I learned that glass is always amorphous, isn't it? If this is true, about which structure you are talking? (structure is a term which is used for different subjects, e.g. (micro)structure, crystal structure, fiber structure...).

If you describe the density as ratio of the (molar) weight and (molar) volume it is only possible that the density increases when the volume decreases (same chemical phase assumed). Or do you mean mixtures? This can happen, e.g. water and alcohol. 1 liter of each results in 1.8l liquid.

I agree with Gertz Nolze,

I would like to add that glass of similar composition can be prepared with different densities. If you make a glass in your lab, you will get higher density when your quenching rate is very slow (similarly low density glass can be prepared by faster quenching rates). But the variations are notices will be very minimum.

Similar effect can be seen in refractive index too.

You may also end up with high density when you by mistake take the glass near to glass transition or crystallisation temperature during annealing treatment.

Thermal history is the key.

If you talk of about glass' network structure (non periodic) for first principle calculation. Kindly give more insight, to answer the question further?

Thank you.

Dear Vani,

First of all, there is nothing called "amorphous glass". Glass by definition is an amorphous material which exhibits a transition region from a supercooled state to an amorphous solid. What Venkateswaran meant about producing a glass with varying density is basically playing with its fictive temperature resulting in density fluctuations at the atomic scale which also leads to a change in its refractive index.

What you are looking for is how to decipher structure of glass using density. For me density is an additive property. It doesn't tell you much about the structure of glass. However, if you can calculate molar volume and excess volume using density and composition of your glasses, you can obtain good information about their structure.

Regarding the method to measure density of glasses, you can easily measure it by Archimedes method to measure density. See the following link: (http://www.physics.smu.edu/~scalise/mechmanual/archimedes/lab.html).

There is a whole chapter on density and molar volume in the book by Prof. Shelby. You may also want to look at the attached paper. Please contact me at [email protected]. I will be happy to help if you need further assistance.

Best,

Ashutosh

Dear guys,

You can refer to the following paper to find the last and most comprehensive definition of glass and many other interesting points.

Article The glassy state of matter: Its definition and ultimate fate

Goel is right. All glasses are amorphous, so the term "amorphous glass" is an oxymoron. Density is usually measured using the Archimedes Method with an electronic balance and distilled water as the immersion medium. If the glass is too soluble in water, you can use kerosene or alcohol or other liquids with precisely known densities. You can also use a helium pyncometer (less accurate, but good for powders or fibers), pyncometer bottle (also best for powders or fibers), sink-float densitometer (best for looking at small changes in density, e.g. due to changes in fictive temperature, irradiation, etc. - I've used this method very successfully myself).

As for structure and density relationships, density trends(really should use molar volume as it is the more fundamental property) have been used to test structural models for at least 100 years. But it can only be considered to agree with predicted trends from a model derived from either spectroscopic studies or from logical arguments. The density of a single specimen can really not be used to tell you anything about structure.

See my book, as suggested by Goel. Read the papers from Coe College by Feller and Affatigato and their many students.

Density itself does not give detailed information about the glass structure. However, it may guide one to support the spectroscopic observations such as the changes in bondings, degree of disorderedness, etc. Thermal history, as suggested by Venkateswaran and others above, may bring small changes in density since it controls both bonding as well as freezing dynamics.

You need to be more specific about your query. Is the glass multicomponent? Does it contains Al, B or P? You can explain the trend in density (and molar volume, if required) using the structural studies.