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Journal of Ceramic Science and Technology 2/2011

Vol. 2, No. 2 · April 2011

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Methods of Quantification of the Internal Structures of Spray Granules

S. Höhn, S. Eckhard, M. Fries, B. Matthey, M. Herrmann, A. Michaelis

Pages 75-88 · DOI: 10.4416/JCST2011-00003

Granules for die pressing applications prepared by means of spray drying need to possess specific properties defined by the end-application. The internal structure of the granules is therefore an important quality-determining property because it influences both the processing properties of the loose granules and the defect distribution in the sintered ceramic part. In this paper, an optimized, artifact-free, gentle and reproducible preparation method based on ion beam technology for exposing the internal granule structures is presented. Model Al2O3 granules are used to demonstrate the possibi …

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Alumina-Doped 2.5Y-TZP produced from Yttria-Coated pyrogenic Nanopowder

F. Kern

Pages 89-96 · DOI: 10.4416/JCST2011-00001

Y-TZP ceramics are widely used owing to their high strength, toughness and abrasion resistance. In this study, pyrogenic zirconia nanopowders were coated with yttria via the nitrate route and blended with 0.5 vol% alumina. Powders were consolidated by hot pressing at 1200 – 1500 °C. The fine-grain TZP materials produced show high strength of 1 GPa. Despite the high toughness of > 9 MPa·√m and high transformability of > 60 %, the ceramics exhibit aging resistance similar to state-of-the-art co-precipitated . The parameters of the Mehl-Avrami-Johnson kinetics indicate that aging of coated …

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Photoactive TiO₂ Nanopowder Synthesized at Low Temperature without a Catalyst

J.-P. Nikkanen, E. Huttunen-Saarivirta, T. Kanerva, T. Kivelä, E. Levänen, T. Mäntylä

Pages 97-102 · DOI: 10.4416/JCST2011-00008

Nanocrystalline titanium dioxide (TiO2) anatase powder was synthesized at 50 °C under normal pressure using the sol-gel method without a base or acid catalyst. The structural and photocatalytic properties of the produced anatase powder were determined with X-ray diffraction, transmission electron microscopy and nitrogen adsorption testing, and compared to those of anatase powder synthesized in a conventional process by calcining at 450 °C. The photocatalytic activity was confirmed with methylene blue (MB) discoloration tests. The obtained results showed that the crystal size of anatase produce …

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Laser-Fused Transparent Microspheres with the Eutectic Composition Al₂O₃-Y₂O₃-ZrO₂ (AYZ)

C. Oelgardt, J. Günster, J. G. Heinrich

Pages 103-110 · DOI: 10.4416/JCST2011-00010

Transparent microspheres with the eutectic composition 65 Al2O3-16 Y2O3-19 ZrO2 (mol%) have been produced by laser fusing with a CO2 laser. The influence of the starting material – not pre-calcined and pre-calcined – as well as the laser power on the resulting microspheres – was investigated. After fabrication, the microspheres were analyzed by means of XRD to quantify the amorphous content of the spheres as well as to identify the residual crystalline phases, with a laser granulometer to measure the particle sizes of the starting material and the resulting microspheres, with DSC to characteri …

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Porous Si-SiC Ceramics Derived by Oxidation from C/C-Si-SiC Composites

V.K. Srivastava, W. Krenkel, V.J.A. D'Souza, H.W. Mucha

Pages 111-118 · DOI: 10.4416/JCST2011-00007

Novel porous Si-SiC ceramics are derived by the oxidation of C/C-Si-SiC fibre matrix composites. The correlated mass loss and obtained open porosity depend on the temperature and holding times of the oxidation process. Microstructure and phase analyses of the Si-SiC composites are performed and supplemented with experimental determinations of the open porosity, the pore size distribution and surface area. These macroscopic properties are influenced by the parameters of the oxidation process. Material parameters like the fibre alignment (weave style resp. fibre length) and phenolic resin type ( …

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Effect of Heat Treatment on Grain Growth of Nanocrystalline Hydroxyapatite Powder

I. Mobasherpour, E. Salahi

Pages 119-124 · DOI: 10.4416/JCST2010-00046

Nanocrystalline hydroxyapatite powder was synthesized with the solution-precipitation method followed by heat treatment in order to evolve phases, which were studied with XRD and TEM techniques. The crystallites sizes were estimated with the Scherrer method and results confirmed with TEM micrographs. The experimental observations showed that nanocrystalline hydroxyapatite can be successfully prepared from raw materials with the precipitation technique. Compared to other techniques, the precipitation technique is a competitive method for nanocrystalline hydroxyapatite synthesis. Moreover, a gro …

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Free Forming of Porous Ceramic Parts by Rapid Freeze Gelation (RFG)

L. Henkel, Chr. Soltmann, L. Vinke, D. Koch, G. Grathwohl

Pages 125-132 · DOI: 10.4416/JCST2011-00004

A novel manufacturing route is presented called rapid freeze gelation (RFG) for the fabrication of silica-sol-based ceramic bodies via freeze consolidation without geometric restrictions. The layer-by-layer shaping method permits a constant freeze velocity over the entire consolidation process. Thus, ceramic parts with homogeneous microstructures can be produced and pore structures can be adjusted as intended. The final pore structure is templated by means of ice crystallization, which is controlled by the freezing conditions and the effect of freezing modifiers such as e.g. glycerol. Ceramic …

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Residual Stress Strengthening in Layered Tricalcium Phosphate (TCP) Bioceramics

E. Hahn, T. Fey, K. Zuo, D.-L. Jiang, P. Greil

Pages 133-138 · DOI: 10.4416/JCST2011-00005

Residual compressive stress formation on the outer surface layers of bioresorbable calcium phosphate multilayer composites was investigated in order to increase their strength. Multilayer laminates of β-Ca3(PO4)2 (TCP) from two different powders were prepared by means of tape casting, laminate pressing, and pressureless sintering. As the laminates cooled from sintering temperature, differences in thermal contraction between the surface layer prepared from a Mg2+-doped β-TCP powder and the core layers caused the generation of surface stresses. The relaxation strain upon removing the surface lay …

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