Self-healing Glass !!!!

[Speedy]

This is a simple 'by the way' question;

Is there such a thing as self-healing glass?

This is something that happened to me recently. A stone hit the windscreen of my car leaving a 2~3" crack. Within 20 mins or so the crack completely disapeared, with the exception of the 'star effect' at the impact point.

I've heard of glass flowing at room temperature (100 year old glass becoming thicker at the bottom)but never self healing.

Speedy

 

[AlanD]

Some polymers are capable of self-healing. They have small capsules of monomer, that when damaged by something like a crack will burst open and will repair itself.

Glass does not do this, to the best of my knowledge. Although you potentially can get short range atomic movement that may cause a crack too seemly disappear.

As for glass flowing over a period of time. This is a totally false myth based upon glass found old cathedrals. The glassmakers of the time did not have the ability to create glass that was flat. When the glass was installed the builders would place the thickest edge along the bottom.

Glass is an amorphous solid, that is glass is a solid without a crystal structure. Any solid (amorphous or crystalline) will undergo atomic migration under stress at low temperature, though a process known as creep. However creep is incapable of the amount of movement some people claim is the process of glass flowing at room temperature.

 

[bilge]

An interesting observation, Speedy.

What you might have seen was the "curing" of the polymeric layer in between the two sheets of shatter proof windshield glass.

I agree with the previous comment. Glass does not flow under its own weight at room temperature. I've done the calculation based on the known viscosity of soda-lime window glass at room temperature, its density, and the time from 1750 to the present. The amount of creep strain is miniscule.