Suppression of α-Quartz in Montmorillonite-SiOC Ceramic Nanocomposites with Water Vapor-Assisted Pyrolysis

Abstract

Bulk montmorillonite-silicon oxycarbide (MMT-SiOC) ceramic nanocomposites were fabricated with either Ar or Ar-H¬2O pyrolytic atmospheres to determine the effect of water vapor on SiO2 phase evolution at the MMT-SiOC interface and selectively etched porosity. While water vapor-assisted pyrolysis selectively removes free C in pure SiOC, surprisingly, MMT and water vapor in combination led to encapsulation, shielding, and retention of C as graphene oxide in MMT-SiOC-H2O ceramics. Crystalline α-quartz phases in MMT-SiOC were converted to amorphous SiO2 phases during water vapor-assisted pyrolysis, leading to 50-75% reductions in specific surface areas of HF-etched MMT-SiOC without changes to the intrinsic pore structure of water vapor-pyrolyzed SiOC. Further pyrolysis to 1400°C led to the dissolution of the aforementioned pore structure due to more extensive carbothermal reduction and refinement of β-SiC nanowhiskers. This work provides a new mechanistic understanding of how inorganic 2D fillers (like MMT) can mediate chemical and structural evolution during polymer-derived ceramic synthesis.