Isothermal Regime Research Articles

Modeling of catagenetic transformation of saturated and alkylaromatic petroleum hydrocarbons

Thermolysis of crude oil at a temperature of 350°C for 1 h with and without aluminosilicates has been conducted in the isothermal regime mode. The composition of liquid and gaseous thermolysis products has been analyzed. The amount of resins and asphaltenes in the liquid products of thermal or thermocatalytic treatment decreases and that of oils increases as compared with the crude oil. The individual composition of saturated hydrocarbons (alkanes, steranes, terpanes) and alkylaromatic compounds (benzenes, naphthalenes, and phenanthrenes homologoues) has been studied. It has been shown that thermolysis increases the amount of thermodynamically more stable m- and p-isomers of alkyltoluenes, and the β-isomers of alkyl-naphthalenes and alkylphenanthrenes. Geochemical parameters for the composition of alkyl substituted benzenes, naphthalenes, and phenanthrenes have been calculated.

An extension to isothermal processes of the theoretical method developed (TMD) to analyze the glass–crystal transformation kinetics by differential scanning calorimetry. Application to the crystallization of the Sb0.16As0.22Se0.62 glassy alloy

It is well known that in the study of the glass–crystal transformation kinetics, sometimes is necessary that both the nucleation frequency and the crystal growth rate depend on time as a power law. To explain the probable physical nature of this time dependence, the theoretical method developed (TMD) for non-isothermal processes, which we have published recently, considers oriented nucleation and oriented growth processes, which are non-linear. In the present article we extend the quoted TMD to isothermal glass–crystal transformations. From this view point, and considering the impingement effect, a procedure has been developed to obtain an evolution equation with the time, t, for the actual volume fraction transformed, x, under isothermal regime. In order to calculate the kinetic parameters corresponding to isothermal processes, we follow the already quoted TMD adequately extended to isothermal regime. Thus, by means of an adequate computer program, from the isothermal experimental data, t and x, obtained by differential scanning calorimetry for each fixed temperature, T, it is possible to choose the corresponding impingement factor, δi, more suitable. Next, by using the corresponding straight regression lines lnt vs. ln[f(x,δi)], the kinetic exponent, n, and the reaction rate constant, KA, are evaluated from the slope and intercept, respectively. Besides, considering that the quoted constant has a temperature dependence of Arrhenius type, the slope and intercept of the straight regression line lnKA vs. 1/T give the values of the kinetic parameters: activation energy and frequency factor, respectively. The quoted extension of TMD and the Johnson–Mehl–Avrami (JMA) model have been applied to the isothermal crystallization kinetics of Sb0.16As0.22Se0.62 glassy semiconductor, since, given the generality of the above-mentioned TMD, the JMA model is a particular case of the already quoted extension of TMD. It is important to indicate that the experimental curve of the actual volume fraction transformed vs. time shows a better agreement with the theoretical curve of the extension of the TMD than with the corresponding curve of the JMA model, confirming the reliability of the quoted extension in order to analyze the isothermal transformation kinetics of the above-mentioned glassy semiconductor.

Pressure‐viscosity behaviour and film thickness in elastohydrodynamic regime of lubrication of ionic liquids and other base oils

ABSTRACTViscosities at high pressures for 16 base oils (six polyolesters, three polyglycols, six ionic liquids and squalane) were used to analyze the influence of their chemical structure on the pressure‐viscosity coefficient, α. Comparisons with literature α values for vegetable bases (canola, soybean and jojoba oils) are also performed. For the molecular lubricants, we found trends that are coherent with the literature, whereas for ionic liquids (ILs), new trends were found. ILs based on tris(pentafluoroethyl)trifluorophosphate anion [FAP]−are those which present higher α values. The role of the lubricants in the central thickness in the isothermal elastohydrodynamic regime of lubrication was evaluated through the product η00.69 α0.56, η0 being the viscosity at 0.1 MPa. One of the [FAP]− ILs provides film thicknesses close to the polyglycols with similar viscosity. Bis(trifluoromethylsulfonyl)imide ILs and the shorter polypropyleneglycoldimethyl ethers are the lubricants that better avoid the changes on the film thicknesses with the temperature owing to a high viscosity index. Copyright © 2013 John Wiley & Sons, Ltd.

Influence of water vapour on the oxidation behaviour of a conventional aluminide and a new thermal barrier coating system sintered from a slurry

In this work, the effect of water vapour on a new thermal barrier coating system synthesised from a slurry containing Al microparticles was studied under isothermal regime at 1100 °C for short oxidation times (50 h). Both dry air and argon gas atmospheres were investigated with increasing water vapour contents (0, 5, 10% RH, relative humidity) and the oxidation mechanisms and growth kinetics of the oxide scales were compared to conventional aluminide coatings up to 50% RH. The phase transformations occurring in the coating were characterised by local Raman micro‐spectrometry with complementary analytical techniques (X‐ray diffraction and FEG‐ESEM/EDS). The results demonstrated that water vapour does not exert a great influence on the oxidation of this type of coatings once an α‐Al2O3 scale is stabilised after an appropriate sintering of the coating. In contrast the combined effect of water vapour and oxidation onto oxide scales grown from raw aluminide coatings was shown to trigger delayed transformation of θ into α‐Al2O3, the appearance of pores and spallation, in particular in air + x %RH.

Thermal degradation of poly(vinyl chloride)/poly(ethylene oxide) blends: Thermogravimetric analysis

Thermal stability of poly(vinyl chloride)/poly(ethylene oxide) (PVC/PEO) blends has been investigated by thermogravimetric analysis (TGA) in dynamic and isothermal heating regime. PVC/PEO blends were prepared by hot-melt extrusion (HME). According to TG analysis, PEO decomposes in one stage, while PVC and PVC/PEO blends in two degradation stages. In order to evaluate the effect of PEO content on the thermal stability of PVC/PEO blends, different criteria were used. It was found that thermal stability of PVC/PEO blends depends on the blend composition. The interactions of blends components with their degradation products were confirmed. By using multiple heating rate kinetics the activation energies of the PVC/PEO blends thermal degradation were calculated by isoconversional integral Flynn–Wall–Ozawa and differential Friedman method. According to dependence of activation energy on degree of conversion the complexity of degradation processes was determined.

Application of Kissinger, isoconversional and multivariate non-linear regression methods for evaluation of the mechanism and kinetic parameters of phase transitions of type I collagen

DSC measurements carried out on type I collagen at different heating rates were used for the kinetic analysis of the endothermic processes of denaturation in water excess and of the phase transition in dry state. The application of isoconversional and “multivariate non-linear regression” methods shows that in both conditions the phase transitions are complex processes exhibiting Lumry–Eyring mechanism (a reversible step followed by an irreversible one), which describes the denaturation of several proteins. The corresponding kinetic parameters were evaluated, and were used for simulation of the thermal behavior of type I collagen in both considered conditions, in non-isothermal regime at different heating rates, as well as in isothermal regime at different temperatures. It was obtained that at relatively low heating rates and temperatures, the investigated complex processes could be satisfactorily described from kinetic point of view by a single step irreversible process.

Rearrangement of hexadecane molecules confined in the nanopores of a controlled pore glass using positron annihilation and differential scanning calorimetry

The solidification/melting of cetane confined in nine silica glasses with specific controlled pores (CPG) with different pore sizes (rp ranging from 3.7–72 nm) has been studied. Samples with variable coefficient of filling of cetane were prepared and analyzed. Combining the indication of the evolving solidification heats (via differential scanning calorimetry, DSC) with the lifetime spectra of positron annihilation, the mechanism of filling of cetane molecules in the pores of the hosting silica glass matrices has been searched. Three independent solidification effects—three independent DSC peaks—were observed in each measuring cycle, namely one crystallization exotherm Rb of the bulk-cetane (if present) and two crystallization sub-peaks Rc1 and Rc2 of the confined cetane in the case of continuous cooling. The temperatures of both Rc1 and Rc2 effects decrease on decreasing the rp of the CPG matrix. The mutual relation between Rc1 and Rc2 has been analyzed. The kinetics of all three steps of the solidification in the continuous-cooling as well as isothermal regimes have been specified.

Theory and practice of a variable dome splitter for gas chromatography-olfactometry

For olfactometric measurements in combination with gas chromatography a device is needed to split the GC effluent between the detector and the sniffing port. Fixed split ratios are obtained by simple flow splitters with appropriate restrictions towards the two outlets. Variable split ratios are possible with additional control flows. One such device is a dome splitter with one input flow (the GC effluent), two output flows (to the two outlets) and two control inputs. Preliminary experiments revealed deviations from the expected split ratios of such a device. The dimensioning of the flow restrictors at only one working point was not sufficient to obtain the expected split ratios over the whole temperature range of a GC run. Therefore a physical model of the flow system has been developed, taking into account the temperature dependence of the restrictors and the internal pressure in the dome. This included the solution of the flow (respectively the mass) balance under the condition of a compressible, isothermal and laminar flow regime. The measurements are in good agreement with theoretical calculations. The model can therefore be used to optimise the dimensions of the restrictions and to calculate the effective split ratio at a given temperature during the GC run.

Kinetics of olive oil pyrolysis

A kinetic study of olive oil pyrolysis has been carried out under different conditions by thermogravimetry. Nine TG runs were performed at nitrogen atmosphere, seven under dynamic conditions and two under dynamic+isothermal regime (constant heating rate until the set temperature was reached and then the set temperature was maintained constant). On the other hand, three dynamic runs were carried out with used olive oil.In addition, a study of the thermal decomposition was also carried out in dynamic runs at helium atmosphere using TG–MS and TG–IR at nitrogen atmosphere in order to observe the evolution of some compounds and to discuss the information that could be obtained.From the overall analysis of the data, a scheme of reactions was proposed and kinetic values were calculated by integration of the differential equations and minimizing the squared differences between the experimental and calculated values. An analysis of the influence of the initial mass on TG runs was performed on the assumption of vaporization processes.

Evaluation of Commercial Lithium-Ion Cells Based on Composite Positive Electrode for Plug-In Hybrid Electric Vehicle Applications: III. Effect of Thermal Excursions without Prolonged Thermal Aging

Understanding the behavior of lithium-ion batteries exposed to thermal excursion is of great interest to plug-in hybrid electric vehicle (PHEV) applications, because vehicles often endure wide weather conditions in operation. Here we investigate a composite {LixMn2O4 + LixNi1/3Mn1/3Co1/3O2}-based commercial cell design to assess performance and degradation under thermal excursion from 25°C; through −20°C, −5°C, 10°C, 25°C, 40°C, and 60°C; to 25°C. In each isothermal regime, a reference performance test with charge and discharge cycles at C/25, C/5, C/2, 1C, and 2C is conducted to quantify cell capacity, rate capability, and other performance variations. The capacity fade caused by the thermal excursion is attributed to origins including loss of active material, degradation in reaction kinetics, and the ohmic resistance increases. Using electrochemical inference techniques, we found that thermal excursion in the range of −5°C to 40°C is benign to capacity fade. Exposure to −20°C and 60°C respectively leads to irreversible fade. The capacity fade at −20°C induced Li inventory loss and did not cause kinetic degradation, whereas the exposure at 60°C resulted in degradation in reaction kinetics. The evaluation protocols and results are helpful in assisting the study of path dependence of cell degradation in thermal aging.

Isothermal Dilatometric Study of Sintering in Kaolin

Solid-state sintering for kaolin samples was studied by dilatometric measurements in the isothermal regime in the temperature range from 600 °C to 1100 °C. The relative expansion was measured for a period of 10h. For the temperatures up to 850 °C, we observed only a small shrinkage (less than 0.5 %), most of which took place within the first 3h of the measurements. For the temperatures above 850 °C, a significant shrinkage occurred for the whole measured time interval and reached up to 2.7 %. Anomalous behavior—a decrease in the shrinkage with the temperature—was observed in the range from 700 °C to 850 °C. The dilatometric measurements are supplemented by porosity distribution measurements. The standard spherical-grains microscopic model was applied to determine that for the initial stages of the sintering process, grain boundary diffusion was the dominant mechanism at lower temperatures (600 °C to 850 °C), whereas lattice diffusion was dominant at higher temperatures (900 °C, 1050 °C, and 1100 °C).

Simulation of thermal decomposition of a polymer at random scissions of C-C bonds

A mathematical formulation of the polymer thermal decomposition model at random scissions of C-C bonds in the backbone is presented. The model is based on ideas about a macrokinetic character of the observed process Polymer → Gaseous products, and the thermofluctuation nature of the bond scission. The suggested approach makes it possible to calculate the decomposition rate in a wide pressure range at any initial molecular weight distribution of the polymer. As an example, a comparison of the calculation results for temperature-time dependences of the conversion degree and decomposition rate with experimental data obtained in isothermal and non-isothermal regimes is performed for linear polyethylene.

Quantum theory with arrow of time: symmetry breaking and non-local spinor realization with non-commuting operators of energy and decay

We present a modified quantum dynamics with a non-Hermitian Hamiltonian ≠ +, and a complex parameter of evolution. The theory is developed with [+, ] = κ2, where κ is the new fundamental constant. It is shown that this theory loses its symmetry in the case of κ ≠ 0. We demonstrate that this theory allows a thermodynamical interpretation and possesses an 'arrow of time' for isothermal and adiabatic regimes of evolution. A realization of this theory is a modified four-dimensional Dirac spinor system, which appears non-local in the physical three-dimensional space.

Non-isothermal Kinetics of Benzo[a]Pyrene Photooxidation in Glyceryl Trioctanoate

Benzo[a]pyrene (BaP) was dissolved in glyceryl trioctanoate, heated in a glass reaction vessel within temperature range 297.95–361.85 K with heating rate of 1 K/min and simultaneously exposed to UV light at wavelength λ = 365 nm at radiation power 20 mW cm−2 in order to study the decrease of BaP concentration due to its photooxidation. The concentration of BaP was determined by HPLC-FD periodically in 5 min intervals. As observed, the BaP concentration decreased from 62.2 μg L-1 to 19.8 μg L-1. From the experimental results, the parameters characterizing the non-isothermal kinetics of BaP photooxidation have been obtained. The parameters were tested at two various isothermal conditions (290.16 and 323.26 K) to verify a suitability of derived parameters. Comparing calculated and measured data of half-lives of BaP decrease at mentioned temperatures it was found that calculated half-lives are in a good accordance with those experimentally obtained values, when relative standard deviations at 290.16 K were 17.0% and 5.4% at 323.26 K, respectively. The kinetic parameters enable the calculation of the rate constant for any temperature in isothermal regime and make possible to model, in general, the kinetics of such processes without a deeper insight into their mechanisms.

Aqueous sol–gel synthesis of zirconium titanate (ZrTiO4) nanoparticles using chloride precursors

Zirconium titanate powders were synthesized by a straightforward sol–gel method using zirconium and titanium chlorides as metal precursors, deionized water as solvent and oxygen donor, and a NaOH solution for adjusting pH to 7. According to transmission electron microscopy, amorphous particles of nearly 5nm in size with a relatively spherical morphology were prepared. Thermogravimetry and differential scanning calorimetery analyses on the xerogel at a heating rate of 10°C/min indicated a crystallization temperature of 690°C, which is comparable with previous reports. Furthermore, via differential scanning calorimetery studies using the Kissinger's equation, the activation energy for ZrTiO4 crystallization was determined to be 850kJ/mol. Structural evaluations in the isothermal regime, using X-ray diffraction experiments, implied the onset of ZrTiO4 crystallization at 550°C.

Estudio de los mecanismos de descomposición isotérmica de austenita en perlita en un acero 0,44C-0,73Mn

The goal of this paper is to determine the austenite-to-pearlite isothermal decomposition mechanisms in a 0.44C-0.73 Mn steel. More precisely, the role of austenitizing temperature (T γ ), and hence the austenitic grain size (AGS), in the kinetics of pearlite formation has been studied. Results allow us to conclude that the average size of pearlitic colonies is increased as the AGS is increased. On the other hand, it appears that the interlamellar spacing of the pearlite does not depend on the T γ but is controlled by the isothermal decomposition temperature of austenite (T). Finally, it was found that formation of pearlite is triggered for small AGS values and isothermal decomposition temperature regimes where the predominant controlling mechanism is due to carbon volume diffusion.

Stochastically driven single-level quantum dot: A nanoscale finite-time thermodynamic machine and its various operational modes

We describe a single-level quantum dot in contact with two leads as a nanoscale finite-time thermodynamic machine. The dot is driven by an external stochastic force that switches its energy between two values. In the isothermal regime, it can operate as a rechargeable battery by generating an electric current against the applied bias in response to the stochastic driving and then redelivering work in the reverse cycle. This behavior is reminiscent of the Parrondo paradox. If there is a thermal gradient the device can function as a work-generating thermal engine or as a refrigerator that extracts heat from the cold reservoir via the work input of the stochastic driving. The efficiency of the machine at maximum power output is investigated for each mode of operation, and universal features are identified.

ELLIPTICAL GALAXY MASSES OUT TO FIVE EFFECTIVE RADII: THE REALM OF DARK MATTER

We estimate the masses of elliptical galaxies out to five effective radii using planetary nebulae and globular clusters as tracers. A sample of 15 elliptical galaxies with a broad variation in mass is compiled from the literature. A distribution function-maximum likelihood analysis is used to estimate the overall potential slope, normalisation and velocity anisotropy of the tracers. We assume power-law profiles for the potential and tracer density and a constant velocity anisotropy. The derived potential power-law indices lie in between the isothermal and Keplerian regime and vary with mass: there is tentative evidence that the less massive galaxies have steeper potential profiles than the more massive galaxies. We use stellar mass-to-light ratios appropriate for either a Chabrier/KTG (Kroupa, Tout & Gilmore) or Salpeter initial mass function to disentangle the stellar and dark matter components. The fraction of dark matter within five effective radii increases with mass, in agreement with several other studies. We employ simple models to show that a combination of star formation efficiency and baryon extent are able to account for this trend. These models are in good agreement with both our measurements out to five effective radii and recent SLACS measurements within one effective radii when a universal Chabrier/KTG initial mass function is adopted.

Simulation of N2O Abatement in Waste Gases by Its Decomposition over a K-Promoted Co-Mn-Al Mixed Oxide Catalyst

Intrinsic data of N2O catalytic decomposition over a K-promoted Co-Mn-Al mixed oxide prepared by the thermal treatment of a layered double hydroxide was used for the design of a pilot reactor for the abatement of N2O emissions from the off-gases in HNO3 production. A pseudo-homogeneous one-dimensional model of an ideal plug flow reactor under an isothermal regime (450°C) was used for reactor design. A catalyst particle diameter of 3 mm is a compromise size because increasing the size of the catalyst particle leads to a decrease in the reaction rate because of an internal diffusion limitation, and particles with a smaller diameter cause a large pressure drop. A catalyst bed of 11.5 m3 was estimated for the target N2O conversion of 90% upon the treatment of 30000 m3/h of exhaust gas (0.1 mol% N2O, 0.005 mol% NO, 0.9 mol% H2O, 5 mol% O2) at 450°C and 130 kPa.

The effect of excitation wavelength on dynamics of laser-produced tin plasma

We investigated the effect of the excitation wavelength on the density evolution of laser-produced tin plasmas, both experimentally and numerically. For producing plasmas, Sn targets were excited with either 10.6 μm CO2 laser or 1.06 μm Nd:yttrium aluminum garnet laser; both are considered to be potential excitation lasers for extreme ultraviolet lithography laser-produced plasma light sources. The electron density of the plasma during the isothermal expansion regime was estimated using an interferometric technique. The Stark broadening of isolated singly-ionized emission was employed for deducing the density during the plasma adiabatic expansion regime. Our results indicate that the excitation source wavelength determines the initial density of the plasma, as well the plume expansion dynamics. Numerical simulation using HEIGHTS simulation package agrees well with the experimentally measured density profile.