Studies on the processing of HTPB‐based fast‐burning propellant with trimodal oxidiser distribution and its rheological behaviour

Abstract

Composite propellants based on hydroxyl terminated polybutadiene/ aluminium powder/ammonium perchlorate (HTPB/Al/AP) are commonly used in solid rocket motors (SRM) in defence and space applications. The solid propellant is a polymeric matrix with high solid loadings of metallic fuel and oxidiser along with some additives. Due to high solid loading, the propellant slurry becomes highly viscous and thus becomes difficult to process. In the case of trimodal distribution of the oxidiser, the effect of viscosity becomes more pronounced and it is difficult to mix and cast the propellant under vacuum owing to its high viscosity. In this paper, rheology of the propellant slurry containing oxidiser in trimodal distribution has been studied and an attempt has been made to find the effect of mixing parameters such as oxidiser addition sequence, mixing temperature and plasticiser concentration on the propellant properties and in improving the ease of processing. The study shows that the processability and pot life can be improved by optimising mixing parameters.

Rheological Impact of Particle Size Gradation on GAP Propellant Slurries

“…In terms of the CL-20/AP/GAP propellant slurries with a given solid content of 65%, the frictional interaction between particles becomes the main factor influencing the rheological properties, while the thermal motion and the repulsive forces of particles are negligible . When particle gradation technology is applied, potential effects are listed as follows: , (1) the finer particles with smooth surfaces act as the lubricant at the contact of particles, which can effectively weaken the frictional interactions between particles with sharp edges, and (2) the step-filling effect of micron-sized, ultrafine, and submicron-sized particles contributes to dense packing, resulting in a decrease in the content of liquids trapped in interparticle spaces, which is not conducive to the slurry flow. Hence, an attempt can be made to illustrate and evaluate the differences in the rheological properties of the slurries in terms of factors affecting the interparticle frictional interactions and particle packing density.…”

“…Otherwise, defects such as voids, shrinkage, and cracks will occur inside the propellant column, which severely defeats the original purpose of developing a solid propellant with high energy and low sensitivity. In response to these challenges, rheological tests have been introduced, and the rheological behavior of the slurries obtained from the experiments allows us to deduce their processability. , Propellant slurries are generally seen as a class of soft matter whose rheological behavior differs from that of solids and liquids, exhibiting viscoelasticity when subjected to deformation and flow. Steady rheological tests and dynamic rheological tests are two of the prevalent rheological measurement methods.…”

Rheo‐kinetic study of 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB‐based composite propellant and evaluation of casting rate

“…In addition, the tailoring of burn rate is performed by incorporating transition metal oxides (TMOs) like copper chromite, ferric oxide, manganese oxide and zinc oxide. However, these TMOs enhance the inert weight and pose an adverse effect on overall processibility 1–7 …”

“…However, 4‐(Dimethylsilyl) butyl ferrocene‐grafted HTPB possess higher viscosity, i.e., 120 Pa.s at 303 K, which is almost 2.5 times that of HTPB, and it directly affects the flow behaviour of the propellant slurry. Rheological characterizations of HTPB‐based basic aluminized composite propellant and correlation with mix viscosity and pot life have been well delineated in literature reports 7,22–27 . Therefore, from the processability aspect of a novel polymeric binder system, it is pertinent to have knowledge about the rheological parameters of the propellant slurry and their dependency on time–temperature.…”

“…However, these TMOs enhance the inert weight and pose an adverse effect on overall processibility. [1][2][3][4][5][6][7] To address the aforementioned problems, a considerable amount of work has been carried out with liquid organic catalysts, based on ferrocenyl derivatives such as n-butyl ferrocene, di-n-butyl ferrocene, di-t-butyl ferrocene, 2,4-dinitrophenyl hydrazine derivatives of acyl ferrocene, 1-pyrrolidinyl methyl ferrocene and ferrocenebased phenylethylamino compounds. [8][9][10][11][12][13] The liquid catalysts act as process aid by reducing the mix viscosity, which in turn allows high solid loading.…”