Polytetrafluoroethylene combustion

Griffiths et al. have been the fost to investigate the UV-VIS spectra of Mg/PTFE flames at various stoichiometries and various pressures [12]. They identified Mg(g), MgF(g), MgO(g) and C2 species in these flames depending on the pressure regime. Table 9.2 shows the signals found for a stoichiometric Mg/PTFE composition (32/68 wt%) at different pressures. 

16) of MTH. (Reproduced with kind permission from Volker Weiser.) 

The pyrolants further yield MgF with signals at 349, 359 and 368 nm as well as a C2 signal at 343 nm. 

Mg2Si/Mg3Al2/Fluorocarbon Based pyrolants 

Species Wavelength (nm) Mg/PTFE (32/68) MgH2/PTFE (34/66) MgBj/PTFE (48/52) Mg3N2/PTFE (57/43) Mg2Si/PTFE (44/56) 

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Davis, S.R. (1990) Theoretical and experimental study of magne-sium/polytetrafluoroethylene combustion. Conference, p. 49. 

Compositions whose products of combustion produce energy in the infrared wave band are generally composed of magnesium powder, polytetrafluoroethylene (PTFE) and a binder. For efficient tactical utilization of the energy developed by the combustion process the composition is normally formed into pellets either by press consolidation or by press extrusion. The process being used at Longhorn at the time the electrostatic problem was encountered was press consolidation. The composition was being consolidated into a pellet... 

A liquid perfluorocarbon was being used as solvent in an oxidation by oxygen under pressure more energy was released than expected [1], It is cautioned that fluorocarbons are not inert to oxidation, presumably to carbonyl fluoride. An explosion has been experienced with perfluorotoluene in like circumstances [2], A correspondent reports that perfluorotoluene is flammable in air, more saturated perfluorocarbons in pure oxygen [3], Another detailed the combustion performance of polytetrafluoroethylene 148 kcal/mole ignition temperature not below 465°C at 7000 psi of oxygen [4], the product is mostly carbonyl fluoride. Other oxidants may also present a risk in extreme circumstances. 

Zook BC, Malek D, Kenney RA Pathologic findings in rats following inhalation of combustion products of polytetrafluoroethylene (PTFE). Toxicology 26 25-36, 1983... 

Polymeric hydrocarbons, such as polyolefins, are readily combustible and can actually serve as a fuel source. In contrast, polytetrafluoroethylene (ptfe) does not bum in air but burns in oxygen or in nitrogen-oxygen mixtures which have a very high oxygen concentration. 

It should not be thought, however, that perfluorocarbons are completely inert toward combustion. Even the very inert perfluorocarbon polymer polytetrafluoroethylene [PTFE, Du Pont s Teflon F(CF2CF2)nF] is thermodynamically unstable in oxygen with respect to CO2 and CF4 (Exercise 12.6) and can burn in a 95% 02/5% N2 mixture at 0.1 MPa, although combustion is hard to initiate because of the nonvolatility of PTFE and the resistance of the thermal degradation products to oxidation. Conflagrations involving more reactive, volatile fluorocarbons such as perfluoro-toluene have been reported.15... 

One of the most successful industrial applications of polymeric catalytic membranes is the Remedia Catalytic Filter System to destroy toxic gaseous dioxins and furans from stationary industrial combustion sources by converting them into water, CO2, and HCl. The system consists of an expanded polytetrafluoroethylene (PTFE) microporous membrane, needle-punched into a scrim with a catalytically active PTFE felt. The catalyst is a V2O5 on a Ti02 support. The microporous membrane captures the dust but allows gases to pass to the catalyst where they are converted at temperatures as high as 260° C. 

Active carbons are obtained by partial combustion and foermal decomposition of various raw materials followed by carbonization and activation. A detailed look at the process of pyrolysis and carbonization of a parent feedstock and the processes of generation of an isotropic porous carbon and its activation illustrates the complexity of reactions involved in its manufacturing. Active carbons are manufactured from a wide variety of materials wood [1, 2], coal [1, 2], bituminous coal [29], rubber [30, 31], ahnond shells [32], oil-palm stones [33], polymers (e.g., vinylopyridine resin [34] and polytetrafluoroethylene [35]), phenolic resins [36], rice husk [37], etc. Very interesting active carbon honeycomb structures were fabricated from combination of synthetic precursors, i.e., phenolic resins, along with several organic and inorganic additives [38]. 

Hoses for offshore applications are in most cases made of abrasion-resistant materials such as poly(vinyl chloride) or polyurethane. Polytetrafluoroethylene hoses have been developed for use as intercormectors to oil or gas combustion chamber burners or turbines. The inert qualities, abflity to withstand the hostile environment, and high-pressure capability suit them to this application. 

The presence of moisture in the gas stream, which above 100 C will be present in the form of superheated steam, will also cause a rapid degradation of many fibres through hydrolysis, the rate of which is dependent on the actual gas temperature and its moisture content. Similarly, traces of acids in the gas stream can pose very serious risks to the filter fabric. Perhaps the most topical example is found in the combustion of fossil fuels. The sulphur that is present in the fuel oxidises in the combustion process to form SO, and in some cases, SO3 may also be liberated. The latter presents particular difficulties because, in the presence of moisture, sulphuric add will be formed. Hence, if the temperature in the collector were to be allowed to faU below the acid dew point, which could be in excess of 150°C, rapid degradation of the fibre could ensue. Polyaramid fibres are particularly sensitive to acid hydrolysis and, in situations where such an attack may occnr, more hydrolysis-resistant fibres, such as those produced from polyphenylene sulphide (PPS), would be preferred. On the debit side, PPS fibres cannot snstain continuous exposure to temperatures greater than 190 °C (or atmospheres with more than 15% oxygen), and where this is a major constraint, consideration would have to be given to more costly materials, such as polytetrafluoroethylene (PTFE). 

In the combustion gases of some fluorinated plastics, highly toxic octafluoroiso-butylene is also present but its hazard is not too great when polytetrafluoroethylene (PTFE) is burning. 

Firstly there are forms of polymers, such as polytetrafluoroethylene, which are intrinsically fire retardant. The second types are rendered fire retardant by the inclusion of a suitable additive in the formulation. These include additives based on antimony, bromine, nitrogen, phosphorus and silicon. An essential requirement for fire retardant polymers used in enclosed spaces is that they do not release any toxic products upon combustion. Ffowever, antimony containing additives are going out of favour due to the release of toxic antimony volatiles upon combustion. The properties and mechanisms by which these polymers operate are discussed in Chapters 1 and 6. The third group of polymers consist of intumescent materials and these are being increasingly used as a means of imparting fire retardancy in polymers and this is discussed in Chapter 7. 

A method for the determination of fluorine in fluorinated polymers such as polytetrafluoroethylene (PTFE) is based on decomposition of the sample by oxygen flask combustion followed by spectrophotometric determination of the fluoride produced by a procedure involving the reaction of the cerium(III) complex of alizarin complexan (1,2-dihydroxy-anthraquinone-3-ylmethylamine N,N-diacetic acid). The blue colour of the fluoride-containing complex (maximum absorption, 565 nm) is completely distinguishable from either the yellow of the free dye (maximum absorption, 423 nm) or the red of its cerium(III) chelate (maximum absorption, 495 nm). 

Using this method Johnson and Leonard [39] obtained from polytetrafluoroethylene a content of 75.8 % fluorine using a silica or boron-free glass combustion flask against a theoretical value of 76%. Using a boroscilicate glass combustion flask they obtained a low fluorine recovery of 72.1 %. 

M. and Gut, Z. (2007) Investigation of the combustion of calcium sili-cide/polytetrafluoroethylene mixtures. Arch. Combust., 27, 69-79. 

For low melting metals such as Al, Mg and Zn, we find that a 0.75 0.05 however, with refractory fuels such as Ti and Zr, a 0.45 0.05. Table 6.1 Hsts Tpif. and onset temperature for steady-state combustion of a number of M/PTFE (polytetrafluoroethylene) pyrolants. 

Combustion of magne-sium/polytetrafluoroethylene. 22nd Joint Propulsion Conference, Huntsville, USA, June 16-18, AIAA-86-1592. 

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