|M.Sc Thesis||Department of Materials Science and Engineering|
|Supervisors:||Prof. Kaplan Wayne D.|
|Prof. Bamberger Menachem|
Spontaneous reactive infiltration of magnesium into porous alumina has been conducted in an argon atmosphere. This process has the potential to be used to produce ceramic matrix composites, using the relatively low cost and high availability alumina and light weight magnesium. The alumina has been thoroughly investigated in the past and therefore has known properties. The products of the reactions between alumina and Mg were found, by XRD and TEM, to be periclase (MgO) and spinel (MgAl2O4). There is also evidence of the existence of aluminum formed from this reaction, by SEM investigations using EDS to measure aluminum in the metal phase and evidence of the formation of the Mg-Al intermetallic b phase (Al12Mg17).
Model wetting experiments were conducted in order to investigate contact angles of the liquid magnesium on the substrates. These experiments help to understand the energy balance, the reactions’ kinetics and find the reaction products.
Two parameters are changed during reactive wetting. The first is the substance in contact with the magnesium, which initially was alumina and gradually becomes periclase, and later in the reaction, spinel. The second is the contact angle of the metal that used to be magnesium and now consist magnesium containing a fraction of aluminum. Both these issues contribute to a process time for spontaneous infiltration, which is too long to be technologically applicable.
The use of nitrogen as a protective gas for the process changed the situation. First, the environment is no longer inert. Oxidation of the magnesium is minimized, but a reaction does occur with the nitrogen. This reaction produces AlN, which reduces the activity of aluminum in the magnesium. This results in a reduced contact angle and allows spontaneous infiltration.