GLASS

Dr Sharipah Ruzaina Syed Aris

GLASS

• Non-crystalline solid because the atoms in glass are randomly arranged.

• Hard, brittle and transparent material• No definite melting point but soften

gradually when heated and resistant to chemicals

• It is composed mainly of sand (silicates, SiO2) and an alkali.

• Is a mixture of sodium silicate, potassium silicate, calcium silicate and lead silicate.

Properties of Glass

• Solid and hard material• Disordered and amorphous structure• Fragile and easily breakable into sharp pieces • Transparent to visible light• Inert and biologically inactive material. • Glass is 100% recyclable and one of the safest

packaging materials due to its composition and properties

• Glass is used for architecture application, illumination, electrical transmission, instruments for scientific research, optical instruments, domestic tools and even textiles. Glass does not deteriorate, corrode, stain or fade and therefore is one of the safest packaging materials.

TYPES OF GLASS

Soda lime glass Soda-lead glass Borosilicate glass Fused silica glass

Soda lime glass

• Most common and less expensive.• The composition of soda-lime glass is normally

60-75% silica (sand), 12-18% soda, and 5-12% lime.

• Appropriate to be use in flat glass in windows (light transmission)

• It has a smooth and nonporous surface that allows glass bottles and packaging glass to be easily cleaned

• resistant to chemical attack from aqueous solutions so they will not contaminate the contents inside or affect the taste.

• Some of the use of soda-lime glass is primarily used for bottles, jars, everyday drinking glasses, and window glass.

Soda-lead glass

• Composed of 54-65% SiO2, 18-38% lead oxide (PbO), 13-15% soda (Na2O) or potash (K2), and various other oxides.

• When the content of PbO is less than 18% is known as crystal glass.

• Easy to melt and much more expensive than soda-lime glass.

• It has a high refractive index giving high brilliance glass (sparkles).

• Make it appropriate for decorating purposes.

Borosilicate glass• composed of silica (70-80%), boric oxide B2O3

(7-13%) and smaller amounts of the alkalis (sodium and potassium oxides) such as 4-8% of Na2O and K2O, and 2-7% aluminum oxide (Al2O3).

• Greater resistance to thermal changes and chemical corrosion.

• Used in the home for cooking plates and other heat-resistant products. It is used for domestic kitchens and chemistry laboratories, this is because it has greater resistance to thermal shock and allows for greater accuracy in laboratory measurements when heating and cooling experiments.

Fused silica glass

Almost 100% silica Highly heat-shock resistant glass Can be heated to extremely high

temperatures and then plunged into ice-cold water without cracking.

Expensive Use in laboratory glassware and optical

fibers

Coloured glass

By adding certain oxides. Exp:

Colour of the glass Chemicals

Red Gold, copper, selenium oxides

Blue Cobalt and copper silicate

Green Chromium and ferrous oxide

Opalescent Calcium phosphate

Yellow Ferric oxide