Non-isothermal kinetics of spin crossover

2017 ◽  
Vol 19 (26) ◽  
pp. 16955-16959 ◽  
Author(s):  
Mark B. Bushuev ◽  
Elena B. Nikolaenkova ◽  
Viktor P. Krivopalov
Keyword(s):  
Activation Energy ◽  
Spin Crossover ◽  
Spin Transition ◽  
Isothermal Kinetics ◽  
Magnetic Studies ◽  
Kinetics Of

Non-isothermal magnetic studies can be used to estimate the activation energy of cooperative spin transition.

Kinetics of spin crossover with thermal hysteresis

2018 ◽  
Vol 20 (8) ◽  
pp. 5586-5590 ◽  
Author(s):  
Mark B. Bushuev
Keyword(s):  
Spin Crossover ◽  
Thermal Hysteresis ◽  
Spin Transition ◽  
Reaction Model ◽  
Magnetic Studies ◽  
Kinetics Of

Non-isothermal magnetic studies allow establishing a reaction model of hysteretic spin transition.

scholarly journals The kinetics of the extraction of caffeine from guarana seed under the action of ultrasonic field with simultaneous cooling

2019 ◽  
Vol 9 (1) ◽  
pp. 26-36 ◽  
Author(s):  
Biljana Koturevic ◽  
Borivoj Adnadjevic ◽  
Jelena Jovanovic
Keyword(s):  
Activation Energy ◽  
Kinetic Parameters ◽  
Reaction System ◽  
Ultrasonic Field ◽  
Conventional Heating ◽  
Isothermal Kinetics ◽  
Correlation Relationship ◽  
Exponential Factor ◽  
Caffeine Extraction ◽  
Kinetics Of

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.

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.

scholarly journals The non-isothermal kinetics of hydroxyapatite formation in kaolin - natural phosphate mixtures

2019 ◽  
Vol 9 (1) ◽  
pp. 1-7
Author(s):  
Fateh Chouia ◽  
Hocine Belhouchet ◽  
Toufik Sahraoui
Keyword(s):  
Activation Energy ◽  
Thermal Analysis ◽  
Differential Thermal Analysis ◽  
Exothermic Peak ◽  
Isothermal Kinetics ◽  
Heating Rates ◽  
Natural Phosphate ◽  
Isothermal Conditions ◽  
Kinetics Of ◽  
Hydroxyapatite Formation

In this work, the activation energy of hydroxyapatite formation in different composites under non-isothermal conditions was determined using differential thermal analysis (DTA). Seven compositions were prepared and studied while varying the percentage of the kaolin from 20 to 80 wt.% at 10% increments. The DTA conducted at heating rates of 10, 20 and 30 K min−1 showed an exothermic peak in all composites in the region 700°C–750°C associated with hydroxyapatite formation. The activation energies measured from non-isothermal treatments for seven compositions (20, 30, 40, 50, 60, 70 and 80 mass% of kaolin) were 194, 178, 178, 209, 162, 146 and 121 kJ mol−1, respectively.   Keywords:energy, kinetics,  kaolin - natural, phosphate mixtures

scholarly journals Iron(III) Azadiphenolate Compounds in a New Family of Spin Crossover Iron(II)–Iron(III) Mixed-Valent Complexes

2019 ◽  
Vol 5 (2) ◽  
pp. 37 ◽  
Author(s):  
Wasinee Phonsri ◽  
David S. Macedo ◽  
Barnaby A. I. Lewis ◽  
Declan F. Wain ◽  
Keith S. Murray
Keyword(s):  
Crystal Structures ◽  
Spin Crossover ◽  
Crystal Packing ◽  
Spin Transition ◽  
Double Salt ◽  
Magnetic Studies ◽  
Cationic Precursor ◽  
New Family ◽  
Double Spin ◽  
Crystal Design

A new family of mixed valent, double salt spin crossover compounds containing anionic FeIII and cationic FeII compounds i.e., [FeII{(pz)3CH}2][FeIII(azp)2]2·2H2O (4), [FeII(TPPZ)2][FeIII(azp)2]2]·H2O (5) and [FeII(TPPZ)2][FeIII(azp)2]2]·H2O·3MeCN (6) (where (pz)3CH = tris-pyrazolylmethane, TPPZ = 2,3,5,6, tetrapyridylpyrazine and azp2− = azadiphenolato) has been synthesized and characterised. This is the first time that the rare anionic spin crossover species, [FeIII(azp)2]−, has been used as an anionic component in double salts complexes. Single crystal structures and magnetic studies showed that compound 6 exhibits a spin transition relating to one of the FeIII centres of the constituent FeII and FeIII sites. Crystal structures of the anionic and cationic precursor complexes were also analysed and compared to the double salt products thus providing a clearer picture for future crystal design in double spin crossover materials. We discuss the effects that the solvent and counterion had on the crystal packing and spin crossover properties.

A mononuclear iron(ii) complex: cooperativity, kinetics and activation energy of the solvent-dependent spin transition

2016 ◽  
Vol 45 (1) ◽  
pp. 107-120 ◽  
Author(s):  
Mark B. Bushuev ◽  
Denis P. Pishchur ◽  
Vladimir A. Logvinenko ◽  
Yuri V. Gatilov ◽  
Ilya V. Korolkov ◽  
...  
Keyword(s):  
Activation Energy ◽  
Spin Crossover ◽  
Spin Transition ◽  
Mononuclear Iron ◽  
Kinetics And Activation Energy

A mononuclear iron(ii) pyrimidine-based complex shows remarkable spin crossover properties and unprecedented thermal robustness.

Crystallization Kinetics of the Cu47.5Zr47.5Al5 Bulk Metallic Glass under Continuous and Iso-Thermal Heating

2011 ◽  
Vol 99-100 ◽  
pp. 1052-1058 ◽  
Author(s):  
Chun Xia Hu ◽  
Gai Lian Li ◽  
Yang Shi
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
The Body ◽  
Avrami Exponent ◽  
Isothermal Kinetics ◽  
Continuous Heating ◽  
Local Activation ◽  
Body Center Cubic ◽  
Local Activation Energy ◽  
Kinetics Of

The crystallization kinetics of Cu47.5Zr47.5Al5 BMG was studied by differential scanning calorimetry (DSC) using the mode of continuous heating and isothermal annealing. It is found that Tg, Tx, and Tp, display a dependence on the heating rate in the case of continuous heating. The activation energies, Eg, Ex and Tp determined by the Kissinger method, yield 445, 264 and 285 kJ/mol, respectively. The local activation energy, E(x), was determined by the Doyle-Ozawa method, which gives the average activation energy 204 kJ/mol. On the other hand, the isothermal kinetics was modeled by the Johnson-Mehl-Avrami (JMA) equation, the Avrami exponent versus crystallization fraction was calculated at different temperatures. Details of nucleation and growth behaviors are discussed in terms of the local Avrami exponent and local activation energy during the isothermal crystallization. X-ray shows that the quenched BMG only includes the glass single phase. The BMG heated to 873 K has the precipitation of the body-center cubic (BCC) CuZr.

scholarly journals Isothermal kinetics of titanium-oxo-alkoxy clusters formation

2011 ◽  
Vol 43 (1) ◽  
pp. 95-104 ◽  
Author(s):  
Z.Z. Baros ◽  
B.K. Adnadjevic ◽  
V.B. Pavlovic
Keyword(s):  
Activation Energy ◽  
Power Law ◽  
Isothermal Kinetics ◽  
Molar Ratio ◽  
Titanium Tetraisopropoxide ◽  
Formation Reaction ◽  
Formation Kinetics ◽  
Power Law Function ◽  
Absorbance Changes ◽  
Kinetics Of

In this article, the influences of titanium tetraisopropoxide Ti(OR)4 (R = Pri) concentration, molar ratio, h = [H2O]/[Ti(OR)4], and temperature, on the formation kinetics of the titanium-oxo-alkoxy clusters (TOAC), were studied. The TOAC formation isothermal kinetics was monitored by measuring absorbance changes versus time in the reaction mixture at predefined wavelength ? = 350 nm. It was determined that the isothermal rate of clusters formation is a power law function of titanium tetraisopropoxide concentration and the molar concentration of water (cw). The kinetic parameters ? and ? were calculated. The apparent activation energy Ea values in the clusters formation reaction has been calculated and correlated with the change of titanium tetraisopropoxide concentration and molar ratio. The model for mechanism of TOAC formation is proposed.

Non-Isothermal Kinetics Analysis of α→β Transformation in Zirconium Alloy

2020 ◽  
Vol 993 ◽  
pp. 344-350
Author(s):  
Zong Pei Wu ◽  
Zhu Qing Cheng ◽  
Zhong Bo Yang ◽  
Wei Yi ◽  
Xiao Lu Xu
Keyword(s):  
Activation Energy ◽  
Room Temperature ◽  
Kinetic Mechanism ◽  
Isothermal Kinetics ◽  
Scanning Calorimetry ◽  
Temperature Ranges ◽  
One Step ◽  
Fwo Method ◽  
Kinetics Of ◽  
Dsc Curves

Differential scanning calorimetry (DSC) was used to study non-isothermal kinetics of α→β transformation of Zr-0.5wt%Sn-0.15wt%Nb-0.5wt%Fe-0.25wt%V alloy. The DSC curves were measured from room temperature to 1030 °C at the heating rate of 15, 20, 30, 50°C /min respectively. The Flynn-Wall-Ozawa (FWO) method was used to get the activation energy (E) of α→β transformation at different conversion ratios. Then the values of activation energy obtained were modified by Ozawa iterative equation. The kinetic mechanism functions of α→β transformation were investigated by Criado-Ortega methods. The results show that the activation energy is related to conversion ratios. It means α→β transformation is not a simple one-step reaction but a complex multi-step reaction. The most probable kinetic mechanism functions are different in different temperature ranges, which are -ln(1-x) for ≤830 °C, [-ln(1-x)]1/2 for 834~848 °C, [-ln(1-x)]2/5for 850~856 °C and [-ln(1-x)]1/3 for 858~868 °C respectively.

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