STA PT 1600 – gypsum sample – TGA+DSC
Gypsum and Quartz – Thermal decomposition – Mortar
A typical application for a mixture of two materials like gypsum and quartz sand is mortar. It is used to hold bricks of a wall together or to fill holes in buildings. The main components of standard mortar are gypsum (calcium sulfate, CaSO4) and quartz sand (silicon oxide, SiO2). They are usually mixed with water to form various hydrates and become a paste that can be used and applied easily. After drying, they become a solid, stone like material. The drying process can be investigated by thermal analysis and also the final product can be investigated by STA, showing its thermal decomposition.
The STA curve above is a thermal decomposition experiment on a dry mortar. It shows a two-step release of H2O from CaSO4 • 2H2O (dihydrate) into CaSO4 • ½H2O (half hydrate) and finally into CaSO4 (anhydrite). The dark blue curve indicates the mass loss percentage and the light blue curve shows the endothermic heat flow. The loss of water requires an entire energy of 121.6 J/g. The total amount of water that is released is 21 % of the sample weight. Between approx. 300°C and 450°C, the exothermic formation of β-CaSO4 with a released energy of 18.3 J/g occurred.