Shaun Patrick Gaus
Published: 1997
Total Pages: 458
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Transient material and energy balances have been utilized to model the reaction-bonded aluminum oxide (RBAO) and alumina-aluminide alloys (3A) processes. The model for the RBAO process considers the diffusion of a gas-phase reactant into a porous solid followed by a solid-gas reaction, while the 3A model considers a solid-solid reaction taking place within a porous solid. The modeling work on the RBAO process reveals that the process may proceed via an ignition/extinguishment phenomenon with thermal runaway. It is believed that this type of behavior can lead to stress development, and subsequent sample cracking. Thus, the model is used to determine conditions under which RBAO bodies may be fired in a controlled manner (i.e., avoiding the runaway reaction). A complimentary experimental study, utilizing simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), in-situ temperature measurements, and analysis of samples fired in a box furnace, verifies the predicted reaction behavior and shows that by controlling the reaction, high Al content powders can be used to produce crack-free RBAO samples. The modeling work on the 3A process demonstrates the effects of various processing parameters on the general reaction behavior. After considering the general behavior, the model is used to predict the reaction behavior of the $TiO\sb2/Al$ system. A reaction sequence for the $TiO\sb2/Al$ system (based on XRD data) is proposed and used to model the system. The effects of the heating rate, the convective heat transfer coefficient, and sample size are investigated.