I am trying to prepare carbon from polymers by the carbonization technique. On carbonization, I am getting ashes on the top of the carbon. Is there any method to avoid it or how can I separate this ash from the carbon?
Dear Ajit,...
the comments of Palash are correct.
Every polymer, when carbonized at temperatures higher than 1000°C within inert atmoshere, does show a carbon yield in between nearly zero and up to 50-70% of original starting weight. This yield normally is in between 10 and 80 % of the theoretical carbon content of the polymer structure (amount of carbon atoms).
Polyacrylonitril has about 50% carbon yield and phenolic resin about 80%.....
There are some possibilities in pretreatment (Polyacrylonitrile p.e. treatment in oxygen in between 200 and 300°C) to stabilize the polymer structure...which is important to get a good carbon structure.
Here my question:
What is the goal of your scientific work?
Which kind of carbon structure you want to get?
Which polymers you have tested up to now?
What is your carbonization procedure (temperature, residence time, atmoshere)?
What polymer are you using? Some polymer produces better quality Carbon than others -- polyacrylonitrile is one of the better ones. Also make sure your oven is oxygen free -- literally! And purged with Argon! 1000 - 1200 degree C should be your target temperature. What do you mean by "ash" on top of carbon? Do you mean loose carbon that is not bound to the bulk or some other composition? If it is loose carbon then just blow it off once you make it. If not check composition and / or contamination in your starting polymer.
Dear Ajit,...
the comments of Palash are correct.
Every polymer, when carbonized at temperatures higher than 1000°C within inert atmoshere, does show a carbon yield in between nearly zero and up to 50-70% of original starting weight. This yield normally is in between 10 and 80 % of the theoretical carbon content of the polymer structure (amount of carbon atoms).
Polyacrylonitril has about 50% carbon yield and phenolic resin about 80%.....
There are some possibilities in pretreatment (Polyacrylonitrile p.e. treatment in oxygen in between 200 and 300°C) to stabilize the polymer structure...which is important to get a good carbon structure.
Here my question:
What is the goal of your scientific work?
Which kind of carbon structure you want to get?
Which polymers you have tested up to now?
What is your carbonization procedure (temperature, residence time, atmoshere)?
"Polymeric Carbons--carbon Fibre, Glass and Char" by Gwyn Morgan Jenkins, Kiyoshi Kawamura is a good reference. It addresses the types of carbon you get from different polymer/monomer sources. It also gives expected carbon yields. I have enjoyed this book immensely.
Besides PAN as suggested by Palash, resorcinol-formaldehyde can be a good source, especially if you are looking for porous carbons with high surface areas. see this excellent review: DOI: 10.1002/adma.200390020
@Ajit...
N doped carbon from carbonization of PANI is possible... see this paper in science
DOI: 10.1126/science.1200832
You should not heat too fast if you want to have a higher carbon yield. Usually, the higher the heating rate, the lower the carbon yield. In your case, you should not heat faster than 3 - 4 °C/min. 10°C/min is too much. A TGA studies would also be interesting to see in which temperature range the weight loss is the higher. Then, you should do a plateau in you heating ramp at the corresponding temperature range, and you'll get a higher carbon yield. Finally, if you want to maximise the N content, don't heat too high (not above 900°C) as N is a very volatile element. Some people even heat not higher than 750°C to get a high N content, but is it still carbon which is obtained in these consitions ? I am not sure ...
Alain
Dear Ajit,
what is the status of your work. Did you get some suitable results? Have you done a DSC (Differtial Scanning Calorimetry) of you polyacrylonitrile fibre? This might help a lot to find the correct reaction temperatures for stabilizing.
Best regards
Michael
I worked with phenol formaldehyde resins and domestic sugar (i.e. saccharose). Typical carbonization treatment is: heating rate 5-10 C/min, N2 or Ar flowing atmosphere, max T = 800C, holding time = 1h.
Phenol formaldehyde resins gives 50-60% of glassy carbon, while sugar gives about 40% of carbon char.
Important thing is: When heating carbon obtained from phenol formaldehyde resins at higher temperatures (1000-1400 C) in N2/Ar - there is no significant weight loss.
In contrast to that, when heating carbon obtained from sugar - sample will lose weight as long as is heated.
Carbons obtained from different precursors possess different surface groups and behave differently during the heat treatment.
Due to all this, you should first write down what properties your carbon should possess - and then find the right carbon precursor.
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