Lucien Elegant

Simulations for evaluation of kinetic methods in differential scanning calorimetry. Part 3 — Peak maximum evolution methods and isoconversional methods

Abstract Various peak maximum evolution methods and isoconversional methods are compared, and the specific characteristics of each method are shown, from a mathematical viewpoint and by using simulated data. A convenient way of correcting the activation energy of the Ozawa method is proposed. Isoconversional methods should be preferred to peak maximum evolution methods, especially when an interpolation on the power and/or the temperature is performed. In the case of a complex mechanism of two parallel reactions, peak maximum evolution methods give only a mean value of the kinetic parameters, while isoconversional methods are useful in describing this complex mechanism.

The Málek method in the kinetic study of polymerization by differential scanning calorimetry

Abstract A comparative kinetic study of polymerization by differential scanning calorimetry (DSC) has been carried out by use of calculations based on the Freeman-Carroll, Ellerstein, Achar-Brindley-Sharp, multiple linear regression and Malek methods. With the Sestak-Berggren model of a modified Malek method, we have extracted kinetic information from curves showing a presence of more than one component using criteria based on the minimization of the difference between experimental and calculated thermograms.

Simulations for evaluation of kinetic methods in differential scanning calorimetry. Part 1. Application to single-peak methods: Freeman-Carroll, Ellerstein, Achar-Brindley-Sharp and multiple linear regression methods

Abstract In order to simplify the choice between different kinetic methods used in differential scanning calorimetry, an interesting way for testing kinetic treatments is proposed, using simulated thermoanalytical curves computed from given kinetic parameters. Applied to the study of a polymerization, we tested the Freeman-Carroll, Ellerstein, multiple linear regression (reaction-order model) and Achar-Brindley-Sharp methods. The test of the validity of the methods is performed using the LSM parameter that represents the fit between the mathematical treatment used in the kinetic model and known data. The study reveals the importance of the number of points used, i.e. the resolution, in the thermoanalytical curve recording, especially for the Freeman-Carroll and Ellerstein methods, there being an increase in the relative error on all the kinetic parameters when the number of points is decreased. Maximum relative errors are reported for the pre-exponential factor calculations. Evaluation of the enthalpy error on the determination of the kinetic parameters has been performed. Simulations obtained with various enthalpies indicate the necessity in such cases of computing a relative dimensionless LSM parameter (relative to the amplitude of the phenomena) in order to compare different thermal effects.

A microcalorimetric method for the measurement of enthalpies of solution of gases in liquids

Abstract An experimental set-up for measuring enthalpies of solution of gases in liquids is described. This apparatus consists of a vacuum line for gas handling and a Tian-Calvet microcalorimeter. The gas quantities are measured by a mercury manometer. The gas is injected into the calorimeter cell through a sintered glass-mercury one-way valve. The various sources of systematic and random errors are analyzed. The experimental method allows the measurement of the reaction stoichiometry and the distinction between fast and slow reactions; on the calorimeter time-constant scale. Along with spectroscopic studies of the reaction products, these features enable a more thorough characterization of the final state than the usual calorimetric techniques used for similar studies. A summary of the applications in the fields of physical organic chemistry, polymer chemistry and natural gas refining is given.

Kinetic study of solid-plastic transitions: Part 1. Comparison of methods describing the transition by differential scanning calorimetry

Abstract Following our research on organic phase-change materials, we tested the different kinetic methods, described in previously established software, on the solid-plastic transition of pentaerythritol using criteria based on the minimization, of the difference between experimental and calculated thermograms obtained by differential scanning calorimetry. The good modelling of the Achar-Brindley-Sharp method, which does not require long calculation times, led to its selection from other differential methods. The Freeman-Carroll and Ellerstein methods are not appropriate for modelling the transition.

Competition between different nucleophilic sites belonging to the same Lewis bases. Part 3. The basicity of arsenic and phosphorus sites relative to borane

After establishing some structural characteristics of a few simple AsR3·BH3 adducts (R = Me, Et, or Ph) by n.m.r. spectroscopy, the reaction of BH3 with a ligand (L) containing both phosphorus and arsenic donor sites (Ph2PCH2CH2AsPh2) has been studied. The superior basicity of phosphorus as compared to arsenic in these adducts is shown by displacement reactions and a calorimetric study. Enthalpic data (in kJ mol–1) obtained for the gas-liquid reactions (i) and (ii) are ΔH1=–160.4 and ΔH2, =–153.4 for M = P, and ΔH1=–76.1 and ΔH2=–111.3 2MPh3(sol)+ B2H6(g) [graphic omitted] 2MPh3·BH3(sol)(i), MPh3(sol)+ BH3(g) [graphic omitted] MPh3·BH3(sol)(ii) for M = As. In the case of L, two stages of compiexation may be separated and the corresponding enthalpies (kJ mol–1) are ΔH1=–165.3 (2L + B2H6) and ΔH2=–155.6 (L + BH3) corresponding to complexation of the phosphorus site, and ΔH1=–60.7 (2L·BH3+ B2H6) and ΔH2=–103.3 (L·BH3+ BH3) corresponding to complexation of the arsenic site.

Hétérocycles contenant du phosphore. Xv. Comportement d'une série d'oxo-2 dioxaphospholanes-1,3,2 vis-à-vis du trifluorure de bore mesures des enthalpies d'addition

Resume Many studies have showed that chemical and biological reactivities of the phosphorylated center depend on the environment of the phosphorus atom. In a series of 2-oxo-1,3,2-dioxaphospholanes, a relative scale of basicity is established using calorimetric measurements. We have correlated the enthalpies of addition, between phosphorus compounds and boron trifluoride, with different effects produced by groups linked to the phosphorus atom.

Kinetic study of solid-plastic transitions: Part 2. Influence of experimental conditions

The aim of this study is to incorporate the influence of different experimental conditions on the thermodynamic and kinetic parameters of the solid-plastic transition of pentaerythritol. The results show the importance of sublimation effects occurring with such phase change materials, which present a high vapour pressure and a low thermal conductivity. The influence on kinetic parameters and thermogram shapes is also discussed, and finally, a solution is proposed to overcome errors linked to the differential scanning calorimetry characterization of transformation of energetic materials, by proceeding to this analysis by means of a thermocouple located in the sample.