SiAlON powders

Changes in the amount of P-SiAlON from the surface of the samples for green and presintered compacts are shown in Figs 6.22 and 6.23, respectively, after sintering in a-SiAlON and A1N-BN powder beds. Both figures clearly illustrate that the A1N-BN powder bed is more effective for the formation of a-SiA10N at the surface than the a-SiAlON powder bed. Formation of an a-SiAlON-rich layer on the component surface is due to the transfer of a-SiAlON-forming ions from the powder bed. This transfer could be in various... 

The sintering of sialon powders can be subject to the same difficulties as experienced with Si3N4, and similar sintering additives (MgO or Y2O3) have been found to assist. The nature of the intergranular phases formed by these oxides during sintering of 3-sialon has been studied by Si, Al, Mg and Y MAS NMR (MacKenzie and Meinhold 1996). 

NMR has shown that X-sialon powder is less stable to high-temperature oxidation than 0-sialon, beginning to lose nitrogen from the Si02N2 units below 940°C and forming mullite at 120(>-1300°C (MacKenzie et al. 1998). 

Because of their high Si02 content, O-sialons show superior resistance to oxidation. The oxidation of O-sialon powder has been studied by Al and Si NMR, which indicates that the octahedral Al thought to be present as an impurity phase in the unoxidised sialon is retained at all oxidation temperatures (MacKenzie et al. 1998). Some of this octahedral Al is present as mullite which forms at 1200-15(X)°C, but at higher temperatures, the oxidation is progressively hindered by the formation of a protective fused layer which is found by Al NMR to contain an unexpectedly high proportion of octahedral Al in the amorphous silica-rich material formed at 1600°C (MacKenzie etal. 1998). 

Figure 5.37. Oxidation of X-sialon powder monitored by A. changes in the amount of tetrahedral Al in the sample as a function of oxidation temperature, and B. changes in the tetrahedral Al shift as a function of oxidation temperature. From MacKenzie et al. (1998).

ROD-LIKE P-SIALON POWDER PREPARED BY A NEW N2-ASSISTED CARBOTHERMAL... 

Rod-Like p-Sialon Powder Prepared by a New Nj-Assisted Carbothermal Reduction... 

In conclusion, a kind of rod-Iike P-Sialon (P-SijAl303N5) powder was prepared through a carbothermal reduction-nitridation method using mesoporous silca as the starting material, combined with a carbon and aluminum nanocasting procedure. The resultant P-Sialon powder can be expected to find its use in preparing high performance Sialon ceramics. 

H. Yoshimatsu, M. Mitomo and H. Mihashi, The Preparation of Sialon Powder from Kaolinite, J. 

H. Yoshimatsu, M. Mitomo and H, Mihashi, Preparation of Sialon Powder from Mixture of Si02 and AI2O3-2H2O by Thermal Carbon Reduction, y. Ceram. Soc. Jpn., 95, 28-32 (1987). 

Shimada, S., Aoki, T, and Kiyono, H. (1998) Early-stage thermal oxidation of carbothermal beta-sialon powder. /. Am. Ceram. Soc., 81 (1), 266-268. 

Yamada S, Emoto H, Ibukiyama M, Hirosaki N (2012) Properties of SiAlON powder phosphors for white LEDs. J Eur Ceram Soc 32(7) 1355-1358... 

Sialon powders produced by one of the techniques discussed above can be shaped by slip casting and subsequently consolidated to a fully dense state by HIPing, or by pressureless sintering in the presence of sintering aids such as yttria, sometimes under addition of seed crystals of P- or a-sialon (Zenotchkine et al., 2004). 

NMR spectroscopy. The effect of Si3N4 and AIN on the fabrication of lithium-aluminosilicate oxynitride glass ceramics has been investigated using NMR spectroscopy.The thermal oxidation of P-sialon powders has been followed using Al and Si MAS NMR spectroscopy. a-Sialon ceramics synthesized from a clay precursor have been characterized using MAS NMR spectroscopy. Al and Si NMR spectra have been reported for Si-Al-O-N glasses. 

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