Measurement of heat flow through cast slabs of calcium sulfate dihydrate

Abstract

Summary Slabs of cast calcium sulfate dihydrate have been used for decades as a heat transfer barrier in commercial and residential construction and are assessed in accordance with the parameters defined by ASTM C1396. The study described herein hypothesizes that minor impurities have significant effects on the high‐temperature performance of these casts. Five thermocouples are cast into a 20‐mm‐thick slab at approximately 4‐mm intervals are measured between ambient and approximately 1000°C in a furnace. Thermal diffusivity and inertia are estimated from this temperature profile. This study compares natural, flue gas desulfurized (FGD) and reagent grade hemihydrates that have been converted into the dihydrate form with distilled water; the common additives kaolin and borax are used to modify the cast. The thermocouple data allow an effective thermal diffusivity (α′) and an effective thermal inertia (I′) to be calculated. The hemihydrate source and kaolin content are found to affect the high‐temperature performance; the FGD source increases the thermal inertia, and kaolin inhibits the formation of other borate compounds through intercalation.