Structure and Formation Kinetics of Mosi2 Composites Formed by Reactive Vapor Infiltration Process

1994 ◽  
Vol 365 ◽  
Author(s):  
W.B. Hillig ◽  
R.M. Ramakrishnan ◽  
M. Broglio ◽  
N. Patibandla
Keyword(s):  
Rate Constant ◽  
Linear Increase ◽  
Growth Rate Constant ◽  
Matrix Composites ◽  
Infiltration Process ◽  
One Dimensional ◽  
Formation Kinetics ◽  
New Process ◽  
Kinetics Of ◽  
Vapor Infiltration

ABSTRACTReactive Vapor Infiltration is a convenient new process for producing high purity MoSi2 matrix composites by reacting compacted mixed Mo + MoSi2 powders ranging from 0 to 80 wt. % MoSi2 with H2 + SiCl4 vapors at temperatures from 1000 to 1400°C. Consideration must be taken of the volumetric increase that accompanies this conversion. The kinetics of the advance of the MoSi2 growth layer and the gravimetric uptake are given as a function of temperature and the composition. The parabolic growth rate constant was independent of composition at least up to 30% MoSi2 composition, but then showed a strong, linear increase with increasing MoSi2 content. There appeared to be a levelling off of rate above 70% MoSi2. The corresponding gravimetric rate constant was relatively insensitive to the starting MoSi2 content. This behavior is at variance with a simple one-dimensional diffusive growth model. Possible reasons for this variance are offered.

A model for front evolution with a nonlocal growth rate

1999 ◽  
Vol 14 (10) ◽  
pp. 3829-3832 ◽  
Author(s):  
Shi Jin ◽  
Xuelei Wang ◽  
Thomas L. Starr
Keyword(s):  
Chemical Vapor ◽  
Ceramic Matrix Composites ◽  
Front Propagation ◽  
Chemical Vapor Infiltration ◽  
Matrix Composites ◽  
Infiltration Process ◽  
Physical Problems ◽  
Eulerian Formulation ◽  
Continuous Filament ◽  
Vapor Infiltration

In this paper we provide a new mathematical model for front propagation with a nonlocal growth law in any space dimension. Such a problem arises in composite fabrication using the vapor infiltration process and in other physical problems involving transport and reaction. Our model, based on the level set equation coupled with a boundary value problem of the Laplace equation, is an Eulerian formulation, which allows robust treatment for topological changes such as merging and formation of pores without artificially tracking them. When applied to the fabrication of continuous filament ceramic matrix composites using chemical vapor infiltration, this model accurately predicts not only residual porosity but also the precise locations and shapes of all pores.

Kinetics of rouleaux formation using TV image analyzer. II. Rat erythrocytes

1983 ◽  
Vol 245 (2) ◽  
pp. H259-H264 ◽  
Author(s):  
T. Shiga ◽  
K. Imaizumi ◽  
N. Maeda ◽  
K. Kon
Keyword(s):  
Kinetic Model ◽  
Rate Constant ◽  
Three Dimensional ◽  
Erythrocyte Aggregation ◽  
Image Analyzer ◽  
One Dimensional ◽  
Specific Pathogen ◽  
Time Courses ◽  
Kinetics Of ◽  
Rouleaux Formation

With the use of a rheoscope combined with a TV image analyzer, the kinetics of specific pathogen-free rat erythrocyte aggregation was studied. Under certain conditions (gamma 7.5 s-1, hematocrit 0.36%, in own plasma, at 25 degrees C) one-dimensional aggregates (rouleaux) were formed without the development of three-dimensional aggregates, perhaps because of very low concentration of gamma-globulin. The observed phenomena could be explained by 1) the erythrocyte sedimentation and 2) the rouleaux formation. The time courses, of the biphasic change in erythrocyte count and of the increments in total area and in the area/count, were successfully simulated by a kinetic model of linear polymerization, assuming a sedimentation rate constant and an association rate constant. Further, a Poissonlike distribution of the length of rouleaux was shown, as predicted theoretically on the basis of the same kinetic model.

scholarly journals An Empirical Rate Constant Based Model to Study Capacity Fading in Lithium Ion Batteries

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Srivatsan Ramesh ◽  
K. Venkata Ratnam ◽  
Balaji Krishnamurthy
Keyword(s):  
Rate Constant ◽  
Film Formation ◽  
Solid Electrolyte Interphase ◽  
Lithium Ion ◽  
Capacity Fading ◽  
Formation Reaction ◽  
One Dimensional ◽  
Battery Systems ◽  
Diffusion And Kinetics ◽  
Kinetics Of

A one-dimensional model based on solvent diffusion and kinetics to study the formation of the SEI (solid electrolyte interphase) layer and its impact on the capacity of a lithium ion battery is developed. The model uses the earlier work on silicon oxidation but studies the kinetic limitations of the SEI growth process. The rate constant of the SEI formation reaction at the anode is seen to play a major role in film formation. The kinetics of the reactions for capacity fading for various battery systems are studied and the rate constants are evaluated. The model is used to fit the capacity fade in different battery systems.

Fiber-Reinforced Tubular Composites by Chemical Vapor Infiltration°

1991 ◽  
Vol 250 ◽  
Author(s):  
D. P. Stinton ◽  
R. A. Lowden ◽  
T. M. Besmann
Keyword(s):  
Mechanical Properties ◽  
Thermal Gradient ◽  
Chemical Vapor ◽  
Chemical Vapor Infiltration ◽  
Forced Flow ◽  
Matrix Composites ◽  
Fiber Reinforced ◽  
Infiltration Process ◽  
Filament Wound ◽  
Vapor Infiltration

AbstractA forced-flow thermal-gradient chemical vapor infiltration process has been developed to fabricate composites of thick-walled tubular geometry common to many components. Fibrous preforms of different fiber architectures (3-dimensionally braided and filament wound) have been investigated to accommodate components with different mechanical property requirements. This paper will discuss the fabrication of tubular, fiber-reinforced SiC matrix composites and their mechanical properties.

Synthesis and Polymerization Kinetics of PMMA in Imidazolium Ionic Liquids

2013 ◽  
Vol 423-426 ◽  
pp. 528-531
Author(s):  
Pei Wang ◽  
Yuan Liu ◽  
Wen Su ◽  
Lian Liu
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Average Molecular Weight ◽  
Propagation Rate ◽  
Polymerization Kinetics ◽  
Growth Rate Constant ◽  
Weight Average Molecular Weight ◽  
Propagation Rate Constant ◽  
Kinetics Of ◽  
Chain Propagation Rate

Polymerization of high molecular weight PMMA was achieved in [BMIM]PF4at reaction temperature 60oC, 65°C and 70 °C, reaction time 60min. The data including the yield, molecular weight and molecular weight distribution of PMMA were analysized. The results showed that the weight average molecular weight of PMMA in [BMIM]PF4is up to 275867, respectively 4 and 7 times of molecular weight in cyclohexane and toluene. Secondly, the polymerization kinetics of PMMA in [BMIM]PF4were tested, the apparent chain propagation rate constant of PMMA are 0.93×104,1.11 ×104and 14.1×104in 60 °C, 65°C and 70 °C. Compared with the growth rate constant in toluene, the polymerization rate constant PMMA in the ionic liquid increased by 4~7 times.

scholarly journals Simulation of the incubation time for the formation of (FeB/Fe2B) bilayer on pure iron

2021 ◽  
Vol 65 (2) ◽  
pp. 49-56
Author(s):  
B. Mebarek ◽  
M. Keddam ◽  
M. Kulka
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Growth Rate ◽  
Rate Constant ◽  
Incubation Time ◽  
Pure Iron ◽  
Boride Layer ◽  
Growth Rate Constant ◽  
Increasing Temperature ◽  
Kinetics Of

Abstract In this work, a mathematical model was used in order to study the growth kinetics of (Fe2B/FeB) bilayer during bori-ding process basing on the second Fick’s law and mass balance equation. The run of the numerical simulation allowed calculating the incubation time (τ) of each boronized layer (Fe2B or FeB), and estimating the effect of this parameter on the growth of the boronized layer. The boride incubation time for forming the FeB or Fe2B layer on the pure iron substrate was incorporated into the present mathematical model. To simulate the value of the growth rate constant and the incubation time for the bilayer configuration, the experimental data available in the literature concerning the boronizing of pure iron were considered. Based on the experimental and simulation results, it was shown that the incubation time decreases with increasing temperature in the FeB and Fe2B phases. It was concluded from this study that the thickness of each boride layer depended on its growth rate constant and on another parameter kτ which was the rate constant of incubation time.The obtained results confirmed the validity of the present mathematical model and gave a good estimate of the incubation time during the formation of each boride layer as well as formulated the variation of this parameter with a mathematical equation. Furthermore, the comparison of experimental data with the simulated results of boronized layer thickness allowed to validate the present model.

Synthesis and Polymerization Kinetics of PMMA in [BMIM]BF6 Imidazolium Ionic Liquids

2013 ◽  
Vol 395-396 ◽  
pp. 411-414 ◽  
Author(s):  
Pei Wang ◽  
Yuan Liu ◽  
Wen Su ◽  
Lian Liu
Keyword(s):  
Molecular Weight ◽  
Rate Constant ◽  
Average Molecular Weight ◽  
Propagation Rate ◽  
Polymerization Kinetics ◽  
Growth Rate Constant ◽  
Weight Average Molecular Weight ◽  
Propagation Rate Constant ◽  
Kinetics Of ◽  
Chain Propagation Rate

Polymerization of high molecular weight PMMA was achieved in [BMIPF6by contrasted in cyclohexane, toluene solvent at reaction temperature 60 C, 65C and 70 C, reaction time 60min. The data including the yield, molecular weight and molecular weight distribution of PMMA were analysized in 3 kind of solvent. The results showed that the weight average molecular weight of PMMA in [BMIPF6is up to 730000, respectively 7 and 10 times of molecular weight in cyclohexane and toluene. Secondly, the polymerization kinetics of PMMA in [BMIPF6were tested, the apparent chain propagation rate constant of PMMA are 10.7×10412.9 ×104and 19.9×104in 60 C, 65C and 70 C. Compared with the growth rate constant in toluene, the polymerization rate constant PMMA in the ionic liquid increased by 5~10 times.

Fabrication of carbon-carbon composites by forced flow-thermal gradient chemical vapor infiltration

1995 ◽  
Vol 10 (6) ◽  
pp. 1469-1477 ◽  
Author(s):  
Sundar Vaidyaraman ◽  
W. Jack Lackey ◽  
Garth B. Freeman ◽  
Pradeep K. Agrawal ◽  
Matthew D. Langman
Keyword(s):  
Thermal Gradient ◽  
Chemical Vapor ◽  
Carbon Matrix ◽  
Chemical Vapor Infiltration ◽  
Forced Flow ◽  
Carbon Cloth ◽  
Matrix Composites ◽  
Infiltration Process ◽  
Order Of Magnitude ◽  
Vapor Infiltration

Carbon fiber-carbon matrix composites were fabricated using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. The preforms for the infiltration were prepared by stacking 40 layers of carbon cloth in a graphite holder. The preforms were infiltrated with carbon using propylene or methane as a reactant, with hydrogen as a diluent. Composites with porosities as low as 7% have been processed within 8-12 h. The highest deposition rate obtained in the present study was ∼3 μm/h, which is more than an order of magnitude faster than the typical value of 0.1-0.25 μm/h for the isothermal infiltration process.

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