Temperature dependence of damping in silica refractories measured via the impulse excitation technique

Using high-temperature impulse excitation the temperature dependence of damping, quantified by the so-called inverse quality factor, has been measured for silica refractories with porosities of 13-17% up to 1200 degrees C. Damping-temperature curves exhibit closed loops between heating and cooling and do not show any indication of damage accumulation after two complete heating-cooling cycles. The temperature dependence of damping exhibits features that are due to an interplay between phase transitions (between the subpolymorphs of tridymite and cristobalite) and microstructure (reversible closure re-opening of preexisting microcracks) and are also known from resonant frequency measurements. Additionally, however, the temperature dependence of damping reveals some details that are undetectable by resonant frequency measurements and may tentatively be attributed to the competition between microcrack closure and increased dry friction (damping peak at approximately 325 degrees C) and to a phase transition of the dicalcium silicate phase shannonite (damping increase in the range 700-800 degrees C).