Glass is not only a material that is defined by its transparency, but it is transparent in its contribution to the modern age, performing its duty as the backbone to the information revolution quietly, in the background of many of our daily routines. Glass is the base material on which many technologies are driving ahead: from the screens on our interactive, touchsensitive phones, computers and tablets and the fibreoptic cables that carry masses of digital information to the more heroic, press-worthy products, such as glass that is self-cleaning or beautiful cut-glass.
By combining glass with other materials, such as plastics, we can enhance its properties and ‘mend’ some of its inherent flaws. Examples include glass that can block out UV-rays, glass that is bullet-proof or shatterproof, and glass fibres that can be added to plastics to enhance their strength.
Soda-lime is one of the most widely used forms of glass and the workhorse of the glass family, exploited for its hardness, transparency and chemical inertness. It is created by fusing several substances and silica (SiO2), in the form of sand, constitutes the largest part, with a mixture of sodium oxide (soda ash) (12–16 per cent), calcium oxide (lime) (5–11 per cent), magnesium oxide (1–3 per cent) and aluminium oxide (1–3 per cent) making up the other ingredients. The addition of the soda serves to reduce the melting temperature and that all-important transparency, with tinges of green, is the result of impurities in the ingredients.
Image: Lemon squeezer
Key features
•Poor thermal shock resistance
•Low cost
•Good resistance to weathering
•Good chemical resistance
•Brittle
•Melts at 1500ºC (273ºF)
•Recyclable
Sources
Widely available.
Cost
Soda-lime glass is very inexpensive.
Sustainability issues
According to the British Glass Manufacturers’ Confederation, the energy saving from recycling a single bottle will power a 100-watt light bulb for almost an hour. As mentioned, the green tint that is present in much standard glass is due to iron impurities. In order to obtain a more brilliant sparkle, a small amount of barium is added.
Production
Soda-lime glass is one of the most versatile types of glass in terms of production. It can be formed by hand to produce one-off art pieces, but is also suited to super high volumes and rapid rates of mass-production. Techniques used include hand blowing, either freeblown or blown into various types of moulds. It can be extruded, cast and cold worked by various cutting and engraving techniques and it can also be drawn into very fine fibres –fibre optics. The term ‘float glass’ is used to describe flat sheets of glass that have been made by being floated down a bath of molten metal.
Typical applications
Its impossible to narrow down the typical applications of soda-lime glass, because it is used in everything from window panes to milk bottles.
–Bohemian glass from the Czech Republic, known for its art glass, contains a large amount of lime and silica giving it a high clarity and brilliance similar to lead glass.
–Float glass
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–Versatile processing –Low cost –Good chemical resistance –Widely available –Recyclable |
–Brittle –Poor thermal shock resistance |