These silver coloured copper-nickel-zinc alloys containing 10-20% nickel (but no silver) can be regarded as special brasses. They polish to a fine silvery colour which accounts for their use over several centuries.
In most respects they show similar corrosion characteristics to the brasses but the higher nickel versions have superior tarnish resistance and resistance to stress corrosion cracking.
They are available in all forms and are used for tableware (silver-plated to give EPNS), telecommunication components, better quality keys, high quality fishing reels and rod fittings, food manufacturing equipment, jewellery, model making, tool brush anchor wire and pins, musical instruments, e.g. ‘silver bands’, flutes, test probes and contact springs.
None, nickel-silvers are copper-nickel-zinc alloys which have an attractive colour when polished.
No, copper alloys also do. Tests have been performed on pure copper, high coppers, brasses, bronzes, copper-nickels and copper-nickel-zincs (sometimes referred to as nickel silvers because of their shiny white colour, even though they contain no silver. Alloys with higher copper content kill organisms faster but, as a general rule, alloys with >60% copper have good efficacy.
‘Antimicrobial Copper’ is shorthand for these efficacious alloys. When choosing a copper alloy for a product it is important to balance the requirements for mechanical properties, manufacturing process and, of course, colour. Copper alloys provide a palette of attractive colours from the yellow of brasses to the dark browns of bronzes.
They can be polished to a silvery appearance.
Copper strip and wire may be produced with a combination of high elastic limit and good corrosion resistance, making them an ideal choice for springs. The main groups of alloys are:
- Phosphor bronze, typically CW451K (PB102) with a yield strength of about 500 N/mm2.
- Nickel-silver, typically CW409J (NS106).This is silver coloured and has excellent tarnish resistance.
- Copper-beryllium CW100C (CB101). This alloy is used where very high yield strength is required (greater than 1000 N/mm2). These alloys are expensive and phosphor bronze will be adequate for most engineering applications.
A useful Specification is BS EN 1654:1998 (Copper and copper alloys. Strip for springs and connectors).