9.1. (NH4)2HPO4 - Urea - H2O
Two investigations of the composition and temperature of the invariant points in this system are available.1,2 But these two sets of data do not agree with each other even with respect to the nature of the equilibrium solid phase. The modifications of urea are the main source of the uncertainty. The evaluation of this question, however, is beyond the scope of this volume. The closely related system (NH4)2HPO4-CO(NH2)2HNO3-H2O was studied by Nabiev et al.3
References:
1
Treshchov, A. G.; Dokl. Timiryazevsk. S. -kh. Akad. 29, 402 (1957).
2
Vereshchagina, V. I.; Endovitskaya, M. P.; Zh. Neorg. Khim. 15, 2818 (1970).
3
Nabiev, M. N.; Tukhtaev, S.; Narkhodzaev, A. Kh.; Yunusov, D. Kh.; Zh. Neorg. Khim. 21, 3152 (1976).