I have used β-SiAlON as an additive in a ceramic matrix composite. The powder mixture was sintered at 1900 C for 2 h.
I want to know what the destiny of the β-SiAlON is?
Does it melt? Is it degraded or decomposed?
Does it convert to a glassy form or will be stable at such conditions?
When heated β-SiAlON to 1900 ° C even in the best vacuum occurs oxidation nitrides of aluminum and silicon to oxides :
2Si3Al3N3O5 + 8O2 = 6SiO2 + 3Al2O3 + 3N2
The resulting mixture 2SiO2-Al2O3 at a temperature of 1900 ° C is a liquid.
Dear Vadim Verlotski,
The furnace vaccum is ~ 10 ^ -7 atm
Would you please attach here a reference about the mentioned reaction?
http://media.johnwiley.com.au/product_data/excerpt/55/35273375/3527337555-11.pdf
First of all you must remember about decomposition of beta-sialon to SiO(g) or to Si(g) at this temperature and vacuum (active oxidation). Active oxidation of Si3N4 at 1500 oC starts at log p(O2) about -9 Pa. It will be worse at 1900 oC. Look at Vaughn W.L. et al, J.A.Ceram Soc, v.73 [6], 1990, p. 1540-43.
Besides, active oxidation also depends on the process of sintering. If you did not apply pressure during the first stage of sintering, the active oxidation (with keeping vacuum at the mentioned level) will accelerate the process. I guess, you lost your beta-siaslon particles in composite.
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