750C Hermetic, Optical Window Design 1

[3sjb1]

Good-day,

In my research, I will be photographing droplets resting on horizontal surfaces inside a steel well in a furnace running at 750C (1400F), though I may later wish to raise the temperature by a few hundred degrees celsius.

To permit imaging, I require an approximately 10-13 cm (4-5") diameter by 2-5 mm (1/8") thick window in the side of the well (open-topped, stainless steel, cylinder, 15 cm (6") diameter, 6.5 cm (1/4") thick walls) that can withstand these temperatures, while remaining hermetically sealed (during later experiments, we will be sealing the top of the well and running a chlorine atmosphere).

As the well is a cylinder, the simple flat, bolt-on type windows I have seen in appropriate sizes do not seem as though they could be modified to work, and most do not meet my temperature requirements.

I was thinking if it would be possible to buy a window (i.e., quartz) hermetically sealed to a ring of metal which I could then weld or screw onto a (threaded) fixture previously welded to the well wall (i.e., a cylindrical tube open at both ends, with one end welded to the well and the other to be attached to the window assembly). If the threaded design were pursued, I would also require an appropriate sealant.

I am interested as to possible window designs or any suggestions or information (i.e., suppliers, etc.) that would be suitable, as well as being low cost (i.e, < CAN$500 (~US$380), excluding labour).

Thank you for your time.

Auf wiedersehen,

James

 

[btrueblood]

I think you will need to modify the side wall of the oven/cylinder, creating a flange to bolt the window assembly to. Typically, the window (quartz) has a step in it, with the step oriented to provide bearing against internal pressure. Packing/sealing materials are then placed between the step and the outer metal flange/carrier assembly. I'd avoid a threaded assembly; the thermal expansion and chances of galling/jamming the threads would advise against that approach. Also, quartz has a very low CTE compared to steels.

The toughest problem I see is sealing hot chlorine gas. I was going to suggest using a quartz window, with a seal of layers of graphite sheet (grafoil is one trade name). But I'm pretty sure the graphite will go away when exposed to hot chlorine? You may have to use several layers of stainless foil as a heat shield (imagine piston rings in an engine) in front of a final teflon or similar material that can hold up to the chlorine, possibly with a cooling jacket near the seal to keep the seal from cooking (Teflon can go to a max. of 550 F?)

You might be able to use a seal of foamed glass (such as obtained by heating sodium silicate solution), this could give enough compliance between the metal and quartz to keep an intact seal, although it will probably fatigue and crack in a few tens of thermal cycles.

Whatever you use, I would recommend ALWAYS doing a bubble leak check of the windows prior to each furnace run with toxic gases.

Good luck,

Ben T.