Fundamental calorimetric measurements of boron oxidation from dry powder suspensions

Boron is a promising fuel with exceptional gravimetric and volumetric heat of combustion, yet its full energetic potential remains difficult to realize, particularly when measured in a calorimeter. This study introduces a method to quantify the calorific output of boron powder suspensions by dispersing the powder is a porous carbohydrate (PC) matrix. The PC matrix has a low heat of combustion to provide the organic framework needed to isolate particles and simulate dry powder suspension burning behavior. Bomb calorimetry experiments were performed to measure the available energy of boron powder combustion representative of a dust environment as a function of particle loading density (i.e., called boron loading fraction, BLF). Results reveal an increase in combustion efficiency with theoretically complete combustion achieved when particles are more isolated from each other (i.e., at low BLF). Pressure measurements in-situ combustion demonstrate that H 2 O gas resulting from PC decomposition promote gas-phase energy conversion by facilitating the gasification of boron oxide (B 2 O 3 ) to metaboric acid (HBO 2 ) and condensation to boric acid (H 3 BO 3 ), as confirmed by X-ray diffraction. These results establish a direct correlation between gas-phase energy conversion and heat of combustion. Results also demonstrate that despite boric acid formation the theoretical heat of combustion for boron oxidation can be achieved. This study introduces a promising framework for measuring the heat of combustion from metals burning in a simulated powder suspension environment and utilizes it to advance the fundamental understanding of boron combustion. This study also discusses the practical limitations of extracting the oxidative potential from boron powder suspensions. • Bomb calorimetry of boron suspensions was made using a starch scaffolding. • Conditions for achieving theoretical maximum heat of combustion at 57.7 kJ/g are shown. • Boron particles well dispersed and isolated maximize heat of combustion. • In-situ pressure measurements quantify energy conversion into the gas phase. • For the case of highest heat of combustion, 100 % chemical energy is deposited into the gas.