Platinum layer

Fig. 9.29 SEM image of porous ceramic material after coating with a platinum layer ( 10nm thickness). Reprinted from [69], 2002, American Chemical Society.

Electrochemical Instrumentation. For the Ru complexes, a 1 cm diameter platinum disk brazed onto a brass holder was used as a working electrode. It was masked with ChemGrip (a teflon based epoxy) except for the upper face. Prior to use, it was polished with 1 micron diamond paste (Buehler) and rinsed with water, acetone and methanol. The working electrode for each Os complex was the uppermost platinum layer of a platinum/carbon layered synthetic microstructure (LSM) (Energy Conversion Devices). The LSM consisted of 200 layer pairs of carbon and platinum whose thicknesses were 24.4 and 17.0 A, respectively and where platinum was the outermost layer. The LSM was placed in 1.0 M H2SO4 and cleaned... 

Once formed, the protons diffuse through the platinum layer and enter deep into the layer of semi-permeable membrane. They travel from the left-hand side of the membrane to its right extremity in response to a gradient in concentration. (Movement caused by a concentration gradient will remind us of dye diffusing through a saucer of water, as described on p. 129.)... 

This nucleation process enhanced the contact between the membrane and the platinum layer grown later. 

Metal oxide coatings Commercial lead dioxide coatings, for example, on titanium, have a higher stability compared with lead or lead alloy anodes with their in situ formed oxide layer. A secure contact between Pb02 and titanium has to be guaranteed, for example, by a platinum layer or at least by a sufficiently large number of platinum crystallites. 

However, their work was complicated by the fact that they used a porous platinum current collector underneath the oxide. If the gaseous atmosphere were able to come in contact with this porous platinum layer then, under reaction conditions, the platinum could exhibit a different oxygen activity from the vanadium phosphate making the e.m.f. of the cell extremely difficult to interpret. 

After annealing at 325°C for 5 min, the Pt2Si layer, about 98 nm thick, was formed in all four initial specimens. During its growth for 10 min, the platinum layer, 115 nm thick, was consumed. Therefore, the first specimen transformed into the Pt2Si—Si(l 11) one. The layer of the PtSi compound... 

In this configuration, the membrane is selective to some reactants or products and the catalyst may be placed on the membrane surface or near the pore entrance such as catalytic electrodes attached to solid electrolytes or a platinum layer on the surface of a vanadium membrane as the catalyst for thermal decomposition of hydrogen sulfide [Edlund and Pledger, 1993]. Solid or liquid catalysts have been attached to membranes or their pores. It has been mentioned previously that this configuration can also be used to control the addition of a reactant through the membrane pores from the other side of the membrane where the second reactant is introduced. 

Most metals can be electrolytically deposited from water-free melts of the corresponding metal salts. It is well known that aluminum, lithium, sodium, magnesium, and potassium are mass produced by electrolytic deposition from melts. Industrial processes for the melt-electrolytic production of beryllium, rare earth metals, titanium, zirconium, and thorium are also already in use. Pertinent publications [74, 137, 163] describe the electrolytic deposition of chromium, silicon, and titanium from melts. Cyanidic melts are used for the deposition of thick layers of platinum group metals. It is with this technique that, for instance, adhesion of platinum layers on titanium materials is obtained. Reports concerning the deposition of electrolytic aluminum layers [17, 71-73, 94, 96, 102, 164, 179] and aluminum refinement from fused salts [161] have been published. For these processes, fused salt... 

The first study of Sn deposition on Pt( 111) was reported by Paffet and Windham in 1989 [42] and a subsequent one on the same system was published by Campbell in 1990 [1]. In both studies, two LEED patterns were observed after annealing a 2x2 and a ( /3x v ) R30°. Both superstructures were interpreted in terms of incorporation of the tin layer in the first platinum layer, but only a qualitative examination of the LEED pattern was performed. Subsequently the results of low energy alkali ion scattering spectroscopy ALISS [43, 21] could be quantitatively interpreted as due to ordered, single atomic layer surface alloys. The ion scattering results have been confirmed and expanded by a quantitative LEED study [34]. The atomic structure of both phases corresponds exactly to that of the topmost layer of the phases with the same periodicity observed on the on PtsSnflll). The LEED and ALISS results for the Sn/Pt(lll) system were confirmed by a recent STM study reported by Batzill et al. [44]. Even though atomic resolution was not attained in this study (only the surface unit mesh could be observed), the results are closely comparable to the atomically resolved ones obtained on the PtaSn(l 11) surface [35]. 

In laboratory-prepared devices (such as oxygen pumps), porous platinum layers that function as both the electrode and current collector are generally deposited on both surfaces of the membrane. 

Thicker platinum layers are used extensively for temperature sensors, for example, deposited on ceramic substrates. Compared to other thin film metals, such as gold, silver, or nickel, platinum has a low thermal expansion coefficient, thus minimizing stress problems due to the differential thermal expansions of the various membrane layers. 

In thin-film technology (layer thickness <1 pm), a microporous platinum layer is deposited on the already fired ceramic by thermal evaporation, sputtering, chemical vapor deposition, or electrolytic or electroless deposition. The microporosity of the thin electrode provides sufficient access of the exhaust gas to the three-phase boundary. 

Kalish and Burstein (60) found that the amount of oxygen adsorbed by a platinum layer adjacent to the surface was about one hundred times that required for a monolayer. Temkin and Kul kova (61) have noted a similar phenomenon for oxygen adsorption on silver. The amount of... 

U. Bardi, A. Santucci, and G. Rovida. Study of the Growth Mechanism of Platinum Layers on the Na<) 7WO3 Single Crystal Surface. Surf. Sci. 162 337 (1985). 

Further heating of the above sample under dihydrogen at 500 °C results in an increase of the number of platinum atoms surrounding tin up to ca 5. This can be explained by a migration of the tin atom into the first platinum layer (Scheme 8). 

Objects to be plated with platinum (cathodes) are prepared in exactly the same way as in any other method of electroplating. Given the cost of platinum, these objects are usually small platinum electrolysis vessels therefore need to hold only a few liters of the solution the vessel will thus usually be a glass or porcelain beaker or a small iron trough coated on the inside with a special alkali- and acid-resistant enamel. If the platinum deposit is too dull, it can be rubbed and scoured in the same way as gilt-ware, and then replaced in the platinum bath to deposit a further platinum layer this treatment may be repeated imtil the required deposit thickness is reached. 

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