I currently have a Chemical Vapour Deposition Reactor setup that I am using to synthesise carbon nanotubes. At the moment, I am doing this by heating a solution of 2.5mol% ferrocene in toluene to 800-900oC in a furnace. The resulting carbon compounds form on the walls of my quartz tube, which each happen to be 1 metre long and 30mm in diameter. So far, the biggest obstacle I have had so far is not the chemistry itself, but actually attempting to clean the quartz tubes following reactions. I have 4 such quartz tubes, all of which are now coated in carbon material (this could potentially be my nanotubes, amorphous carbon or maybe even iron carbide Fe3C, or a bit of all of these).
So far, I have left them to soak overnight in warm soapy water, and attempted mechanical cleaning with brushes. While these cleaning methods helped to a minor degree, they did not come close to removing everything from my tubes. Technicians have suggested using sulfuric acid or nitric acid, but I wanted to confirm if this would be the right way to go about it, or if there is a better way?
Dear Marc Leaney,
As technicians suggested you can use sulfuric acid or nitric acid or aqua regia (which is 3: 1 of HCl: HNO3) for cleaning carbon-contaminated quartz tubes, but be careful while using acids and take necessary precautions. If possible you may try to heat the carbon-coated empty quartz tube at a high temperature of around 1000 degrees under atmospheric conditions or oxygen atmosphere. It will also help to remove carbon from the quartz tube.
Dear Marc Leaney,
If your deposits contain both iron and carbon, a combined cleaning is recommended: first heat in air to 600-700°C to burn off carbon, then rinse with hydrochloric acid to dissolve iron oxide.
I had a similar experience back to many years ago, when I was also doing ferrocene-based CVD. My way at that moment was to use a diluted HF, and leave the used quartz tubes in the solution overnight. I even made a long but thin plastic container for the HF solution. HF was dangerous for sure, but this method worked very well. The back stuff peel off after the process and the tube became very clean. Only one concern, handle HF carefully with protections!
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