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Phase formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures
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2008 (English)In: Journal of the European Ceramic Society, ISSN 0955-2219, Vol. 28, no 4, 747-756 p.Article in journal (Refereed) Published
Abstract [en]

Calcium aluminate is the main constituent in calcium aluminate cements, used in a wide range of applications in construction and mining industries and recently also as biomedical implant. In applications that demand very precise reaction features, such as the biomedical ones, the phase purity is of very high importance. In this paper the formation of CaAl2O4 from CaCO3-Al2O3 powder mixtures has been studied, varying holding times between 1 and 40 h and temperatures between 1300 and 1500 degrees C. Phase formation was studied in samples both quenched from the holding temperatures and in samples slowly cooled. Samples were characterized by X-ray powder diffraction (XRPD), using Guinier-Hagg film data and the Rietveld method, and scanning (SEM) and transmission (TEM) electron microscopy. Samples for TEM with very high site accuracy were produced using focused ion beam microscopy. In addition to CA (CaAl2O4) the samples contained major amounts of CA(2) (CaAl4O7), C(12)A(7) (Ca12Al14O33) and minor amounts of un-reacted A (Al2O3). Trace amounts of C(3)A (Ca3Al2O6) were observed only for samples heated to 1500 degrees C. The amount of the Ca-rich phase C(12)A(7) was found to decrease with time as it reacts with A and, to a less degree, CA(2) to form CA. In agreement with previous studies the amount of CA(2) formed decreases comparatively slowly with time. Its un-reactivity is due to that it is concentrated in isolated porous regions of sizes up to 100 mu m. The formation of the Ca aluminates is found to be in response to local equilibriums within small inhomogeneous regions, with no specific phase acting as an intermediate phase. Samples quenched from 1500 degrees C were found to contain smaller amounts of poorly crystallized phases. A reaction between C and A takes place already at 900 degrees C, forming a meta-stable orthorhombic modification of CA. The orthorhombic unit cell with a = 8.732(2) b = 8.078(2) angstrom, c = root 3 center dot a = 15.124(4) angstrom was verified by electron diffraction, revealing frequent twinning and disorder of the crystallites.

Place, publisher, year, edition, pages
2008. Vol. 28, no 4, 747-756 p.
Keyword [en]
calcium aluminates, calcinations, powders-solid state reaction, microstructure, alkaline earth oxides, Al2O3, CaAl2O4
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-97389DOI: 10.1016/j.jeurceramsoc.2007.08.012ISI: 000253260200007OAI: oai:DiVA.org:uu-97389DiVA: diva2:172325
Available from: 2008-08-19 Created: 2008-08-19 Last updated: 2011-05-11Bibliographically approved
In thesis
1. Calcium-Aluminate as Biomaterial: Synthesis, Design and Evaluation
Open this publication in new window or tab >>Calcium-Aluminate as Biomaterial: Synthesis, Design and Evaluation
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis different aspects of calcium-aluminate (CA) as biomaterial are presented. Calcium aluminate is a chemically bonded ceramic with inherent properties making it suitable for use as biomaterial in some applications. In this thesis the emphasis is put on the basic chemical, physical and mechanical properties that may be achieved using the CA system as well as synthesis of the CA raw material. The basis for using CA in any application is the synthesis of the raw material. Different synthesis routes for producing CA are presented with focus on high temperature routes and the micro-structural and phase development during synthesis. As a base for further understanding of the CA properties a thorough outline of the reaction chemistry for CA is presented also including a description of how the reactions may be controlled and how formulations can be designed. The surface reactions of CA when subjected to simulated body fluid showed that CA is in vitro bioactive. An in vivo study in teeth also indicates that CA produces apatite at the tooth material interface. Dental materials are subjected to a harsh environment in the mouth with high mechanical forces, erosion and thermal changes. Also the demands on precise handling characteristics are high. For these reasons the in vitro evaluation of physical and mechanical properties are important. In this work several mechanical and physical properties of Ca-based formulations for dental applications has been tested using different methods. Some attention is also put on the specific characteristics of CA and the difficulties that arise when new material classes needs to be tested according to consensus standard methods. Finally studies on a CA-based formulation intended for Vertebroplasty is presented. The studies include basic mechanical properties as well as testing the material in an in vitro model utilising synthetic cancellous bone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 87 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 452
Calcium-aluminate, Biomaterial, Dental materials, Vertebroplasty, Chemically Bonded Ceramics, Synthesis
National Category
Biomaterials Science
urn:nbn:se:uu:diva-9173 (URN)978-91-554-7248-1 (ISBN)
Public defence
2008-09-12, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Available from: 2008-08-19 Created: 2008-08-19 Last updated: 2011-07-08Bibliographically approved

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