On the kinetics of the δ′ (Al3Li) phase precipitation in a rapidly solidified Al–Mn–Li–Zr alloy

1991 ◽  
Vol 6 (1) ◽  
pp. 46-52 ◽  
Author(s):  
J. Baram ◽  
A. N. Sembira
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Avrami Equation ◽  
Rate Parameter ◽  
Cast Material ◽  
Strain Gradients ◽  
Cast Sample ◽  
Rapidly Solidified ◽  
Kinetics Of ◽  
Conventionally Cast

The precipitation kinetics of the δ′ (Al3Li) phase in two rapidly solidified samples and one conventionally cast sample of an Al–2.3Li–6.5Mn–0.65Zr (in wt. %) alloy are compared. Following high cooling rates, manganese is retained in solid solution in the aluminum matrix (αAl) up to 6.0 wt.%, far beyond the thermodynamic equilibrium value (0.36 wt.% at 500 °C). Extended solid solution of manganese in aluminum induces strain gradients, similar to those produced by dislocations. The effect of such gradients, the size of which is proportional to the solute atomic fraction, is to enhance lithium precipitation by lowering the activation energy, as observed, and also by affecting the rate parameter. Kinetic thermal analysis has been performed in a series of nonisothermal experiments in the heat flux differential scanning calorimetry (DSC) mode. The precipitation of the δ′ (Al3Li) phase is evidenced by an exothermic peak whose characteristics were analyzed. The rate of transformation (precipitation) is assumed to obey the Johnson–Mehl–Avrami equation. The activation energy for the precipitation process as well as the kinetic rate parameter have been evaluated for the rapidly solidified and the conventionally cast specimens. The activation energy for precipitation is lowered, from 107.0 kJ mol−1 for the conventionally cast material, down to 81.8 kJ mol−1 and 77.0 kJ mol−1 for samples that exhibit manganese solid solubility extensions of 2.10 and 6.00 wt.%, respectively. The rate parameter for the precipitation reaction, which has the generally admitted value of 1.50, for a transformation involving diffusion controlled growth, is affected by the strain gradients, too. Its value is reduced from 1.40 for the slowly cast sample to 1.32 and 1.20, respectively, for the two rapidly solidified samples, as a result of competing mechanisms, namely: growth controlled by diffusion and strain-assisted precipitation.

Kinetic Study on Phosphate Enrichment Behavior in CaO–SiO2–FeO–Fe2O3–P2O5 Steelmaking Slags

2018 ◽  
Vol 37 (5) ◽  
pp. 477-486
Author(s):  
Jin-yan Li ◽  
Mei Zhang ◽  
Min Guo ◽  
Xue-min Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Crystallization Behavior ◽  
Crystallization Rate ◽  
Avrami Equation ◽  
One Dimensional ◽  
Thermal Crystallization ◽  
Steelmaking Slags ◽  
Cooling Schedules ◽  
Kinetics Of

AbstractThe iso-thermal crystallization behavior of phosphate-enriched phase has been experimentally investigated in the rapidly quenched CaO–SiO2–FeO–Fe2O3–P2O5 steelmaking slags under different cooling schedules. The experimental results indicate that increasing endpoint temperature from 1453 to 1533 K and prolonging holding time from 2 to 60 min can result in an increasing tendency of the size of phosphate-enriched phase in the shape of one-dimensional rod. The crystallization kinetics of phosphate-enriched phase in steelmaking slags has been described by Avrami equation. The Avrami constant $$n$$ was obtained to be 0.472, while the crystallization rate constant $$k$$ was recommended as $$\ln k{\rm{= 57}}{\rm{. 40 + 12,273}}{\rm{. 96}}/T - {\rm{8}}{\rm{. 25}}\,\ln T - {\rm{5}}{\rm{. 5}\times{\rm 10}^{- 3}}T$$. Thus, the apparent activation energy $$E$$ of crystallization is recommended as $$E{\rm{= 537}}{\rm{. 60}} - {\rm{206}}{\rm{. 015}}T$$ kJ/mol.

scholarly journals Распад твердого раствора межузельного магния в кремнии

2019 ◽  
Vol 53 (3) ◽  
pp. 314
Author(s):  
В.Б. Шуман ◽  
А.Н. Лодыгин ◽  
Л.М. Порцель ◽  
А.А. Яковлева ◽  
Н.В. Абросимов ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Single Crystal ◽  
Diffusion Activation Energy ◽  
Practical Application ◽  
Float Zone ◽  
Sandwich Method ◽  
Kinetics Of ◽  
Diffusion Activation

AbstractThe decomposition of a solid solution of interstitial magnesium Mg_ i in silicon is studied. Float-Zone dislocation-free single-crystal n -Si with a resistivity of ~8 × 10^3 Ω cm and oxygen and carbon contents of ~5 × 10^14 cm^–3 and ~1 × 10^15 cm^–3 is used in the experiments. The samples are doped using the diffusion sandwich method at T =1100°C followed by quenching. Decomposition of the supersaturated Mg_ i solid solution is studied by observing the kinetics of increasing the resistivity of doped samples resulting from their annealing in the range T = 400–620°C. It is found that the decomposition is characterized by an activation energy of E _ a ≈ 1.6 eV, which is close to the previously determined diffusion activation energy of Mg_ i in silicon. It is also shown that Si:Mg exhibits stable properties at temperatures not exceeding 400°C, which is important for its possible practical application.

Growth kinetics of Cu2ZnSnS4 thin films and powders

2013 ◽  
Vol 28 (S2) ◽  
pp. S228-S241
Author(s):  
M. Müller ◽  
C. L. Azanza Ricardo ◽  
R. Di Maggio ◽  
P. Scardi
Keyword(s):  
Thin Films ◽  
Activation Energy ◽  
Growth Kinetics ◽  
Profile Analysis ◽  
Domain Size ◽  
Avrami Equation ◽  
Line Profile Analysis ◽  
Diffraction Line Profile ◽  
Change In The Mean ◽  
Kinetics Of

The growth kinetics of Cu2ZnSnS4 thin films and powders was studied using in-situ synchrotron data. Isothermal and isochronal measurements were performed at the MCX beamline of the Elettra synchrotron (Trieste, Italy). Diffraction line profile analysis was used to follow the changes in the domain size distribution during isothermal measurements, and the change in the mean volume of the domains was studied using the Johnson-Mehl-Avrami equation. The growth was found to be diffusion controlled from small dimensions while the nucleation rate is temperature dependent. An activation energy of 210 kJ/mol could be estimated. In case of the isochronal data, the evolution of inverse of the integral breadth of the diffraction peaks in dependence on temperature was studied using the Ozawa and Šatava equations. The activation energy determined for the growth process is between 112(2) and 145(5) kJ/mol.

Formation kinetics of nanocrystalline Fe–4 wt.% Al solid solution during ball milling

1997 ◽  
Vol 12 (6) ◽  
pp. 1429-1432 ◽  
Author(s):  
H. G. Jiang ◽  
R. J. Perez ◽  
M. L. Lau ◽  
E. J. Lavernia
Keyword(s):  
Solid Solution ◽  
Ball Milling ◽  
Structural Evolution ◽  
Milling Process ◽  
Avrami Equation ◽  
Scanning Calorimetry ◽  
Diffusion Controlled ◽  
Interphase Boundaries ◽  
Kinetics Of Formation ◽  
Kinetics Of

Formation of nanocrystalline Fe–4 wt.% Al solid solution has been achieved through SPEX ball milling of blended elemental Fe and Al powders. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) have been employed to follow the structural evolution during the ball-milling process. Exothermic peaks exhibited in DSC diagrams of the powders milled for 10 to 60 min yielded thermal enthalpies corresponding to the formation of Fe–4 wt.% Al solid solution, from which the kinetics of formation were found to follow the Johnson–Mehl–Avrami equation. Assessment of the kinetic parameter n reveals a diffusion controlled mechanism, in which grain and interphase boundaries may play a crucial role, during the solid solution formation of Fe–4 wt.% Al.

On the Recrystallisation Characteristics and Kinetics of a 9SMn28 Free Cutting Steel

2007 ◽  
Vol 558-559 ◽  
pp. 333-338 ◽  
Author(s):  
Mahesh C. Somani ◽  
L. Pentti Karjalainen ◽  
Juan H. Bianchi
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Regression Model ◽  
Strain Rate ◽  
Apparent Activation Energy ◽  
Strong Dependence ◽  
Vast Number ◽  
Cutting Steel ◽  
Strain And Strain Rate ◽  
Kinetics Of

The static and metadynamic recrystallisation characteristics of a 9SMn28 (EN 1.0715) free cutting steel have been evaluated by employing the stress relaxation technique. In the steel, the sulphur was bound in the form of numerous MnS inclusions. Fractional softening laws stating the kinetics of static and metadynamic softening behaviour were experimentally determined and compared with the existing literature data for C/C-Mn steels. The analysis of the static recrystallisation data suggested the powers of the strain and strain rate to be -2.7 and -0.13, respectively, and the apparent activation energy was estimated as 177 kJ/mol. The power of grain size was taken from a regression model developed previously that is able to predict the static recrystallisation kinetics of vast number of carbon and microalloyed steel grades. Even though a fraction of Mn was out of the solid solution in the form of sulphides, the predictions by the regression model as accounting the balance Mn in the solid solution were quite close to the experimental data, confirming the applicability of the model. As expected, the metadynamic recrystallisation behaviour showed a strong dependence on the strain rate, the power being -0.78 and the apparent activation energy 57 kJ/mol.

MAGNETIC PROPERTIES, NANOSTRUCTURE AND ORDERING KINETICS OF FePtCu THIN FILMS

2009 ◽  
Vol 23 (06n07) ◽  
pp. 1652-1657 ◽  
Author(s):  
G. J. CHEN ◽  
Y. H. SHIH ◽  
J. S. C. JANG ◽  
S. R. JIAN ◽  
W. C. CHANG ◽  
...  
Keyword(s):  
Thin Films ◽  
Heat Treatment ◽  
Activation Energy ◽  
Solid Solution ◽  
Magnetic Properties ◽  
Heating Rates ◽  
Cu Content ◽  
Fept Alloy ◽  
Ordering Kinetics ◽  
Kinetics Of

In this study, the ( FePt )100- x Cu x ( x =0, 4.6, 6.7, 8.8, 10.9) ( FePtCu ) alloy films were prepared by co-sputtering. The effects of Cu addition content and heat treatment on the nanostructure and magnetic properties of the polycrystalline ( FePt )100- x Cu x films are reported. The experimental results show that the ordering temperature of the ( FePt )100- x Cu x ( x =6.7) films reduced to 320°C, which is much lower than that of the FePt alloy. After heat treatment at 600°C for 1 hour, the ( FePt )100- x Cu x ( x =6.7) film shows a coercive force of 15 kOe and the magnetization of 576 emu/cc. The magnetic properties of the FePtCu films can be adjusted by varying the Cu content in the films. The enhancement of the magnetic properties of the FePtCu films mainly resulted from the formation of the order L 10 phase. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, showed that the addition of Cu atoms reduced the activation energy of ordering from 217 kJ/mol to 87 kJ/mol for the ( FePt )100- x Cu x films ( x = 0 and 6.7, respectively). The reduction of the ordering temperature and corresponding activation energy might due to the solid solution of the Cu atoms in the FePt films.

Isothermal and non-isothermal crystallization kinetics and predictive modeling in the solidification of poly(cyclohexylene dimethylene cyclohexanedicarboxylate) melt

2016 ◽  
Vol 49 (2) ◽  
pp. 132-156 ◽  
Author(s):  
Ying-Guo Zhou ◽  
Wen-Bin Wu ◽  
Gui-Yun Lu ◽  
Jun Zou
Keyword(s):  
Activation Energy ◽  
Crystallization Kinetics ◽  
Isothermal Crystallization ◽  
Avrami Equation ◽  
Melt Crystallization ◽  
Crystallization Activation Energy ◽  
Cooling Rates ◽  
Isothermal Crystallization Kinetics ◽  
Wide Range ◽  
Kinetics Of

Isothermal and non-isothermal crystallization kinetics of polycyclohexylene dimethylene cyclohexanedicarboxylate (PCCE) were investigated via differential scanning calorimetry (DSC). Isothermal melt crystallization kinetics were analyzed using the traditional Avrami equation. Non-isothermal melt crystallization kinetics data obtained from DSC were analyzed using the extended Avrami relation and a combination of the Avrami equation and the Ozawa relationship. The glass transition temperature, equilibrium melting point, isothermal crystallization activation energy, and non-isothermal crystallization activation energy were determined. Furthermore, a predictive method based on the Nakamura model was proposed and was used to describe the non-isothermal crystallization kinetics based on the isothermal experimental data. The results suggested that the original Nakamura equation was not successful in describing the non-isothermal crystallization of PCCE over a wide range of cooling rates. It was found that the non-isothermal crystallization kinetics of PCCE, over a wide range of cooling rates, could best be described by modifying the differential Nakamura equation to include a varied Avrami index.

The kinetics of dehydroxylation of kaolinite

Clay Minerals ◽  
1987 ◽  
Vol 22 (4) ◽  
pp. 447-456 ◽  
Author(s):  
S. A. T. Redfern
Keyword(s):  
Activation Energy ◽  
Reaction Mechanism ◽  
Kinetic Analysis ◽  
Rate Constants ◽  
Avrami Equation ◽  
Isothermal Thermogravimetry ◽  
Temperature Range ◽  
Homogeneous Models ◽  
Kinetics Of ◽  
Fraction Method

AbstractThe dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the temperature range 734 K to 890 K. An empirical activation energy of 222 kJ mol-1 was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (Ea) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in Ea during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges inwards, parallel to (001).

Structural Evolution of Fe Rich Fe-Al Alloys During Ball Milling and Subsequent Heat Treatment

1996 ◽  
Vol 457 ◽  
Author(s):  
H. G. Jiang ◽  
R. J. Perez ◽  
M. L. Lau ◽  
E. J. Lavernia
Keyword(s):  
Heat Treatment ◽  
Solid Solution ◽  
Ball Milling ◽  
Structural Evolution ◽  
Al Alloys ◽  
Avrami Equation ◽  
Transformation Kinetics ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Kinetics Of

ABSTRACTX-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been utilized to investigate the structural evolution of Fe rich Fe-Al alloys during ball milling. It is found that b.c.c. solid solutions can be formed either through ball milling alone or through ball milling together with heat treatment. Thermal diagrams of the milled Fe-Al powders reveal exothermic peaks corresponding to the formation of cc-Fe(Al) solid solution (in both Fe-4wt.%Al and Fe-10wt.%Al) and the formation of FeAl intermetallic compound (in Fe-10wt.%Al). The transformation kinetics of cc-Fe(Al) solid solution in Fe-4wt.%Al were found to follow the Johnson-Mehl-Avrami equation.

KINETICS OF OXYGEN EXCHANGE IN HIGH TEMPERATURE SUPERCONDUCTOR YBa2Cu3O6+x

1990 ◽  
Vol 04 (01) ◽  
pp. 29-35 ◽  
Author(s):  
A. A. STEPANOV ◽  
N. G. HAINOVSKY ◽  
Yu. T. PAVLYUKHIN ◽  
A. I. RYKOV
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
High Pressure ◽  
Oxygen Diffusion ◽  
Reaction Rate ◽  
High Temperature Superconductor ◽  
Oxygen Absorption ◽  
Second Stage ◽  
Two Stages ◽  
Kinetics Of

Kinetics of oxygen absorption in YBa 2 Cu 3 O 6+x has been described. Experiments were performed in the high pressure reactor with constant volume in the temperature range of 150–700°C and oxygen pressure 1.4–10.7 atm. Two stages of oxygen absorption in tetraphase have been discovered. The first is related to the formation of a solid solution of oxygen in Cu(I) layers with the activation energy 0.07 ± 0.01 eV . The second one is oxygen diffusion in the system of short disordered chains ( Cu − O )n with the activation energy 0.30 ± 0.01 eV . Growths of chains and their interaction during the second stage results in the formation of ortho-phase accompanied by further decrease of the reaction rate. Structure-chemical reasons for the multistage mechanism of oxygen absorption are discussed.

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