Teflon chemical stability

Investigations performed by Dupont on the chemical stability of Teflon reveal that Teflon immersed in a 20% HC1 solution at 200°C for extended periods will not absorb any chlorine within detectability limits. In addition, Teflon does not absorb any detectable sulfur from sulfuric acid or sulfur vapor. Therefore, a Teflon H, membrane may prove to be superior to a platinum-group metal membrane for use in sulfur- or chlorinebearing systems. Investigations are currently being performed to determine the feasibility of employing a Teflon membrane as an H2 monitor/controller in hydrothermal test apparatus. 

Ceramic materials, including sapphire, have been used extensively in HPLC pumps for more than 20 years as pistons and check valve components. These materials have also been used to construct heads because of their good chemical stability. The use of ceramics is limited, however, because of high cost and brittleness. Although many systems have one material as the primary construction material, the wetted surfaces of a pumping system can contain several other materials. Therefore, for material-sensitive applications, all the materials in the HPLC eluent flow path should be considered. Materials that may be encountered are polymeric materials for pump seals such as fluoropolymers, polypropylene, and Teflon sapphire pump pistons and check valve seats ruby check valve balls Kalrez, KelF, or ceramic washers and spacers polymer-based transducer components and in older systems connections and joints made with silver solder. 

In these studies, thermodynamic equilibrium conditions were assumed. Constant pH monitoring was used as an estimator of the equilibration times involved, since a stable pH is an overall indicator of the Internal chemical stability of pH dependent processes. In order to allow the assumptions of atmospheric O2 and CO2 partial pressures, water scrubbed compressed air was pumped into the reaction vessels under constant temperature and constant vigorous mixing conditions. The air was introduced by fritted glass bubblers which had been teflon coated while air flowed through them in order to minimize the glass-solution interface. 

Uranous nitrate [U(N03)4] solution is used for the quantitative reduction of plutonium from loaded tributyl phosphate (TBP) phase [8]. Membrane cell technology was investigated for the production of 100% uranous nitrate solution [9], which is to be used in the partition cycle of the PUREX process in the fuel reprocessing plant. The membranes used hitherto have suffered from mechanical instability. A study was carried out at the BARC to obtain 100% uranous nitrate solution using a membrane-based electrolytic cell. The membrane used in this study was a thin polymer film reinforced with a Teflon fabric. The film was used as a separator between the anolyte and catholyte chambers, which are made of perfluorinated polymers, thus offering high thermal and chemical stability. 

Teflon AF is an amorphous copolymer of tetrafluoroethylene (TFE) and 2,2-bis(trifluoromethyl)-4,5-difluoro-l,3-dioxole (PDD). It combines the properties of amorphous plastics, such as optical transparency and solubihty in organic solvents, with those of perfluorinated polymers, including high thermal stability, excellent chemical stability, and low surface energy. Moreover Teflon AF exhibits the lowest dielectric constant (1.90 for Teflon AF 2400) and the lowest re-... 

Polytetrafluoroethylene (PTFE, Teflon, Fluorel) is best known for its excellent chemical stability and low coefficient of friction. Expanded PTFE (ePTFE) contains micropores created by stretching PTFE film and is used in small-diameter vascular grafts and for artificial heart valve sewing rings... 

Huorinated polymers have quite different properties compared to their hydrocarbon counterparts, due to the nature of the C-F bond. They often have a particularly high thermal and chemical stability, insolubility in common organic solvents and resistance to swelling by condensable gases or vapours. Such properties are an advantage for those membrane applications where the separation takes place under harsh conditions. Crystalline perfluoropolymers such as Teflon are extremely stable but their crystalline nature makes them mostly suitable for porous membranes, either for filtration of liquid media, or for instance for membrane distillation processes which take advantage of the... 

Blends of polypyrrole and Teflon were also prepared by the chemical oxidation of pyrrole in an emulsion of Teflon containing the ferric / -toluene sulfonate salt [69]. Pyrrole was added to the ferric salt aqueous solution and mixed with the Teflon emulsion stabilized by Triton X-100. After stirring for 3 hours a finely dispersed blend was obtained. This emulsion was coagulated with ethanol. Conductivity was reported to reach 1 S cm with a percolation behavior. This method could be used for large-scale production of the blend. 

In the hydrogen electrode, usually platinum is applied as electrode material on account of its outstanding catalytic capabilities and its chemical stability. It mostly is Teflon bonded or covered by microporous Teflon membranes (plastic net in Fig. 1.33) to make the surface hydrophobic and so prevent the formation of thicker layers of water that would hinder gas access. The electrolyte is immobilized by soaking fiber felts or knitted textiles of mineral fibers (fuel-cell-grade asbestos paper) or zircon fibers stabilized with yttrium (Zircar cloth). They provide high temperature resistance and chemical resistance for long-life batteries. 

One of the best methods of obtaining efficient mass transport in a highly reproducible manner is by the use of the rotating disc electrode. The RDE consists of a cylindrical metal rod embedded in a larger cylindrical plastic holder (usually Teflon, due to its great chemical stability and inertness). The electrode is cut and polished flush with its holder, so that only the bottom end of the metal cylinder is exposed to the solution. 

Teflon PEA 440 HP is a chemically modified form of PEA 340 that provides additional benefits such as enhanced purity and improved thermal stability. This product is suitable for producing tubing, pipe linings for production of ultrapure chemicals, semiconductor components, and fluid handling systems for high performance filters (31). 

A major development in fluoroplastks is the recent small scale production of Teflon AF, a noncrystaUme (amorphous) fluorocarbon polymer with a high glass transition temperature (240 °C) This optically transparent TFE copolymer is soluble m certan fluorocabons and has the same chemical and oxidative stability as crystallme TFE homopolymers [5]... 

Poly(tetrafluoroethylene) (PTFE), which is also known by DuPont s trade-name Teflon, is a solid at room temperature and has a dielectric constant in the range of 2.00-2.08, while its monomer, tetrafluoroethylene, is a gas at room temperature. PTFE is exceptionally chemically inert, has excellent electrical properties and outstanding stability, and retains its mechanical properties at high temperatures. The problem with PTFE is that it is not processable. A family of commercial polymeric materials known as Teflon AF is believed to be a... 

Chemically universally stabile is poly-tetrafluoroethylene (PTFE, Teflon ), but it is relatively expensive. A problem is the cold flow , that is, the polymer is slowly deformed under the mechanical stress of the pressure on the gaskets and a leakage of the cell can occur (PTFE compounds, e.g. with glass powder or graphite, show a better behavior.)... 

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