14 DAY TRIAL // Most of the metals we use are alloys, combinations in which one chemical is a metal. That's because pure metals rarely have the ideal properties for a certain task, but they can be improved by adding other metals.
Resistance, hardness, melting point and electric conductivity are properties linked to the crystalline structure of the metal. All these modify when mixed with another chemical. Alloys can contain non-metal elements, like silicon, carbon or phosphorus, but most alloys are made entirely from metals. Steel, for example, is an alloy of iron and carbon, but allied steels contain also nickel, silicon, manganese or chromium.
Alloys can be "solid substitutional solution", with elements dissolved in one another. The crystalline network of one element contains the atoms of the other element in positions that would be normally occupied by the atoms of the first element.
The second case is of "solid interstitial solution". The atoms of the second element occupy spaces between the atoms of the crystalline network of the first element.
The third case is the formation of intermetal compounds. Two metals combine chemically for forming a crystalline compound with a reticulate structure. This structure contains atoms of the both metals arranged in a regular pattern. In some alloys, the structure changes in time, and with this their properties. This is called aging.
1.Allied steels have a modified base structure, which makes them harder, softer, more elastic or more resistant, depending on the necessity of the application.
Manganese steel contains 1 % carbon and 11-14 % manganese, being employed for components experiencing high degree of intense abrasion, like excavator bins.
Common stainless steel, called 18-8, is made of iron allied with 18 % chromium, 8 % nickel, and 0.08 % carbon. Other stainless steels contain 12-30 % chromium, with smaller amounts of other metals, like nickel, molybdenum and copper. These steels are used for making bearings' balls, chemical plants' machinery, turbine palettes, washbasins, and cutlery.
2.Coin alloys are resistant to wear and tear. For example, the British one pound coin is made of 70 % copper, 24.5 % zinc and 5.5 % nickel. The 50 pence, 10 pence, and 5 pence coins are made of 75 % copper and 25 % nickel. The 20 pence is made of 84 % copper and 16 % nickel. Two pence and one penny coins are made of 97 % copper, 2.5 % zinc and 0.5 stannum (tin).
3.The oldest alloy made by humans is the bronze, 6,000 years ago. It contains about 75 % copper and 25 % tin. Modern bronzes may not contain tin at all, but a wide array of other metals.
4.Phosphorous bronzes are made by adding 0.5 % phosphorus to a copper-tin bronze, containing 85-90 % copper. With less than 0.3 % phosphorus, the alloy is elastic and non-conductive. This alloy is used for making contact reinforcement for relays, switches acted by electromagnets. The reinforcements are slightly joined for making contact. They do not magnetize, so that they detach easily at switching off the current.
When the phosphorus level is higher, the alloy turns harder, because it forms a chemical called copper phosphore. This alloy is common in machines and engines casings.
5.Lead bronzes are used for casings that must resist to high speeds and pressures. It contains 3.5 % lead added to the phosphorous bronze.
There are also bronzes made of copper, tin and lead (just 0.5 %). They are used for making the sets for vapor conducts and ornamental works. Tin bronzes with 20 % lead are used for high performance casings.
6.Red bronze contains zinc. Traditionally, they contain 88 % copper, 8-10 % tin and 2-4 % zinc. Nickel red bronzes contain 5 % lead. In other times, they were used for making the riffle pipes, now they are used for making machines and bearings.
7.Aluminium bronzes. They do not contain tin at all, but besides aluminium, there may be included nickel, iron or manganese. They are as hard as soft steel and very resistant to corrosion, including of diluted acids. They are used for ships' propellers, heavy hydraulic and chemical machines, reservoirs and acid-resistant pumps.
8.Brass is made of copper and zinc (up to 30 %), and it can include tin, lead or aluminium. It is very ductile (it can be easily stretched for making wires). Initially, it was developed for making bullet tubes (and it is still used for this purpose), but it is also used for making valves and sets for pipes, and also the basements of the light bulbs.
Special brass, harder and more resistant than bullet brass, is obtained by allying copper and zinc with manganese, iron, tin, lead and aluminium. It is easy to process and ship propellers can be made of this.
Argentan is made of copper (65 %), allied with zinc (17 %) and nickel (18 %). It looks like silver (that's why it is also called German silver) and it is used for making cutlery. Usually it is plated with silver, and traded as galvanized argetan (EPNS).
9.Most jewels made of "pure gold" are an alloy containing a standard proportion of gold and other metals for increasing hardness. The number of carats (K) defines how many mass parts of pure gold are found in 24 parts of the alloy.
10.Aluminium alloys contain up to 15 % silicon, plus small amounts of other metals like copper, iron, nickel, manganese and zinc. From these alloys are made cylindric blocks of the engines and pieces for engines and plane fuselage.
Alluminium alloys proper for forging, laminating, and other processes contain up to 7 % magnesium and about 1 % manganese. Extremely strong alloys, largely used in aviation, contain about 5 % zinc and small amounts of copper, magnesium and manganese.
Duralumin contains 3.5-4.5 % copper, 0.4-0.7 % magnesium and manganese and up to 0.7 % silicon. It turns harder by heating till 500o C and sudden cooling in water. In a few days, the alloy turns much harder. It is used for planes, dirigible balons and space ships.