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Introduction of TANYUN Solid Rocket Composite Propellant

TANYUN composite propellant is a kind of propellant composed of polymer binder: hydroxyl-terminated polybutadiene, solid powder oxidizer: ammonium perchlorate, powder metal fuel: aluminum, and other additional components.


Composite solid rocket propellant is referred to as composite propellant, which is mainly composed of crystal oxidizer, binder system (fuel) and metal fuel. Composite propellants are usually classified by binders and named after the structural skeleton of the binder polymer and the chemically active groups it has. For example, carboxyl polybutadiene propellant, referred to as carboxybutadiene propellant (CTPB), is a binder with a carboxy COOH chemically active group. Hydroxyl-terminated polybutadiene propellant, referred to as hydroxybutadiene propellant (HTPB), is a binder with hydroxyl-terminated OH chemically active groups.

Composite propellant is a gunpowder made by mixing and solidifying inorganic oxidizer (ammonium perchlorate, ammonium nitrate, etc.), combustion agent (aluminum powder, etc.) and polymer binder. through
It is often divided into polysulfide rubber composite propellant, polyurethane composite propellant, hydroxyl-terminated polybutadiene composite propellant and carboxyl-terminated polybutadiene composite propellant according to the types of polymer binders. The energy of the composite propellant is higher than that of the double-base propellant, the specific impulse is as high as 2200-2600 N·sec/kg, the combustion controllability is strong, and the pressure index is low. Due to the use of casting molding, it can be made into large grains, which are mostly used for large thrust rockets and missiles.

The composite propellant has relatively high energy characteristics, the actual specific impulse reaches 2 256-2 453N/(kg/s), and the density is about 1.75g/crn3, which is easy to solve the problem of raw materials; the pressure index and temperature coefficient are low, which makes the engine The performance change is small under different operating temperatures; the critical pressure is low, so that the combustion chamber pressure is low, and the shell is light; it still has quite good mechanical properties at low temperatures. After testing this, it has been widely used in various tactical missiles and ballistic missiles.
The production of composite propellants mostly uses vacuum casting technology, that is, the components of the propellant are premixed and blended to form a uniform propellant slurry, and then poured into the engine combustion chamber prepared in advance under vacuum conditions. Vacuum casting can avoid pores in the grain and ensure the quality of the grain. In order to shape the propeller in the engine, the engine needs to be placed in an environment with a specified temperature for curing. The curing temperature and time vary with different propellant formulations. For example, the curing temperature of polybutadiene propellant is 50℃±2℃, and the holding time is 170h. The propellant-cured engine can be put into use after it has passed the inspection of non-destructive inspection techniques such as X-ray, ultrasound, endoscopy, and CT imaging.

Components of TANYUN Composite Propellant
1. Oxidizer
Oxidizer is the component with the most content of composite propellant towel, and its mass fraction generally accounts for 60%-80%. It has a great impact on the specific impulse of the engine, the burning rate of the propellant and the process performance. The main function of the oxidizer is to provide the oxygen required for the combustion of the solid rocket propellant, and to increase the Young's modulus of the propellant as a filler in the binder system. The oxidant has the characteristics of high oxygen content, high enthalpy of formation, high density, low molecular weight gas generated during decomposition, no solidification phase product, good chemical and physical stability, and good compatibility with adhesive brakes. Used as oxidants are lithium perchlorate (LiClO4), potassium perchlorate (KClO4), ammonium perchlorate (NH4CIO4), potassium nitrate (KNO3) and ammonium nitrate (NH4NO3). In addition, nitramine, RDX and octogen (HMX) can be used as oxidants because of their high enthalpy of formation, high density and high oxygen content, which can significantly increase the specific impulse of the propellant.

The widely used oxidant is ammonium perchlorate. The solid rocket propellant using potassium perchlorate as the oxidant has a high burning rate and a large pressure index. Therefore, when high burning rate and high pressure index are required, potassium perchlorate is often used as the oxidant (or together with ammonium perchlorate as the oxidant) propellant. The energy characteristics of solid rocket propellant using ammonium nitrate as oxidant, etc., have low burning rate, low pressure index, clean gas, and low price, and are mostly used in gas generators.

2. Adhesive
The binder is another important component in the composite propellant, and the general content is 10%-15%. Its main function is to firmly bond the solid particles of the oxidizer and the metal powder together, so that the propellant has appropriate mechanical properties, can withstand the load received during operation, storage, ignition and flight, and burns with the oxidizer. At the time, provide combustible C, H and other elements as fuel in the solid rocket propellant. The binders used as composite solid rocket propellants include polysulfide rubber (PS), polyurethane (PU), various polybutadiene (PB), polyvinyl chloride (PVC), etc.

3. Metal fuel
The purpose of adding metal fuel is to increase the combustion temperature of the solid rocket propellant, thereby increasing the characteristic velocity of the propellant and the specific impulse of the engine, and also to suppress the unstable combustion in a certain frequency range and increase the density of the solid rocket propellant. As metal fuels, aluminum (Al), beryllium (Be), lithium (Li), boron (B), magnesium (Mg), and the like are used. Aluminum powder is widely used because of its high combustion calorific value, low price, abundant source and high combustion efficiency. Aluminum powder generally accounts for 50-20% of solid rocket propellant.

4. Curing agent
The curing agent is also an integral part of the adhesive system. The purpose of adding the curing agent is to make the active functional group and the functional group of the binder undergo a chemical chain reaction to cure the propellant through the curing reaction. The type of curing agent varies with the type of adhesive. For example, the curing agent of carboxy-terminated polybutadiene is aziridine and epoxy compound; the curing agent of polysulfide rubber is maleic anhydride and alumina.

5. Other additives
In order to improve the energy characteristics, internal ballistic performance, mechanical properties, processability and storage performance of the composite propellant, additional components are added, including burning rate catalysts (such as Fe2O3, etc.) to improve internal ballistic performance, and rate-reducing agents (such as CaCO3 Wait). Plasticizers and enhancers to improve mechanical properties, diluents (such as styrene) and wetting agents to improve process performance, antioxidants and sensitizers to improve storage performance, etc.

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