Search Results

You are looking at 131 - 140 of 206 items for :

  • "non-isothermal kinetics" x
  • Refine by Access: All Content x
Clear All

Abstract  

A new method of the multiple rate iso-temperature was used to define the most probable mechanism g(α) of a reaction; the iterative iso-conversional procedure has been employed to estimate apparent activation energy E a, the pre-exponential factor A was obtained on the basis of E a and g(α). In this new method, the thermal analysis kinetics triplet of dehydration of calcium oxalate monohydrate is determined, which apparent activation energy E a is 82.83 kJ mol-1, pre-exponential factor A is 1.142105-1.235105 s-1, the most probable mechanism belongs to phase boundary reaction Rn with integral form g(α)=1-(1-α)n and differential form f(α)=n(1-α)1-(1/n), where accommodation factor n=2.40-1.40.

Restricted access

Abstract  

The thermal behavior of sorbitol was studied under non-isothermal conditions, in both air and nitrogen atmosphere. The main process is a deep and continuous dehydration. For the kinetic analysis, the TG/DTG data obtained at five heating rates were processed by three different methods: Friedman, Budrugeac-Segal and non-parametric kinetic, respectively. This analysis indicates a complex reaction with a preponderant chemical process, described by a conversion function (1−α)3/2, accompanied by diffusion.

Restricted access

Abstract  

The decomposition reaction kinetics of the double-base (DB) propellant (No. TG0701) composed of the mixed ester of triethyleneglycol dinitrate (TEGDN) and nitroglycerin (NG) and nitrocellulose (NC) with cerium(III) citrate (CIT-Ce) as a combustion catalyst was investigated by high-pressure differential scanning calorimetry (PDSC) under flowing nitrogen gas conditions. The results show that pressure (2 MPa) can decrease the peak temperature and increase the decomposition heat, and also can change the mechanism function of the exothermal decomposition reaction of the DB gun propellant under 0.1 MPa; CIT-Ce can decrease the apparent activation energy of the DB gun propellant by about 35 kJ mol−1 under low pressure, but it can not display the effect under high pressure; CIT-Ce can not change the decomposition reaction mechanism function under a pressure.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: K. Chrissafis, K. Efthimiadis, E. Polychroniadis, and S. Chadjivasiliou

Abstract  

In this work we study the influence of Mo admixtures on the crystallization process of amorphous Fe78-xMoxSi9B13 (x=1, 2, 3 and 4) alloys by measurements of differential scanning calorimetry and on the soft ferromagnetic properties of the alloys by magnetic measurements. The addition of Mo by replacing Fe, results in magnetic hardening of materials. In DSC curves two peaks appear which are distinct when the concentration of Mo is 1 at.% and partly overlap when the Mo content is 2 at.%. Further increase in the Mo content leads to the appearance of just one peak. The activation energy was calculated both with Kissinger's and isoconversional Flynn, Wall and Ozawa methods.

Restricted access

Abstract  

The decomposition of series of supramolecular compounds, namely inclusion compounds, was studied by means of different thermoanalytical methods, i.e., traditional thermogravimetry, quasi-equilibrium thermogravimetry, and thermomechanical analysis. The series of compounds included the intercalates on the base of fluorinated graphite C2F, the clathrates on the base of carbamide and on the base of coordination compounds and microporous inclusion compounds on the base of coordination compounds. Kinetic parameters of decomposition processes were estimated within the approaches of the non-isothermal kinetics (“model-free” kinetics, linear and non-linear regression methods for the topochemical equation detection). The kinetic stability of the inclusion compounds under heating, the flexibility of the matrix structure, and the thermodynamic stability of the intermediate phases are discussed.

Restricted access

Abstract  

The crystal C81H78N12O6Cd3 was synthesized and its structure was determined by single crystal X-ray diffraction method. The complex crystallizes in the monoclinic system space group P21/n with cell parameters, a=15.959(4) , b=26.222(3) , c=25.907(6) , β=101.60(2). The non-isothermal kinetics of the crystal was studied by use of non-isothermal TG and DTG curves. The kinetic parameters were analyzed by means of integral and differential methods, and mechanism functions of the thermal decomposition reaction for its second step were proposed. The kinetic equation of thermal decomposition is expressed as: dα/dt=Aexp(-E/RT)1.5(1-α)4/3[1/(1-α)1/3-1]−1. The average values of E(kJ mol−1) and lnA/s−1 are 339.25, 43.95, respectively.

Restricted access

Abstract  

The non-isothermal kinetics of dehydration of AlPO4·2H2O was studied in dynamic air atmosphere by TG–DTG–DTA at different heating rates. The result implies an important theoretical support for preparing AlPO4. The AlPO4·2H2O decomposes in two step reactions occurring in the range of 80–150 °C. The activation energy of the second dehydration reaction of AlPO4·2H2O as calculated by Kissinger method was found to be 69.68 kJ mol−1, while the Avrami exponent value was 1.49. The results confirmed the elimination of water of crystallization, which related with the crystal growth mechanism. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the dehydration reaction are calculated by the activated complex theory. These values in the dehydration step showed that it is directly related to the introduction of heat and is non-spontaneous process.

Restricted access

Abstract  

The two complexes of [Ln(CA)3bipy]2 (Ln = Tb and Dy; CA = cinnamate; bipy = 2,2′-bipyridine) were prepared and characterized by elemental analysis, infrared spectra, ultraviolet spectra, thermogravimetry and differential thermogravimetry techniques. The thermal decomposition behaviors of the two complexes under a static air atmosphere can be discussed by thermogravimetry and differential thermogravimetry and infrared spectra techniques. The non-isothermal kinetics was investigated by using a double equal-double steps method, the nonlinear integral isoconversional method and the Starink method. The mechanism functions of the first decomposition step of the two complexes were determined. The thermodynamic parameters (ΔH , ΔG and ΔS ) and kinetic parameters (activation energy E and the pre-exponential factor A) of the two complexes were also calculated.

Restricted access

Summary In order to obtain catalysts, the thermal decomposition of the precursors is a compulsory step. However, kinetic analysis of the decomposition data obtained under non-isothermal conditions lead very seldom to the intimate reaction mechanism. There is also a lack of information because in non-isothermal kinetics, the compensation effect, is rather a rule and unfortunately a source of debate. In order to discriminate between these processes, and the influence of conversion, respectively temperature on the reaction rate, the NPK (non-parametric kinetic - Sempere and Nomen) method was used. This method is based on the singular value decomposition algorithm (SVD) applied on the matrix of reaction rate at corresponding conversion and temperature. This method allows a less speculative determination of the conversion functions and of the kinetic parameters.

Restricted access