(211a) Thermodynamic Testing Methods in Energetic Material Evaluation

The ATK technology group at Lake City Army Ammunition Plant (LCAAP) has developed a new method to incorporate thermal property testing into new material qualification testing. Current LCAAP raw material testing has resulted in materials passing specification testing, yet failing ballistic functional testing. LCCAP conducts testing according to military specifications on candidate materials prior to a ballistics work test. This old test and shoot process analyzes materials for chemical make up and in some cases particle size prior to the functionality testing. With the addition of thermal testing, we can improve the reliability of our new material screening process.

LCAAP mixes solid raw materials into energetic mixes that very rapidly change phase from all solid reactants to gas, liquid and solid products in order to function ammunition properly. For these energetic materials, we need to ensure that we have the right amount of energy available in the system delivered at the proper rate for desired function. We plan to use different thermodynamic techniques to estimate the Gibbs free energy, enthalpy, and entropy. Bomb Calorimetry will provide an estimate of the total energy available in the system, DSC and TGA will provide us with estimate on the enthalpy and entropy. We need these estimates to determine if the required energy is available and if the entropy and enthalpy are in the proper ratio to allow the desired rate transfer to occur. These thermodynamic tests also give us insight into the sensitivity of the new materials and the resulting mixes. Contaminants can change: 1) the onset temperature of mixes, 2) the sensitivity to different initiation mechanisms (i.e. electrostatic discharge, friction and impact), 3) the rate of output and 4) the amount of energy output. Understanding and predicting these responses helps to ensure safe operation of our current processes and aid new mix development.

We may have a situation where we cannot find a match for the mil-spec material. Using the thermodynamic fingerprinting of the baseline material, we will be able to propose methods to ?clean up? contaminated sources or seed purer sources with the required chemicals and prove out the thermal response of the new material to meet the mil-spec. Most of our materials are refined from various natural sources and have differing levels of contamination. Using L. Bruce Railsback's ?An Earth Scientist's Periodic Table of the Elements and Their Ions? we can use the responses on the DSC and TGA scans to identify potential contaminates that may not be found in the current specification testing1.

The small quantities required for these tests will allow us to test gram quantities of materials in a shorter timeframe for screening instead of relying on the pound quantities required for ballistics testing. This will help to speed up and improve new product development, and increase our understanding of the physics behind the materials' function. We will still use ballistics testing as a final prove out of the new materials, but we will have increased our probability of success and limited the resources necessary to screen new materials by using these thermal tests.

1) Railsback, L. Bruce; ?An Earth Scientist's Periodic Table of the Elements and Their Ions?, University of Georgia, Athens, GA, 2004.