Study On Boron's Refinement, Mg/B Composite Powder's Preparation And Their Thermal Oxidation Characteristics

Boron is the most promising fuel additives for solid rocket propellant and explosive for its high heating values. However, it is difficult to carry its high heating values out as a result of the ignition delay and low combustion efficiency. It has been proved that reduction of particle size and composited with reactive metal are two effective methods to improve the ignition and combustion properties of boron. And the performance of boron powder had an intimate relationship with its preparation technology. In order to solve the existing problems, cryomilling was introduced in this study, and then the thermal oxidation characteristics of refined boron and Mg/B composite powders were investigated.Use 40?m boron powders as raw material to study the particle refinement of boron. Particle refinement was achieved by cryomilling, since boron powder with particle size 2~3?m is prepared successfully. And the effect of particle refinement on the thermal oxidation characteristics of boron including the initial temperature(Ti), temperature of the peak for the oxidation of boron(Tp), heat release(Q), the maximum rate of heat release(Rmax) and the reaction efficiency(?) was studied. The result showed that Ti and Tp were decreased by 231.6 oC and 333.9 oC respectively while Rmax was increased by 218% after particle refinement; Ti?Tp and ? were decreased and Rmax was increased with the reduction of particle size when fracture played dominant roles and cold welding could be ignored; However, when cold welding can't be ignored, Ti?Tp and ? were increased and Rmax was decreased with the reduction of particle size.Use 10?m boron powders as raw material to study the grain refinement of boron. Grain refinement was achieved by cryomilling, since boron powder with grain size 25~43nm is prepared successfully. And the effect of grain refinement on the thermal oxidation characteristics of boron was studied. The result showed that Ti and Tp were decreased by 223.9 oC and 296 oC respectivily while Rmax was increased by about 7 times and ? was increased by 15% after grain refining treatment; Ti and Tp were decreased to 460 oC and 470 oC and remained stable respectively with the reduction of crystalline size; Besides Rmax was improved with the reduction of grain size.The magnesium and boron composite powders were prepared by cryomilling with the 20?m boron powders as raw material and choosing magnesium as additives. The effect of technical parameters on the structure of Mg/B composite powders was discussed and it was observed that decrease of Mg's content, increase of ball-to-powder ratio(BPR), rotation speed and cryomilling time, changing the cryomilling direction in turn were effective methods to decrease the grain size and particle size of Mg/B composite powders. Then the effect of grain size, particle size, the content of metal magnesium and boron oxide on the thermal oxidation characteristics were further investigated. Results indicated that: decrease of boron's grain size can make Tp lower, Q and Rmax higher, ? of boron higher to a small degree; decrease of magnesium's grain size was in favor of decreasing Tp slightly, improving Q and Rmax while had little effect on ?; Besides Tp was decreased and ? was increased with the reduction of particle size. The increased content of metal magnesium was benefit to the reduction of Tp while the reduction of boron oxide content would in favor of the enhancement of ?.