Study On The Preparation Of Ultrafine Ammonium Perchlorate By Anti-solvent Recrystallization

Ammonium perchlorate(AP)is one of the most widely used oxidizer in the solid propellant.The percentage of oxidizer in the propellant formulation varies from 60%to 80%by weight.Because of this high percentage in the propellant formulation,the performance of the propellant varies with the oxdemonstrated for preparing superfine AP,anti-solvent crystallization is oneidizer properties,such as size and morphology.Many synthetic approaches have been of the most used approaches.The size and morphology of AP are greatly influenced by the type of solvent or anti-solvent.The researchers are focus on the effect of single solvent,and those about the mixed solvents or anti-solvents are lacked.By changing the volume ratio of the two solvents,the selection of mixed solvents could control the mixed nature of co-solvent,and then manipulate the crystal size and morphology.In this thesis,superfine AP was prepared by anti-solvent crystallization with mixed solvent of DMF/acetone and ethyl acetate as solvent and anti-solvent,respectively.The main works are as follows:1)The AP crystals with different size and morphology were prepared by conventional anti-solvent crystallization by using mixed solvent of DMF/acetone and ethyl acetate as solvent and anti-solvent,respectively.A series of dendritic,cubic-shape crystals featuring a stepped pyramidal hollow on each face and integrated cubic crystals were prepared.It is indicated that the morphology of the crystals was determined by the dominant solvent fraction.When all the AP saturated solution was added with fast feeding rate,the morphology of AP was dendritic.With decreasing the feeding rate,the morphology changed to be cubic.With the increasing of addition amount of AP saturated solution with "slow" feeding rate,the morphology of AP crystals experienced from the edge defective cubic crystals to cubic crystals featuring a stepped pyramidal hollow on each face,in which the layers of stair decreased.On the basis of experimental observations and analyses,a possible model to describe the mechanism of the formation of AP was proposed.Competitive growth occurred among the eomer,edge and face,which leading to the varied size and morphology of AP crystals.2)The AP crystals with varied size and morphology were prepared by ceramic membrane anti-solvent crystallization by selecting the equal volume ratio of DMF/acetone and ethyl acetate as solvent and anti-solvent,respectively.A series of dendritic,hollow cubic crystals and cubic crystals were prepared by manipulating the volume ratio of solvent to anti-solvent and the feeding rate.It is indicated that with increasing the addition amount of anti-solvent and the feeding pressure,the size of the obtained AP crystals were gradually decreased.The particle size and morphology of AP prepared with ceramic membrane,compared to without ceramic membrane,was more regular.