Activation Energy Of Viscous Flow Research Articles

Characterisation and solution properties of a galactomannan from Bauhinia monandra seeds

This study reports on the chemical and physicochemical properties of the polysaccharide isolated from Bauhinia monandra seeds. The seeds were found to contain 17.8% polysaccharide which consisted predominantly of galactose and mannose. The Man/Gal ratio was found to be approximately 4:1and the average molar mass was 2.54×105g/mol. The extracted material was also found to contain a small amount of protein (5.35%). The galactomannan produced highly viscous solution; the viscosity–shear rate profile was best described by the Williamson model. The mechanical spectrum of a 0.5wt% solution showed that G″ was greater than G′ over the frequency range employed while at higher concentrations G′ became greater than G″ above a critical frequency. The solutions obeyed the Cox-Merz rule at low concentrations, but there was some deviation at higher concentrations. Viscosity measurements were undertaken over a range of temperatures and the activation energy of viscous flow was found to be 20.75kJ/mol. The rheological properties of solutions of B. monandra galactomannan indicate that it has comparable characteristics to other commercially important galactomannans such as guar gum and locust bean gum and hence has potential as a thickener in the formulation of food and other related products.

CO2 absorption behavior of azole-based protic ionic liquids: Influence of the alkalinity and physicochemical properties

Recently, chemical fixation of CO2 catalyzed by protic ionic liquids (PILs) has been successfully achieved, suggesting that CO2 absorption behavior plays an important role on CO2 activation and transformation. For this reason, the influence of the alkalinity and physicochemical properties on CO2 absorption behavior of four azole-based PILs, namely [DBNH][Pyr], [DBNH][Im], [DBUH][Pyr], and [DBUH][Im] was discussed in this work. The alkalinity of PILs was determined by potentiometric titration, and free space of PILs was evaluated by thermal expansion coefficient and refractive index. Solubility parameter of PILs was obtained from the activation energy for viscous flow. The results show that PILs with [Pyr]− exhibits stronger alkalinity and larger free space, which can help to improve CO2 capture capacity. Whereas PILs with larger cation size [DBUH]+ exerts higher viscosity, resulting in slower absorption rate of CO2. Furthermore, the CO2 absorption capacity is inversely proportional to the solubility parameter of PILs. The absorption mechanism proved by FT-IR and 13C NMR spectra indicates that [Pyr]− or [Im]− can react with CO2 to form carbamate. Accordingly, considering the CO2 capture capacity and absorption rate, [DBNH][Pyr] may be a good candidate for efficient CO2 capture and activation with low enthalpy of absorption of −38.2kJmol−1.

Effective activation energies of chemical reactions and viscous flow of liquids depending on pressure in tribosystems with boundary and mixed friction

This work presents a kinetic analysis of the probable chemical reactions in a frictional contact zone depending on their energetics, temperature, and pressure, as well as the impact of these factors on the viscous flow of liquids, which can be used as an oily base in tribosystems with mixed boundary friction. The dependences of the effective activation energy and viscous flow of liquids on pressure have been analyzed. It has generally been shown that the effective activation energy of thermally activated chemical reactions and viscous flow depends on the activation volume and consists of standard activation energy under standard conditions and additional components connected with the influence of pressure on these processes.

Influence of resins and asphaltenes on the structural and rheological properties of petroleum disperse systems

The structural and rheological properties of resin-free model petroleum mixtures (MPM) with an asphaltene content of 0 to 6 wt % and the same mixtures with added 3.85 wt % petroleum resins have been investigated. The composition of the mixtures simulates the amount of the main hydrocarbon-group components and distillate fractions in light paraffin-base oils (ρ4 20 = 747.7–789.1 kg/m3). Temperature–dynamic viscosity relationships for cooling the MPM have been obtained, most of which displayed abnormalities in the temperature range of ~40–60°C. Calculations of the viscous-flow activation energy (E μ) have shown that there are abrupt changes in E μ in this abnormality region, which are an indication of structuring processes. By means of Fourier-transform laser diffractomery of MPM solutions in kerosene, it has been found that the particle size of the petroleum mixtures is qualitatively related to the revealed abrupt changes in E μ. It has been shown that these abnormalities correspond to the formation of paraffin–asphaltene associates and their existence is determined by the critical concentration of resins and asphaltenes in the mixtures.

Physicochemical properties of deep eutectic solvents formed by choline chloride and phenolic compounds at T = (293.15 to 333.15) K: The influence of electronic effect of substitution group

Three deep eutectic solvents (DESs) were synthesized using choline chloride (ChCl) and phenolic compounds (phenol, p-cresol, and p-chlorophenol) as hydrogen bond donors (HBD) with a molar ratio of 1:2 (ChCl:HBD). Densities (ρ), viscosities (η), and refractive indices (nD) of DESs were measured at T=(293.15 to 333.15)K under atmospheric pressure. Temperature dependence of ρ and η were fitted by empirical equations, and thermal expansion coefficient (αp) and activation energy for viscous flow (Eη) were obtained accordingly. FT-IR spectra of DESs were determined and compared with the corresponding HBDs. Based on physicochemical properties and FT-IR spectra, the influence of electronic effect of substitution group of HBD on hydrogen bond interaction between ChCl and HBD was explored. The results show that the electronic effect of HBD plays an important role on the strength of hydrogen bond interaction of OH⋯Cl− of DES. The strong electron-withdrawing property of Cl group of p-chlorophenol can strengthen the hydrogen bond interaction of OH⋯Cl−, which leads to higher ρ, η, and nD of DES formed by ChCl and p-chlorophenol. Conversely, CH3 group of p-cresol exhibits electron-donating effect, resulting in weaker hydrogen bond interaction and lower ρ and nD of DES formed by ChCl and p-cresol. Consequently, the strength of hydrogen bond interaction of OH⋯Cl− between ChCl and HBD of DES is as follows: p-chlorophenol>phenol>p-cresol.

Effect of basicity and B2O3 on the viscosity and structure of fluorine-free mold flux

The effect of basicity (weight ratio of CaO/SiO2) and B2O3 on the viscosity and structure of Fluorine-free mold flux for the casting of medium carbon steels was conducted in this article, through the rotating cylinder method combined with the Fourier transform infrared (FTIR) spectroscopy. The results showed that, with the increase of basicity, the viscosity of mold flux was attenuated dramatically, and then kept constant or slight increased in the low temperature region. The reason could be explained as the degree of polymerization (DOP) of the network structure was first reduced significantly with the addition of basicity, and then the further depolymerization is less pronounced with the further increase of basicity. Beside the formation of high melting point substance leads to the slight increase of viscosity. Moreover, it suggested that the viscosity of mold flux is decreased with the addition of B2O3 content, due to the fact that B2O3 is a low melting point oxide which could substantially lower the break temperature of mold flux. The result of FTIR indicated B2O3 acts as network former, and tends to form [BO3]-trihedral and [BO4]-tetrahedral structural units, which would connect with each other to form some simple network structure such as diborate or pentaborate. With the addition of B2O3, the free oxygen ions (O2−) would depolymerize the diborate structural unit, and the depolymerized diborate would link again with free [BO3]-trihedral to form complex pentaborate groups. Moreover, the effect of above addition on the apparent activation energy for viscous flow and break temperature of mold flux also were discussed. The results obtained in this paper provide the detailed study of the structure evolution of Fluorine-free mold flux when B2O3 is added.

Unusual higher viscosity for nanocrystalline titanium powders: Compared to micron titanium powders

We adopted the verified absolute-reaction theory which originates from the quantum chemistry approach as well as the boundary perturbation technique to capture the unusual experimental results by Dabhade et al.: Nanocrystalline titanium powders were found to exhibit lower activation energy for viscous flow and higher (coefficient of) viscosity as compared to micron sized titanium powders when nanocrystalline Ti (micron and nano) powders were expected to exhibit viscous flow during sintering. We also illustrate some formulations which can help us calculate the temperature-dependent viscosity of flowing Ti powders in micro- and nanodomains.

Densities and viscosities for binary mixtures of n-heptane with alcohols at different temperatures

Densities (?) and viscosities (?) of the binary systems n-heptane with alcohols (ethanol, propan-1-ol and propan-2-ol) were measured at temperatures between 288.15 and 308.15 K and at atmospheric pressure, over the whole composition range. The excess values of molar volume (VE) and viscosity (?E) were calculated from experimental measurements. The excess functions of the binary systems were fitted to Redlich?Kister Equation. Comparison between experimental excess molar volume and the one calculated from Flory and Prigogine?Flory?Patterson theories, has also been done. The viscosity results were fitted to the equations of Grunberg?Nissan, Heric?Brewer, Jouyban?Acree and McAllister. Also, the activation energies of viscous flow have been obtained and their variations with compositions have been discussed.

A Direct Correlation between Viscosity and Liquid Structure in Cu-Sn Alloys

The viscosity and liquid structure of Cu100-xSnx (x=10, 20, 30, 40, at.%) melts were investigated. Temperature dependence of viscosity η and correlation length D all shows an exponential decay function (Arrhenius-type equation), which is similar to our former studied Cu-Ag alloys. The correlation between viscosity and liquid structure had been studied. A simple relation between viscosity and correlation length D was found. The ratio of D and η shows a linear relationship with temperature, which is different from our former studied results in Cu-Ag alloys. Among the four Cu-Sn alloys, Cu80Sn20 and Cu70Sn30 alloys have higher activation energy for viscous flow (Ea,V), activation energy for structural evolution (Ea,D), and the slope (γ) of the linear relationship of D/η with temperature due to the Cu3Sn clusters formation.

Effect of Cr2O3 on the properties of stainless steel refining slags and desulfurization

In order to be able to understand the effect of residual Cr2 O3 (0–1.5%) on properties of stainless steel refining slag and desulfurization, the melting temperature and apparent viscosity were measured in the temperature range of 1300 °C to 1500 °C. The results showed that the melting temperature, apparent viscosity and activation energy of viscous flow gradually rise w ith the increase of Cr2 O3 content, and that present a larger increase for the slags with bigger basicity. When the basicity of slag is 1.5, melting temperature increases by 50 °C and apparent viscosity increase by 0.1 Pa.s with the increase of Cr2 O3 content from 0 to 1.5%. But melting temperature and apparent viscosity rise by 100 °C and 0.2 Pa.s for the slags with basicity 1.7, respectively. The small amounts of Cr2 O3 in stainless steel refining slag can reduce the liquidity of slag by inducing the precipitate of CaO.Cr2 O3 with high melting point, which has a negative effect on the desulfurization.

The Glass Transition Temperature and Temperature Dependence of Activation Energy of Viscous Flow of Ovalbumin

Abstract The paper presents the results of viscosity determinations on aqueous solutions of ovalbumin at a wide range of concentrations and at temperatures ranging from 5°C to 55°C. On the basis of these measurements and three models of viscosity for glass-forming liquids: Avramov’s model, free-volume model and power-law model, the activation energy of viscous flow for solutions and ovalbumin molecules, at different temperatures, was calculated. The obtained results show that activation energy monotonically decreases with increasing temperature both for solutions and ovalbumin molecules. The influence of the energy of translational heat motion, protein-protein and protein-solvent interactions, flexibility and hydrodynamic radius of ovalbumin on the rate of decrease in activation energy with temperature has been discussed. One of the parameters in the Avramov’s equation is the glass transition temperature Tg. It turns out that the Tg of ovalbumin solutions increases with increasing concentration. To obtain the glass transition temperature of the dry ovalbumin, a modified Gordon-Taylor equation is used. Thus determined the glass transition temperature for dry ovalbumin is equal to (231.8 ± 6.1) K.

Measurements of the Viscosity of Molten Lithium Nitrate by the Oscillating-cup Method

New experimental data for the viscosity of molten lithium nitrate from its melting point up to about 700 K are reported. The measurements were taken, for the first time, with an oscillating-cup viscometer with an estimated uncertainty of 3 %. The obtained data were compared with previous works. It was concluded that there are still large discrepancies between different sets of data. Our data follow the Arrhenius behavior with an activation energy for viscous flow of $$E_{\eta } \hbox {= 19.3}$$ $$\hbox {kJ}{\cdot }\hbox {mol}^{-1}$$ , slightly higher than previous recommendations.

Atomic displacement energy in amorphous compounds

Atomic displacement energy Δee in multicomponent sheet and lead-silicate glasses is calculated from the free activation energy of a viscous flow. The value of Δee is shown to remain constant in a rather wide range of temperatures in the glass transition region. Satisfactory agreement with calculations of Δee using the current formula incorporating the glass transition temperature and the fluctuation volume fraction frozen at this temperature is obtained. The validity of the above formula not only at the glass transition temperature but also in the temperature region adjacent to it is confirmed.

English

The rheological characteristics of oils isolated from the seeds of Afzelia africana and Detarium microcarpum were studied and compared with rapeseed oil. The effects of shear rate and temperature on the flow characteristics were evaluated. The shear stress- shear rate rheological models: Herschel-Bulkley, Power law, Binghan, Newtonian and Casson were used to determine the flow characteristics. All the oils exhibited non-Newtonian behaviour at shear rates rapeseed oil > Detarium oil. The activation energy of viscous flow followed the same order as viscosity of the oils. The most abundant fatty acids in A. africana oil were cis-11-eicosenoic acid (39 .06%), linolelaidic acid (18.38%) and nervonic acid (10.20%) and in D. microcarpum oil cis-13,16-dicosadienoic acid (20.51%) and linoleic acid (20.37%) and undecanoic acid (14.24%). A. africana contained higher amount of unsaturated fatty acids (92.26%) and long chain fatty acids (C ≥15; 96.00%) than D. microcarpum (unsaturated fatty acids, 66.27%; C ≥ 15; 79.41%). A. africana oil with the greater amount of long chain fatty acids had higher viscosity and activation energy of viscous flow. Key words: Afzelia africana, oil, rheological properties, fatty acid composition, Detarium microcarpum

Study on technology characteristics materials based on polysulfone

The research covers rheological characteristics of melts of polysulfones of domestic brand PSF-190 and foreign brand Udel P-1700 at temperatures ranging from 290 to 360°C. The values of activation energy of viscous flow of polysulfone melts at different temperatures are presented. The flow behavior indexes of melts of polysulfones PSF-190 and Udel P-1700 were determined. For the first time thermal stability curves over a wide temperature range were obtained, and formulas for describing them were presented. Temperature modes for processing the studied polysulfones were suggested. The dependency of density and volume in the temperature range from 23 to 320°C were obtained by the dilatometric method. Besides, constants and coefficients of the state equation of linear thermal expansion were calculated.

Temperature and Concentration Dependence of Viscosity of Binary Mixtures of PEG-1000 + water

Abstract Viscosities of binary mixtures of polyethylene glycol-1000 (PEG-1000) and water were measured precisely in the temperature range 293.15–343.15 K at atmospheric pressure using a high precision viscometer. Viscosity data were used to calculate the activation energy of viscous flow. The activation energy was observed to increase with increase in the concentration of aqueous solutions of PEG which indicated that more energy is required to move the molecule inside the structure with increase in concentration. The measured data provided better understanding to explain the behaviour of macromolecules with respect to change in concentration and temperature. The results were discussed in the light of polymer-solvent interactions. At lower concentration range, the molecules exhibit weak interaction due to dominant repulsive force and at higher concentration the entanglement of polymer chain increases. In view of greater force of interaction between solute and solvent molecules forming hydrogen bonding, there will be an increase in interaction with temperature and concentration.

Investigation of electrolytes of the vanadium redox flow battery (IV): Measurement and prediction of viscosity of aqueous VOSO4 solution at 283.15 to 323.15 K

Viscosity and density for aqueous VOSO4 solution have been measured in the concentration range of (0.05 to 0.3) mol·kg−1 at different temperatures from (283.15 to 323.15) K. On the basis of the measurements, the activation energy of viscous flow has been calculated by Arrhenius equation. A predicting function for the viscosity of aqueous VOSO4 has been proposed based on the viscosity coefficients A and B determined from Jones-Dole equation. In addition, the VO2+-water interaction and its effect on the structure of solvent according to the B-coefficient of VO2+ in dependence of temperature have been discussed. Using the B-coefficients, furthermore, the activation parameters for viscous flow of the solution, Δμ1≠0, Δμ2≠0, and other thermodynamics parameters ΔS2≠0, ΔH2≠0 and ΔCp2≠0 were evaluated. Finally, another empirical model of the viscosity has been investigated on the basis of the Eyring equation with the AAPD of 1.81%, and the maximum relative deviation is 2.77% below 313.15K, but up to 7.01% above 323.15K. Both predicting equations for the viscosities of aqueous VOSO4 are both in good agreement with the experimental results.

Development of Low-Fluoride Slag for Electroslag Remelting: Role of Li2O on the Viscosity and Structure of the Slag

The effect of the substitution of CaF2 with Li2O on the viscosity and structure of low-fluoride CaF2-CaO-Al2O3-MgO slag was studied with an aim to develop low-fluoride slag for electroslag remelting. Increasing Li2O addition up to 4.5 mass pct was observed to significantly reduce the slag viscosity monotonically. Increasing temperature significantly lowered the viscosity of slag, whereas this influence is less effective with increasing Li2O content especially above 3.5 mass pct. The activation energy for viscous flow decreases with increasing Li2O content. The polymerization degree of aluminate networks decreased with increasing Li2O content, as demonstrated by Raman analysis. The dominant structural unit in [AlO4]5−-tetrahedral network is \( {\text{Q}}_{\text{Al}}^{4} \). The amount of symmetric Al-O0 stretching vibrations significantly decreased with increasing Li2O content. The relative fraction of \( {\text{Q}}_{\text{Al}}^{4} \) in the [AlO4]5−-tetrahedral units shows a decreasing trend, whereas \( {\text{Q}}_{\text{Al}}^{2} \) increases with the increase in Li2O content accordingly. The change in slag viscosity with chemistry variation agrees well with the changes in slag structural units.

Cations/Anions Effects of Imidazolium-based Ionic Liquids on the Diffusion Properties of Iron- and Ruthenium-bipyridine/phenanthroline Complexes

The diffusion coefficients of both iron(II)-bipyridine ([Fe(bpy)3]2+), ruthenium(II)-bipyridine ([Ru(bpy)3]2+) are reported in five of different imidazolium-based ionic liquids (ILs) and iron(II)-phenanthroline ([Fe(phen)3]2+), ruthenium(II)-phenanthroline ([Ru(phen)3]2+) in one of imidazolium-based ionic liquid, using cyclic voltammetry and chronoamperometry at microdisc electrodes. Activation energies of diffusion, ED, are calculated for each system. Diffusion coefficient ratios between oxidation and reduction species for both complexes were found to be close to 1. Plots of diffusion coefficients versus inverse viscosity deviate from expected linearity, especially for ILs with different kind of anions, suggesting that anions of the ILs contribute to the values of diffusion coefficients. ED for both complexes in ILs are found slightly larger compared to the activation energies of viscous flow (Eη) for the corresponding IL, indicating that the viscosity is not the only factor determining the diffusion of the complexes. Furthermore, the hydrodynamic radius of complexes in ILs were estimated based on the diffusion coefficient values. They are found to be independent of temperature and ILs viscosity.

Viscosity of liquid Cu–Sn alloys

ABSTRACTWe investigated of the kinematic viscosity of liquid Cu–Sn alloys upon heating and subsequent cooling by the method of the oscillating cylinder. For the liquids alloys Cu75Sn25, Cu50Sn50, Cu48Sn52, Cu32Sn68, and Cu17Sn83, the temperature dependencies of the viscosity upon heating deviate from the Arrhenius relation. The temperature dependencies of viscosity show the Arrhenius-like behaviour upon cooling for all investigated alloys. A discrepancy between the temperature dependencies of viscosity obtained upon heating and cooling arised. We built the concentration dependences of the kinematic viscosity of liquid Cu–Sn alloys upon cooling. The increase of the values of viscosity and activation energy of viscous flow in the concentration range corresponding to the existence of intermetallic compounds Cu3Sn in the solid state was observed. These results were qualitatively interpreted using the concept of microheterogeneities of liquid alloys.