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Combustion Mechanism of Boron Particles

Generally, the combustion stage of boron particles is simpler than the ignition stage, which adopts a predominant heterogeneous surface reaction. Based on experimental data of combustion studies on large boron particles (d > 35 μm), Macek and Mohan believed that the combustion of large boron particles was controlled by diffusion and conformed to the d2 law. In other words, the combustion time of large boron particles was proportional to the square of particle size, similar to that of hydrocarbon droplets. King thought the diffusion transport rate impossible to approach infinity with the decrease in particle size only through diffusion control during boron combustion. King's theoretical research and data analysis found that the combustion stages of large and small boron particles were controlled by diffusion (d2 law) and chemical kinetics (d1 law), respectively. King estimated that the transition from d2 law to d1 law was approximately 15–30 μm in diameter of boron, and the exact transition point depended on pressure. Li and Williams also observed that the combustion of small boron particles (7 and 10 μm) was controlled by chemical kinetics (d1 law). In addition, it was found that the combustion time was equal to the sum of the time needed for oxygen diffusion to the surface of boron particles and boron surface oxidation (2B + O2 B2O2). Based on this discovery, the L-W combustion model was proposed considering both the gas diffusion process and chemical kinetics. To determine the critical conditions of diffusion control and kinetic control, the Y-L combustion model was improved by Kuo, as shown in. The concept of the Damkohler number (Da) is proposed to determine the control mechanism of the boron combustion stage. The Da, widely used in chemical engineering to characterize chemical reaction kinetics in various systems, is usually defined as the ratio of the characteristic time of a chemical reaction to the characteristic time of diffusion of reactants or products. In mathematics, this can be expressed as τt/τr, where τr is the characteristic time of the chemical reaction, and τt is the characteristic time of diffusion. If you are looking for high quality, high purity, and cost-effective Boron powder, or if you require the latest price of Boron powder, please feel free to email contact mis-asia.

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