Kinetics of thermal desorption

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Kinetics of Hydrogen Desorption from Rapidly Solidified Al Cr Alloys

Kinetics of Hydrogen Desorption from Rapidly Solidified Al Cr Alloys

study, thermal desorption spectroscopy (TDS) was applied to detect hydrogen evolution from RS alloys. In fact, hydrogen is the only gas that is appreciably soluble in aluminium and its alloys. Difficulties in detection of hydrogen states in the materials are mainly caused by its high mobility and small quantity. The thermal desorption analysis represents a modern approach to this problem and can be regarded as a superior technique because of its sensitivity and the accuracy of measurements. 14,15) To monitor surface morphology of the foils we employed atomic force microscopy (AFM) and scanning electron microscopy (SEM). It should be noticed that initial research 16,17) on H desorption processes in RS aluminum and preliminary results obtained for its lightly doped RS binary alloys with Ti, Cr and Zr have clearly demonstrated a great difference between hydrogen behavior in RS aluminum foils and one in traditionally processed aluminum samples. 7,18) Therefore the purpose of the present
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Thermal desorption of water ice in the interstellar medium

Thermal desorption of water ice in the interstellar medium

reflecting both a different Avalue, and the different re- action kinetics. A more complete discussion of this com- plex relationship between TPD line shape profiles, bind- ing energies, and desorption kinetics can be found in Woodruff & Delchar (1986) or Attard & Barnes (1998). However, from a comparison between the experimental TPD spectra presented in Fig. 1 and the simulations in Fig. 2, it is reasonable to conclude that the results of this experiment are indicative of zeroth order kinetics. Furthermore, only a single peak is observed in the TPD spectra: even at low coverage it is not possible to decon- volve a monolayer desorption peak from the multilayer peak. Therefore no evidence exists to suggest that the desorption process is coverage dependant, nor that it is possible to distinguish between the multilayer and monolayer desorption processes. These observations are entirely consistent with previous reports on the TPD of ice from other hydrophobic, metal substrates (Kay et al. 1989; Dohn´ alek et al.1999, 2000).
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Temperature Effect on Desorption Kinetics of Benzene on Various Soils

Temperature Effect on Desorption Kinetics of Benzene on Various Soils

Commonly, thermal desorption has been applied as an ex-situ treatment option. Equipment employed is typically rotary dryers or thermal screw units with screw conveyors. Soil is heated and exposed to carrier gas to transport organic compounds volatilized from soil and water. Less common are the in situ thermal techniques of steam stripping and Six Phase Soil Heating. Steam stripping involves the injection of steam into the contaminated zones. The steam not only establishes a pressure gradient to push contaminants to an extraction point, but also increases the vapor pressure which results in an increase in solubility and a decrease in viscosity. Six Phase Soil Heating passes standard AC electrical currents through the soil and is used in conjunction with vapor extraction wells. The increase in temperature due to the electrical current increases the volatilization of some compounds and thus the removal rate of vapor extraction.
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Surface-structure dependence of water-related adsorbates on platinum

Surface-structure dependence of water-related adsorbates on platinum

stepped surfaces yield values ca. 1 kJ mol −1 lower than reported values for ASW. The minor difference is likely a result of the very limited temperature regime over which we need to fit our data as a consequence of using ultrathin films. At the same time, for the thinnest multilayers our values exceed the value reported for CI [5, 6, 34]. We obtain 57.9 and 56.7 kJ mol −1 for Pt(211) and Pt(221), respectively, which is to be compared to 55.9 kJ mol −1 for Pt(111) [5]. Again, our values may be influenced by limitations resulting from the low film thickness. Nevertheless, the clear difference between the obtained results even for the same layer thickness suggests that our very thin CI-like layers are not quite the same as bulk CI. In addition, the layer thickness required to start observing desorption from an ASW phase differs by a factor of two between the two surfaces. The CI-like phase is ∼ 6 monolayers thick on Pt(221) and only ∼ 3 ML on Pt(211). Finally, recognizing that variations between different laboratories occur in establishing desorption energies, we note that the absolute difference between CI-like and ASW layers for our stepped surfaces is significantly larger than that for Pt(111). Hence, if the desorption energy of ASW for our stepped surfaces is off and should align with the indicated value for Pt(111), then the CI-like layers on our stepped surfaces are stabilized even more as compared to Pt(111). Obviously, this only holds if the ASW in our ultrathin layers is structurally the same as thick ASW layers.
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Non-isothermal kinetics of thermal degradation of chitosan

Non-isothermal kinetics of thermal degradation of chitosan

As can be see from Table 2, the average value of the apparent activation energy E and pre-exponential factor A in the Arrhenius equation is higher for the first stage of the thermal degradation of chitosan. The values of the pre-exponential factor for a solid phase reactions are expected to be in a wide range (six or seven orders of magnitude), even after the effect of surface area is taken into account [24]. For first order reactions, the pre- exponential factor may vary from 10 5 to 10 16 min -1 . The low factors will often indicate a surface reaction, but if the reactions are not dependent on surface area, the low factor may indicate a “tight” complex. The high factors will usually indicate a “loose” complex [23]. Even higher Table 1 Effect of the heating rate on the kinetic parameters for the thermal decomposition of chitosan calculated according Coats-Redfern procedure
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Extraction and Direct Quantification of Salicylic Acid in Arabidopsis Using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Extraction and Direct Quantification of Salicylic Acid in Arabidopsis Using Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

available in the literature on how the thermal and electronic properties of a Si wafer change when its porosity increases. 11 it is speculated that the surface feature-dependent electronic and thermal properties to be the main attributors to the observed non-ablative laser desorption ionization-MS. For example, in a photo-thermal model the transformation of photon energy to thermal energy was suggested to result in the abrupt increase of local temperatures, then the subsequent thermal excitation leads to surface-absorbed analyte desorption. Multiple groups have qualitatively disscussed the correlation between the local temperature increase and the observed MS performances, and have estimated the importance of thermal excitation based on the thermal parameters of corresponding bulk materials. 12, 13 Conversely, different opinion has been expressed by Paltauf et al, in which the importance of thermal contribution was considerably smaller due to the fact that little thermally induced fragmentation was observed in SALDI-MS. This notion is supported by the findings that in matrix-assisted laser desorption/ionization (MALDI)-MS thermal excitation is fundamentally constrained by the matrix properties, such as matrix crystal size, matrix energy coupling efficiency, matrix-analyte incorporation, etc, and only plays minor roles. 14
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Study of Rare Gases Behavior in Uranium Dioxide

Study of Rare Gases Behavior in Uranium Dioxide

The behaviour of fission products in uranium dioxide has been a focus of considerable experimental and theoretical attention in the nuclear industry. Xenon and krypton have attracted particular attention due to their high fission yields. During in-reactor irradiation of the nuclear fuel, rare gases are subject to several phenomena: diffusion and precipitation. These phenomena can have adverse consequences on the fuel physical and chemical properties and its in-reactor behavior. When released from the material they induce an increase in the fuel rod pressure detrimental to its integrity. A greater understanding of the mechanisms that underpin rare gas diffusion and precipitation should enable the development of models with a greater predictive capability and also make it possible to optimize fuel microstructures so as to increase the fuel element discharge burnup. The development of models for describing oxide behavior is hindered by the lack of experimental data available. The aim is to contribute to the understanding of the prevailing phenomena and generate sets of fundamental data necessary for modelling rare gas behaviour. The purpose of this work is to better understand the behavior of fission gases by identifying diffusion and bubble nucleation. To do this, studies involving separate effects have been established coupling ion irradiations/implantations with fine characterizations (Thermal Desorption Spectrometry and Transmission electron microscopy).
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Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy

Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy

D 2 are the diffusion coefficients, and k a and k d are the rate constants for adsorption and desorption, respectively. The different kinetic regimes that were obtained for the mesopo- rous materials are shown in Figure 6. In this figure, the data for the 7.2 nm sample is presented, since it possess the highest amount of adsorption sites among the samples tested, and the different regimes thus become more apparent. Both the adsorption and release kinetics involved two regimes, and the rate depends on whether the binding isotherm or the diffusion is dominant. In the initial adsorption regime, the adsorption isotherm is the rate-limiting step. The slope in this regime was thereby determined by the adsorption rate constant (k a ). The calculated k a values for the samples are presented in Table 6. A higher k a was obtained as the pore size increased for the unmodified samples. No trend was observed for the functionalized surfaces; most of them showed about the same adsorption rate per area unit of the internal area.
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Organic and inorganic decomposition products from the thermal desorption of atmospheric particles

Organic and inorganic decomposition products from the thermal desorption of atmospheric particles

The AMS, however, does not measure individual organic molecules and is thus limited in informing on exact source types. The thermal desorption aerosol gas chromatograph (TAG) instrument is an automated in situ instrument to de- termine hourly concentrations of hundreds of major con- tributing organic compounds (Williams et al., 2006, 2010). TAG utilizes a collection and thermal desorption (CTD) cell to collect and thermally transfer samples in helium gas to a gas chromatography (GC) column. Compounds eluting from the GC at different retention times are then detected by quadrupole mass spectrometry, and more recently by high-resolution time-of-flight mass spectrometry in a com- bined TAG–AMS instrument (Williams et al., 2014). The same factor analysis techniques (e.g., PMF) can be used with TAG data to determine the molecular composition of ma- jor contributing components, offering more specific informa- tion to infer source types or aerosol transformation processes (Williams et al., 2010). The CTD-based TAG system with- out online derivatization has limited mass transfer of highly oxygenated OA. While this issue has been addressed to some degree in the semi-volatile TAG (SV-TAG) system with on- line derivatization (Isaacman et al., 2014; Zhao et al., 2013), it is of interest to know what fraction of the total OA mass loading is detected by the TAG system. This important ques- tion is currently undergoing a detailed investigation and is the focus of a future manuscript; however, for the purposes of this work focused on aerosol thermal decomposition, we provide a brief description of what is currently understood regarding mass transfer through the CTD-based TAG system as deployed in multiple field campaigns (e.g., Williams et al., 2007, 2010; Kreisberg et al., 2009; Lambe et al., 2009, 2010; Worton et al., 2011).
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Ultraviolet laser induced submicron spatially resolved super hydrophilicity on single crystal lithium niobate surfaces

Ultraviolet laser induced submicron spatially resolved super hydrophilicity on single crystal lithium niobate surfaces

In order to study the recovery of the contact angle after exposure a number of samples were exposed at 45 mW for 60 s and then stored individually in polypropelene tubs in the dark. Figure 4 shows that the recovery to the initial contact angle takes around 20 days and that the recovery is not a linear function of time but proceeds at a continuously de- creasing rate. If the surface energy change is due to the ad- sorption of water molecules on the crystal surface, as the humidity dependence suggests, and the thermal desorption of these molecules is a random process with constant probabil- ity, then the decay of the surface energy as measured by the cosine of the contact angle should be well modeled by an exponential decay. The decay of the cosine of the contact angle is shown in Fig. 5 with the best fit of the form y= y 0
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EVALUATION OF TREATMENT EFFICIENCY OF DRILLING WASTE WITH THERMAL DESORPTION TECHNIQUE

EVALUATION OF TREATMENT EFFICIENCY OF DRILLING WASTE WITH THERMAL DESORPTION TECHNIQUE

The Directorate of Petroleum Resources (DPR) in Nigeria has also formulated certain guidelines and standards for more effective treatment, recovery and disposal of oily sludge in Part IV Section D 2.0 and 4.0 of the DPR Guidelines. In line with this, the current study evaluated the efficiency of a Thermal Desorption Unit (TDU) facility in the treatment of oily contaminants arising from oil exploration activity in the Niger Delta. The study characterized and determined the levels of contaminants in drilling waste stream before and after treatment, as well as the treatment efficiency of the TDU used. It also identified pollutant gases emissions associated with the treatment process.
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Nonlinear dynamical boundary value problem of hydrogen thermal
desorption

Nonlinear dynamical boundary value problem of hydrogen thermal desorption

The nonlinear boundary-value problem for the diffusion equation, which models gas interaction with solids, is considered. The model includes diffusion and the sorption/desorption processes on the surface, which leads to dynamical nonlin- ear boundary conditions. The boundary-value problem is reduced to an integro- differential equation of a special kind; existence and uniqueness of the classi- cal (differentiable) solution theorems are proved. The results of numerical exper- iments are presented.

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Kinetics and thermal decomposition of Tetrahydrazine lanthanum 2-hydroxy-1- naphthoate

Kinetics and thermal decomposition of Tetrahydrazine lanthanum 2-hydroxy-1- naphthoate

Tetrahydrazine lanthanum 2-hydroxy-1-naphthoate [La 2 (NA) 3 L 4 ] (where NA and L indicate C 10 H 6 (2-O)(1-COO) and N 2 H 4 respectively) was synthesised and characterised by micro elemental analysis, IR spectroscopy, simultaneous TG-DTA and X-ray diffraction (XRD) analysis. The results indicate that the compound loses hydrazine molecules in the temperature range 65 - 150 °C and decomposes to La 2 O 3 at 675 °C through different intermediates, [La 2 O(CO 3 ) 2 ], [La 2 O 2 CO 3 ] at 426 °C and 580 °C respectively. The intermediates of thermal decomposition and final product were confirmed by IR and X-ray diffraction. Coats and Redfern method has been implemented for the estimation of various kinetic parameters viz. energy of activation (E), pre-exponential factor (A),order of decomposition (n).The thermodynamic parameters like enthalpy of activation (H) entropy of activation (S) and free energy of activation (G) have been calculated by using thermogravimetric data.
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Cadmium and cobalt desorption kinetics from soil clays: effect of sorption period

Cadmium and cobalt desorption kinetics from soil clays: effect of sorption period

The objective of this study was, using techniques and models developed previously for studies with synthetic oxides, to examine the effect of sorption period on the subsequent desorption[r]

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Local hyperhemia to heating is impaired in secondary Raynaud's phenomenon

Local hyperhemia to heating is impaired in secondary Raynaud's phenomenon

Accurate and sensitive measurement techniques are a key issue in the quantification of this vascular dysfunction, espe- cially endothelial dysfunction. Different techniques have been used to quantify the microvascular dysfunction in SSc, such as microinjection [7], video microscopy [8], iontophoresis [9] or venous occlusion plethysmography [3], whereas endothelial function of conductance arteries can be monitored using ultra- sonography of the brachial artery [10]. An easier non-invasive technique for monitoring cutaneous vascular function is the response to a given physiological challenge using cutaneous laser Doppler flowmetry. Using cold tests, the response of skin cutaneous blood flow does not significantly differ between pri- mary Raynaud's phenomenon (RP) and SSc [11-13]. The response to brachial artery occlusion, however, gives more interesting results. Indeed, several authors showed a dramatic alteration of the amplitude and kinetics of post-occlusive hyperhemia in patients with SSc in comparison with primary RP or healthy controls [14,15], whereas an altered amplitude but not altered kinetics was described by Rajagopolan et al. [12]. Although the reproducibility of the method is debated, post-occlusive hyperhemia has been proposed for use as a tool to assess microvascular function during therapy in dis- eases such as atherosclerosis [16,17]. This post-occlusive hyperhemia is due both to metabolic and endothelium derived factors. We found, however, using microdialysis and laser Doppler flowmetry, that NO release is not directly involved in such as response [18], which limits the interest of post-occlu- sive hyperhemia as a test of endothelial function in SSc. In contrast, local hyperhemia to local heating in a small area of skin provides interesting information as thermal hyperhemia comprises two separate mechanisms: an initial peak that is axon reflex mediated; and a sustained plateau phase that is NO dependent [19,20]. Thermal hyperhemia might, therefore, be a better tool to assess both endothelial and microvascular function than post-occlusive hyperemia, and as such was recently investigated as a clinical tool to assess endothelial function in diseases such as chronic renal failure [21]. The main objective of our study was to test whether thermal hyperhemia in patients with SSc differed from that in patients with primary RP and healthy controls. The secondary objec- tives were: to compare the kinetics and amplitude of thermal hyperhemia in patients with local or diffuse SSc; to assess any relationship with the Rodnan skin score; and to determine the sensitivity and specificity of thermal hyperhemia in comparison to post occlusive hyperhemia in order to distinguish patients with SSc from those with RP. Given the altered response to local heating we observed in SSc, we also tested in a second study whether this was specific or not, enrolling patients with rheumatoid arthritis, another connective tissue disease that may present with RP.
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Gamma Phase Uranium Molybdenum Fuel Alloys  EUR 4053

Gamma Phase Uranium Molybdenum Fuel Alloys EUR 4053

The characteristics reported are : — gamma stability: thermal transformation kinetics TTT diagrams of the metastable gamma phase; — dimensional stability under thermal cycling and under [r]

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Thermal Desorption Spectroscopy Study on the Hydrogen Trapping States in a Pure Aluminum

Thermal Desorption Spectroscopy Study on the Hydrogen Trapping States in a Pure Aluminum

Hydrogen trapping states in pure aluminum foils with 99.99% purity with different amount of blisters have been investigated by means of thermal desorption spectroscopy. Three peaks are seen in the spectra, where the amount of hydrogen from the third peak at the highest temperature range increases with increasing in the volume fraction of the blisters. Hence, the third peak is revealed to arise from the hydrogen in the blisters. The desorption energy of hydrogen released from the blisters is 76.3 kJ/mol. On the other hand, the first peak is inferred to be due to the hydrogen diffusing with vacancy, considering the diffusion distance of the vacancy as well as untrapped hydrogen atom.
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Desorption Behaviours of Lithium Alanate with Metal Oxide Nanopowder Additives

Desorption Behaviours of Lithium Alanate with Metal Oxide Nanopowder Additives

Solid-state hydrogen storage can be divided into two main categories. The first category is physically bound hydrogen, where the hydrogen gas is physisorbed to a high surface area substrate (exterior or interior) such as carbon nanotubes [2,3]. The second category is chemically bound hydrogen, where the hydrogen has formed a chemical compound with the substrate (e.g., metal hydrides [4-10] and complex hydrides [11-16]) and the hydrogen is desorbed through a thermal decomposition. Before 1997, complex hydride did not attract much attention as a hydrogen storage medium until the discovery by Bogdanovic and Schwickardi [17]. Their study showed that doping NaAlH 4 with Ti compounds enabled reversibility of the hydrogenation/dehydrogenation reaction.
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Kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate in different media

Kinetics of thermal degradation of betamethasone valerate and betamethasone dipropionate in different media

evaluation of the kinetics of thermal degradation of betamethasone esters in phosphate buffer, organic solvents, and cream and gel formulations using a validated HPLC method. The influence of pH and solvent polarity on the degradation reactions has been studied. The effect of phosphate concentration and ionic strength on the rate of thermal degradation has also been evaluated. These aspects have been studied in detail in various media and the rates correlated with different kinetic parameters.

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Bonded repair of composite structures in aerospace application: a review on environmental issues

Bonded repair of composite structures in aerospace application: a review on environmental issues

trend of the thermomechanical behavior of the adhesive [97, 98]. It would be beneficial to select the adhesive and composite patch material with higher glass transition tem- perature, which allow a better performance of the repair joint at higher temperature too. Temperature variations (thermal cycle) are among the most important environmental factors that may affect the durability of adhesively bonded joints for aerospace applica- tions. Sousa et al. [95] studied the effects of thermal cycles on adhesively bonded joints between pultruded glass fibre reinforced polymer. The maximum performance reduc- tion of Elastic Polymer-GFRP joints occurred after 150 thermal cycles, when the ulti- mate load and stiffness decreased by 18% and 22%, respectively. Little changes occurred with additional thermal cycles, which were partly attributed to the occurrence of post- cure phenomena in the elastic polymer adhesive during exposure at higher temperatures [95]. A small number thermal cycles would be advantageous to the joint as an occur- rence of post-cure. Residual thermal stresses are induced at higher temperature of the joint due to the CTE mismatch between the adhesive and the adherends [101]. The higher temperatures facilitate polymer chain mobility and lead to some degree of relaxa- tion of these stresses. However, when cooling the joint, the stress relaxation is reflected in an increased interfacial stress between the substrate and adhesive layer.
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