Metals oxide 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... 

Metal anodes using platinum and precious metal oxide coatings are also incorporated into a variety of designs of impressed current protection for pipeline and deep weU appHcations, as weU as for protection of condenser water boxes in power generating stations (see Pipelines Power generation). 

Table 7-3 Composition and properties of noble metals with metal oxide coatings...

The impressed current method with metal oxide-coated niobium anodes is usually employed for internal protection (see Section 7.2.3). In smaller tanks, galvanic anodes of zinc can also be used. Potential control should be provided to avoid unacceptably negative potentials. Pure zinc electrodes serve as monitoring and control electrodes in exposed areas which have to be anodically cleaned in the course of operation. Ag-AgCl electrodes are used to check these reference electrodes. 

Plate anodes were used for corrosion protection in order to avoid damage due to erosion and cavitation. These consisted of enamelled steel bodies in which a metal oxide-coated titanium anode 1 dm in surface area was fitted. The enamel... 

Precious metals and oxides platinised titanium, platinised niobium, platinised tantalum, platinised silver, solid platinum metals, mixed metal oxide-coated titanium, titanium oxide-based ceramics. 

Canister anodes consist of a spirally wound galvanised steel outer casing containing a carbonaceous based extender which surrounds the primary anode element which may be graphite, silicon iron, magnetite, platinised titanium, mixed metal oxide-coated titanium or platinised niobium, etc. 

The composition of the mixed metal oxide may well vary over wide limits depending on the environment in which the anode will operate, with the precious metal composition of the mixed metal oxide coating adjusted to favour either oxygen or chlorine evolution by varying the relative proportions of iridium and ruthenium. For chlorine production RuOj-rich coatings are preferred, whilst for oxygen evolution IrOj-rich coatings are utilised. ... 

The most recently developed anode for the cathodic protection of steel in concrete is mixed metal oxide coated titanium mesh The anode mesh is made from commercially pure titanium sheet approximately 0-5-2mm thick depending upon the manufacturer, expanded to provide a diamond shaped mesh in the range of 35 x 75 to 100 x 200 mm. The mesh size selected is dictated by the required cathode current density and the mesh manufacturer. The anode mesh is supplied in strips which may be joined on site using spot welded connections to a titanium strip or niobium crimps, whilst electrical connections to the d.c. power source are made at selected locations in a suitably encapsulated or crimped connection. The mesh is then fitted to the concrete using non-metallic fixings. 

The active coating consists of a thermally deposited mixed metal oxide coating, the composition of which is considered proprietary information, although it is known that certain filler materials, e.g. Ta, may be added to the mixed metal oxide to reduce the precious metal content of the coating, and hence the cost of the anode. 

Mixed Metal Oxide Coated Titanium As an alternative to platinised titanium, these materials are finding increasing use in seawater and soil based deep well groundbed applications. 

Fig. 5.18 Schematic and TEM image of reaction scheme to prepare metal nanoparticles encapsulated within metal oxide coating on oxidized MWCNTs. Metal NPs are added to developing metal alkoxide sol followed by addition of oxidized MWCNTs and water for hydrolysis. Adapted with permission from [228], (2012) American Chemical Society.

Fig. 4.1. (a) Micrograph of a circular microhotplate without sensitive layer, (b) SEM-micrograph of a metal-oxide coated microhotplate... 

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. 

Also, other metal oxide coatings are possible, for example, electrochemically deposited manganese dioxide. Moreover, further electrocatalytically active oxides are research objectives, for example, oxides with spinel structure such as CoMu204 [36]. 

Aluminum, chromium, titanium, and several other metals can be colored by an electrochemical process called anodizing. Unlike electroplating, in which a metal ion in the electrolyte is reduced and the metal is coated onto the surface of the cathode, anodizing oxidizes a metal anode to yield a metal oxide coat. In the oxidation of aluminum, for instance, the electrode reactions are... 

No systematic study of inert electrode materials has taken place to date and nothing is known about the anodic processes taking place in ionic liquids. It is probable that noble metal oxide coatings should be suitable but processes such as chlorine evolution will clearly have to be avoided for eutectic-based ionic liquids. The breakdown products of most cations are unknown but it is conceivable that some of them could be potentially hazardous. 

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