Thermal spray coatings

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). 

Newer high velocity thermal spray coating processes produce coatings in compression rather than tension because of the shot peening effect of the supersonic particles on impact. This has permitted coating as thick as 12,500 p.m without delamination as compared to older processes limited to 1,250 p.m. The reduced residence time of particles at temperature minimises decomposition of carbides present in conventional d-c plasma. This improves wear and hardness (qv) properties. 

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)... 

Oeshsle, S. J. and Childs, J. N., Thermal Sprayed Coatings, in Steel Structures Painting Council Manual, Vol. 1, pp. 456-464 (1982)... 

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)... 

The properties of thermal-sprayed coatings vary as a function of processing parameters such as temperature and particle velocity. Generally, such coatings have greater porosity than CVD or PVD coatings and thickness control is more difficultto achieve. Yet the process is economical and undemanding. It can be applied in any location. 

Tucker, R. C., Jr., Thermal Spray Coatings, mASMHandbook, Surface Engineering, 5 497-509, ASMPubl. (1994)... 

By examining the dispersion properties of surface acoustic waves, the layer thickness and mechanical properties of layered solids can be obtained using the SAM. It can be used to analyze the wear damage progress [104], and detect the defects of thermally sprayed coatings [105]. 

Fehringer, G. et al.. Proton-conducting ceramics as electrode/electrolyte materials for SOFCs preparation, mechanical and thermal-mechanical properties of thermal sprayed coatings, material combination and stacks, J. Eur. Ceram. Soc., 24, 705-715 (2004). 

The addition of cerium oxide, for example, to zirconia produces a material with exceptional toughness and good strength [29], Cerium oxide-doped zirconia is used also in thermal barrier spray coatings on metal surfaces(30]. 

Hot-dip aluminizing in a molten bath is only suitable for workpieces with simple shapes which can withstand thermal exposure during hot dipping. Similarly, spray coating is suited only to pieces with a simple geometry. In comparison to other processes, a rather thick layer is necessary to achieve a pore-free coating. 

Nowadays, many advanced techniques are available in the ceramic industry to coat a solid layer onto a solid surface or to make ceramic materials with special properties [99-1 IS], such as spin-coating [99], chemical vapor deposition [100-106], and chemical vapor infiltration [106-109], thermal spray [110-112], plastic spray [113], and spray-coating [114]. The deposition can be caused by conventional heating, by laser beam, or by microwave heating. 

L.Pawlowski, The Science and Engineering of Thermal Spray Coatings, Wiley, Chichester, 1995. 

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