Ultrafine Ammonium Dihydrogen Phosphate, The New Preparation

In this paper,the feasibility and technology regularity of superfine ADP were studied by two preparation methods of freeze-drying and anti-solvent.It was found that both methods of direct freezing and spray freezing were able to get superfine ADP powders with small,uniform distribution and weak agglomeration.The particles were finer and more uniform by spray freezing while the solution segregation Phenomena existed in direct freezing.The conditions with low solution concentration,large surface area,shallow solution loading and fast frozen were in favor of getting superfine ADP of small,uniform distribution and weak agglomeration by method of direct freezing.There were three factors with solution concentration,injection pressure and spray distance which impacted on the granularity of ADP by spray freezing.The solution concentration was the greatest impact,followed by injection pressure,while spray distance was the last.The superfine ADP powders were obtained with the average particle size of 3.12μm When the solution concentration was 0.1mol/L,injection pressure was 0.6Mpa and spray distance was 5cm.The study also found that the method of anti-solvent could prepare the superfine ADP powders,and different sizes of particles could be obtained through the control of experimental conditions.There were three factors with Solvent anti-solvent temperature difference,pressure and stirring speed which impacted on the granularity of ADE The Solvent anti-solvent temperature difference was the greatest impact,followed by pressure, while stirring speed was the last.The superfine ADP powders were obtained with the average particle size of 11.74μm When Solvent anti-solvent temperature difference.was 90℃, pressure was 0.6Mpa and stirring speed was 500r/min.All powders were detected by laser particle size analyzer,SEM,XRD and DSC.The result showed that the ADP particles were 5～13μm with Spherical or irregular shape by direct freezing;3～10μm with Uniform distribution,bar or needle shape by spray freezing; 11～25μm with large particle size and wide distribution by anti-solvent.The crystallization and decomposition temperature of the ADP particles prepared by either direct freezing or spray freezing were reduced to some extent,while anti-solvent changed a little.