Average Value Of Activation Energy Research Articles

Differential scanning calorimetric study of Ga 5Se 95 glass

Results of differential scanning calorimetry, at different heating rates, α, on Ga 5Se 95 glass are reported and discussed. From the heating rates dependence of values of T g and T p, the glass activation energy, E g and the crystallization activation energy, E c, are derived. The crystallization results are interpreted in terms of recent analyses developed for non-isothermal crystallization and also for the evaluation of E c. The crystallization mechanism is then characterized. From the obtained results, the glassy Ga 5Se 95 has two-dimensional growth, the average value of the order of crystallization mechanism, n is 3. The average value of the glass activation energy, E g and crystallization activation energy, E c, for Ga 5Se 95 glass are 189±4 and 69±5 kJ/mol, respectively.

Thermoluminescent response of LiF : Mg,Cu,P+PTFE prepared in Mexico to 90Sr/ 90Y beta particles

Results of study of the thermoluminescent response of LiF : Mg,Cu,P+PTFE irradiated with beta particles are presented and compared with results for LiF TLD-100. Both materials exhibited a linear dose response in the range from 4.35 mGy to 2.17519 Gy. The glow curve of LiF : Mg,Cu,P+PTFE exhibited four peaks while TLD-100 showed six. All the peaks studied for the two materials exhibited first order kinetics. The average values of activation energy were: 1.35, 1.58 and 2.51 eV for LiF : Mg,Cu,P+PTFE; and, 2.04, 2.24, 2.51 and 2.89 eV for LiF TLD-100.

Kinetics of oxychlorination of chromite: Part I. Effect of temperature

Nonisothermal thermogravimetric (TG) analysis was used to evaluate the reactivity of a chromite mineral [(Fe2+, Mg)(Cr, Al, Fe3+)2O4] towards Cl2+CO, Cl2+N2 and Cl2+O2 gaseous mixtures up to 1000°C. Full chlorination and volatilization of reaction products were achieved at about 975°C using Cl2+CO, while only about 40% of the sample have reacted at 1000°C using Cl2+N2 and Cl2+O2.The effect of the temperature on the oxychlorination with Cl2+O2 of the chromite mineral was studied between 600 and 1050°C using isothermal TG measurements. The results show that the oxychlorination of chromite occurs in two stages. The initial stage of the oxychlorination was characterized by average values of apparent activation energy of about 151 and 57kJ/mol for the temperatures lower and higher than 825°C, respectively. While a value of about 262kJ/mol was found for the second stage of the oxychlorination process between 925 and 1050°C. The effects of temperature on the oxychlorination of the simple chromite constituents (Cr2O3, Fe2O3 and MgO) were also studied.

CURING AND RHEOLOGICAL BEHAVIOR OF VINYL ESTER RESINS PREPARED IN THE PRESENCE OF TERTIARY AMINES

Vinyl ester resins V1, V2 & V3 of acid value (∼6 mg KOH g−1 solid) were synthesized using bisphenol-A epoxy and acrylic acid in the presence of triethyl-, tripropyl- and tributyl-, amines in 210, 270 and 340 minutes, respectively. The synthesized resins were characterized by FTIR spectroscopy and a new peak at 2360 cm−1 was observed which is due to attachment of amines to resin structure by hydrogen bond. The curing behavior of synthesized resin containing 40% styrene (w/w) and 2% benzoyl peroxide was studied using DSC technique and found to be affected by presence of amines. Activation energy and frequency factor for the curing reaction increases from 14 Kcal mol−1 to 23 Kcal mol−1. Rheological behavior of resins containing 40% styrene was studied using a Haake Rotovisco RV20 viscometer, and viscosity was found to increase with shear rate up to 200 sec−1. The average values of activation energy at constant shear stress (6-15 Pa) were 12.94, 13.20, 13.70 Kcal mol−1 for V1, V2 and V3, respectively. The activation energy at constant shear rate decreases with an increase in the shear rate.

Isothermal DTA study on crystallization of mica composition-based glass

Isothermal differential thermal analysis (DTA) was used to study the crystallization of a glass with a composition close to that of mica (NaMg 3AlSi 3O 10F 2), with TiO 2 added as a nucleating agent. Two distinct crystallization exotherms in DTA were attributed to the formation of MgTi 2O 5 followed by NaMg 3AlSi 3O 10F 2. By using the Johnson-Mehl-Avrami equation, the activation energy for precipitation of each crystalline phase was evaluated and the crystallization mechanism was analyzed. Results indicate that NaMg 3AlSi 3O 10F 2 growth is a two-dimensional process, controlled by the crystal-glass interface reaction. The average value of activation energy is 256 ± 11 kJ/mol and 275 ± 7 kJ/mol corresponding to MgTi 2O 5 and mica, respectively.

Rheological and thermal behaviour of vinyl ester resin

The rheological behaviour of synthesized vinyl ester resin (VER) based on epoxy novolaks containing methyl, ethyl and butyl acrylates as reactive diluent (40% w/w) was studied using a Haake Rotovisco RV 20 viscometer. The zero-shear viscosity of VER containing acrylates decreases linearly with temperature and increases with the size of the alkyl substituent in the acrylate. The average values of activation energy for flow at constant shear stress (25–100 Pa) were 11.79, 13.29 and 14.75 kcal/mol for VER containing methyl, ethyl and butyl acrylates, respectively. The activation energy at constant shear rate decreases with increase in the shear rate (50–400 sec −1). The curing and decomposition behaviour of the resin containing acrylates as reactive diluent (40% w/w) and benzoyl peroxide (2 phr) as initiator were studied by DSC and TGA. The activation energy for the curing reaction calculated by the Ozawa method, was found to be minimum whereas the thermal stability and the activation energy for the decomposition reaction calculated by the Coats and Redfern method were found to be maximum, for the resin with ethyl acrylate as reactive diluent.

Effect of Frequency and Temperature on Dielectric Properties of Polypropylene at X-Band Microwave Region

Dielectric behaviour of large-molecular weight, high density, sol vent insoluble, isotactic samples of polypropylene have been studied in the X-band microwave region as a function of frequency (8.4-10.835 GHz) at ambi ent temperature (30 ° C) and as a function of temperature ( —120 ° C to 160 ° C) at three different frequencies by the method of Smith and von Hippel as modified by Dakin and Works. The sample exhibits two types of dispersion/relaxation in the semilog frequency plots of ∈' and ∈". The lower frequency dispersion is asso ciated with the crystalline region of the polymer while the higher frequency dispersion is related to the amorphous region of the polymer. Percent relative dispersions and relaxation magnitudes are found to be small. The values of "a" factors corresponding to the two loss peaks are 0.023 and 0.031, respectively. The most probable relaxation times for the two relaxation processes have also been calculated. Three types of dispersions namely β, γ 1, and γ2 have been observed in the ∈" vs. temperature plots at three different frequencies. The av erage apparent energy of a polypropylene molecule associated with its induced dipoles has also been calculated. The average values of the intrinsic activation energy, ΔE', decreases with increase of frequency, changing from 2.764 to 0.886 kcal/mol in the specific frequency region used.

Evaluation of the kinetic parameters of CaF2:Tm (TLD-300) thermoluminescence dosemeters

The kinetic parameters of the first, third and fifth peaks of CaF2:Tm (TLD-300) dosemeters were determined experimentally using methods based on initial rise, peak shape, different heating rates, isothermal decay and numerical fitting method and a comparison was made between the results obtained. The average activation energy values determined by the methods used here were 0.72, 1.16 and 1.77 eV, with mean values for the frequency factor of 2.58*108, 2.89*1013 and 6.16*1016 s-1 for the first, third and fifth peaks respectively. The values of activation energy obtained for each peak using the different methods covered a spread of about 4%. However, the spread for each of the frequency factors was very high.

Glow curve kinetics of self-made CaSO 4:Dy + PTFE thermoluminescent dosimeters

In this paper we present results of various experiments performed to obtain the kinetics parameters for CaSO 4:Dy TL dosimeters which were fabricated by the Instituto Nacional de Investigaciones Nucleares (ININ). Kinetics parameters were evaluated by two methods: the glow curve shape method and the isothermal decay method. The average activation energy value determined by the glow curve shape Method was 0.88. The isothermal decay method shows the activation energy having the value 0.87. The kinetics order was 2.01 and 2.03, respectively. These results are in good agreement among them.

Glucosidases and galactosidases in soils

An improved method to assay activities of α- and β-glucosidases and α- and β-galactosidases in soils is described. It involves extraction and colorimetric determination of the p-nitrophenol released when 1 g of soil is incubated with 5 ml of buffered p-nitrophenyl glycoside solution at 37°C for 1 h. The reagents [0.5 M CaCl 2 and 0.1 M Tris (hydroxymethyl)aminomethan THAM, pH 12] used for extraction of the p-nitrophenol released give quantitative recovery of p-nitrophenol added to soils and do not cause chemical hydrolysis of the substrates. Results showed that these enzymes have their optimum activities at buffer pH 6.0. The initial rates of p-nitrophenol release obeyed zero-order kinetics. β-Glucosidase activity was the most predominant of the four enzymes. The temperature dependence of the rate constant conformed to the Arrhenius equation up to the point of enzyme inactivation (60°C for α- and β-galactosidases and α-glucosidase and 70°C for β-glucosidase). The average activation energy values of these enzymes in three soils were 43.1, 30.8, 57.0 and 32.6 kJmol −1 for α-glucosidase, β-glucosidase, α-galactosidase and β-galactosidase activities, respectively. By using the Lineweaver-Burk plot. the K m values were the lowest for β-glucosidase activity. The V max values varied among the four enzymes and soils studied.

The analysis of the activation energies for self-made TLD-CaSo4:Dy

Abstract In this paper we study the activation energy for TLD-CaSO4:Dy which was fabricated by the Institute of Nuclear Energy Research. Two different methods have been used to determine the activation energy. The methods used were (1) the glow curve shape analysis method which contain four different equations, and (2) the variable heating rate method. The average activation energy values determined by glow curve shape analysis method are about 0.87 eV. The variable heating rate method shows the activation energy having a value of 1.19 eV. The symmetry factor, μ, is 0.52 and the kinetic order is 1.88. The results are compared with those obtained by other authors.

Determination of kinetic parameters for the thermal decomposition of phenolic ablative materials by a multiple heating rate method

The rate of decomposition for two widely used glass- and asbestos-phenolic ablative materials were measured using standard thermogravimetric techniques. Thermograms were obtained at six heating rates ranging from 10°C min −1 to 160°C min −1. From these data the kinetic parameters were determined by a slightly modified version of Friedman's method. Fractional weight loss calculated using the derived kinetic parameters over the temperature range of decomposition agreed with measured values with a mean error of 0.33 and 0.28%, with a standard deviation of errors 0.58 and 0.84% for glass- and asbestos-phenolic, respectively. The 95% confidence for the mean error was 0.22 and 0.44% for the glass-phenolic and 0.14 and 0.42% for the asbestos-phenolic. Also, the activation energy was calculated by the method of Flynn and Wall. The average activation energy values determined by the two methods agreed within 4.6% for both materials.