Civil Engineering Reference
In-Depth Information
Figure 18.
Schematic of apparatus used for controlled transformation rate thermal analysis.
(A)
sample;
(B)
glass or fused-silica cell;
(C)
furnace;
(D)
thermocouple;
(F)
and
(H)
, Pirani
gauges;
(G)
, diaphragm;
(I)
, pumping system.
[4]
Dehydration curves for gypsum at 1 Pa and 900 Pa are presented in
Figs. 19 and 20. The curve obtained at 1 Pa shows only one dehydration step.
The XRD analysis for the final product indicates the presence of
-CaSO
4
.
This agrees with the mass analysis. The mass loss between points
(A)
and
(B)
was about 20.9% comparing favorably with the theoretical mass loss of
water of recrystallization for the transformation of gypsum to anhydrite. A
step at 840°K (567°C) for the gypsum powder is observed at 1 Pa. This
corresponds to the removal of the CaCO
3
impurity (about 2.5%).
β
