Matthew James Watson
Published: 1999
Total Pages: 392
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The ignition phenomena that can occur during the reaction-bonding of aluminum oxide is investigated. It is experimentally characterized through measurements of the combustion temperature and the velocity of the ignition front. One- and two-dimensional, transient, simultaneous material and energy balances are used to model the phenomena in a cylindrical geometry. The models are used to predict the aluminum concentration, oxygen concentration, and temperature distributions as a function of time during ignition. Thermal explosion analysis is utilized to predict the conditions under which samples will ignite, and to calculate furnace temperature programs that will avoid ignition. The aluminum concentration and temperature distributions are used to estimate the elastic stresses that are developed during ignition. Feedback control is applied to the reaction-bonded aluminum oxide system with great success. The heating rate is adjusted automatically based on the reaction rate, measured through differential thermogravimetry. Adjusting the furnace temperature in this way is more reliable and allows the sample to react in a slow and controlled manner, avoiding ignition and cracking altogether. Criteria based on heat transfer and oxygen diffusion considerations are developed to determine the reaction rate set-point, and simplify the process of reaction-bonding considerably.