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MRCHEM
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Why Do Glasses Doesnt Have A Melting Point?
And Are Glasses Liquid?thanks
And Are Glasses Liquid?thanks
LURCH said:The "glass is a liquid" story has been around the web a long time, but I've never heard that bit about glass having no melting point before.
1) Glass is a solid. Not crystaline, but an amorphous solid.
2) Glass melts.
Until about 4 years ago, I was living in Brisbane. Wish I had of known about this then; I could have gone to see it.nazzard said:Another example for a high degree of viscosity is shown in the famous http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml" . thrilling
ZapperZ said:Glass, for all "practical" purposes, can be considered to be a "solid", if we consider that under a normal time span, it maintains its shape. However, the "glassy phase" is actually quite complex and is an active area of study in condensed matter/solid state physics. If you study it like that, you can consider ordinary glass as being a liquid but with an extremely high degree of viscosity. That is why old stain glass windows in medieval churches appear to sag right now.
Physics Monkey said:Actually, I believe this myth that cathedral glasses show signs of flow is actually not true. There was a nice article in the American Journal of Physics some years ago (Am. J. Phys. 66, 392-396, 1998) that basically showed the time scales were wrong. Also, I think the lack of flow in many Roman glasses is taken as further evidence that medieval glasses could not possibly have flowed. As I understand it, the irregularities in thickness are most reasonably attributed to the glass making process used.
ZapperZ said:Actually, I think there was another AJP (or was it Eur. J. Phys.) paper that did a study on this and show that there is actually a "sagging" effect on very heavy glass from medieval churches. I'm not talking about "thickness" irregularities (this is another separate unresolved issue because it can't be just a matter of coincidence that ALL the irregular shaped glass somehow are mounted thick side down). I'll see if I can find it tomorrow.
Zz.
Unfortunately, the part I put in bold is only a second-hand quote, and not the result of the good doctors own research. Let's look and see if any of us can find a statistical study showing how many windows have been found with the thick side up and how many with it down.Some years ago, I heard a remark attributed to Egon Orowan of the Massachusetts Institute of Technology. Orowan had quipped that there might, indeed, be some truth to the story about glass flowing. Half of the pieces in a window are thicker at the bottom, he said, but, he added quickly, the other half are thicker at the top. My own experience has been that for earlier windows especially, there is sometimes a pronounced variation in thickness over a distance of an inch or two on individual fragments. That squares with the experience of conservators and curators who have handled hundreds of panels. Although the individual pieces of glass in a window may be uneven in thickness, and noticeably wavy, these effects result simply from the way the glasses were made.
Physics Monkey said:Very interesting, please let me know what you find. As for the thickness irregularities, I would agree that it would be somewhat unusual for all the windows to be thick side down, but I think some have been found with thick side up.
The melting point of glass can vary depending on the type of glass, with common soda-lime glass having a melting point of around 1500°F (816°C) and borosilicate glass having a higher melting point of around 1700°F (927°C).
Glass has a melting point because it is a solid material made up of a network of atoms that are bonded together. When heated to its melting point, the bonds between the atoms break down and the material transitions from a solid to a liquid state.
At room temperature, glass is technically a solid because it has a fixed shape and volume. However, it is an amorphous solid, meaning it lacks a crystalline structure like other solids. This can give the appearance of a liquid because the molecules are not arranged in a regular pattern.
While glass is not technically a liquid, it does have some properties of a liquid. Over long periods of time, glass can slowly flow and change shape, which can be seen in old stained glass windows that are thicker at the bottom. However, this process is extremely slow and not noticeable in everyday life.
The composition and type of glass, as well as external factors such as pressure and impurities, can all affect the melting point of glass. Different additives can also lower or raise the melting point, making it easier or harder to melt the glass.