Synthesis, Characterization, and Thermal Properties of Mg-3Ca/Fly Ash Composites

This study aims at using Fly Ash (FA) particles as reinforcement particles in the Mg matrix and studying the thermal properties of the novel Mg-3Ca/FA composites produced via liquid processing route. About 3, 6 and 9 wt.% of FA was added to these composites. SEM micrographs of composites show the presence of Mg2Ca at grain boundaries of alpha-Mg, as well as micropores and agglomerates of FA particles. Mg reacts with Fly Ash constituents such as SiO2 and Al2O3 to form MgO, CaO, Mg2Si, CaMgSi and MgAl2O4, which have lower thermal conductivity than the Mg-3Ca alloy. The in situ formed phases created large number of interfaces, which increased with an increase in FA concentration in Mg composites. Decomposition of oxides increases the number of solute elements (Al, Si, etc.) in Mg that induces lattice distortions and reduction in heat flow (HF), Cp and CTE of composites. Evidently, HF, Cp and CTE of FA-reinforced composites are due to lower thermal conductivity of FA and in situ formed metal oxides when compared to that of Mg-3Ca alloy. Addition of 9 wt.% FA to the alloy reduced the Cp (at 100 degrees C) from 0.4033 to 0.2842 J/g degrees C (i.e., by 29.53%) and CTE (at 200 degrees C) from 26.0 to 21.9 (x 10-6)/degrees C (i.e., by 15.57%).