Teflon-based materials

FFAP A teflon-based material Highly polar... 

PEM fuel cells use a solid polymer membrane (a thin plastic film) as the electrolyte. The standard electrolyte material currently used in PEM fuel cells is a fully fluorinated Teflon-based material produced by DuPont for space applications in the 1960s. The DuPont electrolytes have the generic brand name Nafion, and the types used most frequently are 113, 115, and 117 [13, 57-62,68]. The Nafion membranes are fully fluorinated polymers that have very high chemical and thermal stability. This polymer is permeable to protons when it is saturated with water, but it does not conduct electrons. 

For what types of samples and mobile phases is Teflon-based filter material appropriate ... 

N.B. Teflon-based and similar materials fall into the category of chlorinated compounds. Recommendations... 

These vessels are usually made from Teflon-based composite materials, which makes them transparent to the microwave energy and allows for it to be applied directly to the samples for complete and rapid digestion. The vessels are equipped with pressure and temperature sensors which also provide the means to control these parameters. The vessels are placed on a rotating turntable to assure equal distribution of the microwave energy. 

The standard electrolyte material in PEFCs belongs to the fully fluorinated Teflon -based family similar to that produced by E.I. DuPont de Nemours for space application in the mid-1960s. The membrane is characterized by its equivalent weight (inversely proportional to the ion exchange capacity). A typical equivalent weight range is 800 to 1100 milliequivalents per dry gram of polymer. The type used most often in the past was a melt-extruded membrane manufactured by DuPont and sold under the label Nafion No. 117. The perfluorosulfonic acid family of... 

A pipe joint compound of Teflon-based type dope is usually used. Detailed recommendations on these and other materials for various purposes in phosgene service may be obtained from phosgene suppliers. 

The most difficult-to-bond plastics family is polytetrafluoroethylene and the other fluori-nated polymers which are the Teflon-like materials. The widespread use of these polymers as coatings for cookware is, of course, based on this property of nonsticking. The conventional methods of etching which can be useful with other difificult-to-bond plastics, like polyethylene and polypropylene, simply do not work on these fluorinated polymer surfaces. Instead the surfaces must be treated with an exotic mixture of metallic sodium and naphthalene in tetrahydrofuran.( 37,i38) More recently, ionized gases (plasma treatment) have also been used successfully. Once treated the surfaces become bondable using conventional two-part liquid... 

A variety of low-dielectric, low-loss resin systems are available for high-speed circuit apph-cations. These include polytetrafluoroethylene (FTFE or Teflon ), cyanate ester, epoxy blends, and allylated polyphenylene ether (APPE). Likewise, a few different reinforcements and fillers are available that can be used to modify the electrical properties of the base material. Although E-glass is stm the most commonly used fiberglass reinforcement, it should be noted that others are available. In addition, inorganic fillers are sometimes used to modify electrical properties as well. Table 9.6 provides electrical property data on some of the available fiberglass materials. Table 9.7 provides data on some of the base material composites available. 

One must be extremely careful of water quality if the sample is mixed with any water (or steam). Organic solvents are seldom sufQciently pure to be used in aroma isolation without additional cleanup (typically distillation). Any polymer-based materials (containers or tubing) are common sources of contamination. Antifoam additives may contribute as many components to an aroma isolate as the food itself. Stopcock or vacuum greases are known sources of contamination. Bottle closures must be Teflon-coated rather than rubber to prevent the closure from both absorbing some aroma components and contributing others. 

Allows for treatment of difficult-to-treat surfaces. Atmospheric plasma treatment is a viable alternative for a variety of substrates for which corona treating is ineffective. For example, fluoropolymer-based materials, such as Teflon , do not respond to the corona process, but will respond to atmospheric plasma treatment. 

The most chemical-resistant plastic commercially available today is tetrafluoroethylene or TFE (Teflon). This thermoplastic is practically unaffected by all alkahes and acids except fluorine and chlorine gas at elevated temperatures and molten metals. It retains its properties up to 260°C (500°F). Chlorotrifluoroethylene or CTFE (Kel-F, Plaskon) also possesses excellent corrosion resistance to almost all acids and alkalies up to 180°C (350°F). A Teflon derivative has been developed from the copolymerization of tetrafluoroethylene and hexafluoropropylene. This resin, FEP, has similar properties to TFE except that it is not recommended for continuous exposures at temperatures above 200°C (400°F). Also, FEP can be extruded on conventional extrusion equipment, while TFE parts must be made by comphcated powder-metallurgy techniques. Another version is poly-vinylidene fluoride, or PVF2 (Kynar), which has excellent resistance to alkahes and acids to 150°C (300°F). It can be extruded. A more recent development is a copolymer of CTFE and ethylene (Halar). This material has excellent resistance to strong inorganic acids, bases, and salts up to 150°C. It also can be extruded. 

The first CNT-modified electrode was reported by Britto et al. in 1996 to study the oxidation of dopamine [16]. The CNT-composite electrode was constructed with bro-moform as the binder. The cyclic voltammetry showed a high degree of reversibility in the redox reaction of dopamine (see Fig. 15.3). Valentini and Rubianes have reported another type of CNT paste electrode by mixing CNTs with mineral oil. This kind of electrode shows excellent electrocatalytic activity toward many materials such as dopamine, ascorbic acid, uric acid, 3,4-dihydroxyphenylacetic acid [39], hydrogen peroxide, and NADH [7], Wang and Musameh have fabricated the CNT/Teflon composite electrodes with attractive electrochemical performance, based on the dispersion of CNTs within a Teflon binder. It has been demonstrated that the electrocatalytic properties of CNTs are not impaired by their association with the Teflon binder [15]. 

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