| Lanthanum phosphate is the basis for the development of rare earth materials in the optical direction.As an important matrix material,the crystal morphology of lanthanum phosphate is one of the most important factors affecting its performance.Lanthanum phosphate is used as a matrix material doped with other rare earth ions as a sensitive,the defects in the crystal consume the energy of the electron transition,and the luminous intensity and quantum efficiency are affected.Therefore,the study of the synthesis of lanthanum phosphate crystal is the premise of the rare earth luminescent material.In this paper,we studied the preparation of lanthanum phosphate crystals by hydrothermal method,and prepared the morphology of lanthanum phosphate with irregular block shape,pebble shape and similar globular shape.The purity and crystal morphology of lanthanum phosphate samples were discussed,and the four experimental conditions of hydrothermal temperature,time,amount of precipitant and amount of acetic acid were discussed by titration.And under the action of different additives and temperature,the formation mechanism of lanthanum phosphate with different morphology is simply discussed.The main contents of this paper are as follows:（1）In this paper,pure lanthanum phosphate crystals were prepared by hydrothermal method using lanthanum oxide and sodium dihydrogen phosphate,as well as acetic acid as the reaction promoter.The effect of hydrothermal temperature,time,amount of sodium dihydrogen phosphate and acetic acid on the purity of the sample was investigated in detail in the way of controlling variables.The conclusions are as follows:With the increase of temperature and time,the secondary and tertiary ionization of phosphoric acid increases,and the number of ionized phosphate ions increases,which creates conditions for the formation of lanthanum phosphate precipitation in the reaction.As a result,increasing the amount of sodium dihydrogen phosphate provides a material basis for ionization of phosphate ions.Acetic acid is used to dissolve lanthanum oxide in raw materials.When the amount of acetic acid is2.8 ml,lanthanum oxide is dissolved,and acetic acid does not hinder ionization of phosphate ions.（2）By adding glycine and starch to the reaction hydrothermal reaction,the nucleation and growth of crystals were regulated by electrostatic induction of carboxyl groups in glycine.The hot solution of starch has viscosity,viscosity on the one hand controls the velocity of ion movement in the solution,on the other hand,starch contains hydroxyl functional groups,hydroxyl groups as a strong power supply group to form an electric field,increase the attraction between ions,so conducive to local aggregation of La3+and PO43-,the two effects combined to regulate crystal growth.Increasing the temperature to 170℃under hydrothermal conditions to explore whether there is excess sodium dihydrogen phosphate in the system has an effect on crystal recrystallization.Because 170℃of hydrothermal conditions do not reach the dissolution temperature of lanthanum phosphate,but the participation of sodium dihydrogen phosphate acts as a mineralizer,prompting the dissolution of lanthanum phosphate and achieving the effect of recrystallization.（3）The above method synthesized micron-sized lanthanum phosphate crystals.In the current rare earth phosphate applications,nano-sized phosphates are more valuable than micron-sized phosphates,so on this basis,the annealing method is used to refine the grains,to explore the effect of grain refinement under different temperature conditions,and to analyze the reasons for the weakening of the grain agglomeration.A spherical lanthanum phosphate crystal with more uniform particles was obtained by exploring 800℃as the best refining temperature,which has higher application value. |
