That is most likely the glass transition. It occurs for every glass upon heating, with temperature range depending primarily on chemical composition, and to a lesser extent on thermal history. The morphology of the transition depends strongly on thermal history.

You will not find anything on the equilibrium phase diagram, because this is a transition between two non-equilibrium states (glass to supercooled liquid).

See for example:

M. A. Debolt, A. J. Easteal, P. B. Macedo, and C. T. Moynihan, Analysis of Structural Relaxation in Glass Using Rate Heating Data, J. Am. Ceram. Soc. 59, 16 (1976).

C. T. Moynihan, A. J. Easteal, M. A. Debolt, and J. Tucker, Dependence of Fictive Temperature of Glass on Cooling Rate, J. Am. Ceram. Soc. 59, 12 (1976).

Oliver L. G. Alderman Thanks a lot!

I'll check a viscosity range at this temperature, may be it will be the answer.

Hi

Did you check the Tg temperature of glass?. Because generally the amorphous materials may undergo change in their crystalline structure at some particular temperature. Check the cooling curve of this same glass from previous literature and find out at what temperature the glass becomes completely solidifies.

note. Check when the graph is horizontal in a time-temperature graph.

best

To add to the discussion: If you anneal the glass, the endothermic feature you refer to should become larger and more pronounced, if it is a glass transition (you can see this in the papers I cited above).

Answering your questions/notes:

- I suppose, there is no crystallisation/recrystallisation process, it is very unlikely.

- The studied glass is a common colorless transparent (white) glass of a standard composition which I decided to skip in the initial question. Full chemical composition is:

SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O

72,1 2,4 0,1 9 2 14,3 0,1

- We used a cullet of this glass. So its thermal history should be like the one of common container glass, i.e. annealing (after melting and molding)

- There were four experiments with this glass, and every DSC had this peak (603.0, 602.5, 602.1, 601.9 C).

- Now I'll focus on calculations and experiments on viscosity around Tg temperature. However, summer holidays may delay it.

Be sure, I'll keep you in touch.

Thanks!

The glass transition temperatures of silica glasses are high. The endothermic peak or shoulder you specified probably belongs to the glass transition temperature of the glass.

Hi Boris

the feature you show is the glass transition. Most researchers quote the value of Tg, the glass transition temperature, at the "onset" which is at about 565 degrees C in your DSC trace; or the "mid-point" which is about 580 degrees C in your trace. Your glass composition is a typical soda-lime-silica glass, and I would expect a Tg onset of approximately the values shown in your DSC trace so this all makes good sense.

Kindest Regards

Paul.

Boris Goltsman,

You may follow the thermal expansion study of the same system via the Dilatometer to confirm its onset glass transition temperature. However, the onset of the glass transition temperature is commonly reported via the intersection of tangents at the knee of endothermic deep. The onset of the glass transition temperature can vary a little from DSC to dilatometric studies because the glass powders are introduced in the DSC while, bulk glass samples are used for Dilatometric studies.