Results 1 - 10 of 13726
Results 1 - 10 of 13726. Search took: 0.041 seconds
|Sort by: date | relevance|
[en] The desorption kinetics of a chiral compound, R-3-methylcyclohexanone (R-3MCHO), have been measured on both enantiomers of seven chiral Cu(hkl)R and S surfaces and on nine achiral Cu single crystal surfaces with surface structures that collectively span the various regions of the stereographic triangle. The naturally chiral surfaces have terrace-step-kink structures formed by all six possible combinations of the three low Miller index microfacets. The chirality of the kink sites is defined by the rotational orientation of the (1 1 1), (1 0 0) and (1 1 0) microfacets forming the kink. R-3MCHO adsorbs reversibly on these Cu surfaces and temperature programmed desorption has been used to measure its desorption energetics from the chiral kink sites. The desorption energies from the R- and S-kink sites are enantiospecific, , on the chiral surfaces. The magnitude of the enantiospecificity is ≈ 1 kJ mol−1 on all seven chiral surfaces. However, the values of are sensitive to elements of the surface structure other than just their sense of chirality as defined by the rotational orientation of the low Miller index microfacets forming the kinks; changes sign within the set of surfaces of a given chirality. (paper)
[en] Thermodesorption of hydrogen isotopes from graphite is of interest for current thermonuclear fusion experiments since the plasma properties are strongly affected by the recycling of gases between the plasma and the graphite tiles used to protect the limiters and the wall of the tokamak. Graphitic Matrix A3-3 specimens were exposed at 900deg C to deuterium partial pressures of 7.6 or 74 Pa until the adsorption equilibrium was established. Subsequently, the thermodesorption of deuterium was measured at temperatures up to 1700deg C. D2 desorption commenced at ≅ 900deg C. The release spectrum consists of a broad peak with a weak shoulder near 1180deg C for an initial surface concentration of n1(t=0) = 2.2x1014 D/cm2 and a shoulder near 1120deg C for n1(t=0) = 6.6x1014 D/cm2. The maximum of the release rate is observed at Tp = 1500deg C. The results are explained by assuming associative desorption of deuterium with an activation energy of desorption Ed = 3.8 eV/D2 around 1150deg C and release of a large fraction of the absorbed deuterium from pores by a short range diffusion process at higher temperatures. (orig.)
[en] As a result of the exposure of tungsten to a high-intensity plasma flow, it is established that the exposure of recrystallized and plastically deformed samples leads to fundamentally different mechanisms of confinement of plasma particles and associated deformation of the surface. The surface of the exposed deformed samples contains micrometer-sized ruptured blisters: an indication of the formation of subsurface bubbles on a grid of dislocations forming during deformation. Desorption spectra of both types of sample are decomposed into three peaks, corresponding to the detachment of plasma–gas particles from dislocations, deuterium-vacancy clusters, and pores. Plastic deformation, which leads to an increase in the dislocation density, does not change the position of the three peaks in the desorption spectra but increases their amplitude in comparison with the recrystallized material.
[en] Experimental results of H2 desorption from W (poly), with Programed Thermal Desorption, Electron Stimulated Desorption and Variations of Work Function techniques, is presented. Data analysis reveals four differents desorption states. Desorption energies, calculated from data of the three techniques, shows good agreement between them. Some desorption states of H2 present no ion production, with ESD, during desorption. (author)
[pt]Estudos experimentais de desorcao de H2 de W (poli) com Desorcao Termica Programada, Desorcao Estimulada de Eletrons e Tecnicas de Variacao da Funcao Trabalho sao apresentadas. A analise dos dados revela quatro estados de desorcao diferentes. As energias de desorcao, calculadas dos dados das tres tecnicas diferentes, mostra boa concordancia entre elas. Alguns estados de desorcao de H2 nao apresentam producao de ions com ESD durante a desorcao. (A.C.A.S.)
[en] We have studied the trapping states of implanted hydrogen isotopes in pyrolytic graphite and their thermal desorption to understand the mechanisms of fuel recycling/inventory and found that the graphite surface is modified due to formation of radiation damage; that is, the trapping states and desorption behavior change with accumulation of the radiation damage in the graphite. (orig./RK)
[en] The hydrogen behavior of fuel element graphite, IG-110 graphite and carbon brick in HTR-PM has been investigated using the gas charging technique for the hydrogen adsorption and temperature programed desorption (TPD) technique for the hydrogen desorption. The curve of desorbed hydrogen amount as function of H2 concentration in inlet gas shows a linear relation, and a shift from 473°C to 464°C is observed in the TPD curve of the un-saturated adsorbed IG-110 graphite. The desorbed hydrogen amount is increasing with the adsorption increasing from 800°C to 1000°C. The desorption energy values of these three materials are calculated based on the Kissinger equation, and they are almost the same (average number is 66.0kJ/mole). A comparison of the desorbed hydrogen amount among these three materials shows that fuel element graphite has the highest desorbed amount, and carbon brick has the lowest. It corresponds to the trend of the closed porosity for these three materials. (author)
[en] The retention of oxygen implanted in graphite at 1.5 and 3 keV was measured as a function of fluence. At fluences less than 1016 O/cm2 the oxygen was all retained, but at higher fluences the retention saturated. Models describing the retention are discussed which include the effects of sputtering and a saturation limit to the local oxygen concentration. Thermal release of oxygen implanted to saturation at room temperature began at 2500C and was 90% complete by 7500C
[en] Many studies have shown a sharp deuterium desorption from beryllium at around 450 K. In an attempt to model this sharp release, a new model was developed, describing the formation and decomposition of beryllium deuteride. Such a model was found to reproduce the sharp desorption peak in the thermal desorption spectrum. Moreover, in contrast to other models, the new model was able to reproduce the constant deuterium desorption from beryllium held at a constant elevated temperature. Fitting the modeling results to experimental data allowed us to determine the deuterium solubility limit in beryllium, which indicated an endothermic formation of beryllium deuteride. New values of the deuterium surface recombination coefficient were also obtained, differing from the ones found in the literature. (paper)
[en] The precise way of how adsorbed atoms on a cold surface are ejected when the surface is warmed up, is still a difficult physical problem. A considrable progress in understanding this change of state is achieved with the discovery of the phonoatomic effect, a kind of elementary quantum-mechanical desorption process. It has been shown that atoms, adsorbed on a solid surface, could be ejected by phonons, i.e sound or thermal energy quanta. The results and the implications of this work, which was performed at the California Institute of Technology, on gas desorption are exposed and the deep analogy between this effect and the well known photoelectric effect is underlined. 8 figs
[en] In the present study, the sorption behavior of cesium was investigated in Ain Oussera soil around the Es-Salam reactor facility. This study was conducted using batch method under different physicochemical conditions including contact time, ionic strength, pH, solid/liquid ratio and temperature. The results showed that sorption followed pseudo-second-order kinetics with a good regression coefficients (R2 = 0.999). The activation energies were 11.26 and 15.21 kJ mol-1 which correspond to ion-exchange-type sorption mechanism. The adsorption was favored at low temperature and it was exothermic (?H0 < 0, with average value of -1.97 kJ mol-1) and spontaneous (?G0 < 0, with average value of -11.97 kJ mol-1 at 23 degC and -13.2 kJ mol-1 at 60 degC). The presence of competing cations such as K+ and Ca2+ ions in groundwater can significantly reduce the Cs adsorption onto soil. Desorption reaction was also investigated using three reagents with different ionic strengths (deionized water, groundwater and 0.1 M KCl solution). The results showed that Cs ions were preferentially distributed onto high affinity sorption sites.