| 1. |
- Liu, Leifeng, et al.
(författare)
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Self-supported yttria-stabilized zirconia mesocrystals with tunable mesopores prepared by a chemi-thermal process
- 2019
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Ingår i: Journal of Materiomics. - : Elsevier BV. - 2352-8478 .- 2352-8486. ; 5:3, s. 350-356
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Tidskriftsartikel (refereegranskat)abstract
- Mesoporous mesocrystals are highly desired in catalysis, energy storage, medical and many other applications, but most of synthesis strategies involve the usage of costly chemicals and complicated synthesis routes, which impede the commercialization of such materials. During the sintering of dense ceramics, coarsening is an undesirable phenomenon which causes the growth of the grains as well as the pores hence hinders the densification, however, coarsening is desired in the sintering of porous ceramics to expand the pore sizes while retaining the total pore volume. Here we report a chemi-thermal process, during which nanocrystallite aggregates were synthesized by hydrothermal process and then converted to the product by sintering. Through this strategy, we synthesized mesoporous self-supported mesocrystals of yttria-stabilized zirconia with tunable pore size and the process was then scaled-up to industrial production. The thermal conductivity measurement shows that the mesoporous powder is a good thermal isolator. The monolith pellets can be obtained by SPS sintering under high pressure and the mesoporosity is retained in the monolith pellets. This work features facile and scalable process as well as low cost raw chemicals making it highly desirable in industrial applications.
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| 2. |
- Chen, Jinhan, et al.
(författare)
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The effect of hot isostatic pressing on thermal conductivity of additively manufactured pure tungsten
- 2020
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 87
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Tidskriftsartikel (refereegranskat)abstract
- The crack-healing behaviors and microstructure evolution of pure tungsten produced by laser powder bed fusion (LPBF) were studied and compared before and after post hot isostatic pressing (post-HIP) treatment. An average thermal conductivity of 133 W.m(-1).K-1 at room temperature (RT) was obtained after HIP, which was 16% higher than that of as-built sample (115 W.m(-1).K-1). Although the HIP process had little effect on density, it resulted in a large grain size of > 300 mu m accompanied by a decrease in dislocation density and crack healing, which led to a substantial improvement of thermal conductivity of pure tungsten. The positive correlation between relative density and thermal conductivity of as-built tungsten was reported.
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| 3. |
- 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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| 4. |
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| 5. |
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| 6. |
- Liu, Xihe, et al.
(författare)
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CNT-reinforced AlSi10Mg composite by selective laser melting : microstructural and mechanical properties
- 2019
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Ingår i: Materials Science and Technology. - : Informa UK Limited. - 0267-0836 .- 1743-2847. ; 35:9, s. 1038-1045
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nanotube (CNT)-AlSi10Mg composites were fabricated by selective laser melting (SLM). The influence of CNTs on the density, microstructure, and strength of SLM CNT-AlSi10Mg composites was investigated. The addition of CNTs over 0.1 wt-% significantly damaged the density due to the high surface energy of the CNTs. The network Si eutectic had no significant difference in either the SLM AlSi10Mg alloy or the CNT-AlSi10Mg composite. Reserved CNTs with a short scale were observed in the SLM CNT(0.5 wt-%)-AlSi10Mg composite. The ultimate tensile strength of the 0.05 wt-% CNT-AlSi10Mg composite was 441.2 +/- 0.9 MPa, which was higher than that of AlSi10Mg alloy. The grain boundary strengthening played an important role in the reinforcement of CNT-AlSi10Mg composite because of the refined grain.
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| 7. |
- Liu, Xihe, et al.
(författare)
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Microstructure of selective laser melted AlSi10Mg alloy
- 2019
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Ingår i: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 168
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of laser power during selective laser melting (SLM) on the grain morphology and texture component in AlSi10Mg alloy has been investigated, using electron backscattered diffraction (EBSD). Both equiaxed and columnar grainswere observed. The formation of equiaxed grainswas attributed to the huge thermal gradient on the border of melt pool and the columnar to equiaxed transition (CET) occurred in front of the columnar grains. The grain size of lowlaser power samplewas found smaller than that of higher ones. A fine pseudoeutectic structure, in which Si existed as fibrous, was observed because of the high cooling rate. This paper, from a new angle, explained the formations of three different zones across the melt pool, which were differentiated by the morphology of Si phase. The three zones correspond to the three temperature zones, whichwere divided by liquidus and solidus temperature, during the heating by laser beam. The coarse zones are formed by reheating the basic metal to semi-solid state when the temperature is lower than the liquidus temperature but higher than the solidus temperature.
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| 8. |
- Liu, Xihe, et al.
(författare)
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Morphological Development of Sub-Grain Cellular/Bands Microstructures in Selective Laser Melting
- 2019
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:8
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, single-layer and bulk 316 L selective laser melting (SLM) experiments were conducted, fine submicron-scale geometric symmetrical cellular (hexagonal, pentagonal and square), elongated cellular and bands solidification morphologies were found in the laser-melt top surface. Meanwhile, morphological developed sub-grain patterns with quasi-hexagonal cellular, elongated cellular and bands structures (size similar to 1 m) coexisting inside one single macro-solidified grain were also identified. This demonstrated the transitions from quasi-hexagonal-cells to elongated cells/bands, and transitions reverse, occurred in the whole bulk under some circumstances during SLM. Based on the experimental realities, these morphologies are formed by the local convection and Benard instabilities in front of the solid/liquid interface (so-called mushy zones) affected by intricate temperature and surface tension gradients. Quasi-hexagonal cellular convective fields are then superimposed on macro-grain solidification to form the sub-grain patterns and micro-segregations. This explanation seems reasonable and is unifying as it can be expanded to other eutectic alloys with face center cubic (FCC) prevenient phase prepared by SLM, e.g., the Al-Si and Co-Cr-Mo systems.
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| 9. |
- Liu, Yihong, et al.
(författare)
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Failure Modes and Fracture Origins of Porcelain Veneers on Bilayer Dental Crowns
- 2014
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Ingår i: International Journal of Prosthodontics. - : Quintessence Publishing. - 0893-2174 .- 1139-9791. ; 27:2, s. 147-150
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Tidskriftsartikel (refereegranskat)abstract
- The aims of this study were to determine the fracture origins and crack paths in the porcelain of clinically failed bilayer ceramic restorations and to reveal the correlation between the porcelain failures and material properties. Three clinically failed crowns of each material (bilayer zirconia crowns, galvano-ceramic crowns, and porcelain-fused-to-metal crowns) were collected and underwent failure analysis. The fractures found in porcelain veneers showed several characteristics including wear, Hertzian cone crack, chipping off, and delamination. The results indicated that the fracture origins and features of the porcelain in bilayer ceramic restorations might be affected by the rigidity of core materials and thickness of copings.
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| 10. |
- Liu, Yihong, et al.
(författare)
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Self-glazed zirconia reducing the wear to tooth enamel
- 2016
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 36:12, s. 2889-2894
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Tidskriftsartikel (refereegranskat)abstract
- The wear behaviors of a newly developed grade of self-glazed zirconia against the enamel of freshly extracted teeth were investigated under simulated oral stresses and chemical environment. It was revealed that an inherently formed enamel-like surface on self-glazed zirconia that is very smooth on micrometer scale yet with nanoscale roughness has almost the same frictional coefficient against tooth enamel as the well-polished zirconia surface. The wear scars observed on the worn surface of enamel against self-glazed zirconia and well-polished zirconia surface revealed that in both cases fatigue wear is the dominating wear mechanism. It was concluded that the friction and wear performances of both the well-polished and self-glazed zirconia ceramics against natural enamel were very similar, which bears a very strong implication for the clinical safe use of the full contour zirconia restorations, yet the self-glazed zirconia provides sufficiently improved aesthetic appearance that ensures its potential for direct clinical uses.
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| 11. |
- Olsén, Jon, 1983-, et al.
(författare)
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Tailoring hierarchical structures in selective laser melted materials
- 2017
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Ingår i: IOP Conference Series. - : Institute of Physics (IOP).
-
Konferensbidrag (refereegranskat)abstract
- With selective laser melting the potential to manufacture a wide variety of geometries from different materials has presented itself. Interest in this technology keeps growing every year, and with that growth a deeper understanding of the process and resulting materials is urgently needed. In this paper we present a short overview of the structural elements that appear during selective laser melting, and explain how to tailor them to achieve specific structures and material properties. Melt-pools, texture and grains, subgrain cells, and inclusions are the elements discussed herein, and tailoring of these elements can have effects on density, and corrosion resistance, as well as mechanical properties in general.
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| 12. |
- Richards, Stephen, et al.
(författare)
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The genome of the model beetle and pest Tribolium castaneum.
- 2008
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Ingår i: Nature. - 1476-4687. ; 452:7190, s. 949-55
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Tidskriftsartikel (refereegranskat)abstract
- Tribolium castaneum is a representative of earth’s most numerous eukaryotic order, a powerful model organism for the study of generalized insect development, and also an important pest of stored agricultural products. We describe its genome sequence here. This omnivorous beetle has evolved an ability to interact with a diverse chemical environment as evidenced by large expansions in odorant and gustatory receptors, as well as p450 and other detoxification enzymes. Developmental patterns in Tribolium are more representative of other arthropods than those found in Drosophila, a fact represented in gene content and function. For one, Tribolium has retained more ancestral genes involved in cell-cell communication than Drosophila, and some are expressed in the growth zone crucial for axial elongation in short germ development. Systemic RNAi in T. castaneum appears to use mechanisms distinct from those found in C. elegans, but nevertheless offers similar power for the elucidation of gene function and identification of targets for selective insect control.
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| 13. |
- Shen, Zhijian, et al.
(författare)
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Fractography of self-glazed zirconia with improved reliability
- 2017
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 37:14, s. 4339-4345
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Tidskriftsartikel (refereegranskat)abstract
- The fractography of a new grade of zirconia ceramics, known as self-glazed zirconia, was investigated. The as-sintered intact top surface was made with superior smoothness that mimicked the optical appearances of the natural teeth enamel. The beneath surface opposite to this was made hierarchically rough with microscopic pits of the size up to 60. μm together with grain-level roughness of about 2. μm. The three-point bending test of the samples made with the hierarchically rough surface being tensile one demonstrated an average bending strength of 1120. ±. 70. MPa and a Weibull modulus of as high as 18 ascribed to the improved structural homogeneity. Surface topography was found the main origins of crack initiation leading to fracture. The observed unusually predominant transgranular fracture mode of submicron-sized grains disclosed a possible toughening mechanism of disassembling of mesocrystalline grains that differs significantly from the commonly quoted phase transformation toughening of this category of ceramics.
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| 14. |
- Xihe, Liu, et al.
(författare)
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Influence of Carbon Nanotubes on Defects in AlSi10Mg Alloy Fabricated by Selective Laser Melting
- 2019
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Ingår i: Xiyou jinshu cailiao yu gongcheng. - 1002-185X. ; 48:5, s. 1637-1644
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Tidskriftsartikel (refereegranskat)abstract
- Pure AlSi10Mg alloy and carbon nanotubes (CNTs)-AlSi10Mg composite with different CNTs additions were fabricated by selective laser melting (SLM). The CNTs-AlSi10Mg composite is strengthened when the CNTs content is lower than 0.05 wt%. With the increasing CNTs content, however, the strength is decreased significantly because of the poor density. In order to understand the influence of CNTs on the defects in SLMed AlSi10Mg alloy, nano-CT technology was used to get the 3D information of the defects. The results indicate that the volume fraction of large defects (with diameter larger than 50 mu m) in the total volume of defects is increased from 12% to 46% in CNTs(0.5wt%)-AlSi10Mg composite. The number of gas pores in CNTs(0.5wt%)-AlSi10Mg composite are significantly increased. The diameter of gas pores in CNTs(0.5wt%)-AlSi10Mg composite are larger than that in pure AlSi10Mg alloy. The agglomeration of CNTs in the powder and gas adsorption are the fundamental reasons for the increase of the two types of defects.
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| 15. |
- Yuan, Bo, et al.
(författare)
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Fabrication and microstructure of porous SiC ceramics with Al2O3 and CeO2 as sintering additives
- 2016
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 42:11, s. 12613-12616
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, porous silicon carbide ceramics were prepared via spark plasma sintering at relatively low temperatures using Al2O3 and CeO2 as sintering additives. Sacrificial template was selected as the pore forming mechanism, and gelcasting was used to fix the slurry in a short time. The evolution process of the microstructures during different steps was observed by SEM. The influence of the sintering temperature and sintering additives on the shrinkage and porosity of the samples was studied. The microstructures of different samples were characterized, and the mechanical properties were also evaluated.
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| 16. |
- Zhang, Qing, et al.
(författare)
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Andersson-Magnéli Phases TinO2n-1 : Recent Progress Inspired by Swedish Scientists
- 2021
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 647:2-3, s. 126-133
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Tidskriftsartikel (refereegranskat)abstract
- Among homologous series of metal oxides, Andersson-Magneli phases TinO2n-1 (n=4-10) have attracted renewed scientific attention because of their behaviour in electrical conductivity and chemical/thermal stability. Various applications have also been reported for the phases with different values of n, or slightly reduced rutile (TiO2). The characteristic properties of these materials depend strongly on the compositional deviation from TiO2 and the way in which the structure accommodates the deviation. Thus, an urgent requirement is to overcome difficulties in characterizing such materials at atomic resolution. Here, we trace the discovery of the Andersson-Magneli phases, and report the application of recent developments in electron microscopy to reveal the relation, at the local level, between structural characteristics and electronic states, specifically for the materials TinO2n-1 with n=4-8. The electrical conductivity of Ti4O7 has been reported previously to show three clearly distinct states on decreasing temperature from 300 K. For this reason, we focus on Ti4O7 as a representative example of the TinO2n-1 phases and report structural characteristics at temperatures corresponding to each of the three different phases, focusing on the distribution of Ti3+ and Ti4+ cations from analysis of single-crystal XRD data. Electron diffraction experiments and electrical conductivity measurements are also reported.
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| 17. |
- Zhang, Yinping, et al.
(författare)
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Ten cities cross-sectional questionnaire survey of children asthma and other allergies in China
- 2013
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Ingår i: Chinese Science Bulletin. - : Springer Science and Business Media LLC. - 1001-6538 .- 1861-9541. ; 58:34, s. 4182-4189
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Tidskriftsartikel (refereegranskat)abstract
- Asthma, rhinitis and eczema (allergic or non-allergic) have increased throughout the world during the last decades, especially among children. Changes in the indoor environment are suspected to be important causes. China has experienced a dramatic change in indoor environmental exposures during the past two decades. However, such changes and their associations with children's asthma and other health aspects have not been thoroughly studied. China, Children, Homes, Health (CCHH), Phase I, was a cross-sectional questionnaire survey of 48219 children 1-8 years old in 10 Chinese cities during 2010-2012. The questionnaire includes the International Study of Asthma and Allergies in Childhood (ISAAC) core health questions and additional questions regarding housing, life habits and outdoor environment. In health analyses, children aged 3-6 years old were included. The prevalences of doctor diagnosed asthma varied from 1.7% to 9.8% (mean 6.8%), a large increase from 0.91% in 1999 and 1.50% in 2000. The prevalence of wheeze, rhinitis and atopic eczema (last 12 months) varied from 13.9% to 23.7%, 24.0% to 50.8% and 4.8% to 15.8%, respectively. Taiyuan had the lowest prevalences of all illnesses and Shanghai the highest, except for wheezewhere the highest value was for Urumqi. We found (1) no obvious association between disease prevalences and ambient PM10 concentrations and (2) higher prevalences of disease in humid climates with hot summers and cold winters, but with no centrally heated buildings. Associations between the diseases and economic status as indexed by Gross Domestic Product (GDP) requires further study.
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| 18. |
- Zhou, Xin, et al.
(författare)
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3D-imaging of selective laser melting defects in a Co-Cr-Mo alloy by synchrotron radiation micro-CT
- 2015
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 98, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure defects set the mechanical property limits for solid Co-Cr-Mo alloy prepared by selective laser melting (SLM). Previous studies were mainly based on 2D SEM images and thus not able to provide information of the 3D morphologies of the complex defects. In this paper, the remaining porosities in Co-Cr-Mo alloy parts prepared by selective laser melting were presented in relation to the laser processing parameters. In order to understand the defect forming mechanism, accurate 3D images of defects inside SLM fabricated Co-Cr-Mo samples were provided by synchrotron radiation micro-CT imaging of 300 pm thick slices cut from a 10 mm cube. With 3D reconstructed images distinctive morphologies of SLM defects spanning across the consolidated powder layers were generated. The faults can be classified as single layer or multi-layers defects. The accidental single layer defects form as gaps between adjacent laser melt tracks or melt track discontinuousness caused by inherent fluid instability under various disturbances. The first formed single layer defect generates often a multi-layer defect spanning for 2-3 subsequent powder layers. By stabilizing the melt pool flow and by reducing the surface roughness through adjusting processing parameters it appears possible to reduce the defect concentrations.
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| 19. |
- Zhou, Xin, et al.
(författare)
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Balling phenomena in selective laser melted tungsten
- 2015
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 222, s. 33-42
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) of pure tungsten was carried out and the relevant consolidation issues were investigated. It was observed that balling of melted droplets at the laser focal points and entrapped cavities hindered the preparation of fully dense parts. An analysis of the balling mechanism reveals that SLM of tungsten is a process where melt spreading and solidification compete with each other and the final result is determined by intrinsic tungsten properties and the set laser processing parameters. Melted tungsten droplets wetted its own solid substrate at a low speed driven by capillary force, but solidified simultaneous at a high speed driven by the existing steep temperature gradient. Melted droplets solidified before spreading completely and kept their globular geometry instead of creating a flat layer. Tungsten bodies reaching a density of 14.8-15.2 g/cm(3) were prepared with an open irregular porosity and surface roughness. With a second laser scanning the balling W droplets were remelted at the building surface resulting in a much smoother appearance with less porosity and indicated a way to further improve relative density, near 16 g/cm(3) (82.9% theoretical density). Oxidation must be avoided, as any oxide contamination enriched preferably around the melt pool edge, changing the surface tension gradient and the thermocapillary convection thereby increasing balling.
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| 20. |
- Zhou, Xin, et al.
(författare)
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Textures formed in a CoCrMo alloy by selective laser melting
- 2015
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 631, s. 153-164
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Tidskriftsartikel (refereegranskat)abstract
- Unique crystal textures formed by selective laser melting of a CoCrMo alloy were characterized by electron backscattered diffraction. Preferred crystallographic orientations were found for individual grains in the solid alloy microstructure. Along the building or radial grain growth direction in the rapidly cooling melt pool the formed columnar grains were not purely < 001 > or < 111 >, as reported before, but a concurrence of < 001 > and < 011 >. Along the scanning direction, a (011) < 100 > texture was limited to the outmost surface whereas in the solid bulk the preferred orientation was a < 001 > fiber texture.
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| 21. |
- Chaim, Rachman, et al.
(författare)
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Low-temperature spark plasma sintering of NiO nanoparticles
- 2011
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 528:6, s. 2936-2940
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Tidskriftsartikel (refereegranskat)abstract
- NiO nanoparticles of 20 nm in diameter were spark plasma sintered between 400 °C and 600 °C for 5 and 10 min durations. Application of 100 MPa pressure from room temperature resulted in densities between 75% and 92%. The final grain size was between 26 nm and 68 nm. Lower densities were recorded when 100 MPa was applied at the SPS temperature. Two shrinkage rate maxima of 3.4 × 10−3 s−1 and 2 × 10−3 s−1 were observed around 390 ± 10 °C and at the SPS temperature. The two shrinkage rate maxima were related to densification by particle sliding followed by diffusional grain boundary sliding during the heating. The strong effects of the surface and interfacial processes which are active during the SPS were highlighted.
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| 22. |
- Eriksson, Mirva, et al.
(författare)
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Transparent hydroxyapatite ceramics with nanograin structure prepared by high pressure spark plasma sintering at the minimized sintering temperature
- 2011
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 31:9, s. 1533-1540
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Tidskriftsartikel (refereegranskat)abstract
- A hydrothermally processed bulky powder composed of loosely aggregated nano-sized rods was consolidated by spark plasma sintering. The use of a high pressure cell allows the application of pressure up to 500 MPa. It was found that applying of high pressure is beneficial for widening up the kinetic window for attaining dense HAp nanoceramics. The high transparency of HAp nanoceramics obtained in this study is ascribed to the high density and homogeneous nano-grained structure achieved besides the unique intrinsic optical properties of the HAp crystal itself, i.e. its low refractive index and very small birefringence. Achieving full densification at the minimized sintering temperature allows for the first time the preparation of transparent HAp nanoceramics with stoichiometric composition, i.e. avoiding the loss of structural water that commonly takes place during the conventional ways of sintering.
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| 23. |
- Eriksson, Mirva, et al.
(författare)
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Transparent hydroxyapatite nanoceramics by high pressure spark plasma sintering at the minimized sintering temperature
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- For direct observation of the bio-interfacial reactions with improved spatial and temporal resolution by confocal microscopy transparent hydroxyapatite nanoceramics are demanded. The aim of the present study was to, through detailed kinetics study and micostructural characterization, define a processing window within which transparent HAp nanoceramics can be produced by spark plasma sintering of dry powders. A lab-made hydrothermally processed bulky powder composed of loosely aggregated nanorods and a commercial granulated-powder composed of irregular shaped nanorods were tested. The use of a high pressure cell allows the application of pressure up to 500 MPa. It was found that applying of high pressure is beneficial for widen up the processing window for attaining dense HAp ceramics with nano grained microstructure. The high transparency of HAp nanoceramics obtained in this study is ascribed to the high density and homogeneous nano-structure achieved besides the unique intrinsic optical properties of the HAp crystal, i.e. its low refractive index and very small birefringence. Achieving full densification at the minimized sintering temperature allows for the first time the preparation of transparent HAp nanoceramics with stoichiometric composition, i.e. avoiding the loss of water that commonly encountered during the conventional ways of sintering.
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| 24. |
- Hao, Wenming, et al.
(författare)
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Core-Shell and Hollow Particles of Carbon and SiC Prepared from Hydrochar
- 2019
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 12:11
-
Tidskriftsartikel (refereegranskat)abstract
- The applications of silicon carbide (SiC) include lightweight materials with thermal shock resistance. In this study, core-shell C-SiC particles were synthesized by compacting and rapidly heating a hydrochar from glucose by using strong pulsed currents and infiltration of silicon vapor. Hollow particles of SiC formed on removing the carbon template. In contrast to related studies, we detected not only the pure 3C polytype (-SiC) but also significant amounts of the 2H or the 6H polytypes (-SiC) in the SiC.
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| 25. |
- Hou, Xu, et al.
(författare)
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PDGF-CC blockade inhibits pathological angiogenesis by acting on multiple cellular and molecular targets
- 2010
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 107:27, s. 12216-12221
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Tidskriftsartikel (refereegranskat)abstract
- The importance of identifying VEGF-independent pathways in pathological angiogenesis is increasingly recognized as a result of the emerging drug resistance to anti-VEGF therapies. PDGF-CC is the third member of the PDGF family discovered after more than two decades of studies on PDGF-AA and PDGF-BB. The biological function of PDGF-CC and the underlying cellular and molecular mechanisms remain largely unexplored. Here, using different animal models, we report that PDGF-CC inhibition by neutralizing antibody, shRNA, or genetic deletion suppressed both choroidal and retinal neovascularization. Importantly, we revealed that PDGF-CC targeting acted not only on multiple cell types important for pathological angiogenesis, such as vascular mural and endothelial cells, macrophages, choroidal fibroblasts and retinal pigment epithelial cells, but also on the expression of other important angiogenic genes, such as PDGF-BB and PDGF receptors. At a molecular level, we found that PDGF-CC regulated glycogen synthase kinase (GSK)-3beta phosphorylation and expression both in vitro and in vivo. Activation of GSK3beta impaired PDGF-CC-induced angiogenesis, and inhibition of GSK3beta abolished the antiangiogenic effect of PDGF-CC blockade. Thus, we identified PDGF-CC as an important candidate target gene for antiangiogenic therapy, and PDGF-CC inhibition may be of therapeutic value in treating neovascular diseases.
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| 26. |
- Istomin, S. Ya., et al.
(författare)
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Crystal structure and high-temperature electrical conductivity of novel perovskite-related gallium and indium oxides
- 2014
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Ingår i: Journal of Solid State Electrochemistry. - : Springer Science and Business Media LLC. - 1432-8488 .- 1433-0768. ; 18:5, s. 1415-1423
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Tidskriftsartikel (refereegranskat)abstract
- Novel complex oxides Sr2Ga1+x In1-x O-5, x = 0.0-0.2 with brownmillerite-type structure were prepared in air at T = 1,273 K, 24 h. Study of the crystal structure of Sr2Ga1.1In0.9O5 refined using X-ray powder diffraction data (S.G. Icmm, a = 5.9694(1) , b = 15.2091(3) , c = 5.7122(1) , chi (2) = 2.48, R (F) (2) (=) 0.0504, R (p) = 0.0458) revealed ordering of Ga3+ and In3+ cations over tetrahedral and octahedral positions, respectively. A partial replacement of Sr2+ by La3+ according to formula Sr1-y La (y) Ga0.5In0.5O2.5+y/2, leads to the formation of a cubic perovskite (a = 4.0291(5) ) for y = 0.3. No ordering of oxygen vacancies or cations was observed in Sr0.7La0.3Ga0.5In0.5O2.65 as revealed by electron diffraction study. The trace diffusion coefficient (D (T)) of oxygen for cubic perovskite Sr0.7La0.3Ga0.5In0.5O2.65 is in the range 2.0 Au 10(-9)-6.3 Au 10(-8) cm(2)/s with activation energy 1.4(1) eV as determined by isotopic exchange depth profile technique using secondary ion mass spectrometry at 973-1,223 K. These values are close to those reported for Ca-doped ZrO2. High-temperature electrical conductivity of Sr0.7La0.3Ga0.5In0.5O2.65 studied by AC impedance was found to be nearly independent on oxygen partial pressure. Calculated values of activation energy at T < 1,073 K for hole and oxide-ion conductivities are 0.96 and 1.10 eV, respectively.
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| 27. |
- Jiang, Q. H., et al.
(författare)
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High-temperature ferroelectric phase transition observed in multiferroic Bi0.91La0.05Tb0.04FeO3
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:1, s. 12909-
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Tidskriftsartikel (refereegranskat)abstract
- A single-phase Bi0.91La0.05Tb0.04FeO3 polycrystalline ceramic was fabricated by spark-plasma-sintering the precursor powder prepared by a sol-gel method. Temperature-dependent properties of polycrystalline Bi0.91La0.05Tb0.04FeO3 were characterized by x-ray diffraction, dielectric, and piezoelectric measurement. The x-ray diffraction results revealed a phase transition near 700 degrees C. Especially, temperature-dependent dielectric behavior demonstrated that there was a dielectric abnormal peak at about 697 degrees C, in addition to those two well-known dielectric abnormal peaks at 337 degrees C (Neel temperature) and 831 degrees C (Curie temperature). The observations, together with thermal depoled behavior, suggest a ferroelectric-ferroelectric phase transition from R(3)c to Pbnm at around 700 degrees C.
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| 28. |
- Jing, Zhao, et al.
(författare)
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Effect of Multistep Processing Technique on the Formation of Micro-defects and Residual Stresses in Zirconia Dental Restorations
- 2014
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Ingår i: Journal of Prosthodontics. - : Wiley. - 1059-941X .- 1532-849X. ; 23:3, s. 206-212
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Tidskriftsartikel (refereegranskat)abstract
- Purpose The clinical failures of zirconia dental restorations are often caused by extrinsic artifacts introduced by processing. The aim of this study was to investigate the micro-defects and residual stresses generated during the multistep process of zirconia dental restorations. Materials and Methods Thermal spray granulated 3Y-TZP powders were dry pressed by two tools exhibiting distinctly different Young's moduli, cold isostatic pressed (CIP-ed), and pressure-less fully sintered. The green bodies pressed by a stiff tool were treated with different procedures: direct milling (green milling) followed by fully sintering; half-sintering and milling (raw milling) with or without fully sintering; and fully sintering followed by grinding. The fully sintered 3Y-TZP crowns were clinically adjusted using both a diamond bur and SiC bur, respectively. Phase composition and microstructure of the pressed, milled, and ground surfaces were studied by XRD and SEM. Results Tetragonal phase was the main phase of all detected 3Y-TZP specimens. Excessive residual stresses introduced by raw milling and grinding were confirmed by a strained T (111) peak, monoclinic phase, and obviously changed I(002)(t)/I(200)(t) ratio. The residual stresses would form a compressive stress layer, while it was too shallow to inhibit crack propagation even for ground specimens. Large voids with high-coordination numbers were the common packing micro-defects. Once formed, they were barely healed by CIP-ing and sintering. A stiff pressing tool was confirmed to be useful for reducing the surface packing voids. Milling removed the surface voids, but was no help for the interior ones. Raw milling introduced more serious chippings, most originating from the existing packing voids, than green milling due to its brittle failure and was less recommended for production. Grinding dense 3Y-TZP caused surface grain refinement and much more severe micro-defects, especially when clinical adjustment was applied by diamond bur compared to SiC bur. Conclusions Micro-defects and residual stresses are introduced and accumulated through the entire production chain and determine the final microstructure of zirconia dental restorations. Several procedural improvements are offered and expected to reduce processing micro-defects.
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| 29. |
- Kaluzhskikh, M. S., et al.
(författare)
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High-temperature crystal structure and transport properties of the layered cuprates Ln(2)CuO(4), Ln=Pr, Nd and Sm
- 2011
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Ingår i: Journal of Solid State Chemistry. - : Elsevier BV. - 0022-4596 .- 1095-726X. ; 184:3, s. 698-704
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature crystal structure of the layered cuprates Ln(2)CuO(4), Ln = Pr, Nd and Sm with tetragonal T'-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)approximate to 1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln(2)CuO(4) shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO(2)-planes (TEC(Pr-O1)= 11.7 ppm K(-1)) in comparison with other cuprates: TEC (Nd-O1)=15.2 ppm K(-1) and TEC (Sm-O1)= 15.1 ppm K(-1). High-temperature electrical conductivity of Pr(2)CuO(4) is the highest one in the whole studied temperature range (298-1173 K): 0.1-108 S/cm for Pr(2)CuO(4), 0.07-23 S/cm for Nd(2)CuO(4) and 2 X 10(-4)-9 S/cm for Sm(2)CuO(4). The trace diffusion coefficient (D(T)) of oxygen for Pr(2)CuO(4) determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2 X 10(-13) Cm(2)/S (973 K) and 3.8 X 10(-10) Cm(2)/S (1173 K) which are in between those observed for the manganese and cobalt-based perovskites.
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| 30. |
- Leebens-Mack, James H., et al.
(författare)
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One thousand plant transcriptomes and the phylogenomics of green plants
- 2019
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Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 574:7780, s. 679-
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Tidskriftsartikel (refereegranskat)abstract
- Green plants (Viridiplantae) include around 450,000-500,000 species(1,2) of great diversity and have important roles in terrestrial and aquatic ecosystems. Here, as part of the One Thousand Plant Transcriptomes Initiative, we sequenced the vegetative transcriptomes of 1,124 species that span the diversity of plants in a broad sense (Archaeplastida), including green plants (Viridiplantae), glaucophytes (Glaucophyta) and red algae (Rhodophyta). Our analysis provides a robust phylogenomic framework for examining the evolution of green plants. Most inferred species relationships are well supported across multiple species tree and supermatrix analyses, but discordance among plastid and nuclear gene trees at a few important nodes highlights the complexity of plant genome evolution, including polyploidy, periods of rapid speciation, and extinction. Incomplete sorting of ancestral variation, polyploidization and massive expansions of gene families punctuate the evolutionary history of green plants. Notably, we find that large expansions of gene families preceded the origins of green plants, land plants and vascular plants, whereas whole-genome duplications are inferred to have occurred repeatedly throughout the evolution of flowering plants and ferns. The increasing availability of high-quality plant genome sequences and advances in functional genomics are enabling research on genome evolution across the green tree of life.
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| 31. |
- Li, Kailun, et al.
(författare)
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Crack suppression in additively manufactured tungsten by introducing secondary-phase nanoparticles into the matrix
- 2019
-
Ingår i: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 79, s. 158-163
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Tidskriftsartikel (refereegranskat)abstract
- In this study, an effective strategy was developed to suppress cracking by introducing secondary-phase ZrC nanoparticles into a tungsten (W) matrix. Pure W and W-0.5wt%ZrC bulks were additively manufactured via the laser powder bed fusion (LPBF) technique, and their cracking behaviour was compared. It was observed that the crack density of W-ZrC was reduced by 88.7% compared with that of pure W. The grains in W-ZrC were obviously refined compared with the grains in pure W, which significantly increased the cracking resistance. In addition, ZrC diminished the oxygen impurities, further increasing the cracking resistance. This study provides a promising strategy for the additive manufacturing of high-quality W by introducing secondary-phase nanoparticles into the metal matrix.
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| 32. |
- Li, K., et al.
(författare)
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Effect of Ta addition on the fuzz formation of additively manufactured W-based materials
- 2020
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 60:6
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Tidskriftsartikel (refereegranskat)abstract
- As a divertor plasma-facing material, W will experience high-flux plasma irradiation. In particular, severe surface morphology change like fuzz formation can be induced by He plasma irradiation. In this study, fuzz formation on additively manufactured W and W-Ta was investigated. Rolled W, laser-powder-bed-fused (LPBFed) W and W-Ta were exposed to high flux (similar to 10(23) m(-2) s(-1)) He plasma in the linear plasma generator Magnum-PSI with ion energy 12-13 eV at 1273 K. The mean thickness of the fuzz at grain interiors of rolled W, LPBFed W and W-Ta was measured as 0.37 mu m, 0.71 mu m and 0.23 mu m, respectively. The fuzz suppression in LPBFed W-Ta can be attributed to the synergetic effect of solid-solution, dislocation, and secondary-phase nanoparticles. Abnormally grown fuzz was observed near the pre-existing cracks of LPBFed W, while no such structure was found in LPBFed W-Ta. It is found that dislocations play a crucial role in inhibiting fuzz growth. This is confirmed by the difference in fuzz structure in rolled W and LPBFed W, where rolled W has a much greater dislocation density compared to LPBFed W. This work suggests that the fuzz growth kinetics may be tuned by tailoring the microstructures using the LPBF technique.
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| 33. |
- Lin, Yuan-Hua, et al.
(författare)
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Electrical transport properties of La2CuO4 ceramics processed by the spark plasma sintering
- 2007
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Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 90:12, s. 4005-4008
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Tidskriftsartikel (refereegranskat)abstract
- Highly dense La2CuO4 ceramics have been prepared by the spark plasma sintering technique. Temperature dependence of electrical conductivity indicates that La2CuO4 ceramics sintered at over 875 degrees C exhibit a metal-like behavior, which should be ascribed to the special La2CuO4 crystal structure and its correlation splitting of the half-filled d(x2-y2) band. Our experimental data indicate that all of the La2CuO4 samples exhibit positive thermoelectric power in the whole measuring temperature range, indicating that the majority of charge carriers are holes. It is desirable to obtain good thermoelectric performance for this system by optimizing the electrical properties and reducing the thermal conductivity.
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| 34. |
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| 35. |
- Liu, Chong, et al.
(författare)
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Microstructural refinement in spark plasma sintering 3Y-TZP nanoceramics
- 2016
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 36:10, s. 2565-2571
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Tidskriftsartikel (refereegranskat)abstract
- A commercial 3Y-TZP nanopowder was consolidated by spark plasma sintering (SPS) techniques. By special die-upset designs, each possible influence from the electric field, uniaxial pressure and heating rate was peeled to identify its contribution. Besides density and grain growth, the evolution of pore structure was consulted to clarify the relationships between microstructural development and densification kinetics. The results showed that neither electric current nor fast heating had no decisive contributions while external force was a necessity for the microstructural refinement. The authors proposed that the essentially underlying mechanism was the intensive particle rearrangement, which involves no grain growth but particle close-packing through grain rotation and sliding. The full advantages of this mechanism can be taken in rapid heating conditions, which combined with the application of higher pressures, make the SPS family of techniques to have advancement in the preparations of nanoceramics over their conventional counterparts characterized by slow heating features.
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| 36. |
- Liu, Jingyin, et al.
(författare)
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Biomineralization stimulated peri-titanium implants prepared by selective laser melting
- 2015
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Ingår i: Journal of Materiomics. - : Elsevier BV. - 2352-8478 .- 2352-8486. ; 1:3, s. 253-261
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Tidskriftsartikel (refereegranskat)abstract
- Titanium implants prepared by selective laser melting (SLM), a method of additive manufacturing, were subjected to implantation in beagle dogs for two and four weeks. Argon ion beam-polished cross sections of the implants after in vivo tests were characterized by scanning electron microscope (SEM) to evaluate the bone–implant interface and the early peri-implant biomineralization with sufficiently improved resolution. Two bone mineralization mechanisms were disclosed. As early as two weeks after implantation, a layer of new bone was found to form directly on the implant surface and bone in-growth was also observed. Osseointegration was found to establish partly at the tip of the implants. After healing for four weeks it was found that osseointegration was established around the entire tip of the implants, whereas only partly at the third thread region of the implants. The experimental evidences observed reveal that an inherent highly porous surface of the titanium implants generated by selective laser melting is favorable for new bone apposition.
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| 37. |
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| 38. |
- Liu, Jing, et al.
(författare)
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Dielectric, piezoelectric, and ferroelectric properties of grain-orientated Bi3.25La0.75Ti3O12 ceramics
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 102:10, s. 104107-
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Tidskriftsartikel (refereegranskat)abstract
- By dynamic forging during Spark Plasma Sintering (SPS), grain-orientated ferroelectric Bi3.25La0.75Ti3O12 (BLT) ceramics were prepared. Their ferroelectric, piezoelectric, and dielectric properties are anisotropic. The textured ceramics parallel and perpendicular to the shear flow directions have similar thermal depoling behaviors. The d(33) piezoelectric coefficient of BLT ceramics gradually reduces up to 350 degrees C; it then drops rapidly. The broadness of the dielectric constant and loss peaks and the existence of d(33) above the permittivity peak, T-m, show that the BLT ceramic has relaxor-like behavior.
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| 39. |
- Liu, Jing, 1976-
(författare)
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Nano and Grain-Orientated Ferroelectric Ceramics Produced by SPS
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nano-powders of BaTiO3, SrTiO3, Ba0.6Sr0.4TiO3, a mixture of the composition (BaTiO3)0.6(SrTiO3)0.4 with particle sizes in the range of 60 to 80 nm, and Bi4Ti3O12 with an average particle size of 100 nm were consolidated by spark plasma sintering (SPS). The kinetics of reaction, densification and grain growth were studied. An experimental procedure is outlined that allows the determination of a “kinetic window” within which dense nano-sized compacts can be prepared. It is shown that the sintering behaviour of the five powders varies somewhat, but is generally speaking fairly similar. However, the types of grain growth behaviour of these powders are quite different, exemplified by the observation that the kinetic window for the (BaTiO3)0.6(SrTiO3)0.4 mixture is 125 oC, ~75 oC for Bi4Ti3O12, ~25oC for BaTiO3 and SrTiO3, while it is hard to observe an apparent kinetic window for obtaining nano-sized compacts of Ba0.6Sr0.4TiO3. During the densification of the (BaTiO3)0.6(SrTiO3)0.4 mixture the reaction 0.6BaTiO3+0.4SrTiO3 → Ba0.6Sr0.4TiO3 takes place, and this reaction is suggested to have a self-pinning effect on the grain growth, which in turn explains why this powder has a large kinetic window. Notably, SPS offers a unique opportunity to more preciously investigate and monitor the sintering kinetics of nano-powders, and it allows preparation of ceramics with tailored microstructures.The dielectric properties of selected samples of (Ba, Sr)TiO3 ceramics have been studied. The results are correlated with the microstructural features of these samples, e.g. to the grain sizes present in the compacts. The ceramic with nano-sized microstructure exhibits a diffuse transition in permittivity and reduced dielectric losses in the vicinity of the Curie temperature, whereas the more coarse-grained compacts exhibit normal dielectric properties in the ferroelectric region.The morphology evolution, with increasing sintering temperature, of bismuth layer-structured ferroelectric ceramics such as Bi4Ti3O12 (BIT) and CaBi2Nb2O9 (CBNO) was investigated. The subsequent isothermal sintering experiments revealed that the nano-sized particles of the BIT precursor powder grew into elongated plate-like grains within a few minutes, via a dynamic ripening mechanism.A new processing strategy for obtaining highly textured ceramics is described. It is based on a directional dynamic ripening mechanism induced by superplastic deformation. The new strategy makes it possible to produce a textured microstructure within minutes, and it allows production of textured ferroelectric ceramics with tailored morphology and improved physical properties.The ferroelectric, dielectric, and piezoelectric properties of the textured bismuth layer-structured ferroelectric ceramics have been studied, and it was revealed that all textured samples exhibited anisotropic properties and improved performance. The highly textured Bi4Ti3O12 ceramic exhibited ferroelectric properties equal to or better than those of corresponding single crystals, and much better than those previously reported for grain-orientated Bi4Ti3O12 ceramics. Textured CaBi2Nb2O9 ceramics exhibited a very high Curie temperature, d33-values nearly three times larger than those of conventionally sintered materials, and a high thermal depoling temperature indicating that it is a very promising material for high-temperature piezoelectric applications.
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| 40. |
- Liu, Jiang, et al.
(författare)
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Rice-paddy field acts as a buffer system to decrease the terrestrial characteristics of dissolved organic matter exported from a typical small agricultural watershed in the Three Gorges Reservoir Area, China
- 2019
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Ingår i: Environmental Science and Pollution Research. - : SPRINGER HEIDELBERG. - 0944-1344 .- 1614-7499. ; 26:23, s. 23873-23885
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Tidskriftsartikel (refereegranskat)abstract
- Agricultural watersheds are a crucial contributor of terrestrial dissolved organic matter (DOM) for the adjacent aquatic environment. Recently, ecological engineering of the buffer zone such as a rice-paddy field was established to reduce the export of nutrients and contaminants from a small agricultural watershed. However, the potential of the rice-paddy field to reduce the terrestrial signature of DOM is unclear. Therefore, two small agricultural sub-catchments (i.e., sub-1 and sub-2) with different land uses and hill slope angles in the Three Gorges Reservoir (TGR) area of China were studied from 2014 to 2015. The results showed that the terrestrial DOM signals are indicated by optical indices (SUVA(254), S-R, fluorescence index) in the steeper and more forest covered, but rice-paddy field buffered sub-catchment (i.e., sub-2) decreased significantly, as compared to the reference sub-catchment (i.e., sub-1). Regardless of seasonal variations, the rice-paddy field retained a buffering role to reduce the terrestrial property of DOM and the highest capacity was observed during the rice-growth period. However, during storm events, the differences of DOM properties for two sub-catchments were not significant, because the buffer system was weakened. Finally, environmental implications of the role of such a buffer zone in the TGR areas are discussed. These results demonstrate that rice-paddy fields are successful in mitigating the terrestrial property of exported DOM, but the weaker performance during storm events still needs to be considered.
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| 41. |
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| 42. |
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| 43. |
- Liu, Jing, et al.
(författare)
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Visible and infrared transparency in lead-free bulk BaTiO3 and SrTiO3 nanoceramics
- 2010
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 21:7
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Tidskriftsartikel (refereegranskat)abstract
- Multifunctional transparent ferroelectric ceramics have widespread applications in electro-optical devices. Unfortunately, almost all currently used electro-optical ceramics contain a high lead concentration. In this work, via coupling of spark plasma sintering with high pressure, we have successfully synthesized bulk lead-free transparent nanostructured BaTiO3 (abbreviated as BTO) and SrTiO3 (STO) ceramics with excellent optical transparency in both visible and infrared wavelength ranges. This success highlights potential ingenious avenues to search for lead-free electro-optical ceramics.
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| 44. |
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| 45. |
- Liu, Leifeng, et al.
(författare)
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Dislocation network in additive manufactured steel breaks strength-ductility trade-off
- 2018
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Ingår i: Materials Today. - : Elsevier BV. - 1369-7021 .- 1873-4103. ; 21:4, s. 354-361
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Tidskriftsartikel (refereegranskat)abstract
- Most mechanisms used for strengthening crystalline materials, e.g. introducing crystalline interfaces, lead to the reduction of ductility. An additive manufacturing process - selective laser melting breaks this trade-off by introducing dislocation network, which produces a stainless steel with both significantly enhanced strength and ductility. Systematic electron microscopy characterization reveals that the pre-existing dislocation network, which maintains its configuration during the entire plastic deformation, is an ideal modulator that is able to slow down but not entirely block the dislocation motion. It also promotes the formation of a high density of nano-twins during plastic deformation. This finding paves the way for developing high performance metals by tailoring the microstructure through additive manufacturing processes.
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| 46. |
- Liu, Yi, et al.
(författare)
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Dehydroxylation of hydroxyapatite in dense bulk ceramics sintered by spark plasma sintering
- 2012
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 32:11, s. 2691-2696
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Tidskriftsartikel (refereegranskat)abstract
- Dense transparent hydroxyapatite (HAp) nanoceramic samples were prepared by spark plasma sintering of a commercial available granulated nanopowder. This made it possible for investigating the dehydroxylation behaviours of HAp in fully dense bulks. Post-SPS thermal annealing was performed in a temperature interval of 800 to 1100 degrees C in air. The phase analysis and microstructural characterization revealed that the dehydroxylation in fully dense HAp was initiated above 900 degrees C and its kinetics seems to be determined by the water vapour diffusion. Accordingly, a gradient structure consisting of porous interiors and a peculiar surface topography reflecting the water vapour escaping patterns were observed in samples experienced severe dehydroxylation.
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| 47. |
- Liu, Yihong, et al.
(författare)
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Fracture and interfacial delamination origins of bilayer ceramic composites for dental restorations
- 2010
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 30:6, s. 1297-1305
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Tidskriftsartikel (refereegranskat)abstract
- Alumina and zirconia (Y-TZP) based bilayer ceramic dental composites with core to veneer thickness ratio (R-value) of 1: 1 and 2:1 were fabricated through an established dental laboratory multi-steps-firing procedure. Their flexural strengths were determined by three-point bending test. A combinational approach of numerical simulations by finite element analysis associated with direct fractography investigation was applied to elucidate the origins of fracture and interfacial delamination and the influence of physical properties mismatch between core ceramic and veneer porcelain. A newly developed argon ion beam cross-section polishing technique was used to conduct fine polishing required for close investigating of the core-veneer interface under scanning electron microscope. For the same core ceramic no significant difference was observed in determined flexural strength of two groups of bilayer composites. The flexural strength of the bilayer composites is similar to 55% and similar to 35% of the core ceramics and achieved similar to 90% and 70-77% of the predicated value respectively in case of Y-TZP and alumina based composites. Numerical simulations by finite element analysis indicate that the often observed interfacial delamination in Y-TZP based bilayer composites has a clear origin of the severe physical properties mismatch between veneer porcelain and core ceramics, particularly the flexural strength, which may be prevented by increasing the flexural strength of veneer porcelain to above 300 MPa. The observation of the formation of microcracks in alumina core immediately one grain-thick under the veneer-core interface warns the possible thermal damages initiated during the veneering operation.
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| 48. |
- Liu, Y. H., et al.
(författare)
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Bilayered ceramic dental composites with adhesive or reactive bonded interfaces
- 2013
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Ingår i: Advances in Applied Ceramics. - 1743-6753 .- 1743-6761. ; 112:4, s. 227-234
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Tidskriftsartikel (refereegranskat)abstract
- By close inspection of the well polished cross-sections, two categories of interfaces were classified, namely, adhesive bonding between veneering porcelains and zirconia or alumina cores versus reactive bonding between veneering porcelains and cores of glass infiltrated alumina or lithium disilicate based glass ceramics. Argon ion beam cross-section polishing technique was applied to achieve gentle and fine polishing required for high resolution interfacial characterisation by scanning electron microscopy. The observations suggest that it is desirable to enhance the interfacial reactive bonding in order to avoid delamination in alumina and zirconia based composites.
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| 49. |
- Liu, Yi, et al.
(författare)
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Micro-hydrothermal reactions mediated grain growth during spark plasma sintering of a carbonate-containing hydroxyapatite nanopowder
- 2014
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 34:16, s. 4395-4401
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Tidskriftsartikel (refereegranskat)abstract
- A carbonate-containing hydroxyapatite nanopowder was consolidated by spark plasma sintering at the temperatures ranging from 650 to 1100 degrees C. It was found that the water released by dehydroxylation was trapped inside the nanopores in the densified HAp bodies over 900 degrees C. Based on the analysis by the X-ray diffraction, Fourier-transform infrared spectrometry and scanning electron microscope, the water-nanopore system was evaluated and its effect on the grain growth was also investigated. It was revealed that the water existed inside the closed nanopores most probably resulted in the formation of local micro-hydrothermal environments inside bulk HAp ceramics during SPS. Therefore, the grain growth was enhanced by the local micro-hydrothermal reactions activated above 900 degrees C. In addition, abnormal grain growth was also observed when a higher temperature or higher heating rate was employed, which may be attributed to the local highly active hydrothermal reactions.
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| 50. |
- Liu, Yi, et al.
(författare)
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Reactive consolidation of layered-ternary Ti(2)AlN ceramics by spark plasma sintering of a Ti/AlN powder mixture
- 2011
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Ingår i: Journal of the European Ceramic Society. - : Elsevier BV. - 0955-2219 .- 1873-619X. ; 31:5, s. 863-868
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Tidskriftsartikel (refereegranskat)abstract
- A reactive consolidation process for preparing ternary Ti(2)AlN ceramics was investigated by spark plasma sintering (SPS). A Ti/AlN powder mixture with a molar ratio of 2:1 was consolidated at temperatures ranging from 800 to 1450 degrees C. The phase composition and microstructure evolution during the process were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with an energy dispersive spectroscopy (EDS). A series of intermediate phases, namely TiN, Ti(3)Al, Ti(3)AlN and TiAl were indentified, which revealed a reaction pathway towards the formation of Ti(2)AlN.
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