Results and Discussion
The dissolution behavior of Dy2O3 in molten CaCl2
Figure 1 shows a typical time series for the dissolution process of Dy2O3 in pure molten CaCl2 at 1173 K (900 °C). A circle around each particle was used to enhance the boundary. It can be seen from Fig. 1 that the spherical Dy2O3 particle slowly shrinks in time, while the particle remains spherical (even after 7270 s). No surface reaction was observed and the particles remained smooth and spherical during dissolution.
The Dy2O3 particle was quenched after it was immersed in molten CaCl2 for two hours at 1173 K (900 °C). The element maps shown in Fig. 2 illustrate that the outline of the Dy2O3 particle is well defined. Four elements were detected: Cl, Ca, O and Dy. Figure 2 shows that O and Dy diffused in the melt, but there is no sign of
Fig. 1 Time series of CSLM images of a spherical Dy2O3 particle in molten CaCl2 at 1173 K (900 °C)
Cl diffusing into the Dy2O3. This indicates that no new compounds form on the surface of the Dy2O3 particle.
Figure 3 compares the microstructure of the cross section of a Dy2O3 particle before (Fig. 3a) and after (Fig. 3b) immersion into molten CaCl2 for 2 h at 1173 K (900 °C). The cross-section was polished with 1 pm diamond paste after grinding with different emery papers. The as-polished samples were then platinum coated and analyzed by SEM. It is can be observed that the particle with a bigger grain size disappeared after it was contact with molten CaCl2(Fig. 3b).