Thermal-sprayed zinc coatings

In thermal-sprayed zinc coatings, layer thicknesses of 0.050-0.150 mm are the maximum reached. These layers consist mainly of pure zinc, with a certain amount of zinc oxide and pores depending on the layer thickness and spraying technique. The much lower protective effect of spray galvanisation at the same layer thickness is probably due to the lack of the iron-zinc alloy phase. 

Thermally sprayed soluble coatings of zinc or aluminium (or their aUoys) are also used. Practical experience exists in the USA, among others, on bridges. Another sacrificial system is based on a zinc foil attached to the concrete surface via an ion-conducting gel adhesive [52-54]. Sacrificial CP systems have obvious advantages of simplicity and ease of application the main questions concern their effective service life. 

Thermal sprayed Aluminium/Zinc/Indium - A proprietary variation on thermal sprayed zinc that uses an alloy to enhance the current rather than a humectant. A 300 micrometre thick coating is applied by arc spray. Approrimately 35,000 m had been applied up to May 2003. Adhesive zinc sheet - A proprietary system consisting of rolls of zinc 0.25 mm thick, 25 mm wide with a conductive gel adhesive on one side. The installed system can be painted. The edges must be sealed against water ingress as the gel can swell and leak. 

As stated in the anode descriptions earlier, there are also two NACE test methods for cathodic protection anodes. These are TM 0294 on embeddable anodes (mixed metal oxide coated titanium, mesh, ribbon, tnbes, rods and conductive ceramic tubes) and TMO1105-2005 on organic-based condnc-tive coating anodes. In addition there is a specification for applying thermal sprayed zinc anodes to concrete American Welding Society (2002). 

D. Zinc-15% Aluminum Thermally Sprayed Alloy Coatings... 

Table 2.30 Relative Performance of Thermally-Sprayed Zinc-Aluminum Coatings 34 Years"... 

German, G. (1978). Corrosion prevention with thermal-sprayed zinc and aluminum coatings. Proc. Anniversary Symposium, Atmospheric Factors Affecting the Corrosion of Engineering Metals, ASTM STP 646. ASTM, Philadelphia, pp. 74-82. 

Ziac foil coated with a conductive, pressure-sensitive adhesive is used for repair of other ziac coatings or for imparting corrosion resistance at field sites. The 0.08-mm ziac tape or sheet has a 0.025-mm coaductive adhesive. The laminate is cut to size and pressed tightly to activate the adhesive. Conductive tape can be wrapped around pipe, especially around welds or connections. The corrosion resistance of this material is iatermediate between galvanized or thermally sprayed coatings and zinc-filled paints (21,50). 

Endoh, M., Influence of Surface Roughness of Mild Steel Substrate on Adhesive Strength of Zinc Sprayed Coatings . Proc. 8th Int. Thermal Spray. Conf., American Welding Society, pp. 492-502 (1976)... 

Nagaska el ai., Weathering Test on Zinc, Aluminium and Zinc-Aluminium Alloy Sprayed Coating for 5000 Days, Proc. lOth Int. Thermal Spray. Corf., DVS, Diisseldorf, Poster report (1983)... 

Shaw, B. A. and Moran, P. J., Characterization of the Corrosion Behaviour of Zinc-Aluminium Thermal Spray Coatings , Corrosion 85, Boston, March 1985, NACE, Houston. Paper 212 (1985)... 

Protecting a surface from corrosion by coating can be accomplished by a number of well-established processes which include paints, metal plating (with zinc or cadmium), diffusion, thermal spraying, and, more recently, vapor deposition processes. Of these physical vapor deposition (PVD) is used extensively in corrosion protection. Typical applications are ... 

The zinc-hydrogen anode system uses 10-20 mm thick zinc sheet anodes attached to the concrete with ionically conductive hydrogel adhesive. Field trials have shown that this system is capable of supplying sufficient current for effective corrosion control. The thermal-sprayed alloy anode system utilizes a metallization (flame or arc spraying) process to form a metallized coating on the concrete surface. The two most promising anode materials were Al-Zn-In alloy and zinc (16). 

Thermal spray aluminium and zinc coatings with a paint system on top provide first class corrosion protection with very long lifetime under most natural conditions, and have been extensively used on steel structures, e.g. road bridges [ 10.44]. 

Klinge R. Sprayed zinc and aluminium coatings for the protection of stractural steel in Scandinavia. Proceedings 8th International Thermal Spray Conferance, American Welding Society, 1976 203-213. 

Childs, J. N., Zinc sprayed coatings in a liquid cargo tanker ship, Proc. 8th Int. Thermal Spray. 

Zinc coating alloys with improved corrosion resistance have developed rapidly, particularly those with S or 55% aluminum additions and applied by hot dipping, those with 15% aluminum for thermal spraying, and those with nickel or small amounts of a wide range of other elements applied by plating. The special properties of each group, including improved corrosion resistance, are identified. 

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