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Reactive Shell Model for Boron Oxidation

An approach suitable for quantitative description of oxidation of porous powders with a complex particle morphology is developed and applied for a 95% pure boron powder. It is shown that boron particles, which are agglomerates of nanosized, partially fused primary particles, can be represented as spheres with reactive porous shells and impenetrable cores. The oxidation of such powders is assumed to occur volumetrically within the reactive shells. The shell thickness is obtained from simple experiments with the actual powders. To determine the thickness, thermo-gravimetric measurements are performed and processed for powders with different but overlapping particle size distributions. The processing uses measured powder particle size distributions to assign fractions of the powder mass gain to individual particle size bins. Selection of the appropriate initial reactive shell thickness makes it possible to ensure that particles of the same size present in samples with different size distributions oxidize in ...