Glass is a fluid?

[rakuenso]

I read an article back in 9th grade that glass was an uber viscous fluid. Apparently they measured the glass murals of ancient cathedrals and found that the bottom of the glass was thicker than the top of the glass. Any one know how or what contributes to its viscousness?

[H2SO4]

its an amorphous solid. Meaning it is never a liquid nor a solid. Notice glass just slowly gets soft when hot. Like putty.

 

I don't know why it is like this, but of curse it does have somethng to do with the bonds.

[akcapr]

they probly made it that thick

[YT2095]

the coal tar product called Pitch is similar, if left alone it will actualy Drip once every 10 years or so

[mezarashi]

I read an article back in 9th grade that glass was an uber viscous fluid. Apparently they measured the glass murals of ancient cathedrals and found that the bottom of the glass was thicker than the top of the glass. Any one know how or what contributes to its viscousness?

 

To say that glass is a solid or fluid is probably incorrect. Glasses and other polymers of its kind have a very unusual molecular arrangement upon "freezing". I was quite surprised myself when I first learnt this, but there is no cut-off temperature for glass becoming "solid". Instead, there is a temperature range called the glass transition temperature (search google for this term for more info). Above this temperature glass acts like a rubbery material. Below this temperature range, it acts like a brittle material.

 

It is important to know the characterization of solid and liquid as described by material scientists. For most materials, the molecules will crystallize (form an ordered arrangement, FCC, BCC, Zinc-Blend, etc.) when the substance falls below the freezing temperature and releases energy in the form of heats of fusion. Glass doesn't do this. The molecules just get stuck. At the transition temperature some molecules may still be able move past one another until the temperature is lowered enough until close to none will be able to. It is believed that this state of class is metastable meaning that it should over time crystallize, but I think its stability is still a hot topic in academia.

 

Another interesting note: when glass is at its transition temperature, molecules may slide past one another. There are no discontinuities like in substances like H2O where 0 degrees marks the distinction between water and ice. So you will find that if you are using glass-like polymers in machines that get slightly heated up. Over a prolonged enough exposure you may get the glass melting and forming a new shape! It's a very slow process of course maybe over the course of a week.

[swansont]

Urban legend, and there's plenty out on the web setting the record straight.

 

As H2SO4 stated, it's an amorphous solid. It has the glass transition to solid form instead of undergoing a phase change, which is why it's called (tah dah!)a glass transition.

 

Old glass wasn't perfectly flat. They installed it thick side on the bottom for structural reasons.

[Bettina]

Old glass wasn't perfectly flat. They installed it thick side on the bottom for structural reasons.

 

Grrrr...My dad told me awhile ago, that in very old homes glass became thicker on the bottom because glass was a liquid. Further he said thats why it loosens up.

 

I'm gonna check...

 

Bettina

[ydoaPs]

since it is an amorphous solid, it will "flow" down VERY slowly. that is why old windows make things look wavy.

[Cap'n Refsmmat]

No, old windows are wavy because it's blown glass, not sheet glass.

[ydoaPs]

not that old. sheet glass does it too.

[DQW]

As Swansont pointed out the reason that old windows are bottom heavy is not because glass flows (that really has been debunked). In fact the time constant over which typical silicate glass flows is roughly of the order of millions of years (or longer). However, glass has liquid-like properties beyond its simply being an amorphous solid.

 

Because glass has properties that make it solid-like as well as some that make it liquid-like, it falls under a different category of phases, called (you guessed it) "glasses". Their physics is quite complex because they are nonequilibrium creatures !

 

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

 

http://hypertextbook.com/physics/matter/glass/

[swansont]

As Swansont pointed out the reason that old windows are bottom heavy is not because glass flows (that really has been debunked). In fact the time constant over which typical silicate glass flows is roughly of the order of millions of years (or longer). However' date=' glass has liquid-like properties beyond its simply being an amorphous solid.

 

Because glass has properties that make it solid-like as well as some that make it liquid-like, it falls under a different category of phases, called (you guessed it) "glasses". Their physics is quite complex because they are nonequilibrium creatures !

 

http://math.ucr.edu/home/baez/physics/General/Glass/glass.html

 

http://hypertextbook.com/physics/matter/glass/[/quote']

 

In that context it is possible to come up with a material that has a glass transition at room temperature, so that it could be liquid. But that's not the case for window glass, even the old stuff.

[vrus]

 

Another interesting note: when glass is at its transition temperature' date=' molecules may slide past one another. There are no discontinuities like in substances like H2O where 0 degrees marks the distinction between water and ice.

[/quote']

 

The giant macromolecular structure of Graphite, one of the allotropes of Carbon has a similar structure to what you are saying about glass. That arrangement is what allows it to conduct electricity. Is it possible that glass can also do this at the transition temperature you mentioned ?

[Obba]

Just to throw a spanner into everybodys works,

 

Every liquid, soft and hard material will eventually 'flow' down - towards the centre of gravity.

It might be slow, but it will happen.

[Tetrahedrite]

The giant macromolecular structure of Graphite, one of the allotropes of Carbon has a similar structure to what you are saying about glass. That arrangement is what allows it to conduct electricity. Is it possible that glass can also do this at the transition temperature you mentioned ?

Not quite, glass is amorphous, having no regular repeating unit cell. Graphite, on the other hand, is in fact crystalline (it falls into the hexagonal xtal system from memory). What gives graphite the ability to conduct electricity is that it has layers of delocalised electrons in between the graphene sheets.

[mezarashi]

The giant macromolecular structure of Graphite, one of the allotropes of Carbon has a similar structure to what you are saying about glass. That arrangement is what allows it to conduct electricity. Is it possible that glass can also do this at the transition temperature you mentioned ?

 

As Tetrahedrite just said. The sliding you get in graphite is sliding between sheets of it rather than the sliding of individual molecules. But most importantly, graphite's ability to conduct comes from its pi-bonding rather than its ability for its crystal sheets to slide past one another.

 

A transition temperature range does not exist for graphite as there is a clear distinction between liquid graphite and its solid crystalline form.

[Skye]

What gives graphite the ability to conduct electricity is that it has layers of delocalised electrons in between the graphene sheets.

I thought it was because of the alternating double and single bonds within the sheets?

 

(edit: Actually I suppose it would have to be both, in order for electrons to flow through the material)

[YT2095]

The giant macromolecular structure of Graphite, one of the allotropes of Carbon has a similar structure to what you are saying about glass. That arrangement is what allows it to conduct electricity. Is it possible that glass can also do this at the transition temperature you mentioned ?

 

IIRC from my old chem lessons, glass in it`s liquid state Will conduct electricity also

[BigMoosie]

...Apparently they measured the glass murals of ancient cathedrals and found that the bottom of the glass was thicker than the top of the glass...

 

That is true, however some time after they measured a couple more of them and found that some were thicker at the top or sides, it turned out the windows were just made badly and unfortunately they happened to measure the only windows with the bulge at the bottom.

[mrblond5311]

I've got a weird question. What would happen if we "super-cooled" it? Kind of like what you can do with water & bring it below the freezing point so fast it doesn't have enough time to freeze at 0 centigrade. Let's say we bring it to -20 centigrade!

[RyanJ]

I've got a weird question. What would happen if we "super-cooled" it? Kind of like what you can do with water & bring it below the freezing point so fast it doesn't have enough time to freeze at 0 centigrade. Let's say we bring it to -20 centigrade!

 

 

It would probably turn to a true crystalline substance in that case but then again maybe not.

By the way I would not call it super cooling, if you took it does to say 1K then that may be considered super-cooled I think

 

Cheers,

 

Ryan Jones

[jdurg]

Super-Cooling means that a liquid is brought down below its freezing point but still remains a liquid. One degree below the freezing point of a pure liquid is considered 'super-cooled'. It's a similar principle to super-saturation.

[ecoli]

Why can't it be solid AND fluid? What's wrong with that thinking?

[RyanJ]

Why can't it be solid AND fluid? What's wrong with that thinking?

 

|Like light being a particle and a wave you mean? I suppose that would work as it is true

 

Cheers,

 

Ryan Jones

[YT2095]

it`s an amorphous solid, there`s no specific transition between solid/liquid phases, but at SRTP it`s considered a solid.