Glass

Question 1

Describe the structure of glass

Answer 1

It is an amorphous structure, most are made up of silica tetrahedrons

Question 2

What are the three types of oxides used to make glass?

Answer 2

Glass formers, Intermediates and Modifiers

Question 3

What are intermediates used for?

Answer 3

Help to extend The amorphous structure, however can’t make glass by itself

Question 4

What are modifiers used for?

Answer 4

The break covalent bonds, as a result the viscosity of the glass decreases, therefore lower temps can be used to make glass.
Changes the property of glass

Question 5

Describe the graph of viscosity for a crystalline material.

Answer 5

As temp increases viscosity increases and at Tm viscosity decreases rapidly

Question 6

Describe the graph of viscosity for amorphous materials

Answer 6

Gradual decrease in viscosity as temp increases (looks like 1/x graph)

Question 7

Describe the process of glass annealing and why glass has to be annealed

Answer 7

Raw material melted,then glass is quenched causing thermal stresses due to high temp drop. Annealing- using rollers heat below Tg then cool down extremely slowly in furnace, causing the thermal stresses to be removed

Question 8

How is laminated safety glass formed?

Answer 8

Thin layer of polymeric film is placed in between two panels of glass, everything is compressed (releasing air pockets), reheated to low temp causing a composite to form which sticks everything together

Question 9

What is the softening point?

Answer 9

Glass will deform under its own weight ( glass is formed above softening point).

Question 10

Describe the process of tempering and initial conditions

Answer 10

Used to increase mechanical properties, can only use annealed glass, Tempering- reheat to above Tg but below softening point, then quench. This causes compressive forces to be produced at the surface and tensile forces to be produced in the centre making it harder tougher

Question 11

Describe the process of pressing glass

Answer 11

Glass gob is squashed into shape of mould

Question 12

Describe the process of blow moulding

Answer 12

Softened glass gob forms parison, parison injected with compressed air into shape of mould

Question 13

Describe the process of the float glass process

Answer 13

Furnace heats glass, glass passes over molten tin to ensure even thickness and a smooth surface, glass is then annealed in a lehr( industrial annealing furnace). Glass is then cooled

Question 14

Describe the process of producing glass fibres

Answer 14

Raw material put in furnace and refined, molten glass collected by winders, glass fibres coiled up