Coppers and Copper Alloys
(c) Vin Callcut 2002-2017. Small extracts can be used with acknowledgements to 'Oldcopper.org' website.
Helpful comments are very welcome.
Table of ContentsCOPPER with
Nickel Silvers and Paktong
COPPER AND HEALTH
We cannot live without Copper
How much copper?
Copper in the Environment
COPPERS AND COPPER ALLOYS
There is a wide range of shapes/forms available in copper base materials. There is also a very large variety in generic types of copper alloy and chemical compositions available. This provides many possible property combinations, often unique to copper base alloys, making the alloys suitable for applications in virtually every area of human activity. Copper forms alloys more freely than most metals, and with a wide range of alloying elements. Zinc, tin, nickel and aluminium are the most common alloying additions and produce the following alloy types -
· tin makes Bronze
· tin and phosphorus makes Phosphor bronze
· aluminium makes Aluminium bronze
· zinc makes Brass
Zinc and lead makes leaded free-machining brass
· tin and zinc makes Gunmetal
· nickel makes Copper-nickel
· nickel and zinc make Nickel silver
- These are the popular types of copper, each suitable for a variety of uses.
· Deoxidised copper (usually deoxidised with phosphorus - or boron in the case of castings) is a material that can readily be brazed or welded without fear of embrittlement. It may be known colloquially as 'Deox' and is used for the manufacture of tubing for fresh water and for hot water cylinders.
· High conductivity (HC) electrolytically refined copper (sometimes known as tough pitch copper or 'electro' ), with a nominal conductivity of 100% IACS (International Annealed Copper Standard), is used for most electrical applications such as busbars, cables and windings. High conductivity copper is very readily worked hot and cold. It has excellent ductility which means that it can be easily drawn to fine wire sizes and it is available in all fabricated forms.
· Oxygen-free High Conductivity Copper (OFHC®) similar to conventional high conductivity copper in properties but is melted and cast in an oxygen free atmosphere. It is used in electronic equipment, high-vacuum applications, to make good glass-to-metal seals and to make high conductivity loudspeaker leads for domestic Hi-Fi equipment.
Bronzes are alloys of copper and tin can contain from around 2 up to 40% tin. Bronze is one of the oldest alloys known since tin was fairly readily available to be used to harden copper. Not many materials have had an entire epoch named after them! They are used for many decorative and industrial purposes but are not now in significant domestic use. Mention is made of their usefulness in the millennia when bronzes were cheaper than brasses. With tin price as it is compared with zinc, those days are not likely to return. Bronzes are now another enthusiasm altogether and form a good topic for coverage in many other books.
For the record, the tin contents used are:
2 to 7% for malleable bronzes. The low end is typical for coinage. 5% is popular for the manufacture of hard strip or wire springs, generally in a phosphor bronze that also contains about 0.3% phosphorus.
9 to 12% is used now in cast bronzes and phosphor bronzes for the manufacture of heavy duty bearings used in automotive gearboxes amongst other applications. It was also a popular composition with the Greeks and Romans.
Around 17% is used for statuary and other works of art, being easily cast to thin section and weldable.
20-30% is used to give the resonance needed in bell metal and for cymbals. Alloys with this much tin are far too brittle for other purposes.
30 to 40% is used to give the very hard white metal used in the old bronze mirrors. This is now known as Speculum Metal and has also seen service in scientific instruments.
Bronzes may also have additions of lead and zinc for some applications. Lead improves machinability and reduces bearing friction. Both improve castability and make the metal mixture price of the alloy slightly cheaper. These additions bring in terms for alloys such as ‘Leaded Bronze’, ‘Gunmetal’, ‘Leaded Gunmetal’ and ‘Leaded Red Brass’(US). All of these will occasionally be found in domestic equipment.
The word ‘bronze’ also occurs legitimately in ‘Aluminium Bronzes’, can be a bit vague with ‘Manganese Bronzes’ (actually High Tensile Brasses) and is also used to try to give an air of respectability to some other copper alloys.
Brasses are copper alloys in which the main alloying element is zinc. The generic term 'brass' covers a wide range of materials suitable for many different types of application. There are two main types of brasses, those most suitable for cold working and the others that are used for casting, extrusion and hot stamping. The cold working brasses contain up to 37% zinc, the others typically 40%. The colour of brass varies with zinc content but it takes years of experience to be able to estimate the zinc content accurately. Experienced industrial samplers can examine the colour of fresh drillings estimate the zinc content of commercial alloys to within 0.5%.
Gilding metals (10 to 20% Zn) are used for architectural metalwork, papermaking, jewellery strip and applications requiring suitability for brazing and enamelling.
‘Cartridge brasses’ or ‘70/30 brasses’ (30% Zn) have the maximum ductility of the copper-zinc range and are used for deep drawing.
‘Common brass’, (63/37 or 64/36 brasses) containing 36% zinc, is the most usual composition used for brass sheet.
Brasses used for casting, hot stamping and extrusion normally have Such compositions, all derived from Muntz metal, with about 40% zinc, allow the production of complex, machinable high strength shapes at low material cost.
Other elements are added to the brasses to produce materials for different applications. Free-machining brass (containing 39% zinc and 3% lead) has for decades been the standard alloy against which the machinability of other metals has been judged. The lead is present as fine particles that help chip forming of the swarf so that it can clear away from the tool tip.
High tensile brass. The first of these was possibly ‘Delta Metal’ which was a brass to which iron was added for extra strength. They are now brasses with additions of aluminium, iron and manganese and other elements in proportions varied to suit the combination of strength, corrosion resistance, hardness, ductility, solderability and other properties required. They offer very significant increases in strength and hardness, similar to those properties associated with aluminium bronzes and are employed for heavy duty applications of which aircraft landing gear components are typical.
When about 1% tin is added to copper-zinc, Naval brass or Admiralty brass is produced depending upon the ratio of copper and zinc.
Under certain conditions in seawater and aggressive domestic water supplies, brass can be subject to a corrosive attack called dezincification. The addition of around 0.1% arsenic, and with careful production quality control, produces an alloy free from this problem. It meets the needs of the water supply industry so is used for pipe fittings, stop-cocks, water meters and other components of plumbing and heating installations.
Nickel Silvers and Paktong
Nickel silvers are a group of copper-nickel-zinc alloys with a higher strength than conventional brasses. Usually the nickel content is between 10 and 18% but it can be higher. They are an attractive colour, becoming more silvery the higher the nickel content. They have good mechanical properties, good corrosion resistance and are easily fabricated. For decorative uses they are frequently plated with silver to give ‘EPNS’ (Electro-plated Nickel Silver). Gold plating is also applied for spectacle frames and electrical contacts. It is an alloy closely resembling silver and yet costing only a fraction of its price. Much of the research on nickel silver was undertaken in Germany and France around 1824-25 when investigators directed their efforts at improving the ancient Chinese copper-nickel-zinc alloy which had been brought to Europe in the 17th and 18th Centuries and first analysed by the Swedish chemist Engestrom in 1776.
The European version of the Chinese name is 'Paktong' or 'Pakfong' - said to be derived from 'pek' meaning white and 'tung' meaning copper. In some respects, the Chinese names were more appropriate than their modern counterparts since the nickel content is rarely above 25%, and silver, as an element, is completely absent. As in Canada, there was a rich lode of copper ore in the mountains containing a relatively high nickel content that could be co-refined to give a copper-nickel alloy. This melts at a temperature higher than copper but the Chinese found that the addition of zinc reduced the melting temperature to more convenient values. Fortunately they had supplies of zinc ore to hand and the Paktong alloy was made in Canton before the metal was exported.
When the alloys were first produced in Britain a year or two after their introduction in mainland Europe, they were called ‘German Silver' - a name which was only discarded during the early part of the 20th century and may now give problems under the Trades Descriptions Act.
Originally the main outlet for nickel silver was for decorative metalwork such as jewellery, watchcases, flatware, hollowware and tableware - articles where the decorative colour was of paramount importance. Now they are also important architectural and engineering materials. Most nickel silvers can be cold worked. The proportions of copper, zinc and nickel are such as to retain the characteristics of the ‘alpha’, cold working brasses. The colour of the alloy becomes whiter as the nickel content is increased. The most popular alloys contain between 12 and 18 per cent but some may have up to 25 per cent.
For castings and hot working by extrusion or pressing, there are special nickel silvers with higher zinc contents known as nickel brasses or sometimes ‘silver bronzes’. These are used for decorative metalwork, door handles and handrails. As extrusions, these are mainly used for architectural purposes in frames for doors, windows, lifts and carpet rails.
Sheffield Plate, or better Old Sheffield Plate applies to items made with copper sheet that has had silver fused to both sides of it prior to finish rolling. It is said to have been invented by Thomas Boulsover around 1750. While copper has been fused to silver and gold for centuries, this was generally done when the article being made was nearly at its finished shape. He realised that the ductility of the metals was similar and would enable thin sheet to be made very economically. ‘Plates’ of silver are laid on one or both sides of a thick sheet of copper and the resultant sandwich fused at the melting point of silver (9600C) using a borax flux as used for brazing. The metal was then rolled on down to required thickness. From this material, craftsmen could produce tableware using silversmiths’ techniques and giving the appearance of solid silverware at a fraction of the cost.
The thickness of silver applied varied according to the depth of metal needed for engraving details in the wares. Initially silver formed one tenth of the total thickness of the plate and there is at least one example where the ratio is one to five. Craftsmanship on products was at least equal to that used on solid silver. The thickness ratio settled down to about 1 silver to 14 copper. As the price of, and taxes on, silver rose, so techniques were developed for economy including ‘letting in’ pieces with thicker copper where deep engraving was likely, for example where an inscription or coat of arms would be needed. In the last period of manufacture ‘Sheffield Light Silver Plating’ was made at a ratio of 1 to 60, having less silver on the surface than electro-plated wares then had.
While the process started in Sheffield, it was soon adopted also in Birmingham. The quality of that made in the Soho factory of Matthew Boulton was very high and he became the largest single manufacturer. Elsewhere it varied. It was also made in Nottingham and London and outside Britain in France, Russia and Germany.
Copper sulphate is commercially the most important copper compound, once called ‘blue vitriol’ from its close association with sulphuric acid. It is generally the starting stock for the manufacture of most other copper compounds. World consumption is around 200,000 tons per year, of which approximately 75% is used in agricultural applications. Since copper sulphate is an excellent fungicide it is vital in ‘Bordeaux Mixture’ and ‘Burgundy Mixture’ compositions that have preserved vineyards from ruinous attack by fungus.
Cupric oxide, cuprous oxide, copper acetate, cupric chloride, copper oxychloride, cupric nitrate and copper napthenate are other copper compounds used selectively for various purposes for their ease of use or other special properties.
Other uses include:
· electrolyte for copper refining
· anti-fouling paints
· dietary addition to correct copper deficiency in soil or animals
· catalysts for many industrial processes in the petrochemical and rubber industry and for textile manufacture.
· additives to cement for controlling setting rate and lichen growth
· addition as fungicide to plaster
· mordants for dyeing
· colourings for paints, glass and fireworks
· molluscicide for countering snail-borne liver fluke and bilharzia.
· preservatives for paints, adhesives, timber, textiles and bookbindings.
Copper as a trace element is essential to the health of plants, animals and humans. Too little copper can cause deficiency diseases. We absorb copper into our bodies through nutritional intake i.e. meat, fish, cereals and vegetables.
Copper is an effective biocide which results in it controlling organisms such as legionella in water circulating systems and in it restricting marine biofouling when used, for example, as copper-nickel alloy cladding on boat and ship's hulls and offshore structures. Copper compounds are used for their beneficial fungicidal effects on plants; for example, cupric carbonate is employed in copper-based fungicide that is accepted by many organic regimes.
The use of brass or copper instead of other materials for doorknobs and fingerplates in hospitals helps to reduce the spread of nosocomal infections such as the common cold. Copper bracelets are worn by many people and are said to improve the health of the wearer; for example, absorption through the skin can help to relieve arthritic discomfort.
Amongst others, a very warm commendation of the benefits of copper was given by Dr John Rutty in an address to the Royal Society in 1760. Presenting the medical virtues of the vitriolic liquid found in the springs at Parys Mountain in Anglesey he recommended it ‘as a powerful detergent, repelling, bracing, styptic, cicatrizing, anti-scorbutic and deobstruent medicine, as hath appeared by the notable cure they have affected, not only by external use in inveterate ulcers, the itch, mange, scab, tetterous eruptions, dysenteries, internal haemorrhages, in gleets, the fluor albus and diarrhoea, in the worms, agues, dropsies and jaundice.’
Copper is one of a relatively small group of metallic elements that are essential to human health. These elements, along with amino and fatty acids as well as vitamins, are required for normal metabolic processes. Copper is a constituent of many enzymes involved in numerous body functions and is a constituent of hair and of elastic tissue contained in skin, bone and other body organs. There are a number of important copper-containing proteins and enzymes, some of which are essential for the proper utilisation of iron.
The adult body contains between 1.4 and 2.1mg of copper per kilogram of body weight. To maintain this concentration, it is recommended that the daily intake of copper should be 0.4mg/day for children aged 1-3 years and 1.2 mg/day for adults.
Copper-rich foods include most nuts, seeds, chickpeas, liver and oysters. Natural foods such as cereals, meat and fish generally contain sufficient copper to provide up to 50% of the required daily intake. The copper content of supply water is usually measurable but insufficient in its own right to provide the balance of the normal daily intake.
It is rare that problems are found with too much copper in a system. Most copper salts in excess are powerful emetics and overdoses are usually rejected. Only very occasionally, as with the very rare Wilson’s Disease, does a body retain excessive copper.
Being a trace element essential for the health of plants, animals and humans, the distribution and concentration of copper in the environment is important. Typically there is 1 microgram per litre of copper in fresh water supplies. The optimal concentration in living organisms is around 1,000 micrograms per litre and the body metabolism normally adjusts the concentration to be within optimum range.
In the ground, copper is normally present in compounds that are not easily soluble in water. Only a limited percentage, normally less than 1%, is available in soluble form for bioavailability. This can be taken up by the roots of plants as required and is then recycled as leaves and wood decay, concentrating in the top 100mm or so of the soil. Additionally or alternatively, copper is replenished when organic manure is spread. Intensive farming without this recycling can lead to copper deficiency that has to be made up when fertiliser is applied.