Non-isothermal crystallization of K<Subscript>2</Subscript>O·TiO<Subscript>2</Subscript>·3GeO<Subscript>2</Subscript> glass

The crystallization of K₂O·TiO₂·3GeO₂ glass under non-isothermal condition was studied. In powdered glass with particle sizes less than 0.15 mm, surface crystallization was dominant and an activation energy of crystal growth of E _a,s=327±50 kJ mol⁻¹ was calculated. In the size range 0.15 to 0.45 mm, both surface and volume crystallization occurred. For particle sizes >0.45 mm, volume crystallization dominated with spherulitic morphology of the crystals growth and E _a,v=359±64 kJ mol⁻¹ was calculated.     

Crystallization in glasses monitored by thermomechanical analysis

Thermomechanical analysis (TMA) can be used as a sensitive tool to follow crystallization behavior in non-crystalline materials. Newly developed method is based on slowing down of sample deformation caused by viscous flow above the glass transition due to macroscopic crystal growth. It is shown that a typical TMA sigmoidal curve reasonably well corresponds to direct measurement of crystal growth kinetics by means of optical microscopy. The method has been used to study crystallization kinetics in Ge₃₈S₆₂ glass. The TMA measurement is able to detect earlier stages of crystallization than obtained by differential scanning calorimetry measurement. The activation energy obtained from the shift of extrapolated end of TMA curve with heating rate (E = 263 ± 7 kJ mol^?1) is similar to the activation energy of ??-GeS₂ crystal growth in Ge₃₈S₆₂ glass (E _G = 247 ± 23 kJ mol^?1) obtained from direct optical microscopy measurements.     

Structural relaxation of amorphous Ge38S62 studied by length dilatometry and calorimetry

The structural relaxation of Ge₃₈S₆₂ glass has been studied by length dilatometry and calorimetry. The Tool-Narayanaswamy-Moynihan model was applied on obtained data of structural relaxation and parameters of this model were determined: Δh*= 483±2 kJ mol^-1, ln(A/s)= -81±1, β= 0.7±0.1 and x=0.6±0.1. Both dilatometric and calorimetric relaxation data were compared on the basis of the fictive relaxation rate. It was found that the relaxation rates are very similar and well correspond to the prediction of phenomenological model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Viscosity and structural relaxation of 15Na<Subscript>2</Subscript>O·<Emphasis Type="Italic">x</Emphasis>MgO·(10−<Emphasis Type="Italic">x</Emphasis>)CaO·75SiO<Subscript>2</Subscript> glasses

Temperature dependence of viscosity of title glasses (x=0, 2, 4, 6, 8, 10, abbreviated as M0, M2, M4, M6, M8, and M10, respectively) was measured by rotational viscometry (high temperature region: 10²−10^6.5 dPas) and thermomechanical analysis (low temperature region: 10^8.5−10^11.5 dPas) and described by the Vogel-Fulcher-Tammann equation. The MgO/CaO equimolar substitution (i.e. the increasing x value) smoothly shifts the high temperature viscosity to higher values. In the low temperature region the mixed alkali effect is demonstrated, and the highest viscosities are observed for the glasses M0 and M10. In the low temperature range the activation energy of viscous flow linearly decreases with the increasing x value (E _act/kJ mol⁻¹=479−9.0x). No significant dependence of activation energy on x was found in the high temperature range (E _act/kJ mol⁻¹=238.1±4.2). The structural relaxation was measured by thermomechanical experiment and theoretically interpreted in the frame of Tool-Narayanaswamy-Mazurin’s model. The broadening of the relaxation time spectrum was observed for the calcium-magnesium glasses in comparison with the pure calcium or magnesium glasses.     

Degradation behavior and kinetic study of ABS polymer

The degradation kinetics of the ABS terpolymer (acrylonitrile-butadiene-styrene) was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900°C in nitrogen atmosphere applying three different heating rates: 5, 10 and 20°C min⁻¹. The Vyazovkin model-free kinetic method was used to calculate the activation energy (E) of the degradation process as a function of conversion and temperature. Between 20 and 80% of conversion, E was calculated and the figures were: for ABS GP, E is 204.5±11.5 kJ mol⁻¹ (medium value); for ABS HI, E is 239.0±9.8 kJ mol⁻¹; for ABS HH, E is 242.4±5.4 kJ mol⁻¹.     

Non-isothermal kinetics of free-radical polymerization of 2,2-dinitro-1-butyl acrylate

The free-radical bulk polymerization of 2,2-dinitro-1-butyl-acrylate (DNBA) in the presence of 2,2′-azobisisobutyronitrile (AIBN) as the initiator was investigated by DSC in the non-isothermal mode. Kissinger and Ozawa methods were applied to determine the activation energy (E _a) and the reaction order of free-radical polymerization. The results showed that the temperature of exothermic polymerization peaks increased with increasing the heating rate. The reaction order of non-isothermal polymerization of DNBA in the presence of AIBN is approximately 1. The average activation energy (92.91±1.88 kJ mol ⁻¹) obtained was smaller slightly than the value of E _a=96.82 kJ mol⁻¹ found with the Barrett method.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

Determination of the Thermal Degradation Kinetic Parameters of Carbon Fibre Reinforced Epoxy Using TG

In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to 20°C min⁻¹ . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference, a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere for each step is between 40–50 kJ mol⁻¹ upper than E _a calculated in inert atmosphere. The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (E _a ≈130 kJ mol⁻¹ ) even though the thermal degradation in nitrogen flow presents a maximum E _a for 15% mass loss (E _a ≈60 kJ mol⁻¹ ). This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature Oscillations Characterized by An Overall Activation Energy

Temperature oscillations obtained during the heterogeneous catalytic oxidation of ethanol on Pd-Al₂ O₃ in a dynamic calorimeter were characterized by an overall activation energy. This parameter was determined by a non-isothermal kinetic method using the minimum and maximum values of the oscillations temperature. Using the bifurcation diagram with the oxygen as a bifurcation parameter an E value between 27.6 and 28.2 kJ mol^-1 was obtained. With ethanol as bifurcation parameter the E values lies between 28.1 and 31.1 kJ mol^-1 for 3.5 to 4.0 vol% ethanol and between 25.8 and 27.6 kJ mol^-1 for 4.0 to 4.7 vol% ethanol. These results have been discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surface segregation measurements of In and S impurities from a dilute Cu(In,S) ternary alloy

The surface segregation of In and S from a dilute Cu(In,S) ternary alloy were measured using Auger electron spectroscopy coupled with a linear programmed heater. The alloy was linearly heated and cooled at constant rates. Segregation data of a linear heat run showed surface segregation of In that reached a maximum surface coverage of 25% followed by S, which reached a coverage of 30%. It was found that after In had reached a maximum surface coverage, it started to desegregate as soon as the S enriched the surface until In was completely replaced by S. The segregation parameters, namely, the pre‐exponential factor (D₀), activation energy (Q), segregation energy (ΔG?) and interaction energy (Ω) were extracted from the measured segregation data for both In and S segregation in Cu by simulating the measured segregation data with a theoretical segregation model (modified Darken model). The segregation parameters obtained for In segregation in Cu are D₀ = 1.8 ± 0.5 × 10^?5 m² s^?1, Q = 184.3 ± 1.0 kJ.mol^?1, ΔG? = ?61.4 ± 1.4 kJ.mol^‐1, Ω_Cu?In = 3.0 ± 0.4 kJ.mol^?1; for S segregation in Cu the parameters are D₀ = 8.9 ± 0.5 × 10^?3 m² s^?1, Q = 212.8 ± 3.0 kJ.mol^?1, ΔG? = ?120.0 ± 3.5 kJ.mol^?1, Ω_Cu?S = 23.0 ± 2.0 kJ mol^?1 and the In and S interaction parameter is Ω_In?S = ?4.0 ± 0.5 kJ.mol^?1. The initial parameters used for the Darken calculations were extracted from fits performed with the Fick's and Guttmann model. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermokinetics on the reaction of formation of Dy[(C5H8NS2)3(C12H8N2)]

The enthalpy change of formation of the reaction of hydrous dysprosium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen•H₂O) in absolute ethanol at 298.15 K has been determined as (-16.12 ± 0.05) kJ•mol^-1 by a microcalormeter. Thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), rate constant and kinetics parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of the reaction have also been calculated. The enthalpy change of the solid-phase reaction at 298.15 K has been obtained as (53.59 ± 0.29) kJ•mol^t-1 by a thermochemistry cycle. The values of the enthalpy change of formation both in liquid-phase and solid-phase reaction indicated that the complex could only be synthesized in liquid-phase reaction.

     

Stereoelectronic control of the retro diels–alder reaction in 8-(N-pyrrolidyl)bicyclo[4.3.0]nona-3,7-diene isomers

The cis- and trans-annulated isomers of 8-(N-pyrrolidyl)bicyclo[4.3.0]nona-3,7-diene show different propensities for the retro Diels–Alder fragmentation following electron impact ionization. Molecular ions of the cis-annulated isomer decompose predominantly via the retro Diels–Alder reaction to give [C₉H₁₃N] ⁺· fragments of the appearance energy (AE)=8.45±0.05eV and critical energy E_c=133±8kJ mol^?1. The trans-annulated isomer gives abundant [M–H]⁺ (AE=9.34±0.08eV) and [M–C₆H₆]⁺· fragments, in addition to [C₉H₁₃N]⁺· ions of AE=8.98±0.05eV and E_c=181±8kJ mol^?1. The ionization energies (IE) were determined as IE_cis=7.07±0.05 eV and IE_trans=7.10±0.06eV. The stereochemical information is much less pronounced in unimolecular decompositions of long-lived (metastable) molecular ions which show very similar fragmentation patterns for both geometrical isomers. Nevertheless, the isomers exhibit different kinetic energy release values in the retro Diels–Alder fragmentation; T_0.5=3.8±0.3 and 4.8±0.2 kJ mol^?1 for the cis and trans isomer respectively. Topological molecular orbital calculations indicate that the retro Diels–Alder reaction prefers a two-step path, with a subsequent cleavage of the C(5)? C(6) and C(1)? C(2) bonds. The open-ring distonic intermediate represents the absolute minimum on the reaction energy hypersurface. The cleavage of the C(1)? C(2) bond is the rate-determining step in the decomposition of the cis isomer, with the critical energy calculated as 137 kJ mol^?1. The cleavage of the C(5)? C(6) bond becomes the rate-determining step in the trans-annulated isomer because of stereoelectronic control. The difference in the energy barriers to this cleavage in the isomers (ΔE=95k Jmol^?1) provides a quantitative estimate of the magnitude of the stereoelectronic effect in cation radicals.     

Kinetics of D,L–Lactide Polymerization Initiated with Zirconium Acetylacetonate

The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol⁻¹. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy E_a=44.51±5.35 kJ mol⁻¹, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol⁻¹ K⁻¹. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.     

Crystallization of spodumene-diopside in the las glass ceramics with CaO and MgO addition

Crystallization, morphology and mechanical properties of a spodumene-diopside glass ceramics with adding different amount of CaO and MgO in Li₂O-Al₂O₃-2SiO₂ were investigated. With CaO and MgO addition, the crystallization temperature (T _p) decreased, the value of Avrami constant (n) decreased from 3.2±0.3 to 1.4±0.2, the activation energy (E) increased from 299±3 kJ mol⁻¹ to 537±5 kJ mol⁻¹. The crystalline phases precipitated were h-quartz solid solution, β-spodumene and diopside. The mechanism of crystallization of the glass ceramics changed from bulk crystallization to surface crystallization. The grain sizes and thermal expansion coefficients increased while flexural strength and fracture toughness of the glass-ceramics increased first, and then decreased. The mechanical properties were correlated with crystallization and morphology of glass ceramics.     

Kinetics and mechanism of thermal polymerization of hexafluoropropylene under high pressures

The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization, and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The activation energy (E _act = 132±4 kJ mol⁻¹) and activation volume (ΔV ₀ ^≠ = −27±1 cm³ mol⁻¹) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based on the assumption about a biradical mechanism of polymerization initiation was proposed.     

Direct kinetic parameters for the reaction of Br atoms with neopentane

Laser flash photolysis coupled with resonance fluorescence detection of Br atoms was employed to investigate the temperature dependence of the reaction Br + neo‐C₅H₁₂ (1) between 688 and 775 K. The following Arrhenius preexponential factor and activation energy were determined (±1 σ): A₁ = (6.89 ± 2.27) 10¹⁴ cm³ mol⁻¹ s⁻¹ and E_A,1 = 57.61 ± 2.05 kJ mol⁻−¹ The only other kinetic parameters reported for the reaction of Br atoms with neo‐C₅H₁₂ were obtained from competitive kinetic experiments relative to Br + C₂H₆. Comparison with our direct results is hampered by uncertainties in the kinetic data for the reference reaction that may need reinvestigation. The standard enthalpy of formation for the neo‐C₅H₁₁ radical was estimated to be 34.7 and 41.6 kJ mol⁻¹, depending on the value of the activation energy assumed for the reverse reaction neo‐C₅H₁₁ + HBr (−1). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 49–55, 2001     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

Evaluation of the 3-hydroxy pyridine antioxidant effect on the thermal-oxidative degradation of HTPB

The effect of the mixture of two antioxidants has been evaluated on the thermal-oxidant degradation of the hydroxyl-terminated polybutadiene (HTPB) because of its importance in the coatings and adhesives industries. 2,2-Methylene bis(4-methyl-6-tertiarybutylphenol) or A.O.2246 and 3-hydroxy pyridine have been considered as antioxidants in this study as a common HTPB antioxidant and an active antioxidant, respectively. The thermal-oxidant degradation behavior of the HTPB has been investigated in the presence of a mixture of two antioxidants by TGA and DTG tests, and, subsequently, the results of these tests have been interpreted by two model-free methods, e.g., Kissinger–Akahira–Sunose and Friedman methods. The results revealed that the mixture of two antioxidants affected the activation energy of the thermal-oxidant degradation reaction of the HTPB. The calculated activation energy value obtained from the Kissinger–Akahira–Sunose method was about 199 ± 1 kJ⋅mol⁻¹. In addition, the E_a value at various conversion rates has also been calculated by using the Friedman method. This method showed that the highest E_a value in the thermal-oxidant degradation reaction belonged to the initiation step of the reaction (about 299 kJ⋅mol⁻¹). Moreover, the lowest activation energy value was correlated to the second step of the degradation reaction at a conversion rate of 0.6 (about 184 kJ⋅mol⁻¹).     

Sigmatropic [1,3]-boron shift (permanent allylic rearrangement) in 3-allyl-3-borabicyclo[3.3.1]nonanes

2D ¹H-¹H EXSY NMR spectroscopy show that the free energy of activation ΔG ^≠ in six 3-allyl-3-borabicyclo[3.3.1]nonane derivatives is significantly higher (72–86 kJ mol^?1) than that in typical allylboranes (48–66 kJ mol^?1). For the first member of the series, viz., 3-allyl-3-borabicyclo[3.3.1]nonane, the activation parameters of the permanent allylic rearrangement were also determined (ΔH ^≠ = 82.7±3.4 kJ mol^?1, ΔS ^≠ = ?11.8±10.3 J mol^?1 K^?1, E _A = 85.5±3.4 kJ mol^?1, lnA = 29.2±1.2).