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Grain growth by multiple ordered coalescence of nanocrystals during spark plasma sintering of SrTiO3 nanopowders
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
2012 (Engelska)Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, nr 18, s. 6405-6412Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Sintering is the most widely applied densification process for manufacturing polycrystalline materials in powder metallurgy and ceramic industries. Grain growth behavior during sintering has a crucial influence on the final microstructure and thus the achieved performance. So far, it has been accepted that grain growth, based on classic crystal growth theory, takes place via atomic diffusion driven by excess interfacial energy. This paper presents a novel grain growth mechanism resulting from multiple ordered coalescence of nanocrystals via the activation of rapid grain motions. In rapid solid-state sintering of a strontium titanate (SrTiO3) nanopowder, individual SrTiO3 nanocrystals can act as the building blocks and self-assemble to form larger grains. A quasi-liquid interfacial film achieved by surface melting of the nanocrystals plays an essential role in this new process by facilitating the grain motion and ordered coalescence of nanocrystals. The imperfect ordered coalescence of nanocrystals introduce deep structural heterogeneities characterized by the unique quasi-interfaces inside grown grains of single crystal signature. The quasi-interfaces consist of the vacancy arrays and/or aggregated line defects.

Ort, förlag, år, upplaga, sidor
2012. Vol. 60, nr 18, s. 6405-6412
Nyckelord [en]
Coalescence, Interface, Grain growth mechanism, Rapid sintering, Nanocrystals
Nationell ämneskategori
Kemi
Identifikatorer
URN: urn:nbn:se:su:diva-83785DOI: 10.1016/j.actamat.2012.08.027ISI: 000310663300017OAI: oai:DiVA.org:su-83785DiVA, id: diva2:578581
Anmärkning

AuthorCount:2;

Tillgänglig från: 2012-12-18 Skapad: 2012-12-14 Senast uppdaterad: 2019-11-20Bibliografiskt granskad
Ingår i avhandling
1. Grain growth by Ordered Coalescence of crystallites in Ceramics: Grain Growth Mechanisms, Microstructure Evolution and Sintering
Öppna denna publikation i ny flik eller fönster >>Grain growth by Ordered Coalescence of crystallites in Ceramics: Grain Growth Mechanisms, Microstructure Evolution and Sintering
2013 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Materials and Environmental Chemistry (MMK), Stockholm University, 2013. s. 80
Nationell ämneskategori
Materialkemi Oorganisk kemi
Forskningsämne
oorganisk kemi
Identifikatorer
urn:nbn:se:su:diva-88628 (URN)978-91-7447-677-4 (ISBN)
Disputation
2013-06-13, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (Engelska)
Opponent
Handledare
Anmärkning

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.

Tillgänglig från: 2013-05-16 Skapad: 2013-03-22 Senast uppdaterad: 2013-06-14Bibliografiskt granskad

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