4.2C - Glass

Glass is primarily composed from silca sand (silicon dioxide) together with limestone (calcium carbonate) and Soda Ash (sodium carbonate) and small quantities of a few other chemicals.

It takes a great amount of energy to produce glass from sand, melting point around 1700 Celsius so scrap glass is added. This makes recovery of glass important. Adding scrap glass makes the process more economical.

Characteristics of glass

• Transparency, allows light to pass through thus allowing you to see the contents of a jar or through a window.

• Colour, colour can de deigned in my adding chemicals

• Strength – low tensile strength but high compressive strength

• Brittleness, it has a low impact strength and thus will shatter easily (low toughness).

• Hardness, high hardness and wont scratch readily.

• Un-reactivity – is chemically inert so leaching of acid based contents is not a problem.

• Non-Toxic due to its un-reactivity therefore suitable for food storage.

• Non-porous, thus will hold liquids or stop moisture seeping from outside.

• Insulator.

• 100% recyclable and is continuously recyclable

Design contexts

There are different types of glass which are used in a variety of design contexts.

Recovery and disposal of glass

• Recycled glass is known as cullet which is added to new raw materials to make new glass.

• It reduces the energy required thus the costs in producing new glass.

• When recycled the glass is separated into the same colours groups (due to chemical compounds) then are crushed .

• Improves environmental concerns such as the extraction of raw materials, energy consumption, and reduced pollution.

• It is continuously recyclable