Desorption Of Cesium Ions Research Articles

Desorption of Cesium Ions from Vermiculite with Sea Water by Hydrothermal Process

Cesium ions (Cs+) strongly intercalated in vermiculite clay (Verm) had been effectively removed using sea water for its free utility, totally environmental friendly feature, and within containing n...

Nature of the sites involved in the process of cesium desorption from vermiculite

Three particle size fractions of sodium-saturated vermiculite (10–20, 1–2 and 0.1–0.2μm), differing only in their ratios of external-to-total sorption sites, were used to probe the nature of the sites involved in desorption of cesium ions. The sorption was investigated for initial aqueous concentrations of cesium ranging from 5.6×10−4 to 1.3×10−2mol/L, and the cesium desorption was probed by exchange with ammonium ions. The results showed that (1) the amounts of desorbed cesium were strongly dependent on the particle size for a given initial aqueous cesium concentration and (2) the amounts of desorbed cations (Na+ and Cs+) strongly decreased with increasing initial cesium aqueous concentration, irrespective of the particle size investigated. Quantitative analysis of these results suggested that cesium ions sorbed on external (edge+basal) sorption sites can be desorbed by ammonium ions. As a contrast, most of cesium ions sorbed on interlayer sites remain fixed due to the collapse of the structure under aqueous conditions. This study provides important information, such as the nature of the sites involved in the exchange process, when the thermodynamic formalism is considered to describe the ion-exchange process involving cesium and high-charge swelling clay minerals in polluted soil environments.

Field electron emission and field desorption of cesium from graphene

Field electron emission and field desorption of cesium ions from a monatomic graphene film on Ir and graphene clusters in amorphous carbon are investigated using field electron microscopy and continuous-mode field desorption microscopy. The deposition of cesium on amorphous carbon with graphite clusters leads to inversion of the emission (i.e., emission from the emission centers disappears against the back-ground of uniform emission from the previously nonemitting surface). In both systems, ion current pulses are observed during field desorption in a stationary electric field. During field desorption from the graphene film, current pulses of Cs+ ions with a duration shorter than 0.1 s appear from the plane faces of the iridium point. During desorption from graphite clusters, ion current pulses form a pattern of “collapsing rings” on the screen. Possible mechanisms of the observed processes are considered using the model of cesium intercalation by graphite and by the graphene layer and the desorption of Cs atoms under the action of the electric field, as well as the “flip” of the dipole moment during the cesium intercalation.

Cesium ion emission from a graphene surface on iridium in a high-intensity electric field

Features of cesium ion emission from a graphene film on iridium in a 107–108 V cm−1 electric field of are studied. Field electron and desorption images demonstrate that the film consists of regions (islands) 20–100 nm in size. Intercalated cesium lies under the film. There is continuous desorption of cesium ions from the defects in the graphene film and the regions of where islands abut one another. Cesium ions arrive at the desorption sites from the intercalated state.

Desorption Kinetics at Atmospheric Pressure: Alkali Metal Ion Emission from Hot Platinum Surfaces

The kinetics of potassium and cesium ion desorption from platinum surfaces have been studied with field reversal technique under atmospheric conditions. Rapid electric field reversal outside the surface disturbs the surface population of alkali metal atoms by retarding or accelerating desorbing ions, and the flux of ions from the surface is monitored to determine rate constants for desorption. Ion desorption from polycrystalline platinum surfaces in air is studied to evaluate the potential of the method for in situ high-pressure investigations. Rate constants in the range 10-2−103 s-1 are obtained at surface temperatures of 820−1290 K, and activation energies (frequency factors) of 2.49 ± 0.06 eV (3.7 × 1013 s-1) and 1.80 ± 0.09 eV (5.4 × 1011 s-1) are determined for K+ and Cs+, respectively. The results are in excellent agreement with literature data obtained under ultrahigh vacuum conditions, which confirms that the field reversal technique can be successfully applied under pressurized conditions. The i...

Rate constants for thermal cesium ion desorption on clean and graphite-covered iridium studied by laser-induced desorption

Desorption of cesium ions from clean and graphite-covered polycrystalline iridium was studied at surface temperatures of 600–910 K. Cs was adsorbed on the surface and the population decay due to thermal desorption was followed to obtain desorption rate constants. The surface population of Cs at different times was probed by laser-induced desorption, which gave a signal of laser-induced desorbed ions proportional to the surface concentration. With this method ionic rate constants in the range 10−5−10−1s−1 were obtained. The desorption energy of Cs+ on Ir was found to be 2.07±0.16 eV, in agreement with previous experimental results. On graphite-covered Ir three parallel desorption modes were found, all with a desorption energy of 1.8 eV, but with frequency factors of 7 × 108, 9 × 109 and 2 × 1011 s−1, respectively. The highest frequency factor corresponds to desorption from a state with a desorption energy of 1.8 eV on the graphite layer. The two lower factors are due to Cs at graphite grain bounderies, and between the graphite layer and the Ir surface. Diffusion of these populations to the state on top of the graphite layer, followed by desorption, is concluded to be the mechanism behind the observed results.

Cesium ion desorption from oxygen and carbon adlayers on platinum surfaces with nanosecond time resolution: variation of desorption parameters with time available for surface diffusion and degree of surface heterogeneity

Cesium ion desorption from oxygen and carbon adlayers on platinum surfaces with nanosecond time resolution: variation of desorption parameters with time available for surface diffusion and degree of surface heterogeneity

Cesium ion desorption from oxygen and carbon adlayers on platinum surfaces with nanosecond time resolution: Variation of desorption parameters with time available for surface diffusion and degree of surface heterogeneity

Measurements of ionic cesium desorption from surfaces at temperatures above 1100 K have been made with the so-called field reversal method. Time constants down to 30 ns have been measured with very low surface densities of Cs. The prexponential factors for desorption from clean platinum and graphite covered platinum surfaces are close to 10 12 s −1, in agreement with simple desorption theory. However, for slightly oxygen covered surfaces and for carbon layers formed at low temperatures the preexponential and the desorption energy become significantly larger, while a strict Arrhenius form is retained. This is proposed to be due to the influence of surface inhomogeneity and surface diffusion, in line with the theoretical description of simultaneous diffusion and desorption recently given by Nordholm. In the oxygen case, the adsorbed oxygen is considered to be the origin of the heterogeneity, while in the carbon layer case the surface, which has been formed at low temperature, is disordered and may contain many strongly binding sites. The influence of bulk diffusion on the desorption is also described.