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–H₂O 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. The crystalline α-quartz phase in MMT–SiOC was converted to an amorphous SiO₂ phase 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.