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Thermal Properties of Nitrogen-Rich Ca-α-Sialons
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
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2009 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 29, no 16, 3409-3417 p.Article in journal (Refereed) Published
Abstract [en]

Nitrogen-rich Ca-α-Sialon (CaxSi12−2xAl2xN16 with x = 0.2, 0.4, and 0.8, 1.2 and 1.6) ceramics were prepared from the mixtures of Si3N4, AlN and CaH2 powders in a hot press at 1800 °C using a pressure of 35 MPa and a holding time of 4 h, and then were investigated with respect to reaction mechanism, phase stability and oxidation resistance. In addition the sample with x = 1.6 was prepared in the temperature range 600–1800 °C using a pressure of 35 MPa and a holding time of 2 h. The α-Sialon phase was first observed at 1400 °C but the α-Si3N4 and AlN phases were still present at 1700 °C. Phase pure Ca-α-Sialon ceramics could not be obtained until the sintering temperature reached 1800 °C. The phase pure nitrogen-rich Ca-α-Sialon exhibited no phase transformation in the temperature range 1400–1600 °C. In general, mixed α/β-Sialon showed better oxidation resistance than pure α-Sialon in the low temperature range (1250–1325 °C), while α-Sialons with compositions located at α/β-Sialon border-line showed significant weight gains over the entire temperature range tested (1250–1400 °C). The phases formed upon oxidation were characterized by X-ray, SEM and TEM studies.

Place, publisher, year, edition, pages
2009. Vol. 29, no 16, 3409-3417 p.
Identifiers
URN: urn:nbn:se:su:diva-25769DOI: 2122/10.1016/j.jeurceramsoc.2009.07.015ISI: 000270694400014OAI: oai:DiVA.org:su-25769DiVA: diva2:200493
Note
Part of urn:nbn:se:su:diva-8568Available from: 2009-02-26 Created: 2009-02-17 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Synthesis and Characterization of Nitrogen-rich Calcium α-Sialon Ceramics
Open this publication in new window or tab >>Synthesis and Characterization of Nitrogen-rich Calcium α-Sialon Ceramics
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, a synthesis concept has been developed, which uses nitrogen-rich liquid phases for sintering of Ca-α-sialon ceramics. First, keeping the Si/Al ratios constant, the effects of N/O ratio on the properties and microstructure were investigated through a liquid phase sintering process. Second, nitrogen-rich Ca-α-sialon ceramics, with nominal compositions: CaxSi12-2xAl2xN16, x < 2.0, was synthesized and characterized. Third, mechanical and thermal properties of nitrogen-rich Ca-α-sialons were investigated in terms of high temperature deformation resistance,reaction mechanism, phase stability and oxidation resistance, and further correlated to their phase assemblage and microstructure observation.

It has been found that increasing the N/O and Ca/Al ratio simultaneously in the materials could result in development of a microstructure with well shaped, high-aspect-ratio Ca-α-sialon grains, and an improvement in both toughness and hardness.

For the nitrogen-rich Ca-α-sialon, mono-phasic α-sialon ceramics were obtained for 0.51 ≤ x ≤ 1.32. The obtained Ca-α-sialon ceramics with elongated-grain microstructures show a combination of high hardness and high fracture toughness. Compared with the oxygen-rich Ca-α-sialons, the nitrogen-rich Ca-α-sialons exhibited approximately 150 oC higher deformation onset temperatures and decent properties even after the deformation.

The α-sialon phase was first observed at 1400 oC, however the phase pure Ca-α-sialon ceramics couldn’t be obtained until 1800 oC. The nitrogen-rich Ca-α-sialons were thermal stable, no phase transformation observed in the temperatures range1400-1600 oC. In general, mixed α/β-sialon showed better oxidation resistance than pure α-sialon in the low temperature range (1250-1325 oC), while α-sialons with compositions located at α/β-sialon border-line showed significant weight gains over the entire temperature range (1250-1400 oC).

Place, publisher, year, edition, pages
Stockholm: Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, 2009. 57 p.
Keyword
Nitrogen-rich, SiAlON, Sintering, Microstructure, Properties
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-8568 (URN)978-91-7155-823-7 (ISBN)
Public defence
2009-03-20, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
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Available from: 2009-02-26 Created: 2009-02-17Bibliographically approved

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