Magnesium / Teflon / Viton

Magnesium / teflon / viton (also MTV or MagTef ) is a pyrotechnic composition , which especially in military decoys is used. It's a mixture of Magnesium , Teflon and Viton . Teflon ( polytetrafluoroethylene , ) and Viton ( vinylidene fluoride - Hexafluorisopropen - copolymer , ) are trademarks of the company DuPont . ${\displaystyle (C_{\mathrm {2} }F_{\mathrm {4} })_{\mathrm {n} }}$ ${\displaystyle (CH_{\mathrm {2} }CF_{\mathrm {2} })_{\mathrm {n} }(CF(CF_{\mathrm {3} })CF_{\mathrm {2} })_{\mathrm {n} }}$

history

Pyrotechnic sets based on magnesium / Teflon / Viton, or also called MTV sets, have been used in infrared decoy ammunition since the 1950s . From the acronym MTV, the term “MTV flare ” , which is used in particular in the English-language literature, for pyrotechnic decoys based on MTV is derived. Another colloquial formulation for MTV is “MagTef” in German and English-speaking countries.

The term pyrolant is also used for a pyrotechnic charge that mainly generates heat .

chemistry

While conventional, visual pyrotechnic flares , e.g. B. sodium nitrate ,, contained as an oxidizing agent , the polytetrafluoroethylene ,, acts as a fluorine source in MTV sets . The very high reaction enthalpy , in the reaction of magnesium with PTFE is based on the formation of magnesium fluoride having a very high negative standard enthalpy having ( ): ${\displaystyle NaNO_{\mathrm {3} }}$ ${\displaystyle (C_{\mathrm {2} }F_{\mathrm {4} })_{\mathrm {n} }}$ ${\displaystyle \Delta _{\mathrm {R} }H}$ ${\displaystyle \Delta _{\mathrm {f} }H^{o}=-1124kJmol^{-1}}$

${\displaystyle 2nMg+(C_{\mathrm {2} }F_{\mathrm {4} })_{\mathrm {n} }\longrightarrow 2nMgF_{\mathrm {2(s)} }+2nC,\Delta _{\mathrm {R} }H=-1438kJmol^{-1}}$ (1)

Since a lot of soot is produced and a lot of heat is released when burning MTV, the combustion flame of MTV can be described as a gray body with high emissions .

Depending on the stoichiometry , i.e. the ratio of the substance quantities of the substances used, MTV shows different burn rates and also delivers different reaction products. With a constant Viton® content, the burning rate increases with increasing magnesium content. However, the burning rate of MTV, as well as that of other metallized pyrotechnic sets, is largely determined by the specific surface, i.e. the grain size and shape of the magnesium. Basically, a magnesium powder with a high specific surface area provides a higher burning rate. The main reaction products for MTV include 30-65% magnesium fluoride , carbon black and gaseous magnesium.

Magnesium-rich compositions with a proportion of 55-65% magnesium are used for decoys. In these compositions only part of the magnesium used reacts with the PTFE. The major part is evaporated and reacts with the atmospheric oxygen just like the carbon according to the following reaction sequence.

${\displaystyle mMg+(C_{\mathrm {2} }F_{\mathrm {4} })_{\mathrm {n} }\longrightarrow 2nMgF_{\mathrm {2(s)} }+(m-2n)Mg_{\mathrm {(g)} }+2nC,m\geq 2n}$ (2)

${\displaystyle (m-2n)Mg_{\mathrm {(g)} }+2nC\longrightarrow (m-2n)MgO_{\mathrm {(s)} }+2nCO_{\mathrm {2} }}$(3)

safety

Pyrotechnic sets based on magnesium / polytetrafluoroethylene with a content of 25–90% magnesium are explosive substances according to the steel sleeve test according to Section II and the drop hammer test according to Section III Appendix III to the SprengG . Due to their sensitivity and their reaction behavior, these substances are classified under number 1.1.2 of BGV B5. Quote: Sentences of this group explode to a small extent when dammed up (including self- damming ). Their burning rate is strongly dependent on the mass. These sentences are mechanically or thermally very sensitive. MTV sets are also extremely sensitive to electrostatic discharge , which is why measures against static charging must be taken during their manufacture and processing.

Decoys applications

Due to the high combustion temperature of MTV of 2000 K and the high emissivity of the carbon formed as an intermediate, MTV flames are very good infrared emitters. For this reason, aircraft and helicopters can effectively with MTV flares against surface to air - and air-air -Flugkörper the 1st and 2nd generation such. B. Defend the AIM-9 Sidewinder , AIM-9-A. For the same reason, MTV and its performance were only published sporadically until the beginning of the 1980s. It was not until 1997 that the underlying US patent, US 5,679,921, filing year: 1958, which had previously been classified as secret, was released and published by the US government. Despite the meanwhile widespread worldwide distribution of missiles with seeker heads that can overcome MTV-based decoys, MTV flares are still part of the standard loading of countermeasure systems. Together with spectrally matched decoys, they help, as part of the so-called “cocktail solution”, to defend against unidentified threats.

literature

• E.-C. Koch: Metal-Fluorocarbon Based Energetic Materials , Wiley-VCH, 2012 , 360 pages. doi : 10.1002 / 9783527644186

Individual evidence

1. ↑ E.-C. Koch, A. Dochnahl: IR Emission Behavior of Magnesium / Teflon / Viton (MTV) Compositions. In: Prop., Expl., Pyrotech. 25 2000 , 37. doi : 10.1002 / (SICI) 1521-4087 (200001) 25: 1 <37 :: AID-PREP37> 3.0.CO; 2- #
2. ↑ Ernst-Christian Koch: Metal-Fluorocarbon-Pyrolants: III. Development and Application of Magnesium / Teflon / Viton (MTV). In: Propellants, Explosives, Pyrotechnics. 27, p. 262, doi : 10.1002 / 1521-4087 (200211) 27: 5 <262 :: AID-PREP262> 3.0.CO; 2-8 .
3. ↑ Ernst-Christian Koch: Metal-Fluorocarbon-Pyrolants IV: Thermochemical and Combustion Behavior of Magnesium / Teflon / Viton (MTV). In: Propellants, Explosives, Pyrotechnics. 27, p. 340, doi : 10.1002 / prep.200290004 .
4. ↑ BGV B5 (VBG 55a) Explosives - General Regulation, Jedermann-Verlag, 69021 Heidelberg, 2001.
5. ^ V. Weiser, E. Roth, E.-C. Koch, Investigation of Magnesium-Fluorohydrocarbon Flames using Emission Spectroscopy, 37th International Annual Conference of ICT , June 27-30, 2006 , Karlsruhe p. 161.
6. ^ GT Hahn, PG Rivette, RG Weldon: US Patent 5,679,921 (1997), The United States of America as represented by the Secretary of the Navy.
7. ^ SI Erwin: "Smart" Flares Being Designed to Defeat Heat-Seeking Missiles , National Defense Magazine , December 2003 , 88 , 14.