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Aluminum can react with water and produce hydrogen. Researchers have developed different methods to promote the reaction of aluminum with water for hydrogen generation. Most of these methods considered ball milling of aluminum necessary prior to the reaction. In spite of numerous works on activation of aluminum powder to react with water, the activation process of aluminum powders is not optimized, and there is not enough knowledge on the kinetics and mechanism of the reaction. This research is to fill this gap. Considering the energy consumption in ball milling, firstly, we optimized the milling time based on the highest rate of hydrogen generation. Then, contributions of milling process to activation of the aluminum powder were evaluated. We found that microstructural refinement has a significant contribution in promoting the reaction. Therefore, we studied the mechanism of grain refinement of aluminum particles during ball milling. We used electrochemical tests to better understand the reaction of aluminum with hot water and effect of addition of water-soluble salts was also studied. The shrinking core model was modified to predict the kinetics of the reaction. It was found that ball milling promotes the reaction in two ways: a) increasing the instability of the microstructure (by refining the microstructure) and, b) decreasing the particle size of the powders. A considerable increase in amount of the grain boundaries was found as the reason for instability of the microstructure. Deformation banding and subgrain rotation were identified as the mechanisms responsible for introducing new boundaries during milling. For the pure aluminum, the small size and the laminated structure of particles at the medium stage of milling increased the rate of the reaction, and further milling destroyed the laminated structure and consequently decreased the reaction rate. For the aluminum-salt mixtures, there is no optimum milling time as it was observed for the pure aluminum powder. However, more milling after a certain time does not have any significant influence on the reaction rate of aluminum-salt mixture. The addition of water-soluble salts (potash or salt) considerably increased the hydrogen generation rate. Comparison of different distributions of the salt in the aluminum particles revealed that chemical aspect of the presence of salt is negligible compared to the structural modifications. Finally, considering the changes in thickness and porosity of the hydroxide layer formed on the aluminum particles, the traditional shrinking core model was modified for the reaction of aluminum particles with hot water.

A comprehensive mathematical model of the hot extrusion process for aluminum alloys has been developed and validated. The model is capable of predicting the material flow behaviour and microstructure evolution that occurs in aluminum alloy AA3003 during extrusion. The plasticity module was developed using a commercial finite element package, DEFORM, a transient Lagrangian model which couples the thermal and deformation phenomena and is able to predict the temperature, strain rate and strain distribution in the billet/extrudate at any position in the container and die. Validation of the model against industrial data indicated that it gave excellent predictions of the pressure and temperature history during extrusion. Material flow effects during extrusion such as surface cladding (a transverse weld defect) as one billet is fed in after another through the die were also well predicted. The results of the FEM model for material flow and thermomechanical history were post processed using MATLAB software to predict the grain deformation and stored energy in the extruded material as well as the thickness and extent of the transverse weld defect. Finally, the model predictions for microstructure and transverse weld were compared to microstructure observations. The stored energy or driving pressure for Static Recrystallization (SRX) and Geometric Dynamic Recrystallization (GDRX) and how they are influenced by extrusion parameters were investigated using the mathematical model and experimental measurements. The experimental measurements for grain thickness and microstructural features made using Electron Back Scattered Diffraction (EBSD) technique and optical microscope show good agreement with model predictions. The mathematical model was then used to assess the effect a change in die design would have on the flow behaviour of the material during extrusion and on the transverse weld that forms.

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No description available.

Thesis (M.S.)--Ohio University, March, 1994. / Title from PDF t.p.

Thesis (Ph.D.)--Washington State University. / Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--University of Hong Kong, 1991.

Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Singh, Preet M.; Committee Member: Carter, W. Brent; Committee Member: Gokhale, Arun, M.; Committee Member: Neu, Richard; Committee Member: Sanders, Thomas H., Jr.. Part of the SMARTech Electronic Thesis and Dissertation Collection.