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Dynamic Pore Coalescence in Nanoceramic Consolidated by Two-Step Sintering Procedure
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
2013 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 33, no 11, 2087-2092 p.Article in journal (Refereed) Published
Abstract [en]

Two-step sintering (TSS) concept was adopted in the consolidation of 3 mol% yttria doped zirconia nanopowder. Partially densified bodies with 87% theoretical density (TD) were firstly prepared using high-pressure spark plasma sintering (SPS) technique and followed by second-step pressureless sintering. The samples achieved only 96% TD final density after 30 h soaking. It was found that the densification process was impeded by dynamic pore coalescence with a pore growth factor of 10. The phenomenon was explained by the coalescence of interconnected small pores generated by differential sintering of nanoceramic green compacts. Such pore coalescence was accompanied with particle movement, which resulted in sintering state deviating from the frozen state. Present results indicated that the active range for particle rearrangement was greatly extended during nanoceramic sintering and the efficiency of TSS approach was greatly dependent on the homogeneity of green bodies

Place, publisher, year, edition, pages
2013. Vol. 33, no 11, 2087-2092 p.
Keyword [en]
Nanoceramics, two-step sintering (TSS), Densification, Grain growth
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-89299DOI: 10.1016/j.jeurceramsoc.2013.03.015ISI: 000319539500004OAI: oai:DiVA.org:su-89299DiVA: diva2:616941
Funder
Swedish Research Council, 621-2008-5730
Note

AuthorCount: 3;

Available from: 2013-04-19 Created: 2013-04-19 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Grain growth by Ordered Coalescence of crystallites in Ceramics: Grain Growth Mechanisms, Microstructure Evolution and Sintering
Open this publication in new window or tab >>Grain growth by Ordered Coalescence of crystallites in Ceramics: Grain Growth Mechanisms, Microstructure Evolution and Sintering
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Grain growth and densification process play the two most crucial roles on the microstructure evolution and the achieved performances during sintering of ceramics. In this thesis, the grain growth of SrTiO3, BaTiO3-SrTiO3 solid solutions and Si3N4 ceramics during spark plasma sintering (SPS) were investigated by electron microscopy.

SrTiO3 ceramics starting from nanopowders were fabricated by SPS. A novel grain growth mechanism was discovered and named as ordered coalescence (OC) of nanocrystals. This mechanism involved nanocrystals as building blocks and is distinguished from atomic layer epitaxial growth (AEG) in classical sintering theory. The results also revealed that the dominant grain growth mechanism can be changed by varying heating rates. Low rate (10°C/min) gives AEG, whereas high rates (≥ 50°C/min) yields three-dimensional coalescence of nanocrystals, i.e. OC.

BaTiO3-SrTiO3 sintered bodies were made by SPS of BaTiO3 and SrTiO3 nanopowders mixtures. A novel Sr1-xBaxTiO3 “solid solution” with mosaic-like single crystal structure was manufactured by OC of the precursor crystallites. This reveals a new path for preparation of solid solution grains or composites.  

Si3N4 ceramics were prepared from α- or β-Si3N4 nanopowders at the same SPS conditions. The anisotropic OC of precipitated β-Si3N4 crystallites gives elongated β-Si3N4 grains at 1650°C using α-Si3N4 nanopowder. In contrast, AEG leads to the equi-axed β-Si3N4 grains using β-Si3N4 nanopowder. The metastable α- to β-Si3N4 phase transformation and OC accelerates anisotropic grain growth.

Grain motions contribute to the densification process during pressureless sintered 3Y-ZrO2 (>87%TD) or SPS of SrTiO3 (>92%TD) ceramics. This extends the sintering range for active grain re-arrangement over that predicted by classical theory.

In this thesis a new grain growth mechanism (OC) is proved by using SPS and nanopowders. By OC the microstructural evolution can be manipulated.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2013. 80 p.
National Category
Materials Chemistry Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:su:diva-88628 (URN)978-91-7447-677-4 (ISBN)
Public defence
2013-06-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Submitted. Paper 4: Manuscript. Paper 7: Accepted.

Available from: 2013-05-16 Created: 2013-03-22 Last updated: 2013-06-14Bibliographically approved

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