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COPPERS AND COPPER ALLOYS.
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Bronzes.
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Brasses.
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Nickel Silvers and Paktong.
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Sheffield Plate.
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Copper Compounds.
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COPPER AND HEALTH..
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We cannot live without Copper
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How much copper?.
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Copper in the Environment
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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 -
COPPER with
·
tin makes
Bronze
·
tin and phosphorus makes
Phosphor bronze
·
aluminium makes
Aluminium bronze
·
zinc makes
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
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
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 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
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
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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.
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