scholarly journals Determination of activation energy of sintering of ThO2-U3O8 pellets using the master sintering curve approach

2003 ◽  
Vol 35 (3) ◽  
pp. 125-132 ◽  
Author(s):  
T.R.G. Kutty ◽  
K.B. Khan ◽  
P.V. Hegde ◽  
A.K. Sengupta ◽  
S. Majumdar ◽  
...  
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
High Temperature ◽  
Constant Heating Rate ◽  
Heavy Water Reactor ◽  
Activation Energy Of Sintering ◽  
Constant Heating ◽  
Kinetics Of ◽  
Powder Metallurgy Route

ThO2 containing around 2 to 3 % U233O2 is considered as fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). High-density ThO2-UO2 pellets have been fabricated by powder metallurgy route using ThO2 and U3O8 powders as the starting materials. U3O8 decomposes to UO2 during high temperature sintering and forms a solid solution with ThO2. The densification behaviour and sintering kinetics of the above were evaluated using a high temperature dilatometer using constant heating rate experiments. To evaluate the activation energy of sintering, a master sintering curve approach has been used. The activation energy for sintering for the above composition in air was found to be 500 kJ/mol.

scholarly journals Reaction sintering of the 2ZnO-TiO2 system

2007 ◽  
Vol 39 (2) ◽  
pp. 127-132 ◽  
Author(s):  
N. Obradovic ◽  
N. Labus ◽  
T. Sreckovic ◽  
S. Stevanovic
Keyword(s):  
Activation Energy ◽  
Ball Mill ◽  
High Energy ◽  
Reaction Sintering ◽  
Constant Heating Rate ◽  
Time Intervals ◽  
High Energy Ball Mill ◽  
Energy Ball ◽  
Constant Heating ◽  
Kinetics Of

Sintering kinetics of the mechanically activated ZnO-TiO2 system was studied. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill for different time intervals from 0 to 300 minutes. Formal phenomenological analyses were performed in order to describe the specimen?s behavior during isothermal sintering at 1100oC. Non-isothermal sintering was investigated by dilatometer measurements up to 1100oC with a constant heating rate. The Dorn method was applied in order to give information on the activation energy. .

Interface Controlled Diffusional Creep of Cu + 2.8 at.% Co Solid Solution

2012 ◽  
Vol 322 ◽  
pp. 33-39 ◽  
Author(s):  
Sergei Zhevnenko ◽  
Eugene Gershman
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Surface Tension ◽  
High Temperature ◽  
Creep Behavior ◽  
Pure Copper ◽  
Diffusional Creep ◽  
High Temperature Creep ◽  
Temperature Range ◽  
Different Temperatures

High-temperature creep experiments were performed on a Cu-2.8 ат.% Co solid solution. Cylindrical foils of 18 micrometers thickness were used for this purpose. Creep tests were performed in a hydrogen atmosphere in the temperature range of about from 1233 K to 1343 K and at stresses lower than 0.25 MPa. For comparison, a foil of pure copper and Cu-20 at.% Ni solid solution were investigated on high temperature creep. Measurements on the Cu foil showed classical diffusional creep behavior. The activation energy of creep was defined and turned out to be equal 203 kJ/mol, which is close to the activation energy of bulk self-diffusion of copper. There was a significant increase in activation energy for the Cu-20 at.% Ni solid solution. Its activation energy was about 273 kJ/mol. The creep behavior of Cu-Co solid solution was more complicated. There were two stages of diffusional creep at different temperatures. The extremely large activation energy (about 480 kJ/mol) was determined at relatively low temperature and a small activation energy (about 105 kJ/mol) was found at high temperatures. The creep rate of Cu-Co solid solution was lower than that of pure copper at all temperatures. In addition, the free surface tension of Cu-2.8 ат.% Co was measured at different temperatures from 1242 K to 1352 K. The surface tension increases in this temperature range from 1.6 N/m to 1.75 N/m. There were no features on the temperature dependence of the surface tension.

scholarly journals Apparent activation energy for densification of α-Al2O3 powder at constant heating-rate sintering

2008 ◽  
Vol 31 (6) ◽  
pp. 903-906 ◽  
Author(s):  
W. Q. Shao ◽  
S. O. Chen ◽  
D. Li ◽  
H. S. Cao ◽  
Y. C. Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Heating Rate ◽  
Constant Heating Rate ◽  
Al2o3 Powder ◽  
Α Al2o3 ◽  
Constant Heating

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.

Synthesis and Determination of the Kinetic Parameters for Non-Isothermal Decomposition of Complexes Ln(thd)3phen

2006 ◽  
Vol 530-531 ◽  
pp. 506-512 ◽  
Author(s):  
Wilton Silva Lopes ◽  
Crislene Rodrigues da Silva Morais ◽  
A.G. de Souza
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Lanthanide Complexes ◽  
Reaction Order ◽  
Decomposition Reaction ◽  
Cylindrical Symmetry ◽  
Boundary Reaction ◽  
Phase Boundary Reaction ◽  
Kinetics Of

In this work the kinetics of the thermal decomposition of two ß-diketone lanthanide complexes of the general formula Ln(thd)3phen (where Ln = Nd+3 or Tm+3, thd = 2,2,6,6- tetramethyl-3,5-heptanodione and phen = 1,10-phenantroline) has been studied. The powders were characterized by several techniques. Thermal decomposition of the complexes was studied by non-isothermal thermogravimetry techniques. The kinetic model that best describes the process of the thermal decomposition of the complexes it was determined through the method proposed by Coats-Redfern. The average values the activation energy obtained were 136 and 114 kJ.mol-1 for the complexes Nd(thd)3phen and Tm(thd)3phen, respectively. The kinetic models that best described the thermal decomposition reaction the both complexes were R2. The model R2 indicating that the mechanism is controlled by phase-boundary reaction (cylindrical symmetry) and is defined by the function g(α) = 2[1-(1-a)1/2], indicating a mean reaction order. The values of activation energy suggests the following decreasing order of stability: Nd(thd)3phen > Tm(thd)3phen.

Long-Range Diffusion of Hydrogen in Solid-Solution PdCe Alloys as Deduced from Absorption Experiments

2008 ◽  
Vol 273-276 ◽  
pp. 381-387 ◽  
Author(s):  
Giovanni Mazzolai
Keyword(s):  
Activation Energy ◽  
Solid Solution ◽  
Thermal Decomposition ◽  
Diffusion Coefficient ◽  
High Temperature ◽  
Diffusion Constant ◽  
Absorption Data ◽  
Friction Measurements ◽  
And Diffusion ◽  
Diffusion Of Hydrogen

The diffusion of H and the thermal decomposition of hydrides have been investigated at high temperatures in two PdCe alloys of composition 5% and 9% Ce. It has been found that the H diffusion coefficient obeys an Arrhenius-type of law with the following values of the activation energy W and diffusion constant D0, ( )     = ± × = ± − s m D W eV 2 7 0 2 2 10 0.20 0.02 (Pd95Ce5 alloy) ( )     = ± × = ± − s m D W eV 2 7 0 2 1 10 0.24 0.01 (Pd91Ce9 alloy) The high-temperature absorption data match the low-temperature ones deduced from internal friction measurements, indicating that Ce atoms do not act as strong trapping centres for H. Thermal decomposition of hydrides in the Pd95Ce5H0.008 alloy occurs in a single stage showing a homogeneous solid solution state of the H-Me system.

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.

scholarly journals Torrefaction of Sewage Sludge: Kinetics and Fuel Properties of Biochars

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 565 ◽  
Author(s):  
Jakub Pulka ◽  
Piotr Manczarski ◽  
Jacek Koziel ◽  
Andrzej Białowiec
Keyword(s):  
Activation Energy ◽  
Sewage Sludge ◽  
Thermal Transformation ◽  
Fuel Properties ◽  
Process Time ◽  
Technological Aspect ◽  
Heating Value ◽  
Valuable Product ◽  
Kinetics Of

We propose a ‘Waste to Carbon’ thermal transformation of sewage sludge (SS) via torrefaction to a valuable product (fuel) with a high content of carbon. One important, technological aspect to develop this concept is the determination of activation energy needed for torrefaction. Thus, this research aimed to evaluate the kinetics of SS torrefaction and determine the effects of process temperature on fuel properties of torrefied products (biochars). Torrefaction was performed using high ash content SS at six (200~300 °C) temperatures and 60 min residence (process) time. Mass loss during torrefaction ranged from 10~20%. The resulting activation energy for SS torrefaction was ~12.007 kJ·mol−1. Initial (unprocessed) SS higher heating value (HHV) was 13.5 MJ·kg−1. However, the increase of torrefaction temperature decreased HHV from 13.4 to 3.8 MJ·kg−1. Elemental analysis showed a significant decrease of the H/C ratio that occurred during torrefaction, while the O/C ratio fluctuated with much smaller differences. Although the activation energy was significantly lower compared with lignocellulosic materials, low-temperature SS torrefaction technology could be explored for further SS stabilization and utilization (e.g., dewatering and hygienization).

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