Thermal behavior and laser-induced heating characteristics of boron agglomerates in various atmospheric conditions.

Boron particles in solid-fuel ramjet combustion chambers typically exist in agglomerated form, and the gas composition within the chamber includes not only air but also propellant combustion products such as water vapor and CO₂. This study investigates the thermal behavior, laser heating characteristics, and condensed-phase heating products of boron agglomerates in six distinct atmospheres: N₂, O₂, air, water vapor, CO₂, and Ar. Thermal oxidation tests revealed that the reaction between boron and O₂ dominates in an air atmosphere, while boron can still react with N₂ in air to form granular boron nitride. Laser-induced heating resulted in ejection phenomena occurring in boron agglomerates when subjected to N₂, air, water vapor, Ar, or O₂ atmospheres, with the O₂ atmosphere being the most conducive, exhibiting an average of 47 occurrences for individual agglomerates. The ejection process and frequency were found to be comparable in the air, Ar, and water vapor atmospheres, with an average ejection frequency ranging from 7 to 11 times. Although the ejection phenomenon occurred in the N₂ atmosphere, its frequency was low, with an average of only two occurrences. Agglomerates underwent significant expansion before ejection, while single-particle boron did not exhibit ejection or expansion in any of these atmospheres. The highest surface temperatures of boron agglomerates upon laser heating in air, water vapor, N₂, and Ar atmospheres were 2697.7 K, 2416.2 K, 2408.9 K, and 2392.1 K, respectively. Analysis of condensed-phase heating products revealed that boron agglomerates reacted with N₂ or CO₂ to form boron nitride or boron carbide, respectively. [ABSTRACT FROM AUTHOR]