Non-Toxic Gas Generators for Airbags
Development of Non-Toxic Gas Generating Compositions for Automobile Airbag Inflators
Tech Area / Field
- CHE-IND/Industrial Chemistry and Chemical Process Engineering/Chemistry
- CHE-POL/Polymer Chemistry/Chemistry
- CHE-SYN/Basic and Synthetic Chemistry/Chemistry
8 Project completed
Senior Project Manager
Rudneva V Ya
Institute of Problems of Chemical Physics, Russia, Moscow reg., Chernogolovka
- Institute of Organic Chemistry, Russia, Moscow
- Fraunhofer Institute Chemische Technologie, Germany, Pfinztal\nTRW Automotive, USA, AZ, Mesa
Project summaryThe objective of the project is the development of new-generation gas generating (GG) compositions for automobile airbag inflators (AAB), which are free of toxic components and do not yield toxic combustion products. The development of such compositions should allow the exclusion of a gas purification system, thus providing for low prime cost and mass production of safe automobile airbag inflators.
Perfect self-burning gas generator compositions for reliable application in AAB should meet certain requirements: high yield of gases per unit weight, high burning rate and its specified dependence on pressure, lack of high-toxicity substances in raw ingredients, lack of solid particles and high-toxicity substances in combustion products (e.g., nitrogen and carbon monoxides), stability in a wide temperature range, and fixed properties upon long storing at higher temperatures. Non-toxic GG formulation should not contain metal and halogen compounds, should possess zero or slightly positive oxygen balance and a combustion temperature of ~2000-2200K. Due to essential shifting of water steam conversion equilibrium below 2000K (CO2+H2->CO+H2O) to the left, the latter condition provides a low content of both CO and water in combustion products; the water acts like aerosol particles with their «roasting» effect on AAB surface.
At present GG formulations, based on sodium azide, formulations of ballistic powder types, and formulations based on ammonium nitrate (AN), are the most applicable in AAB. All have some essential drawbacks. For example, compositions based on metal azides are dangerous because of high toxicity of azides and the possible release of explosive gaseous hydrazoic acid under emergency conditions. In addition, to purify the gas from aerosol particles (sodium oxide and carbonate), expensive filters should be installed. Compositions of ballistic powder types have a high combustion temperature, thus resulting in a high content of toxic products, carbon and nitrogen monoxides, in the generated gas. The technical arrangement of their absorption is even more complicated than the removal of aerosol particles from the gas. For compositions based on ammonium nitrate (AN), it is difficult to achieve the high burning rate, required for AAB operation. Also, due to phase transitions in AN crystalline lattice, mechanical decomposition of formulations is possible, thus leading to uncontrolled change of burning rate.
Therefore, studies for development of self-burning compositions meeting all of the above requirements are of both applied and scientific importance. Such research is necessary to increase AAB efficiency, to reduce their cost and weight, and to decrease the level of toxicity of both compositions and combustion products. On the other hand, the data obtained may be used as a scientific basis for developing formulations of various applications for fast gas release when different requirements are set to the temperature, burning rate, gas composition, etc.
To solve this problem the available compositions could be modified. For example, the most suitable composition AN + guanidine nitrate (NGu) may be modified in several ways:
1. Stabilizing AN phase state with salts free of metal ions. Long-term investigations performed at IPCP confirm the possibility of stabilization.
2. To decrease AN fraction and to improve burning parameters, NGu could be replaced by a propellant with a higher oxygen balance. Such low-enthalpy groups as -COO, -OH, -O-, -C=O, -CONH2, etc., together with energetic groups of -NO2, -NNO2, -ONO2 type, should be oxygen carriers in these compounds. If AN content is low, stabilization of its phase states is not required.
3. Total or partial replacement of AN by a new oxidizer, e.g., tetra (trinitroethoxy) carbon (TTNEOC) or its analogs. The melting point of TTNEOC is 153°C and, under certain conditions, it can meet the requirements for stability. Also, if a composition comprises only organic substances, aqueous technology may be used to manufacture porous charges.
A more promising approach is to search and synthesize essentially new compounds, to develop GG compositions of a new generation. When essentially new formulations are developed, a search for new CHNO-compounds, which would combine a high oxygen content (so that they could act as oxidizers) and a relatively low value of standard formation enthalpy, is of major importance. The latter condition is necessary for low combustion temperatures and, thus, low content of CO and NO in combustion products. To achieve the combination of high oxygen content and low value of standard formation enthalpy, C-O-C-, C=O, COO, OH, HNCONH groups should be included into the molecule. The formation of such essentially new compounds (mainly oxidizers) is an independent scientific problem.
The project offers to cover theoretical and experimental analysis of all possibilities of metal-free CHNO-compounds for AAB, a search for optimal compositions considering the cost and safety aspects, and development of the technology for their production.
A team of specialists, formerly successfully involved in the development and production of solid propellants and explosives, will participate in the project. Potential participants of the project, employees of IPCP and IOC, are highly qualified researchers with considerable experience in the field of thermodynamics of high-energy processes, thermal stability and compatibility of chemical compounds, combustion of high-energy compositions, and synthesis of new nitrogen-containing chemical compounds.
Expected results and their application. As a result of the project implementation:
– The dependence of combustion temperature of formulations CnHmNkO2n+0.5m on composition, enthalpy and pressure will be determined and computer programs will be developed to seek formulations that meet certain requirements.
– A wide range of new organic compounds containing -OH, -O-, -C(O)-O-, >CO, HNCONH, etc., groups with a relatively low value of standard formation enthalpy, which are promising for AAB compositions, will be defined.
– New ways of phase transition stabilization in ammonium nitrate will be found.
– Ways to increase thermal stability of compositions based on TTNEOC and some onium salts of nitrogen-containing organic or inorganic acids, including dinitramide, will be found.
– New CHNO-compounds will be synthesized, for their use as oxidizers or oxygen-containing propellants for compositions with a combustion temperature of about 2000K; their physical-chemical properties will be studied and ways to increase their stability will be determined.
– Regularities of ignition and combustion will be defined for formulations meeting thermal stability requirements; ways to control the combustion rate and regularities will be developed (addition of catalysts, using ingredients with a certain granular composition, etc.); ways and technological techniques will be developed to control the delay time of ignition.
– Optimum compounding will be defined, theological characteristics of composite materials and ways to control them will be determined.
– Ways to form the charges will be developed, providing for possible burning rate control.
The scientific significance of the project is to find new high-efficiency ingredients for self-burning compositions of a civil application, to develop methods to predict their properties, and to find and synthesize essentially new chemical compounds with both high oxygen content and low value of standard formation enthalpy.
The practical significance of the project is determined by its ultimate objective, that is, the development of new high-efficiency non-toxic gas generating compositions for automobile airbag inflators. The final results will be applicable in the industry of transport safety systems, because the development of such compositions should allow the exclusion of a gas purification system and should provide for low prime cost and mass production of safe automobile airbag inflators. Also, the results obtained when synthesizing and stabilizing new compounds with many oxygen-containing groups may be used in pharmaceutical chemistry.
The project entirely meets ISTC aims because it provides scientists and personnel, formerly engaged in weapons development, with an opportunity to conduct research aimed at peaceful activity. It also promotes the genuine integration of Russian scientists into the international scientific community and supports basic and applied research and technology development for peaceful purposes.
The project is a culmination of theoretical and experimental investigations and engineering developments. It involves the following:
1. Analysis of primary information on available systems. Thermodynamic analysis of the dependence of combustion temperature for CnHmNkO2n+0,5m formulation on the composition, heat contents and pressure. Development of programs for a computer search of formulations with desired combustion temperature.
2. Study of stabilization of AN phase states in the entire range of operation temperatures by incorporating different additives into the AN lattice.
3. Synthesis of new low-enthalpy organic compounds CnHmNkOx with oxygen excess (x>2n+0,5m) or deficiency (x<2n+0,5m), and their testing as oxidants and propellants for GG compositions.
4. Prognosis and estimation of the thermal stability of ingredients and compositions. Investigation of compositions with TTNEOC and some onium salts of nitrogen-containing organic or inorganic acids, including dinitramide, as oxidants.
5. Investigation of ignition and combustion regularities for formulations, meeting requirements for thermal stability. Search for catalysts of combustion and granular composition, that provides necessary rate and law of combustion, study of ways of particle formation.
6. Development of the technology for production of the charge with all necessary properties.
Considerable experience in theoretical and experimental studies of combustion and explosion accumulated at IPCP while developing solid propellants and powders, and experience of IOC in synthesis of nitrogen- and oxygen-containing compounds will be used for implementation of the project.
Experimental methods of investigation, including thermal gravimetric, calorimetric, methods of chemical, X-ray and spectral (IR-, UV-, mass- and NMR) analysis available in IPCP and IOC will be used. New experimental equipment will be manufactured for high-temperature kinetic investigations.
Computing base and considerable experience of IPCP in mathematical modeling and numerical solution of the problems of chemical kinetics, thermodynamics, and combustion will be used. Programs will be developed to seek formulations in databases of ingredients and molecular fragments. This will ensure selection of new promising compounds for synthesis.
Conventional approaches will be used and new ones will be developed for synthesis of CHNO-compounds with a high nitrogen and oxygen content, allowing the combination of energetic and “ballast” groups in the same molecule. Methods for synthesis of new oxidants will be also developed, mainly, new dinitramides salts and TTNEOC analogs.
The kinetic method of forced aging will be used to study ingredient stability and compatibility. Combustion regularities will be studied in a wide range of temperatures and pressures. To control a mass burning rate approaches typical for materials science of energetic condensed systems will be used.