Preparation And Research On Ignition And Combustion Performance Of Mg-Al-B Alloy Fuel

Metal fuel plays a very important role in energetic materials.Boron powder has become an important component in propellants and pyrotechnics because of its high calorific value of mass and volume.However,the ignition of boron powder is difficult.The high viscous surface oxide film inhibits the contact between boron powder and oxygen,making it difficult to release its high calorific value and high energy.In order to solve these problems,magnesium,aluminum and other elements are added to boron powder for alloying,so as to improve the activity,combustion calorific value,energy release efficiency and other properties of boron powder.MgB₂,AlB₂ and Mg_0.5Al_0.5B₂ and a series of Mg-Al-B alloy powders with different atomic ratios were prepared by vacuum sintering and characterized by X-ray diffraction,scanning electron microscope,energy dispersive spectrometer and true density tester.The results show that a series of Mg-Al-B alloys with high purity and uniform element distribution are formed at the sintering temperature of 1000℃.The true densities of prepared MgB₂,AlB₂,Mg_0.5Al_0.5B₂ alloy powder samples were 2.61 g·cm^-3,2.94 g·cm^-3and 2.92 g·cm^-3,which were higher than 2.33 g·cm^-3 of amorphous boron powder.The combustion calorific value,ignition point and thermal oxidation characteristics of the samples were measured and analyzed by oxygen bomb calorimeter,ignition point tester and synchronous thermal analyzer.Measured results show that the combustion heat of Mg_0.5Al_0.5B₂ alloy powder reached 29350 J·g^-1,which was 68.8%higher than that of amorphous boron powder;Its volumetric calorific value is as high as 85.66k J·cm^-3,which is 111.4%higher than that of amorphous boron powder;After mixing with sodium nitrite powder,the measured ignition point is 396℃.It is a combustion agent with high activity and high energy density.The volumetric calorific value of mg-al-b mixed powder with this ratio is 49.88 k J·cm^-3,which is far lower than Mg_0.5Al_0.5B₂ alloy powder,but its ignition point is only 335℃,which is more active than alloy powder.During the temperature programmed process,the alloying of Mg-Al-B plays an obvious role in promoting the thermal oxidation reaction of boron powder.The oxidation ratio of binary and ternary Mg-Al-B alloy powder is much higher than that of pure boron powder.The oxidation ratio of Mg-Al-B alloy powder with atomic ratio of 9:1:20 reaches 95.3%at 1600℃,while the oxidation percentage of amorphous boron powder is only 70.4%.The laser ignition experimental platform was built.The flame shape change,ignition delay time,flame temperature,heating rate and other characteristics of powder samples during ignition and combustion were observed,measured and analyzed by high-speed camera,infrared thermal imager and optical fiber spectrometer.Results show that the flame colors of magnesium,aluminum and boron are bright white,yellow and cyan respectively.During its ignition process,magnesium and aluminum will be ignited first,so as to drive the ignition of boron.Some samples will produce splashed explosives when ignited.The alloying of Mg-Al-B can obviously promote the ignition and combustion of powder.Under the action of 900W laser,the ignition delay of Mg_0.5Al_0.5B₂ alloy powder is only 19 ms,which is 42.4%shortr than that of amorphous boron powder;The highest heating rate is 3933 K·s^-1,which is 18.3%higher than that of amorphous boron powder;The maximum combustion temperature is 1683℃,which is 17.7%higher than that of amorphous boron powder.