It is clear that AS 1892802 of K2O for CaO in sample G–Zr considerably improved its sinterability. The maximum density for sample G–Zr at 1300 °C was approximately 87%, whereas the addition of only 2 mol% K2O increased it up to 94% at a much lower temperature (1050 °C). The DSC curves reveal that the K2O addition reduces the tendency of crystallization such that the sample with 6 mol% K2O does not exhibit a distinct crystallization peak.
Fig. 7a and b present the XRD patterns of samples G and G–Zr heat treated at various temperatures, respectively. Sample G exhibits one reflection centered at 2θ=32° connective tissue corresponds to the crystallization of apatite at 850 °C. This sample heated between 950 °C and 1200 °C revealed maxima that matched to β-wollastonite and apatite. At 1300 °C, the wollastonite transformed to pseudo-wollastonite, and a sharp maximum appeared at 2θ=22°, which was attributed to cristobalite.