Effects Of Explosive Microstructures On Their Properties

In order to better understand the effects of explosive microstructures on properties, two kinds of explosive materials, inorganic compound ammonium nitrate(AN) and organic compound 1,3,5-triamino-2,4,6-trinitrobenzene(TATB) which have different natures and application fields, and their explosive formulations have been discussed. The microstructures(porosity,pore structure,surface character,etc.) and properties(suck as thermal decompose temperature, detonator ignition sensitivity,etc.) of different state AN and ANFO have been mainly researched. Synchronously, the microstructures and properties of TATB powder and TATB based composite also have been studied.Judged by N₂ adsorbtion isotherm, AN samples should belong to coarse pore materials. The microstructures of different states AN and ANFO are much different, for example, the density of industry unexpanded sample is high and porosity is low relatively, particles' surface is smooth, the number of protuberance,hole and crack is also less than expanded samples. After expanded, the average pore diameter has no remarkable change, but pore volume increase and density falls markedly, the aberrance of crystal shape is severe, there are many defects of protuberances, pointedness, pores and cracks appear on the particles surface, so the particles surface shows a accidented structure characteristics. The pore structure and particles surface charaters of expanded samples are ralated with their prepared conditions. The process of smashing and sieving make particles size and shape much close, some pores are destroyed, so the pore number decreases, porosity reduces and specific surface area falls.Fractal dimension is used to compare the coarse degree of AN particles relatively quantificationally in our research and the fractal dimension calculate formula suited for treating AN's mercury intrusion adsorption curve is selected and modified. The order of fractal dimension value obtained respectively from mercury intrusion adsorption curve and N₂ adsorbtion isotherm is accordant and consistent with the order of particles coarse degree which obtained by SEM. Fractal dimension values indicate that the coarse degree of unsieving AN samples is much different while 40 mesh AN samples have a little difference.The thermal sensitivity and detonator ignition sensitivity of AN and ANFO mainly depend on the number of pores, the more the number of pores is, the more the hot spots formed under outside thermal action and shock wave have, so explosives happen reaction and ignition more easily. The experimental results also show that ANFO states and charge conditions have an evident effect on formulations' detonation properties, in a certain range, the explosive detonation capability increases along with the water content reduces, particles size decreases, charge height enhances, charge density increases and charge diameter augments. When other conditions are restricted, the order of ANFO detonation capability is accorded with the order of AN particles coarse degree (i.e. fractal dimension) while isn't accorded with the order of specific surface area or porosity, so ANFO particles coarse degree is the remarkable factor of determining explosive detonation capability. The experimental results of polymethyl methacrylate method also indicate expanded ANFO has much higher detonation velocity and detonation pressure than common ANFO sample, the detonation pressure increase with the reduce of explosives particles size,too. Based on these results of ignition and detonation capability, the ignition and detonation reaction mechanism of ANFO are expounded, i.e., there are two different reaction phases during ANFO's ignition and detonation developing process, one is the phase of hot spots forming and ignition, the other is the phase of detonation growing.When some selective inorganic additives are added into ANFO formulations, although the explosive's micro structures have no evident change, the ignition and detonation capability increase. However, the selective organic surfactant can change ANFO sample microstructures, so the ignition sensitivity and detonation capability change, the order of detonation capability is agree with the order of particles coarse degree.The phase transition behavior of different state AN are also studied, the results show that the reduce of particles size is helpful to restrain the phase transition of III-II, and there seems have some relations between the AN phase transition behavior and particles surface characters, that is: when modified AN particle surface microstructure has little change, the phase transition behavior doesn't has remarkable change; potassic salts can smooth the AN particles surface, so the modified AN samples have little phase transition of IV-III; Oxide,Cu(NO₃)₂, (NH₄)₂SO₄,MgSO₄ and other mineral coarsen the AN particles surface, so the phase transition behavior of III-II can be restrained. But this rule should be further approved or modified by more systemic experiments.TATB samples microstructures are correlated nearly with the preparation methods. Most directly synthesizing sample's particles size is beyond 10μm, specific surface area is low, particles shape is similar to sphericity and particles size is asymmetry, particles surface is coarse. While the samples' average size which prepared by several fined methods is within submicron grade, above 98% particles size is smaller than 200nm, the specific surface area of air-flow smashing sample is close to that of recrystalling samples, while the specific surface area of mechanical milling samples is quite low. The particles shape of air-flow smashing samples is also similar to sphericity and particles surface is smooth.For recrystalling samples, the particles shape is erose, profile is similar to slice or spherical and shape's difference is great under low multiple SEM, while under high multiple SEM,the particles shape is similar to strip. When the recrystalling samples are smashed by air-flow, the particles shape becomes symmetrical and regular. The order of particles coarse degree obtained by SEM is accorded with the order of fractal dimision gained by small anglex ray scattering method(SAXS).TATB pore structures are investigated by two methods, one is N₂ absorption method, the other is synchrotron radiation SAXS technique.The measuring results of N₂ method show that synthesizing samples have little pores but recrystalling samples have many pores, air-flow smashing samples and recrystalling-airflow smashing samples have a few pores. The SAXS testing results also show that preparation methods have an obvious effect on TATB microstructures and the samples particles surface coarse degree can be compared by fractal dimension value.The thermal decompose temperature,5seconds explosion point temperature and short pulse ignition sensitivity are correlated with TATB microstructures, especially rest on the pore number.The short pulse ignition sensitivity and detonation complete degree are inverse with charge density and direct with porosity, when the porosity is adjacent, the detonation capability mainly determined by fractal dimension.The ingredients of TATB based composite prepared by solvent quick removing method and high energy impacting method can be composited at micro-nano scale, composite particles size is symmetrical and shape is similar.While the ingredients particles shape of machanical mixtures is distinct, the particles contact area is limited and some sensitive explosive particles are bared and expose to external action, so its impact sensitivity is higher than that of composite.