| 521. |
- Li, Duan, et al.
(författare)
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Dense and strong ZrO2 ceramics fully densified in <15 min
- 2019
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Ingår i: Advances in Applied Ceramics. - : Informa UK Limited. - 1743-6753 .- 1743-6761. ; 118:1-2, s. 23-29
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Tidskriftsartikel (refereegranskat)abstract
- Crack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600–1700°C for 3–5 min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300–1200 nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244 ± 139 MPa, 13.3 ± 0.3 GPa and 5.5 ± 0.1 MPa m1/2, respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.
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| 522. |
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| 523. |
- Li, Duan, et al.
(författare)
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Densification as an exothermic process revealed by rapid high temperature consolidation of BaTiO3 nanopowder
- 2014
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Ingår i: Advances in Applied Ceramics. - 1743-6753 .- 1743-6761. ; 113:4, s. 251-256
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Tidskriftsartikel (refereegranskat)abstract
- Densification is an exothermic process according to the classical sintering theories; however, it has never been explored experimentally. In the present work, such heat release was successfully detected from nanosized BaTiO3 nanopowder compact, which was rapidly consolidated by spark plasma sintering. A reduction of total power consumption was observed immediately when rapid densification occurred. The effects of the deviation of overall electric resistance on total power consumption were analysed. The temperature at which a falling inflection point of the power supply was observed can be used as an indicator of the minimum temperature required for densification. This would be of help for defining the 'kinetic window' for processing of nanoceramics in sintering practice.
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| 524. |
- Li, Duan, et al.
(författare)
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Preparation of nasal cavity-like SiC-Si3N4 foams with a hierarchical pore architecture
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:35, s. 27891-27900
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Tidskriftsartikel (refereegranskat)abstract
- Rigid SiC-Si3N4 foams with hierarchical porosity were prepared through protein-based gel-casting followed by radiant sintering in a modified spark plasma sintering (SPS) set-up. The porous bodies sintered at 1500-1700 degrees C for only 10 minutes achieved a compressive strength of 15-21 MPa while keeping a porosity of 60-70 vol%. Gradient porous structures, with pore sizes ranging between 1 to 100 mm, were intersected by the growth of hybrid SiC and Si3N4 nanowires inside the pores resulting in a nasal cavity-like appearance. Gas permeability at room temperature (25 degrees C) and 600 degrees C was evaluated. Darcian permeabilities and non-Darcian permeabilities of all the prepared foams at room temperature fell within (0.354-1.55) x 10(-12) m(2) and (1.60-6.33) x 10(-8) m, respectively. Measurement of the Darcian and non-Darcian permeabilities at 600 degrees C were much higher, at 1.71 x 10(-11) m(2) and 2.68 x 10(-7) m, respectively. The microstructure, stability, gas flow properties and the green synthesis route reveal the potential of these ceramic foams to be used as industrial PM filters for airborne pollutions.
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| 525. |
- Li, Duan, 1987-
(författare)
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Rapid sintering of ceramics by intense thermal radiation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sintering is an important processing step for obtaining the necessary mechanical stability and rigidity of ceramic bulk materials. Both mass and heat transfer are essential in the sintering process. The importance of radiation heat transfer is significantly enhanced at high temperatures according to the well-known Stefan-Boltzmann’s law. In this thesis, we modified the pressure-less spark plasma sintering set-up to generate intense thermal radiation, aiming at rapid consolidation of ceramic bulk materials. This approach was named as “Sintering by Intense Thermal Radiation (SITR)” as only thermal radiation contributed.Firstly, the heat and mass transfer mechanisms during the SITR process were studied by choosing zirconia ceramics as references. The results revealed that the multiple scattering and absorption of radiation by the materials contributed to the heat diffusion. The observed enhanced densification and grain growth can be explained by a multiple ordered coalescence of zirconia nanocrystals using high heating rates.Secondly, the temperature distribution during the SITR process was investigated by both numerical simulation and experimental verifications. It showed that the radiator geometry, sample geometry and radiating area were influencing factors. Besides, the change of material and geometry of the radiators resulted in an asymmetric temperature distribution that favored the formation of SiC foams. The foams had gradient structures with different open porosity levels and pore sizes and size distributions.Finally, ceramic bulk materials were successfully fabricated by the SITR method within minutes. These materials included dense and strong ZrO2 ceramics, Si3N4 foams decorated with one-dimensional nanostructures, and nasal cavity-like SiC-Si3N4 foams with hierarchical heterogeneities. Sufficient densification or formed strong necks were used for tailoring these unique microstructures. The SITR approach is well applicable for fast manufacture of ceramic bulk materials because it is clean and requires low energy consumption and properties can be controlled and tuned by selective heating, heating speed or temperature distribution.
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| 526. |
- Li, Duan, et al.
(författare)
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Rapid sintering of ceramics with gradient porous structure by asymmetric thermal radiation
- 2015
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 98:12, s. 3631-3634
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Tidskriftsartikel (refereegranskat)abstract
- In this study, thermal radiation was employed for sintering silicon carbide foams that achieved a gradient porous structure. The simultaneous use of graphite and carbon fiber reinforced carbon composite (Cf/C) radiators resulted in an axial temperature gradient of ~600°C along the cylindrical sample, as confirmed by both numerical simulation and experimental measurement. By sintering the cylinder top at 1600°C for 5 min, the porous SiC body achieved an axial pore size gradient from ~106 ± 36 μm to ~250 ± 84 μm and an open porosity from 41.4 to 79.8 vol%. This work indicates the potential of sintering by intense thermal radiation technique for rapid manufacturing functionally graded materials through asymmetric assembly of thermal radiators.
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| 527. |
- Li, Duan, et al.
(författare)
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Rapid sintering of silicon nitride foams decorated with one-dimensional nanostructures by intense thermal radiation
- 2014
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Ingår i: Science and Technology of Advanced Materials. - : Informa UK Limited. - 1468-6996 .- 1878-5514. ; 15:4
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Tidskriftsartikel (refereegranskat)abstract
- Silicon nitride foams were prepared by direct foaming and subsequent rapid sintering at 1600 °C. The intense thermal radiation generated under the pressureless spark plasma sintering condition facilitated necking of Si3N4 grains. The prepared foams possessed a porosity of ~80 vol% and a compressive strength of ~10 MPa, which required only ~30 min for the entire sintering processes. Rapid growth of one-dimensional SiC nanowires from the cell walls was also observed. Thermodynamic calculations indicated that the vapor–liquid–solid model is applicable to the formation of SiC nanowires under vacuum.
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| 528. |
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| 529. |
- Li, Duan, et al.
(författare)
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Sintering by intense thermal radiation (SITR) : A study of temperature distribution by simulation and experiments
- 2015
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 35:12, s. 3303-3309
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Tidskriftsartikel (refereegranskat)abstract
- The modeling and a confirming experimental study of a sintering process by using intense thermal radiation (SITR) is demonstrated. Experiments were conducted in a modified spark plasma sintering set-up for the purpose of rapid consolidation of porous SIC ceramics. A finite element method based software package, COMSOL Multiphysics, was employed to simulate the temperature distributions with two different die geometries. Experimental verifications were performed by sintering of SiC foams and measuring the temperature differences between two fixed points on the die and samples at 1000-1800 degrees C. SiC foams sintered under two geometries with 10 mm' dwell resulted in the formation of grain necks. The compressive strengths are 19.2 +/- 0.7 MPa (65.0 +/- 0.1 vol% porosity) and 15.3 +/- 1.9 MPa (69.0 +/- 0.3 vol% porosity), respectively. The simulation and experimental results showed that the temperature distributions are strongly related to these geometries.
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| 530. |
- Li, Duan, et al.
(författare)
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Structural study of disordered SiC nanowires by three-dimensional rotation electron diffraction
- 2014
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Ingår i: Materials Research Express. - : IOP Publishing. - 2053-1591. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- The structure of disordered SiC nanowires was studied by using the three-dimensional rotation electron diffraction (RED) technique. The streaks shown in the RED images indicated the stacking faults of the nanowire. High-resolution transmission electron microscopy imaging was employed to support the results from the RED data. It suggested that a 2H polytype is most possible for the nanowires.
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