Dr. Sunil Jain, DRDO Scientist

Thesis Abstract:

To meet the diverse and challenging requirements solid propellant technology

has come a long way from the simple double base propellants to the current day

complex high-energy propellants. Composite propellant is one of the important class

of propellants used worldwide widely. Composite propellants are basically

composed of an elastomeric binder, in which solid particles of oxidizer, fuel, and

additives are incorporated. For present rockets and missiles, ammonium perchlorate

(AP) is used as an oxidizer, HTPB as a prepolymer and aluminium powder as a

metallic fuel. For achieving flawless performance in rocket motors, composite

propellant must have optimized mechanical, ballistic, etc. properties. Ballistic

performance parameters of composite propellants consist of burning rate, pressure

index, specific impulse, characteristic velocity, etc. Burning rate, which is one of the

important ballistic properties of composite propellants, is defined as the rate of

regression of burning surface in the direction perpendicular to the propellant burning

surface. It is generally expressed in mm/s and written along with the pressure at

which it is determined. The composite propellant burning rate depends on variety of

elements such as propellant composition, combustion chamber pressure, initial

propellant temperature, etc. To realize the required burning rate of composite

propellant formulation at any particular pressure, generally, the amount and particle

size of oxidizer is varied. For optimum ballistic and mechanical properties of

composite propellants, the oxidizer Ammonium perchlorate (AP) is used in different

size fraction or modals. The increase in fine AP fraction enhances burning rate,

however, it also causes increase in propellant slurry viscosity which has a

detrimental effect on the aim of achieving defect free grains. Further, the fine AP

particles are difficult to process and handle, hence, high loading of AP fine is not

favoured for achieving higher burning rate composite propellants.

The other way to fulfil the requirement of high burning rate is by incorporation

of chemical compounds in propellant formulation which acts as burning rate

modifiers or enhancers. The most common burning rate modifiers are transition

metal oxides (TMOs) and their complexes. Generally, the burning rate modifiers are

added in small quantity may be less than 2% of total composition to limit the inert

weight with respect to energy (specific impulse). They lower the decomposition

temperature of AP and/or binder which results in enhancement of propellant burning

XIII

rate. Burning rate modifiers can be solid or liquid. However, liquid burning rate

modifiers are not preferred as they greatly increase the propellant sensitivity and also

cause processing difficulties.

Application of smaller particle size of the metal oxides result in large

enhancement in propellant burning rate as smaller particles have larger surface area.

This large surface area has more number of atoms/molecules on the particle surface

causing enhancement of catalytic activity of oxide. Application of nano TMOs for

composite propellant burning rate enhancement and related fields have been reported

previously. Further, Bi or multi-metal oxides are found to be more effective in

catalyzing AP decomposition and /or enhancing burning rate of composite propellants

than single oxides. This may be due to the selectivity of metals for intermediate

chemical reactions in propellant combustion. Multimetal oxides can also encompass a

possibility of having crystal defects due to substitution which may result in more

activity of multimetal oxides.

The exhaustive literature survey discloses that limited details are available on

the effect of bimetallic oxides (perovskite oxides, ferrites, etc.) on burning rate of

HTPB/AP/Al based composite propellant formulations. Thus, in the present study,

different bimetallic oxides were characterized and then evaluated in standard

composite propellant formulations to ascertain their effect on mechanical and ballistic

properties of the propellant.

Further, ballistic properties measurement using ballistic evaluation motors

static testing was carried out for one of the bimetallic oxide studied. For this purpose

two grain configurations were studied in detail. Tubular grain configuration was

optimized considering the neutrality. A novel double funnel port grain configuration

was designed and compared with the existing configuration. Following was the

research plan followed:

 Characterization of the bimetallic oxides

 Thermal decomposition of ammonium perchlorate in the presence bimetallic

oxides

 Evaluation of bimetallic oxides in propellant composition

 Ballistic evaluation motors (BEM) grain design for improved neutrality

 Ballistic properties measurement using ballistic evaluation motors static

testing