Study On Mixed Crystal Properties Of Ammonium Potassium Nitrate

Potassium nitrate is mixed fertilizer with potassium and nitrogen,it has no chloride.It also has excellent physical and chemical properties,so it is a kind of important chemical raw material.Because of the existence of potassium ammonium nitrate solid solution when producing potasssium nitrate by using a complex reaction with potassium cloride and ammonium nitrate,it is diffcult to get high quality potassium nitrate.Therefore,we get the information of crystal structure,compositions and thermal properties of potassium ammonium nitrate have a great significance to the separation and purification of high quality potassium nitrate.In order to explore the crystallization features of potassium ammonium nitrate mixed crystal,the crastal growth,structrue and thermal property were studied in this paper.The solubility of KNO₃-NH₄NO₃-H₂O system at 25?was determined by equilibrium method.Through exploring the effect factor of crystals growth with different cooling rate and mixing rate,experience showed that too slow mixing rate leaded to the aggregation of the crystal and too fast mixing rate leaded to the smaller particle crystals.When the cooling rate set more than 2.5?/h,the appearance of crystal is needle and the morphology is incomplete.When the minxing rate was set at 120r/min and cooling rate was set at 1?/h,the particle diameter size is suitable and the shape is relatively complete.The single crystals of K_x?NH₄?_1-xNO₃?0<x<1?for different compositions were grown for the first time by a method of constant speed cooling rate and characterized by XRD,SXRD,SEM and FTIR.The results show that the single crystals have two different types,that is,ammonium potassium nitrate?0.60<x<1?and potassium ammonium nitrate?0<x<0.51?,the SEM photos showed those appearance were hexagonal prism and four prism respectively.The XRD and FFIR results show that the crystals are continuous solid solution,the crystal cell parameters of different main phases are very different,but the same as crystal system.With NH₄⁺replaced by K⁺,the crystal morphology changed.The thermal stability of the solid solutions prepared was studied by using TG-DSC.The results showed that the mixed crystal potassium ammonium nitrate resoled for the instability of ammonium nitrate.The solid solution ammonium potassium nitrate presents the properties of melting for overcoming the ionic bonds.From the TG diagrams of the K_x?NH₄?_1-xNO₃ with different components,we found that the decomposition temperature of the solid solution became rised with the X gradually increased.When the temperature at350?those decomposed completely.The thermal stability of the solid solution increased with the NH₄⁺decreasing.