Synthesis of an Al/MgAl2O4 in situ metal matrix composite from silica gel

An aluminum/MgAl2O4 in situ metal matrix composite has been synthesized using silica gel containing B98% SiO2 in an Al–5Mg alloy. The thermodynamics and kinetics of MgAl2O4 formation have been discussed in detail. A transition phase of composition between MgO and MgAl2O4 has been detected in the SEM-EDS analysis of the particles extracted from the composite by a 25% NaOH solution. This confirms the gradual transformation of MgO to MgAl2O4 by the reaction 3SiO2(s)12MgO(s)14Al(l)-2MgAl2O4(s)13Si(l). The stoichiometry, n, of MgAl2O4 has been found to sustain close to 1 and the crystallite growth of MgAl2O4 has been stopped at DB30 nm in the composites held at 7501C up to 10 h.