The Effect Of Additives On The Safety Performances Of Ammonium Nitrate And Its Regularity

Ammonium nitrate is one of the most important nitrogen compounds in the chemical industry and agriculture.It has been widely used in nitrogen fertilizers,industrial explosives and propellant.Many large accidents and illegal use involving AN happened frequently in the recent years,the harm brought by AN has aroused great attention and vigilance.There have been several attempts to improve the thermal stability of AN.However,there is not much research focus on the relationship between thermal stability and explosive performance of AN.The effect of crystal structure,the mixing process and different types of additives on the thermal stability and explosive properties of AN also has not been studied.Whether increasing thermal stability of AN could suppress the detonation of AN still unknown.To solve these problems,this paper systematically studied the crystal structure,thermal stability and explosive performance of AN and ANFO.Urea,monoammonium phosphate(MAP),potassium chloride(KCl)and sodium chloride(NaCl)were selected as additives from compound fertilizer,flame inhibitor and phase stabilizer,and two kinds of mixing methods were used to prepare modified AN and ANFO.In the re-crystallization process,K+ ions can replace NH4+ ions in the crystal lattice and form a solid solution because of their similar ionic radius,thereby reducing weaker hydrogen bonds.8%KCl can cause the disappearance of phase ?.Na+can only partially replace NH4+ ions and enter into the AN crystals as impurity,so the temperature of ?(?)? phase transition will increase,but the effect is not obvious.Weak acidity cannot completely break weak hydrogen bonds of AN,so MAP will reduce temperature of ?(?)? phase transition.For the mechanical mixing method,the friction,heat exchange and thermal cycle have an influence on the ?(?)? transition of AN,but the effect is also not obvious.The crystal structure studies show that the mixing methods and additives affect the re-crystallization process of AN.The changes in microscopic crystal structure may affect the thermal stability and explosive performance of AN.The thermal stability of AN was studied by DSC.The results of thermal analysis experiment indicate that urea can substantially increase the thermal stability of AN.The onset temperature of AN-5%urea is increased from 203.50? to 289.10?.MAP also has a good effect.NH3,a decomposition product of urea and MAP,would not only inhibit the first step of thermal decomposition reaction of AN but also consume the autocatalytic factor NO2.Chloride will increase the generation rate of mediate product[NH3NO2+],so it has a catalytic effect on the thermal decomposition of AN.The maximum exothermic peak of AN-10%KCl is reduced from 286.75? to 263.12?.Cl-ion can greatly accelerate the decomposition of AN in acidic condition.Without acidic conditions,the catalytic effect is limited.When the content of chloride increases,the onset temperature will increase.MAP and AN can form double salt during re-crystallization process.NH4+ and NO3-will separate the oxidation group and reduction group and affect the reaction between them,thereby improving the AN thermal stability.For chloride,the increase of moistufe content is conducive to acid accumulation,so the solution mixing method is not suitable to improve the thermal stability of AN.The Koenen test is used to measure the sensitivity of solid substances to intense heat with varied confinement.The results show that improving the thermal stability of AN can effectively reduce the sensitivity of AN to hyperthermia.To suppress thermal explosion of AN,AN need to mixed with 30%KCl.KCl and NaCl cannot effectively inhibit the thermal explosion of AN and ANFO.The results that the additives that increase the thermal stability of AN can effectively reduce the thermal sensitivity of AN.The UN gap test is used to measure the ability of a substance under confinement in a steel tube to propagate a detonation by subjecting it to the detonation from a booster charge.The results show that AN-50%urea mixtures can still produce a steady detonation in the UN gap test.Urea cannot reduce the ability to propagate a detonation.However,KCl and NaCl can effectively inhibit AN detonation.For solution mixing method,AN-15%KCl mixtures cannot produce a steady detonation in the UN gap test.The results of UN gap test show that improving the thermal stability of AN to suppress the detonation of AN isn't reliable.When the size of particles decreases,the detonation velocity first increases and then decreases.In the range of 20-100 mesh,the detonation velocity of AN increased from 1.17km/s to 1.61km/s and then decreased to 1.54km/s.The detonation velocity reaches the maximum within the range of 60-80 mesh.For mechanical mixing method,the detonation velocity of modified AN both decreased when the mass of additives increase.For solution mixing method,the additives will affect the packing density,crystal structure and surface properties of AN.The detonation velocity of the AN-5%KCl and AN-5%NaCl mixture both is higher than pure AN.However,with the increase of additive content,the detonation velocity will decrease,and the effect of suppressing detonation of AN is better.