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Alloys: Uses & Properties

Instructor: Hemnath (Vikash) Seeboo

Taught Science (mainly Chemistry, Physics and Math) at high school level and has a Master's Degree in Education.

In this lesson, we will discuss how alloys are made. We will also learn about the properties and the wide ranging uses of the various different alloys.

What Are Alloys?

You may not know what an alloy is, but you've probably used one even today! Metallurgists have developed a wide range of different alloys over time. Think of the different utensils that you have in the kitchen or the dental fillings that are used to treat cavities by the dentist, or even the jewels that you wear. These are all examples where alloys are being used in our everyday lives.

An alloy consists of two or more elements mixed together in the molten states. The mixture is then allowed to solidify in a metal or in a sand mold. Every alloy contains a main element, usually a metal, which has a percentage composition that is usually 50% or more.

But why don't we use the metals directly? Metals are certainly useful, but they do not fit all purposes. Alloys to the rescue! In general, alloys have been found to be stronger and harder, less malleable, less ductile, and more corrosion-resistant than the main metal making the alloy.

An alloy mixture is stronger because it contains atoms from different elements that are different in sizes. The atomic arrangements prevents the different atomic layers from sliding over each other if stretched or bent.

Let's take a look at the composition, properties, and uses of four very common alloys.

Bronze

Bronze is an alloy traditionally consisting of mainly copper (78-95%) and tin (5-22%). Depending on the intended usage, it does occasionally contain metals such as manganese, aluminum, zinc, nickel and non-metals such as phosphorus and silicon. Historically, bronze was made before 3000 BC when one pound of copper was mixed with two ounces of tin.

The word 'bronze' comes from the Italian word 'bronzo', meaning 'bell metal'. Besides its sonorous quality, bronze does not generate sparks when struck against a hard surface, making a great material for bells in schools and churches.

Bell made from bronze
Bronze bell

Bronze is also used to make hammers and wrenches.

  • When a small amount of phosphorus is added to the copper-tin mixture, bronze is found to become stronger, more fatigue-resistant and wear-resistant. 'Phosphor bronze' finds its applications in valves, bushings, shafts, gears and bearings.
  • Bronze containing aluminum, called 'aluminum bronze', renders the alloy especially corrosion-resistant, with major uses in pipe fittings, pumps, gears, ship propellers, and turbine blades.

Gold Alloys

Gold in its pure state is very soft and this makes the metal highly malleable and ductile. Gold is commonly used in the jewelry industry, so how is gold changed into chains, rings or earrings? By alloying it with other metals such as copper, silver, and zinc.

Gold alloys are not only hardened, but a variety of colors can be obtained. For example, soft green gold is obtained when gold (75%) and silver (25%) are mixed and alloyed.

Gold alloys have entered the world of electronics as well. When copper and silver are added to gold, its ability to transfer heat and electricity is bettered.

Coupled with its high corrosion resistance, gold alloys are being used in gold-plated connectors as integral parts of plugs and sockets for cable terminations, integrated circuit sockets, and printed circuit boards. These are used in computers, spacecraft, communications equipment, and jet aircraft engines.

The medical industry also uses gold-based alloys, this time containing variable amounts of platinum, rhodium, nickel, titanium and zinc. The most prevalent use of gold alloys is in dental restoration as found in crowns and bridges.

Teeth made of gold
Gold teeth

Gold alloys offer high durability and least reactivity towards the conditions that are present in the mouth.

Steels

Steel is an alloy of iron. To make steel, we take pure iron and add specific amount of carbon. This results in the formation of low-carbon steel and high-carbon steel.

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