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Transparent hydroxyapatite nanoceramics by high pressure spark plasma sintering at the minimized sintering temperature
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Department of Materials Chemistry.
State Key Lab of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

For direct observation of the bio-interfacial reactions with improved spatial and temporal resolution by confocal microscopy transparent hydroxyapatite nanoceramics are demanded. The aim of the present study was to, through detailed kinetics study and micostructural characterization, define a processing window within which transparent HAp nanoceramics can be produced by spark plasma sintering of dry powders.  A lab-made hydrothermally processed bulky powder composed of loosely aggregated nanorods and a commercial granulated-powder composed of irregular shaped nanorods were tested.  The use of a high pressure cell allows the application of pressure up to 500 MPa. It was found that applying of high pressure is beneficial for widen up the processing window for attaining dense HAp ceramics with nano grained microstructure. The high transparency of HAp nanoceramics obtained in this study is ascribed to the high density and homogeneous nano-structure achieved besides the unique intrinsic optical properties of the HAp crystal, i.e. its low refractive index and very small birefringence. Achieving full densification at the minimized sintering temperature allows for the first time the preparation of transparent HAp nanoceramics with stoichiometric composition, i.e. avoiding the loss of water that commonly encountered  during the conventional ways of sintering.

Keyword [en]
Hydroxyapatite, nanoceramics, optical transparency, sintering
Research subject
Materials Chemistry
Identifiers
URN: urn:nbn:se:su:diva-38653OAI: oai:DiVA.org:su-38653DiVA: diva2:312042
Available from: 2010-04-23 Created: 2010-04-23 Last updated: 2010-04-27Bibliographically approved
In thesis
1. Spark Plasma Sintering Enhancing Grain Sliding, Deformation and Grain Size Control: Studies of the Systems Ti, Ti/TiB2, Na0.5 K0.5 NbO3, and Hydroxyapatite
Open this publication in new window or tab >>Spark Plasma Sintering Enhancing Grain Sliding, Deformation and Grain Size Control: Studies of the Systems Ti, Ti/TiB2, Na0.5 K0.5 NbO3, and Hydroxyapatite
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The unique features of the Spark plasma sintering (SPS) were used to investigate the sintering and deformation behaviour of titanium and titanium–titanium diboride composites, and to control the sintering and grain growth of ferroelectric Na0.5K0.5NbO3 (NKN) and of hydroxyapatite (HAp). In the SPS the samples experience a temperature different from that recorded by the thermocouple (pyrometer) used and this temperature difference has been estimated for Ti and NKN.

 

Sintering and deformation of titanium was investigated. Increasing heating rate and/or pressure shifted the sintering to lower temperatures, and the sintering and deformation rates changed when the α→β phase transition temperature was passed. Fully dense Ti/TiB2 composites were prepared. The Ti/TiB2 composites could be deformed at high temperatures, but the hardness decreased due to the formation of TiB. 

 

The kinetic windows within which it is possible to obtain fully dense NKN and HAp ceramics and simultaneously avoid grain growth are defined. Materials have a threshold temperature above which rapid and abnormal grain growth takes place. The abnormal grain growth of NKN is due to a small shift in the stoichiometry, which in turn impairs the ferroelectric properties. Fully transparent HAp nanoceramics was prepared, and between 900 and 1050 oC elongated grains are formed, while above 1050 oC abnormal grain growth takes place.NKN samples containing grains of the sizes 0.35–0.6 µm yielded optimum ferroelectric properties, i.e. a high remanent polarization (Pr = 30 µC/cm2) and high piezoelectric constant (d33= 160 pC/N). The ferroelectric domain structure was studied, and all grains exhibited a multi-domain type of structure.

Place, publisher, year, edition, pages
Stockholm: Department of Materials and Environmental Chemistry, Stockholm University, 2010. 81 p.
Keyword
Spark plasma sintering, plastic deformation, grain growth, titanium, TiB2, hydroxyapatite, Na0.5K0.5NbO3, ferroelectric, transparent
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-38681 (URN)978-91-7447-072-7 (ISBN)
Public defence
2010-05-25, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of doctoral defense the following articles were unpublished and had a status as follows: Article 4: Manuscript; Article 5 : Manuscript Available from: 2010-05-04 Created: 2010-04-26 Last updated: 2010-04-27Bibliographically approved

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