Re: [ATM] Microwave heating of glass

[GARY FUCHS <gary@rcn.com>]

"Since the energy level is readily controlled on any microwave"

I recall hearing that home microwave ovens have only one energy level and that the "lower" settings cycle full power for varying periods. Is that true? If so, what impact, if any, might that have on the annealing?

Gary Fuchs


---- Original message ----
>Date: Mon, 7 Jan 2008 09:28:02 +0100 (MET)
>From: Dominic-Luc Webb <dlwebb@canit.se>  
>Subject: Re: [ATM] Microwave heating of glass  
>To: Ian Williams <i.r.williams@bristol.ac.uk>
>Cc: ATM Superheros <atm@atmlist.net>
>
>
>Several things to point out here, as this is potentially usefeul
>for making mirrors.
>
>1. A form would be needed, either for the shapre of the mirror
>or as a crucible. We would need to think on appropriate
>material for a microwave.
>
>2. There are a few quite cheap ways to get the temperature needed
>to get this process started. There are a number of heating elements
>that could reach this temperature (600-800 C ???).
>
>3. Getting broken glass melted enought to mix and fuse properly
>without a lot of bubbles and stress is a whole separate issue. I
>have accomplished the same thing that microwave video did by just
>burying a lot of glass into a pit in my garden and burning a
>fire around it. There are no practical size limitations, so massive
>mirrors are possible. However, when starting with a lot of
>broken glass, the pieces first become kind of high viscosity liquid,
>much like syrup, but the different pieces won't truly mix, although
>they might fuse as the system cools. I think a much higher
>temperature must be needed for mixing, and it is not clear if a
>microwave is up to this task, especially since we would be most
>interested in melting sufficient glass to make larger mirrors.
>Smaller mirrors of the size that would fit into a typical microwave
>can be made with plate glass, which questions the useful of the
>microwave, unless it can be scaled up to a larger size. Indeed,
>I have considered applying this classical physics demonstration
>by combining the microwave elements to a larger chamber. I never
>got far with this partly because it was clear that when I am
>ready for the larger mirror, the pit in my garden will likely
>just work. Since the fire pit is buried, it has a cheap and
>convenient means for slow annealing....
>
>4. A proper way to anneal would be needed. Since the energy
>level is readily controlled on any microwave, this might be
>doable through use of progressively lower settings over time.
>I am actually concerned about the non-uniformity of the energy
>within a microwave. I suspect there would be a lot of hot and
>cold spots. This would need to be made more homogeneous.
>
>
>Dominic Webb
>
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