| Oblate propellant with micro-pores (OPM), whose size is from some microns to millimeters, is a kind of new propellant, in which there are a lot of pores. The porous structure of OPM enhances gas-generating rate significantly. OPM is usually applied in civilian and military fields, such as short barrel weapons, smokeless fireworks and automobile airbags. The combustion performance of OPM is closely related to its pore structure. Therefore, pore-forming mechanism of OPM is the base for pore structure control technology. Furthermore, it is very important to grasp the inter-relationships between pore structure and combustion performance for its practical application. Based on one-step processing method, the pore-forming mechanism and the pore structure control technology were studied in this dissertation. Meanwhile, the effect of pore structure on the combustion performance was studied and the application of OPM in display shell was explored.Firstly, based on the characteristics of one-step processing method, several possible pore-forming mechanisms were proposed and verified. The result showed that water was the key factor of pore formation. Pores were achieved from two main ways,"diffuse water" and "enfolded water"."Diffuse water" pore-forming mechanism was implemented through the liquid-liquid phase separation:the mixture of water and ethyl acetate caused for the mass transfer effect, water and ethyl acetate could diffuse via the surface of nitrocellulose emulsion droplet. When the balance of three-phase system composed of nitrocellulose, ethyl acetate and water was broken, the liquid-liquid phase separation happened, forming the rich polymer phase and the lean phase. Then the lean phase wrapped in the rich phase formed different shapes of droplets after the following process. With the evaporation of solvent, polymer solution was cured and shaped. Eventually water led to the pores formation."Diffuse water" pore-forming mechanism mainly led to two different sizes of pores:one was spherical pores whose diameter distributed unevenly from10to200microns. These pores were mainly closed structure and randomly distributed in OPM. The other was globular or catenulate pores whose diameters were less than10microns and distributed uniformly. These pores were mainly via pore structure and filled OPM."Diffuse water" pore-forming mechanism took place in the whole forming technology process."Enfolded water" pore-forming mechanism was that:the stirring effect got the water into the nitrocellulose emulsion droplet in the form of water droplets, and finally led to the pores formation. The pores caused by "enfolded water" were mainly spherical and closed structure in the size of0.1～200microns, and randomly distributed in OPM with uneven diameters."Enfolded water" pore-forming mechanism mainly happened between the process of "adding water" and "adding gelatin solution".Secondly, based on pore-forming mechanism of one-step processing method and compared with the production of porous materials in other fields, the improved one-step processing method was proposed. In addition, the methods were explored for preparing OPM with different pore structures, including via pore structure, closed pore structure and layered structure. OPM with above structures was successfully prepared by means of changing shape, chemical foaming, hydrolyzing solvent and others. The average internal pore diameter, pore numbers and pore structure could be controlled by changing formula or technical conditions, which laid the groundwork for studying the relationship between pore structure and combustion performance of OPM. For instance,7%sodium sulfate solution was used as dispersion medium for controlling pore structure by chemical foaming. Big pores inside OPM were generated when solvent was evaporated by14.3%,42.9%and57.1%. However, it was via pore structure when28.6%solvent was evaporated. Small-pores were closed pore structure in this process.Thirdly, the samples of oblate propellants with different pore structure were tested in the closed bomb respectively. The relationships among pore structure, mass burning rate and progressive combustion were studied. The results showed the smaller the bulk density of the propellant, the larger the mass burning rate, the stronger the progressive combustion for same pore structure. It could be concluded that the bigger the average pore diameter and the more pore quantity, the stronger the convective burning and the stronger the progressive combustion. While pore structure was different, the mass burning rate of the oblate pore propellants was different. The mass burning rate decreased gradually with the big-pore closed pore structure, small-pore closed pore structure, layered structure, big-pore closed pore structure, small-pore via pore structure, big-pore via pore structure, small-pore via pore structure, big-pore via pore structure and small-pore closed pore structure. The dynamic activity of dense propellant was lowest, followed by the propellant with big closed pore, with small closed pore, with big closed pore, with small-pore via pore, with layered structure, with big via pore, with small via pore, with big via pore and with small closed pore. The structure effect of the big-pore on the combustion was considerably greater than small-pore. Analysis suggested when the propellant surface was ignited, the convective combustion generated by the hot gas spread to the internal propellant. The big pore dominated the mass transfer of the combustion gas, so the propellant with big-pore via pore structure owed greater progressive combustion, while the propellant with big-pore closed pore structure owed less progressive combustion.Fourthly,①the major problems on the launch process of fireworks display with smokeless propellant were analyzed, for example, the low and unstable launch height, and the residue in launch ground. According to the interior ballistic process of fireworks display, the smokeless propellant cannot replace the traditional black powder mainly because that the mass burning rate and ignition performance were low. Theoretically, the mass burning rate could be improved by increasing the flame spreading rate and the effective combustion area, then the launch performance could also be improved. The flame spreading rate of OPM was8times of dense oblate propellant, there would be a greater promoted space after being processed. Compared with black powder, the smog density was reduced by98.1%, OPM had the potential to replace black powder and be a smokeless propellant of smokeless fireworks display.②Based on the influence on the flame spreading rate and effective combustion area of OPM, the author studied the effects of propellant morphology, air tightness of the launch canister, moisture rate, effective combustion area and other factors on the launch performance. The experiment parameters were optimized in order to explore the powder charging structure and the condition of OPM to replace the conventional black powder. The results showed that the sensitizing MOSPs which were prepared by changing the shape, property of the waste propellant, by adding some proportion of adhesion, burning rate modifiers and igniter, could be reformed to specification modules. These modules could greatly enhance the combustion performance of the smokeless propellant. Under the condition of half charge weight of traditional black powder and the moisture absorption ratio from1.0%to1.9%, it could satisfy the ballistic index of launch height, stability, pressure and environmental index of1.2-inch display shell. The application in smokeless display shell propelling charge with MOSP could be realized in this condition. |
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