Ignition Threshold Energy Determination for Reactive Materials Using a Pneumatic Impact Testing Appartus

Abstract

Reactive Metals International, Inc. (RMII), a fully owned subsidiary of Mach I Inc.has designed, built and tested a Pneumatic Impact Testing Apparatus (PITA) for qualitative and quantitative analysis of the impact ignition threshold energies for consolidated reactive materials. The PITA has proven to be an essential tool for routine, cost effective impact testing of reactive materials. The PITA can launch a spherical (0.375" diameter) steel projectile at energies ranging from 10 Joules to greater than 450 Joules corresponding with projectile velocities of 100 fps to greater than sound speed. A calibration curve of projectile velocity vs. launch gas pressure has been generated and is utilized in determining impact energies. Ignition is detected through a Si photodetector and overpressure from the ignition event is measured using a piezoresistive pressure transducer. Both detectors are mounted to the wall of a catch box in close proximity to the sample, which is mounted against a steel target plate. The ignition threshold energy was demonstrated for several compositions including a thermite type material, a metal-metal intermetallic and a metal-metalloid. Samples were prepared by high energy ball milling and consolidated into 0.250" pellets using a hydraulic press. The effectiveness of the PITA is exemplified by its accuracy, high throughput and low cost for the routine evaluation of impact-ignition sensitivities/energies for reactive materials. Typically, ignition threshold energies for reactive materials can be determined with a sensitivity of a few Joules. The time necessary to produce the ignition data for a material can be done in a single day using 20-30 rounds. Nomenclature RM= Reactive Metal PITA = Pneumatic Impact Testing Apparatus RMII = Reactive Metals International Inc. PCA = Process Control Agent fps = feet per second rpm = rotations per minute