Types and Properties of Glass
The kinds and properties of glass are varied by the kind of glass it is. Glass type is determined by additives during manufacture and the process used to make the glass.
Float glass is produced by floating molten glass over a bed of a liquid tin, which has a
low melting temperature. Float glass is made from a mixture of sand, limestone, soda ash,
dolomite, iron oxide and salt cake which are heated to a temperature of 1500 degrees
Float glass is high quality like sheet glass with good optical clarity like plate glass.
Commonly know as BPSG this type of glass is used in semiconductor device fabrication. The
glass includes Boron and Phosphorus impurities.
Bulletproof glass or, as it should be more properly known, bullet resistant glass is
actually constructed of either strong plastics such as polycarbonate or layers of laminated
Due to the layering of glass and plastic sheets bulletproof glass is very thick, varying
Crown glass has good optical and mechanical properties and is resistant to chemical and
environmental impact. These properties of glass makes it ideal for lenses and in optical instruments. These
properties were once useful for glazing but as crown glass could only be made in small
quantities it was surpassed by modern variations.
FSG has a low dielectric constant which makes it ideal for use in integrated circuit
Most commonly used when privacy is required, frosted glass allows light to pass through it
but obscuring it so that the view is not clear. Frosted glass is produced by sand blasting
or acid etching float glass.
GeSbTe is a phase change material which is used for applications such as rewritable DVD's.
The glass alloy has a crystallisation temperature of 400°C and a melting point of 600°C. A
process of heating the alloy to its melting and crystal state allow the DVD's memory to be
erased and re-written.
Insulated glass, or double glazing as it is more commonly referred to consists of two sheets
of glass separated by a sealed inner core filled with air which provides insulation.
Insulating glass is used in homes in colder climates to improve thermal performance.
Laminated glass is used most commonly when safety is paramount. Unlike normal float glass
laminated glass does not break into harmful pieces when it is broken. Two panes of glass
sandwich a resin core which allow the glass panes to stay complete when broken.
Heat Resistant Glass
Borosilicate glass is a type of heat resistant glass which is most commonly known as Pyrex.
Heat resistant glass is not affected by changes in temperature due to it having a low
thermal expansion coefficient. Rapid heating can cause it to break but instead of shattering like float glass it is most likely to fracture in one place. Heat resistant glass is less
dense than normal glass.
Toughened glass is used primarily because of its safety features. Toughened glass is impact
resistant and when it is broken it shatters into small, harmfless cubes. Toughened glass
is made from annealed glass which is heated and then rapidly cooled. The rapid cooling
places internal stresses on the glass which allow it to be strong and break into regular
cubes. Due to the internal stresses toughened glass cannot be cut to size after the
toughening process, therefore all shapes must be cut before the toughening process.
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