Dependence Of Activation Energy Research Articles

Assessment of activation energy of enthalpy relaxation in sucrose-water system: effects of DSC cycle type and sample thermal history

The purpose of this study is to critically analyze different methods of calculation of activation energy of relaxation in sucrose-water system from differential scanning calorimetry data. We consider the use of different thermal cycles for calculations together with Moynihan and Kissinger equations. We study the effect of two methods of glass transition temperature determination (half-step and inflection point) on the activation energy values. Along with experimental DSC data, we use the data simulated using Tool–Narayanaswamy–Moynihan model to validate the use of cooling and heating curves and to check the reproducibility of the activation energy calculations. The obtained results show that the thermal cycle with equal cooling and heating rates provides the most reliable data set and the glass transition temperature definition using inflection point rather than half step can be recommended for calculations. Moreover, due to technical reasons, heating rather than cooling scans provide the most reliable results of activation energy calculations. Furthermore, a simple method based on the width of the glass transition region shows reasonable results for single scan experiments. The activation energies of the glass transition in sucrose-water system with different water contents and different thermal histories were studied. Since it is impossible to apply traditional methods based on Moynihan equation for the activation energy evaluation for freeze-dried samples, we propose using another method based on the properties of the recovery peak. Combining the results obtained by different methods, we present a dependence of activation energy in sucrose-water system on water content. The results show that water decreases the activation energy of relaxation process in sucrose matrix.

Sintering Mechanism and Enhanced Piezoelectric and Crystal Structural Properties of (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 Lead Free Ceramics

A lead-free piezoelectric ceramic, (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (hereafter (1-x)BZT-xBCT), was investigated for functional device applications. Lead-free piezoelectric materials with high piezoelectric charge coefficients and voltage coefficients are indispensable for functional industrial applications. Piezoelectric ceramic specimens tend to shrink in size during the sintering process without melting. This study focused on this phenomenon as a unique characteristic of piezoelectric ceramic materials, and derived the materials’ activation energies from this phenomenon, employing the Arrhenius relationship. Then the estimated activation energy was employed to determine the relationship between the piezoelectric properties and crystalline properties, while varying sintering temperature and chemical stoichiometric composition. Piezoelectric properties can change depending on the sintering temperature and process conditions. Crystalline properties and piezoelectric properties can be influenced by the sintering temperature and holding times. In this research, sintering temperature dependent structural and dielectric properties were investigated. (1-x)BZT-xBCT ceramics showed the highest piezoelectric coefficient of 470 pC/N. Sintering temperature dependent shrinkage rate and activation energy were estimated and calculated for the various sintering processes. In this research, two different activation energies for the shrinkage process were estimated.

Catalytic combustion of heavy oil using γ-Fe2O3 nanocatalyst in in-situ combustion process

In this work, γ-Fe 2 O 3 nanoparticles were synthesized by co-precipitation method and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, dynamic light scattering, X-ray diffraction, and Mössbauer spectroscopy techniques. By co-precipitation method, ultrafine γ-Fe 2 O 3 quasi-spherical individual nanoparticles with the average diameter of 9.1 nm and the surface free of capping ligands were successfully synthesized. The catalytic effect of the synthesized γ-Fe 2 O 3 nanoparticles upon the combustion performance and kinetic of heavy oil combustion was studied by porous medium thermo-effect cell (PMTEC) together with isoconversional kinetic analysis using Ozawa-Flynn-Wall method. The results show that the combustion performance of heavy oil was substantially increased by γ-Fe 2 O 3 nanoparticles. The reaction intervals of low temperature oxidation (LTO) and high temperature oxidation (HTO) were shifted to lower temperature with an obvious increase in temperature caused the exothermic oxidation reactions. In addition, the fingerprint of the dependence of effective activation energy on conversion degree shows that the effective activation energy was reduced by about 20–35 kJ/mol during the whole combustion process. These observed improvements make γ-Fe 2 O 3 nanoparticle a promising catalyst for catalyzing heavy oil combustion. • Ultrafine γ-Fe 2 O 3 nanoparticle (9.1 nm) was synthesized by co-precipitation method. • Co-precipitation method avoids high temperature (200–500 °C) oxidizing step. • γ-Fe 2 O 3 substantially improves combustion performance of heavy oil. • γ-Fe 2 O 3 greatly shifts reaction intervals into lower temperature. • γ-Fe 2 O 3 reduces effective activation energy by about 20–35 kJ/mol.

Study of the crystallization behaviour in arsenic-sulphide glasses doped with Pb

A kinetic analysis of the crystallization processes in arsenic-sulphide glasses doped with Pb was performed using the DSC method. According to the results of X-ray diffraction measurements of the annealed Pb3(As2S3)97 samples, it was found that the crystallization processes take part through the formation of As2S3, As-S and PbS centers. The dependence of crystallization activation energy on crystallized fraction determined using both Kissinger, Akahira and Sunose (KAS) and Vyazovkin methods, revealed that the first and second crystallization are a single-step processes, while the third one is a complex one. Using the methods of Šatava, Ozawa, and Ozawa-Chen, the occurrence of voluminous 3D crystal growth in investigated samples was found. Glass stability parameters indicated on increase in crystallization affinity with Pb content.

Grain and grain boundary behaviors and electrical transport properties of TiO<sub>2</sub> nanowires under high pressure

In this work, anatase Titanium dioxide (TiO<sub>2</sub>) nanowires are synthesized by the hydrothermal method, and its grain and grain boundary behaviors and electrical properties are investigated by alternating current (AC) impedance method under high pressure (up to 34.0 GPa). The relationship between the frequency dependence of impedance <i>Z''</i> and pressure indicate that the conduction mechanism of anatase phase TiO<sub>2</sub> nanowires in the test pressure range is electronic conductivity. It should be noted that the characteristic peaks of <i>Z''</i> move toward high frequency region with pressure increasing, demonstrating that the effect of grain interior on impedance becomes apparent. Additionally, the overall variation trends of grain and grain boundary resistance go downward with pressure increasing, and the descent rate of grain boundary is larger than those of grain before and after phase transition. However, in a range of phase transition (8.2–11.2 GPa, from anatase to baddeleyite phase), grain boundary resistance shows a discontinuously change (increases to 11.2 GPa and then decreases). Based on the different variation trends of grain and grain boundary resistance, it becomes obvious that the phase transition from anatase to baddeleyite phase first occurs at the surface of grain, and then extends to the interior of grain gradually. Also, as an intrinsic characteristic, the relaxation frequency is independent of the geometrical parameters. The pressure dependence of activation energy is obtained by fitting the pressure dependence of relaxation frequency. The activation energy of grain and grain boundary decrease with pressure increasing, implying that the contribution of pressure on the conductivity of sample is positive. Furthermore, the space charge potential for the whole test pressure range is positive, which is determined by the relationship between pressure and relaxation frequency. This fact illustrates that the anion defects are easily formed in the space charge region, and the oxygen defects are the main inducement for TiO<sub>2</sub> phase transformation.

Application of model-free and multivariate nonlinear regression methods for evaluation of the kinetic scheme and kinetic parameters of thermal decomposition of low density polyethylene

A sort of low density polyethylene (LDPE) was characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), thermal analysis methods (TG, DTG, DTA) in nitrogen flow at constant heating rates of 2.50, 5.00, 9.91, 14.98 and 19.92 K min−1 and at other five temperature programs, coupled TG + FTIR analysis, and DSC analysis in nitrogen flow. The kinetic analysis of TG data has been performed using an algorithm consisting of the following three successive steps: (1) the application of model-free (isoconversional) methods for evaluation of apparent activation energy dependence on the conversion degree, (2) the processing of the TG data recorded at constant heating rates to assess the possible kinetic schemes and the corresponding kinetic parameters, and (3) the selection of the kinetic scheme characteristic of the thermal decomposition of LDPE by comparing the experimental TG curves with the reconstructed ones corresponding to the temperature programs used. It has been pointed out that the overall process of thermal decomposition of LDPE consists of four successive stages with the Avrami-Erofeev kinetic models (An) - reaction order (Fn) -reaction order (Fn) - three-dimensional diffusion (D3). This kinetic scheme and corresponding kinetic parameters is suitable for prediction of thermal behavior of LDPE in some temperature programs and can be used for the design of pyrolysis reactors necessary for the conversion of LDPE waste into low molecular mass chemicals, which can be used as raw materials for chemical and petrochemical industry.

Charge transport mechanisms in monovalent doped mixed valent manganites

In this communication, we report the results of the studies on structural and transport properties of monovalent Na+ doped La1–xNaxMnO3 (LNMO; x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30) manganites synthesized by conventional ceramic method. X-ray diffraction (XRD) and Rietveld refinements reveal the single phasic nature of LNMO manganites without any detectable impurity within the measurement range. Temperature dependent resistivity, under different applied magnetic fields, has been performed on LNMO samples. Samples understudy exhibit metal to insulator (semiconductor) transition at temperature TP which is strongly influenced by the substitution of Na+ at La3+ site. r – T plots also exhibit resistivity upturn behavior at low temperature well below 40K under all the applied fields. Variation in TP and resistivity has been discussed in the context of the competition between the transport favoring tolerance factor and zener double exchange (ZDE) mechanism and transport degrading Jahn–Teller (JT) and size variance effects. In order to understand the mechanisms responsible for the charge transport in metallic and semiconducting regions and to explore the possible electronic processes responsible for the observed low temperature resistivity minima in all the presently studied LNMO manganites, various models have been employed. It has been found that VRH mechanism gets successfully fitted to the resistivity data in the semiconducting region while ZDE polynomial law is responsible for the charge conduction in metallic region for all the presently studied LNMO samples. A strong dependence of activation energy on the Na+ – content as well as applied magnetic field has been discussed in the context of variation and interrelations between the structural parameters. Charge conduction in metallic region has been discussed in the light of electron–phonon interactions which is influenced by the Na+ – content and applied magnetic field. Electrostatic blockade model has been employed to understand the low temperature resistivity minima behavior. Blocking energy for the charge carriers shows a dependence on the magnetic energy provided to the charge carriers. Present study can be useful to understand and to control the charge conduction in the manganites and hence to design the manganite based thin film devices for various spintronic applications.

Thermokinetic behavior of the Al2O3-PbO-B2O3 glasses

Thermokinetic behavior of the Al2O3-PbO-B2O3 glassy system was investigated by means of differential scanning calorimetry, X-ray diffraction analysis and Raman spectroscopy. The glass transition kinetics was described in terms of the Tool–Narayanaswamy–Moynihan model. The compositional evolution of the relaxation parameters was explained in terms of the structural changes and movements of the characteristic structural units detected by Raman spectroscopy. Crystal formation in the studied glassy matrices was investigated in dependence on composition and particle size. The crystal growth was suppressed by increasing particle size as well as by increasing Al2O3 content; formation of crystalline boron oxides was replaced by formation of mixed Al2O3/PbO oxides and Pb4B2O7 phase. The nucleation-growth Johnson-Mehl-Avrami model and the empirical autocatalytic model of Šesták and Berggren were used to describe the complex crystallization kinetics. The Avramov-Šesták concept of temperature dependent activation energy was successfully applied and tested on the real-life experimental data. The corresponding methodology was critically reviewed.

Effect of Al addition on the thermal properties of lead -tin alloy

The effect of aluminium addition on the thermal parameters of Pb–Sn alloy was investigated. The technique of Differential Thermal Analysis (DTA) was selected to determine the phase transformation temperatures and the effect of varying heating rates. Thermal parameters such as melting temperature (Tm), crystallization temperature (Tc), the true melting temperature (Tonset), initial melting peak temperature (Ton), end melting peak temperature (Toff), enthalpy of fusion, activation energy of melting (Em) and activation energy of crystallization (Ec) were calculated. The dependence of activation energies of melting and crystallization with Al content have been discussed in detail.

Isothermal crystallization kinetics of an industrial-grade Zr-based bulk metallic glass

Bulk metallic glasses (BMGs), due to their amorphous structure, exhibit remarkable mechanical properties, and there is an increasing interest in their commercialization. For the industrial fabrication of BMG, knowledge about the isothermal crystallization kinetics of industrial-grade BMG is required. Previous investigations on isothermal crystallization kinetics are mainly based on high-purity samples with very good glass forming ability and/or mainly limited to the low temperature regime. In the present study, a systematic investigation on the isothermal crystallization kinetics of an industrial-grade Zr-based BMG (Zr59.3Cu28.8Al10.4Nb1.5 at.%, trade name: AMZ4) has been performed using conventional and flash differential scanning calorimetry.We report the time-temperature-transformation (TTT) diagrams of the AMZ4 with two different oxygen levels. The diagrams cover the temperature range from glass transition temperature up to liquidus temperature, that have the typical “C-shaped” noses. Faster crystallization of the higher oxygen level AMZ4 was observed, and the underlying mechanisms were investigated. The universal isothermal Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was employed to model the isothermal crystallization kinetics. Satisfactory match was achieved between the experimental facts and the JMAK model, and the interfacial energies between the crystalline phase and liquid were determined as ∼0.04 J/m2 for the industrial-grade AMZ4. The crystallization fraction dependence of Avrami index and activation energy is studied and found to be neglectable in the JMAK modeling. The critical casting thicknesses were estimated based on the TTT diagrams.

Features in low-temperature electrical resistivity of amorphous Cd3As2 films due to hopping conductivity with changing activation energy

Amorphous Cd3As2 films were deposited on single-crystalline SrTiO3 substrate by high-frequency non-reactive magnetron sputtering. Electrical resistivity of the film, measured within 3-75 K range, increases at cooling. Below ∼70 K, negative transverse magnetoresistance observed. Features in electrical resistivity and magnertoresistance can be attributed to variable-range hopping conductivity of the Mott type with local activation energy, which is temperature-dependent. Two temperature ranges in the hopping conductivity observed. Appearing two ranges is in qualitative accordance with the Mott-Davis energy-band model developed for amorphous semiconductors. High temperature range of the hopping conductivity is attributed to electron hops between localized states, positioned inside band tails, whereas electron hops between localized states, positioned inside Fermi-peak, can be responsible for low-temperature range. At taking into account temperature dependences of local activation energy, universal expression for various mechanisms of the hopping conductivity could be successfully applied to analyze the experimental data.

Charge Carrier Dynamics of Electrochemically Synthesized Poly (Aniline Co-Pyrrole) Nanospheres Based Sulfur Dioxide Chemiresistor

ABSTRACT Poly(aniline co – pyrrole) (PAP) nanospheres (diameter ~50 nm) have been synthesized by using cost-effective electrochemical oxidation of monomers, i.e., aniline, and pyrrole (1:1 ratio), and evaluated as sulfur dioxide chemiresistor. PAP chemiresistor exhibited an improved sensing response (6.1%) toward a low concentration of sulfur dioxide (5 parts per million) compared to its precursor-based chemiresistors at room temperature. It is attributed to the remarkable characteristics of PAP, such as higher surface-to-volume ratio, larger effective surface area, higher branching, and lower conductivity value. Furthermore, the cause of low conductivity was evaluated using low-temperature direct current charge transport studies. The dependence of activation energy on temperature discarded the probability of band conduction mechanism in the synthesized PAP nanospheres. PAP nanospheres were found to possess 3-Dimensional VRH conduction of charge carriers. The low conductivity of PAP nanospheres is further explained by evaluating Mott’s parameters, i.e., characteristic temperature, hopping radius, hopping energy, and density of states.

Influence of poly(ethylene oxide) sample preparation on the results of thermogravimetric analysis

Aim: To investigate whether the sample preparation process of poly(ethylene oxide) (PEO) affects kinetic analysis of the thermal degradation process. Kinetic analysis was performed to describe the course of a chemical reaction regardless of the reaction conditions and the reaction system complexity. One differential method, the Friedman method, and one integral Kissinger-Akahira-Sunose method (KAS), were applied in this work. Methods: The PEO sample was prepared in 4 different ways. Thermogravimetric analysis was performed to determine the thermal degradation of prepared samples. Infrared spectroscopic analysis was performed during the preparation of the PEO film obtained by casting from the solution. Results: Dynamic thermal decomposition of PEO, regardless of the method of preparation, takes place through a single decomposition stage, which is manifested by the appearance of one peak on derivative thermogravimetric (DTG) curve. During the preparation of the PEO film, the procedure was carried out at a temperature higher than its melting temperature (Tm=65°C). After the cooling, the obtained sample didn’t solidify and it had an intense odor of acetic acid, which was confirmed by infrared spectroscopic analysis. Samples III and IV were re-prepared at a temperature lower than the melting point of PEO, obtaining samples of satisfactory quality. Conclusion: In order to prepare poly(ethylene oxide) films by solution casting technique, drying should be carried out at temperatures below the melting point of PEO. If TG analysis of pure PEO powder is compared with the results of hot pressed samples and solution cast samples, it can be concluded that the preparation of the sample doesn’t affect the thermal stability of the PEO. The dependence of activation energy calculated by the differential Friedman and integral KAS method on conversion is constant for all samples in a broad conversion range, regardless of how the samples were prepared. The hot pressed samples and solution cast samples have lower activation energy than the commercial PEO powder.

Geographical and Seasonal Thermal Sensitivity of Grazing Pressure by Microzooplankton in Contrasting Marine Ecosystems

Grazing pressure, estimated as the ratio between microzooplankton grazing and phytoplankton growth rates (g:μ), is a strong determinant of microbial food-web structure and element cycling in the upper ocean. It is generally accepted that g is more sensitive to temperature than μ, but it remains unknown how the thermal dependence (activation energy, Ea) of g:μ varies over spatial and temporal scales. To tackle this uncertainty, we used an extensive literature analysis obtaining 751 paired rate estimates of μ and g from dilution experiments performed throughout the world’s marine environments. On a geographical scale, we found a stimulatory effect of temperature in polar open-ocean (∼0.5 eV) and tropical coastal (∼0.2 eV) regions, and an inhibitory one in the remaining biomes (values between −0.1 and −0.4 eV). On a seasonal scale, the temperature effect on g:μ ratios was stimulatory, particularly in polar environments; however, the large variability existing between estimates resulted in non-significant differences among biomes. We observed that increases in nitrate availability stimulated the temperature dependence of grazing pressure (i.e., led to more positive Ea of g:μ) in open-ocean ecosystems and inhibited it in coastal ones, particularly in polar environments. The percentage of primary production grazed by microzooplankton (∼56%) was similar in all regions. Our results suggest that warming of surface ocean waters could exert a highly variable impact, in terms of both magnitude and direction (stimulation or inhibition), on microzooplankton grazing pressure in different ocean regions.

A probabilistic model for assessing uncertainty and sensitivity in the prediction of monochloramine loss in French river waters

Monochloramine (NH2Cl) is increasingly used as alternative disinfectant to free chlorine in industrial plants. After use in cooling systems, the waters are released to the environment and residual NH2Cl may be discharged into the receiving waters. As NH2Cl is suspected to exhibit toxicity towards aquatic organisms, a proper risk assessment of its occurrence in environmental waters is needed to prevent adverse effects on wildlife.For this purpose, a comprehensive model simulating monochloramine loss in natural riverine waters was developed. This model incorporates the following processes: (i) autodecomposition; (ii) reaction with nitrite and bromide; (iii) oxidation with Dissolved Organic Carbon (DOC); (iv) oxidation with organic fraction of Suspended Particulate Matter (SPM); (v) reactions in bottom sediments and (vi) volatilization. The model was also designed to conduct uncertainty and sensitivity analysis. It was tested on several French rivers submitted to discharges of monochloraminated effluents and on several seasonal conditions.Uncertainty analysis allowed evaluation of confidence intervals related to NH2Cl half-lives in natural waters. It was shown that simulation intervals are in good agreement with experimental data obtained on the same rivers. Sensitivity analysis using an EFAST variance decomposition approach allowed identification of the most influential parameters on half-life determination. It was shown that the kinetic rate describing rapid reaction of NH2Cl with DOC is by far the most sensitive parameter, demonstrating the predominance of such reactions in the loss process. Variables or parameters involved in temperature dependence (temperature and activation energy) can also significantly influence model results. To a lesser extent, wind velocity is the most sensitive parameter explaining uncertainty in the prediction of volatilization, with a high level of interactions with other parameters, showing that loss through volatilization can be essential in some specific conditions only. This study then identified the most important research priorities for improving the prediction of NH2Cl half-lives in natural rivers.

Pyrolytic degradation of spent coffee ground: A thermokinetic analysis through the dependence of activation energy on conversion and temperature

This work focuses on the thermal degradation of spent coffee ground (SCG) under a non-oxidizing atmosphere using thermoanalytical techniques (TGA-DTG/DSC). The study describes the thermokinetic behavior of SCG through the dependence of activation energy (Eα) as a function of the conversion degree (α) and temperature (T), through the combined use of different model-free kinetic algorithms. The dependencies of Eα on α and T exhibit different steps and critical stages, which define the control mechanism and the yield in the desired products. The obtained trends reflect the complexity of the process and highlight the limitations of traditional isoconversional approaches in describing the behavior of processes that involve several phases and multi-components. The present study discloses the direct dependence of the rate constant, k, on the temperature, T, and predicts the influence of the saturation pressure (P) of the gaseous products on both the control mechanism and the products yield in the pyrolysis process, as a function of the heating program (β). Furthermore, the study shows that the degradation rate (dα/dt)p of each pseudocomponent (hemicellulose, cellulose and lignin) at the maximum rate temperature, Tp, satisfies that, f(α)p is independent of β, and, hence, f’(α), is independent of α at that instant. Therefore, kinetic behavior at maximum conversion rate, can be unequivocally described through a simple first-order kinetic law (f(α) = 1-α). Finally, the findings this study, provide recommendations of wide relevance and practical interest, to understand, control and modulate the thermochemical conversion of lignocellulosic wastes into value-added products.

Insight into master plots method for kinetic analysis of lignocellulosic biomass pyrolysis

The determination of the kinetic triplet including the activation energy, frequency factor, and kinetic mechanism function is a key objective in kinetic analysis of solid-state reactions like lignocellulosic biomass pyrolysis. The master plots method is usually used to determine the kinetic mechanism function once the activation energies as a function of conversion are estimated from an isoconversional method. A critical study of the master plots method has been performed by analyzing theoretically simulated processes with varying activation energies and frequency factors. The accuracy of the resulting kinetic mechanism function calculated by the master plots method is strongly dependent on the variation degree of the frequency factor with conversion and the conversion dependency of activation energy from isoconversional methods. The utilization of the master plots method without considering the variation degree of the frequency factor with conversion may result in misestimating kinetic mechanism function.

PHYSICO-CHEMICAL PARAMETERS OF SIBERIAN LARCH (LARIX SIBIRICA) BARK EXTRACTED WITH WATER-AMINO-ALCOHOLIC EXTRACTANTS

This paper presents the results of a thermal analysis, that involved thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC), of natural bark of Siberian larch (Larix sibirica Ldb.) vs. the bark extracted with 5% water-monoethanolamine (MEA) and (vs.) 5% water-triethanolamine (TEA). Thermogravimetric data obtained in an oxidative (air) atmosphere allowed us to identify temperature ranges of thermal decomposition stages for the larch bark samples, as well as to determine the corresponding mass loss and mass loss rate at programmed heating. The Ozawa-Flynn-Wall (OFW) method was used to calculate the dependence of activation energy of the thermal decomposition of experimental samples on the conversion degree (Еа = f(a)); the symbate run of Еа = f(a) curves was established. The DSC data obtained agreed with those of TG/DTG. The integral heat of the bark thermal decomposition (9.60 kJ/g and 14.12 kJ/g for MEA and TEA, respectively) indicated the bark to be competitive with other biofuels, such as briquetted lignin, wood pellets, sunflower husk, rapeseeds, and straw.

Impact of surface heterogeneity on IR line profiles of adsorbed carbon monoxide on models of interstellar grain surfaces

ABSTRACTSurface heterogeneity of model amorphous silica films used as a model for interstellar grain surfaces is revealed through the application of the pre-exponential optimized inversion method to previously reported sub-monolayer thermal desorption studies of carbon monoxide (CO) desorption. The impact of that surface heterogeneity, as represented by the coverage dependence of the CO activation energy for desorption from the amorphous silica surface, on the IR spectroscopy of the CO stretching vibration is explored through vibrational line profile synthesis. Comparison is then made to previous investigations of CO line profiles on this surface and on amorphous solid water as reported in Taj et al. (2017, 2019a). A tentative conclusion is drawn that CO vibrationally promoted desorption from, and diffusion on, the amorphous silica surface may be responsible for the correspondingly short vibrational excited state lifetime of CO on that surface. The contrast with CO on amorphous solid water, where direct and rapid vibrational relaxation into the solid water phonon bath occurs, is highlighted. The consequences of this from the standpoint of CO deposition on grain surfaces are discussed.

The Temperature Dependence of the Electrical Conductivity Activation Energy of the of Aqueous Electrolyte Solutions

The procedure for determining the activation energy of conductivity Еκ is analyzed depending on the temperature step ΔT. It is shown that with increasing ΔT, the error in the calculation of Eκ decreases, but the calculated value of Eκ decreases. In order not to lose the temperature dependence of the activation energy, it is necessary to choose the optimal value of Δt. In our opinion, this value should not exceed 5 – 10 °C. Taking into account the decrease in concentration with increasing temperature due to a decrease in density has virtually no effect on the accuracy of determining Eκ, provided that ΔT is 5 – 10 °C. It has been shown that in the temperature range 20 – 80 °C, the activation energy of conductivity decreases with increasing temperature. This decrease is due to the rupture of intermolecular hydrogen bonds of the solvent with increasing temperature. It was suggested that the movement of ions in an aqueous solution may be accompanied by the breaking of hydrogen bond of the solvent.