| 1. |
- Kocjan, Andraz, et al.
(författare)
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Processing of zirconia nanoceramics from a coarse powder
- 2015
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:4, s. 1285-1295
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Tidskriftsartikel (refereegranskat)abstract
- We have merged the benefits of coarse-grained and nanocrystalline powders by the consolidation and sintering of coarse, yet nanostructured, mesoporous Y-TZP powder. The powder was composed of loosely aggregated, nanoscale crystallites, which can be seen as secondary particles or agglomerates. Their homogeneous, defect-free packing proved to be a viable pathway for the processing of zirconia nanoceramics. The powder consolidation yielded homogeneous green bodies with hierarchical heterogeneities in terms of intra- and inter-particle pore packing. The hierarchical heterogeneities had a pronounced effect on the densification and grain growth. The intra-particle pore coalescence along with a frozen interparticle porosity, prolonged the pore-pinning effect, separating the densification and grain-growth mechanisms. Increased heating rates promoted the grain-growth and densification via a competitive mechanism of primary crystallite ordered coalescence, while by applying pressure, the crystallite growth was completely prevented, making such a coarse powder suitable for the fabrication of zirconia nanoceramics.
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| 2. |
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| 3. |
- Pouchly, Vaclav, et al.
(författare)
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Two-stage master sintering curve applied to two-step sintering of oxide ceramics
- 2013
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 33:12, s. 2275-2283
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Tidskriftsartikel (refereegranskat)abstract
- Tetragonal (3 mol% Y2O3) and two cubic zirconia (8 mol% Y2O3) as well as alumina green bodies were used for the construction of the Master Sintering Curve (MSC) created from sets of constant-rate-of-heating (CRH) sintering experiments. The activation energies calculated according to the MSC theory were 770 kJ/mol for Al2O3, 1270 kJ/mol for t-ZrO2, 620 kJ/mol and 750 kJ/mol for c-ZrO2. These values were verified by an alternative approach based on an analysis of the densification rate in the intermediate sintering stage. The MSCs established from the Two-Step Sintering (TSS) experiments showed at high densities a significant deflection from those constructed from the CRH experiments. This deflection was explained by lower sintering activation energy in the closed porosity stage. A new two-stage MSC model was developed to reflect the change in sintering activation energy and to describe TSS. The efficiency of TSS of four materials under investigation was correlated with their activation energies during the final sintering stage.
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| 4. |
- Wang, Ling, et al.
(författare)
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Intensive particle rearrangement in the early stage of spark plasma sintering process
- 2015
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Ingår i: Journal of Asian ceramic societies. - : Informa UK Limited. - 2187-0764. ; 3:2, s. 183-187
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Tidskriftsartikel (refereegranskat)abstract
- The densification behaviors of 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) ceramics during spark plasma sintering (SPS) were analyzed both using the master sintering curve (MSC) approach and by evaluating the temperature dependent evolution of density and densification rate. It was found that densification curves could hardly be fitted using one apparent activation energy value by MSC conception, by which it indicated that more than one densification mechanisms were involved in SPS. Moreover, dependent neither on applied pressure (20-100 MPa) nor heating rates higher than 50 degrees C/min, the maximum densification rate had always been observed at rather similar similar to 78% of theoretical density (TD) accompanied with negligible grain growth. An intensive particle rearrangement mechanism was proposed to dominate the rapid densification to 78% TD in early stage of SPS process, by which it yielded the considerable faster densification rate than those achievable by diffusion-related processes. (C) 2015 The Ceramic Society of Japan and the Korean Ceramic Society.
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| 5. |
- Xiong, Yan, et al.
(författare)
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Preparation of Transparent 3Y-TZP Nanoceramics with No Low-Temperature Degradation
- 2014
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 97:5, s. 1402-1406
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Tidskriftsartikel (refereegranskat)abstract
- The progresses of the relative density, average grain size (GS), and maximum pore size entering into the final sintering stage are investigated in 3mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) compacts in the range of 87%similar to 99% theoretical density. It is found that during conventional pressureless sintering, the pores in the compact enlarged dramatically, which appears to be the major obstacle for preparing fully dense nanoceramics. Transparent 3Y-TZP nanoceramics with an average GS of 87nm were prepared by exploiting microstructural refinement on nanoscale. The yields a maximal optical transmittance of 67% and shows no noticeable low-temperature degradation after 100h aging at 134 degrees C under a hydrothermal pressure of two bars.
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| 6. |
- Xiong, Yan, et al.
(författare)
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Preparation of Transparent Nanoceramics by Suppressing Pore Coalescence
- 2011
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 94:12, s. 4269-4273
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Tidskriftsartikel (refereegranskat)abstract
- Microstructural developments in nanoceramics were investigated in 3Y-TZP compacts with relative density (RD) exceeding 93%. Special attentions were paid to the evolutions of pore structures. It was found that the densification process of nanoceramic compacts with apparently close porosity was greatly jeopardized by pore coalescence. This observation was interpreted by the coalescence of locally interconnected pores originated from inhomogeneous packing of particles. The pore coalescence can be suppressed by application of an external pressure. The processing principle was demonstrated by spark plasma sintering (SPS) with extended holding at a minimized sintering temperature. The highly dense 3Y-TZP nanoceramics containing no large pores became optically transparent.
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