Platinum coating

Cathodic Protection Systems. Metal anodes using either platinum [7440-06 ] metal or precious metal oxide coatings on titanium, niobium [7440-03-17, or tantalum [7440-25-7] substrates are extensively used for impressed current cathodic protection systems. A prime appHcation is the use of platinum-coated titanium anodes for protection of the hulls of marine vessels. The controUed feature of these systems has created an attractive alternative... 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

Six iron anodes are required for corrosion protection of each condenser, each weighing 13 kg. Every outflow chamber contains 14 titanium rod anodes, with a platinum coating 5 /tm thick and weighing 0.73 g. The mass loss rate for the anodes is 10 kg A a for Fe (see Table 7-1) and 10 mg A a for Pt (see Table 7-3). A protection current density of 0.1 A m is assumed for the coated condenser surfaces and 1 A m for the copper alloy tubes. This corresponds to a protection current of 27 A. An automatic potential-control transformer-rectifier with a capacity of 125 A/10 V is installed for each main condenser. Potential control and monitoring are provided by fixed zinc reference electrodes. Figure 21-2 shows the anode arrangement in the inlet chamber [9]. 

Although molybdenum is resistant to molten glass, except leaded, molybdenum components not coated with glass but exposed to the oxidising furnace atmosphere corrode rapidly due to volatilisation of molybdenum oxide above 370°C. To overcome this, stirrers etc. for use in glass plant are physically clad with platinum sheet in vulnerable areas. Modern plating techniques have enabled dense platinum coatings to be put onto the surface of the molybdenum and it is expected that this technique will be exploited further in the near future. 

Cathodic protection applications in fresh water include use of ferrite-coated niobium , and the more usual platinum-coated niobium . Platinised niobium anodes have been used in seawater, underground and in deep wells " and niobium connectors have been used for joining current leads Excellent service has been reported in open-seawater, where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud ... 

By a mechanism similar to that discussed in relation to platinum coating, titanium can function as a conducting jig to support aluminium components and assemblies in conventional anodising baths. In this application the exposed titanium acquires the insulating film, but allows current to pass to the aluminium at the points of contact . 

Platinum coatings may also be thermally sprayed or sputtered onto the titanium, to provide uniform well-bonded coatings. Titanium rod may also be spiral wound with platinum wire. However, the use of these techniques is limited. 

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

The electrons necessary to effect the reduction of gaseous oxygen come from the external circuit, and enter the oxygen half-cell through the layer of platinum coating the cathode, thereby explaining why the electrons in Equation (7.14) are subscripted with Pt . 

The electrodes of conductivity cells are usually made of platinum coated with platinum black with a known area. Although in many cells the distance between the electrodes is adjustable, for any series of experiments it must be held constant and for many calculations the precise value is required. The cells must be thermostatically controlled because any changes in temperature will cause significant alteration of conductivity values. 

Y. D. Jin, Y. Shen, and S. J. Dong, Electrochemical design of ultrathin platinum-coated gold nanoparticle monolayer films as a novel nanostructured electrocatalyst for oxygen reduction, J. Phys. Chem. B 108, 8142-8147 (2004). 

Pb02 is also applicable as a coating on a suitable carrier material (see Sect. 2.4.1.1.10). Pb02-coated titanium anodes with good stability are commercially available. On platinum or platinum-coated titanium a coating of Pb02 for laboratory use can easily be prepared electrochemi-cally (e.g. [28]). 

The SHE also utilizes the catalytic properties of platinum, so the electrode monitoring the energy of the H" " H2 couple is made of platinum coated with platinum black. Platinum black is a layer of finely divided Pt metal, which catalytically speeds up the dissociation and association of H-H molecules. The catalysis here aids the speed at which equilibration is attained so that the measurement is more likely to be performed reversibly. 

Kirkendall void formation can, however, be prevented from occurring by choosing the right metal species. For example, whereas platinum coating on copper is subject to the Kirkendall void creation process, the same coating on electrodeposited nickel is free of it even if heated to as high as 600°C for many hours (more than 10 hours ). 

Smooth platinum, lead dioxide and graphite are anode materials commonly used in electrooxidation processes. All show large overpotentials for oxygen evolution in aqueous solution. Platinum coated titanium is available as an alternative to sheet platinum metal. Stable surfaces of lead dioxide are prepared by electrolytic oxidation of sheet lead in dilute sulphuric acid and can be used in the presence of sulphuric acid as electrolyte. Lead dioxide may also be electroplated onto titanium anodes from lead(Il) nitrate solution to form a non-porous layer which can then be used in other electrolyte solutions [21],... 

Maier CU, Specht M, Bilger G (1996) Hydrogen evolution on platinum-coated p-silicon photocathodes. Int J Hydrogen Energy 21 859-864... 

Radon can be isolated from radium by several methods. An aqueous solution of radium salt such as radium bromide is heated, liberating radon. Radioactive bombardment then decomposes water to oxygen and hydrogen. Radon is separated from the gaseous mixture by condensation in tiny tubes placed in liquid air. The tubes then are sealed by melting. A gold or platinum coating is applied to form the radon seeds used in radiation therapy. 

FIGURE 18.2 Scanning electron micrographs of silicon microneedles, (a) Silicon microneedles micro-fabricated using a modified form of the BOSCH deep reactive ion etching process. The microfabrication process was accomplished at CCLRC Rutherford Appleton Laboratory (Chilton, Didcot, Oxon, UK). The wafer was prepared at the Cardiff School of Engineering, Cardiff University, UK. Bar = 100 pm (b-d) platinum-coated silicon microneedles prepared using a wet-etch microfabrication process performed at the Tyndall National Institute, Cork, Ireland. Bar = 1 mm (b), 100 pm (c,d). 

Fig. 52. Scanning with a platinum coated SFM tip over a SAM surface containing terminal azide groups in the presence of H2 leads to the reduction of azide groups to primary amino groups. Derivatization of the resulting amine surface with aldehyde-modified latex beads results in specific labelling of the reduced areas. Reproduced from [469]...

---