Alloys

Goal of the class

• To introduce alloys and their uses

• Question of the day: Why is carbon added to iron?

• Previous Answer: Long chains of carbon atoms make up the backbone of crude oil constituents.

What is an Alloy?

• Alloy is a mixture of two or more elements with a certain fixed composition in which the major component is a metal.

• Examples include:– Stainless steel– Bronze– Solder

Why Make Alloys?

• To increase the hardness and strength of a metal

• To prevent corrosion or rusting

• To improve the appearance of the metal surface

Bronze

• Bronze is an alloy consisting primarily of copper and the addition of other metals, usually tin.

• A very important advancement in human history (Bronze Age).

• Used for 3rd place medals.

Properties of Bronze

• Hard and Strong• Doesn’t corrode easily• Has shiny surface

Steel

• Steel is composed of 99% iron and 1% carbon.

• It is very hard and strong and used in the construction of buildings and bridges.

Steel

Stainless Steel

• Contains the following:– 74% iron– 8% carbon– 18% chromium

• Stainless steel is strong, shiny and corrosion resistant.

Stainless Steel

Nickel Titanium

• Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium

• Nitinol alloys exhibit two closely related and unique properties: – shape memory– superelasticity

Amalgam

• In dentistry, amalgam is an alloy of mercury with various metals used for dental fillings.

• It commonly consists of– mercury (50%)– silver (~22–32% )– tin (~14%)– copper (~8%)– other trace metals

Aluminium Alloys

• Duralumin, used in aircraft manufacture, is 96 percent aluminium and 4 percent copper and other metals.

Aluminium Alloys

Atomic Arrangements

• When force is applied, layers of atoms in pure metal slide. So, metals are ductile.

• There are empty space between the atoms. When it is knocked, the shape of the metal changes. So, metals are malleable.

Atomic Arrangements

• The presence of atoms of other metals that are of different sizes disturb the orderly arrangement of atoms in the metal. This reduces the layer of atoms from sliding. Thus, an alloy is stronger and harder than its pure metal.

Homework

• Please complete Chemical Building Blocks workbook page 53-54