Glass
Glass is made mainly by melting silica (silicon dioxide, SiO₂) from sand, together with other materials, and cooling it quickly. Ordinary window glass is soda-lime glass, made from sand, sodium carbonate and limestone. Glass is transparent, hard, brittle and chemically unreactive, and it is a good electrical insulator.
Key idea
Different additives give glass different properties: adding boron oxide makes heat-resistant borosilicate glass, while adding lead(II) oxide makes sparkling lead crystal glass.
Types of glass
- Soda-lime glass – windows, bottles and jars (cheap and easy to shape).
- Borosilicate glass – laboratory apparatus and cookware, because it withstands sudden heating without cracking.
- Lead crystal glass – decorative glassware, because it is heavy and sparkles.
Ceramics
Ceramics are made from clay and other minerals, shaped while soft, then hardened by firing (heating) at a very high temperature. Ceramics are hard, brittle, chemically inert, have a very high melting point, and are good heat and electrical insulators. Common examples are floor tiles, pottery, bricks and the white insulator around a spark plug. Modern advanced ceramics are even used in cutting tools and in the heat shields of spacecraft, because they stay hard and stable at temperatures that would melt or weaken most metals.
One useful feature of glass is that it can be recycled. Used bottles and jars can be crushed, remelted and shaped into new glass again and again without losing quality, which saves raw materials and energy. Ceramics, however, are much harder to recycle once they have been fired.
Comparing the two
| Property | Glass | Ceramic |
|---|---|---|
| Transparency | usually transparent | usually opaque |
| Brittleness | brittle | brittle |
| Melting point | high | very high |
| Electricity | insulator | insulator |
Example
In a Malaysian home, glazed ceramic tiles cover bathroom floors because they are hard, water-resistant and easy to clean, while heat-resistant borosilicate glass is used for the measuring jugs in the science laboratory.
Remember
Both glass and ceramics are hard but brittle – they shatter rather than bend when struck sharply, and both are good insulators of heat and electricity.