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2 1998

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Development of the phase composition in the carbothermally derived beta-sialon ceramics.

Sopicka-Lizer M., Metselaar R.

Inżynieria Materiałowa

1998

R. XIX, nr 4

735-738

Carbothermally derived beta-sialon powders with different phase composition were presureless sintered with or without yttria additives. Then they were isothermally annealed in nitrogen. XRD study has shown changes in the phase composition after sintering and annealing at 1450 degrees centigrade. Development of the phase composition was dependent on the composition of the starting beta-sialon powders (presence of AlN or 15R phase) and yttria admixture. It has been found that sintering of carbothermally derived powders shifted the composition of the ceramics towards beta-sialon with higher z-value. Further annealing in nitrogen could lead to decomposition of sialon polytypoid phases and was accompanied by slow oxidation at low oxygen partial pressure.

Aqueous processing of SiAlON powders.

Kudyba A., Serkowski S., Hintzen H.T., Metselaar R.

Inżynieria Materiałowa

1998

R. XIX, nr 4

1268-1271

To manipulate and understand the suspension behaviour in water of carbothermally prepared Ca-alpha-SiAlON and beta-SiAlON powders, to be processed by slip casting, different characterization methods were applied. These concerned: zeta potential, ESA, rheological sedimentation and floc size measurements. The best deflocculation was found at pH 10-11 where both investigated powders showed the lowest viscosity (below 10 MPa's), the lowest sediment volumes and the highest absolute of zeta potentials. At this pH the suspensions where considered to have the most favourable condition for this chosen process. The powders showed similar suspension behaviour (viscosity, behaviour, sedimentation behaviour, isoelectric points) suggesting similar surface characteristics probably due to resemblance of the surface due to oxidation treatment after carbothermal synthesis. Rheometry and zeta potential were found to be fast techniques providing the most useful and complete information of slip behaviour allowing a good choice of suspension parameters.