scholarly journals Glow curve analysis by Gauss-Lorentz function

2013 ◽  
Vol 28 (1) ◽  
pp. 45-51 ◽  
Author(s):  
Zdravko Vejnovic ◽  
Milos Pavlovic ◽  
Marina Kutin ◽  
Milorad Davidovic

A new method for fitting glow curves, described in a mixed order kinetics model, with Gauss-Lorentz function is shown. Theoretical expressions of the mixed order kinetics model are shown in a new way, so that the values of kinetic parameters can be obtained through the geometric parameters. When the model is described in this way it is possible to calculate precisely the kinetic parameters such as activation energy, pre-exponential factor and the factor a= n0/(h + n0). At the same time, obtained values of geometric parameters of the experimental curve, which is described with the Gauss-Lorentz function, can be used to estimate the kinetic model, in which thermoluminescence relaxation occurs. This gives a possibility of a new application of Gauss-Lorentz function to be used as a criterion for assessing model of relaxation, when it is not known in advance. The accuracy of fitting is studied, for the specific cases of computer simulated thermoluminescent curves with one peak.

2018 ◽  
Vol 11 (1) ◽  
pp. 34
Author(s):  
Praswasti PDK Wulan ◽  
Widodo W Purwanto ◽  
Yuswan Muharam ◽  
Anindya Adiwardhana

Kinetic Parameter of Methane catalytic Decomposition Reaction into Nanotube Carbon with Ni-Cu-Al Catalyst. Development of production technology of nanotubes carbon through catalytic conversion of hydrocarbons will be efficient and effective if based on knowledge of the nucleation and growth mechanism of carbon nanotubes. Most of the research that focused on identifying the main products of reaction and estimate the activation energy. Growth kinetics and mechanism data of carbon nanotubes not completely available, so that process kinetics models are always based on experimental kinetic data. The objective of this research is to obtain kinetic parameters of catalytic decomposition of methane using the catalyst Ni-Cu-Al with composition of 2:1:1 which was prepared by co-precipitation method using natrium carbonate solution precipitant. Experimental kinetic data were taken in the temperature range of 650-750 °C and pressure of 1 atmosphere. Kinetic data were tested by micro-kinetic model derived from the catalytic surface reaction mechanism. The most appropriate kinetic model with experimental result is the adsorption stage which shows that consumption of intermediate (reaction surface) faster than the formation of intermediate (adsorption of methane). Kinetic parameters obtained are activation energy of 40,6 kJ/mole and pre-exponential factor of 8,625 x 106. Keywords: methane decomposition, hydrogen, carbon nanotubes, co-precipitation, kinetics of reactionAbstrak Pengembangan teknologi produksi karbon nanotube melalui konversi katalitik hidrokarbon akan efisien dan efektif jika didasarkan pada pengetahuan mekanisme nukleasi dan pertumbuhan karbon nanotube. Sebagian besar studi melakukan riset yang difokuskan pada identifikasi produk utama reaksi dan estimasi energi aktivasi. Data kinetika dan mekanisme pertumbuhan karbon nanotube tidak tersedia dengan lengkap sehingga model kinetika proses selalu didasarkan pada data kinetika eksperimen. Pada penelitian ini, dilakukan studi untuk memperoleh parameter kinetika reaksi dekomposisi katalitik metana menggunakan katalis Ni-Cu-Al dengan target komposisi 2:1:1 yang dipreparasi dengan metode kopresipitasi menggunakan presipitan larutan natrium karbonat. Data kinetika eksperimen diambil pada rentang temperatur 650-750 oC dan tekanan 1 atmosfer. Data kinetika diuji dengan model kinetika mikro yang diturunkan dari mekanisme reaksi permukaan katalis. Model kinetika yang paling sesuai dengan hasil percobaan adalah tahap adsorpsi yang menunjukkan bahwa konsumsi intermediate (reaksi permukaan) lebih cepat dari pembentukan intermediate (adsorpsi metana). Parameter kinetika yang diperoleh berupa Energi aktivasi sebesar 40,6 kJ/mol dan faktor pre-eksponensial 8,625 x 106.Kata kunci: dekomposisi metana, hidrogen, karbon nanotube, kopresipitasi, kinetika reaksi


Author(s):  
Sukhamoy Bhattacharyya ◽  
Partha Sarathi Majumdar

The shape of a thermoluminescence (TL) glow curve has fundamental importance for calculating the characteristic parameters of trap levels within the band gap. TL analysis are mostly based on the three-parameter general order kinetics model. The parameters are activation energy, order of kinetics, and frequency factor. Peak shape method is one of the most prominent methods for extracting the activation energy from a TL curve. An overview of different peak shape methods along with an alternative approach formulated directly from basic TL equations is presented in this chapter. Generally, peak shape method requires prior knowledge of order of kinetics to determine activation energy which creates a difficulty due to the non-uniqueness of symmetry factor for a particular value of order of kinetics. A modified version of peak shape method which is free from this constraint is discussed here. Activation energies from experimental curves of tremolite and actinolite are estimated using peak shape method. Limitation of peak shape method for saturated TL peaks with heavy retrapping is also discussed.


2019 ◽  
Vol 9 (1) ◽  
pp. 26-36 ◽  
Author(s):  
Biljana Koturevic ◽  
Borivoj Adnadjevic ◽  
Jelena Jovanovic

AbstractThe kinetics of isothermal extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling (UESC) was investigated. The isothermal kinetics curves were measured at temperatures range T = 17-58°C. Using the model-fitting method it was determined that the kinetics of caffeine extraction can be described by a theoretical Jander three-dimensional diffusional model. The values of the rate constant were calculated for different temperatures, as well as the kinetic parameters (activation energy (Ea) and pre-exponential factor (lnA)). Based on the results obtained, it is concluded that the rate constants of caffeine extraction under UESC are about 2 times higher in comparison to the values obtained for the extraction in the conditions of conventional heating (CH). The activation energy of the caffeine extraction under the UESC $\left( E_{\text{a}}\,^{\text{UESC}}=19.4\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right)$is lower than the values are for CH $\left( E_{\text{a}}\,^{\text{CH}}=21.8\,\text{kJ}\cdot \text{mo}{{\text{l}}^{-1}} \right).$Energy consumption for UESC is four times lower than for CH conditions. It is shown that there is a linear correlation relationship between kinetic parameters obtained for UESC and CH conditions. The changes in the values of kinetic parameters are explained by the model of selective transfer of energy from the reaction system to the reactant molecules.


2012 ◽  
Vol 455-456 ◽  
pp. 872-879 ◽  
Author(s):  
Yan Bao ◽  
Jia Wu ◽  
Xiao Ping Hu

The oxidation of N-phosphonomethyliminodiacetic acid (PMIDA) to prepare glyphosate (PMG) over active carbon was investigated. Experiments were carried out with O2 as the oxidizing agent in a 150-mL autoclave made in stainless steel, with reaction temperature ranging from 323.15 to 353.25K and the pressure from 0.12 to 0.40 MPa. The macro kinetic model of the reactions in series was developed, and the pre-exponential factor and activation energy were estimated from the measured data in experiments. The influence of dissolved oxygen concentration was also considered in this macro kinetic model. The results indicated that the two step reactions are all one-order to reactant (PMIDA or PMG) and 0.3 or 0.07 to O2 respectively. The active energy was 12.98kJ/mol for the first step reaction and 10.87kJ/mol for the second step reaction.


2013 ◽  
Vol 575-576 ◽  
pp. 81-86 ◽  
Author(s):  
Feng Ling Ma ◽  
Hui Min Qi ◽  
Ya Ping Zhu ◽  
Xiao Wen Ren ◽  
Fan Wang

The kinetics of the thermal cure and ceramization of preceramic prehydropolysilazane (PHPS) was investigated by thermogravimetric analysis (TGA) under nitrogen atmosphere. The results indicated that the gases captured during the thermal cure and ceramization process of PHPS, which had three main weight loss events. The corresponding kinetic parameters including activation energy, pre-exponential factor and empirical order of the thermal cure and ceramization stages were evaluated by using Ozawa and Kissinger metnods, respectively.


2016 ◽  
Vol 852 ◽  
pp. 315-322 ◽  
Author(s):  
Min Chen ◽  
Xuan Xiao ◽  
Xue Feng Zhang

The reduction kinetics of ilmenite was investigated. Phase evolution during the reduction process was identified by XRD and morphology change was observed using SEM. Kinetic parameters of the activation energy and pre-exponential factor were determined by Kissinger-Akahira-Sunose (KAS) method and Coast-Redfern method&artificial isokinetic relationship (IKP) respectively. Results showed that when the reaction of titanium suboxides makes a growing contribution, the conversion dependence of activation energy has an ascending trend. When the conversion exceeded 0.7, the reactants almost consumed, and the process was controlled by diffusion.


2022 ◽  
Author(s):  
Zixiang Cui ◽  
Yidi Xue ◽  
Yongqiang Xue ◽  
Mengying Wang ◽  
Jiaojiao Chen ◽  
...  

The desorption kinetic parameters (the desorption activation energy (Ed) and the desorption pre-exponential factor (A)) and the surface acidity (the strength and number of acid sites) of spherical and octahedral...


2014 ◽  
Vol 953-954 ◽  
pp. 230-234
Author(s):  
Dong Yu Chen ◽  
Yan Qing Hu

In order to find out the appropriate kinetic model for biomass pyrolysis, pyrolysis experiments of four samples (untreated biomass, HCl-washed, 3%KCl-treated and 10% KCl-treated) of sweet sorghum bagasse were performed by Thermogravimetry (TG) separately at different heating rates. The pyrolysis data was processed by the methods of Ozawa、Coats-Redfern integration and Achar-Brindley-Sharp differential, and the kinetic parameters were calculated. The results showed that the activation energy from deduced mechanism functions is more approach to the Ozawa’s than that from tentative mechanism functions, and the deduced mechanism functions can more realistically reflect the dynamic process four samples of sweet sorghum bagasse pyrolysis.


2011 ◽  
Vol 391-392 ◽  
pp. 1230-1234
Author(s):  
Pu Hong Wen

The thermal behavior and thermal decomposition kinetic parameters of podophyllic acid and picropodophyllic acid in a temperature-programmed mode have been investigated by means of DSC and TG-DTG. The kinetic model functions in differential and integral forms of the thermal decomposition reactions mentioned above for leading stage were established. The kinetic parameters of the apparent activation energy Ea and per-exponential factor A were obtained from analysis of the TG-DTG curves by integral and differential methods. The most probable kinetic model function of the decomposition reaction in differential form was 2/3•α-1/2 for podophyllic acid and 1/2• (1-α)-1 for picropodophyllic acid. The values of Ea indicated that the reactivity of picropodophyllic acid was highter than that of podophyllic acid in the thermal decomposition reaction. The values of the entropy of activation ΔS≠, enthalpy of activation ΔH≠ and free energy of activation ΔG≠ of the reactions were estimated.


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