Time for a Picture

So, what's this? (Answer below.)


Despite my horrible picture-taking skills, it's probably easy to see that it's a carbon*-coated silica tube.


The way my supervisor did this was interesting. Basically, coat the interior of the tube with some organic solvent (acetone, ethanol, whatever you use to wash stuff) and heat it evenly along its length (till almost white-hot, but not to the point when the glass softens too much). The heat carbonizes the organic material and leaves behind soot**. Repeat coating/heating until the tube is evenly covered with carbon. This stuff does stick to the tube - it stood up to several light rinses***.

Frankly I'm surprised that the solvent didn't ignite on its own, but this procedure apparently works pretty well.

This particular tube has a slight problem, which is why I can take it and photograph it - there's actually an air bubble trapped between the carbon and the glass tube. I eventually gave up trying to take a picture of said bubble, so you'll just have to take my word for it.

Why this tube is covered with carbon is left as an exercise to the reader.

*I hesitate to call it graphite. Amorphous carbon, graphite, maybe even a few buckyballs - who knows what's in there?
**Well, that is a redundant sentence.
***Moral of the day: when the supervisor hands the tube to you after rinsing it with acetone, and tells you to check one more time whether the coating is still solidly there, do NOT immediately follow instructions and hold it up-side-down to your eye - I did that, and the acetone came flooding down. Thank goodness for safety glasses.