28th November 2009 - 12:19 AM
(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.
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
SI006015 Silicon Powder, Max. Particle size : 45micron, Purity : 99.5% 412€/200g
SI006010 Silicon Powder, Max. Particle size : 150micron, Purity : 97.5% 568€/2kghttp://www.advent-rm.com/items.asp?criteri...nenumber=SI9002
really looks like broken remains of wafers...
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/
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.
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.