why is glass called super cooled liquid?

Question

if a liquid is cooled it becomes a solid,so y not call glass a solid than a super cooled liq?

Answer 1

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 2

OK to answer this question we have to define cool and hot. Everything has a point where it turns into gas. There is also a point where something turns into solid. These temperatures are different for all things. For example: water become heated and turns into steam at 100C. However the temperature for that to happen with iron is different. The same goes for freezing point.

So we go to glass, If glass was solid it would stay the same for all the ages if it is undisturbed. However, this is not the case. If you take a look at old windows the bottom is thicker than the top. This is because glass is not truely solid. Glass is in more of a gel like state. However since this is not solid it is liquid. But since it is moving at such a slow speed it is very close to solid. Now if we cool a liquid enough it turns into solid. But since glass is still technically liquid the glass is super cooled, because of how close to solid it is.

Answer 3

Glass as a liquid:

One common misconception is that glass is a super-cooled liquid of practically infinite viscosity at room temperature and as such flows, though very slowly. Glass is generally treated as an amorphous solid rather than a liquid, though different views can be justified since characterizing glass as either 'solid' or 'liquid' is not an entirely straightforward matter. However, the notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical evidence or theoretical analysis.

Hope you understand this.

Answer 4

Supercooled Liquid

Answer 5

Responder locke9k is close. Water has a definite freezing point: at 0.1 C it is melted, and at -0.1 C it is frozen. Except when it isn't -- you can cool water below the normal freezing point and it may not start to crystallize into ice until you agitate it or add a bit of ice. This is called supercooling.

The supercooling of glass is different. Glass does not have a specific temperature at which it transitions between a liquid and a solid state. As you cool melted glass, it gets more and more viscous, but does not actually freeze. What happens is that the viscosity gets so high that the molecules cannot arrange themselves in a crystalline structure, so the glass remains amorphous (as another responder has correctly noted). At room temperature, it is still liquid, but so viscous that the flow is essentially invisible.

It is worth noting that glass is not pure silica; various salts, such as lead oxide, sodium chloride, or boron compounds are added. Pure silica has a definite melting point (1722 C); when heated, it undergoes a number of phase transitions before it gets hot enough to melt. But the added salts increase the viscosity, so one no longer has a definite melting point or freezing point.

Answer 6

Glass is a amorphous solid. All amorphous solids have tendency to flow though very slowly. Hence glass is considered a super cooled liquid. That is why the glass window and door is slightly thicker at the bottom than at the top.

Answer 7

Lets see the terminology GLASS, Crystal, crystalline solids supercoold Liquids ..........non crystalline solids quasicrystals etc all comes under the subject of Cystallography..........in crystallography what we do bacically we carry our the diffraction experiment using x-ray neutrons or electrons........these experiments tells us that whether the sample under investigation is crystalline or not...............if you carry out the diffraction experiments on glass this experiment will tell you that the glass is amouphous state as that of any liquid.......and along with the diffraction if you carry our mossbour experiments you will see that the glass molecules are not fixed to perticular position they move with very slow speed....(this is other than vibrations) withinn the solids...........hence the glass is called the supercooled liquid..................if you visit some old chirch in germoney you will find that the thickness of the glasses on windows is not uniform it is higher at lover level and lower at higher level this confirms that the glass molecules flow downword and hence become thick at lower portion........i hope this answer your question.........
best wishes

Answer 8

ok. i am not an expert on glass. but i did won (yes... #1) last year State Chemistry Competition of high school student (known as Chemathon). one of the questions in the competition was about glass. so i know some stuff on this topic.

GLASS: it is defined in chemistry term as silicon dioxide or SiO2. SiO2 has a molecular bent (VSPER model) of 105.5 degrees. since it is a semi metal and has the property of Carbon, it comes in many forms in the world.

SiO2 is normal sand (yes the beach...lol). SiO2 is ionic, thus its melting pt is high. so it is solid in room temp. but when it is melted into liquid, property changes. as the molten sand (very hot) is cooled very fast or "super cooled," it cannot return to the solid phase. particles are still too far apart to form bonds before it is "locked" in place, like liquid, far apart due to the sudden drop of temp. instead, it is an imtermidiate form of liquid and solid. we call this "amorphous solid phase." why? because it has both liquid and solid characteristics. like has solidify shape (solid) and clear (liquid).

this is WHY?

does this answer you QUESTION? hope you like it. enjoy.

^_^

Answer 9

glass at 'room' temp is really a very slow moving liquid.

For example-
They've measured really old stained glass windows and found that the bottom of a panel is thicker than the top because it is very very slowly flowing downward.

Answer 10

because if you did not super cool it it would loose the blown shape

as a liquid glass is picked up and put in to shape all the time becoming more solid ,if it is blown the final shape is delicate because it is still soft .
by super cooling it .the shape is secured