[dinoviki]

I work with quartz tube of 64mm diameter and 1m in length. I use it for combustion visualization inside a furnace and often end up with combustion deposits on the inner walls of the quartz tube. The materials I primarily combust are Coal, Wood, Switchgrass (Solids), Isooctane, and Hexadecane (Liquids). The deposit formation is high while working with the solids than that of liquids.

I am looking for some ideas on cleaning this deposit. Scrubbing off the deposit is not a good option for me both in terms of accessibility to clean and formation of scratches on the tube (Disrupt visualization).

Is there any chemical solution that would solve my problem ?

Thank you.

[curiouscat]

A saturated NaOH or KOH solution in ethanol or methanol might be worth a shot. Another option is to pass a steam / air mix through the tube for a few hours. This should burn off a lot of the coke.

Solvents? Ether? Acetone?

The trick will be not dissolving away the tube itself (though quartz is quite inert).

If those don't work bring out the heavy ammunition: Aqua Regia, Peroxide solution, or Chromic Acid.

[tlahren]

If it's true Quartz and not just pyrex glass then you can try to bake off the "char" in a muffle furnace at about 800 or 850°C.  A quartz tube should withstand that temp. Run the furnace at 800 or 850 for about 4 hours then let the tube cool overnight in the furnace after turning it off.

Not sure if the bases will work but a strong oxidizing acid like H2SO4 or Chromic Acid may work as well.  I would say the muffle furnace is the easiest if you have one.  Most labs and universities have one laying around somewhere.

Because of the nature of the material you may need to use multiple steps (i.e., Bases then Acids then furnace), but try the furnace first.  This should volatilize any organic material that is left and oxidize any pyrolized (graphitic) carbon to CO2 and evolve as a gas.  Other components should volatilize and or oxidize as well.  You may be left with some non-volatile minerals or salts which should be easily dealt with using a 10% HNO3 bath.