Reactive Materials Studies

Abstract

Finite size effects on aluminum/Teflon reaction channels under combustive environment: A Rice-Ramsperger-Kassel-Marcus and transition state theory study of fluorination Abstract. Three experimental techniques have been used to investigate the impact ignition of reactive materials. The three techniques are direct impact, indirect impact, and two-step impact. For the first two techniques, time-resolved light spectroscopy was used to identify reaction species from solid PTFE/Al reactive material. A common observation for these two techniques is that heating and some reaction was observed during initial impact of the PTFE/Al reactive material but the majority of the reaction appeared to occur following material breakup and subsequent impact with a secondary surface. There was no spectral evidence for aluminum-fluorine combustion. For the two-step impact technique, the reactive material was initially pulverized as it passed through a thin plate and then subsequently ignited when the debris cloud impacted a rigid anvil. All three experiments were observed with high-speed photography.

Influence of Processing Techniques on Mechanical Properties and Impact Initiation of Al-PTFE Reactive Material

“…The light is a sign of deflagration or explosion. It can be seen from the recovered sample (see Figure 6c) that the start of reaction was near the edge of the sample where shear deformation concentrates most intensely (a similar reaction pattern reaction has been observed by Ames [14] and Lee et al [15]). Then the reaction propagated from the edge to the center of the sample and quenched.…”

Experimental Study on Impact‐induced Initiation Thresholds of Polytetrafluoroethylene/Aluminum Composite

“…3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 Figure 4(a) shows the collision and reaction situation, in which the sample passes through a brittle-fracture stage and then progresses to impact-induced initiation. Impacting, fracture and fragmentation, initiation, subsequent fragmentation and violent reaction were included as described by Lee et al [10]. Samples fracture and fragment first, instead of initiating or igniting upon impact with the target.…”

“…Based on the velocity and pressure continuity in the interface: (9) Substituting Equation (7) and Equation (8) into Equation (9) yields: (10) The impact pressure at the interface can be calculated by substituting Equation (10) into Equation (7) or (8): (11) Four unknown parameters, P x1 , U x1 , z 1 and z 2 (or P x2 , U x2 , z 1 and z 2 , exist in Equation (10) and Equation (11). To calculate the impact pressure, the equations have to be closed.…”

“…In general, two main impact-initiation mechanisms of reactive materials can be distinguished, namely, the mechanoand thermochemical mechanisms; however, the categorization of initiation of PTFE/Al into one of the above is unclear. Ames [9] and Lee et al [10] attribute the initiation to large strain deformation, shear bands, and fractures, and they believe that the high temperature that is generated during impact is insufficient to produce initiation. Hunt et al [11] proposed that the high strain rate and stress convert mechanical energy into thermal energy to promote ignition.…”

Reactions of Al-PTFE under Impact and Quasi-Static Compression

“…Ames [2] and Lee et al [3] observed that large strain deformations, shear bands, and fractures formed during the impact play a significant role in the initiation of Al-PTFE. Although Ames [4] did not express explicitly that it is a mechanochemical process, he believed that high temperatures generated in the impact were not sufficient to produce initiation.…”