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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A study of ignition and propagation of combustive synthesis reaction between titanium and carbon

Hernandez-Guerrero, Abel 23 July 1991 (has links)
Combustive Synthesis or Self-Propagating High-Temperature Synthesis (SHS), is an energy-efficient combustion method of producing metallic, ceramic and composite materials from their constituent powders. This thesis presents the results of an experimental and numerical evaluation of the propagation velocity for the SHS solid-solid reaction of titanium and carbon, as well as a study of the ignition process for the reaction. The experimental results show the dependency trend of the wave propagation speed on various parameters: diameter of the reactant compact, density of the compact, reactant mixture composition, and dilution of the reactant mixture with the inert product TiC. Conditions at which the reaction ceases to propagate in a self-supporting manner are also identified. This thesis attempts to generalize the existing experimental observations of the gasless SHS process by means of a dimensional analysis, thus offering a mechanistic framework within which future developments can be correlated. The implementation of the new reaction kinetics model of Kanury and some suitable dimensionless variables permit the main factors affecting the process to be embedded in a single key parameter, the Da number. This parameter includes the overall effects of thermal properties, stoichiometry of the reaction, carbon particle size, a process constant, a compression effect and the diffusion of one reactant through an intermediate complex. The study of propagation covers a broad range of possible Da numbers that could arise for different conditions found in experiments. A section in numerical calculations of the preheated length is included as well. Comparison of the numerical and experimental results for propagation are found to be in reasonable agreement, thus validating the suitability of the analytical model. The numerical study includes an examination of the ignition problem for a stoichiometric mixture, using a prescribed surface temperature boundary condition. For this condition, an ignition threshold curve is determined above which ignition will always occur and below which no ignition is possible. / Graduation date: 1992
2

A theoretical and experimental study of self-propagating high-temperature synthesis of titanium carbide

Huque, Ziaul 10 January 1991 (has links)
Self-propagating high-temperature synthesis (SHS) is a new method of producing advanced ceramic materials and offers an attractive alternative to conventional methods of materials processing. An experimental investigation was carried out to determine the SHS reaction wave propagation speed in a vertical cylindrical compact made from a mixture of titanium and graphite powders. Ignition was accomplished by radiatively heating the top surface of the cylinder by resistively heated tungsten heating coils. Syntheses were carried out in inert argon environment and under atmospheric pressure. Propagation speeds were determined by analyzing the temperature distribution with time at two locations at known axial distance. Effects of various system parameters, such as, density and diameter of the initial compact, different mixing ratios of the reactants and dilution with product, on reaction propagation speed were determined. A numerical model was also developed to predict the propagation speed. A two-dimensional formulation was adopted with both radiative and natural convective heat loss from the periphery of the cylindrical compact using constant values of properties and kinetic parameters. Two different kinetic models describing the reactions involving solids are employed to calculate the wave speed using a finite difference scheme. The calculated results were compared with the experimental data. Trends of the results with Kanury kinetic model were found to be in better agreement with the experiments. Results showed no significant effect of heat loss on the propagation speed within a practical range of compact diameter. Quenching conditions of the reaction for titanium rich and carbon rich cases and also for the case of dilution with the product were identified. Variation of propagation speed with sample initial density showed a maximum value at densities between 2.1 gm/cm³ and 2.2 gm/cm³. During the synthesis, the samples were found to expand axially. Hence the final product obtained was highly porous with densities below 50% of the density of TiC. / Graduation date: 1991

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