Expansion and shrinkage of lightweight vermiculite material at high temperatures

Abstract

Vermiculite materials are widely used as insulation material in the industry, fire protection systems, and fire stoves. The high dimensional stability of vermiculite boards ensures that thermal runways in the insulation lining are avoided. Vermiculite boards for high-temperature applications are produced from thermally expanded vermiculite and alkali silicate binder. Here, we show the impact of potassium silicate binder and vermiculite source on the dimensional stability of vermiculite boards. The vermiculite boards expand at 500–830 °C and shrink stepwise at 1000–1250 °C and 1400 °C, respectively, when heated at 10 °C min−1 in ambient air. The expansion process is discussed in relation to the boards containing non-expanded particles and metal carbonates. The evolved gas analysis indicates that the CO2 release from metal carbonates is the potential cause of the expansion of some vermiculite types. The shrinkage is initiated by the dehydroxylation of the clay structure. The binder promotes crystallisation during the shrinkage, ceasing the shrinkage process at higher temperatures. The expansion and shrinkage of vermiculite boards are anisotropic and depend on the board density and vermiculite origin. These findings provide new insights into the expansion and shrinkage behaviour of vermiculite boards.