Fluoropolymers, electrochemical

The product of the reaction (5.5.29) is, however, unstable against subsequent interchain crosslinking and insertion of supporting electrolyte cations. The electrochemical carbonization of fluoropolymers was recently reviewed by L. Kavan. 

Electrochemical corrosion processes also include a number of processes in organic chemistry, involving the reduction of various compounds by metals or metal amalgams. A typical example is the electrochemical carbonization of fluoropolymers mentioned on p. 316. These processes, that are often described as purely chemical reductions, can be explained relatively easily on the basis of diagrams of the anodic and cathodic polarization curves of the type shown in Fig. 5.54. 

Various fluoropolymer equipment, for example, connectors and valves, is available from laboratory suppliers (at a high price). The principle of a simple, quick, and inexpensive method for connections of electrochemical cells using PTFE tubes is shown in Fig. 4. 

Kavan, L. Electrochemical carbonization of fluoropolymers. In Chemistry and Physics of Carbon, Vol. 23, New York Marcel Dekker, 1991 69. 

The theoretical treatment presented (Eqs 4.1-4.5) is applicable also for direct wet electrochemistry on Pt cathode in aprotic electrolyte solution [12,13] (Table 4.1) and for some other chemical reductants, Rj, viz. benzoin dianion [14] and sodium dihydronaphthylide [15] (Table 4.1). Apparently, the decision between chemical and electrochemical carbonization may not be straightforward. The latter scenario requires a compact solid electrolyte with mixed electron/ion conductivity to be present at the interface. This occurs almost ideally in the reactions of solid fluoropolymers with diluted alkali metal amalgams [3]. If the interfacial layer is mechanically cracked, both electrochemical and chemical carbonization may take place, and the actual kinetics deviates from that predicted by Eq. 4.4 [10]. There is, however, another mechanism, leading to the perturbations of the Jansta and Dousek s electrochemical model (Eq. 4.4). This situation typically occurs if gaseous perfluorinated precursors react with Li-amalgam [4,5], and it will be theoretically treated in the next section. 

Kavan, L. Dousek, F.P. Micka, K. The role of ion transport in the electrochemical corrosion of fluoropolymers. Preparation and properties of n-doped polymeric carbon with mixed ion/electron conductivity. Solid State Ionics 1990, 38. 109-118. 

Fabric-backed sheets of almost all fluoropolymers, whether perfluorinated or partially fluorinated, can be purchased for lining equipment. Several companies offer these product including Electrochemical Engineering and Manufacturing, SYMAEIT and Allied Supreme Corp.l" ... 

PFCA salts (e.g., the sodium and ammonium salts) are an industrially important class of anionic PFCA surfactants. Electrochemical fluorination has been employed to manufacture APFO, an emulsifier used in the production of fluoropolymers and other PFCAs. Hydrolysis of the acid fluorides obtained by electrochemical fluorination results either in the free carboxylic acids or the respective salts. A major problem associated with the hydrolysis of PFCA fluorides is the presence of HF from the electrochemical fluorination and the hydrolysis of the PFCA fluorides with water." The technical process of isolating fluoride-free PFCA derivatives has, therefore, been optimized to reduce the fluoride content of the final product to trace amounts. An example of such a process is shown in Figure 18.6. °... 

Characterization of Structure and Microtexture of Carbon Materials by Magnetoresistance Technique, F. Hishiyama, Y. Kaburagi, and M. Inagaki Electrochemical Carbonization of Fluoropolymers, L. Kavan Oxidation Protection of Carbon Materials, Douglas W. McKee... 

Thiophene fluoropolymers, which are provided with high thermal stability, chemical inactivity and hydro-phobicity, have been synthesized electrochemically [141], Alkyl spacers were inserted between the thiophene ring and the fluoroalkyl groups in the monomer (10) in order to neutralize their unfavourable electronic effects. In these conditions, the introduction of up to 50% of fluorine in the structure has been shown to lead to elastomeric materials with a higher electroactivity than polyalkyIthiophenes [141],... 

T. Kallio, K. Jokela, H. Ericson, R. Serimaa, G. Sundholm, P. Jacobsson and F. Sundholm, Effects of a fuel cell test on the structure of irradiation grafted ion exchange membranes based on different fluoropolymers, J. Appl. Electrochem. 33, 505 (2003). 

The focus of this section is on the corrosion phenomena of the GDL substrate graphite fibers driven by solid-liquid surface chemical interactions and surface energetics. Particular importance is assigned to uncoated areas of fibo s by hydrophobic fluoropolymer and interfacial zones between fiber and fluoropolymer. Since Teflon products such as PTFE and FEP are known to have excellent thermal resistance, electrochemical corrosion stability, chemical durability, and mechanical properties, the GDL and MPL fluoropolymer phase is not considered to be vulnerable in a PEFC operating enviromnent. 

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