04-02-2013, 12:50 PM
An Introduction to Glass Technology
[attachment=49522]
What is Glass?
Glass is a state of matter, not a material
Amorphous material, or glass, is a solid whose atoms are arranged with no long term order
The opposite of amorphous materials is a crystalline material
Crystalline materials have some periodic crystal structure that results in long term order
Silicon Dioxide, SiO2
Chemically, SiO2 is an ideal glass network former
Silicon-Oxygen chemical bonds are strong and covalent
Each Silicon bonds to four Oxygen atoms, giving a 3D structure
Easy to cool liquid SiO2 into an amorphous state because quartz only forms over a geologic time span
Properties of Commercial Glass
Typical commercial glasses contain SiO2, with Na+ and Ca2+ modifiers
Very high theoretical strength
Very high resistance to corrosion
Thermal and electrical insulator
Easy to work into shape
Cheap to manufacture
Transmits visible light, but absorbs infrared and ultraviolet
Thermal Tempering to Increase Strength of Glass
Form molten glass into desired shape, and cool very rapidly
Surface is cold while inside is still hot
Mismatch in temperature gives rise to compressive stress on the surface
Glass does not break under compression, so result is a much stronger sample
Ion-Exchange Process to Increase Strength of Glass
Glass initially contains small modifiers, such as Na+
Glass is placed in a molten salt, often containing K+
Na ions slowly diffuse out of glass, while K+ ions diffuse in
K+ ions are much larger than Na+, giving rise to compressive stress near the surface
Result is a much stronger sample, as with thermal tempering
Summary
Any material that lacks long-range order is a glass
SiO2 has many properties that make it the most successful commercial glass
Network modifier ions can be added to engineer more desirable material properties
Modern processing technology, such as thermal tempering or ion-exchange, can further improve material properties
[attachment=49522]
What is Glass?
Glass is a state of matter, not a material
Amorphous material, or glass, is a solid whose atoms are arranged with no long term order
The opposite of amorphous materials is a crystalline material
Crystalline materials have some periodic crystal structure that results in long term order
Silicon Dioxide, SiO2
Chemically, SiO2 is an ideal glass network former
Silicon-Oxygen chemical bonds are strong and covalent
Each Silicon bonds to four Oxygen atoms, giving a 3D structure
Easy to cool liquid SiO2 into an amorphous state because quartz only forms over a geologic time span
Properties of Commercial Glass
Typical commercial glasses contain SiO2, with Na+ and Ca2+ modifiers
Very high theoretical strength
Very high resistance to corrosion
Thermal and electrical insulator
Easy to work into shape
Cheap to manufacture
Transmits visible light, but absorbs infrared and ultraviolet
Thermal Tempering to Increase Strength of Glass
Form molten glass into desired shape, and cool very rapidly
Surface is cold while inside is still hot
Mismatch in temperature gives rise to compressive stress on the surface
Glass does not break under compression, so result is a much stronger sample
Ion-Exchange Process to Increase Strength of Glass
Glass initially contains small modifiers, such as Na+
Glass is placed in a molten salt, often containing K+
Na ions slowly diffuse out of glass, while K+ ions diffuse in
K+ ions are much larger than Na+, giving rise to compressive stress near the surface
Result is a much stronger sample, as with thermal tempering
Summary
Any material that lacks long-range order is a glass
SiO2 has many properties that make it the most successful commercial glass
Network modifier ions can be added to engineer more desirable material properties
Modern processing technology, such as thermal tempering or ion-exchange, can further improve material properties