氮、磷、钾（N-P-K）全水溶复合肥是今后化肥发展的主要品种。目前我国多采用简单的物理混合来生产，故产品的混合均匀性、水溶性和流动性以及存储均存在一定问题。为此，本项目拟首先采用等温法测定(NH2)2CO-NH4H2PO4-KCl-H2O四元体系的相平衡，并选用合适的模型，如修正Apelblat方程、λh 方程和 NRTL 模型，关联溶解度数据；采用X粉末衍射、能谱仪、以及扫描电镜等仪器分析鉴定该体系固液平衡时的固相组成和结构。在此基础上对该体系冷却结晶过程进行研究。目前，尚无研究者对该体系的相平衡和结晶过程进行专门研究。本项目通过上述研究，最终确定该体系固液平衡时的固相组成和结构，并开发出制备(NH2)2CO-NH4H2PO4-KCl共晶体，或三元聚集体的冷却结晶工艺。

Water soluble fertilizer containing nitrogen, phosphorus and potassium (N-P-K) would be widely used in the future. Nowadays, it is made of nitrogenous fertilizer, phosphatic fertilizer and potash fertilizer by physical mixing in our country, so the property of this product, such as mixing uniformity, water solubility, fluidity and storability is not perfectly. It is necessary to develop a new technique to overcome these problems in production of soluble fertilizer. In this work, firstly， the phase equilibrium of the quaternary systems ((NH2)2CO-NH4H2PO4-KCl-H2O )would be determine by the isothermal method and the solubilities of (NH2)2CO, NH4H2PO4 and KCl in water were maybe correlated with some model such as the modified Apelblat equation, λh equation and NRTL model. The metastable solubilities of the aqueous quaternary system were determined by the isothermal evaporation method. Secondly, the composition and structure of the solid phase in this phase equilibrium system were characterized by X powder diffraction, energy spectrometer and scanning electron microscope. Finally, the cooling crystallization process of the quaternary system would be studied. These works have not been reported in literatures. Through these researches, the solid-liquid phase equilibrium of the systems will be determined and the composition and structure of solid phase will be characterized, and the new process of co- crystallization for (NH2)2CO-NH4H2PO4-KCl-H2O by cooling crystallization may be developed.