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June 2024
Conference Paper
Title
Chemical inter-substance reactions of energetic materials-Enhancing the use of assessing methods
Abstract
Assessing chemical stability and compatibility of energetic materials is already a long lasting task. Up to present, mostly traditional or in character near traditional materials have been tested and evaluated. For them the established methods work mostly well. Newer materials as FOX-12, ADN, new organic oxidizers based on the nitro formate group, new energetics based on nitrogen-rich molecular groups as triazol and tetrazol are entering into the development and formulation departments and may reach or in part have reached demonstrator level and even in-service level as FOX-12 (carbamoylguanidinium dinitramide). In part, some newer materials show good chemical stability, another part has to be evaluated with care. Both groups have in common that the experience with known materials is not transferable directly to new ones when
considering the limit values for inter-reaction conversion. An adapted assessment is necessary. Often the assessment is based on methods like DSC and TGA, which provide results with small amounts of material in a short time, which is seen as great advantage. Main decomposition peaks lying at higher temperatures are used to assess the thermal stability. But the evaluation of chemical stability and compatibility for in-service temperature ranges between 15 and 40°C is not possible with them. The often overseen effect of the temperature weighting already observable with reactions in parallel with different activation energies will be demonstrated and the consequences by this effect discussed. For reliable assessment the experimental determinations must be performed in such a way to cover the time-temperature load of the material at in-service conditions also by the test conditions. This is named TEL (thermal equivalent load) principle. Further only with certain extents of reaction conversions, at least 4 to 6 %, at not to high temperatures a suitable assessment of chemical stability and chemical compatibility can be achieved. The interest with compatibility evaluation is to get the information on the inter-reaction conversion at defined test times and test temperatures of substances in contact, means on the so-called inter-reactivity. The way to achieve this is not as simple as typical standards propagate. A further demand must be to parameterize the temperature dependence of the inter-reactions. The next question is the about the allowed extent of inter-reaction conversion with methods as gas generation, heat generation and mass loss. Until now, this question is not satisfactorily answered, especially with heat generation and gas generation, which are determined by heat flow microcalorimetry and vacuum stability test apparatus, respectively. A way to come to con-clusive values will be outlined and discussed. The method mass loss is in advantage; therewith the extent of conversion can be determined directly. With suitable instrumentation, a direct inter-reaction analysis (DIRA) in mixtures can be achieved.
considering the limit values for inter-reaction conversion. An adapted assessment is necessary. Often the assessment is based on methods like DSC and TGA, which provide results with small amounts of material in a short time, which is seen as great advantage. Main decomposition peaks lying at higher temperatures are used to assess the thermal stability. But the evaluation of chemical stability and compatibility for in-service temperature ranges between 15 and 40°C is not possible with them. The often overseen effect of the temperature weighting already observable with reactions in parallel with different activation energies will be demonstrated and the consequences by this effect discussed. For reliable assessment the experimental determinations must be performed in such a way to cover the time-temperature load of the material at in-service conditions also by the test conditions. This is named TEL (thermal equivalent load) principle. Further only with certain extents of reaction conversions, at least 4 to 6 %, at not to high temperatures a suitable assessment of chemical stability and chemical compatibility can be achieved. The interest with compatibility evaluation is to get the information on the inter-reaction conversion at defined test times and test temperatures of substances in contact, means on the so-called inter-reactivity. The way to achieve this is not as simple as typical standards propagate. A further demand must be to parameterize the temperature dependence of the inter-reactions. The next question is the about the allowed extent of inter-reaction conversion with methods as gas generation, heat generation and mass loss. Until now, this question is not satisfactorily answered, especially with heat generation and gas generation, which are determined by heat flow microcalorimetry and vacuum stability test apparatus, respectively. A way to come to con-clusive values will be outlined and discussed. The method mass loss is in advantage; therewith the extent of conversion can be determined directly. With suitable instrumentation, a direct inter-reaction analysis (DIRA) in mixtures can be achieved.