Activation Energy Of Evaporation Research Articles

Ion evaporation-induced tip streaming from liquid drops of ionic liquids

Ion evaporation from charged surfaces of ionic liquids has aroused significant interest due to its wide range of applications in various fields, such as ionic liquid ion sources (ILIS), electrospray thrusters, and high-precision etching, among others. This study delves into the transient electrohydrodynamics of ionic liquid drops undergoing ion evaporation with the assistance of an externally applied electric field. A transient electrohydrodynamic (EHD) model is developed to make up for the dearth of direct observation (visualization). A structure morphologically resembling the traditional cone-jet is depicted, featuring charged jets emitted from the drop's ends that subsequently break into tiny droplets. In contrast to the traditional cone-jet, this structure forms through a distinct mechanism, with charge depletion induced by ion evaporation playing a crucial role. A comprehensive exploration of parameter influences reveals the following key findings: (a) the normalized radius of the jets increases with the augmentation of the dimensionless number Ξ, which is defined as the ratio of the electric potential energy of ions to their activation energy for evaporation; (b) enhancing the electric Bond number Bo, which quantifies the ratio of Maxwell stress to surface tension, expedites the temporal evolution of tip streaming.

About the possible cause of pressure pulsations in the combustion chamber of the P230 solid-fuel accelerator of the Ariane-5 rocket

The causes of pressure pulsations in the combustion chamber of the solid-fuel booster of the "Arian-5" rocket have been hypothesized. The assumption is that the burning drops of red-hot aluminum are a source of thermal radiation, the radiation temperature of which is proportional to the activation energy of the evaporation of the oxidizer - ammonium perchlorate, and this causes an increased burning rate of solid rocket fuel and the appearance of pressure pulsations in the combustion chamber. The results of calculations by French and Pakistani researchers are analyzed and compared with the author's calculations. As a result of the author's calculations, it was shown that the dimensions of aluminum drops can be the dimensions of half-wave vibrators - antennas of infrared radiation. In the process of burning, there is a rapid and continuous change in their wavelength and activation energy of perchlorate evaporation.

Thermogravimetric Determination of the Kinetics of Petroleum Needle Coke Formation by Decantoil Thermolysis.

This work presents the results of thermogravimetric analysis of decantoil. The microstructure of the extracted petroleum coke during the thermolysis of decantoil in an inert nitrogen atmosphere at 1000 °C was studied by scanning electron microscopy and interpreted as acicular. The model free kinetic approach based on Friedman’s isoconversion method was used to calculate the kinetic characteristics of decantoil thermolysis-activation energy and pre-exponential factor. The individual hydrocarbon composition of decantoil was determined by gas chromatography mass spectrometry, which was used to determine the activation energy of evaporation of its fractions. The total energy spent on the chemical reactions of cracking and thermopolycondensation was determined when the degree of decantoil conversion was changed from 0.1 to 0.9.

КИНЕТИКА ИСПАРЕНИЯ МЕТАЛЛОВ ИЗ Sb–Pb–Ag СПЛАВА ПРИ ВАКУУМНОЙ ПЕРЕГОНКЕ

Most of today's research is mostly concentrated on the thermodynamics of the separation of polymetallic alloys by vacuum distillation, as it allows you to determine whether the direction and limitation of the flow of the metallurgical reactions. While studying the kinetics of evaporation of metals it is possible to identify the effective process conditions, such as temperature, vacuum grade and duration of distillation required in the design process for the separation of the components of the alloys. The goal of the work was to determine the rate of evaporation of the metals from the Sb–Pb–Ag alloys of different composition depending on temperature and pressure, and identify the limiting stage of the process. In the making prototype models, sample source metal was welded in an induction furnace in argon atmosphere of high purity, to obtain the alloy composition, mol. %: 16–77 Sb; 75–20 Pb; Ag 9–3. It this work the kinetics of evaporation of metals from Sb–Pb–Ag alloy in temperature range 823–1073 K and a pressure of 1.33–133 Pа is defined, as described by the first order equation. Values of the apparent rate of the first order constants with the sublimation of metals from the melt depends on temperature, pressure and chemical composition of the alloy. The total mass transfer coefficients of lead, antimony, silver ( k Me , m· . s –1 ) evaporation of Sb–Pb–Ag (0,55–0,40–0,05) of the alloy is (3.718–7.852)·10 –7 , (1.194–2.436)·10 –7 , (1.859–3.790)·10 –10 at T = 823–1073 K, P = 13.3 Pa, respectively. The calculated apparent activation energy of evaporation of the metals from the Sb–Pb–Ag alloy: E = 20,93–46,41 kJ/mol. The apparent activation energy of evaporation of the metals, calculated by the Arrhenius equation leads to the conclusion of an easier evaporation of components from the composition of the Sb–Pb–Ag alloy compared to pure metal: E = 150–280 kJ/mol. It is shown that quantitative transport of lead and antimony in the gas phase does not limit the speed in vacuum distillation. The evaporation of the metals from the Sb–Pb–Ag alloy is controlled jointly by mass transfer, mainly in the liquid phase, as well as through the surface layer at the phase interface liquid–gas in the studied experimental conditions. Increasing temperatures above 823 K increases the rate constants of the evaporation k Me components Sb–Pb–Ag alloy. Reducing system pressure less than 133 Pa contributes to the sublimation of antimony, lead and silver.

Heterogeneous kinetics of H<sub>2</sub>O, HNO<sub>3</sub> and HCl on HNO<sub>3</sub> hydrates (<i>α</i>-NAT, <i>β</i>-NAT, NAD) in the range 175–200 K

Abstract. Experiments on the title compounds have been performed using a multidiagnostic stirred-flow reactor (SFR) in which the gas phase as well as the condensed phase has been simultaneously investigated under stratospheric temperatures in the range 175–200 K. Wall interactions of the title compounds have been taken into account using Langmuir adsorption isotherms in order to close the mass balance between deposited and desorbed (recovered) compounds. Thin solid films at 1 µm typical thickness have been used as a proxy for atmospheric ice particles and have been deposited on a Si window of the cryostat, with the optical element being the only cold point in the deposition chamber. Fourier transform infrared (FTIR) absorption spectroscopy in transmission as well as partial and total pressure measurement using residual gas mass spectrometry (MS) and sensitive pressure gauges have been employed in order to monitor growth and evaporation processes as a function of temperature using both pulsed and continuous gas admission and monitoring under SFR conditions. Thin solid H2O ice films were used as the starting point throughout, with the initial spontaneous formation of α-NAT (nitric acid trihydrate) followed by the gradual transformation of α- to β-NAT at T > 185 K. Nitric acid dihydrate (NAD) was spontaneously formed at somewhat larger partial pressures of HNO3 deposited on pure H2O ice. In contrast to published reports, the formation of α-NAT proceeded without prior formation of an amorphous HNO3 ∕ H2O layer and always resulted in β-NAT. For α- and β-NAT, the temperature-dependent accommodation coefficient α(H2O) and α(HNO3), the evaporation flux Jev(H2O) and Jev(HNO3) and the resulting saturation vapor pressure Peq(H2O) and Peq(HNO3) were measured and compared to binary phase diagrams of HNO3 ∕ H2O in order to afford a thermochemical check of the kinetic parameters. The resulting kinetic and thermodynamic parameters of activation energies for evaporation (Eev) and standard heats of evaporation ΔHev0 of H2O and HNO3 for α- and β-NAT, respectively, led to an estimate for the relative standard enthalpy difference between α- and β-NAT of −6.0 ± 20 kJ mol−1 in favor of β-NAT, as expected, despite a significantly larger value of Eev for HNO3 in α-NAT. This in turn implies a substantial activation energy for HNO3 accommodation in α- compared to β-NAT where Eacc(HNO3) is essentially zero. The kinetic (α(HCl), Jev(HCl)) and thermodynamic (Peq(HCl)) parameters of HCl-doped α- and β-NAT have been determined under the assumption that HCl adsorption did not significantly affect α(H2O) and α(HNO3) as well as the evaporation flux Jev(H2O). Jev(HCl) and Peq(HCl) on both α- and β-NAT are larger than the corresponding values for HNO3 across the investigated temperature range but significantly smaller than the values for pure H2O ice at T < 200 K.

Migration and Chemical Consumption of Deltamethrin and Piperonyl Butoxide from Polyethylene in Aqueous Media

Deltamethrin (DM), an important insecticide (synthetic pyrethroid) together with synergist piperonyl butoxide (PBO), is used for food storage and insect control purposes. It is often impregnated in polymers for controlled and effective release of insecticide. The migration and chemical consumption of DM and PBO from moulded polyethylene sheets was studied. The thermal behaviour of pristine DM and the prepared polyethylene compound was studied by differential scanning calorimetry. DM did not crystallize and remained in a liquid state after cooling to room temperature. Evaporation rates and activation energies of evaporation were determined by thermogravimetry for pristine DM, PBO, a solution of DM and PBO and for the PE compound. Evaporation from the DM/PBO solution was greater than that predicted from the evaporation rates of the individual compounds, which suggested that the DM/PBO solution obeyed non-ideal solution properties. The migration of DM and PBO from the polyethylene was studied in liquid water at 80 and 95 °C and in air of different relative humidities (60 and 80%) at 80 °C. Exposure to liquid water caused degradation and hydrolysis of the ester bond in DM, present in the prepared material, and generated species containing hydroxyl groups. Liquid chromatography and infrared spectroscopy showed a significant migration of the active species in liquid water, whereas the loss of DM and PBO in air at 80°C (60 and 80 %RH) was negligible over 30 days.

Void evolution in polycarbonate at elevated temperatures

The void evolution in polycarbonate (PC) at elevated temperatures was investigated. Internal cylindrical cracks and voids were induced in PC by Nd-YAG laser irradiation. During the annealing at temperatures of 177–197 °C, the spherical void grows to a maximum size, which then decreases, and is finally leveling off. A model of void evolution based on the evaporation and condensation mechanisms for growth and shrinkage is proposed. The theoretical predictions are in good agreement with the experimental data. The activation energies of evaporation and condensation processes are determined to be 477.31 and 611.49 kJ/mol, respectively.

DSC study on hyaluronan drying and hydration

The processes of hyaluronan (HYA) drying and hydration were studied using differential scanning calorimetry. In the first approach the isoconversional Kissinger–Akahita–Sunose (KAS) method was applied in order to determine actual activation energies of evaporation of pure water and water from concentrated HYA solutions. Since the evaporation is a single-step process, the activation energies for pure water provided results consistent with tabulated values of evaporation enthalpies. In the course of water evaporation from hyaluronan solution a break in increasing enthalpy followed by a decrease below 0.34 g of water per 1 g of HYA was observed. This result confirmed earlier observation that at this particular water content evaporation from hyaluronan is compensated by heat evolution associated with the formation of new bonds in hyaluronan supramolecular structure. Subtraction of water evaporation enthalpy from enthalpies obtained for HYA concentrated solution provided a possibility to extrapolate the evaporation enthalpies to the concentration (approximately 2 g of water per 1 g of HYA) at which free water is not present any longer and only bound water starts being evaporated from the HYA solution. Similar results were obtained in the second approach in which using slightly modified “traditional” freezing/thawing experiment, melting enthalpy of ice was plotted against water fraction in HYA. It was found out that the melting enthalpy of ice exponentially increases from 0.8 up to 2 g of water per g of hyaluronan where it reaches and keeps the melting enthalpy of hexagonal ice. It was shown that both approaches can serve as alternatives providing an additional insight into the state of water and biopolymers in highly concentrated solutions.

Diffusion in polymers dependence on crosslink density

Kinetics of N-methyl pyrrolidone evaporation from swollen photo-crosslinked polyacrylate was monitored thermogravimetrically at temperatures ranging from 323 to 398 K. Crosslink density dependence of evaporation kinetics was investigated in photo-crosslinked polyacrylates with crosslinked density ranging from ≈1.2 × 102 to ≈1.7 × 104 mol m−3 and number of main chain atoms between crosslinks ranging from ≈70 atoms to ≈6 atoms, respectively. As was shown, evaporation kinetics was controlled by the solvent diffusion in polymer. Activation energies of evaporation (diffusion) were deduced from the rate measurements at different temperatures. Apparent activation energy of evaporation decreased from 48.7 to 31.1 kJ mol−1 with crosslink density increase. Activation energy of pure N-methyl pyrrolidone evaporation was 50.6 kJ mol−1. Decrease of the rate of solvent diffusion and unexpected decrease of diffusion activation energy with increase of crosslink density of swollen polymer matrix was explained by decrease in polymer chain segments mobility, as indicated by Eyring’s approach to diffusion in polymers.

Activation energies for evaporation from protonated and deprotonated water clusters from mass spectra

Experimental mass abundance spectra are used to extract evaporative activation energies (dissociation energies) for protonated water clusters, (H(2)O)(N)H(+), and deprotonated water clusters, (H(2)O)(N)OH(-), in the size range up to hundred molecules. The inversion is achieved by application of the shell correction method adapted from nuclear physics to the abundance spectra. The well known abundance anomaly for protonated clusters which occurs for N=20-22 is found to have the characteristic behavior of a shell closing, whereas other apparent magic numbers are only prominent peaks in the abundance spectra because of the instability of the evaporative precursor. For the deprotonated clusters, we find a similar shell closing for N=55-56.

Evaporation from the (1 1 0) surface of PETN

In order to provide insight into coarsening mechanisms of pentaerythritol tetranitrate (PETN), we performed kinetic Monte Carlo (KMC) simulations of evaporation from the predominantly exposed (1 1 0) surface. Our KMC simulations show that different surface structures, such as islands and straight step segments, move in very different ways during evaporation. We show that closed surface structures (e.g. islands or convex step edges) evaporate faster than open features (e.g. straight or concave step edges) due to inexhaustible sources of kink sites in their edges. From Arrhenius plots of step velocities we obtained activation energies for evaporation that are in excellent agreement with predictions from a model and recent experimental data. The effects of surface diffusion on evaporation rates are discussed within a rate theory model.

Quantitative Thermodynamic Analysis of Sublimation Rates Using an Atomic Force Microscope

Atomic force microscopy (AFM) has been successfully used to study the activation energy for evaporation of pentaerythritol tetranitrate (PETN) nanoislands formed by spin coating. These islands are annealed isothermally in the temperature range of 30-70 degrees C for a given time and are scanned with AFM in contact mode at room temperature. The volume of these islands does not change significantly up to about 35-40 degrees C indicating that sublimation is not significant below 40 degrees C. Above 40 degrees C, the islands start shrinking, and the rate of weight loss is analyzed as a function of temperature. The activation energy of evaporation using AFM was found to be similar to that for bulk PETN crystals using thermogravimetric analysis (TGA) at higher temperatures (110-135 degrees C). These results demonstrate that AFM is a useful tool to measure thermodynamic properties with a nanoscale probe.

Surface Ostwald-ripening and evaporation of gold beaded films on sapphire

The kinetics of morphological evolutions of gold nanoparticles on alumina, resulting from evaporation and surface Ostwald-ripening coarsening, have been investigated by means of Auger electron spectroscopy. When the fraction of the covered area is small, the kinetics of evaporation can be related to the desorption of adatoms. In the temperature range 943–1043 K we obtained the evaporation flux J(m-2s-1)=4.8×1027exp[-196±9 (kJ/mol)/RT]. The experimental activation energy of evaporation of gold from a sapphire surface, Qevap=196±9 kJ/mol, is lower than the tabulated value of enthalpy of sublimation of gold, ΔHsubl=368 kJ/mol. At lower temperatures, in the range 623–778 K, Ostwald-ripening experiments, carried out on nanosized clusters, yield the mass transfer surface diffusion coefficients of gold on alumina, Ds(m2/s)=2.6×10-14exp[-58±9 (kJ/mol)/RT]. These results, providing information on the evolution of granular gold films such as those used in catalysts or sensors, are compared to previous data on similar systems.

Evaporation from Water−Ethylene Glycol Liquid Mixture

Evaporation rates were determined for water-ethylene glycol liquid mixtures with different mole fractions, where the evaporation rate expressed as mg min(-1)/area was used because of the presence of two kinds of molecular species. The rate increased with increasing temperature and decreased with increasing mole fraction of ethylene glycol, almost obeying ideal mixing of the two components, although a small positive deviation was observed over the mole fraction from 0 to 0.5 of ethylene glycol at higher temperatures. The activation energy of evaporation was determined from the temperature dependence of the evaporation rate, where the energy was an apparent one because the composition of evaporated species was not determined. The activation energy increased with decreasing temperature and with increasing mole fraction of ethylene glycol, where the energy obeyed the ideal mixing at lower temperatures while it positively deviated at higher temperatures. The evaporation rates were examined by surface tension of the liquid mixture, but any definite relation between them was not found. Both the evaporation rate and the activation energy were found to be determined mainly by the mole fraction in the surface layer from which the evaporation takes place. Finally, the new concept of surface excess was presented, where the surfactant molecules were concentrated and formed a bimolecular layer at a certain distance beneath the air/solution interface.

Physical organogels: mechanism and kinetics of evaporation of the solvents entrapped within network scaffolding

A series of hydrocarbon gels (based on leaded petrol and decalin) using physically crosslinked networks have been prepared using Al-salt of fatty acid as the physical gelling agent. The effects of gel network scaffolding on the mechanism and kinetics of evaporation of the solvents from the gels were investigated using conventional, isothermal and modulated thermogravimetric analysis. It has been clearly observed that the evaporation of solvent from gels followed a complex evaporation pattern compared to the pure solvent. It appears that with increase in network scaffolding the maximum rate of evaporation of the solvent decreases and its distribution become broader. The activation energy of evaporation for these solvents was found not to be dramatically dependent on the concentration of the gelator and tightness of the network scaffolding. Amongst different methods employed, isothermal measurements provided reliable information about the mechanism of evaporation. Modulated thermogravimetric analysis proved to be an efficient method to achieve kinetic parameters of evaporation from a single dynamic experiment. Scanning electron microscopy was used to probe for both dry gelator and gel network after evaporation of the solvents for evaluation of their surface morphology.

Meta-stable condensation induced by collisions with rare-gas atoms at a substrate surface from a plasma

Collisions between high-energy particles and surface atoms on a substrate surface strongly influence the condensation state of constituent atoms. We investigated a meta-stable condensation state of mercury in plasma on glass substrates. A thin glass cell was developed for ensuring the accuracy of density measurement of mercury. Below 310 K, the activation energy, 0.67 eV, estimated from the temperature dependence of emission intensity from Hg 7 3S 1 level coincided with the activation energy for evaporation of mercury atoms from a liquid surface. Above 310 K, the activation energy decreased to 0.34 eV, which showed the transition from 3D condensation to 2D condensation. The effect of high-energy particles from a plasma was investigated by measuring the time dependence of emission intensity from mercury 546 nm after the switch off period of a plasma. To clarify the contribution of the diffusion process and heating rate, d T/d t, the dependence of the emission intensity was measured. Meta-stable condensation states with intermediate activation energies were observed at 1 K/min<d T/d t<4 K/min.

Binder removal from injection moulded zirconia ceramics

Binder removal from a wax-based zirconia ceramic moulding has been investigated in terms of solid content of the mouldings (45–55 vol%), heating rate (0.5–5°C min −1), sample form (powder and block), and sample thickness (0.5–5 mm). Experimental results show that the samples with lower surface-to-volume ratio or more solid content has greater restriction to binder transport which reduces binder removal kinetics to a significant extent. Such a transport restriction can be minimised or eliminated by using the sample in a powdered configuration. The behaviour of binder pyrolysis is considerably modified by the presence of inorganic particles, which may be considered as a result of catalytic reaction. Activation energy of pyrolysis of the binder is evaluated directly based on the existing kinetics models through the use of the resulting weight loss–temperature curve. The activation energy for evaporation obtained is smaller than that for thermal degradation suggesting that for the binder with low molecular weight currently employed, evaporation may be considered as a dominant mechanism for binder removal. This finding is also in well agreement with literature results.

A comparison of the thermal decomposition of preservatives, using thermogravimetry and rising temperature kinetics

The thermal behaviors of benzoic, sorbic and citric acids, which are three commonly used preservatives, were studied by thermogravimetry. The kinetic mechanisms of evaporation and/or decomposition in air and nitrogen were determined and compared. Benzoic acid completely evaporated via a zero-order kinetic mechanism. Sorbic acid partially evaporated by a zero-order kinetic mechanism, with the production of a transition compound. Citric acid decomposed to a transition compound by a combination of kinetic mechanisms. A majority of the process followed zero-order kinetic principles, with the evaporation of most of the sample. The activation energies of evaporation and the pre-exponential terms were calculated and compared.

Real-Time Kinetic Measurements of the Condensation and Evaporation of D2O Molecules on Ice at 140 K &lt; T &lt; 220 K

The kinetics of condensation of D218O water vapor on D216O ice was studied in the temperature range 140−220 K. The measurements have been performed in real time using the pulsed valve technique in a low-pressure flow reactor. Ice samples were prepared by several different methods. The uptake coefficient γ was observed to decrease with increasing surface temperature, and varied from γ = 0.06 to 0.8. A significant dependence of γ on the method of preparation of the ice has been found. At 180 K, γ = 0.13 for single-crystal ice, 0.18 for ice condensed from the vapor phase, and approximately 0.25 for bulk ice obtained from freezing liquid D216O. The uptake coefficient attained a value of γ = 0.8 at 140 K for cubic ice prepared by vapor condensation at 140 K. The activation energy for evaporation of D2O at low temperatures (140−190 K) has been measured as 12.2 kcal/mol, whereas it decreases to 8.3 kcal/mol at higher temperatures (190−220 K). The rate of evaporation at 200 K corresponds to the loss of approximately 70 ± 10 formal monolayers per second. The experimental results suggest the formation of loosely bound water adsorbed to the surface of ice whose bond energy is estimated to be 4.0 ± 0.4 kcal/mol, independent of the type of ice.

Surface structure variation caused by annealing

The variation of surface microstructure caused by annealing for a Pt single crystal is studied by means of reflection electron microscopy (REM). The monatomic steps are characterized by fractal dimensions. The fractal dimension of a monatomic step increases during annealing. The increasing fractal dimension during annealing indicates that new kinks appear at the straight section of the atomic step. The higher the fractal dimension of a step, the faster the step migration. This phenomenon is expained using the activation energy of evaporation. Although the step migration and expansion of atomic depressions caused by annealing are often observed, atomic islands formed by atom deposition have not been observed in our experiments.