Thursday, May 11, 2006

Chemistry of Anodization Part2

This will probably be my last post as my co-op has ended. It was a valuable learning experience and I am sorry that I did not post more but I didn't want to be redundant. I hope this will benefit others in some way. If anyone who visits this site has any questions, feel free to ask.

I have found that each anodization is unique which is due to deviations of concentration in solution preparation and temperature. Such can be found in this research paper:
The effect of temperature and concentration on the self-organized pore formation in anodic alumina. M Almasi Kashi and A Ramazani, Institute of Physics Publishing, 38 (2005), 2396-2399.
Reproduced by permission of ESC - The Electrochemical Society
Conditions for fabrication of ideally ordered anodic porous alumina using pre-textured Al.
Hidetaka Asoh, Kazuyuki Nishio, Masashi Nakao, Toshiaki Tamamura, Hideki MasudaJournal of The Electrochemical Society, Vol148 (4), B152-B156, 2001

Though I can't say that all of my anodizations went perfect....
Unfortunately this happened due to the anode stirp comming in contact with the stainless steel screw. I am not sure how long it went on but the high current was enough to burn through the fiberglass circuit board.

Happy Anodizing!

Friday, May 05, 2006


I guess this is a good time to discuss a little about what happens after I make these alumina membranes. I can not get too specific about the research that anyone else is doing so I am just going to give information as to what has been done in the past with CVD, carbon nanotubes, and alumina membranes. As far as the synthesis of the CNT goes this is the end of the journey.

Chemical Vapor Deposition
The idea is simple - make the carbon nanotubes in the nanopores that we got with the alumina membrane.
The task is difficult. How can one get carbon into tubes and tunnels all the way through? The easiest way is to let the carbon do the work by moving through an atmosphere at a slightly elevated pressure. That sounds good but what about the carbon? We could by it in powder form and blow it through but that could clog up any tiny instruments used not too mention you can see the carbon with your naked eye and we need it in nano sized clumps.
The solution - heat a gas of hydrocarbons around the alumina membranes until it naturally breaks down and deposits onto the membrane. This is how in general, the CVD procedure works.
After inserting your alumina membrane samples into a furnace (usually in some kind of glass or quarts tube) you eliminate all of the air in the tube by blowing a heavy gas (in my case Argon) so when the carbon is released it doesn't react with the atmosphere and oxidize. While you are blowing Ar through the tube, the furnace is heating up so when you switch to the hydrocarbon gas it immediately meets the high temperature and breaks down. You also do not want a lot of carbon. The goal is to make "tubes" meaning there is some finite diameter that the carbon must leave open so we can do experiments. A mixture of hydrocarbons and a lighter gas that won't decompose or deposit onto the membranes is sufficient. The process takes around 6 hours not to mention the heating up and cooling down time for the furnace.

The Purification
We now have our glossy carbon coated membranes with carbon deposited into the nanotubes. Now to get the nanotubes out.... OH NO! I forgot my nano-sized tweezers in my other pants. Well it isn't any near that tedious. To remove all the unused membrane from around our nice CNT, we simply have to break them up in basic solution that will dissolve the membranes. This also requires some heat for about 3-4hours. Once time is up, just filter and neutralize the nanotubes, and you are set. Well until you need to anneal them that is....