A micromechanistic model of the combustion synthesis process: Part II. Numerical simulation

1994 ◽  
Vol 9 (10) ◽  
pp. 2605-2619 ◽  
Author(s):  
Yangsheng Zhang ◽  
Gregory C. Stangle
Keyword(s):  
Theoretical Model ◽  
Combustion Synthesis ◽  
Quantitative Description ◽  
Computer Experiments ◽  
The Self ◽  
Synthesis Process ◽  
Energy Redistribution ◽  
Precise Control ◽  
Physical And Chemical ◽  
Proper Balance

A series of computer experiments was conducted for the self-propagating combustion synthesis process in the Nb-C system, based on the general theoretical model that was developed previously.1 A detailed and quantitative description was given for the various physical and chemical processes that take place during the combustion synthesis process. The results are presented at various length scales in order to provide an insight into understanding the mechanisms that are responsible for the self-propagating behavior. It was shown that a fundamental understanding and precise control of the process require a strong emphasis on the joint contributions of the rates of the various mass and energy redistribution processes that occur during the combustion synthesis process. A proper balance of each of the elementary process rates must be achieved to give rise to self-propagating behavior. This paper illustrates some of the capabilities of the general theoretical model in quantitatively describing the self-propagating combustion synthesis process.

A micromechanistic model of the combustion synthesis process: Part I. Theoretical development

1994 ◽  
Vol 9 (10) ◽  
pp. 2592-2604 ◽  
Author(s):  
Yangsheng Zhang ◽  
Gregory C. Stangle
Keyword(s):  
Theoretical Model ◽  
Combustion Synthesis ◽  
Computer Experiments ◽  
Theoretical Development ◽  
Synthesis Process ◽  
Fundamental Understanding ◽  
Independent Variable ◽  
Physical And Chemical ◽  
Disordered Porous Media ◽  
Point Of Departure

A theoretical model of the combustion synthesis process has been developed. In particular, a set of nonlinear and interrelated partial differential equations is given that accounts for all of the relevant physical and chemical processes that occur during the combustion synthesis process. The appropriate conservation equations for thermal energy, mass, and momentum densities are correctly described—for each phase at each point in the sample—at all times during the process. In addition, details of the necessary interphase transfer terms are expressed in a number of constitutive relationships, in which the dependence of an independent variable upon its dependent variable(s) is given explicitly. In doing so, microstructural details are accounted for, derived primarily from percolation concepts as applied to disordered porous media. All assumptions that are incorporated into the theoretical model have been tabulated in detail. This theoretical model establishes an approach to the development of a sound, quantitative, and fundamental understanding of the combustion synthesis process, particularly with respect to the processing-microstructure-properties relationship. It also provides a point of departure for conducting detailed, quantitative computer experiments of the combustion synthesis process.

A micromechanistic model of the combustion synthesis process: Mechanism of ignition

1998 ◽  
Vol 13 (1) ◽  
pp. 146-155 ◽  
Author(s):  
Cheng He ◽  
Gregory C. Stangle
Keyword(s):  
Combustion Synthesis ◽  
Feedback Loop ◽  
External Source ◽  
Constant Heat Flux ◽  
Synthesis Process ◽  
Ignition Process ◽  
Reaction Proceeds ◽  
Physical And Chemical ◽  
Influential Parameters ◽  
Proper Balance

A micromechanistic model of the combustion synthesis has been extended to study the detailed mechanism and influential parameters of a combustion synthesis process, as well as the development of ignition criteria in the Nb–C system. The case of constant heat-flux ignition conditions has been used to illustrate the details of the ignition process, in order to elucidate the various physical and chemical processes that take place during the initial stages of the combustion synthesis process; however, the results of this study can be generally extended to the other modes of the ignition process. The results showed that the ignition criteria for the Nb–C system corresponded to the establishment of a proper balance between the rates of enthalpy redistribution within the sample, and to the establishment of a kind of positive feedback loop during the ignition process that is necessary for self-propagation to occur. If the heat supplied from an external source to initiate the combustion synthesis process is less than a certain critical value, the combustion wave stops at a certain short distance from the ignition surface. Otherwise, the reaction proceeds in a self-propagating manner.

A micromechanistic model of the combustion synthesis process: Influence of intrinsic kinetics

1998 ◽  
Vol 13 (8) ◽  
pp. 2269-2280 ◽  
Author(s):  
Cheng He ◽  
Chantal Blanchetiere ◽  
Gregory C. Stangle
Keyword(s):  
Pore Size ◽  
Combustion Synthesis ◽  
Kinetic Mechanism ◽  
Product Formation ◽  
Point Of View ◽  
Synthesis Process ◽  
Intrinsic Kinetics ◽  
Physical And Chemical ◽  
The Relationship ◽  
Proper Balance

A micromechanistic model of the combustion synthesis of NbC has been developed by combining the results of an experimental study of the intrinsic, pore-level kinetic mechanism [C. He. and G. C. Stangle, J. Mater. Res. 10, 2829–2841 (1995)] and a theoretical model developed previously [Y. Zhang and G. C. Stangle, J. Mater. Res. 9, 2592–2604 (1994); 9, 2605–2619 (1994)], in order to account for the various physical and chemical processes that take place during the combustion synthesis process. Results of the present investigation are interpreted from both a macroscopic and a microscopic point of view. Moreover, the relationship between the microscopic processes and macroscopic features of the combustion synthesis process is discussed. The results show that the formation of a combustion wave in the Nb-C system corresponded to establishment of a proper balance between the rates of enthalpy redistribution within the sample. Furthermore, the pore size had a significant influence on the combustion synthesis process: smaller pores gave rise to a higher area of contact between the reactants, which in turn gave rise to a higher rate of enthalpy increase due to the enhanced rate of product formation. The influence of the pore size distribution on the process is also discussed.

A micromechanistic model of the combined combustion synthesis-densification process

1995 ◽  
Vol 10 (7) ◽  
pp. 1828-1845 ◽  
Author(s):  
Yangsheng Zhang ◽  
Gregory C. Stangle
Keyword(s):  
Combustion Synthesis ◽  
Volume Fraction ◽  
Mechanical Load ◽  
Computer Experiments ◽  
The Self ◽  
Synthesis Process ◽  
Densification Process ◽  
Quantitative Understanding ◽  
Solid Phases ◽  
Total Volume Fraction

A series of computer experiments has been conducted in order to study the combined combustion synthesis-densification process, in which a mechanical load is applied to a sample as it undergoes a combustion synthesis process. The current work is an extension of a theoretical model of the combustion synthesis process that was developed previously.1,2 In this work, the appropriate constitutive equations for sample deformation have been incorporated, in order to account for the pore-volume change that may take place when the mechanical load is applied, thus densifying the sample. It was shown that the brief appearance of a liquid phase in the combustion wave front provides an important opportunity for densification when the self-propagating combustion synthesis process is conducted in conjunction with an applied mechanical load. That is, the concomitant decrease in the (local) total volume fraction of the solid phases—due to the elementary melting and dissolution processes that also occur (locally)—effectively lowered the (local) apparent yield strength of the sample, thus allowing for the compaction and densification of the sample (i.e., locally). Results indicated that the mechanical load should be applied at the instant at which the sample is ignited, in order to ensure that articles whose density is uniform throughout the sample can be fabricated. This work provided a more detailed and quantitative understanding of this unique process for preparing dense articles by the self-propagating combustion synthesis process, that is, when it is conducted in conjunction with an applied mechanical load.

A micromechanistic model of the combustion synthesis process: Modes of ignition

1998 ◽  
Vol 13 (1) ◽  
pp. 135-145 ◽  
Author(s):  
Cheng He ◽  
Gregory C. Stangle
Keyword(s):  
Heat Flux ◽  
Theoretical Model ◽  
Combustion Synthesis ◽  
Variable Temperature ◽  
Theoretical Work ◽  
Constant Heat Flux ◽  
Point Of View ◽  
Synthesis Process ◽  
Ignition Process ◽  
Constant Heat

A theoretical model of the combustion synthesis process has been developed to study the ignition of a self-propagating combustion synthesis process in the Nb–C system. Compared with most of the previously published theoretical work on this subject, this model provides a much more detailed description of the combustion synthesis process from a microscale point of view, due to the fact that it takes into consideration the various microprocesses, such as the melting of reactants, the diffusion and mixing of reactants, and the formation of products. Different ignition modes, including constant-temperature ignition, constant-heat-flux ignition, and variable-temperature ignition, are considered in this work. The key parameters that influence the ignition process are also discussed.

scholarly journals Combustion synthesis of metal carbides: Part II. Numerical simulation and comparison with experimental data

2005 ◽  
Vol 20 (5) ◽  
pp. 1269-1277 ◽  
Author(s):  
A.M. Locci ◽  
A. Cincotti ◽  
F. Delogu ◽  
R. Orrù ◽  
G. Cao
Keyword(s):  
Experimental Data ◽  
Combustion Synthesis ◽  
Quantitative Description ◽  
Scale Model ◽  
Metal Carbides ◽  
Fitting Procedure ◽  
High Temperature Synthesis ◽  
Complex Picture ◽  
Model Reliability ◽  
Physical And Chemical

Based on the general theoretical model proposed in Part I of this work [J. Mater. Res. 20, 1257 (2005)], a series of numerical simulations related to the self-propagating high-temperature synthesis in the Ti–C system is presented. A detailed and quantitative description of the various physical and chemical processes that take place during combustion synthesis processes is provided in Part II of this work. In particular, the proposed mathematical description of the system has been discussed by highlighting the relation between system macroscopic behavior obtained experimentally with the modeled phenomena taking place at the microscopic scale. Model reliability is tested by comparison with suitable experimental data being nucleation parameters adopted for the fitting procedure. The complex picture emerging as a result of the model sophistication indicates that the rate of conversion is essentially determined by the rate of nucleation and growth. In addition, comparison between model results and experimental data seems to confirm the occurrence of heterogeneous nucleation in product crystallization.

Toward Developing a Conceptual Framework to explain Positive Thinking Based on Islamic View

2016 ◽  
Vol 2 ◽  
Author(s):  
Mohammad Kodayarifard ◽  
Bagher GhobariBonab ◽  
Saeed Akbari ZardKhaneh ◽  
Enayatollah Zamanpour ◽  
Saeid Zandi ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Cultural Values ◽  
Attachment Theory ◽  
Relational Theory ◽  
The Self ◽  
Automatic Thoughts ◽  
Thinking Styles ◽  
Positive Thinking ◽  
Future Expectations ◽  
Islamic View

The aim of the present study was to critically review theories and approaches related to positive thinking and to develop a theoretical model based on Islamic view, which is compatible with cultural values in Iran. To fulfill the stated aim, philosophical and historical foundations of positive thinking in different schools of thought including Leibnitz, Sadra, Kant, Freud and James were critically reviewed. In addition, the theoretical constructs associated with positive thinking including hope, positive automatic thoughts and paradigms of Seligman, Scheier and Carver in this regard were critically studied. Finally, based on the attachment theory of Bowlby, positive thinking was established on and its applications were explained for individuals' thinking styles about past events, present interpretations of events and future expectations. Since the attachment theory is a relational theory, positive thinking in this paradigm was discussed in a way that included individuals' relationship with transcendental being, others, nature, and the self.

Nanocrystals: The Preparation, Precise Control and Application Toward the Pharmaceutics and Food Industry

2018 ◽  
Vol 24 (21) ◽  
pp. 2425-2431 ◽  
Author(s):  
Cao Wu ◽  
Zhou Chen ◽  
Ya Hu ◽  
Zhiyuan Rao ◽  
Wangping Wu ◽  
...  
Keyword(s):  
Food Industry ◽  
Chemical Properties ◽  
Preparation Methods ◽  
Precise Control ◽  
Significant Process ◽  
Technology Applications ◽  
And Performance ◽  
Physical And Chemical ◽  
Analytical Technology ◽  
And Chemical Properties

Crystallization is a significant process employed to produce a wide variety of materials in pharmaceutical and food area. The control of crystal dimension, crystallinity, and shape is very important because they will affect the subsequent filtration, drying and grinding performance as well as the physical and chemical properties of the material. This review summarizes the special features of crystallization technology and the preparation methods of nanocrystals, and discusses analytical technology which is used to control crystal quality and performance. The crystallization technology applications in pharmaceutics and foods are also outlined. These illustrated examples further help us to gain a better understanding of the crystallization technology for pharmaceutics and foods.

scholarly journals CdSe QD Biosynthesis in Yeast Using Tryptone-Enriched Media and Their Conjugation with a Peptide Hecate for Bacterial Detection and Killing

Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1463 ◽  
Author(s):  
Vishma Pratap Sur ◽  
Marketa Kominkova ◽  
Zaneta Buchtova ◽  
Kristyna Dolezelikova ◽  
Ondrej Zitka ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Synthesis Process ◽  
Synthesis Methods ◽  
Bacterial Cells ◽  
Cdse Qds ◽  
Yeast Saccharomyces Cerevisiae ◽  
Shape Distribution ◽  
Transmission Electron ◽  
A Cell ◽  
Physical And Chemical

The physical and chemical synthesis methods of quantum dots (QDs) are generally unfavorable for biological applications. To overcome this limitation, the development of a novel “green” route to produce highly-fluorescent CdSe QDs constitutes a promising substitute approach. In the present work, CdSe QDs were biosynthesized in yeast Saccharomyces cerevisiae using a novel method, where we showed for the first time that the concentration of tryptone highly affects the synthesis process. The optimum concentration of tryptone was found to be 25 g/L for the highest yield. Different methods were used to optimize the QD extraction from yeast, and the best method was found to be by denaturation at 80 °C along with an ultrasound needle. Multiple physical characterizations including transmission electron microscopy (TEM), dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDX), and spectrophotometry confirmed the optical features size and shape distribution of the QDs. We showed that the novel conjugate of the CdSe QDs and a cell-penetrating peptide (hecate) can detect bacterial cells very efficiently under a fluorescent microscope. The conjugate also showed strong antibacterial activity against vancomycin-resistant Staphylococcus aureus (VRSA), methicillin-resistant Staphylococcus aureus (MRSA), and Escherichia coli, which may help us to cope with the problem of rising antibiotic resistance.

scholarly journals Uncertainty Avoidance as a Moderating Factor to the Self-Congruity Concept: The Development of a Conceptual Framework

SAGE Open ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 215824402110018
Author(s):  
Shaohua Yang ◽  
Salmi Mohd Isa ◽  
T. Ramayah
Keyword(s):  
Theoretical Model ◽  
Conceptual Framework ◽  
Significant Contribution ◽  
Integrated Model ◽  
Uncertainty Avoidance ◽  
The Self ◽  
Destination Marketing ◽  
Tourism Research ◽  
Revisit Intention ◽  
Conceptual Paper

The aim of this article was to propose a framework based on the theory of self-congruity and on Hofstede’s uncertainty avoidance. The framework was to combine destination personality, self-congruity, uncertainty avoidance, and tourists’ revisit intention. The present conceptual paper proposed an integrated model of self-congruity which incorporates the effect of uncertainty avoidance. More importantly, the uncertainty avoidance was introduced as a moderator between self-congruity and revisit intention. Based on the theoretical framework proposed in this article, the estimated results affirmed the applicability of the theory of self-congruity for tourism research. Moreover, by extending the theoretical model through the incorporation of a variable of uncertainty avoidance in the context of tourism, this article offers a significant contribution to the tourism literature. It is important to understand how the theory of self-congruity applies across a broad cultural spectrum. This article also offers several implications for destination marketing organizations from a practical perspective.

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