Linear shrinkage, resilience and microstructural changes in high temperature insulating wools in maximum use temperature range

Abstract

To describe important thermal properties of high temperature insulating wool (HTIW) materials, firing experiments have been performed at temperatures above their classification temperature and following shrinkage and resilience measurements for three HTIW material groups: AES (alkaline earth silicate wool), aluminium silicate wool (RCF) and polycrystalline wool. A temperature range of 1000–1600°C has been chosen. At industrial application temperatures the HTIW products should not reveal significant shrinkage behaviour, and their mechanical properties should be maintained after exposure to elevated temperatures. This is an important and critical aspect for these high temperature insulation materials. Microstructural examination after firing at different temperatures shows increasing crystallisation as a result of phase formation, leading to increased density and shrinkage. At classification temperature these processes enhance bending of fibres and fibre thickness in the length direction which also leads to higher shrinkage. These effects are supported by sintering processes of single fibres and diffusion at junction points. At high temperatures strong crystal growth takes place. The resulting crystals on the surface achieve dimensions larger than the fibre diameter.