Publications

Effects of chemical modification on calcium sulfate castings exposed to high temperature

Engbrecht, Dick C.; Hirschfeld, Deidre H.

Calcium sulfate dihydrate is the primary ingredient in passive gypsum drywall fire barrier systems. The endothermic properties of calcium sulfate dihydrate are well known and exploited in these systems. Researchers in fire modeling have extensively studied the endothermic properties of gypsum up to 500°C. This study reports on the influence of selected chemical and mineral constituents on dimensional and thermal property changes in gypsum casts in excess of the critical crystal dehydration temperature (between 500° and 1000°C). Gypsum from natural and flue gas desulfurization (FGD) sources used in commercial operations were evaluated for changes by differential thermal analysis/thermogravimetric analysis (DTA/TGA), Fourier transform infrared (FTIR) spectroscopy, Raman spectra analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Petalite and Gerstley borate were added to a basic formula used in commercially manufactured wallboard for fire barrier systems. The analysis of the data identified significant changes in density and hardness of the gypsum casts related to the addition of Petalite and Gerstley borate.