Platinized titanium 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. 

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... 

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]. 

The anodes are platinized titanium (titanium plated with 5 microns of platinum) the cathodes are also titanium plated with 2.5 microns of platinum. All gaskets are Viton GF (peroxide grade), and the cell membranes are DuPont Nation 324. Flow through the cells is in parallel using manifolds with /4-inch fluid-flow inlet port orifices to provide equal flow to all cells. 

End plates and ports to be PVDF-lined ductile cast iron. Gaskets to be Viton for agent and Viton GF for energetics. Electrodes to be platinized titanium, pinhole-free, to a thickness of 5 micrometers for the anodes and 2.5 micrometers for the cathodes. 

Platinum, Platinum plating has found application in the production of platinized titanium, niobium, or tantalum anodes which are used as insoluble anodes in many other plating solutions (see Metalanodes). Plating solutions were often based on platinum "P" salt, which is diamminedinitroplatinum(II). A dinitroplatinite sulfate—sulfuric acid bath has been used to plate direcdy onto titanium (129). This bath contains 5 g/L of the platinum salt, pH adjusted to 2.0 with sulfuric acid. The bath is operated at 40°C at 10—100 A/m2. Other baths based on chloroplatinic acid have been used in both acid and alkaline formulations the acid bath uses 20 g/L of the platinum salt and 300 g/L hydrochloric acid at 65° C and 10—200 A/m2. The alkaline bath uses 10 g/L of the platinum salt, 60 g/L of ammonium phosphate and ammonium hydroxide to give a pH of 2.5—9.0. The alkaline bath can be plated direcdy onto nickel-base alloys acid baths require a gold strike on most metals. 

Dow-Huron cell — Electrochemical cell for hydrogen peroxide production. A diaphragm-divided cell employing a carbon chips-PTFE composite as cathode material fed with air. At the anode oxygen is developed at, e.g., a platinized titanium electrode. 

Scott [11] compared three types of circulating particulate electrodes for copper recovery from dilute solutions (Fig. 1) spouted (circulating) beds, vortex beds, and moving beds. The beds contained 500— 700 pm spherical copper particles positioned on a stainless steel cathode feeder, and a platinized titanium anode. All electrodes performed similarly in terms of copper recovery current efficiencies. Recovery was found to be more efficient at low pH and high metal concentrations. The spouted bed electrode was preferred on the basis of scaleup. 

Yen and Yao [16] used a fin-type titanium cathodic current feeder (Fig. 2) in a fluidized-bed electrode to achieve enhanced copper recovery from dilute solutions. Copper particles served as the fluidized-bed cathode and platinized titanium screens were used as the anode, where oxygen evolution occurred. The feeder with the longer fin yielded higher current densities at increasing Reynolds numbers and larger bed expansions as compared with the short fin or the planar current feeder. The increased currents were due to the increased rate of copper deposition on the fluidized particles. 

The cathode material is usually stainless steel, a nickel alloy, or titanium. Graphite, lead dioxide, platinized titanium, and DSA are some of the materials that have been used as an anode. The cells are operated at a current density of between 0.1 and 0.5 A/cm. The majority of the cells used to produce hypochlorite have the parallel-plate type of geometry [81]. 

As anode material, smooth platinum, as foil or net, is most widely used. In nonaqueous solvents, additionally, platinized titanium, gold, hard graphite and ruthenium dioxide on titanium have been employed. To keep the amount of the costly platinum low, the foils have been glued to a graphite support. With vitreous or baked carbon in protic solvents (methanol, ethanol, water) dimer yields nearly comparable to those at platinum have been obtained. ... 

Anode reactions that produce dissolution or oxidation of the electrode metal are avoided by selection of resistant metals such as platinum. The use of a thin layer of platinum on a substrate of less expensive metal (e.g., titanium) moderates the expenditures for anodes. However, titanium is not suitable for reversible electrodes, because it is attacked by the H2 generated at the cathode.ls When the polarity of the electrodes must be reversed periodically, as in the EDR process, platinized niobium has been used. 

Precious metals are used for impressed current anodes because they are highly efficient electrodes and can handle much higher currents than anodes fabricated from other materials. Precious metal anodes are actually platinized titanium or niobium anodes the platinum is either clad or electroplated on the substrate. 

Anodes of a corrosion-resistant material such as Pt, PbSbAg, graphite, magnetite or high-silicon iron are normally used in impressed current installations. Pt is often used as a thin layer on a substrate of another material, e.g. in the form of platinized titanium. A corroding material, such as scrap steel, can also be used, but additional anode material must be supplied regularly in this case. 

For these reasons, the cathodic corrosion protection of chemical plant parts is restricted to neutral solutions, service water, and alkalis. Various types of anodes are available for the protection of container interiors. Platinized disk electrodes, bar anodes, and titanium basket anodes are used. They are now supplied ready for installation and are designed in such a way that, in continuous operation, they can emit 8-10 A at a current density of 6-8 A/dm. ... 

All anode systems require an electrical connection. Given their modest conductivity this usually consist of a series of wires (platinized titanium, platinized niobium copper, carbon fibres or other comparatively inert materials) running through the coating at a separation of 0.5-1. Om. Unfortunately, the nomenclature used for the early anode systems has been misappUed... 

Titanium covered by platinum or by dioxide of manganese, ruthenium, iridium or other substances is most commonly used as an anode. Graphite and graphite covered with lead dioxide have also been used as anodes. Under some conditions, high pH and absence of salts in the anolyte, nickel can be used as the anode. Stainless steel is commonly used as the cathode. If current reversal is employed, the same material, platinized titanium or graphite, is used for both electrodes. Electrode chambers should be flushed with a large flow of rinse solution in order to remove the electrode reaction products. 

The electrochemical formation of all these peroxyanions requires a high positive potential and to facilitate such conditions it is normal to use an acidic medium and either a Pt or Pb02 anode. Because platinum is often superior it is usual to use a platinized titanium, tantalum or niobium surface or a thin platinum foil spread on a base-metal support. 

It is clearly desirable that the deposit has an even thickness over the whole of the surface to be electroplated. This requires the potential to be the same at all points over the surface of the cathode and this is impossible to attain when the object to be plated has a complex shape. To some extent the evenness of the deposit can be improved by introducing auxiliary anodes (usually platinized titanium electrodes where the reaction is oxygen evolution) at various positions in the electrolyte, the objective being to increase the cathode current density at points where it would otherwise be very low, i.e. at points on the cathode furthest from the normal anodes (e.g. in holes or recesses in the object being plated). The problem with this approach, however, is that a totally new cell geometry is necessary for each new plating job and in any case its success is limited. Hence, in general, we are dependent... 

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