scholarly journals Crystallization Kinetics of α-Hemihydrate Gypsum Prepared by Hydrothermal Method in Atmospheric Salt Solution Medium

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 843
Author(s):  
Zhongqi Wei ◽  
Qin Zhang ◽  
Xianbo Li
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Hydrothermal Method ◽  
Crystallization Kinetics ◽  
Calcium Sulfate ◽  
Control Process ◽  
Effect Of Temperature ◽  
Model Calculations ◽  
Crystallization Curve ◽  
Kinetics Of

α-Calcium sulfate hemihydrate (α-HH) is an important cementitious material, which can be prepared by hydrothermal method from calcium sulfate dihydrate (DH) in an electrolyte solution. Study of the conversion kinetics of DH to α-HH in NaCl solution is helpful for understanding the control process. In this paper, X-ray diffraction (XRD) patterns were applied to study the effect of temperature on the crystallization kinetics of α-HH to determine the kinetic parameters. The research results show that the sigmoidal shape of the α-HH crystallization curve follows the Avrami-Erofeev model, which describes the crystallization kinetics of α-HH formation. Applying Arrhenius law in experimental data and model calculations, an apparent activation energy of 124 kJ/mol for nucleation and an apparent activation energy of 810 kJ/mol for growth were obtained. By adjusting the temperature of the solution, the number of α-HH nucleation and growth steps increases, which can effectively increase the DH-α-HH conversion rate in the NaCI solution.

Morphology, Crystalline Structure and Isothermal Crystallization Kinetics of Polybutylene Terephthalate/Montmorillonite Nanocomposites

2005 ◽  
Vol 13 (1) ◽  
pp. 61-71 ◽  
Author(s):  
Defeng Wu ◽  
Chixing Zhou ◽  
Xie Fan ◽  
Dalian Mao ◽  
Zhang Bian
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
Crystallization Temperature ◽  
Isothermal Crystallization ◽  
Polymer Chains ◽  
Isothermal Crystallization Kinetics ◽  
Clay Particles ◽  
Nucleation Sites ◽  
Kinetics Of ◽  
Montmorillonite Nanocomposites

The melt intercalation method was employed to prepare poly(butylene terepathalate)/montmorillonite nanocomposites, and their microstructure was characterized by wide angle X-ray diffraction and transmission electron microscopy. The XRD results showed that the crystalline plane such as (010), (111), (100) was smaller than that of pristine PBT, which indicates that the crystallite size of PBT in the nanocomposites could be diminished by adding clay. Moreover, the isothermal crystallization kinetics of PBT and PBT/MMT nanocomposites was investigated by differential scanning calorimetry (DSC). During isothermal crystallization, the development of crystallinity with time was analysed by the Avrami equation. The results show that very small amounts of clay dramatically increased the rate of crystallization and high clay concentrations reduced the rate of crystallization at the low crystallization temperatures. At low concentrations of clay, the distance between dispersed platelets was large so it was relatively easy for the additional nucleation sites to incorporate surrounding polymer, and the crystal nucleus was formatted easily. However, at high concentrations of clay, the diffusion of polymer chains to the growing crystallites was hindered by large clay particles, despite the formation of additional nucleation sites by the clay layers. At the higher crystallization temperature, the crystallization of the nanocomposites was slower than that of the pure PBT under the experimental conditions, which means that with the increase in chains mobility at the high crystallization temperature, the crystal nuclei are harder to format, and the hindering effect of clay particles on the polymer chains was stronger than the nucleating effect of the layers. In addition, the activation energies of crystallization for PBT and its nanocomposites were calculated by the Arrhenius relationship, and the results showed that the nanocomposites with a low clay content had the lower activation energy values than PBT, while high amounts of clay increased the activation energy of PBT.

THE KINETICS OF CUPRENE GROWTH

1950 ◽  
Vol 28b (7) ◽  
pp. 358-372
Author(s):  
Cyrias Ouellet ◽  
Adrien E. Léger
Keyword(s):  
Nitric Oxide ◽  
Activation Energy ◽  
Carbon Monoxide ◽  
Apparent Activation Energy ◽  
Copper Catalyst ◽  
Maximum Velocity ◽  
Static System ◽  
Reaction Velocity ◽  
First Order ◽  
Kinetics Of

The kinetics of the polymerization of acetylene to cuprene on a copper catalyst between 200° and 300 °C. have been studied manometrically in a static system. The maximum velocity of the autocatalytic reaction shows a first-order dependence upon acetylene pressure. The reaction is retarded in the presence of small amounts of oxygen but accelerated by preoxidation of the catalyst. The apparent activation energy, of about 10 kcal. per mole for cuprene growth between 210° and 280 °C., changes to about 40 kcal. per mole above 280 °C. at which temperature a second reaction seems to set in. Hydrogen, carbon monoxide, or nitric oxide has no effect on the reaction velocity. Series of five successive seedings have been obtained with cuprene originally grown on cuprite, and show an effect of aging of the cuprene.

Non-Isothermal Crystallization Kinetics of Mg61Zn35Ca4 Glassy Alloy

2017 ◽  
Vol 898 ◽  
pp. 657-665
Author(s):  
Dao Zhang ◽  
Wang Shu Lu ◽  
Xiao Yan Wang ◽  
Sen Yang
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
Isothermal Crystallization ◽  
Melt Spinning ◽  
Glassy Alloy ◽  
Heating Rates ◽  
Isothermal Crystallization Kinetics ◽  
Complex Process ◽  
Activation Energy Of Crystallization ◽  
Kinetics Of

The non-isothermal crystallization kinetics of Mg61Zn35Ca4 glassy alloy prepared via melt-spinning were studied by using isoconversion method. The crystalline characterization of Mg61Zn35Ca4 was examined by X-ray diffraction. Different scanning calorimeter was used to investigate the non-isothermal crystallization kinetics at different heating rates (3-60 K/min). The calculated value of Avrami exponent obtained by Matusita method indicated that the crystalline transformation for Mg61Zn35Ca4 is a complex process of nucleation and growth. The Kissinger-Akahira-Sunose method was used to investigate the activation energy. The activation energy of crystallization varies with the extent of crystallization and hence with temperature. The Sestak-Berggren model was used to describe the non-isothermal crystallization kinetics.

scholarly journals Kinetics of carbothermic reduction of synthetic chromite

2014 ◽  
Vol 50 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Y. Wang ◽  
L. Wang ◽  
J. Yu ◽  
K.C. Chou
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Reduction Process ◽  
X Ray Diffraction ◽  
X Ray ◽  
Chromite Ore ◽  
Current Reduction ◽  
Increasing Temperature ◽  
Isothermal Mode ◽  
Kinetics Of

In order to optimize the current reduction process of chromite, a good knowledge of reduction mechanism involved is required. The basic component in chromite ore is FeCr2O4, thus, kinetic investigation of synthetic FeCr2O4 with different amount of carbon were carried out in the temperature range of 1473K to 1673K under both isothermal and non-isothermal mode. The iron can be easily reduced compared with chromium. And higher reduction degree of chromite can be achieved by increasing temperature and carbon content. With the supporting of X-ray Diffraction and Scanning Electron Microscope methods, the formation of metallic products followed the sequence: Fe-C alloy, (Fe,Cr)7C3and Fe-Cr-C alloy. Kinetics analysis showed that the first stage was controlled by nucleation with an apparent activation energy of 120kJ/mol, while the chromium reduction was controlled by crystallochemical transformation with an apparent activation energy of 288kJ/mol.

Kinetics of the addition of acids to olefins with and without boron fluoride catalysis

1967 ◽  
Vol 45 (1) ◽  
pp. 11-16 ◽  
Author(s):  
G. A. Latrèmouille ◽  
A. M. Eastham
Keyword(s):  
Activation Energy ◽  
Acetic Acid ◽  
Apparent Activation Energy ◽  
Trifluoroacetic Acid ◽  
Similar Rate ◽  
Ethylene Dichloride ◽  
Kcal Mole ◽  
Rate Law ◽  
Boron Fluoride ◽  
Kinetics Of

Isobutene reacts readily with excess trifluoroacetic acid in ethylene dichloride solution at ordinary temperatures to give t-butyl trifluoroacetate. The rate of the reaction is given, within the range of the experiments, by the expression d[ester]/dt = k[acid]2[olefin], and the apparent activation energy is about 6 kcal/mole. The rate of addition is markedly dependent on the strength of the reacting acid and is drastically reduced in the presence of mildly basic materials, such as dioxane. The boron fluoride catalyzed addition of acetic acid to 2-butene can be considered to follow a similar rate law, i.e. d[ester]/dt = k[acid·BF3]2[olefin], but only if some assumptions are made about the position of the equilibrium [Formula: see text]since only the 1:1 complex is reactive.

Characteristics and thermal decomposition kinetics of wood-SiO2 composites derived by the sol-gel process

Holzforschung ◽  
2017 ◽  
Vol 71 (3) ◽  
pp. 233-240 ◽  
Author(s):  
Ke-Chang Hung ◽  
Jyh-Horng Wu
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Apparent Activation Energy ◽  
Sol Gel ◽  
Weight Percent Gain ◽  
Weight Percent ◽  
Decomposition Kinetics ◽  
Thermal Decomposition Kinetics ◽  
Sol Gel Process ◽  
Kinetics Of

Abstract Wood-SiO2 composites (WSiO2Cs) were prepared by means of the sol-gel process with methyltrimethoxysilane (MTMOS) as a reagent, and the physical properties, structure and thermal decomposition kinetics of the composites has been evaluated. The dimensional stability of the WSiO2Cs was better than that of unmodified wood, especially in terms of the weight percent gain (WPG), which achieved values up to 30%. The 29Si-NMR spectra show two different siloxane peaks (T2 and T3), which supports the theory about the formation of MTMOS network structures. Thermal decomposition experiments were also carried out in a TG analyzer under a nitrogen atmosphere. The apparent activation energy was determined according to the iso-conversional methods of Friedman, Flynn-Wall-Ozawa, modified Coats-Redfern, and Starink. The apparent activation energy between 10 and 70% conversion is 147–172, 170–291, 189–251, and 192–248 kJ mol−1 for wood and WSiO2Cs with WPGs of 10, 20, and 30%, respectively. However, the reaction order between 10 and 70% conversion calculated by the Avrami theory was 0.50–0.56, 0.35–0.45, 0.33–0.44, and 0.28–0.48. These results indicate that the dimensional and thermal stability of the wood could be effectively enhanced by MTMOS treatment.

Catalytic Oxidation of 4,4'-Dibromobiphenyl in Sub-Critical Water with Mn0.9-Co0.1-Ce-Oxide

2011 ◽  
Vol 282-283 ◽  
pp. 13-16
Author(s):  
Jin Yang Chen ◽  
Ru Yi Ruan ◽  
Zhi Li
Keyword(s):  
Activation Energy ◽  
Reaction Time ◽  
Apparent Activation Energy ◽  
Hydrothermal Method ◽  
Subcritical Water ◽  
Degradation Kinetics ◽  
Removal Rate ◽  
Oxidative Degradation ◽  
Cod Removal Rate ◽  
Co Precipitation

A complex mental oxide Mn0.9-Co0.1-Ce-oxide was prepared by co-precipitation-hydrothermal method and it was used as catalyst to oxidative degradation of 4,4- dibromobiphenyl (4,4’-DBB) in subcritical water. The optimization conditions is obtained as follows: 5% Mn0.9-Co0.1-Ce-oxidecatalyst, m(H2O2):m(4,4’-DBB)=200:1,temperature of 613K, reaction time of 20 minutes, and COD removal rate is more than 99 %. In the temperature range of 603–633 K, the degradation kinetics is studied and apparent activation energy is 35.92 and 46.69 kJ/mol for no catalyst and 5% Mn0.9-Co0.1-Ce-oxide, respectively.

Effect of Temperature on the Electrode Kinetics of Totally Irreversible and Quasi-Reversible Polarographic Reductions

1977 ◽  
Vol 32 (4) ◽  
pp. 416-419 ◽  
Author(s):  
Sudhindra Swarup Sharma ◽  
S. K. Jha ◽  
Mukhtar Singh
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Effect Of Temperature ◽  
Electrode Kinetics ◽  
Polarographic Behaviour ◽  
Kinetics Of ◽  
Reversible Reduction

The polarographic behaviour of Ni(II), Co(II), Zn(II) and Mn(II) has been studied in 0.1 M KNO3. The temperature span studied varies from 15 to 55 °C. The reduction of Ni(II) and Co(II) has been found to be totally irreversible and that of Zn(II) and Mn(II) quasi-reversible over the temperature span studied. The kinetic parameters, kf,h0 and ana for the totally irreversible reductions have been calculated by KOUTECKY’S treatment while for quasi-reversible reduction the kinetic parameters (a and ks,h) have been evaluated by GELLINGS’ method. The activation energy of the totally irreversible reductions has also been determined. The effect of temperature has been discussed in terms of the variations in the values of the kinetic parameters.

Nitridation Isothermal Kinetics of In Situ β-Sialon Bonded Al2O3-C Refractories

2016 ◽  
Vol 697 ◽  
pp. 572-575
Author(s):  
Xue Qing Yang ◽  
Nai Peng ◽  
Cheng Ji Deng
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Isothermal Kinetics ◽  
Nitridation Reaction ◽  
Result Show ◽  
Different Temperatures ◽  
Two Stages ◽  
Kinetics Of ◽  
And Diffusion

The kinetics of in-situ β- Sialon bonded Al2O3-C (SAC) refractories were investigated by TGA techniques via isothermal nitridation experiments at different temperatures. The result show that the nitridation process of in-situ β-Sialon bonded Al2O3-C refractories can be divided into two stages: the nitridation reaction rate controlling stage in the first 10 min, and the apparent activation energy of nitridation reaction is 370 kJ/mol ; then the reaction is controlled by both chemical reaction and diffusion rate in the following 110 min, the apparent activation energy of nitridation reaction is 410 kJ/mol.

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