The stability of synthetic Mg
3 (PO
4)
2·22H
2O (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 Mg
3 (PO
4)
2·8H
2O (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 Na
2CO
3 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.
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