Additive-assisted pressureless sintering of carbothermal β′-sialon: an X-ray and solid-state MAS NMR study
1996
β-Sialon pellets (Si6 –zAlzOzN8 –z; z= 2.45) prepared from carbothermally synthesised sialon powder were sintered in N2 at 1400–1700 °C with additions of 15 mol% each of Al2O3, MgO and Y2O3, and 10 mol% each of various combinations of these oxides. The most effective densifying agent is Y2O3, both alone and in combination, followed by MgO and Al2O3. XRD and multinuclear MAS NMR (27Al, 92Si, 25Mg and 89Y) studies revealed traces of X-phase sialon, SiC and an X-ray amorphous glass-like phase in the starting material, and were used to monitor phase changes during sintering. Y2O3 by itself and with other additives forms Y3Al5O12(YAG) with β′-sialon; at higher temperatures, an aluminium-rich polytypoid sialon and yttrium-containing glass are formed, to the detriment of the strength of the sintered body. MgO initially forms MgAl2O4, lowering the sialon z-value. At higher temperatures, this further reacts to form a glass containing magnesium in both tetrahedral and octahedral sites. A12O3 reacts with β′-sialon, increasing its z-value. The NMR spectra confirm the XRD phase analyses and provide information about phases not detectable by XRD, and about the possible constitution of the glasses formed.
Keywords:
- Correction
- Source
- Cite
- Save
- Machine Reading By IdeaReader
23
References
12
Citations
NaN
KQI