Volume 2, Issue 4 (April 2005)
The Effect of Aluminum Content Variation on Burning Rate, Pressure-Propellant Area Ratio Relationship, and Other Properties of Hydroxyl Terminated Polybutadiene Based Composite Propellants
In this study, three different HTPB (hydroxyl terminated polybutadiene) based composite propellants were developed by varying the aluminium (Al) content 16, 18, and 20 %; and the effect of aluminium content variation on burning rate, P-K relationship, viscosity, heat of explosion, density, and hardness of the propellants developed were investigated. Propellants were cured at 65°C for 7 days, and then applied to the small test motors and kept at three different temperatures (−42, −15, and 50°C) for a night (8 h) before testing. Tests on the small motors were performed with three different K values (200, 250, and 300) statically. As a result of this, two relationships were determined, and the coefficients of those relationships are also given in Table 1.
First relationship: P = d Ky (1), where P = pressure; y = K index; d = P-K relationship constant; and K = Propellant-area ratio. This relationship shows that pressure is highly affected by K values at 50°C in each of three compositions.
Second relationship: r = a Pn (2), where P = pressure; r = burning rate; a = burning rate constant; and n = combustion index.
This relationship also shows that burning rate has the lowest value in the propellant containing 20 % Al. Therefore; it was observed that the burning rate exponent (n) was below the safety limit value of 0.4 in three compositions, which shows that Al content should not exceed 18 %. These results also indicate that viscosity and hardness remain constant, density increases, and heat of explosion decreases with increasing Al content in the three compositions.