Kinetics of B2 and D03 Ordering: Theory

1990 ◽  
Vol 186 ◽  
Author(s):  
L. Anthony ◽  
B. Fultz
Keyword(s):  
Range Order ◽  
Rate Theory ◽  
Probability Method ◽  
Interatomic Potentials ◽  
Second Stage ◽  
Activated State ◽  
State Rate ◽  
Two Stages ◽  
Kinetics Of ◽  
Path Probability Method

AbstractMonte-Carlo simulations (MCS) and the path probability method (PPM) were used to study disorder→order transformations in bcc alloys having the AB3 stoichiometry. Both methods used an explicit vacancy mechanism of ordering and an activated-state rate theory for the vacancy jumps. We studied the evolution of short-range order (SRO) as well as B2 and D03 long-range order (LRO) in alloys that began as random solid solutions. The growth rates of SRO and LRO were significantly higher for the PPM than for the MCS. We attribute this difference to improper handling of correlated vacancy motions in the PPM. The PPM also suffered from an artificial incubation time for the initiation of LRO. Both the MCS and the PPM showed that SRO has a tendency to develop in two stages. In the first stage there is a quick relaxation of the SRO by itself. In the second stage, which occurs with a longer time constant, the SRO and LRO grow simultaneously. Parametric plots of one order parameter against another, here termed “kinetic paths”, are discussed. A variety of different kinetic paths through the B2 and D03 order parameters can be predicted theoretically, depending on the choice of interatomic potentials. This range of calculated kinetic paths is broad enough to encompass our experimental results of SRO and LRO evolution in Fe3Al.

Kinetics of Mixed Low-Level Waste Incapsulation Using Iron Phosphate Chemically Bonded Cement

2006 ◽  
Vol 932 ◽  
Author(s):  
A.S. Aloy ◽  
T.I. Koltsova ◽  
E.N. Kovarskaya ◽  
M.Yu. Silin
Keyword(s):  
Formation Process ◽  
Iron Phosphate ◽  
Structural Formation ◽  
Low Level ◽  
Second Stage ◽  
Bivalent Iron ◽  
Acid Reaction ◽  
The Moment ◽  
Two Stages ◽  
Kinetics Of

ABSTRACTThe iron phosphate cement (IPC) structure formation process has been studied by Mossbauer spectroscopy. The IPC is formed as a result of interaction of iron oxides with orthophosphoric acid and could be used as a matrix for immobilization of low-level radioactive waste.The structural formation process has been shown may be considered to consist of two stages. The first stage lasts to the moment of setting, when the diffusion process goes on in the liquid phase. At this stage the main fragments of the structural polymeric frame of the IPC are developed consisting of iron (+2) and (+3) phosphates. The rate of the oxides-with-phosphoric-acid reaction as well as the time of hardening depends on the bivalent iron content.The second stage begins from the moment of setting when the diffusion becomes slower. At this stage the process is characterized by the negligible increase in the iron phosphates (+2), (+3) content and transformation of the previously formed phosphates.The nuclear gamma-resonance (NGR) parameters have been determined of FeH3(PO4)2·2.5H2O, forming in the hematite (Fe2O3) based IPC: isomeric shift (IS) = 0.46 mm/s, quadrupole splitting (QS) = 0.197 mm/s, FWHM =0.282 mm/s.

Kinetic paths of B2 and DO3 order parameters: Theory

1989 ◽  
Vol 4 (5) ◽  
pp. 1132-1139 ◽  
Author(s):  
L. Anthony ◽  
B. Fultz
Keyword(s):  
Time Dependence ◽  
Nearest Neighbor ◽  
Temporal Evolution ◽  
Initial Conditions ◽  
Interatomic Interaction ◽  
Order Parameters ◽  
Rate Theory ◽  
Bcc Lattice ◽  
Activated State ◽  
State Rate

It is shown that a binary alloy with an AB3 stoichiometry on a bcc lattice may develop various combinations of B2 and DO3 order along its kinetic path toward equilibrium. The temporal evolution of these two order parameters is analyzed with an activated-state rate theory. Individual vacancy jumps are treated in a master equation formalism that involves first-nearest-neighbor (1nn) and second-nearest-neighbor (2nn) interactions. In our formulation, a set of coupled differential equations is obtained describing the time-dependence of six order parameters. These equations were integrated numerically for a variety of interatomic interactions and initial conditions. It was found that the relative rates of B2 and DO3 ordering, and hence the path of the alloy through the space spanned by the B2 and DO3 order parameters, depend on the relative strengths of the interatomic interaction potentials and on the temperature. For very strong 2nn interactions, a transient B32 structure was observed to develop at early times, although this phase disappeared as equilibrium was approached.

Oxidation Kinetics of the Sintered Iron Parts Steam Treated in an Industrial Continuous Furnace

2010 ◽  
Vol 660-661 ◽  
pp. 243-248
Author(s):  
Eduardo Nunes ◽  
Ivan Gilberto Sandoval Falleiros
Keyword(s):  
Oxidation Kinetics ◽  
Continuous Furnace ◽  
Steam Treatment ◽  
Sintered Iron ◽  
Second Stage ◽  
Parabolic Law ◽  
Controlling Mechanism ◽  
Iron Diffusion ◽  
Two Stages ◽  
Kinetics Of

It has been studied a steam treatment process in an industrial continuous furnace for sintered iron parts in a temperature range varying from 490 to 570 °C and sample´s sintered densities of 6,52 and 6,77 g / cm3 . The tests have showed oxidation kinetics with two stages, each of them obeying a parabolic law. The first stage was faster than the second. The oxidation time when the oxidation kinetics of the first stage has changed for the second stage showed off very sensitive to the process temperature and sintered densities of the parts which are in agreement with the process rate controlling mechanism that was found to be the iron diffusion through the oxide layer.

Rubberised fabric for fuel soft storage tanks*

2018 ◽  
Vol 45 (7) ◽  
pp. 322-324
Author(s):  
Yu.N. Rybakov ◽  
A.V. Dedov ◽  
D.S. Plokhoi ◽  
D.V. Kolotilin
Keyword(s):  
Diffusion Processes ◽  
Motor Fuel ◽  
Residual Monomer ◽  
Experimental Conditions ◽  
Second Stage ◽  
Before And After ◽  
Nitrile Rubbers ◽  
Two Stages ◽  
Kinetics Of

The kinetics of extraction of dibutyl sebacinate by different grades of motor fuel from rubberised fabric based on a blend of nitrile rubbers SKN-26M and SKN-40M was investigated. The kinetics was determined according to the GOST 9.030-74 standard from the change in weight of the specimen after holding in fuel at 50°C and drying. The change in quality of the fuel after contact with the fabric was recorded from the change in the content of existent gum in fuel according to GOST 1567-97 (ISO 6246-95) and its acidity according to GOST 5985-79 before and after contact with the rubberised fabric. It was shown that the process of extraction proceeds in two stages, the time of the first of which under experimental conditions is not dependent on the type of fuel. The rate of the first stage is much higher than the rate of the second stage. The relation of rates and proportion of extracted fuel at the first and second stages depends on the type of fuel. It can be asserted that the surplus amount of extracted substances is made up of impurities, which include residual monomer or its derivatives and substances used in the synthesis of the rubber. The mechanism of extraction with extractant counterflow into the vulcanisate and its dependence on the grade of petrol is proposed, based on allowance for the diffusion processes in the system.

Kinetics of Mg2Sn Synthesis Reaction under Isothermal Condition

2010 ◽  
Vol 146-147 ◽  
pp. 1712-1716
Author(s):  
Yu Feng Wu ◽  
Wen Bo Du ◽  
Zhao Hui Wang ◽  
Tie Yong Zuo
Keyword(s):  
Isothermal Condition ◽  
Growth Control ◽  
Nucleation And Growth ◽  
Synthesis Process ◽  
Synthesis Reaction ◽  
Isothermal Reaction ◽  
Second Stage ◽  
Two Stages ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of Mg2Sn synthesis reaction was studied under isothermal condition in the present paper. Results indicated that the isothermal reaction of Mg2Sn was controlled by two reactive mechanisms: the nucleation and growth control in the first stage corresponding to the Avrami exponent, m≈3, and the phase boundary control in the second stage corresponding to m≈1.1. The reactive activation energy (Ea ) for the two stages was 293.6 kJ·mol-1 and 358.1 kJ·mol-1, respectively. The microstructural evolution in Mg2Sn synthesis process was in good agreement with the two reactive mechanisms.

Metal Dusting Corrosion of 9Cr-1Mo Steel in Propane-Butane Gas Mixture

2009 ◽  
Vol 289-292 ◽  
pp. 477-483
Author(s):  
Zbigniew Grzesik ◽  
Marek Danielewski ◽  
Stanisław Mrowec
Keyword(s):  
Total Pressure ◽  
Petrochemical Industry ◽  
Diffusion Processes ◽  
Metal Dusting ◽  
Second Stage ◽  
Reaction Proceeds ◽  
Two Stages ◽  
Kinetics Of ◽  
Low Rate ◽  
Propane Butane

The kinetics and mechanism of metal dusting corrosion of 9Cr-1Mo steel, commonly used in CCR platforming units, have been studied as a function of temperature (773 – 1173 K) in propane-butane atmosphere, being the mixture of 70 vol. % of propane and 30 vol. % of butane with the total pressure equal 105 Pa. The kinetics of corrosion have been studied thermogravimetrically in the apparatus enabling the mass changes of corroded sample to be followed continuously with the accuracy of the order of 10-6 g. It has been found that metal dusting corrosion in this atmosphere, modeling in some way industrial environments in petrochemical industry, is complex and two-stages of linear kinetics may be distinguished. In the first stage, which may be considered as an incubation period, the reaction proceeds with rather low rate, which increases dramatically in the second stage, the beginning of which depends strongly on temperature. Linear course of reaction indicates that chemical reactions and not diffusion processes determine the rate of corrosion. This conclusion is confirmed by the fact, that the layer of corrosion products is not compact but considerably porous.

scholarly journals Kinetics of Glass Transition Simulated by Path Probability Method

2005 ◽  
Vol 46 (12) ◽  
pp. 2811-2816 ◽  
Author(s):  
Tetsuo Mohri ◽  
Yoshitaka Kobayashi
Keyword(s):  
Glass Transition ◽  
Probability Method ◽  
Kinetics Of ◽  
Path Probability Method

Kinetics of Ordering in Fe3Al: Experiment

1990 ◽  
Vol 186 ◽  
Author(s):  
Brent Fultz ◽  
Zheng-Qiang Gao ◽  
Lawrence Anthony
Keyword(s):  
Long Range ◽  
Order Parameter ◽  
Range Order ◽  
Disordered Materials ◽  
Long Range Order ◽  
X Ray ◽  
Different Temperatures ◽  
Two Stages ◽  
Rates Of Growth ◽  
Kinetics Of

AbstractAlloys near the Fe3Al stoichiometry were prepared far from thermodynamic equilibrium by rapid solidification methods. These highly disordered materials were then annealed at low temperatures to develop B2 and D03 order. Both shortrange and long-range order (SRO and LRO) were measured by Mössbauer spectrometry and by x-ray diffractometry, respectively. The SRO was found to evolve in two stages: an initial quick growth of the SRO alone, followed by a slower growth of SRO along with LRO. As expected, at lower temperatures the absolute rates of growth of order were suppressed, but more interestingly, the relative rates of growth of B2 and D03 long-range order parameters were different at different temperatures of annealing. When the B2 order parameter is graphed against the D03 order parameter, at lower temperatures the “kinetic path” through this graph shows that B2 order evolves relatively more rapidly than D03 order.

scholarly journals Studies of precipitation during the decomposition process of phosphorus-containing compounds

2019 ◽  
Vol 80 (4) ◽  
pp. 312-315
Author(s):  
M. M. Ganbarov ◽  
M. M. Ataev ◽  
K. K. Gazvini
Keyword(s):  
Raw Materials ◽  
Environmentally Friendly ◽  
Decomposition Process ◽  
Second Stage ◽  
Phosphorus Containing ◽  
Neutralization Process ◽  
The Absolute ◽  
Two Stages ◽  
Kinetics Of

The kinetics of the process of using phosphorus-containing mineral compounds by their decomposition, which are actual problems, has been studied. At beginning of the it have been notified that the process takes place in two stages. These stages of the process are differed from each another mainly by rate of process realization, because a rate of the first stage is much more that a rate of the second stage. This fact is a reason of the deep research of kinetic of given process. Apart from that a detailed study of these processes connect with some problems of enter prices. All these question are analizied in the work, also the information by methodical carry out of experiments. Regime parameters correlation of components, concentrations of components, a time requite for realization of process are presented. The dependence of degree by different mass correlation of components from the time realization of process are also shown. In the work the types existence of precipitate, monitite brush it are shown. On base of received date a dissolubility of the base received product are graphically presented. In the work an influence of mass correlation of CaO?P2O5 and time of process realization on precipitation is studied. It have been determined that by 650C temperature a mass correlation of the base components must be equal to one, by that a time being used on neutralization process don’t play the practical role, because its increase and decrease don’t influence practically on process indices. The results shown that by equality of components CO?P2O5=1 correlation during four hours the precipitation degree makes up to 90,66 % and during 1 hour this index is 78,2 % for duringthe remaining three during this index is increased on 12 %. By using of these received data these is a possibility determination of the optimum technological conditions for given process. it is shown that there are opportunities to achieve processivization, to increase the use of raw materials and to obtain an environmentally friendly product with the introduction of regime parameters and component ratios in the absolute state.

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