Chemguide: Support for CIE A level Chemistry
Learning outcome 9.1(e)
This statement is a brief introduction to some ceramic materials involving Period 3 elements.
Before you go on, you should find and read the statement in your copy of the syllabus.
The IUPAC Gold Book defines ceramic as
In the first sentence, the word "sintered" refers to the process of sintering. Sintering happens when you heat a powdered material to a temperature below its melting point, and new bonds are formed between the grains of powder to form one large mass.
The most commonly used definition (including by CIE) tends to include what the note says. There are several modern ceramic materials which don't actually involve a metal. The syllabus, for example, includes silicon(IV) oxide, and there is a past question which tells you that silicon carbide, SiC, is used in ceramics, and asks you to deduce things about it.
This is such a huge topic that I will just stick closely to what the syllabus asks.
Physical properties of ceramics
Ceramics all have giant structures of one type or another, with strong bonds between the atoms (or ions) which make them up.
The physical properties
The strong bonds holding the atoms (or ions) together in three dimensions will make the ceramic hard and strong, but also brittle.
Think about a ceramic wall or floor tile as a simple example. The tile is obviously hard, and you can stand on a floor tile, or place heavy furniture on it without it breaking - so it is strong. On the other hand, it isn't difficult to break a tile in half by snapping it, especially if you score a shallow line on it first with a cutting tool - it is brittle.
This is unlike a metal, which would bend before it fractured - you can bend or stretch metals. Atoms in metals can roll over each other without breaking the bonds. In a ceramic, you either have to break covalent bonds in three dimensions or, if you distort an ionic lattice, it brings like charges together, which splits the lattice apart. The lattice is either all in one piece, or else broken apart.
Ceramics have high melting points because of the need to break the strong covalent or ionic bonds holding the giant structure together. It takes a very high temperature to do this.
Most ceramics are good electrical insulators. If they are covalent, there are no free electrons to move around. If they are ionic, the ions aren't free to move in the solid.
Examples of electrically conducting (including superconducting) ceramics are beyond the scope of this syllabus.
Some specific examples
This deals with the uses of modern ceramic materials involving magnesium oxide, aluminium oxide and silicon(IV) oxide, and the relationship with their structures.
Ceramics made from magnesium oxide are used in (amongst other things):
Various web sources describe this as the most important oxide ceramic.
Uses of aluminium oxide ceramics include:
Silicon(IV) oxide (silicon dioxide)
Uses of silicon dioxide ceramics include:
© Jim Clark 2010 (last modified May 2014)