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Sialon Ceramics Prepared by Using CaH2 as a Sintering Additive
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.
2008 (English)In: Journal of the American Ceramic Society, ISSN 0002-7820, Vol. 91, no 9, 2997-3004 p.Article in journal (Refereed) Published
Abstract [en]

In developing elongated a-sialon grains, a nitrogen-rich liquidphase sintering method was introduced by using CaH2 as asintering aid, so as to vary the N/O ratio of the liquid phaseformed in the sintering process while keeping the Si/Al ratiosconstant. With increasing addition the phase contents changedfrom single b-sialon to dual b/a-sialons and to single Ca-a-sialon.At low N/O ratios the microstructures contained mainlyequiaxed b-sialon grains, and at high N/O ratios well facetedelongated Ca-a-sialon grains. The improved toughness(KIC57.8 MPa .m1/2) and hardness (HV10517.5 GPa) propertiescan be attributed to the formation of interlocked microstructures.High-temperature compressive deformation testsindicated that the deformation onset temperature is determinedmainly by the Si/Al and N/O ratios, whereas the deformationrate is affected by the microstructure, i.e., the morphology andamounts of elongated a-sialon grains and residual glass phase,especially for the sialons with low N/O ratios.

Place, publisher, year, edition, pages
2008. Vol. 91, no 9, 2997-3004 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-25767DOI: 10.1111/j.1551-2916.2008.02549.xISI: 000259151000035OAI: oai:DiVA.org:su-25767DiVA: diva2:200491
Note
Part of urn:nbn:se:su:diva-8568Available from: 2009-02-26 Created: 2009-02-17 Last updated: 2012-03-23Bibliographically 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
Opponent
Supervisors
Available from: 2009-02-26 Created: 2009-02-17Bibliographically approved

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