Why is glass often called a super cooled liquid?

Answer 1

Glass doesn't have a true crystalline structure and will flow very slowly over time. Analysis of stained glass windows from old cathedrals in Europe has shown that the glass is thicker at the bottom than at the top due to gravity.

Answer 2

Because some people like to sound smarter than they actually are.

Glass is an amorphous solid.

There are some esoteric points in thermodynamics having to do with phase transitions that cause some people to refer to it as a "supercooled liquid", though that's an exceptionally poor term for glass as it's already used for materials that really clearly are liquids and which crystallize rapidly given a very slight stimulus (in other words, not much like glass).

It's only "liquid" in an extremely narrow technical sense, and in actual practice it exhibits most of the characteristics of solids and essentially none of the characteristics of liquids, so most scientists prefer to call it an amorphous solid or simply a glass. Those who call it a supercooled liquid are mainly those who like to show off by repeating things they don't really understand.

If you want to know if someone is in that category or just being exceptionally technical, ask them to explain exactly what kind of phase transition occurs at the glass transition temperature. If they look confused, that's a big plus in the "just showing off" column.

Answer 3

Glass was once mistakenly believed to be a slow-flowing liquid because window panes in old buildings were thicker at the bottom, and people mistakenly assumed that the glass had flowed over time (this actually has to do with the way glass window panes were made at the time). We now know that glass is a true solid, not a slow-flowing liquid.

Answer 4

In short, it is reasonable to refer to a glass both as an amorphous solid and as a supercooled liquid, depending on context. A explanation and discussion of this follows.

It is important that the usage words "liquid" and "solid" depend strongly on context. First of all, they can be meant in a thermodynamic or a rheological (dealing with deformation and flow).

First, let us discuss what "supercooled" actually means. Below their freezing temperature, materials are thermodynamic equilibrium is in the solid state. This means that the materials 'want to be' in the solid state because it is of the lowest energy. A supercooled liquid, however, is below its 'freezing point,' yet is unable to achieve its desired equilibrium state. This is because some mechanism allowing it to achieve that state is simply not proceeding quickly enough. In the case of supercooled water, this process may be seeding of initial crystallization sites. In other words, if the water is very pure and its container is very smooth, there is nowhere for the ice to start freezing. I

From a thermodynamic sense, typical solids such as water undergo a first order phase transition from a liquid to a solid. This means that their energy undergoes an abrupt change with as to temperature as the material is cooled. (This is why you have to add a great heat to water to boil it even when it is at 100 degrees celcius.) Furthermore, the material undergoes a clear transition in how it is ordered. It goes from a disordered state to a well ordered crystalline state. In the case of a glass, however, due to either the size of the molecules or other factors, the material effectively becomes trapped in its disordered state as it cools. It is sometimes said to go through a second order thermodynamic transition. This means that there is not an abrupt change in properties such as its energy. It does not become crystalline and the nature of its organization may be largely unchanged. It is thus, in a sense, a supercooled liquid; it is below its thermodynamic freezing point and yet has not crystallized. In the case of a glass, however, the timescale for crystallization may effectively be forever at room temperature. In a sense, it does not have a practical 'freezing point', but rather a 'glass transition temperature'. It has, however, gone through a significant change in the timescale of molecular motion. In both the case of the simple liquid to crystal transition and the liquid to glass transition, the transition can be characterized by a dramatic reduction in how far molecules of the material will move in a given time period.

This leads us to the rheological consideration of a solid versus a liquid. What this focuses on is the relative time scale (speed) for deformation of the substance. For a particular time scale, things that deform fairly rapidly and continuously are considered fluids. Those that do not are considered solids.

Glass is an amorphous solid. It is amorphous because it is disordered, or largely noncrystalline. For experiments and phenomenon on a typical time scale it furthermore/ behaves as a solid. In other words, if I hit glass it rebounds or shatters rather than flows. However, on the timescale of small forces applied over long time periods, glass behaves as a liquid. For instance, glass under the influence of gravity will slowly but measurably deform, thickening at its bottom and thinning at its top. This pheonmenon can be observed in old castle windows.

The concepts of 'solid' and 'liquid' are, as you can see, more complex that it would appear on the surface. Understanding these concepts leads to a greater understanding of the principals of thermodynamics and molecular motion.

Answer 5

glass when is heated gets into molten state and when gets cooled is compactly get arranged that is the electrons gets arranged compactly

Answer 6

It used to be believed that it had some liquid properties but now it is believed that that was an error. Glass is a solid but it has no crystalline properties it is vitreous.

Answer 7

Over time,the glass has flowed slowly downward,just like a liquid.