Control of pore size by metallic fibres in glass matrix composite foams produced by microwave heating

The application of microwave radiation as the heating source for the fabrication of glass foams reinforced with metallic fibres has been investigated. A soda-borosilicate glass powder was chosen for the matrix. The metal fibres were Hastelloy X fibres in volume concentration of 0, 2 and 10%. The fibre diameter was 8 pm and length was 100 mum. The microwave heating process was carried out in a self constructed over-moded microwave applicator operating at the 2.45 GHz ISM frequency. The glass foamed during processing leading to greater than 50 vol.% of spherical pores. The samples were characterised in terms of pore size and distribution, density, metal fibre distribution and interface characteristics. Adding stainless steel fibres to the glass composite prevented the glass from fracturing during processing and resulted in a more even distribution of finer pores. It is proposed that porosity formed during microwave heating as a consequence of localised glass matrix overheating in correspondence with the presence of metal fibres, caused by the preferential microwave absorption exhibited by the Hastelloy X fibres themselves and by the micro-regions of the matrix heated well above the glass softening temperature.