I've been researching carbon fiber reinforced silicon carbide. It
seems the process goes something like this:
1.make a CF felt preform,
2. impregnate it with low viscosity polymer resin and catalyst,
3. polymerize,
4. carbonize under nitrogen atmosphere,
5. (repeat 2-4)
6. (graphitize?),
7. dip in molten silicon metal,
8. allow to infiltrate and react.

If this is how the process goes then the carbon fiber will be exposed
to the silicon metal during infiltration. Why doesn't it turn into
silicon carbide? Do they coat it with something that prevents
conversion to SiC?

Also, how do they melt silicon metal with graphite electrodes but not
destroy the electrodes?

Where do you buy metallurgical grade silicon in small quantities?
(~100 lbs)

I'm interested in this technology for radial turbine blades and stator
vanes. Any comments are welcome

Hello my names Del Crabtree and I am working on a graphite barrel for a new firearm that I am developing. I need to ask a few questions about maybe making the barrels and chambers out of graphite. I understand that the properties of graphite allow it to dissipate heat at a very fast rate. My only concern is that a barrel must not only be very ridged but must be able to flex with the pressure wave and snap back into place.
Is this a possibility? I know that it sounds good in theory, but is it practical? If it is the fact that it is so light weight would make it a real viable option for my project. I am trying to design my assault rifle around a new type of cassless ammunition that uses a solid propellant rather than gun powder. The ballistics are off the chart, the only problem is that it burns very quickly and has a very high flash point.
If you could maybe send me in the right direction I would appreciate it very much. Thank you
Del Crabtree
sniperdel@yahoo.com

Hi Mov42!
(I don't make weapons, sorry, but hi Sniperdel nevertheless)

SiC is desired in carbon fibres reinforced SiC. In fact, I believe (but am not quite sure) all Si is converted to SiC in these composites. Or at least at the fibre-matrix interface, the SiC phase is very useful to obtain a good bond.

Pure Si is, sadly enough, a very bad material for mechanical engineering because it's too brittle. Let a single-crystal disk with D=50mm and t=300µm fall on concrete from h=100mm and it breaks. Pity, every other property would be fantastic. Invent a tough silicon alloy, and you may become famous and perhaps rich.

On the other hand, SiC has acceptable properties as a massive ceramic, as well as a filling in aluminium, titanium and steel cermet.

More, Si melts at 1414°C and SiC at >2730°C so formation of SiC at the fibre-matrix interface may well stop spontaneously, and SiC from the graphite electrode in the Si melt will be in small amounts, I'd say. Just let it sink in the melting pot.
http://en.wikipedia.org/wiki/Silicon_carbide

So no single precaution is taken to avoid SiC, I guess.

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Metallurgy in wagon quantities uses FeSi or similar, rather than pure Si, as silicon typically makes few % of common alloys. Though, you can get metallurgical Si from chemists like Wacker, as a step in the production of semiconductor Si.

https://www.goodfellow.com sells silicon in small amounts, even in non-semiconductor quality (price differs radically):
https://www.goodfellow.com/home.aspx?LangType=2057 like
SI006015 Silicon Powder, Max. Particle size : 45micron, Purity : 99.5% 412€/200g
SI006010 Silicon Powder, Max. Particle size : 150micron, Purity : 97.5% 568€/2kg

http://www.advent-rm.com/items.asp?criteri...nenumber=SI9002 330Gbp/kg
really looks like broken remains of wafers...

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Graphite electrodes: I guess they dissolve slowly in silicon, just like in steel. Melting temperatures are similar anyway.

Having some C in the molten Si that will convert to SiC is no drawback, or even an advantage if you want to dissolve less C from the fibres. Could much more C in the liquid save you the impregnation-carbonization steps?

And if you want (improbable) to avoid this carbon, just heat silicon by another method. It doesn't need huge temperatures.
http://www.webelements.com/silicon/

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If you want to make trials on existing parts before producing yours, you can buy some. I got some from DLR in Germany. Porsche lets produce parts as brake material.

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Fingers crossed for your turbine - at least at first sight, it looks like a good idea. As brake material, SiC is excellent for short-term high temperature, resistance to heat gradients and shocks, relatively good heat conductivity (for a ceramic) and low thermal expansion. DLR can certainly tell you more about long-term oxidation. Don't forget impact resistance.

I didn't need cooling channels nor other complicated forms on brakes; maybe you can obtain them at initial shaping. Once SiC is obtained, the composite can only be grinded, not milled nor turned.

http://en.wikipedia.org/wiki/Silicon_carbi...ctural_material

"In the 1980s and 1990s, silicon carbide was studied in several research programs for high-temperature gas turbines in the United States, Japan, and Europe. The components were intended to replace nickel superalloy turbine blades or nozzle vanes. However, none of these projects resulted in a production quantity, mainly because of its low impact resistance and its low fracture toughness."

-> But this is for massive SiC, not for the carbon fibre composite with SiC matrix.

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I never saw delamination on such composites. No idea why. But could carbon whiskers added to the matrix be useful against that?

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Wiki means the matrix is SiC, not Si. This may require temperatures much higher than silicon's melting point, so that either Si or C can at least diffuse through the already formed SiC at the interface.