Fabrication of dense polymer-derived silicon carbonitride ceramic bulks by precursor infiltration and pyrolysis processes without losing piezoresistivity

Dense polymer-derived silicon carbonitride (SiCN) ceramic bulks were fabricated by powder consolidation following precursor infiltration and pyrolysis (PIP) densification. The density and open porosity of the ceramics varied from 1.42g/cm(3) and 32.75% before the PIP to 2.29g/cm(3) and 3.64% after the PIP, respectively. The electrical conductivity of the ceramics sharply increased from 6.26x10(-10)S/cm before the PIP process to 3.20x10(-7)S/cm after the 1st cycle of PIP and then gradually increased to 6.89x10(-6)S/cm after four cycles of PIP. However, the piezoresistive coefficient did not change with the PIP. The Raman and electron paramagnetic resonance results show that the graphitization level of free carbon in ceramics derived from PIP was higher than the ceramics derived from powder consolidation. The high graphitization level of free carbon leads to a high conductivity, and thus the conductivity of ceramics increased significantly after the PIP process. The carbon cluster size, which is related to the gauge factor of piezoresistivity, did not change significantly after the PIP process; thus, the gauge factor did not change significantly. Dense, large-scale polymer-derived ceramics were fabricated by combined conventional powder consolidation and PIP without the loss of piezoresistivity. These ceramics have potential application as both structural and functional components that can bear loads as well as monitor variations in external stress.