The stability of synthetic Mg3 (PO4) 2·22H2O (TMP 22) was studied under atmospheres with various water vapor pressures at 25-70°C.
The sample of TMP 22 was decomposed and changed to be in an amorphous state under a relative pressure (P/P0) of water vapor of less than 0.2 at 25-30°C. In saturated water vapor at 55°C, the crystal lattice of TMP 22 was retained for more than 10 hr and then converted to Mg3 (PO4) 2·8H2O (TMP 8). On the other hand, TMP 22 became amorphous within 2 hr at 41°C in air (P/P0=0.5-0.6).
The conversion of TMP 22 to TMP 8 also occurred at 50-70°C within 5 hr in distilled water, the aqueous solutions of Na2CO3 and NaOH, and the mother liquor after the precipitation of TMP 22. Under these conditions, it has been found that the conversion time to TMP 8 was reduced remarkably in comparison with those of TMP 8 preparations previously reported. Therefore, the conversion process stated here is applicable to a rapid synthesis of TMP 8.
