Heat-induced structural and mechanical changes of basalt wool

Abstract

Changes in the mechanical properties during heat treatment were investigated for three basalt wools of different compositions and production conditions. Below 600 °C the increased liquation of fibres results in enhanced embrittlement. Decrease of the tensile strength can be found only at the beginning of structural changes which are indicated by the changes in density (from 600 up to 800 °C). Above 600 °C an intensive crystallization induced by the oxidation of Fe(II) is observable which - due to the simultaneous deterioration of fibre elasticity and tensile strength - gives rise to an abrupt ceasing of the mechanical stability. This phenomenon takes place in the x-ray amorphous region, therefore, the change of fine structure can be observed only by means of electron diffraction at temperatures above 400 °C. The applicable temperature range of basalt wools is influenced by the mechanical properties of the original fibres besides the changes in structure during heat treatment. One of the samples, which had originally low strength, became easily breakable during treatment and could not be evaluated after a heat treatment at 400 °C. This phenomenon was found at 650 and 700 °C for the other two basalt wools that had more favourable parameters originally.