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Galvanised hand rail Crystalline surface of a hot-dip galvanized handrail, known as "spangle" Protective effect: completely rusted letter box mounted to a hot-dip galvanized wall Steel strip coming out of the zinc pot of a continuous vertical hot-dip galvanizing line. Hot-dip galvanization is a form of galvanization.
Galvanized surface with visible spangle. Galvanization (also spelled galvanisation) [1] is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are coated by submerging them in a bath of hot, molten zinc. [citation needed]
The chosen content of zinc depends on the required productivity and part configuration. High zinc improves the bath's efficiency (plating speed), while lower levels improve the bath's ability to throw into low current densities. Typically, the Zn metal level varies between 20 and 50 g/L (2.7-6.7 oz/gal). The pH varies between 4.8 and 5.8 units.
A common example of galvanic corrosion occurs in galvanized iron, a sheet of iron or steel covered with a zinc coating. Even when the protective zinc coating is broken, the underlying steel is not attacked. Instead, the zinc is corroded because it is less "noble". Only after it has been consumed can rusting of the base metal occur.
The difference can be measured as a difference in voltage potential: the less noble metal is the one with a lower (that is, more negative) electrode potential than the nobler one, and will function as the anode (electron or anion attractor) within the electrolyte device functioning as described above (a galvanic cell).
Corrugated galvanised iron (CGI) or steel, colloquially corrugated iron (near universal), wriggly tin (taken from UK military slang), pailing (in Caribbean English), corrugated sheet metal (in North America), zinc (in Cyprus and Nigeria) or custom orb / corro sheet (Australia), is a building material composed of sheets of hot-dip galvanised ...
In comparison to a zinc (galvanized) coating galvannealed has better spot weldability, and is paintable, [4] Due to iron present in the surface alloy phase galvanneal develops a reddish patina in moist environments - it is generally used painted. [5] Zinc phosphate coating is a common pre-painting surface treatment. [4]
The polarity of the cell is determined as follows. Zinc metal is more strongly reducing than copper metal because the standard (reduction) potential for zinc is more negative than that of copper. Thus, zinc metal will lose electrons to copper ions and develop a positive electrical charge. The equilibrium constant, K, for the cell is given by: