The Fabrication Of Bulk Monolithic SiOC Ceramics And Micro-Parts

The synthesis of ceramics via polymer pyrolysis is a new method which has been developed in recent years. The method has the advantages of enabling the design of the ceramics at the molecular level, allowing forming of complicated shapes and having a lower ceramic formation temperature. The ceramics from this route possess superior high temperature properties that are not reached by the conventional sintered ceramics, which are important materials, attractive for high temperature applications. Moreover, the process of polymer-to-ceramic transformation shows ability for the fabrication of ceramic MEMS parts because of their unique processing advantages over conventional method. However, a number of obstacles have to be overcome. before the full realization of practical applications of this process and the ceramics. One key issue is cracking of the ceramic cracking of the ceramics due to the large weight loss and volume shringking in the process of pyrolysis. In the present work, we developed methods of suppressing cracking of ceramics and forming of precursors, by which we fabricated non-cacking silicon oxicarbide (SiOC) bulk ceramics and micro-parts.By introducing polydimethysilioxane (PDMS) as a second molecular phase into mixture of polysiloxane precursor consisting of polyhydromethylsiloxane (PHMS) and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcycletetrasiloxane (D4Vi), we found that the cracking of cured precursors and ceramics was effectively avoided at both the macroscopic and microscopic scales. In this way, we successfully fabricated bulk and crack-free SiOC ceramics from PDMS+PHMS+D4Vi, with the dimension of 30 mm. Despite of the ceramics having 20% pores, their hardness attains 8.1 GPa.Moreover, SiOC ceramic micro-parts and patterned microstructures were fabricated from their metal masters, via mold transfer, liquid cast, crosslink and pyrolysis using PHMS+D4Vi liquid as precursors. The mixture of the PHMS and D4Vi liquids was cast with the master transferred polydimethylsiloxane (PDMS) negative molds and solidified by controlled heating to induce hydrosilylation reactions between PHMS and D4Vi. Since both the precursors and mold materials are polysiloxanes, their chemical similarities ensure the excellent contact between the two phases that allows the precise duplication of the master microstructures into the polysiloxanes. Strategies were developed in use of a two-step controlled heating and a polysiloxane as support in the processes of demolding, crosslinking and pyrolysis to ensure the bonding qualities of the crosslinked and pyrolyzed microstructures. Along this route, we obtained dense and crack-free SiOC ceramic micron-gears and arrayed holes of well duplicated microstructures with the resolution down to sub-microns. Moreover, the polysiloxanes allow the direct imprint with the metal masters to form inversed microstructures of SiOC ceramics, as demonstrated by the successful fabrication of micro-channels and various motifs of SiOC ceramics from their metal counterparts.