7.4. NH4H2PO4-NH4NO3-H2O Solubility in the NH4H2PO4-NH4NO3-H2O system has been reported in nine papers.1-9 Figure 16 shows the data of some of these papers as well as the related data of two papers in which the title system was studied as a boundary of a multicomponent system.10,11 According to Fig. 16, the data of Tudorovskaya and Margolis10 for solutions saturated with both NH4H2PO4 and NH4NO3 seem to be in error when compared with the rest of the data.
Solubility isotherms have also been reported at temperatures higher than 100 °C. Fridman et al.4 presented a network of isotherms and a smoothing Eq. [1].
x = a –t/b [1]
where x is the mass % water, t is the temperature, and a and b are constants. No temperature limits are given for the validity of this equation. The results of Fridman can be compared with those of Varlamov et al.8 for the region 140 °C to 170 °C and those of Margolis and Glazova5 at 100 °C and 110 °C. The agreement is not good. The values reported by Varlamov, et al.8 and by Margolis and Glazova5 show a slightly higher water content than do those of Fridman, et al.4 Some investigators4,8 report the existence of anhydrous solutions in the regions rich in NH4NO3. Varlamov et al.8 paid special attention to the solubility values in these areas. The evaluator attempted to compare the isotherms of Bergman and Bochkarev1-3 with values calculated using Eq. [1]. The agreement was very poor. More experimental work is needed to resolve these differences.