| 1. |
- Kalousek, Radek, et al.
(författare)
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Rapid heating of zirconia nanoparticle-powder compacts by infrared radiation heat transfer
- 2017
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 37:3, s. 1067-1072
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Tidskriftsartikel (refereegranskat)abstract
- Homogeneous rapid sintering of nanoparticle powder compacts of yttria-stabilized zirconia was achieved by the radiation heat transfer. Green bodies were prepared by cold isostatic pressing (CIP) at various pressures providing different porosity of samples before sintering. Pressure-less sintering was performed in air at a heating rate of 100 degrees C/min up to the 1500 degrees C/1 min. Scanning electron microscopy, mercury intrusion porosimetry, and Archimedes technique were used to characterize the microstructure and to determine the density of the green and sintered bodies. Contrary to expectations, our results reveal opposite dependence of the green- and sintered densities on the CIP pressure. Since the whole sintering process does not exceed 10 min, to propose what processes are responsible for observed results, our attention is focused on the radiation heat transfer from furnace heating elements into the ceramics. Our arguments are supported by numerical calculations of the electromagnetic field enhancement in/between particles.
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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. |
- Salamon, David, et al.
(författare)
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Rapid Grain Growth in 3Y-TZP Nanoceramics by Pressure-Assisted and Pressure-Less SPS
- 2015
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 98:12, s. 3706-3712
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Tidskriftsartikel (refereegranskat)abstract
- Pressure-less spark plasma sintering (SPS) is a new approach during which rapid densification of ceramic nanopowder green bodies is accompanied by rapid grain growth. Although the origin of this phenomenon has not yet been fully understood significant, difference in grain growth between pressure-less and pressure-assisted SPS was expected. In this work 3Y-TZP nanopowder with average particle size of 12 nm was consolidated using two-step approach: (1) at an intermediate temperature (600 degrees C to 1000 degrees C) SPS warm pressing followed by (2) high temperature (1400 degrees C to 1600 degrees C) pressure-less SPS. The standard one step pressure-assisted SPS experiments were quoted as references. Rapid grain growth was observed during both pressure-less and standard SPS. The samples prepared by both approaches at the same sintering temperature (1400 degrees C1600 degrees C) achieved identical grain size and grain size distribution, if large pores were eliminated in early stage by SPS warm pressing. The electric current, electromagnetic field, and mechanical pressure is proven to have a negligible direct influence on grain growth in 3Y-TZP ceramics at temperatures above 1000 degrees C under standard SPS conditions.
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| 5. |
- Salamon, David, et al.
(författare)
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Rapid sintering of crack free zirconia ceramics by pressure less spark plasma sintering
- 2012
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 66:11, s. 899-902
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Tidskriftsartikel (refereegranskat)abstract
- Heating of a ceramic green body is a key step in sintering. We have created inside a spark plasma sintering apparatus pressure-less sintering conditions that allow homogeneous and extremely rapid heating. Dense and crack-free zirconia ceramic was sintered at heating rates of up to 500 degrees C min(-1) and dwell times of 2 min. This extremely fast sintering process is accompanied by extremely rapid grain growth, indicating a non classical sintering mechanism. No grain size gradients were observed inside the sintered zirconia ceramics.
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| 6. |
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| 7. |
- Trunec, Martin, et al.
(författare)
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Warm pressing of zirconia nanoparticles by the spark plasma sintering technique
- 2008
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 59:1, s. 23-26
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Tidskriftsartikel (refereegranskat)abstract
- Zirconia nanoparticles were densified by pressureless sintering and spark plasma sintering (SPS). The evolution of relative density and pore size distribution in powder compacts during these sintering processes were compared. It was found that pore size increase was suppressed during SPS and that this facilitated the densification. The combined sintering process (low-temperature pre-sintering by SPS followed by pressureless sintering) was performed to confirm the advantage of the low-temperature SPS technique (referred to as SPS warm pressing).
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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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