IrC - 5-1-2015 at 22:34
Aluminum Oxynitride has the formula Al23-1/3xO27+xN5-x and one patent describing its synthesis, EP 1305259 B1 has me wondering why is Carbon used when
it is not in the formula of Aluminum Oxynitride. I can see where the Carbon goes (monoxide) but what is its function? My first guess is it is being
used to break down the Alumina so that the Al can react with N2. However the Carbon not seem to me to function like a catalyst in this process. If
the temperature was very high would not Al, N, and O combine without the need for the monoxide requiring a sealed exhaust from my kiln to the outside?
Is the purpose for the Carbon merely to lower the temperature required?
From the patent:
"The specific reactions that occur in the process are represented in equations 1-2.
(1) 23Al2O3 + 15C + 5N2 → 18Al2O3 + 10AIN + 15CO↑
(2) (9+1/3x)Al2O3 + (5-x)AIN → Al23-1/3xO27+xN5-x
As shown in Equation 1, a portion of alumina, carbon, and nitrogen react to form aluminium nitride, and carbon monoxide gas is produced. This reaction
can occur at about 1650-1750°C. The formed aluminium nitride then reacts with alumina, e.g., at about 1750-1850°C, to form AION. Synthesis of AION
by carbothermal nitridation, e.g., by conventional batch processing, can take up to about 20 to 30 hours to complete.
A method according to claim 4, characterised by continuously introducing the aluminium oxide particles and carbon particles into the chamber (30);
andreacting aluminium oxide particles and carbon particles continuously introduced into the chamber while continuously mixing the aluminium oxide
particles and carbon particles within the chamber and while passing nitrogen gas over the mixing aluminium oxide particles and carbon particles with
the temperature of the chamber being so maintained as to continuously convert the aluminium oxide particles, carbon particles and nitrogen into the
aluminium oxynitride."
Attachment: EP1305259A1.pdf (187kB)
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Pasrules - 5-1-2015 at 22:54
The abstract of this paper (pg.2) mentions the role of carbon in a system greater than 1625degC
Page
http://dspace.mit.edu/handle/1721.1/37162
Download
http://dspace.mit.edu/bitstream/handle/1721.1/37162/09878921...
IrC - 6-1-2015 at 12:28
Thanks I will study it. Do you have access to the full paper.
Pasrules - 6-1-2015 at 13:29
No i do not sorry not even my university connection gives me access to it.
IrC - 6-1-2015 at 21:30
It answered my question about the carbon, it is used as a reducing agent while simultaneously increasing vapor pressure. The latter being important to
ALON formation.