Structural and thermal properties of boron nanoparticles synthesized from B_2O_3 + 3Mg + kNaCl mixture

摘要

Amorphous boron nanoparticles were synthesized by heating a B_2O_3 + 3 Mg + kNaCl (k is the number of moles of NaCl) exothermic mixture in a laboratory oven at 800 ℃ under argon flow. NaCl was used as inert material to decrease the maximum combustion temperature of the reaction mixture when it was self-ignited after the melting of Mg at 650 ℃. The size of the boron nanoparticles extracted from the final product by acid leaching ranged between 30 and 300 nm for k values ranging from 1 to 5. Moreover, increasing the value of k from 1 to 5 resulted in an increase in the specific surface area of the nanoparticles from 40 to 74 m~2 g~(-1). However, at k = 10, a decrease in the specific surface area to 47.56 m~2 g~(-1) was recorded due to incomplete reduction of B_2O_3. The ignition point of boron nanoparticles in air as estimated using a thermocouple was approximately 300 ℃. Digital camera recording of the combustion process of boron nanoparticles in air revealed that the burning speed of the nanoparticles increased significantly from 0.3 to 15 cm/s when k increased from 1 to 5.