My.Y. Benarchid

Thermal study of chromium–phosphorus-doped tricalcium aluminate

Abstract The evolution with the temperature of the composition of some mixtures of CaCO 3 , Al 2 O 3 , Cr 2 O 3 and P 2 O 5 has been investigated. The influence of chromium and phosphorus additions on the thermal decomposition of CaCO 3 and the formation of the tricalcium aluminate have been observed. The synthesized solid solutions have been characterized through X-ray diffraction (XRD). The free lime content has been determined by chemical analysis. The formation of the cubic polymorph of C 3 A with Cr and P additions less than 4.24 wt.% Cr 2 O 3 and 3.97 wt.% P 2 O 5 was shown. The temperatures of the decarbonation and the enthalpy variations during the raw firing have been studied. The results showed that the presence of the Cr 2 O 3 and P 2 O 5 oxides lowered the decomposition of CaCO 3 . The enthalpy of decarbonation and the enthalpy of the formation of the solid solutions based on tricalcium aluminate formation decreased when the concentrations of additives increased.

The effect of Cr{sub 2}O{sub 3} and P{sub 2}O{sub 5} additions on the phase transformations during the formation of calcium sulfoaluminate C{sub 4}A{sub 3} S-bar

The study describes the influence of chromium and phosphorus additions on the phase transformations during the formation of the calcium sulfoaluminate Ca{sub 4}Al{sub 6}SO{sub 16} from CaCO{sub 3}-Al{sub 2}O{sub 3}-CaSO{sub 4} mixtures. The temperatures of decarbonation reaction were measured by means of differential thermal analysis. The enthalpy variations at different heating temperatures were determined by isothermal calorimetry. The results show that the Cr{sub 2}O{sub 3} and P{sub 2}O{sub 5} additions lower the onset temperature of decarbonation. The energy requirement at high temperature of the doped mixtures is less, compared to that of mixtures without dopants. The formation of solid solutions is followed by X-ray diffraction. The higher concentrations of additives hinder the formation of the C{sub 4}A{sub 3} S-bar phase.