Addition of RDX/HMX on the Ignition Behaviour of Boron-Potassium Nitrate Pyrotechnic Charge

Boron-potassium nitrate (B-KNO3) (25/75) is a well-known pyrotechnic composition whichfinds application as energy-release system for small-calibre rockets and pyrogen igniters forlarger motors. The decomposition of the oxidiser in this composition is endothermic which canbe activated by the addition of high explosives, which decompose exothermically. This paperdescribes the influence of two nitramine explosives, RDX and HMX, on the ignition characteristicsof B-KNO3 composition using thermogravimetry, differential scanning calorimetry, heat andpressure output measurements. Different compositions were prepared by varying the amount ofRDX/HMX from 10 per cent to 50 per cent. Thermal studies on the B-KNO3/high explosivemixtures reveal that these undergo two-stage decomposition. The first stage corresponds to thedecomposition of high explosive and the second stage corresponds to that of the reaction betweenB and KNO3. Kinetic parameters were calculated for both the stages of TG curves using Coats-Redfern and Mac Callum-Tanner methods. Ignition temperature of B-KNO3 decreases on theaddition of RDX/HMX while the onset of RDX or HMX decomposition is not significantly affectedby B-KNO3. The pressure output of B-KNO3 increases on adding RDX/HMX. The heat outputof B-KNO3 is not much affected by the addition of RDX or HMX, even though the heat ofexplosion of RDX and HMX are low. This is due to the reaction between the combustion productsof RDX/HMX and reaction products of B-KNO3 to form more exothermic products like B2O3,releasing extra heat. The flame temperature of the charge increases while the average molecularweight of the products of combustion decreases as the RDX/HMX content increases. Thus, thecharge, on addition of RDX or HMX, produces higher pressure output, maintaining the heatoutput at comparable levels

Thermal Studies on Boron-Based Initiator Formulation.

Boron-potassium nitrate pyrotechnic composition can be converted into a hot wire-sensitive initiator formulation by the addition of an extra fuel. viz. lead thiocyanate. The ignition temperature of this composition depends on the percentage of thiocyanate in the mix and follows a binomial fit. The kinetic parameters. viz. activation energy E and pre-exponential factor A of the charge have been calculated from TG and DSC curves using different approaches developed by Coats-Redfern and Kissinger. Ignition delays measured from isothermal TG runs were found to yield equally good values of E and A. A comparison of these values for the tricomponent system' with those of the bicomponent systems as well as of the ingredients suggests that the starting reaction in this formulation is the reaction between lead thiocyanate and potassium nitrate which energises the main reaction between boron and potassium nitrate. leading to ignition