Non-monotonic dependence of high-temperature stability of stone wool fibres on pre-oxidation time and temperature

Stone wool is a sustainable, fire-safe insulation material, and its fire-safety depends on its high-temperature stability (HTS). It is known that the HTS of stone wool fibres can be enhanced by pre-oxidation (i.e., heat treatment in air) at temperatures below or at its glass transition temperature (Tg). However, so far, a quantitative trend of HTS with varying pre-oxidation temperature (Tpre-ox) and time (tpre-ox) remains unknown. In this study, we quantified the change of HTS of stone wool fibres with a Tg of 677 °C as functions of both Tpre-ox and tpre-ox through a hot-stage microscope. The derived results revealed striking non-monotonic trends in the HTS of stone wool fibres. The HTS first increased with Tpre-ox from 500 to 630 °C for tpre-ox of 15 minutes, but declined beyond 630 °C. The HTS was significantly improved upon pre-oxidation for merely 2 minutes, at 677 °C, then dropped with extending tpre-ox to 16 hours, and finally increased again with tpre-ox up to 16 days. The origin of the non-monotonic trend was explored by characterizing the crystallization behaviour, thermal expansion, surface composition, and surface morphology in stone wool fibres after pre-oxidation.