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Showing 14 results for Kinetics

Bafghi M. Sh., Adeli M., Mohammadi Nikoo H.,
Volume 1, Issue 3 (9-2004)
Abstract

Two commercial methods are used for the production of strontium carbonate:1) Direct conversion of Celsetite to strontium carbonate by hot sodium carbonate,2) Carbothermic reduction of celestite with coal followed by water leaching of strontium sulfide(SrS) and its conversion to strontium carbonate.The present study has been made on the carbothermic reduction of celestite ores of Varamin (Iran) mines. Effects of temperature, time, pellet size, particle size of celestite ore, pellet compactness and type of reducing agent have been studied. In the range of 800-1100°C, reduction rate increases notably with temperature, which may mean that the reduction is predominantly chemical controlled. Activation energy of around 22.5 kcal/mol supports the idea of chemical control mechanism. Further support for this postulation is provided by the following facts:1) Increasing rate with carbon reactivity (graphite, coal, and charcoal)2) Small dependency of rate on pellet compactness.3) Small dependency of rate on pellet size
A. Ataie1,, S. Heshmati-Manesh1,, S. Sheibani1,, G. R. Khayati,y. Firozbakht,
Volume 5, Issue 1 (3-2008)
Abstract

Abstract: In this paper solid state reduction of high carbon ferrochromium-chromite composite pellets in the temperature range of 900-1350°C was investigated. A two stage reduction mechanism is proposed. The first stage is likely to be controlled by the chemical reaction with activation energy of 127.2kJ/mol. In the second stage, solid state diffusion of carbon through the reaction product layer is suggested to be rate controlling. The activation energy of this stage was calculated to be 93.1kJ/mol. The reduction process was found to be favored by high temperatures as well as high vacuum. The results also show that pre-milling of initial mixture has a negative effect on the reduction degree.
M. Mossanef, M. Soltanieh,
Volume 5, Issue 4 (12-2008)
Abstract

Abstract: The possibility of vanadium carbide coating formation on AISI L2 steel was studied in molten salt bath containing 33 wt% NaCl- 67 wt% CaCl2. In this research, the effects of time, temperature and bath composition on growing layer thickness were studied. The vanadium carbide coating treatment was performed in the NaCl-CaCl2 bath at 1173, 1273 and 1373 K temperatures for 3, 6, 9 hours and in bath containing 5, 10, 15, 25 wt% ferrovanadium. The presence of VC formed on the surface of the steel substrate was confirmed by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction analysis. The layer thickness of vanadium carbide and surface hardness ranged between 4.8 to 25.7 µm and 2645 to 3600 HV, respectively. The kinetics of layer growth was analyzed by measuring the depth of vanadium carbide layer as a function of time and temperature. The mean activation energy for the process is estimated to be 133 kJ/ mol.


Javad Bahrami, Mohammad Hossein Paydar, Nader Setoudeh, Mohammad Hossein Shariat,
Volume 6, Issue 4 (12-2009)
Abstract

  Abstract

  The effect of mechanical activation using an attrition mill on the particle size of an ilmenite concentrate and its effect on the ability of the concentrate for Iron separation during hydrochloric acid leaching and the kinetics of the dissolution process have been investigated. It was observed that mechanical activation in an attritor significantly enhances the dissolution of iron in hydrochloric acid while have a slight effect on dissolution of titanium. With the mechanically activated ilmenite using an attrition mill, leaching conversion at 90 oC reached to 80%. The kinetic data of leaching of mechanically activated ilmenite was found to follow shrinking core model. Mechanically activating ilmenite using the attrition mill was found to cause the activation energy of leaching to be decrease from 43.69 , found for samples leached without mechanically activated, to 18.23 .


R. Khoshhal, M. Soltanieh, M. Mirjalili,
Volume 7, Issue 1 (3-2010)
Abstract

Abstract:

titanium sheets in pure molten aluminum at 750

and X-Ray Diffraction Analysis results, TiAl

intermetallic layer thickness increases slowly at primary stages. After that an enhanced growth rate occurs due to layer

cracking and disruption. Presumably, reaction starts with solving titanium into the molten aluminum causing in

titanium super saturation and TiAl

intermetallic layer which consequently leads to TiAl

energy of intermetallic layer formation and growth was developed by measuring titanium thickness decreases.

In this work, kinetics of intermetallic compounds formation in Al-Ti system was studied by immersingoC, 850 oC and 950 oC. According to Scanning Electron Microscopy3 is the only phase can form at the interface. Observations revealed that3 formation. At this stage, growth may be controlled by aluminum diffusion through3 formation at the interface of Ti-TiAl3. Furthermore, activation

A.m. Rashidi, A. Amadeh,
Volume 7, Issue 2 (6-2010)
Abstract

Abstract:

nanocrystalline nickel samples with the grain size of ~25 nm were prepared via direct current electrodeposition and

aluminized for different durations by pack cementation method at 500

means of SEM, EDS and XRD techniques. According to results, short time aluminizing resulted in the formation of a

single aluminide layer whereas at long duration two distinct aluminide layers were formed. The growth kinetics of the

coating was non-parabolic at short times while it obeyed the parabolic law at long duration. The parabolic growth

rate constant of single phase coating formed on electrodeposited samples was about 30 ìm / h1/2 approximately 3 times

greater than the data reported for coarse grained nickel (8.4 ìm / h1/2). Meanwhile, the overall growth rate constant

was decreased to 11.7 ìm / h1/2, when double aluminide layers formed on nanocrystalline nickel.

In this research, aluminizing behavior of ultra fine-grained nickel was investigated. For this purpose,oC. The aluminide layers were examined by

M.sh. Bafghi, A.h. Emami, A. Zakeri, J. Vahdati Khaki,
Volume 7, Issue 2 (6-2010)
Abstract

Abstract:

has been investigated. It has been shown that the mechanism of leaching reaction is diffusion through the product layer

and does not undergo any change as a result of mechanical activation in a wide range of experimental conditions.

Leaching rate is strongly influenced by milling intensity and the effect of ball to powder mass ratio is stronger than

milling time. Curve fitting of experimental data shows that leaching rate constant is approximately a linear function

of ball to powder mass ratio, while it obeys a power function with regard to the milling time.

The kinetics of chalcopyrite leaching in a ferric sulfate media for raw and mechanically activated samples

M. Nusheh*, H. Yoozbashizadeh,
Volume 7, Issue 2 (6-2010)
Abstract

Abstract:

the competition between the precipitation of cobalt ions and evolution of hydrogen gas on the cathode surface during

the reduction process in a sulfate bath, investigation on the mechanism of metal precipitation is of great importance.

In the present work, study on the kinetics of cobalt electrowinning and the mechanism of the involved reactions have

been carried out. The obtained results, confirm the mechanism of cobalt precipitation by depletion of hydroxides. The

effects of temperature and scan rate parameters were studied on electrowinning of cobalt by cyclic voltammetry

technique. The diffusion coefficient and rate constant of the reactions were measured and calculated by performed

experiments.

Nowadays cobalt is mostly produced through the electrowinning process of sulfate solutions. Regarding to

M. Sheikhshab Bafghi, M. Karimi, M. Adeli,
Volume 10, Issue 4 (12-2013)
Abstract

In the present study, reduction of zinc oxide from the pellets made of steelmaking electric arc furnace dust has been investigated. Effects of such parameters as the type of carbon material (graphite, coke and charcoal) as well as time and temperature on the reduction reaction have been examined. The reduced (dimensionless) time method was applied to perform a kinetic analysis of the system. Experimental results showed that increasing the temperature in the range of 925-1150°C results in a remarkable increase in the reduction rate. It was also shown that the reduction process is controlled by chemical reaction. Meaningful difference in the activation energy values calculated for reduction with graphite (24.75 kcal/mol), coke (18.13 kcal/mol) and charcoal (11.52 kcal/mol) indicate the predominant role of chemical reaction (carbon gasification) in the overall reaction rate and its rate-controlling mechanism. Carbothermal reduction of pelletized EAF dust proved to be an efficient reduction method, so that above 90% reduction was achieved in about one hour at temperatures around 1100°C.
M. Krishna, R. Nandini, A.v. Suresh, K. Narasimha Rao ,
Volume 15, Issue 2 (6-2018)
Abstract

An efficient solid-state approach was established to synthesize (K0.5Na0.5) NbO3 ceramics using calcination kinetics and microwave assisted sintering. Milling of carbonate and oxide raw materials were carried out for 15h to obtain homogeneous nano particles. The crystallite size of 5.30 nm was obtained for the KNN system after calcination through optimized parameters and observed to be stoichiometric in nature. The obtained nano particles showed phase transition from orthorhombic to tetragonal crystal structure without any secondary phases. The high relative density and tetragonality ratio of KNN ceramics obtained through optimized sintering parameters yielded with significant piezoelectric and ferroelectric properties.
 

E. Mohammadi, M. Pourabdoli,
Volume 16, Issue 2 (6-2019)
Abstract

The effect of mechanical activation on the kinetics of ammoniacal thiosulfate leaching of a refractory oxide gold ore containing 2.8 ppm Au was investigated. The gold extraction of 99.81% was achieved by 16 h leaching of a sample mechanically activated for 60 minutes. The gold extraction observed for a similar reference sample without mechanical activation was only 55%. Studies revealed that leaching progresses at two different rates depending on the leaching time (0-2 h and 2-16 h). It was observed that diffusion through an ash layer as a dominant mechanism controls the leaching of samples mechanically activated up to 45 minutes during total leaching time, while reaction control and liquid film diffusion are dominant mechanisms for leaching of a sample mechanically activated for 60 minutes during 0-2 h and 2-16 h, respectively. The extraction observed during the ash diffusion step depends significantly upon mechanical activation time.  Mechanical activation of 60 minutes results in high gold extraction in this step which when combined with subsequent chemical reaction gives close to 100% gold extraction in a 16 hour leach.  Mechanical activation for up to 45 minutes leads to a modest improvement in overall gold extraction compared with the reference test without mechanical activation

A. Bahrami, F. Kazemi, J. Abdolahi Sharif,
Volume 17, Issue 1 (3-2020)
Abstract

Kinetic models are the most important instruments for predicting and evaluating the performance of flotation circuits. To determine the kinetic order and rate of flotation of a gilsonite sample, flotation experiments were carried out in both rougher and cleaner stages. Experiments conducted using the combinations of petroleum-MIBC, gas oil-pine oil, and one test without any collector and frother. Five first order kinetic models were applied to the data obtained from the flotation tests by using the Matrix Laboratory software. Statistical analysis showed that the classic first order model perfectly matched the rougher and cleaner results performed using petroleum-MIBC combination. The kinetic constants (k) were calculated as 0.04 (s-1) and 0.01 (s-1) for the rougher and cleaner, respectively. Rougher and cleaner tests without collector and frother also matched with the modified gas/solid adsorption and rectangular models with the k values of 0.05 (s-1), and 0.01 (s-1), respectively. The relationship between flotation rate constant, maximum combustible recovery and particle size were also studied. The results showed that the maximum flotation combustible recovery and flotation rate were obtained with an intermediate particle size both in the rougher and cleaner flotation processes. The combustible recovery and flotation rate in the rougher flotation process were higher than that in the cleaner flotation process.
Shadi Moshayedi, Hossein Sarpoolaky, Alireza Khavandi,
Volume 19, Issue 2 (6-2022)
Abstract

In this paper, chemically-crosslinked gelatin/chitosan hydrogels containg zinc oxide nanoparticles (ZNPs), were loaded with curcumin (CUR), and their microstructural features, physical properties, curcumin entrapment efficiency, and drug release kinetics were evaluated using scanning electron microscopy (SEM), the liquid displacement method, and UV–Vis spectroscopy. The in vitro kinetics of drug release was also studied using First-order, Korsmeyer-Peppas, Hixon-Crowell, and Higuchi kinetic models. The SEM micrographs confirmed the formation of highly porous structures possessing well-defined, interconnected pore geometries. A significant reduction in the average pore sizes of the drug-loaded hydrogels was observed with the addition of ZNPs and CUR to the bare hydrogels. High value of drug loading efficiency (~ 72 %) and maximum drug release of about 50 % were obtained for the drug-loaded scaffolds. It was found that curcumin was transported via the non-Fickian diffusion mechanism. It was also shown that the kinetics of curcumin release was best described in order by Hixon-Crowell, Higuchi, and Korsmeyer-Peppas models, demonstrating that drug release was controlled by diffusion, degradation, and swelling of the drug carrier. However, lower degree of fitting was observed with First-order kinetic model.

Mohammad Javad Sohrabi, Hamed Mirzadeh, Saeed Sadeghpour, Reza Mahmudi,
Volume 20, Issue 4 (12-2023)
Abstract

Deformation-induced α΄-martensite generally forms at shear bands in the coarse-grained austenite, while it nucleates at grain boundaries in the ultrafine-grained (UFG) austenite. The available kinetics models are related to the nucleation on the shear band intersections, and hence, their application to investigating the kinetics of α΄-martensite formation for the UFG regime cannot be justified. Accordingly, in the present work, the general Johnson–Mehl–Avrami–Kolmogorov (JMAK-type) model was implemented for comparing the kinetics of α΄-martensite formation in the UFG and coarse-grained regimes using an AISI 304L stainless steel. On the experimental front, the X-ray diffraction (XRD) patterns and the electron backscattered diffraction (EBSD) maps were used for phase and microstructural analyses, respectively. It was revealed that the simple JMAK-type model, by considering the dependency of the volume fraction of α΄-martensite on the strain, is useful for modeling the experimental data, predicting the nucleation sites based on the theoretical Avrami exponents, and characterizing the transformation kinetics at low and high strains.

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