“Study on the Factors Affecting Inverse Burn Rate and Delay Time of Binary Pyrotechnic Delay System”

The pyrotechnic delay plays a critical role in providing a time interval between two successive explosive events in the explosive train. The delay composition is filled into a metal tube in the form of compressed powder, consisting of fuel, oxidizer, and binder. The Inverse burn rate (IBR, s/cm) of the delay composition is a determining factor that plays a vital role in providing delay time within a particular column length of the delay element. In the present study, an experimental investigation was conducted on the inverse burn rate of a B/BaCrO4/NC-based binary delay system by varying the stoichiometry (10/90), where boron serves as the fuel, barium chromate as the oxidizer, and nitrocellulose (NC) acts as the binder. The effect of stoichiometry on density, heat of reaction, particle size, crystallite size, and thermal conductivity of the composition, as well as the impact of these parameters on the inverse burn rate (IBR) and delay time of the binary delay composition, has been studied. The method for controlling all these parameters has been discussed. The effect of hardware and temperature conditioning on delay time was studied experimentally. Results revealed that, as the percentage of boron decreases and barium chromate increases, the heat of reaction and thermal conductivity of the composition decrease; the density, crystallite size and particle size of the composition increase. It is evident that these parameters significantly affect IBR and delay time. The B/BaCrO4/NC binary delay shows IBR ranging from (0.22–1.59 s/cm) with reliable burning and smooth propagation at all temperature conditions in different hardware. The composition supported combustion, having up to 3% boron and more than 10% boron, it becomes a flash composition. The B/BaCrO4/NC binary delay composition burns slower and produces more delay time in brass hardware as compared to aluminum hardware. The thermal conductivity of the hardware plays a critical role in achieving a tunable delay time within the specified column length of the delay tube. This research work is useful to tailor the IBR and to improve the consistency in the delay time of pyro devices.