Oxidation of Boron in Air

Kostuchenko, N. D.; Vovchuk, J. I.; Kiro, S.A.

doi:10.1615/intjenergeticmaterialschemprop.v2.i1-6.100

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“…When applied in energetic materials, amorphous boron is preferred due to its high specific area and high reaction activity. However, boron can easily be oxidized in air [3] and is not completely oxidized due to the formation of a glassy layer of boric oxide at the reaction interface [4], which considerably decreases the heat release of the system. Due to its difficulty in ignition [5] and long combustion time [6][7][8], the utilization of the calorific value of boron during the oxidation process turns out to be very limited.…”

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Ignition and Combustion Behavior of Sintered‐B/MgB₂ Combined with KNO₃

Sun

Ren

Jiao

et al. 2020

Propellants Explo Pyrotec

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To further enhance the performance of B/KNO 3 (BPN) igniter, sintered B/MgB 2 (s-B/MgB 2 ) powder was proposed to be used as a boron substitute. The amount of heat release was tested by oxygen bomb and thermogravimetry/differential scanning calorimetry (TG/DSC). s-B/ MgB 2 /KNO 3 (sBPN) igniter could not release as much heat as BPN igniter in the oxygen bomb due to the reduced calorific value of the s-B/MgB 2 . However, calculations show that s-B/MgB 2 reached an over 90 % heat release efficiency in oxygen bomb, compared to that of 53.34 % for boron. At heating rate of 10 K min À 1 in TG/DSC experiment, 19.5 % sBPN (sBPN with 19.5 wt. % s-B/MgB 2 powder) has a heat release of 1815 J g À 1 and experienced an exothermic span of 2.10 min, whereas it took 24.5 % BPN (BPN with 24.5 wt. % boron powder) 3.45 min to release 1465 J g À 1 . The pressuretime curve (P-t curve), burning rate and combustion tem-perature were determined. The P-t curve indicates that the combustion pressure was more readily established with the sBPN than with the BPN. The maximum pressure rise of sBPN was 362.0 Pa ms À 1 , whereas the figure for BPN is 77.2 Pa ms À 1 . Coupled with infrared radiation (IR) temperature thermometer, the distribution of the flame temperature field during combustion was obtained. It is shown that the combustion temperature of 19.5 % sBPN igniter is approximately 800 K higher than that of 24.5 % BPN. IR images of the combustion process show that the temperature difference of the 19.5 % sBPN flame is smaller than that of the 24.5 % BPN. 19.5 % sBPN also produces more hot residue, which contains KMgF 3 , resulting in a longer high-temperature duration. The higher combustion pressure and temperature and more residue may enable the sBPN to readily ignite the following charge.

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