Preparation and Combustion Mechanism of Boron-Based High-Energy Fuels

Abstract

Due to the characteristics of high energy density and a high calorific value, boron has become a high-energy fuel and shows great potential to be a high-performance candidate for propellants. However, the wide applications of boron are still limited by the characteristics of easy oxidization, ignition difficulty, a long combustion duration, and combustion products that readily adhere to the surface and inhibit full combustion. Therefore, how to overcome the shortcomings and improve the combustion efficiencies of boron-based fuels have become the highlights in exploring novel high-performance energetic materials. In this paper, the prevalent preparation methods and the corresponding combustion mechanisms of boron-based energetic materials are briefly summarized. The results showed that the boron-based energetic materials can be prepared by surface coating, mechanical milling, and ultrasonic mixing methods. At the same time, the corresponding ignition delay and combustion efficiency were also analyzed according to different combustion tests. The results showed that the boron-based composites with different additives had different combustion characteristics. The combustion of boron-based energetic materials can be optimized by removing surface oxide layers, providing extra heat, inhibiting the formation of or the rapid removal of the combustion intermediates, and increasing the diffusion rate of oxygen. With the improvement of the combustion efficiency of boron-based energetic materials, boron-based high-energy fuels will become more and more widely adopted in the future.

Combustion and mechanical property enhancement strategy based on SA surface activated boron powders

“…It affects the propellant's preparation process and mechanical properties [8][9][10]. Moreover, because of the oxide layer of B particles, a molten liquid layer will be formed during the combustion process, which greatly delays the ignition of B particles and reduces the combustion e ciency [11][12][13].…”

Mechanical activation effecton the structure and properties of SHS compounds

“…A large number of publications are devoted to the study of the influence of mechanical activation on the structure and properties of boron SHS-composites. The results of the study of the structure of mechanicallyactivated powders with different ratio of components and properties of compact materials on their basis are presented in the papers [1,2,3].…”

“…Consequence of alternation of these processes is the homogenization of the particle composition with the increase of the processing time [4,6,7]. As a result, a composite powder is formed with a developed interfacial surface between the components.Repeated intensive mechanical action on the powder mixture leads to the formation of a highly defective, far from the equilibrium atomic structure of composite particles [1,3,5,[8][9][10]. The processing not only reduces the size of the reagents, but it also increases the area of contact between them, cleanses the contact surface from oxide films and other impurities, accumulates defects of the crystal structure.…”

“…In similar methods and in terms of physical content of the tasks of mechanochemical synthesis of substances, it is decided to characterize the synthesis process by the amount of energy output -the relative number of moles of a new substance divided by the amount of work spent on its production [3,4]. For the synthesis of composite powders, the ratio of the specific inter-phase surface of the components to the energy consumed is a natural similar criterion.…”

“…Many studies note that mechanical activation results in a sharp decrease in the self-ignition temperature, usually determined by the method of differential thermal analysis. For example, for the «Ti-C» system, the ignition temperature drops from 1600 K for inactivated mixtures to 770K after 5-10 h of low energy activation [7]; for the Ti-Si system -from 1,670 K to 870K (several hours of activation) [7]; For the Ti-Si-C system (3Ti+Si+2C composite) -from 1190K to 430K after 90 minutes of activation, and at 106th minute the mixture is self-ignited directly in the grinding drum at a temperature of 340K [3].…”