Study On Anti-hygroscopicity Of Modified Ammonium Nitrate Particles By The Fatty Acid Surfactant

In this paper,the surface of ammonium nitrate particles was modified to obtain the optimum coating process conditions and products,ammonium nitrate particles coated with surfactant to reduce the hygroscopicity.The method of surface adsorbed-coating was used to modify the surface of ammonium nitrate particles.The coating process conditions were investigated by using industrial ammonium nitrate particles as raw material,A and B as dispersion medium,Stearic acid as coating agent.Firstly,the four different polar groups with different chain length surfactants containing only C,H,O,and N elements were selected as coating materials.Judging by the hygroscopicity decline and the mass fraction of the coating layer to ammonium nitrate particles,the effects of different experimental operation and environments condition on hygroscopicity of ammonium nitrate raw material were explored to improve the coating process,and then the effects of different surfactants with the polar groups and Non-polar groups coated ammonium nitrate on hygroscopicity were preliminarily compared based on the literature and the surfactant that had better function than other surfactant materials at the same coating process condition was selected as coating agent in further research.Secondly,the comprehensive optimization experiment of coating process were carried out,and then the effects of the process conditions such as surfactant dosage,the mixture ratio of two solvents,reaction temperature and reaction time on coating hygroscopicity of ammonium nitrate were investigated and optimized by the preliminary exploratory experiments and orthogonal experiment.The optimum preparation process conditions were obtained.On the basis of the experiment conditions of orthogonal optimization,the effects of process factors on both the hygroscopicity decline and the mass fraction of coating layer of coated ammonium nitrate particles were investigated.Finally,based to the optimum process conditions,the amplification experiments for 20g/batch ammonium nitrate from 5g/batch were carried out.With the help of SEM and FTIR,the surface morphology and structure of coating modified ammonium nitrate samples were further characterized.The results showed that the hygroscopicity decline of 5g modified ammonium nitrate sample was increased by 3?5%via pretreatment as removing the trace water in solvent.The optimum process conditions of adsorbed-coating experiments were that Stearic acid was selected as coating agent,the optimal process parameters were that 6g dried ammonium nitrate was used as raw material,the m(C18H36O2,Stearic acid)was 2g,the v(A):v(B)was 15mL:15mL,the adsorption coating process was conducted under stirring,that reaction temperature was 65?,reaction time was 1.5h and cooling time was 6h,then the coated ammonium nitrate samples were filtered and dried.The hygroscopic testing conditions were that temperature was 35 ?,relative humidity was 68%,hygroscopicity test time was 24h,under these conditions,the hygroscopicity decline of 5g modified ammonium nitrate sample was 34.4%with the mass fraction of the coating layer 0.76%(w/w)to ammonium nitrate particles.And the optimum process was scaled up to 20g/batch ammonium nitrate by same proportion of meterials,the hygroscopicity testing conditions were that the temperature was 35 ?,the relative humidity was 92%,hygroscopicity test time was 24h,under these conditions,the hygroscopicity decline of 20g modified ammonium nitrate sample of processing amplification experiments was 29.7%with the mass fraction of the coating layer 1.01%(w/w)to ammonium nitrate particles.The hygroscopicity decline of the above two samples was higher than the highest value reported in references.The results of scanning electron microscopy(SEM)showed that the surface of modified ammonium nitrate samples was smooth with reducing holes and cracks on the surface compared with the surface of uncoated samples.The result of FTIR showed that the surface of ammonium nitrate was coated by the surfactant.In this study,comparing with the report in existing literature,the coatingprocess and method were further improved,and the capability of anti-hygroscopicity for modified ammonium nitrate particles was obviously improved.This coating process will lay the foundation for experimental study on the anti-hygroscopic coating process for the ammonium nitrate and other ammonium nitrate salt.