PTFE, alkali-activated

Mg(II) forms a complex with 8-hydroxyquinoline-5-sulfonic acid (37) at pH 9.0 with Tris-HCl buffer, which can be determined by ELD (X x = 388 nm, ka = 495 nm) with micellar enhancement by cetyltrimethylammonium chloride (38). Masking of Ca(II) is achieved by EGTA (19). The method was applied in a SIA system for analysis of natural waters . After elution of the Mg(II) ions adsorbed on an alkali-activated PTFE tube with 0.1 M HCl and addition of A,A -bis(salicylidene)-2,3-diaminobenzofuran (39), the end analysis was by fluorometric determination of the Mg(II) complex (kex =475 nm, kfl = 545 nm). Possible interference of Ca(II) is masked on addition of the chelating agent... 

Selection of Corrosion-Resistant Materials The concentrated sofutions of acids, alkalies, or salts, salt melts, and the like used as electrolytes in reactors as a rule are highly corrosive, particularly so at elevated temperatures. Hence, the design materials, both metallic and nonmetallic, should have a sufficiently high corrosion and chemical resistance. Low-alloy steels are a universal structural material for reactors with alkaline solutions, whereas for reactors with acidic solutions, high-alloy steels and other expensive materials must be used. Polymers, including highly stable fluoropolymers such as PTFE, become more and more common as structural materials for reactors. Corrosion problems are of particular importance, of course, when materials for nonconsumable electrodes (and especially anodes) are selected, which must be sufficiently stable and at the same time catalytically active. 

KU, in co-operation with a German battery manufacturer, managed within a short time to produce silver GDE with a low PTFE content and to adapt them to the chlor-alkali technology in test cells. An examination of the GDE manufactured using a special process shows that the active silver centres of the GDE are held together by PTFE filaments in the form of a spider s web (Fig. 16.14). 

Platinum-iron on alumina catalysts were characterized by Mbssbauer spectroscopy (Section 4) and their activity tested. Iron in clusters with high Pt Fe ratios, about 5, and fully combined with platinum, was catalytically inert for the CO-H2 synthesis reaction, attributed to a decrease in the electron density of the iron as indicated by the Mbssbauer isomer shift. The direction of electron transfer was opposite to that proposed for alkali-metal promoted iron catalysts. At low Pt Fe ratio, 0.1, ferromagnetic iron as well as Fe " ions and PtFe clusters were produced and dominated the activity/selectivity pattern. Rhodium on silica catalysts produced C2-compounds containing oxygen, specifically acetic acid, acetaldehyde and ethanol, with methane as the other major product. The addition of iron moved the C2-product formation sharply in favour of ethanol and now methanol was also formed. ... 

Jansta, J. Dousek, F.P. Riha, J. Quantitative explanation of the mechanism of corrosion of PTFE caused by active alkali metals. J. Appl. Polym. Sci. 1975, 19, 3201- 3210. 

Generally, PTFE is not susceptible to nucleophilic attack because of the absence of double bonds. It is still suseeptible to loss of fluorine by electrophilic attack particularly under heat and over long periods of exposure. Alkali metals, which are highly reactive elements, sueh as eesium, potassium, sodium, and lithium, are among the most likely candidates for abstraction of fluorine from PTFE by an eleetrophilic mechanism. Certain other metals such as magnesium can attack PTFE if they are highly activated hy etching or other means. 

---