Platinized anodes

Electroflotation cells vary in capacity between 1 and 50 m, the largest size giving the capability of dealing with up to 150 m of water per hour. In a typical specification the plant will reduce 1000 p.p.m. solids and 600 p.p.m. oils to 30 p.p.m. and 40 p.p.m. respectively. The components of the cell will be selected mainly for durability and low cost. The tank will be steel or a cheap plastic depending on size the cathode will be a steel and the anode platinized titanium or lead dioxide on titanium. 

Figure 6.11 and (b) J he Uur Anode " platinized titanium prtibe an tide system being installed inside a hollow bridge in Ntirway,... 

Anodes Platinized titanium should be replaced when operating voltages are excessive or when thick coatings develop on the anode surfaces. 

Nonconsumable Anodes. Platinized anodes utilize a few micrometers thick surface coating of platinum on titanium, niobium, or tantalum substrates. Restricting the use of platinum to a thin surface film has important cost advantages. For extended life, the thickness of the platinum surface layer can be increased. The corrosion resistance of the substrate materials is important due to the presence of discontinuities in the platinum surface coating that invariably will occur in practice. It is important that the potential of unplatinized areas on these anodes does not exceed the critical depassivation value for a given substrate material. 

In such cases basket anodes are frequently used. These have a relatively large surface and work at a low driving voltage due to their special construction. A cylinder of platinized titanium-expanded metal serves as the basket to which a titanium rod is welded. This serves as the current lead and carrier, and ends in a plastic foot that contains the cable lead and at the same time serves as the mounting plate. The expanded metal anode exhibits a very uniform anode current density distribution, even at large dimensions, in contrast to the plate anode. The reason is the many comers and edges of the metal that make the point effect only evident at the outer edges of the anode. 

A current with ripples can lead to a high consumption rate for platinized titanium anodes and their premature failure. The residual ripple should be limited to 5% (see Section 7.2.2) [7],... 

Galvanic or impressed current anodes are used to protect these components. The anode material is determined by the electrolyte zinc and aluminum for seawater, magnesium for freshwater circuits. Platinized titanium is used for the anode material in impressed current protection. Potential-regulating systems working independently of each other should be used for the inlet and outlet feeds of heat exchangers on account of the different temperature behavior. The protection current densities depend on the material and the medium. 

The internal cathodic protection of pipes is only economic for pipes with a nominal width greater than DIN 400 due to the limit on range. Internal protection can be achieved in individual cases by inserting local platinized titanium wire anodes (see Section 7.2.2). 

Partially platinized titanium impressed current anodes were chosen because contamination of the feed water by anodic decomposition products had to be avoided. Four pure zinc reference electrodes were installed in the tank to control and regulate the potential. The supports for the anodes were of polypropylene, which can operate for short periods up to 100°C, in contrast to the usual PVC supports used in cold water. 

Figure 21-1 shows the object to be protected and the arrangement of impressed current anodes and reference electrodes. A central anode and two ring anodes of platinized titanium wire 3 mm in diameter provided with additional copper wire conductors are installed here. It is worth noting that the central anode is suspended from a float, whereas the ring anode is mounted on plastic supports. The zinc reference electrodes are also on floats near the inner side of the bell, while the 17 reference electrodes are mounted on plastic rods on the bottom of the cup and in the ring... 

An Kathoden aus Silber-Palladium (Platin-Anode) in 5%iger Schwefelsaure erzeugter Wasserstoff kann ebenfalls zur selektiven Reduktion von Alkinen herangezogen werden. So erhalt man z. B. in jeweils quantitativer Ausbeute aus... 

Die Reduktion der y-Lactone von On-sauren verschiedener Monosaccharide zu den entsprechenden Monosacchariden wird in einer geteilten Zelle an einer Quecksilber-Kathode undBlei- bzw. Platin-Anode in schwach saurem, waBrigen Milieu (Borat-Puffer) ausgefiihrt. Auf diese Weise sind d-Arabinose, n-Mannose, d-Talose, d-Ribose u. a. mit guter Ausbeute zuganglich1-4. 

Bei der reduktiven Elektrolyse von l-Chlor-2-methyl-2-phenyl-propan in waBrigem DMF (Leitsalz Tetrabutylammoniumtosylat) an Quecksilber (—2,4 V Platin-Anode) wird neben tert.-Butyl-benzol (—70% d.Th.) auch Isobutyl-benzol erhalten4. 

Die Reduktion von l-Fluor-l,l,2,2-tetrabrom-athan in verdiinnter Salzsaure (geteilte Zelle Blei-Kathode und Platin-Anode) liefert unter vollstandiger Debromierung ncben Fluoracetylen das Acetylen selbst (zusammen 67-75% d.Th.), als Zwischenstufe entsteht 1 -Fluor-1,2-trans-brom-athen, das direkt elektrolysiert ausschlieBlich Acetylen liefert2 ... 

Interessante Trimere liefert 2-Mcthyl-propanal. Bei der Beschickung der beiden Elek-trodenraume einer geteilten Zelle (Platin-Elektroden) mit 2-Methyl-propanal/Tetra-butylammonium-hexafluorophosphat entsteht an der Anode 2,4,6-Triisopropyl-1,3,5-trioxan (95% d. Th.) und an der Kathode 4-Hydroxy-5,5-dimethyl-2,6-diisopropyl-l,3-dioxan (90% d. Th.), jeweils in sehr hoher Ausbeute1 ... 

As anode material, smooth platinum in the form of a foil or net seems to be most universally applicable [32, 33]. In nonaqueous media, platinized titanium, gold, and nonporous graphite can also be used [56]. PbO -, MnOj- or FejO -anodes do not lead to Kolbe-dimers [57], except for PbO in acetic acid [58]. 

FIGURE 10.9 Galvanostatic charging curve for a platinized platinum electrode in 0.1 M H2SO4 solution (1) anodic scan, (2) cathodic scan. 

Sidheswatan P, Lai H. 1971. A study of intermediates adsorbed on platinized platinum during the anodic oxidation of formaldehyde. J Electroanal Chem 34 173-183. 

The behaviour of hydrogen and methanol at constant oxidation rates can be compared in Fig. 2.1. Using platinized platinum anodes a constant current density was applied in a 0.5mol/L-1 H2S04 solution containing (a) H2 p — 1 bar) and (b) ImolL-1 CH3OH solution. While no more than 20 mV overpotential are... 

In this connection, cyclic voltammetric measurements on the electrochemical reduction of C02 at n-Ti02 and platinized Ti02 film electrodes were reported a little later by Augustynski and co-workers.87 The existence of two electrochemically detectable species resulting from C02 reduction was suggested by anodic peaks on the cyclic voltammograms (Fig. 4). Unfortunately, however, no... 

Y. Lee, B.K. Oh, and M.E. Meyerhoff, Improved planar amperometric nitric oxide sensor based on platinized platinum anode. 1. Experimental results and theory when apphed for monitoring NO release from diazeniumdiolate-doped polymeric films. Anal. Chem. 76, 536-544 (2004). 

Electrochemical biosensors based on detection of hydrogen peroxide at platinized electrodes were found to be more versatile allowing a decrease in detection limit down to 1 i,mol L 1 [109]. However, all biological liquids contain a variety of electrochemically easily oxidizable reductants, e.g. ascorbate, urate, bilirubin, catecholamines, etc., which are oxidized at similar potentials and dramatically affect biosensor selectivity producing parasitic anodic current [110]. 

Similar results of photoelectrolysis of water in cells with n-type SrTi03 single-crystal anode and platinized Pt cathode were reported around the same time in a preliminary communication by Mavroides et al. [53] who measured the maximum quantum efficiency... 

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