Effect of medium-high temperature conditioning on the mechanical properties of single quartz fibres

This work adopted multi-scale characterizations to investigate the effects of exposure to medium-high temperatures (600–800 °C) on the mechanical properties of single quartz fibres, focusing on whether bulk property changes, i.e., Young's modulus, density and fracture toughness, occur and can be related to the thermal strength loss, herein quantified as 75% up to 86% with increasing temperature. Investigation of the fracture surfaces through scanning electron microscopy revealed that failure originated from the fibre surface regardless of heat treatment. Neither bulk crystallization was highlighted through X-ray diffraction nor relevant changes or gradients of Young's modulus and hardness were disclosed over the fibre cross-sections through high-speed nanoindentation mapping. A 9% increase in fracture toughness measured through micro-pillar splitting revealed a slightly improved crack propagation resistance that cannot compensate for the drastic effect responsible for strength reduction, which is discussed in terms of surface-controlled mechanisms involving the development and growth of surface flaws.