Activation Energy For Thermal Desorption Research Articles

Influence of mineral species on oil–soil interfacial interaction in petroleum-contaminated soils

The mineral species in soils vary in a wide variety of places, thus resulting in the petroleum-contaminated soil (PCS) with complex characters. Thus, the research on the effect of mineral species on oil-soil interactions in PCS takes on a critical significance. In this study, the desorption and adsorption behaviors of aromatic hydrocarbons (Ar) on two minerals surfaces were examined. Meanwhile, the interfacial forces between minerals and Ar were studied and the sources of these forces were analyzed. Moreover, molecular dynamics (MD) simulations were conducted to gain insight into the interfacial interaction mechanisms. As revealed by the results of this study, in comparison with Qs–Ar (quartz sand, Qs), Mnt–Ar (montmorillonite, Mnt) contaminants required higher temperature and activation energies for thermal desorption (201.95 kJ·mol−1vs. 127.82 kJ·mol−1). The above difference was generated since the adhesive forces between Ar and Mnt surfaces were greater than those between Ar and Qs. As indicated by the analysis of the adhesion force sources, the van der Waals forces were responsible for facilitating oil adhesion to mineral surfaces, even though the electrostatic force prevented oil–mineral adhesion. Furthermore, the hydrophobic forces facilitated adhesion in 3 nm. The MD results demonstrated that compared with the Qs system, there existed larger binding energies between Ar and Mnt, a lower diffusion coefficient for Ar on the Mnt surface, as well as more significant adsorption of Ar on Mnt. In general, the different mineral species affect the strength of the interaction at the oil–soil interface, which is a guideline for proposing targeted oil-soil separation measures.

Kinetics of Hydrogen Desorption From Ni—In Composites, Synthesized by Electrochemical Method

The results of the study of the kinetics of the thermal desorption spectrum of deuterium accumulated with Ni64In36-Dx composites synthesized by the method of electrochemistry are presented. The limits of desorption temperatures for ionimplanted deuterium were determined depending on the implanted dose. The measured content of deuterium alloy is 4 at. D/at. Met (~8.7 wt. % D; ~4.6 wt. % hydrogen). The formation of the deuterium thermal desorption spectrum depends on the implantation dose. An increase in the content of implanted deuterium contributes to the formation of a solid solution of hydrogen isotope in the electrochemical composite Ni64In36 with a destruction temperature in vacuum of ~520 K and nickel hydride with hydrogen with a decomposition temperature of ~330 K. The calculation of the activation energy of thermal desorption is produced for a hydrogen peak with a temperature of maximum 500 K. Arrhenius polyterms were obtained for two values of the reaction order index:  = 1 and  = 2. Arrhenius polyterms demonstrate the second order of reaction and the quadratic dependence of the desorption rate on the number of implant particles. The activation energy for a peak with a maximum temperature of 500 K is 2.9 eV, which indicates low energy extraction of the hydrogen isotope

Observation of an exceptionally high apparent kinetic order in the thermal desorption of D2 from the Si(100) surface

Isothermal desorption and angular distribution measurements of D2 recombinatively desorbing from the Si(100)-(2 × 1) surface are reported for the coverage range of 0.5 to 1.0 monolayer (ML). Above 0.9 ML, the apparent kinetic order of the desorption process is ≥5, far larger than the order of ∼1, for which this reaction is now well known in the surface science community. Below 0.9 ML, the order declines monotonically until it reaches a constant value of ∼1 at a coverage of 0.7 ML. Correspondingly, as the coverage decreases, the activation energy for thermal desorption increases from 1.96 eV to 2.45 eV, while the angular distribution of desorbing D2 molecules sharpens from a cos2 θ det distribution to a cos5 θ det distribution. The changing kinetics and dynamics as the coverage decreases from 1 ML can be understood in terms of a transition at ∼0.8–0.9 ML from the 4H (and perhaps 3H) desorption mechanism to the 2H mechanism. We propose that the high apparent kinetic order is due to an unexpectedly rapid decline in 4H configurations (four D atoms bound as Si–D in adjacent Si dimers) caused by competition from the slower, first-order 2H desorption pathway.

Tritium accumulation and release from Li2TiО3 during long-term irradiation in the WWR-K reactor

Proposed mathematical and software analysis of reactor experiments allowed interpretation of the experimental results of a tritium release study. Tritium was continuously generated by the reaction of lithium-6 with thermal neutrons for various thermal conditions of lithium metatitanate (Li2TiO3). The main gas release parameters were calculated in order to assess the potential use of lithium metatitanate in tritium breeders. These parameters were: gas release rate, tritium retention, retention time, activation energy for thermal desorption as HT, activation energy for volume diffusion as Т+, and the corresponding pre-exponential (frequency) indexes.

Temperature-dependent activation energy for silicon desorption processes

A theoretical analysis is presented of the temperature dependence of the activation energy for thermal desorption of silicon from textured tantalum tape. The curves derived from experimental data for the initial stages of desorption are in qualitative agreement with calculation results, which makes it possible to estimate lateral interaction forces and the adatom-substrate interaction energy as a function of surface coverage and to predict structural changes in the film.

Thermal desorption of dysprosium from tungsten microcrystal

Activation energy for thermal desorption of dysprosium from a tungsten microcrystal of about 300 nm diameter was determined by means of the field-emission method. The desorption was detected from the whole W emitter surface in the temperature range 1490–1665 K for dysprosium average coverage θ < 0.06 monolayer. The average activation energy was determined to be 4.09 ± 0.06 eV/atom and the frequency factor to be about 10 11 s −1. The energy may mainly concern the desorption from the atomically rough regions of the microcrystal.

Permeation of hydrogen through amorphous ferrum membrane

Hydrogen permeation through amorphous and recrystallized foils of Fe-based alloys was investigated. It was found that surface layers of both types of samples were enriched by metalloids. These layers prevented permeation of hydrogen from molecular and atomic phases. Only the ionization of the gas in glow discharge near the upstream side of foils resulted in big permeation fluxes. Kinetics of flux relaxation to the steady-state values revealed reversible trapping in amorphous alloy. Permeation flux demonstrated Arrhenius linear dependence for recrystallized samples and non-monotonous for amorphous ones. Values of steady-state flux through amorphous foils were several times higher than through ordered samples at temperatures below 200°C. The mechanism of hydrogen transport is proposed taking into account re-emission and diffusion processes. Activation energies for thermal desorption and diffusion are evaluated.

モリブデナイト結晶中の水素の拡散，脱離の観察

Diffusion and desorption of hydrogen in a bulk of molybdenite crystal are studied by measurement of gas emitted from the bulk crystal during cleavage experiment for observation of gases in a bulk, electron stimulated desorption (ESD) for measurement of hydrogen concentration on the surface and temperature programmed desorption (TPD) for estimating ion of an activation energy of diffusion and desorption process. The cleavage and ESD experiments are performed to observe the change of hydrogen concentration in the bulk and on the surface by the sample heating. These experiments show that a mount of hydrogen in the bulk reduces at about 500°C and that the hydrogen concentration on the surface and thermal desorption of hydrogen from the bulk also begin to increase around 500°C. The increase of hydrogen concentration on the surface suggests that the activation energy for thermal desorption is lager than the diffusion energy in the bulk to (0001) surface. However, in this case this may not be applicable because of similar temperature behavior of surface hydrogen and desorbed hydrogen. The mechanism of the diffusion and the desorption process is discussed. The activation energy for the desorption induced by diffusion of hydrogen in the bulk to (0001) surface is about 76 kJ/mol.

Inertness of SiC surfaces against Si atoms and clusters

Si atom and cluster interaction with 6H-SiC (0001) Si surfaces was studied using thermal desorption measurement and scanning tunneling microscopy (STM). Heating SiC at 1500°C in an ultrahigh vacuum produced an inert surface. When this surface was exposed to Si vapor containing clusters, Si atoms and Si2–4 clusters were observed to recoil at 400°C. STM showed that the surface had a 63×63R30° superstructure. The activation energy for thermal desorption of Si, Si2, and Si3 from the surface was found to be 46, 49, and 66meV. These low values indicate the physisorption of Si atoms and clusters. STM showed that, when the surface was supplied with Si vapor at room temperature, Si clusters formed at step edges, leaving the 63×63R30° structure intact and verifying the surface's inertness.

Field emission microscopy study of cesium adsorbed on ZrB2 and TiB2

Field emission microscopy was used to investigate the thermal desorption of cesium from ZrB2 and TiB2 surfaces. Described is a method of extracting the work function and effective emitting area from the Fowler–Nordheim data with minimum assumptions. Work functions were measured after heating at successively higher desorption temperatures, assuming a value of 2.2 eV for the cesium saturated surface. The minimum value of the work function for the cesium coated ZrB2 surface was 2.04±0.1 eV, while that of the TiB2 surface was 1.74±0.05 eV. Average work functions of the thermally cleaned ZrB2 and TiB2 surfaces were found to be 3.78 eV and 5.44 eV, respectively. Activation energies for thermal desorption of cesium from ZrB2 and TiB2 were found to be 1.1±0.1 and 0.71±0.2 eV, respectively.

Infrared spectroscopy and photodesorption of condensed phase ammonia

We have characterized the adsorption and thermal desorption of thick films of NH 3 and ND 3 condensed on Ag(111) with Fourier transform reflection absorption infrared spectroscopy and temperature programmed desorption. Over the coverage range of 1–50 monolayers, the asymmetric stretch (2513 cm −1 for ND 3 and 3380 cm −1 for NH 3) and symmetric deformation (832 cm −1 for ND 3 and 1078 cm −1 for NH 3) modes of ammonia are the most intense features in the vibrational spectra. Temperature programmed desorption yields an activation energy for thermal desorption of NH 3 and ND 3 multilayers of 23.8 kJ mol −1 and 24.7 kJ mol −1, respectively. At a coverage of 50 ML we used 193 nm light to stimulate molecular desorption from the multilayers and measured time-of-flight spectra. All time-of-flight spectra were bimodal; the average translational energies of the two components were 3150±100 K and 550±50 K. The fast channel is ascribed to ammonia molecules ejected from the vacuum–film interface while the slower channel is ascribed to ammonia molecules desorbing from deeper layers of the film. At 50 ML the angular distribution of photodesorbed ammonia peaks between 20° and 40° off the surface normal.

Influence of oxygen on the thermal desorption of Cs from Si(100)

This paper describes the thermal desorption of Cs from oxidized Si(100), measured as a function of sample temperature and oxygen coverage. The desorption process is found to be governed by a broad distribution of the activation energy for thermal desorption of the Cs atoms, which reflects the considerable inhomogeneity of the Si surfaces. The weight of the distribution is found to shift to higher activation energy with increasing oxygen coverage of the Si substrates.

Collision-induced desorption (CID) of NO from Pt{111}: a comparison between the CID binding energy and the activation energy for thermal desorption

The Xe and Kr collision-induced desorption cross-sections for NO adsorbed on Pt{111} at 100 K are reported as a function of translational energy in the range of 1.9 to 3.8 eV. The minimum energy required for desorption is extracted using extrapolation to the zero of cross-section. The measured threshold energies exhibit total energy scaling for both beams using two angles of incidence, 45° and 15°. The threshold energies required to desorb NO from Pt{111} were determined experimentally to be 2.55 eV and 2.05 eV using Xe or Kr respectively. Using a hard sphere/cube collision model the NO-Pt{111} binding energy was calculated to be 1.12 ± 0.02 eV using either the beam of Xe or Kr. Comparison of this binding energy with the measured activation energy for thermal desorption supports an adsorption/desorption model having no precursor to the chemisorption state.

Surface silicon-deuterium bond energy from gas-phase equilibration.

The bond strength of deuterium (D) to the surface of silicon was determined to be 2.67[plus minus]0.1 eV from measurements of the amount of D on the surface in equilibrium with D[sub 2] gas at various pressures. This was done by measuring the amount of D on surfaces of closed internal microcavities using nuclear reaction analysis. The binding of D to a silicon surface is significantly weaker than the Si-H bond in silane which has been assumed in the past to indicate the strength of the surface Si-H bond. The fact that the Si-D bond strength is comparable to the activation energy for thermal desorption of H from Si suggests a possible reaction path for desorption in which the first and rate-determining step is the dissociation of a Si-H bond followed by the exothermic reaction between the released H atom and a second Si-H to form a H[sub 2] molecule and two Si- dangling bonds. Our result also gives a value of 1.8 eV for the activation energy for dissociative adsorption of D[sub 2] on silicon. The number of bond sites is comparable to the number of Si atoms on the cavity surfaces calculated from the total cavity surface areamore » determined by TEM.« less

Properties of lithium tetraalkylborate complexes in adsorption and desorption of oxygen

Lithium tert-butyltrialkylborates are capable of chemisorbing oxygen. The activation energy for thermal desorption of oxygen from [t-C4H9OB(OR)3]Li·nO2 at 298–548 K increases with decreasing degree of O2 sorption and with increasing length of the alkyl substituent; for complexes with R=n-C4H9, n-C7H15, and n-C10H21, the values increase from 48.90 to 70.92 kJ/mole.

Activation energies for thermal desorption of hydroxyl radicals from single-crystal platinum(111) and polycrystalline platinum foil surfaces

Activation energies for thermal desorption of hydroxyl radicals from single-crystal platinum(111) and polycrystalline platinum foil surfaces

Iss observations of aluminum surfaces under hydrogen ion bombardment

The shadowing effect of ISS was applied to observe the surface behavior of H atoms implanted with 500 eV/atom on a high-purity A1 sample. This study confirmed that this technique is powerful to observe the retention kinetics of H atoms especially on the topmost material surface with simultaneous analysis for surface contaminants such as oxygen during irradiation with hydrogen ions.The result obtained from the initially cleaned surface showed a remarkable increase in the H retention with increasing fluence of H2+ up to about 1018 H/cm2 at room temperature, depending on the fluence of predamage given by He+ ions, but showed no increase in the retention at the temperatures above 100 ° C. Therefore, because Al is a metal well known to be passive for chemisorption of H2 molecules and H atoms, it was concluded that the observed H retention originates from the traps produced by radiation damage. The activation energy for thermal desorption of the trapped H atoms was estimated to be 1.1±0.4 eV by ISS measurements.The oxygen-covered surface showed a rapid increase in the retention at fluence of less than 1017 H/cm2.

Thermal desorption of CO, O 2 and CH 4 molecules from Ni(111) single crystals

The thermal desorption of CO, O 2 and CH 4 molecules from a Ni(111) single crystal surface has been studied by Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES) and Mass Spectroscopy. The crystal surface was exposed to the above molecules at pressures from 10 -9 to 10 -5 Torr. Surface structures and bonding were studied by the above techniques. The absolute coverage of the molecules on the surface was measured and activation energies for thermal desorption were measured for each case.

Adsorption, surface migration and thermal desorption of LaB6 on tungsten surface using field emission microscopy

Investigations on the adsorption, surface migration and thermal desorption of LaB6 on the tungsten surface are made using as simple field emission microscope. The distribution of the absorbate over the surface, as the tip is heated progressively at higher temperatures, has been broadly classified in two stages corresponding to two different temperature ranges, 850-1100K and 1700-1950K. During the first stage, protrusions grow on (111) planes, with the estimated activation energy 1.0 eV and the pre-exponential factor 104 s-1. In the second stage, these protrusions are dispersed, resulting in a 'well-spread' pattern. Further heating in the same temperature range causes thermal desorption of the adsorbate, leaving the tungsten tip clean. The average activation energy for thermal desorption has been estimated to be 5.1 eV with a pre-exponential factor 1012 s-1. The results suggest that LaB6 evaporates as atomic La and B from the tungsten surface. The behaviour of the adsorbate over the surface is discussed in the light of the results.

Adsorption of silicon on molybdenum in a field emission microscope

Abstract The adsorption, surface diffusion, and thermal desorption of silicon on molybdenum have been investigated by field emission microscopy. The average work function of silicon covered molybdenum field emitter decreases with a simultaneous reduction in the total field emission current. This suggests the resonance tunneling of the field-emitted electrons. With low coverage, boundary free surface diffusion occurs at 565 °K on the [111] zones. Above 585 °K diffusion occurs with a sharp boundary and an activation energy of 50.9 kcal/mole in the (211) → (100) direction. Adsorption of silicon on molybdenum tips at and above room temperatures is anisotropic. The activation energy of thermal desorption from (111) and (411) planes is 63.3 and 123.9 kcal/mole respectively. Annealing the silicon covered tip at 1000°K produces a silicon enriched surface phase with new crystal planes.