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

To further enhance the performance of B/KNO₃ (BPN) igniter, sintered B/MgB₂ (s-B/MgB₂) 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/MgB₂/KNO₃ (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/MgB₂. However, calculations show that s-B/MgB₂ 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⁻¹ in TG/DSC experiment, 19.5 % sBPN (sBPN with 19.5 wt. % s-B/MgB₂ powder) has a heat release of 1815 J g⁻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⁻¹. The pressure-time curve (P-t curve), burning rate and combustion temperature 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⁻¹, whereas the figure for BPN is 77.2 Pa ms⁻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 KMgF₃, 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.