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I am an fire safety engineer trying to build a fire model which I could use to demonstrate basic fire behavior in enclosures. In general, the model is a box (for example 0,3*0,3*0,2 m or larger) with one opening. Inside the box is the burner (gas burner or some material which burns).

At the university, we always used models built out of gypsum plaster. It was cheap, easy to connect and it could resist quite high temperatures (around 700 degrees Celsius).

Is there any kind of transparent material which could be used in such an application? If I understand correctly, the highest temperature which thermoplastics could withstand are about 270 degrees Celsius. Quartz glass is too brittle I think, and probably too hard to cut out.

Is there a material like this? Or if there are multiple materials, which one(s) are least expensive?

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  • $\begingroup$ Borosillicate glass, don't know the prices range.. $\endgroup$ – Mech_Engineer Jul 6 '17 at 12:40
  • $\begingroup$ Whatever material you use, I strongly recommend mounting an external piece of wire screen / chickenwire as a safeguard against possible glass shatter. $\endgroup$ – Carl Witthoft Jul 6 '17 at 13:12
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My first thought was Pyrex, but it's a brand name for heat resistant glassware. Glassware for laboratories and kitchen is made from Pyrex.

In the US, heat resist glassware seems to be made from tempered soda-lime glass, but outside the US borosilicate glass is used.

Depending on how the borosilicate glass is made, glass with different softening points can be made.

The softening point (temperature at which viscosity is approximately 107.6 poise) of type 7740 Pyrex is 820 °C (1,510 °F).

For your purposes, borosilicate glass would be more appropriate.

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    $\begingroup$ And as for where to obtain it - fireplace inserts suppliers; large sheets of this glass are commonly used in the fireplace inserts, and replacements are available in common trade for when one breaks in someone's fireplace. $\endgroup$ – SF. Jul 6 '17 at 13:03
  • $\begingroup$ It's important to note that these types of glass not only have a high softening point but are reasonably unlikely to shatter under uneven heat loads (which cause differential thermal expansion across the sheet). $\endgroup$ – Carl Witthoft Jul 6 '17 at 13:11
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Borosilicate glass with an indium tin oxide (ITO) coating? A mixture of indium oxide and tin oxide as ITO is used as a transparent coating for - usually - display applications. However, it had a melting point in excess of 1500 degrees C

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  • $\begingroup$ Why is the ITO coating required? The OP didn't specify a need for electronic conductivity. $\endgroup$ – Chemomechanics Jul 9 '17 at 20:11
  • $\begingroup$ As a high temperature transparent coating. No idea if tin oxide is transparent usually $\endgroup$ – Beerhunter Jul 9 '17 at 22:13
  • $\begingroup$ The ITO is a micron thick or less; it imparts no thermal robustness. It's there to conduct electricity. $\endgroup$ – Chemomechanics Jul 10 '17 at 0:17
  • $\begingroup$ I know, the thought was high mp of transparent oxides might bolster the operating temp $\endgroup$ – Beerhunter Jul 10 '17 at 16:55
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The best answers on this site are when xkcd has an answer as well. In addition to borosilicate glass, sapphire windows are pretty common, and can handle a wide variety of high intensity flames. Quartz (fused silica) also works well - in fact there are quite a few window materials to chose from, including calcium fluoride and magnesium fluoride.

Of course, the plain window is impossible unless you can mount it properly. As you mentioned, quartz or any other brittle material glass is difficult to machine and cut properly. Fortunately, holders for these windows are already made as industrial products, that can be procured at any time. The cost comes down to viewing diameter. These wind up being a larger impact on cost then the actual window, so window material selection is usually determined based upon long-term costs, not short term costs.

The downside to these glass ports is the viewing area isn't very big. There is enough for you to see through with your eyes, but nobody else. So they're not very good for demonstration purposes. But they've been tested against pressure loading and temperature loading and are designed not to shatter. Just be prepared to purchase a few of them so you can give a good demonstration to several people simultaneously.

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