Thermal Shock Damage in Castables: Microstructural Changes and Evaluation by a Damping Method

摘要

The thermal shock behaviour of different compositions of high alumina castables, varying in particle size distribution and cement content, has been regarded in particular by using a non-destructive testing device based on impulse excitation. The castable compositions reveal a great variation in their grain size distribution. Typical LCC compositions with grog grains up to 6 mm were regarded as well as castables consisting of fines from 10 up to 500 μm in maximum with less cement content. On all castables thermal shock tests have been applied by quenching them from 1 100℃. A steep thermal gradient was chosen to distinguish the thermal shock behaviour of the different castable compositions after each cycle. To quantify the microstructural damages due to thermal shock a non-destructive testing method based on impulse excitation where a vibration is induced within a castable sample of the size 150 × 25 × 20 mm{sup}3 by mechanical impulses. This vibration is picked up by a microphone, the electrical signal is adapted and amplified. Finally resonance frequencies with their damping loss factor are measured. On one hand Young's Modulus (E) and internal friction (Q-1) have been measured by using a damping analyser. On the other hand Young's Modulus was determined using a conventional frequency generator to achieve resonance frequency. Aim of the study is to evaluate the difference of the testing methods: Young's Modulus achieved by damping or by resonance frequency measurements applied on heterogenous materials of different grain size distributions. Further focus is the application of internal friction measurements on refractory materials in regard of its sensitiveness. Due to the use of different castable compositions the influence of the particle size and the damage detection induced by thermal shocks by the given testing methods are worked out.