Average Value Of Activation Energy Research Articles

Modeling the Flow Curve Characteristics of 410 Martensitic Stainless Steel Under Hot Working Condition

The hot deformation behavior of AISI 410 martensitic stainless steel was investigated by conducting hot compression tests between 1173 K (900 °C) and 1423 K (1150 °C) and between strain rates of 0.001 s−1 to 1 s−1. The hyperbolic sine function described the relation well between flow stress at a given strain and the Zener–Hollomon parameter (Z). The variation of flow stress with deformation temperature gave the average value of apparent activation energy as 448 kJ/mol. The strain and stress corresponding to two important points associated with flow curve (i.e., peak strain and the onset of steady-state flow) were related to the Z parameter using power-law equations. A model also was proposed based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation to estimate the fractional softening of dynamic recrystallization at any given strain. This model can be used readily for the prediction of flow stress. The values of n and k, material constants in the JMAK equation, were determined for the studied material. The strains regarding the peak and the onset of steady-state flow were formulated in term of applied strain rate and the constants of the JMAK equation. A good agreement was found between the predicted strains and those obtained by the experimental work.

Non-isothermal phase transformation kinetics of ω phase in TB-13 titanium alloys

The ω phase transformation kinetics of TB-13 titanium alloy has been analyzed by non-isothermal dilatometry. The average value of local activation energy determined is about 91.7 kJ/mol. The nucleation and growth mechanism of the ω phase has been investigated by the non-isothermal local Avrami exponent. Both the local Avrami exponent and the local activation energy during the ω phase transformation process change significantly with the transformed volume fraction, indicating that the ω phase transformation mechanism in this alloy varies at different stages. The local Avrami exponent lies between 1 and 2 in a wide transformed volume fraction range of 0.17–0.95, indicating that the dominating mechanism of ω phase transformation in TB-13 titanium alloy is the three-dimensional growth with a near-zero nucleation rate.

Kinetics of dehydrogenation in Ti600, TC21 and Ti40 alloys

Abstract The dehydrogenation kinetics of Ti600, TC21 and Ti40 alloys has been studied using a tubular thermohydrogen processing furnace and simultaneous DTA-TG apparatus. The results show that the initial dehydrogenation temperatures in Ti600, TC21 and Ti40 alloys were 580 °C, 600 °C and 540 °C, respectively. At the initial stage of dehydrogenation, the passive layer on the alloy surface was the barrier to enhance the diffusion activation energy. Therefore, activation energy decreased with the increase of reacted fraction. At the initial stage, values of activation energy for the three alloys were 255 kJ/mol, 322 kJ/mol and 177 kJ/mol, respectively. After incubation period, the dehydrogenation average values of activation energy were 200 ± 5 kJ/mol, 240 ± 5 kJ/mol and 155 ± 5 kJ/mol, respectively.

Crystallization Kinetics and Electrical Relaxation of BaO-0.5Li2O-4.5B2O3Glasses

Transparent glasses in the composition BaO-0.5Li(2)O-4.5B(2)O(3) (BLBO) were fabricated via the conventional melt-quenching technique. X-ray powder diffraction combined with differential scanning calorimetric (DSC) studies carried out on the as-quenched samples confirmed their amorphous and glassy nature, respectively. The crystallization behavior of these glasses has been studied by isothermal and nonisothermal methods using DSC. Crystallization kinetic parameters were evaluated from the Johnson-Mehl-Avrami equation. The value of the Avrami exponent (n) was found to be 3.6 +/- 0.1, suggesting that the process involves three-dimensional bulk crystallization. The average value of activation energy associated with the crystallization of BLBO glasses was 317 +/- 10 kJ/mol. Transparent glass-ceramics were fabricated by controlled heat-treatment of the as-quenched glasses at 845 K/40 min. The dielectric constants for BLBO glasses and glass-ceramics in the 100 Hz-10 MHz frequency range were measured as a function of the temperature (300-925 K). The electrical relaxation and dc conductivity characteristics were rationalized using electric modulus formalism. The imaginary part of the electric modulus spectra was modeled using an approximate solution of the Kohlrausch-Williams-Watts relation. The temperature-dependent behavior of stretched exponent (beta) was discussed for the as-quenched and heat-treated BLBO glasses.

Kinetic studies of the partial oxidation of gasoline (POXG) over a Ni– [formula omitted] catalyst in a fixed-bed flow reactor

The kinetics of the partial oxidation (POX) reforming of gasoline was studied over a Ni– CeO 2 catalyst as a function of gasoline and oxygen molar flow rates as well as reaction temperature in a tubular fixed-bed reactor. The kinetic experimental runs were conducted at atmospheric pressure, a temperature range of 673–1023 K, gas hourly space velocity (GHSV) in the range of 160,000 and 940,000 h - 1 , and oxygen/carbon ratio in the range of 0.25–1.0. The reaction mechanisms were developed and modeled using the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) formulations. Out of the 18 models developed and tested one model based on the LHHW formulation was adopted after evaluating the average absolute deviation and activation energy values and compared to values obtained with the empirical power law model. The best model to describe the reforming process under the given conditions was a dual-site LHHW model involving the dissociative adsorption of gasoline ( C 8.27 H 15.10 ) and oxygen ( O 2 ) followed by bimolecular surface reaction as the rate-determining step.

Crystallization kinetics in As–Se–Sn glassy system

The crystallization kinetics of As30Se70−xSnx chalcogenide glasses where x=0, 1, 2 and 3 have been discussed under non-isothermal conditions by differential thermal analysis (DTA). From the heating rate dependence of the glass transition temperature (Tg) and the crystallization temperature (Tc), the values of the activation energy of glass transition (Eg) and activation energy of crystallization (Ec) are evaluated. Most of the above mentioned glassy compounds have three-dimensional growth mechanism, according to the average value of Avrami index (n). The calculated average values of activation energies of crystallization have been used for the estimation of the thermal stability as well as the glass-forming tendency.

<b>Inhibition of the corrosion of mild steel in hydrochloric acid by isatin and isatin glycine</b>

The inhibition of corrosion of mild steel in hydrochloric acid by isatin glycine (ING) and isatin (IN) at 30-60 oC and concentrations of 0.0001 M to 0.0005 M was studied via weight loss method. At the highest inhibitor concentration studied ING exhibited inhibition efficiency of 87% while IN exhibited 84% at 60 oC. A chemical adsorption mechanism was proposed on the basis of the temperature effect and obtained average activation energy values of 143.9 kJ/mol for ING and 118.5 kJ/mol for IN. The two inhibitors were confirmed to obey the Langmuir adsorption isotherm equation at the concentrations studied. Also a first-order type of mechanism was proposed from the kinetic treatment of the result. The difference in the inhibitory properties of the inhibitors was explained in terms of the difference in their molecular structures and solubility rather than difference in molecular weights alone.KEY WORDS: Corrosion, Inhibition of corrosion, Mild steel, Isatin glycine, Isatin, AdsorptionBull. Chem. Soc. Ethiop. 2006, 20(2), 253-258.

Curing Behavior of Epoxy Resin Using Controllable Curing Agents Based on Nickel Complexes

AbstractSummary: The curing reaction kinetics and mechanism of the diglycidyl ether of bisphenol A (DGEBA) with three complexes of Ni(II) with diethylentriamine (Dien), Pyrazole (Pz) and Pyridine (Py) as ligands have been studied using differential scanning calorimetry (DSC). The curing reaction was characterized by high cure onset and peak maximum temperatures. The kinetics of the curing reaction were evaluated using the Ozawa method. The average values of activation energy for the three nickel complexes increased in the order: Dien‐based curing agent > Pz‐based curing agent > Py‐based curing agent. Three main curing mechanisms (catalytic, complex cation and free ligand polymerization path) have been proposed depending on the cure temperature. It was also shown that the cure kinetics of DGEBA with Dien‐ and Py‐based complexes could be described by the Sestak‐Berggren equation. The water absorption, chemical resistance and thermal stability of the thermosets were also studied. The results showed that the thermoset obtained with the Py‐based complex was more thermally stable than those obtained with the other two curing agents.Activation energy versus conversion plots for the epoxy systems studied.imageActivation energy versus conversion plots for the epoxy systems studied.

Thermal stability of soy-based polyurethanes

New types of polyurethanes were prepared by reacting diisocyanates and formiated soy polyols with different OH functionalities. Thermal properties and degradation kinetics were investigated by TGA. All prepared PU's showed at least two-weight loss steps, the first one, around 210 °C. Thermal stability of these PUs depends strongly on urethane groups per unit volume and an increase in the weight loss was observed as a result of the increased amount of urethane groups. Degradation kinetics behavior of the soy-based polyurethanes was investigated according to the Flynn method. Different average activation energy values were obtained from isothermal and isoconversional curves, 140.6 KJ/mol and 62.8 KJ/mol, respectively, indicating the complexity of the PUs degradation process.

Grafting of Vinyl Monomers onto Sodium Salt of Partially Carboxymethylated Guar Gum: Comparison of Their Reactivity

: The optimum reaction conditions for affording maximum percentage of grafting have been established in the case of grafting of acrylonitrile (AN), methyl acrylate (MA), methyl methacrylate (MMA), and ethyl methacrylate (EMA) onto sodium salt of partially carboxymethylated guar gum (Na-PCMGG, ) using ceric ammonium nitrate (CAN) as a redox initiator in an aqueous medium by using different reaction parameters. Under the optimized reaction conditions, the following reactivity order of monomers was observed: AN > MA > MMA > EMA. The plausible explanation for this observed order of reactivity has been furnished. The thermal behavior of different graft copolymers of Na-PCMGG () has been studied at four different heating rates by thermogravimetric analysis (TGA) and the results obtained have been analyzed by employing Osawa as well as Freeman-Carroll (multiple heating rate) methods for the evaluation of activation energy (E). The values of E calculated at various constant conversions as well as the average activation energy values (for both the steps of thermal degradation) calculated according to Osawa as well as Freeman-Carroll methods, for all the four different graft copolymers of Na-PCMGG (), have been found to be in good agreement with each other. The evidence of grafting has been ascertained by spectral (IR/1H-NMR) and scanning electron microscopic (SEM) methods.

Calorimetric and thermal decomposition kinetic study of Tb(Tyr)(Gly)3Cl3�3H2O

The solid-state ternary complex of terbium chloride with L-tyrosine and glycine, [Tb(Tyr)(Gly)3Cl3·3H2O], was synthesized and characterized. Using a solution-reaction isoperibol calorimeter, the enthalpy of reaction for the following reaction, TbCl3·6H2O(s)+Tyr(s)+3Gly(s)=Tb(Tyr)(Gly)3Cl3·3H2O(s)+3H2O(l), was determined to be (5.1±0.6) kJ mol-1. The standard enthalpy of formation of Tb(Tyr)(Gly)3Cl3-3H2O at T=298.15 K has been derived as -(4267.3±2.3) kJ mol-1. The thermal decomposition kinetics of the complex was studied by non-isothermal thermogravimetry in the temperature range of 325-675 K. Two main mass loss stages existed in the process of the decomposition of the complex, the kinetic parameters for the second stage were analyzed by means of differential and integral methods, respectively. Comparing the results of differential and integral methods, mechanism functions of the thermal decomposition reaction for its second stage were proposed. The kinetic equation can be expressed as: dα/dt=Aexp(-E/RT)(1-α)2. The average values of the apparent activation energy E and pre-exponential factor A were 213.18 kJ mol-1 and 2.51·1020 s-1, respectively.

Phase transformations of some poly(vinyl alcohol)–NiCl2 composites

AbstractSamples of poly(vinyl alcohol)–NiCl2 composites containing up to 30 wt% NiCl2 were prepared by casting in order to study phase transformation–structural change relationships of these samples before and after heat treatment. Differential thermal analysis (DTA) thermograms were recorded at 10, 15, 20 and 30 °C min−1. For untreated samples four endotherms were assigned as: rotation of hydroxyl groups in the glassy state, glass transition, structural transition in the rubber‐like state, and melting transition. Ultrasonic attenuation measurements were carried out to confirm these transitions in the glassy and rubber‐like states. In the glassy state, the effect of NiCl2 addition is explained in terms of chain stiffness due to the creation of local crosslinked regions in amorphous parts of the polymer. Average values of activation energies for glass transition were calculated using both methods of Kissinger and Ozawa. However, addition of NiCl2 had an opposite effect on the heating rate independent crystallization melting temperature (Tm), relative to that on Tg. The DTA thermograms of heat‐treated samples indicated that square planar NiCl2 molecules were embedded in the polymer matrix with no local crosslinking role due to the formation of conjugated polyenes along the polymer chains by thermal treatment. Copyright © 2003 Society of Chemical Industry

Kinetics of carbothermic reduction of magnesia and zinc oxide by thermogravimetric analysis technique

The rates of carbothermic reduction of magnesia and zinc oxide have been investigated using a thermogravimetric analysis technique under argon and CO atmospheres. The experimental results show that zinc oxide can react with carbonaceous materials more easily than magnesia. Both magnesia and zinc oxide can be reduced by charcoal at a lower temperature than by graphite. The carbothermic reduction of magnesia starts at a higher temperature in CO atmosphere than in Ar atmosphere. A kinetic model was developed to analyze the experimental results. The average activation energy value of carbothermic reduction by charcoal calculated from the data of non‐isothermal experiments is 210 kJ/mol for magnesia and 222 kJ/mol for zinc oxide, respectively.

One‐Step Synthesis of Hybrid Composites of Poly(6‐hexanelactam) Combining Solid Tribological Additives and Reinforcing Components

AbstractFour types of composites of polyamide 6 with hybrid tribological additives were synthesized via anionic adiabatic “in situ” polymerization of 6‐hexanelactam (ε‐caprolactam) initiated with metallic sodium and activated with cyclic trimer of phenyl isocyanate or diphenylmethane 4,4′‐diisocyanate. The optimization of the initiator/activator systems in the range of 0.3 to 1.2 mol‐% and of the initial polymerization temperatures from 125 to 150 °C preceded the composite preparation. Combinations of fillers and their maximum applied concentrations (in wt.‐%) were the following: MoS2/graphite/oil (5/16/9), carbon fibers/graphite/oil (5/20/10), copper phthalocyanine (7), and B2O3 (11). Analysis of selected composites encompassed water extraction, DSC, and DMTA measurements. All tested fillers decreased the polymerization rate, polymer yield, melting temperature and crystalline fraction. Polymerization rate constants of the neat polyamide 6 obtained for various initial temperatures obeyed the Arrhenius plot giving an average activation energy value of 78.6 kJ · mol−1.Rate of polymerization as a function of the total fillers content in adiabatic anionic polymerization of 6‐hexanelactam (A: MoS2 + G/O, Na/PIC, B: CPC, Na/MDI, C: MoS2 + G/O, Na/MDI, D: CF + G/O Na/MDI).magnified imageRate of polymerization as a function of the total fillers content in adiabatic anionic polymerization of 6‐hexanelactam (A: MoS2 + G/O, Na/PIC, B: CPC, Na/MDI, C: MoS2 + G/O, Na/MDI, D: CF + G/O Na/MDI).

Crystallization kinetics of an amorphous Zr–Cu–Ni alloy: calculation of the activation energy

The activation energies of amorphous Zr–Cu–Ni alloy under continuous heating conditions have been calculated using different methods based on differential scanning calorimetry (DSC) data. The activation energy for crystallization of amorphous Zr 70Cu 20Ni 10 alloy are determined as 313, 411, 293, 253 and 286 kJ/mol by means of the Kissinger, Ozawa, Cheng, Gao and Wang and Matusita equations, respectively. However, under isothermal crystallization the average value of activation energy of amorphous Zr 70Cu 20Ni 10 alloy is 355 kJ/mol. As for the amorphous Zr 70Cu 20Ni 10 alloy, the Ozawa equation gives the largest value of activation energy and the Gao and Wang equation shows the smallest one. The difference in the activation energy for crystallization of an amorphous alloy may be attributed to the different approximations in these models.

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.