1. Glass – a solid or a liquid?
Kyle Foo (9)
Good afternoon, today I will be presenting on whether glass is a solid or a liquid.

2. Introduction Can we pour glass? Can we draw a pint of glass?
In a commonsense way, glass being a liquid is almost impossible. Can we pour a cup of glass? Can we draw a pint of obsidian? To understand this further, we need to know what glass is made of.

3. What is glass made of Most common type of glass - soda-lime glass
70-74% silica
Sodium carbonate to lower the melting point to 1500°C to simplify processing
Lime, magnesium oxide and aluminum oxide added to provide for a greater chemical durability
The most common type of glass is soda-lime glass. Soda-lime glass is 70-74% silica. It gets the name ‘soda’ from the sodium carbonate added to it to lower the melting point to 1500°C so that processing of the glass will be easier, whereas the name ‘lime’ comes from the calcium oxide added to it to provide for a greater chemical durability.

4. Who and how was glass discovered
the first true glass was made in coastal north Syria, Mesopotamia or Old Kingdom Egypt
The earliest known glass objects were beads
The history of creating glass can be traced back to 3500 BCE in Mesopotamia. It is believed the first true glass was made there. The earliest known glass objects were glass beads.

5. How glass is used Optical waveguides Modern glass art Windows Etc.
How glass is used. Glass is used for many objects. Apart from the common glass objects, like windows, mirrors, etc; it is also used in optical waveguides, scientific equipment like microscopes, and even be made of works of art.

6. Glass – a solid or a liquid?
Instead of asking “Is glass a solid or liquid?” Why not we change the question to ….

7. Glass – an amorphous solid or a supercooled liquid?
“Is glass an amorphous solid, or a supercooled liquid?”

8. The molecular structure of glass
Crystal
Glass
Now I will be explaining the molecular structure of glass. As you can see here, the crystal solid is rigid and uniform throughout. This is because when it freezes, it arranges itself into lattices. However, because glass comes from a supercooled liquid, its molecular shape is irregular.

9. Conversion from liquid to solid for…
Crystal
Glass*
The liquid is cooled
At the freezing point, the molecules arrange themselves in a lattice
Intermolecular forces hold them together
It is now a solid
The liquid is cooled
It remains liquid even below its melting point and becomes supercooled
Its viscosity rises rapidly and continuously
It forms a thick syrup
It eventually forms an amorphous solid
This table compares the ways that both crystal and glass respectively transform from liquid to solid. I am sure most us are already familiar with crystal. So I would not bore you with the points. But something to take note of under glass is that it remains liquid even below its melting point. When a substance is liquid below its melting point, we call it a supercooled liquid. However, this can only happen if the rate of cooling is faster than the rate that molecules can crystallize. Another example of a supercooled liquid is freezing rain.
* The transition into glass only happens if the cooling rate is faster than the rate at which molecules can organize into a crystalline state

10. Characteristics of supercooled liquids
A liquid lowered below its freezing point WITHOUT becoming a solid
exists in stratiform and cumulus clouds
there are freezers that supercools drinks so that when it is opened it ‘slushes’ over
A supercooled liquid is a liquid lowered below its freezing point, without becoming a solid. It exists naturally in certain types of clouds. One example of a supercooled liquid is the 7-Eleven ‘Slurpee’, which when opened, turns into a solid and ‘slushes’ over.

11. Characteristics of amorphous solids
No long-range atomic order
Has the properties of a solid
In principle, given a sufficiently high cooling rate, any liquid can be made into an amorphous solid
Examples are cotton candy, polystyrene, custard
Another way of looking at glass is using the concept of amorphous solid. What is amorphous solid? An amorphous solid has no long-range atomic order. It means that its molecular structure is not uniform throughout. An amorphous solid has the properties of a solid. It can be made from a supercooled liquid. Examples are cotton candy, polystyrene and even custard.

12. But doesn’t glass flow?
Have you ever seen an antique window pane? These window panes are fatter at the bottom than on top. This has led many people to the misconception that glass is a liquid, thinking that the glass flows downwards over time. However, this is caused because of a certain glass-making technique popular during that time. For glass to completely turn into a liquid without heating it, it would take 10 to the power of 32 years. This is many times longer than the estimated age of the universe! In other words, no one has proven this hypothesis.

13. Conclusion I conclude that glass is an amorphous solid, as:
It fits the criteria for being an amorphous solid, and
It does not flow
In conclusion, glass is an amorphous solid because it fits the criteria of being an amorphous solid and it does not flow.

14. Bibliography http://en.wikipedia.org/wiki/Glass
Thank you very much for your attention. I hope you find the discussion interesting.