Investigation of percolation in borosilicate glass matrix composites containing conducting segregated networks
Pruyn, Timothy L.
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Glass matrix composites containing a conducting filler such as antimony tin oxide (ATO) or silicon carbide whiskers (SiCw) have the potential for applications such as transparent electrodes, heating elements, and electromagnetic shielding. For these applications, the composite performance is highly dependent on the microstructure of the composite and the interactions the added filler has with one another. In this research, borosilicate glass-matrix composites were fabricated using a processing method that creates segregated percolated networks at low concentrations of conducting fillers. The conducting fillers were hot pressed with the glass microspheres at temperatures near the glass transition temperature (550°C) using various pressures. Upon hot-pressing at these low temperatures, the glass microspheres deformed into faceted polyhedra and the fillers were displaced to the edges of the glass particles, resulting in percolation. The processing method used in this study was able to bypass many of the current composition and densification issues associated with the creation of percolated networks in glass composites. In some cases, the formation of these percolated networks resulted in a 12-13 orders of magnitude decrease in the resistivity. Using a non-destructive electrical measurement technique, ac impedance spectroscopy (IS), the changes in the electrical properties were tracked as the conducting networks developed. Using IS in conjunction with other techniques, correlations were made between the electrical properties, the filler interfaces, and the influence the processing parameters had on the development of the percolation networks within these composites.