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171.
Y.F. Cheng 《Electrochimica acta》2007,52(7):2661-2667
In this work, electrochemical techniques were utilized to investigate the hydrogen evolution reaction on X-70 pipe steel and the hydrogen permeation through the steel in near-neutral pH environmental condition. The results demonstrate that the steel has always been in an active-dissolution state in near-neutral pH solution and there is no film formed on the steel surface. Hydrogen evolution is inhibited by anodic polarization of the steel, which is attributed to the alternation of hydrogen evolution mechanism and kinetics on the anodially polarized steel. Combined with slow strain rate tensile tests, it is found that the high susceptibility of steel to stress corrosion cracking (SCC) is always associated with a high hydrogen permeation current. A thermodynamic model was developed, by analyzing the change in free-energy of the steel in the presence and absence of hydrogen and stress, to determine the interactions of hydrogen, stress and anodic dissolution at the crack-tip. The role of hydrogen involvement in pipeline near-neutral pH SCC could be determined quantitatively by characterizing the effect of hydrogen concentration on the dissolution rate of steel and the synergism of hydrogen and stress to promote crack growth. 相似文献
172.
The effects of a thin RBaCo2O5 + δ (R= Pr, Nd, Sm, Gd) layer coating on the oxygen permeation flux through Ba0.5Sr0.5Co0.8Fe0.2O5 + δ(BSCF) membrane were investigated. Due to the high oxygen adsorption and desorption rate constants ka and kd of the RBaCo2O5 + δ (R112) materials and the porous structure of the coating layers, the oxygen permeation flux through the BSCF membranes can be enhanced remarkably. It was found that the reaction between Pr112 and BSCF also has significant influence on the oxygen permeation flux. The reaction between Pr112 and BSCF forms impurities which may block oxygen permeation flux. However, Nd112, Sm112, and Gd112 do not react seriously with BSCF, therefore, coating layers of these materials can significantly enhance the oxygen permeation flux of BSCF membranes. 相似文献
173.
Sonia EscolásticoCecilia Solís José M. Serra 《International Journal of Hydrogen Energy》2011,36(18):11946-11954
This contribution presents the preparation, permeation and stability study of mixed protonic-electronic conducting membranes based on the system Nd5LnWO12. The tungstates Ln6WO12 are proton conducting crystalline materials, which show sufficient protonic and electronic mixed conductivity and stability in moist CO2 environments to consider them as potential candidates for the separation of hydrogen at high temperatures. Hydrogen separation properties of A-substoichiometric Nd6WO12 and Nd5LaWO12 were systematically analyzed, i.e. the influence of the H2 concentration in feed stream, humidification degree and operating temperature on the hydrogen separation was studied. Finally, the stability of these materials at different temperatures and CO2-rich and sulfur-containing environments was evaluated. 相似文献
174.
In this paper, we present a theoretical analysis of the frequency response of a continuous-flow adsorber with periodic modulation
of the inlet flow-rate to measure multicomponent diffusion kinetics in porous media. Micropore diffusion kinetics is assumed
for the intraparticle mass transfer mechanism and three different shapes of microparticle are considered: slab, cylinder,
and sphere. Simulation results for a binary system show that the frequency response of the faster diffusing component is strongly
influenced by the slower component. The out-of-phase characteristic function of the frequency response of the faster diffusing
component shows maximum and minimum points. The deviation between these maximum and minimum values becomes smaller when the
cross-terms of diffusivity go to zero, while the deviation becomes larger when the cross-terms of the adsorption equilibrium
constant go to zero. Contrary to the behaviour of the out-of-phase function of the faster diffusing component, the out-of-phase
function of the slower diffusing component shows no extrema at all. The in-phase characteristic function of the frequency
response of the continuous-flow adsorber is not affected by the overflow parameter. 相似文献
175.
The influence of mixture composition on the temperature distribution in the counter flow heat exchanger used in mixture Joule–Thomson refrigerators is investigated in this paper. A perfect heat capacity matching between the supply and the return streams can be achieved by optimizing the mixture composition. The deeper reason is that in two-phase state the latent heat makes a very important contribution in the overall heat capacity for multicomponent non-azeotropic mixtures. The theoretical results are compared with experimental data; both theoretical and experimental results agree well with each other. The results show that the temperature profile as well as the locations of the pinch points is determined by the mixture compositions. Therefore, it is possible to get a perfect temperature distribution using optimal mixture. This becomes another criterion of the optimization of mixture composition. 相似文献
176.
For the analysis of polymers soft ionization mass spectrometry, in which only molecular ions are observed, can provide the complete distribution of chains (length, composition, end-groups) in under ten minutes on microgram quantities of material. Moreover, molecular ion information of neat organic pigments or those present in crosslinked networks can also be furnished. No other analytical technique can supply these data in such a short time. The application of mass spectrometry to the characterization of materials used in today's high performance automotive coatings is presented. These include functional monomers, several acrylic copolymers, organic pigments and an epoxide prepolymer. While there are a variety of mass spectrometric techniques, in this paper we will highlight the techniques that we have found useful for the characterization of organic coating components. The selection of the mass spectrometric technique is dictated by the molecular weight of the material and to a lesser extent the chemical composition. We used potassium ionization of desorbed species (K+IDS) performed on a quadrupole mass spectrometer for materials under 1000 Daltons (Da). However, many of the ingredients used in current automotive finishes fall between 1000 and 10 000 Da. For these materials we used a Fourier transform mass spectrometer (FTMS) which is well suited for this mass range and boasts the highest resolution and mass accuracy available. Direct desorption/ionization using a carbon dioxide laser is our standard method of sample introduction. Recently, we coupled a gel permeation chromatograph to our FTMS using an electrospray ionization interface. This hyphenated technique offers one of the most powerful characterization methods for the coatings chemist. 相似文献
177.
178.
M.A. Izquierdo-Gil 《Chemical engineering science》2008,63(22):5531-5539
Single gas permeation experiments results using neon, argon, nitrogen and methane are reported. From gas permeation experiments the characteristic parameters of the Knudsen and Poiseuille transport mechanisms were determined by means of an equation derived from the “Dusty-Gas” model. The experiments were performed at different temperatures from 303.15 to 323.15 K, in order to study the temperature influence on those parameters. For PVDF and PCTE membranes the influence of the temperature on Ko and Bo parameters was not significant. Gas influence was also investigated for both types of membrane, a slight tendency of Ko to decrease with increase in molar mass and a very slight tendency of Bo to increase with increase in molar mass, although these trends were not fulfilled by neon gas. 相似文献
179.
Seong Min Cho Hyeon Yong Lee Jin-Chul Kim 《Journal of the American Oil Chemists' Society》2007,84(9):859-863
Lipid nanoparticles containing hinokitiol (HKL) were prepared by a melt–emulsification method. Stearic acid was used as a
lipid for the matrix material of the nanoparticles. According to results from transmission electron microscopy (TEM) and dynamic
light scattering (DLS), most of the nanoparticles were less than 100 nm. When nanoparticles containing HKL were scanned on
a differential scanning calorimeter, no endothermic peak of HKL was observed. This means that HKL in the lipid matrix of the
nanoparticles is in a dissolved state. In an 18-h permeation study using hairless mouse skin mounted on a diffusion cell,
the amount of HKL encapsulated in the nanoparticles transported to the receptor cell was five to ten times more than for HKL
dissolved either ethanol or propylene glycol. Therefore, stearic acid nanoparticles strongly enhanced permeation of the skin
by HKL. 相似文献
180.
The electrochemical permeation technique for studying transport and trapping of hydrogen in Fe-40 at.% Al alloy at temperatures of 5, 25, 45 and 65 °C was used in the paper. The influence of temperature on the effective hydrogen diffusion coefficient, hydrogen permeation rate and hydrogen solubility was determined. The activation energy of hydrogen diffusion in iron aluminide in the studied temperature range was also determined. 相似文献