Transient kinetics of nucleation and crystallization: Part II. Crystallization

1991 ◽  
Vol 6 (10) ◽  
pp. 2097-2102 ◽  
Author(s):  
G. Shi ◽  
J.H. Seinfeld
Keyword(s):  
Experimental Data ◽  
Large Time ◽  
Volume Fraction ◽  
Time Dependent ◽  
Transient Kinetics ◽  
Amorphous Phases ◽  
Time Limits ◽  
The Stability ◽  
Analytical Expressions ◽  
Kinetics Of

Analytical expressions for the time-dependent crystallized volume fraction are derived from new results for the transient rate of nucleation reported in Part I. Conventional formulations that have been used in interpreting crystallization experimental data and for assessing the stability of amorphous phases are shown to be large time limits of the newly derived expressions. An approach for assessing the stability of an amorphous phase is proposed.

scholarly journals On the Stability of 3C-SiC Single Crystals at High Temperatures

2012 ◽  
Vol 717-720 ◽  
pp. 493-496
Author(s):  
Deborah Dompoint ◽  
Irina G. Galben-Sandulache ◽  
Alexandre Boulle ◽  
Didier Chaussende ◽  
Dominique Eyidi ◽  
...  
Keyword(s):  
Single Crystals ◽  
Volume Fraction ◽  
Diffuse Intensity ◽  
X Ray ◽  
Partial Dislocations ◽  
X Ray Scattering ◽  
Transmission Electron ◽  
The Stability ◽  
Kinetics Of ◽  
Evolution With Time

The 3C-6H polytypic transition in 3C-SiC single crystals is studied by means of diffuse X-ray scattering (DXS) coupled with transmission electron microscopy (TEM). TEM reveals that the partially transformed SiC crystals contain regions of significantly transformed SiC (characterized by a high density of stacking faults) co-existing with regions of pure 3C-SiC. The simulation of the diffuse intensity allows to determine both the volume fraction of transformed material and the transformation level within these regions. It is further shown that the evolution with time and temperature of the transition implies the multiplication and glide of partial dislocations, the kinetics of which are quantified by means of DXS.

scholarly journals Dynamic stability of functionally graded plate under in-plane compression

2005 ◽  
Vol 2005 (4) ◽  
pp. 411-424 ◽  
Author(s):  
Andrzej Tylikowski
Keyword(s):  
Asymptotic Stability ◽  
Power Law ◽  
Volume Fraction ◽  
Direct Method ◽  
Functionally Graded ◽  
Time Dependent ◽  
Power Law Distribution ◽  
Graded Materials ◽  
Plane State ◽  
The Stability

Functionally graded materials have gained considerable attention in the high-temperature applications. A study of parametric vibrations of functionally graded plates subjected to in-plane time-dependent forces is presented. Moderately large deflection equations taking into account a coupling of in-plane and transverse motions are used. Material properties are graded in the thickness direction of the plate according to volume fraction power law distribution. An oscillating temperature causes generation of in-plane time-dependent forces destabilizing the plane state of the plate equilibrium. The asymptotic stability and almost-sure asymptotic stability criteria involving a damping coefficient and loading parameters are derived using Liapunov's direct method. Effects of power law exponent on the stability domains are studied.

Determination of the Grain Coarsening Temperature in Nb Microalloyed Steels by Multiphase-Field Model

2016 ◽  
Vol 879 ◽  
pp. 921-925
Author(s):  
Jeong Min Kim ◽  
Sok Yun Hong ◽  
Ji Hun Jang ◽  
Kyung Jong Lee
Keyword(s):  
Field Model ◽  
Volume Fraction ◽  
Mean Field ◽  
Time Dependent ◽  
Microalloyed Steels ◽  
Pinning Force ◽  
Grain Coarsening ◽  
Dimensional Growth ◽  
Kinetics Of

The grain coarsening temperature in Nb microalloyed steels is investigated by multiphase-field model. In this study, the pinning force is treated as time-dependent using mean-field kinetics of precipitates including volume fraction and their size. The grain size is calculated with time under various temperature range. The grain coarsening temperature is determined by the ratio of the largest radius of grain vs. the average grain radius criteria (Rmax / Ravg > 2.94) in two-dimensional growth. Through this model, it is possible to simulate grain growth in microalloyed steels more precisely.

Extraction of dithiocarbamic acids from solutions of their salts

1982 ◽  
Vol 47 (11) ◽  
pp. 2876-2881 ◽  
Author(s):  
Drahomír Oktavec ◽  
Bohumil Síleš ◽  
Ján Remeň ◽  
Václav Konečný ◽  
Ján Garaj
Keyword(s):  
Aqueous Phase ◽  
Time Dependent ◽  
Absorption Bands ◽  
Decomposition Reactions ◽  
Maximum Extraction ◽  
The Stability ◽  
Kinetics Of ◽  
Alkali Salts ◽  
Nm Range

The extraction of dithiocarbamic acids with chloroform from aqueous phase containing their alkali salts has been investigated with regard to the fact that absorbing strongly in the 200-310 nm range, the acids interfere with the spectrophotometric determination of metals whose dithiocarbamate ligands exhibit their analytical absorption bands in that region. The amount of the dithiocarbamic acids formed depends on the kinetics of their formation and decomposition reactions and on the pH of the aqueous phase. The stability of the acids in chloroform extracts is highly time dependent. The maximum extraction of the acids (R2NCS2H) is attained at the following pH (R, pH): CH3 5.0, C2H5 5.9, C3H8 6.3, C4H9 6.8, C5H11 6.9, C6H13 6.9, iso-C3H7 7.2, iso-C4H9 6.9; for (CH3, iso-C3H7)NCS2H 7.3, C5H10NCS2H 7.2, C4H8ONCS2H 5.2.

Simulation of the Onset of Rotating Stall

2001 ◽  
Author(s):  
Christopher J. Freitas ◽  
Anthony J. Smalley
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Stability Limit ◽  
Rotating Stall ◽  
Time Dependent ◽  
Navier Stokes ◽  
Width Ratio ◽  
Threshold Condition ◽  
Flow Angle ◽  
The Stability

Abstract This paper presents the results of a series of numerical simulations exploring the stability of fluid flow in vaneless diffusers of centrifugal compressors. Three-dimensional, time-dependent, Reynolds-averaged Navier-Stokes simulations were performed for a fixed diffuser width ratio. Effective flow angle was varied from simulation to simulation in order to predict the threshold angle at which the instability — rotating stall — is manifested and maintained. The predicted threshold angle or stability limit is in excellent agreement with experimental data. The simulations reveal a two-stall cell configuration at the threshold condition.

A fuzzy neural network approach for modeling the growth kinetics of FeB and Fe2B layers during the boronizing process

2018 ◽  
Vol 106 (6) ◽  
pp. 603 ◽  
Author(s):  
Bendaoud Mebarek ◽  
Mourad Keddam
Keyword(s):  
Neural Network ◽  
Experimental Data ◽  
Fuzzy Neural Network ◽  
Treatment Time ◽  
Calculation Model ◽  
Average Error ◽  
Network Approach ◽  
Neural Network Approach ◽  
Fuzzy Neural ◽  
Kinetics Of

In this paper, we develop a boronizing process simulation model based on fuzzy neural network (FNN) approach for estimating the thickness of the FeB and Fe2B layers. The model represents a synthesis of two artificial intelligence techniques; the fuzzy logic and the neural network. Characteristics of the fuzzy neural network approach for the modelling of boronizing process are presented in this study. In order to validate the results of our calculation model, we have used the learning base of experimental data of the powder-pack boronizing of Fe-15Cr alloy in the temperature range from 800 to 1050 °C and for a treatment time ranging from 0.5 to 12 h. The obtained results show that it is possible to estimate the influence of different process parameters. Comparing the results obtained by the artificial neural network to experimental data, the average error generated from the fuzzy neural network was 3% for the FeB layer and 3.5% for the Fe2B layer. The results obtained from the fuzzy neural network approach are in agreement with the experimental data. Finally, the utilization of fuzzy neural network approach is well adapted for the boronizing kinetics of Fe-15Cr alloy.

Kinetics of Various 99mTc-Sn-Pyrophosphate Compounds in the Rat

1977 ◽  
Vol 16 (04) ◽  
pp. 157-162 ◽  
Author(s):  
C. Schümichen ◽  
B. Mackenbrock ◽  
G. Hoffmann
Keyword(s):  
Normal Saline ◽  
Half Life ◽  
Compound A ◽  
Short Half Life ◽  
Low Concentrations ◽  
The Stability ◽  
Kinetics Of ◽  
In Vitro Stability

SummaryThe bone-seeking 99mTc-Sn-pyrophosphate compound (compound A) was diluted both in vitro and in vivo and proved to be unstable both in vitro and in vivo. However, stability was much better in vivo than in vitro and thus the in vitro stability of compound A after dilution in various mediums could be followed up by a consecutive evaluation of the in vivo distribution in the rat. After dilution in neutral normal saline compound A is metastable and after a short half-life it is transformed into the other 99mTc-Sn-pyrophosphate compound A is metastable and after a short half-life in bone but in the kidneys. After dilution in normal saline of low pH and in buffering solutions the stability of compound A is increased. In human plasma compound A is relatively stable but not in plasma water. When compound B is formed in a buffering solution, uptake in the kidneys and excretion in urine is lowered and blood concentration increased.It is assumed that the association of protons to compound A will increase its stability at low concentrations while that to compound B will lead to a strong protein bond in plasma. It is concluded that compound A will not be stable in vivo because of a lack of stability in the extravascular space, and that the protein bond in plasma will be a measure of its in vivo stability.

Symmetrizable Difference Dchemes

2005 ◽  
Vol 5 (1) ◽  
pp. 3-50 ◽  
Author(s):  
Alexei A. Gulin
Keyword(s):  
Initial Data ◽  
Difference Scheme ◽  
Difference Schemes ◽  
Time Dependent ◽  
Stability Boundaries ◽  
Typical Representative ◽  
Variable Weight ◽  
The Stability ◽  
Conditions Of Stability ◽  
The Right

AbstractA review of the stability theory of symmetrizable time-dependent difference schemes is represented. The notion of the operator-difference scheme is introduced and general ideas about stability in the sense of the initial data and in the sense of the right hand side are formulated. Further, the so-called symmetrizable difference schemes are considered in detail for which we manage to formulate the unimprovable necessary and su±cient conditions of stability in the sense of the initial data. The schemes with variable weight multipliers are a typical representative of symmetrizable difference schemes. For such schemes a numerical algorithm is proposed and realized for constructing stability boundaries.

Features of the kinetics of cyclic elastoplastic deformation diagrams at dwells in cycles and superimposition of variable stresses on them

2020 ◽  
Vol 86 (12) ◽  
pp. 46-53
Author(s):  
M. M. Gadenin
Keyword(s):  
Experimental Data ◽  
Elastoplastic Deformation ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Loading Cycle ◽  
Additional Variable ◽  
Dynamic Creep ◽  
Variable Stresses ◽  
Kinetics Of ◽  
Deformation Diagrams

The goal of the study is determination of the regularities of changes in cyclic strains and related deformation diagrams attributed to the existence of time dwells in the loading modes and imposition of additional variable stresses on them. Analysis of the obtained experimental data on the kinetics of cyclic elastoplastic deformation diagrams and their parameters revealed that in contrast to regular cyclic loading (equal in stresses), additional deformations of static and dynamic creep are developed. The results of the studys are especially relevant for assessing the cyclic strength of unique extremely loaded objects of technology, including nuclear power equipment, units of aviation and space systems, etc. The experiments were carried out on the samples of austenitic stainless steel under low-cycle loading and high temperatures of testing. Static and dynamic creep deformations arising under those loading conditions promote an increase in the range of cyclic plastic strain in each loading cycle and also stimulate an increase in the range of elastoplastic strain due to active cyclic deformation. At the same time the existence of dwells on extrema of stresses in cycles without imposition of additional variable stresses on them most strongly affects the growth of plastic strain ranges in cycles. Imposition of additional variable stresses on dwells also results in the development of creep strains, but their growth turns out to be somewhat less than in the presence of dwells without stresses imposed. The diagrams of cyclic deformation obtained in the experiments are approximated by power dependences, their kinetics being described in terms of the number of loading cycles using corresponding temperature-time functions. At the same time, it is shown that increase in the cyclic plastic deformation for cycles with dwells and imposition of additional variable stresses on them decreases low cycle fatigue life compared to regular loading without dwells at the same stress amplitudes, moreover, the higher the values of static and dynamic creep, the greater decrease in low-cycle fatigue life. This conclusion results from experimental data and analysis of conditions of damage accumulation for the considered forms of the loading cycle using the deformation criterion of reaching the limit state leading to fracture.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

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