Study On The Ignition And Combustion Characteristics Of Boron And Aluminum-magnesium-boron Alloy

Boron has been widely used in propellant additives because of its high calorific value,low consumption,clean combustion products and other advantages.However,the shortcomings of boron,such as difficulty in ignition,easy agglomeration,and insufficient combustion,restrict the application and promotion of boron.To solve this problem,aluminum and magnesium can be added to boron to form an aluminum-magnesium-boron alloy to improve the ignition and combustion properties of boron.In this paper,boron and aluminum-magnesium-boron alloys are used as the research objects,and a laser ignition and combustion performance test platform for boron and aluminum-magnesium-boron alloys is built.Influence,comparative analysis of the ignition and combustion performance of boron and aluminum-magnesium-boron alloy are investigated in detail,and the combustion mechanism of boron and aluminum-magnesium-boron alloy are analyzed.According to the thermogravimetric results,it is inferred that the boron oxidation reaction process can be subdivided into three stages:the first stage is the early stage of the reaction(27??400?),and the sample weight gain rate tends to zero;the second stage is the middle stage of the reaction(400??742?).B₂O₃began to melt,and the weight gain rate of the sample began to change,reaching the maximum value of 6.87%/min at 742?,and then began to slow down;the third stage is the late stage of the reaction(?742?).The aluminum-magnesium-boron alloy formed by adding aluminum-magnesium has a major change in its stage characteristics.The sample weight gain rate of the aluminum-magnesium-boron alloy reaches the maximum value of 8.61%/min at 674?,which has entered the third stage ahead of schedule(?674?).The ignition temperature is reduced by about 60?,and the ignition delay time is shortened by about 1.3ms.The results of laser heating ignition experiments show that the combustion of boron and aluminum-magnesium-boron alloys is generally divided into ignition process and combustion process.When the heating power is low,the ignition process of boron and aluminum-magnesium-boron alloys can be further subdivided into three stages,and the stage characteristics are basically similar to the thermogravimetric results.For boron element,the surface temperature of the sample in the first stage(0?400?)is heated by laser radiation,which is the early stage of the reaction.In the second stage(400??900?),when the temperature of the sample reaches about450?(the melting point of B₂O₃),the oxide film begins to melt.As the sample temperature increases,boron continuously combines with oxygen in the air to form a boron oxide film.The heating rate has changed,which is the middle of the reaction.In the third stage(about 900??1030?),as the temperature continues to rise,B continuously dissolves in B₂O₃and reacts with it to form a new polymer(BO)_n.The temperature rise curve gradually tends to be flat.It is the late stage of the reaction.As boron burns,its surface temperature continues to rise(?1030?).The addition of aluminum and magnesium has a major impact on the second stage of boron,which increases the temperature rise rate of boron during the ignition process by more than 5times and reduces the ignition delay time by?1/3.When the heating power is high,the ignition process of boron and aluminum-magnesium-boron is completed in a very short time,the heating rate is basically the same,and the laser power density has a great influence on the temperature rise rate.Therefore,when the ignition power density is low,the huge advantages brought by the addition of aluminum and magnesium to boron ignition can be highlighted.The combustion results of boron and aluminum-magnesium-boron alloys in different atmospheres show that the addition of aluminum-magnesium also has a huge impact on the combustion characteristics of boron.When the oxygen concentration is high,green flame is obviously observed during the burning of boron and aluminum-magnesium-boron.As the oxygen concentration decreases,the duration of the green flame becomes shorter and shorter,and it is not even observed.Under pure nitrogen,boron and aluminum-magnesium-boron alloy hardly react.With the increase of oxygen concentration,the burning time of boron and aluminum-magnesium-boron alloy is shortened,and the burning temperature is getting higher and higher.However,the overall combustion temperature of boron is higher than that of aluminum-magnesium-boron alloys.When the oxygen concentration is 20%-100%,the overall combustion temperature of boron is about 500?higher.In a pure oxygen environment,the temperature difference is about 1500?.In a pure oxygen environment,the combustion products of boron are H₃BO₃,B(OH)₃,(BO)and unburned B,while the combustion products of aluminum-magnesium-boron are mainly B₂O₃,Al₂O₃,Mg O,and the intermetallic phases Al B,Mg B,Al Mg B are completely decomposed and combustion is relatively complete.However,the size of the combustion products of aluminum-magnesium-boron is relatively large,and it is necessary to further study the formation process and mechanism of agglomerates to weaken its agglomeration effect.The research in this paper is of great significance to the understanding of the ignition and combustion mechanism of boron,and the improvement of the ignition and combustion performance of boron through alloying methods,and provides a reference for the application of boron in propellants.