| 1. |
- Chen, Qingguo, et al.
(author)
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Preparation and properties of Ce0.5Nd0.5PO4 monazite ceramics by pressureless sintering and spark plasma sintering (SPS)
- 2024
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In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 50:12, s. 20803-20810
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Journal article (peer-reviewed)abstract
- LnPO4·nH2O rhabdophane/monazite is an important actinide-bearing material in the back end of the nuclear fuel cycle. In this work, using Nd3+ to simulate trivalent actinides, Ce0.5Nd0.5PO4·0.667H2O rhabdophane was synthesized by the wet-chemistry method in 90 °C and pH = 1 solution. The sintering behavior of associated Ce0.5Nd0.5PO4 monazite ceramics was investigated by pressureless sintering and spark plasma sintering (SPS), along with appraising their chemical stability. The results reveal that Ce3+ is successfully replaced by Nd3+ in the rhabdophane lattice, and rhabdophane can transform to monazite with a temperature over 750 °C. SPS can compact the ceramic sample at a lower temperature compared to pressureless sintering even if the grain size is smaller. Adding a pre-sintering process of 900 °C before SPS and pressureless sintering will further improve the density and Vickers hardness of ceramics. For the chemical stability of Ce0.5Nd0.5PO4 monazite ceramics, Ce is more likely to be leached compared to Nd, and the ceramics prepared by SPS with a pre-sintering process have the lowest normalized leaching rates, associated with the values of 2.03 × 10−5 g·m−2·d−1 and 0.75 × 10−5 g·m−2·d−1 for Ce and Nd, respectively.
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| 2. |
- Hu, Qi, et al.
(author)
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Preparation and dielectric properties of La doped NBCCTO ceramics
- 2022
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In: Journal of Electroceramics. - : Springer Nature. - 1385-3449 .- 1573-8663. ; 48:3, s. 117-126
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Journal article (peer-reviewed)abstract
- CaCu3Ti4O12 ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical application in engineering is hindered. In this paper, Na0.25Bi0.25LaxCa0.5-3x/2Cu3Ti4O12 (NBLCCTO) ceramics were prepared by solid phase synthesis. The effects of sintering temperature and La content on dielectric properties of NBLCCTO ceramics were studied. The results show when the sintering temperature is 1030celcius and La content is 0.05, NBLCCTO ceramics show better dielectric properties. Its dielectric constant has epsilon(r) = 22,231 at 1 kHz and its dielectric loss is 0.0546 at 10 kHz. Appropriate doping of La can lead to grain refinement and enlarge specific surface area of grain boundary, thus increasing resistivity and reducing dielectric loss. Therefore, NBLCCTO ceramics have lower dielectric loss than Na0.25Bi0.25Ca0.5Cu3Ti4O12 (NBCCTO).
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| 3. |
- Hu, Qi, et al.
(author)
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Temperature stable dielectric properties of Mg2TiO4-MgTiO3-CaTiO3 ceramics over a wide temperature range
- 2023
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In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 49:2, s. 1997-2006
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Journal article (peer-reviewed)abstract
- The zero resonant frequency temperature coefficient (zf) of microwave dielectric ceramics (MWDCs) at high and low temperature have attracted great attention in the development of microwave communication equipment. In this work, the Mg2TiO4-MgTiO3-CaTiO3 (MMC) ceramics with meeting the application requirements of 5G communication were prepared by traditional solid-phase sintering after investigating the relationship among phase compositions of xMg2TiO4-(0.931-x)MgTiO3-0.069CaTiO3 and 0.34Mg2TiO4-0.591MgTiO3-yCaTiO3, sin-tering process, and dielectric properties in detail. The results show that the dielectric properties of MMC ceramics are strongly affected by the phase relative contents of MgTiO3, Mg2TiO4 and CaTiO3. For instance, MMC ceramics with approximate zf = 0 is contributed by mutual compensation of Mg2TiO4 and MgTiO3, in which the Mg2TiO4 phase plays an important role in decreasing the zf value; and the increase of CaTiO3 will greatly increase the epsilon r value for MMC ceramics, while has a negative effect in the Q x f value. After three-phase regulation, the 0.32Mg2TiO4-0.611MgTiO3-0.069CaTiO3 microwave dielectric ceramic has a better dielectric temperature sta-bility, associated with dielectric properties of er = 19.7, Q x f = 55,400 GHz (at 8.43 GHz), zf-= 4.5 ppm/degrees C (-40 degrees C-25 degrees C), and zf+ =-5.1 ppm/degrees C (25 degrees C-90 degrees C).
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| 4. |
- Liu, Hang, et al.
(author)
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Investigation of Nd3+ incorporation in Ce-rhabdophane : Insight from structural flexibility and occupation mechanism
- 2022
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In: Journal of The American Ceramic Society. - : John Wiley & Sons. - 0002-7820 .- 1551-2916. ; 105:7, s. 4974-4985
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Journal article (peer-reviewed)abstract
- LnPO(4)center dot 0.667H(2)O rhabdophane has been considered as a potential material for the precipitation of actinides from radioactive waste liquid, owing to its outstanding characteristics of high actinide bearing and easy synthesis in acid solutions. However, a comprehensive understanding of the actinide occupation and the precipitation response of rhabdophane to remove actinides has yet to be established. In this study, the effect of ions concentration and pH values on the detailed precipitation reaction of CexNd1-xPO4 center dot 0.667H(2)O rhabdophane in acid solutions are systematically investigated. Some specific issues such as structural distortion and flexibility, and occupation mechanism are discussed by combining with experiments and density functional theory (DFT) calculation. The results reveal that ions concentration and pH values have a significant impact on the crystallization nucleation step before 12 h. The obtained removal rate of Nd3+ is more than 99% in pH 1-5 solutions with the ions concentration of 0.05-0.1 mol/L. Moreover, incorporating Nd in CePO4 center dot 0.667H(2)O rhabdophane will easily result in the lattice distortion in b-axis. DFT calculation and X-ray photoelectron spectroscopy (XPS) results reveal that Nd is preferentially incorporated in nonhydrated site to form a weaker binding energy of NdO8 polyhedron.
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| 5. |
- Tang, Jiayuan, et al.
(author)
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Reduction of the sintering temperature and dielectric loss of the CCTO ceramic by doping tellurite glass
- 2021
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In: Ceramics International. - : Elsevier. - 0272-8842 .- 1873-3956. ; 47:7, Part A, s. 10006-10012
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Journal article (peer-reviewed)abstract
- CaCu3Ti4O12 (CCTO) ceramics can be modified by a multi-component glass system, which shows an influence on the improvement of the sintering process and dielectric properties. In this work, we fabricate the low dielectric loss CCTO ceramics at a low sintering temperature by using the tellurite glass of TBZCBS (TeO2-B2O3-ZnO-CaO-BaO-SrO) as an additive. The study manifests that the sintering temperature of TBZCBSdoped CCTO ceramics could be reduced to 1030 degrees C when the amount of TBZCBS glass is 10 wt%, decreasing 70 degrees C compared to the CCTO ceramic without using an additive. Simultaneously, its loss tangent value at 1 kHz can also decline to similar to 0.0174 from similar to 0.1783. Moreover, we also concluded that the electric properties of TBZCBS-doped CCTO ceramics relate to the amount of TBZCBS glass. The nonlinear J-V properties and breakthrough electric field are improved with an increase of the TBZCBS glass content, confirming the dielectric properties and the electric properties are mainly relevant to the grain boundary properties of CCTO ceramics.
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| 6. |
- Wang, Shanlin, et al.
(author)
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Design of Continuous Transport of the Droplet by the Contact-Boiling Regime
- 2021
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:1, s. 553-560
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Journal article (peer-reviewed)abstract
- Joule-heat-driven directional transport of liquid droplets has comprehensive engineering applications in various water and thermal management, cooling systems, and self-cleaning. Generally, the driving force for the transport of liquid droplets was always observed at an extremely high Leidenfrost temperature, which limits the potential application between liquid boiling and Leidenfrost points. In this work, we design a new strategy to directionally drive the transport of droplets by blockading the vapor cushion at a temperature much lower than the Leidenfrost point. On the surface of the microhole arrays, we observed the continuous rebound behavior of ethanol droplets at T-s = 110 degrees C. Employing the thermal multiphase lattice Boltzmann model, the continuous rebound behavior was reproduced, verifying that the driving force was provided by the blockaded vapor pressure in microholes. By cooperating with the Laplace pressure difference, we directionally transport ethanol and water droplets on the horizontal asymmetrical concentric microridge surface. The horizontal velocity of water is 11.25 cm/s at T-s = 180 degrees C, similar to the traditional ratchets at the Leidenfrost point. The design of microtextures enriches the fundamental understanding of how to drive droplets at far below the Leidenfrost point and pushes the application in nongravity-driven self-cleaning and cooling systems.
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| 7. |
- Wang, Shanlin, et al.
(author)
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Large-Scale Fabrication of Wettability-Controllable Coatings for Optimizing Condensate Transfer Ability
- 2021
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:7, s. 2476-2484
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Journal article (peer-reviewed)abstract
- Systematic regulation of hydrophilic regions plays a key role in optimizing the heterogeneous hydrophilic-hydrophobic surface for promoting condensate transfer ability (CTA) under subcooling or high-humidity conditions. In this work, we develop an operable method to fabricate wettability-controllable coatings by regulating the mass ratio of superamphiphobic and superamphiphilic powder (MRP). By investigating the synergic relationship between CTA and MRP, we display an interesting competition between condensation and detachment of condensates. The initial dewing rate associated with reflecting phase change heat transfer capacity could be continuously strengthened by promoting MRP, while the detachment capacity with respect to improving the long-term condensing rate can be limited by the excessive superamphiphilic microregions. Based on this, we have optimized the threshold of MRP for promoting the condensation heat transfer ability and the water harvesting efficiency with the values of 10:0-8:2 and 10:0-4:6, respectively. This work provides important guidance in designing and optimizing heterogeneous hydrophilic-hydrophobic surfaces for multiple industrial applications including heat management, water harvesting, and desalination.
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| 8. |
- Ye, Mingliang, et al.
(author)
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Preparation and characterization of SiC-ZAC composite material for immobilizing the simulated radioactive graphite
- 2022
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In: Progress in nuclear energy (New series). - : Elsevier. - 0149-1970 .- 1878-4224. ; 143
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Journal article (peer-reviewed)abstract
- For the safe treatment and disposal of radioactive graphite, SiC-ZAC (ZAC: ZnO-Al2O3-CaO glass-ceramic) composite materials were designed, in which ZAC is used as a sintering additive. The performance of ZAC was firstly studied by ASTM C1285 leaching test to obtain a formula composition with high chemical stability. Then, using the optimized formula of ZAC, the SiC-ZAC composites were prepared by vacuum calcination at 1350 degrees C-1410 degrees C for the immobilizing of simulated radioactive graphite, and the structure and compositions of SiC-ZAC composites were studied by XRD, SEM, EDS. The material Gibbs free energy function method was used to calculate the thermodynamics of SiC-ZAC composites to investigate the reaction ways among Si, C and ZAC. The results show the Z30 (30 wt% ZnO, 44.91 wt% Al2O3, 25.09 wt% CaO) glass-ceramic is the applicable formula composition due to its high chemical stability, in which the normalized elemental mass loss of Zn, Al, Ca are 10(-)(6) g/m(2)-10(-)(5) g/m(2), 10(-1) g/m(2), 10(-1) g/m(2) respectively. Calcined at 1350 degrees C for 2 h, the B-Z30(0)-1(70.05 wt% Si, 29.95 wt% C) sample can be obtained with the phase compositions of beta-SiC, alpha-SiC and a small amount of residual graphite. Moreover, the formations of Ca2Al2SiO7 and CaAl4O7 crystalline phase had a negative effect on the immobilization of simulated radioactive graphite in SiC-ZAC composites.
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| 9. |
- Ye, Mingliang, et al.
(author)
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Preparation and properties of situ-sintered SiC ceramics aided by ZnO-Al2O3-CaO
- 2022
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In: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 890
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Journal article (peer-reviewed)abstract
- The safe treatment and disposal of radioactive graphite waste is becoming an important issue worldwide. The objective of this paper is to prepare the SiC-ZAC (ZAC: ZnO-Al2O3-CaO) composite ceramic for immobilizing radioactive graphite, where ZAC is as sintering additives. The effects of the sintering system and ZAC content on the phase compositions, microstructure, and properties of SiC-ZAC composite ceramic are studied by XRD, SEM-EDS, TEM-EDS, linear shrinkage, Vickers hardness, and thermal conductivity. By vacuum hot pressing sintering at 1600 degrees C for 1 h, the results show that the S-35-160 0 (65 wt% SiC, 10.5 wt% ZnO, 15.72 wt% Al2O3, 8.78 wt% CaO) sample is the potentially applicable formula composition due to its better performance, in which the Vickers hardness and the thermal conductivity are 165.2 HV10, 14.6 W m(-1) k(-1) respectively, and the normalized elemental mass loss of Si, Al and Ca are 0.0064-0.0108 g/m(2), 21.4784-24.7837 g/m(2), 56.9108-67.5637 g/m(2) after 42 days at pH = 5/7/9 solution, respectively. Importantly, ZAC sintering additives can form the bond phases of CaAl4O7, CaAl2O4, Ca3Al2(OH)(12), and Ca2Al2SiO7 under relatively low temperatures to reduce the sintering temperature for SiC ceramics. Meanwhile, the existing form of the Zn element is revealed: one part of the Zn forms glass phase, and the other part volatilized by carbothermic reduction.
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| 10. |
- Zhao, Xiaofeng, et al.
(author)
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Exploring the relationship between Ln leaching and Ln-O binding energy in monazite (Nd, Sm, Eu)
- 2022
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In: Journal of The American Ceramic Society. - : John Wiley & Sons. - 0002-7820 .- 1551-2916. ; 105:1, s. 553-563
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Journal article (peer-reviewed)abstract
- Understanding the chemical durability of waste forms is important for the long-term deep geological disposal of actinides. However, in-depth investigations on the leaching mechanism of monazite ceramic waste forms remain to be poorly understand. Inspired by the degradation process of Ce-monazite controlled by the fracture of Ce-O bond of (010) surface under the action of permeable water molecules, the relationship between Ln leaching and Ln-O binding energy in LnPO(4) (Ln = Nd, Sm, Eu) monazites is investigated by combining dissolution experiments and first-principles calculations. The dissolution experiments are performed in 0.001 mol/L HCl solutions at 363 K. Before and after leaching, the phase compositions of specimens are carefully investigated by refined XRD and GIXRD, and the results confirm that the dissolved phases in contact with the leachate are LnPO(4) monazite. Some specific issues are discussed in detail by first-principles calculations, such as the bond length, charge transfer, electron localization function, and chemical bond properties. Moreover, the boundary conditions of crystal-growing of LnPO(4) monazite are investigated to define the chemical potential that is used to calculate the defect formation energy (Ef) of Ln vacancy in (010) surface. Importantly, the Ef results show the difficulty order of forming a vacancy defect of Ln on (010) surface is Eu > Sm > Nd, which is consistent with the leaching stability of Ln in LnPO(4) (Ln = Nd, Sm, Eu) monazite.
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