Glass

Question 1

What are some features that Glassy materials have?

Answer 1

• non-crystalline structure (lack long-range, repeatable order)
• typically produced from the liquid state by continuous cooling
• glasses exhibit the “glass transition temperature” (Tg)
• glasses can be formed from most liquids if the cooling rate is high enough

Question 2

What are Amorphous Materials?

Answer 2

• possess an amorphous structure (like glasses)
• spontaneous decomposition without softening
• lack of internal stability to retain supercooled state

Question 3

What are Glasses?

Answer 3

• supercooled liquids
• vapor-deposited phases stable enough to exhibit Tg
• gels and sols that exhibit Tg

Question 4

Typical glass contains what?

Answer 4

• formers
• fluxes
• stabilizers

Question 5

Define Formers

Answer 5

• make up the largest percentage of the mixture to be melted (usually in the form of sand)

Question 6

Define Fluxes

Answer 6

• this lowers the temperature at which the former will melt

- common ones are sodium carbonate (soda) and potassium carbonate (potash)

Question 7

Define Stabilizers

Answer 7

• make the glass strong and water resistant

- common one is calcium carbonate

Question 8

True or False

There was always stabilizers in glass.

Answer 8

FALSE

Originally stabilizers were not added to glass. B/c of this, glass was not stable and weak towards water.

Question 9

What are the types of forces that may act on a glass material?

Answer 9

• tensile force
• compressive force
• shear force

Question 10

Define Tensile Force

Answer 10

• force that exerts a pull on the material
• if mild, there is a pull on the material without permanent deformation
• if force is strong, it may cause permanent deformation (glass will fracture before deformation)

Question 11

Define Compressive Force

Answer 11

• acts to squeeze the material

Question 12

Define Shear Force

Answer 12

• acts on the material in a manner similar to a pair of shears to slide one part of the material in one direction and another in the opposite direction

Question 13

What causes Glass to Break?

Answer 13

• only from tensile strain
• tensile forces are the most important in glass fracture because they give rise to tensile strain within the glass
• under normal environmental conditions glass undergoes brittle fracture
• b/c glass has no grain structure the fracture surfaces are relatively smooth

Question 14

What are some terms that are needed to be known for Glass Fractography?

Answer 14

• mirror
• mist
• hackle
• wallner lines