On the microstructure of ceramic hollow microspheres

Metal matrix syntactic foams (MMSFs) are relatively new materials which have increasing interest in the field of aviation and packaging industry. They are metal matrix composites, and their porosity is ensured by the incorporation of ceramic hollow microspheres. In this paper the microstructure of the ceramic hollow microspheres as reinforcing element was investigated. SL150, SLG and SL300 type ceramic microspheres were investigated. They contain various oxides, mainly Al_2O_2 and SiO_2. Energy dispersive X-ray spectroscopy (EDS) maps were recorded from the sections of the microspheres´ wall. The results showed that the Al_2O_3 and SiO_2 distribution was not equal; the Al_2O_3 phase was embedded in the surrounding mullite and SiO_2 phase in the form of needles. EDS along a line in aluminium matrix syntactic foams was carried out in order to investigate the possible reaction between the aluminium matrix and the ceramic microspheres. Due to the uneven distribution of Al_2O_3 rich particles, the molten aluminium can reduce the SiO_2 rich parts of the microspheres and the wall of the microspheres become damaged and degraded. This chemical reaction between the microspheres and the walls can make the infiltration easier, but the resulting mechanical properties will be lower due to the damaged microsphere walls