Glass – an amazing science

Today’s video is about a topic I have dedicated a few years of my career to! I’m even Some patents About it as an inventor!

Some of the usual supplements for those who want to dig a little deeper.

To put it simply I’ve treated quartz like it has a unique crystal structure actually it’s more complex than that often here’s the kind of phase diagram we have

In particular we see that quartz will undergo several transitions between different crystalline phases before melting at about 1700°C.

Concerning the viscosities of all these materials, they are often modeled using empirical equations of the type

\(\log (\eta) = A + \frac{B}{T-T_0}\)

It is called VFT (Vogel-Fulcher-Tammann initials). We recognize Arrhenius’ law except for the presence of T0 which isn’t very physical as it seems to indicate a difference, but T0 is generally much lower than the temperatures at which we know how to measure viscosity.

Incidentally on the issue of glass overflow from stained glass windows, the dimensional analysis gives a little more value than the paper you mentioned (but still ridiculously small). I didn’t dig to find the source of the difference but anyway we see that from the moment we have such a high viscosity the risk of windows leaking is very low!

Regarding glass, there are still a lot of things I haven’t mentioned, in particular the tempering processes that make it possible to strengthen it. The most classic is thermo-strengthening, which is what’s used for glass used in furniture and car windows (except for windshields, which are generally laminated). But there is also a very entertaining process of ‘chemical hardening’, where we cause an exchange of ions to create stresses on a surface. If I remember correctly, this is what makes it possible to make glass which is now widely used for the surface of mobile phone screens.

Concerning glass-ceramics, it seems another good example of a serendipitous discovery: see History portion of the Wikipedia article.

Regarding the role of glass ceramics in telescope mirrors, you can go to This example Using the material “ZERODUR” of the ELT (Extremely Large Telescope) receiver mirrors in Chile, of which I showed a schematic diagram in the video.

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