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Humid Air (humid + air)

Distribution by Scientific Domains

Polymers and Materials Science	60%
Chemistry	20%

Selected Abstracts

Control of Domain Orientation in Block Copolymer Electrolyte Membranes at the Interface with Humid Air

ADVANCED MATERIALS, Issue 2 2009
Moon Jeong Park
Domain orientation in polymer electrolyte membranes is tuned by controlling its sulfonation level and the moisture content of the air. At low sulfonation levels, highly ordered hydrophobic cylinders oriented perpendicular to the film surface are obtained, when the film is in humid air. Increasing the sulfonation level results in a transition from perpendicular to parallel orientation. [source]

Environmental and frequency effects on fatigue crack growth rate and paths in aluminium alloy

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1-2 2005
S. A. MICHEL
ABSTRACT The environmental and frequency effects on fatigue crack growth in aluminium alloys are studied theoretically and experimentally. 2024-T351 and 7075-T651 tested in corrosive environments (humid air or technically purified nitrogen) show a constant crack growth rate (da/dN) at low values of the effective stress intensity range (,Keff). Typical well-known fits of this curve (da/dN vs ,Keff) do not reflect the plateau-like region. A new model of crack growth is presented, which physically attributes this region to the formation and subsequent fracture of a crack tip oxide layer. The thickness of this layer is measured with X-ray photon electron spectroscopy. At higher loads, other mechanisms are understood to be active. The model parameters are determined from constant amplitude tests, and are valid for a given material and environment. In 7075-T651 tested in nitrogen, with R= 0.1 and 83 Hz, unexpected macroscopical crack branching is observed when ,Keff reaches approximately 3.0 MPa ,m. [source]

High-Performance Solution-Processable Poly(p -phenylene vinylene)s for Air-Stable Organic Field-Effect Transistors

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2005

Abstract The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side chain (linear or branched), and the processing of several solution processable alkoxy-substituted poly(p -phenylene vinylene)s (PPVs) on the charge-carrier mobility in organic field-effect transistors (OFETs) is investigated. We have found the highest mobilities in a class of symmetrically substituted PPVs with linear alkyl chains (e.g., R1, R2,=,n -C11H23, R3,=,n -C18H37). We have shown that the mobility of these PPVs can be improved significantly up to values of 10,2,cm2,V,1,s,1 by annealing at 110,°C. In addition, these devices display an excellent stability in air and dark conditions. No change in the electrical performance is observed, even after storage for thirty days in humid air. [source]

Control of Domain Orientation in Block Copolymer Electrolyte Membranes at the Interface with Humid Air

A new type of EFHAT power generation system with effective utilization of latent heat

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2005
Hongguang Jin
Abstract On the basis of synergetic integration of an externally fired humid air turbine (EFHAT) cycle and effective recovery of latent heat from the exhaust gas of gas turbine, we have proposed a new type of EFHAT power generation system with effective utilization of latent heat, different from traditional EFHAT system. Due to use of clean humid air as working substance, latent heat can be recovered and utilized to generate hot water for the humidifier. This will enhance the humidification ability, giving rise to performance improvement of the system. As a result, at the turbine inlet temperature of 1123 K, the thermal efficiency of this new system may be expected to be as high as 47,48%. Additionally, we obtained the analytical expressions of system performance, and disclosed the relative relationship of system efficiency between the new EFHAT system and the pure externally fired power system. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Kinetics and Mechanism of Formation of Barium Zirconate from Barium Carbonate and Zirconia Powders

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2003
Alberto Ubaldini
The formation of BaZrO3 from very fine (70,90 nm) ZrO2 powders and coarser (,1 ,m) BaCO3 powders has been studied in dry and humid air up to 1300°C using TGA/DTA, XRD, SEM, TEM, and EDS microanalysis. In the temperature range 900°,1100°C, barium is rapidly transported at the surface of the ZrO2 particles and reacts, forming BaZrO3. The compound grows as a concentric layer with gradual consumption of the central ZrO2 particle. The overall formation kinetics of BaZrO3 is well described by a diminishing core model, and the most likely rate-determining step is a phase-boundary process at the ZrO2,BaZrO3 moving interface. The size and shape of the final particles is generally determined by the morphology of the starting ZrO2 particles and not by that of the BaCO3. The reaction is faster in humid air than in dry air, and the activation energy decreases from 294 kJ·mol,1 (dry air) to 220 kJ·mol,1 (humid air). When the fraction reacted is >80,90 mol%, the reaction rate rapidly decreases. [source]

Influence of the relative humidity on film formation by vapor induced phase separation

POLYMER ENGINEERING & SCIENCE, Issue 4 2003
H. Caquineau
The formation of polymer films produced by the phase separation process occurring when a cast poly(etherimide)/N-Methyl-2-Pyrrolidone solution was exposed to humid air was studied. It was found that above a relative humidity value of 27%, the films presented a cell-like structure. The size of the cells was shown to decrease when the relative humidity increased. This effect was more pronounced at the film/substrate interface than near the surface. A cell-size gradient from one face of the film to the other was also clearly observed. A phenomenological model has been proposed to explain the morphology obtained by a phase separation induced by the water vapor in the studied system, takin into account thermodynamics and kinetics considerations. In this model, the cell-like structure setting up is shown to result from a nucleation and growth process accompanied by a coalescence coarsening. It was illustrated by a composition path on the ternary phase diagram. It was shown how the relative humidity influenced the film composition leading to the preferential nucleation compared to the growth and coalescence of the cells. Finally, it was found that the cell-size anisotropy resulted in the solvent and non-solvent mass transfers in the film, bringing to the fore the determining role of kinetics. [source]

The quantification of carbon dioxide in humid air and exhaled breath by selected ion flow tube mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2009
David Smith
The reactions of carbon dioxide, CO2, with the precursor ions used for selected ion flow tube mass spectrometry, SIFT-MS, analyses, viz. H3O+, NO+ and O, are so slow that the presence of CO2 in exhaled breath has, until recently, not had to be accounted for in SIFT-MS analyses of breath. This has, however, to be accounted for in the analysis of acetaldehyde in breath, because an overlap occurs of the monohydrate of protonated acetaldehyde and the weakly bound adduct ion, H3O+CO2, formed by the slow association reaction of the precursor ion H3O+ with CO2 molecules. The understanding of the kinetics of formation and the loss rates of the relevant ions gained from experimentation using the new generation of more sensitive SIFT-MS instruments now allows accurate quantification of CO2 in breath using the level of the H3O+CO2 adduct ion. However, this is complicated by the rapid reaction of H3O+CO2 with water vapour molecules, H2O, that are in abundance in exhaled breath. Thus, a study has been carried out of the formation of this adduct ion by the slow three-body association reaction of H3O+ with CO2 and its rapid loss in the two-body reaction with H2O molecules. It is seen that the signal level of the H3O+CO2 adduct ion is sensitively dependent on the humidity (H2O concentration) of the sample to be analysed and a functional form of this dependence has been obtained. This has resulted in an appropriate extension of the SIFT-MS software and kinetics library that allows accurate measurement of CO2 levels in air samples, ranging from very low percentage levels (0.03% typical of tropospheric air) to the 6% level that is about the upper limit in exhaled breath. Thus, the level of CO2 can be traced through single time exhalation cycles along with that of water vapour, also close to the 6% level, and of trace gas metabolites that are present at only a few parts-per-billion. This has added a further dimension to the analysis of major and trace compounds in breath using SIFT-MS. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Doping of C60 Fullerene Peapods with Lithium Vapor: Raman Spectroscopic and Spectroelectrochemical Studies

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008
Martin Kalbá
Abstract Raman spectroscopy and in situ Raman spectroelectrochemistry have been applied to the study of the lithium vapor doping of C60@SWCNTs (peapods; SWCNT=single-walled carbon nanotube). A strong degree of doping was proven by the disappearance of the radial breathing mode (RBM) of the SWCNTs and by the attenuation of the tangential (TG) band intensity by two orders of magnitude. The lithium doping causes a downshift of the Ag(2) mode of the intratubular C60 by 27,cm,1 and changes the resonance condition of the encapsulated fullerene. In contrast to potassium vapor doping, the strong downshift of the TG band was not observed for lithium doping. The peapods treated with lithium vapor remained partially doped even when they were exposed to humid air. This was reflected by a reduction in the intensity of the nanotube and the fullerene modes and by the change in the shape of the RBM band compared with that of the undoped sample. The Ag(2) mode of the intratubular fullerene was not resolved after contact of the lithium-doped sample with water. Lithium insertion into the interior of a peapod and its strong interaction with the intratubular fullerene is suggested to be responsible for the air-insensitive residual doping. This residual doping was confirmed by in situ spectroelectrochemical measurements. The TG band of the lithium-doped peapods did not undergo an upshift during the anodic doping, which points to the formation of a stable exohedral metallofullerene peapod. [source]

Visco-elastic changes of vocal fold mucosa related to high and low relative air humidity

CLINICAL OTOLARYNGOLOGY, Issue 4 2000
R.J.B. Hemler
Objective. To study the effects of high and low relative air humidity (RH) on the visco-elastic properties of the vocal fold cover. Materials and methods. The vocal fold mucosa of sheep larynges was microdissected. The mucosal specimens were attached on one side to an oscillator and on the other side to a force transducer. A sinusoidal oscillation (stress) was applied to the specimen and the transduced force (strain) was recorded in two different conditions of a continuous passing airflow: either dry air (RH = 0%) or humid air (RH = 100%). Of the recorded stress and strain curves the gain and phase-shift between the curves were computed and from these parameters stiffness and viscosity were calculated. In both air conditions the deep surface of the specimen was in contact with a saline bath. Results. Stiffness and viscosity both increased significantly more in dry air than in humid air. This increased stiffness and viscosity returned to baseline values after rehydration. Conclusion. We conclude that these findings indicate that changes in the RH of the airflow passing over the vocal cords influences the visco-elastic properties of the vocal cord cover. [source]