Metal films oxidation

The polycrystalline metal film/oxidic solid electrolyte system provides a reasonable approximation to nanocrystalline metal/metal oxide catalysts. 

Since the FHH method is relatively simple, it was widely used for determining the surface fractal dimension of several solids, including active carbons [35, 56], aerogels [57], metal films, oxides and related compounds [55]. In particular, Pfeifer and Lui [55] have provided an almost comprehensive review on this topic. Section 6.5 will briefly review applications to soils. 

Under severe conditions and at high temperatures, noble metal films may fail by oxidation of the substrate base metal through pores in the film. Improved life may be achieved by first imposing a harder noble metal film, eg, rhodium or platinum—iridium, on the substrate metal. For maximum adhesion, the metal of the intermediate film should ahoy both with the substrate metal and the soft noble-metal lubricating film. This sometimes requires more than one intermediate layer. For example, silver does not ahoy to steel and tends to lack adhesion. A flash of hard nickel bonds weh to the steel but the nickel tends to oxidize and should be coated with rhodium before applying shver of 1—5 p.m thickness. This triplex film then provides better adhesion and gready increased corrosion protection. 

Thin films of photochromic silver complex oxides were prepared by anodic oxidation of silver metal films (15). Complex oxides, such as Ag2V04, Ag SiO, and Ag2P04, darkened by exposure to visible light, but required heating to 150—250°C for thermal bleaching. 

Figure 8 Quantitaftive high depth resolution profile of O and N in a Ti metal film on Si, using electron-gas SNMS in the direct bombardment mode. Both O and N are measured with reasonably good sensitivity and with good accuracy both at the heavily oxidized surface and at the Ti/Si interface.

In XPS, chemical information is comparatively slowly acquired in a stepwise fashion along with the depth, with alternate cycles of sputtering and analysis. Examples of profiles through oxide films on pure iron and on Fe-12Cr-lMo alloy are shown in Fig. 2.9, in which the respective contributions from the metallic and oxide components of the iron and chromium spectra have been quantified [2.10]. In these examples the oxide films were only -5 nm thick on iron and -3 nm thick on the alloy. 

Metal/metal oxide Metal filmed with oxide in a solution of OH giving an A//M,Oy/OH electrode whose potential is dependent on pH. Sb/Sb20j/0H- Bi/Bi20j/0H-... 

In order that the possibility of contamination of catalysts with traces of oxides could be eliminated Campbell and Emmett (51) studied the catalytic activity of metallic films of nickel and its alloys with copper or gold. They were deposited under a high vacuum and then sintered (alloys also homogenized) in hydrogen at 5 cm Hg pressure at 350°C or 500°C. The films were subsequently allowed to cool to room temperature and only... 

Figure 15. Electrocapillary energy for the formation of a breakthrough pore in a thin surface oxide film on metals as a function of pore radius.7 AE E - Epzc, where Epzc is the potential-of-zero charge of the film-free metal. Al is the activation banier for the formation of a breakthrough pore and r is its critical radius. M, metal OX, oxide film EL, electrolyte solution, h a 2 x I O 9 m, am = 0.41 J m-2, a = 0.01 J m-2, ACj= 1 F m"2. a, AE=0.89 V b, AE=0.9 V c,A = 1.0 V. (From N. Sato, J. Electmckem. Soc. 129,255,1982, Fig. 2. Reproduced by permission of The Electrochemical Society, Inc.)...

Before constructing an electrode for microwave electrochemical studies, the question of microwave penetration in relation to the geometry of the sample has to be evaluated carefully. Typically only moderately doped semiconductors can be well investigated by microwave electrochemical techniques. On the other hand, if the microwaves are interacting with thin layers of materials or liquids also highly doped or even metallic films can be used, provided an appropriate geometry is selected to allow interaction of the microwaves with a thin oxide-, Helmholtz-, or space-charge layer of the materials. 

Etching- metal and oxide etch equipment are used to remove excess parts of the deposited film. High density plasma sources... 

In the anodic polarization of metals, surface layers of adsorbed oxygen are almost always formed by reactions of the type of (10.18) occurring in parallel with anodic dissolution, and sometimes, phase layers (films) of tfie metal s oxides or salts are also formed. Oxygen-containing layers often simply are produced upon contact of the metal with the solution (without anodic polarization) or with air (the air-oxidized surface state). 

The surface-phase layers will difier in character depending on the stractures of metal and oxide. On certain metals (zinc, cadmium, magnesium, etc.), loose, highly porous layers are formed which can attain appreciable thicknesses. On other metals (aluminum, bismuth, titanium, etc.), compact layers with low or zero porosity are formed which are no thicker than 1 pm. In a number of cases (e.g., on iron), compact films are formed wfiicfi fiave a distorted lattice, owing to the influence of substrate metal stracture and of the effect of chemical surface forces. The physicochemical and thermodynamic parameters of such films differ from tfiose of ordinary bulk oxides. Because of the internal stresses in the distorted lattice, such films are stable only when their thickness is insignificant (e.g., up to 3 to 5 nm). 

Different electrochemical surface treatments have found extensive use for the purposes of providing metal parts with particular properties, appearance, and shape. This includes the apphcation of superficial oxide or salt films (see Section 16.3), metal films (Section 16.5), and a number of methods that exploit the selective anodic dissolution of different segments of the metal surface. We examine briefly a few examples of the latter type. 

Numerous materials have been used to fabricate open tubular columns. Most early studies were conducted using stainless steel tubing and later nickel tubing of capillary dimensions [147-149]. These materials had rough inner surfaces (leading to non-uniform stationary phase films), metal and oxide impurities at their surface which were a cause of adsorption, tailing, and/or decomposition of polar solutes and because their walls were thick, thermal Inertia that prevented the use of fast temperature programming. None of these materials are widely used today. 

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