Non-isothermal short-range-order kinetics of binary alloys as influenced by solute-vacancy complexes

A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach. The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures. An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use of DSC trace data. A value of 89.12±0.32 kJ mol^-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation energy corresponding to the ordering process as influenced by quenching temperature was also assessed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Short-range-ordering Kinetics of Cu—5 At.% Zn Influenced by Solute—Vacancy Complexes and Cold Rolling

A modified first-order kinetic law which takes into account defect decay during an ordering process was employed to predict the short-range-order kinetics of a quenched and a quenched-deformed Cu—5 at.% Zn alloy, in conjunction with experiments performed by isothermal calorimetry. The effective activation energy of point defect migration and its temperature dependence strongly suggest the contribution of bound vacancies to the ordering process. An estimate of 91.2 kJ mol^–1 was made for the activation energy of solute—vacancy migration by applying an effective rate constant, a value in very good agreement with that obtained from previous non-isothermal experiments. The isothermal curves were utilized to determine the ordering energy: w=–2.90 kJ mol^–1. In conjunction, a parametric study of the defect sink density was performed in order to assess its influence on the calculated isothermal curve profiles.This revised version was published online in November 2005 with corrections to the Cover Date.     

Dsc Evaluations in F.c.c. Solid Solutions of Short-range-order Kinetics As Influenced by Bound Vacancies

A modified first order kinetic law, which describes the roles of bound and unbound vacancies, is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. The model has been applied to differential scanning calorimetry (DSC) curves of Cu–5 at%Zn quenched from different temperatures. Activation energy for migration of solute-vacancy complexes was also assessed from the kinetics of short-range-order using DSC traces. A value of 89.5±0.32 kJ mol^–1 was obtained. The relative contribution of bound and unbound vacancies to the ordering process as influenced by quenching temperature was determined. In conjunction, a parametric study of the initial total defect concentration and effective energy for defect migration was performed in order to envisage their influence on the calculated DSC profiles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Non-isothermal short-range-ordering by excess vacancies in αCu−Zn alloys

The kinetics short-range-order (SRO) in quenched Cu-30 at.% Zn, Cu-25 at. %Zn and Cu-20 at. %Zn was investigated by differential scanning calorimetry (DSC). It was evidenced a growing atomic mobility with increasing Zn content. From the DSC traces it is inferred that ordering is established in one stage, assisted by excess vacancies. As the quenching temperature increases considerable reordering occurs during cooling from the quenching temperature. The variation in the SRO non-isothermal behaviour with quenching temperature and composition is interpreted in terms of the atomic mobility and the degree of disorder together with the concentration of vacancies retained by quenching. Activation energies which control the mean life of vacancies and those which control the ordering rate were very similar, indicating that the mobility of vacancies is highly effective in generating SRO. Such activation energies are somewhat lower than the effective energies which control the kinetics of the process obtained from the DSC traces, suggesting that the presence of solute-vacancy complexes may be important as the Zn concentration increases. This feature was confirmed by an estimation of the solute-vacancy binding energy. It was also inferred that divacancy formation is unlikely in the alloys under study.     

Kinetic study of polyurethanes formation by using differential scanning calorimetry

Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 72±3 kJ mol^-1 and for aromatic isocyanates it is 55±2 kJ mol^-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 70±5 kJ mol^-1 with oxypropylated polyols and 50±3 kJ mol^-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol^-1 . In the case of two parallel reactions (situation for IPDI and TDI 2-4) best fits are observed considering two different activation energies.     

Determination of kinetic parameters for atom formation at constant temperature in graphite furnace atomic absorption spectroscopy

A new method for the simultaneous determination of the kinetic order and activation energy for atom release under isothermal condition in a graphite furnace has been developed. Tungsten wire probe atomization was employed to examine the validity of the present method. By means of this model, the kinetic parameters for the atomization of Bi, Ge, Pb and Mn at constant temperatures were successfully determined. The values of the kinetic order and activation energy were found to be 0.67 ± 0.01 and 302 ± 8 kJ mol⁻¹ for Bi, 1.01 ± 0.08 and 109 ± 2 kJ mol⁻¹ for Ge, 0.46 ± 0.01 and 159 ± 2 kJ mol⁻¹ for Pb and 0.97 ± 0.03 and 372 ± 5 kJ mol⁻¹ for Mn, respectively. The atomization mechanism for these four elements from the tungsten probe surface was also discussed.     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

Non-isothermal Kinetics of the Thermal Decomposition of 3-Nitro-1,2,4-triazol-5-one Magnesium Complex

Introduction3 Nitro 1,2 ,4 triazol 5 one (NTO)metalcomplexeshavemanyspecialstructuresandsomepotentialusesinammunition .1 4 Wepreviouslypreparedanddeterminedthecrystalstructureofitsmagnesiumcomplex ,5andinthispaper ,wediscusseditsthermalbehaviorbyDSCandTG/DTGtechniquesandstudieditsnon isothermalkineticsbythemeansoftheKissingermethod ,theOzawamethod ,thedifferentialmethodandtheintegralmethod .ExperimentalSample[Mg(H2 O) 6 ](NTO) 2 ·2H2 Owaspreparedasfollows :AcalculatedamountofMg(OH…     

Temperatures and kinetics of anatase to rutile transformation in doped TiO<Subscript>2</Subscript> heated in microwave field

The influence of aliovalent ions such as Mn, Cr, Fe, Mo, and V on the temperature and kinetics of anatase to rutile phase transformation in TiO₂ heated in microwave field was studied in this work. The results indicated that heat treatment method and dopants considerably affected the anatase-to-rutile phase transition temperature and kinetics of transformation. The activation energy for anatase to rutile transformation of TiO₂ derived from the isothermal data was found to be 328.4 kJ mol^–1, which was considerably reduced by the addition of dopants in TiO₂ matrix. The activation energy for Mo, Mn and V doped samples was 252.0, 101.3 and 96.4 kJ mol^–1, respectively.     

Investigation of the thermal properties of [Cd(hydet-en)2Pd(CN)4] AND [Zn(hydet-en)2Pd(CN)4] single crystals

Thermal properties of the single crystals have been investigated by thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. The thermodynamic parameters such as activation energy and enthalpy and thermal stability temperature of the samples were calculated from the differential thermal analysis (DTA) and TG data. The activation energies for first peak of DTA curves were found as 496.65 (for Cd–Pd) and 419.37 kJ mol^–1 (for Zn–Pd). For second peak, activation energies were calculated 116.56 (for Cd–Pd) and 173.96 kJ mol^–1 (for Zn–Pd). The thermal stability temperature values of the Cd–Pd and Zn–Pd compounds at 10°C min^–1 heating rate are determined as approximately 220.7 and 203°C, respectively. The TG results suggest that thermal stability of the Cd–Pd complex is higher than that of the Zn–Pd complex.     

Kinetics and heats of sublimation and evaporation of 1,3,3-trinitroazetidine (TNAZ)

TNAZ (1,3,3-trinitroazetidine) is a relatively new, powerful, steam castable, strained ring explosive. Owing these characteristics it is of considerable interest to the energetic material community. A relatively high vapour pressure, volume contraction and formation of shrinkage cavities in the solidification of its melt may be considered as some of its disadvantages. The kinetics and heats of TNAZ sublimation and evaporation were studied by the non-isothermal and isothermal thermogravimetry method. The activation energy of 94-102 kJ mol^-1 was found for TNAZ sublimation, while the activation energy of 60-81 kJ mol^-1 was found for TNAZ evaporation. The enthalpy of TNAZ sublimation at the melting temperature was found to be 95 kJ mol^-1, and the enthalpy of TNAZ evaporation equals 66 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of reagents solvation on enthalpy change of glycine-ion protonation and silver(I) glycine-ion complexation in aqueous-dimethylsulfoxide solutions

The thermal decomposition process and non-isothermal decomposition kinetic of glyphosate were studied by the Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA). The results showed that the thermal decomposition temperature of glyphosate was above 198?°C. And the decomposition process was divided into three stages: The zero stage is the decomposition of impurities, and the mass loss in the first and second stage may be methylene and carbonyl, respectively. The mechanism function and kinetic parameters of non-isothermal decomposition of glyphosate were obtained from the analysis of DTA?CTG curves by the methods of Kissinger, Flynn?CWall?COzawa, Distributed activation energy model, Doyle and ?atava-?esták, respectively. In the first stage, the kinetic equation of glyphosate decomposition obtained showed that the decomposition reaction is a Valensi equation of which is two-dimensional diffusion, 2D. Its activation energy and pre-exponential factor were obtained to be 201.10?kJ?mol^?1 and 1.15?×?10¹⁹?s^?1, respectively. In the second stage, the kinetic equation of glyphosate decomposition obtained showed that the decomposition reaction is a Avrami?CErofeev equation of which is nucleation and growth, and whose reaction order (n) is 4. Its activation energy and pre-exponential factor were obtained to be 251.11?kJ?mol^?1 and 1.48?×?10²¹?s^?1, respectively. Moreover, the results of thermodynamical analysis showed that enthalpy change of ??H ^??, entropy change of ??S ^?? and the change of Gibbs free energy of ??G ^?? were, respectively, 196.80?kJ?mol^?1,107.03?J?mol^?1?K^?1, and 141.77?kJ?mol^?1 in the first stage of the process of thermal decomposition; and 246.26?kJ?mol^?1,146.43?J?mol^?1?K^?1, and 160.82?kJ?mol^?1 in the second stage.     

Cure kinetics of thermosetting bisphenol E cyanate ester

Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally, thermosetting polymers with high glass transition temperatures (T _g) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester (BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature yet polymerizes as a cross-linked thermoset with a high T _g of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high T _g amorphous network. In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal curing. The activation energy from the autocatalytic model is 60.3 kJ mol⁻¹ and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between T _g and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol⁻¹ based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.     

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.     

1H and 13C NMR studies of some aromatic dilactones (precursors of paracyclophanes)

Carbon-13 and proton NMR data of macrocyclic diaromatic dilactones are presented. The observed behaviour of the spectra as a function of temperature shows that the energy barrier for the re-orientation of the side chains is lower than 49 kJ mol^?1 (12 kcal mol^?1) and that the energy barrier for the rotation of the aromatic rings is larger than 99 kJ mol^?1 (24 kcal mol^?1). Hence, chiral substituted dilactones of this type will be resolvable, and the enantiomers can be easily handled at room temperature.     

Isoconversional kinetic study of alachlor and metolachlor vaporization by thermal analysis

The vaporization kinetics of two acetamide pesticides, namely alachlor and metolachlor, was studied by thermogravimetric analysis under nonisothermal conditions (using heating rates between 1.0 and 10 K min^?1). A model‐free isoconversional method of kinetic analysis was proposed, and activation energy dependences on the extent of conversion α for nonisothermal experiments were given. An increase in activation energy is shown for alachlor from 50 to 60 kJ mol^?1, while E values do not significantly vary in the range α > 0.1: 63 kJ mol^?1 for metolachlor while 60 kJ mol^?1 for alachlor. At the end of vaporization (0.9 < α < 1.0), the activation energies are in close agreement with the enthalpies of vaporization calculated from DSC measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 74–80, 2005     

Non-isothermal kinetic analysis and feasibilty study of medium grade crude oil field

In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a limestone matrix. Experiments were performed at a heating rate of 10°C min⁻¹, whereas the air flow rate was kept constant at 50 mL min⁻¹ in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol⁻¹ in LTO region and 189–229 kJ mol⁻¹ in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.     

Kinetic phenomena in non-crystalline materials studied by thermal analysis

The structural relaxation and viscosity behavior of Ge₃₈S₆₂ glass has been studied by thermomechanical analysis. The relaxation response to any thermal history is well described by the Tool-Naraynaswamy-Moynihan model. The apparent activation energy of structural relaxation is very close to the activation energy of viscous flow (Eη=478±12 kJ mol^-1). However, the activation energy of crystal growth obtained by optical microscopy is about one half of this value. Similar result has been obtained from isothermal DSC measurement (Ea=220±20 kJ mol^-1). The kinetic analysis of these data reveals interface controlled crystal growth with zero nucleation rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal Decomposition of Strontium and Barium Malonates

The thermal decomposition of strontium and barium malonates has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, DSC, XRD and IR spectroscopic techniques. DSC of these malonates has been recorded both in oxygen and nitrogen atmospheres. The decomposition is a single step process and the end product formed is carbonate. The energy of activation and frequency factor values for the decomposition of strontium malonate are 547 kJ mol⁻¹ and 10⁴¹ s⁻¹ respectively. The activation energy and frequency factor values for isothermal dehydration of barium malonate sester-hydrate are 57–111 kJ mol⁻¹ and 10⁷–10¹² s⁻¹ respectively and the corresponding values for decomposition from DSC are 499.5 kJ mol⁻¹ and 10⁴⁴ s⁻¹ respectively. The higher thermal stability of strontium malonate as compared to that of barium salt is ascribed to its being anhydrous so that decomposition proceeds without restructuring. Their thermal stabilities have also been compared with that of respective oxalate salts. This revised version was published online in July 2006 with corrections to the Cover Date.