differences in the electron density distributions of the HOMO orbitals.

Mixed oxide ion and proton conduction and p-type semiconduction in BaTi0.98Ca0.02O2.98 ceramics

Ca-doped BaTiO3, BaTi0.98Ca0.02O2.98 is primarily an oxide ion conductor with activation energy 0.77(1) eV when annealed at 700 °C and measured in an atmosphere of dry N2. On exposure of this sample to moisture, proton conduction dominates the conductivity at low temperatures with activation energy 0.42(1) eV but the sample reverts to mainly oxide ion conduction above ∼500 °C as water is lost from the sample. When samples are annealed at 700 °C and measured in an atmosphere of dry O2, p-type semiconduction with activation energy 0.70(2) eV dominates. The nature of the conducting species was determined by a combination of conductivity measurements as a function of oxygen partial pressure and characteristic features in low frequency impedance data.

Study of solid/liquid and solid/gas interfaces in Cu–isoleucine complex by surface X-ray diffraction

The enzymes could be understood like structures formed by amino acids bonded with metals, which act as active sites. The research on the coordination of metal–amino acid complexes will bring light on the behavior of metal enzymes, due to the close relation existing between the atomic structure and the functionality. The Cu–isoleucine bond is considered as a good model system to attain a better insight into the characteristics of naturally occurring copper metalloproteins. The surface structure of metal–amino acid complex could be considered as a more realistic model for real systems under biologic working conditions, since the molecular packing is decreased. In the surface, the structural constrains are reduced, keeping the structural capability of surface complex to change as a function of the surrounding environment.In this work, we present a surface X-ray diffraction study on Cu–isoleucine complex under different ambient conditions. Cu(Ile)2 crystals of about 5mm×5mm×1mm have been growth, by seeding method in a supersaturated solution, presenting a surface of high quality. The sample for the surface diffraction study was mounted on a cell specially designed for solid/liquid or solid/gas interface analysis. The Cu–isoleucine crystal was measured under a protective dry N2 gas flow and in contact with a saturated metal amino acid solution. The bulk and the surface signals were compared, showing different atomic structures. In both cases, from surface diffraction data, it is observed that the atomic structure of the top layer undergoes a clear structural deformation. A non-uniform surface relaxation is observed producing an inhomogeneous displacement of the surface atoms towards the surface normal.

Extremely Fast 1 μmol · mol−1 Water-Vapor Measurement by a 1 mm Diameter Spherical SAW Device

When a surface acoustic wave (SAW) is excited on a spherical surface, a naturally collimated SAW propagates around the equator hundreds of times. The propagation characteristics such as the velocity and amplitude are affected by adsorbed and/or reacted molecules on the surface, and the changes are accumulated by multiple turns of propagation. This enables highly sensitive detection of adsorbed molecules including water vapor. In this paper, the development and testing of a 1 mm diameter spherical SAW sensor, which is capable of measuring water vapor at concentrations well below 1 μmol · mol−1H2O in N2, are reported. The rise time from 10% to 90% of the spherical SAW sensor to a step change from dry N2 to 1 μmol · mol−1H2O in N2 was approximately 15 s.

ChemInform Abstract: Simple and Convenient Methods for N‐Arylation of Heterocycles and Diphenylamine.

AbstractOptimized conditions are elaborated for the process, which can be carried out in the absence of ligands and without the need of a dry N2 atmosphere.

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.