Ignition of MTV

The ignition of energetic materials unlike the steady-state combustion is a transient process. It is affected by thermal conductivity of the pyrolant, k density, p specific heat, Cp) surface area. A ignition temperature, T Ta = ambient temperature and heat flow into the material, q. The time to ignition as derived by McLain [1] reads 

The ignition of Magnesium/Teflon/Viton (MTV) by radiative or conductive heat transfer has been investigated in order to understand processes in both bulkhead and laser igniters (Table 7.1). Lombard appears to be the first to have tested radiative ignition of MTV. He used a solar furnace that allowed a maximum irradiance, H = 100 W cm [2]. Mg/PTFE (polytetrafiuoroethylene) samples of unknown stoichiometry were tested at = 20 W cm. The ignition temperature was determined from radiometric measurements and was found to be quite low, 217 °C. This corresponds to 29 s irradiation at the reported irradiance level and translates into a heating rate of 6 K s.  

Metal-Fluorocarhon Based Energetic Materials, First Edition. Ernst-Christian Koch. 

5 wt% Magnesium, granular chips, Gran 16 30.7wt% Teflon 7C 15.8wt% Viton A Type III Igniter 

0wt% Magnesium, atomized Mg spheres 30.0wt% Halon blend G10/G80 16.0wt% Viton A 

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Thermal ignition of MTV is understood to start in the condensed phase with heat release by either Grignard-type reaction of Mg with molten PTFE (Eqs. (6.5)... 

The ignition delay for thermal ignition of MTV is depicted in Figure 7.7 for a particular formulation as a function of temperature. 

Figure 7.7 Ignition delay for thermal ignition of MTV pellets on a hot plate [13].

Haq, I.U. and Chaudhri, M.M. (1989) Dielectric breakdown and ignition of MTV compositions. 14th International Pyrotechnics Seminar, jersey, Channel Islands, September 18-22, p. 135. 

Bhingarkar et al. have investigated ignition sensitivity and interior ballistic performance of MTV igniter modified with boron [28]. In this context they performed the TG on BTV (25/65/10) (Figure 5.23). 

Figure 7.3 Influence of oxygen partial pressure on ignition delay of MTV at 0.1 MPa and Hi, = 400 Wcm [8].

The grain in its final geometry is applied with both intermediate and first fire to facilitate ignition transfer and ignition of the pellet. Figure 18.20 depicts a cross section of a 1 x 1 in. flare grain with applied intermediate fire based on MTV slurry. Figure 18.21 depicts ram-extruded cruciform 1 x 1 in. pellet with both first and intermediate fire applied [24]. 

The thermal sensitivity of MTV and Magnesium/Poly(carbon monofluoride)/ Viton MPV is significant, and the substances are classified easily ignitable. Ignition temperatures for MTV formulations are listed Table 19.4. 

The ignition energies for a series of samples of different composition and thickness are shown in Figure 19.11. For three series of MTV compositions, SR 886 B, F and E, which differ only in the type and ratio of PTFE particles used, the minimum ignition energy rises with sample thickness. The electrical setup is shown in Figure 19.12. 

The dielectric breakdown voltage of MTV igniter compositions as a function of modifiers added has been studied in [28, 30). 

Table 19.7 Ignition sensitivities of MTV composition containing 16wt% Viton A.

Peretz, A., Investigation of Pyrotechnic MTV Compositions for Rocket Motor Igniters , AIAA Paper 82-1189,1982. 

Figure 7.6 Influence of spot size on critical energy fluence to ignition MTV [14].

Peretz, A. (1982) Investigation of pyrotechnic MTV compositions for rocket motor igniters. 18th Joint Propulsion Conference, Cleveland, June 21-23, AIAA-82-1189. 

The pressurisation rate of various MTV igniter materials as function of both Mg and Viton content has been investigated by Ozkar et al. [10]. At low Viton content (4-8 wt%), the highest pressure is obtained with rather fuel-lean compositions. However, at 10 wt% Viton the maximum pressure is obtained for f (Mg) > 48 wt% (Figures 12.4 and 12.5). 

Caulder, S.M., Leon, J.R. and Luense, L. (2006) Compositional factors affecting the ballistic properties of Magnesium/Fluorocarbon (MTV) igniters. 

G. (1990) Development of an MTV composition as igniter for rocket propellants. 15th International Pyrotechnics Seminar, Boulder, CO, July 9-13, p. 721. 

Apart from its use in decoy flares, MTV is also used in propellant igniters, and therefore, MTV crumb obtained from shock gel process is extruded in small round or cruciform strands of 2.3-2.4mm diameter. The extrusion is carried out at 121 °C, 4 MPa for round and 8.3 MPa for cruciform strands. Finally, the strand is cut with guillotine type cutter or band saw into length of 3.8-5.8 mm [29, 30]. 

The accumulation of bulk amounts of the MTV composition in production poses a significant hazard. The reaction of loose MTV in a number of different configurations with respect to the amount of composition, type of container and type of ignition has been investigated [44-47]. 

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