JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY
·
2021
·
IF 8.067
Longkang Cong,Shouyang zhang
High-entropy oxides (HEOs) are considered promising thermal barrier coating (TBC) materials due to their unique thermophysical performances induced by the entropy effects. In this work, (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 high entropy hafnate, as a thermal barrier coating (TBC) material, was successfully synthesized by solution combustion method for the first time. From the X-ray diffraction, scanning electron microscopy, and transmission electron microscopy results, it is confirmed that (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 has pure single-phase ordered pyrochlore structure with highly homogeneous composition at both micrometer and nanometer scales. The synthesized (La 0.2 Ce 0.2 Pr 0.2 Sm 0.2 Eu 0.2 ) 2 Hf 2 O 7 possesses excellent phase stability at 1600 °C and demonstrates a low thermal conductivity (1.0–1.24 W·m −1 ·K −1 ) which is lower than those of rare earth hafnates (RE 2 Hf 2 O 7 , RE = La, Ce, Pr, Sm, Eu). Therefore, it provides a new perspective and potential to prompt the next generation TBC materials with better performance.
研究领域:
材料科学
·
陶瓷工程
✓ 已验证
产品关联
DOI
高影响因子
ChemSusChem
·
2022
·Vol. 15
·期 11
·e202200474
·
IF 9.14
Shuai Li,Shenghai Yang,Kangkang Li,Yanqing Lai,Chaoyong Deng,Changhong Wang
Graphical A green system for hafnium alkoxide synthesis was proposed. Simultaneous heterogeneous Hf dissolution and ethanol dehydrogenation followed by spontaneous solution-based binding of alkoxy with Hf 4+ ions gave Hf(OEt) 4 . After the optimum conditions – electrolyte, temperature, current densities, etc. – had been determined, a proof-of-concept experiment achieved waste-free production of Hf(OEt) 4 with high purity and yield. Besides the system‘s green credentials, it showed a high net profit of 30 477 USD per kg Hf(OEt) 4 and could be extended to the synthesis of other hafnium alkoxides. The conventional thermal method of preparing hafnium alkoxides [Hf(OR) 4 , R=alkyl] – excellent precursors for gate-dielectric HfO 2 on semiconductors – is severely hindered by its unsatisfactory environmental and economic burdens. Herein, we propose a promising electrodissolution-coupled Hf(OR) 4 synthesis (EHS) system for green and efficient electrosynthesis of Hf(OR) 4 . The operational principle of the electrically driven system consists of two simultaneous heterogeneous reactions of Hf dissolution and alcohol dehydrogenation, plus a spontaneous solution-based combination reaction. In applying ethanol as solvent and Hf metal as electrodissolution medium, we achieved waste-free production of high-purity hafnium ethoxide [Hf(OEt) 4 ] with an equivalent “a concomitant” reduction in CO 2 emission of 187.33 g CO 2 per kg Hf(OEt) 4 and a high net profit of 30 477 USD per kg Hf(OEt) 4 . This system is very competitive with the thermal process, which unavoidably releases substantial waste and CO 2 for a net profit of 27 700 USD per kg Hf(OEt) 4 . We anticipate that the environmental and economic benefits of the EHS process could pave the way for its practical application.
研究领域:
材料科学
·
化学工程
✓ 已验证
产品关联
DOI
PubMed
高影响因子
CERAMICS INTERNATIONAL
·
2022
·
IF 5.532
Yuan Liu,Weiwei Liu,Yang Zhou,Jingbo Chen,Zhiguo Wang,Wen Du,Jianhui Wen,Jun Cao,Dou Zhang
To investigate the influence of modification of ceramic fillers on the dielectric properties of polymer-based composites, TiO 2 and core-shell structured TiO 2 @HfO 2 nanowires were synthesized, and investigated in this study. TiO 2 nanowires/polyvinylidene fluoride (PVDF) and TiO 2 @HfO 2 nanowires/PVDF nanocomposites were prepared using the solution casting method. The experimental results showed that the TiO 2 @HfO 2 nanowires/PVDF composites had improved dielectric properties compared with that of the TiO 2 nanowires/PVDF composites. Owing to the enhanced interfacial polarisation by the multilevel interface, the composites with 10 wt % TiO 2 @HfO 2 nanowires achieved the highest permittivity of 12.56 at 1 kHz, which was enhanced by ∼72% compared to the PVDF matrix. The electric field was evenly distributed by building the fillers with a gradient dielectric constant. The characteristic breakdown strength of the composite with 5 wt % TiO 2 @HfO 2 reached 377.76 kV/mm, compared with that of 334.37 kV/mm for the composite with 5 wt % TiO 2 nanowires. This study initiated a novel strategy for preparing dielectrics with high dielectric constant and improved breakdown strength.
研究领域:
材料科学
·
电气工程
✓ 已验证
产品关联
DOI
高影响因子
Journal of Environmental Chemical Engineering
·
2023
·
IF 7.7
Liangping Xiong,Kai Lyu,Yiyang Zeng,Chuting Yang,Fangting Chi,Sheng Hu,Xinggui Long
Tetravalent metal (e.g., Zr 4+ , Hf 4+ ) phosphonate frameworks featuring remarkable chemical and radiolytic stabilities have been newly utilized as high-performing adsorbents for actinide in harsh solutions. Nevertheless, the practical applications have been impeded by the as-synthesized powder form that is not compatible with continuous actinide recovery or removal. Herein, we incorporate hafnium phosphonate (HfP) fine powder into polyacrylonitrile (PAN) via a simple and economical electrospinning technique, engendering a stable and hydrophilic nanofibrous membrane with the first-rank permeate flux for the potential treatment of a large volume of actinide-containing wastewater. This composite membrane can capture more than 90% Th(IV) at ppm level and 95% Pu(IV) and 90% Np(V) at tracer amount level in strong acidic solutions, which retains the excellent adsorption efficacy of HfP powder. Besides, it has a breakthrough volume larger than 880 mL for Th(IV) and 760 mL for U(VI) at the ppb level under a high permeate flux of 785 ± 11.2 L·m -2 ·h -1 , representing one of the top nanofibrous membranes for the dynamic removal of actinides. This work will pave an avenue for fabricating highly efficient and stable adsorptive membranes, which are promising candidates for capturing actinides from large-volume of acidic nuclear wastewater.
研究领域:
材料科学
·
核化学与放射化学
✓ 已验证
产品关联
DOI
高影响因子
CERAMICS INTERNATIONAL
·
2024
·
IF 5.1
Bohan Sun,Cuiyan Li,Haibo Ouyang,Ruinan Gao,Tianzhan Shen,Yanlei Li
The synthesis of hafnium carbide nanowires (HfC NWs ) on carbon fibers was successfully achieved by employing HfCl 4 and furfuryl alcohol as precursor materials, facilitated by Ni-assisted catalytic pyrolysis . In the polymerization and cross-linking processes of furfuryl alcohol, hafnium cations play a crucial role, leading to the atomic-level amalgamation and effectively enhancing the reactivity of the Hf-O-C system. The nucleation of HfC NWs takes place at 1300 °C, followed by growth through a solid-liquid-solid (SLS) mechanism. Carbon fibers were uniformly coated with tens micrometer-long HfC NWs having an approximate diameter of 500 nm. Notably, the tips of these HfC NWs exhibited clean surfaces free of Ni catalyst particles, indicating their root growth model. This novel catalyst-assisted pyrolysis method holds great potential for enabling cost-effective large-scale production of transition metal carbide nanowires.
研究领域:
材料科学
·
化学工程
✓ 已验证
产品关联
DOI
高影响因子
RSC Advances
·
2018
·Vol. 8
·期 69
·39284-39290
·
IF 2.936
Youlin Jiang,Dewei Ni,Qi Ding,Bowen Chen,Xiaowu Chen,Yanmei Kan,Shaoming Dong
Nano-crystalized HfC was successfully synthesized based on an aqueous solution-derived precursor using hafnium tetrachloride and sucrose as raw materials. The precursor can be converted to pure phase HfC after pyrolysis at ∼600 °C and subsequent carbothermal reduction reaction at ∼1600 °C, with a ceramic yield of around 46.3%. Reaction mechanisms of the synthesis process are revealed based on FT-IR, TG-DSC, TEM analysis and thermodynamic calculations, etc. The obtained HfC nanoparticles possess an equiaxial shape with an average particle size of ∼73 nm. Oxygen content of the as-synthesized HfC powders is as low as 0.64 wt%, which exists in the form of an amorphous Hf–O–C thin layer covering the surface of the HfC particles. This feasible and promising method for HfC particle synthesis is believed to be suitable for the fabrication of continuous fibers reinforced HfC ceramic matrix composites.
研究领域:
材料科学
·
无机化学
✓ 已验证
产品关联
DOI
PubMed
高影响因子
JOURNAL OF ALLOYS AND COMPOUNDS
·
2018
·
IF 3.779
Jun Cheng,Xiaozhou Wang,Jun Wang,Hao Wang,Shengxuan Hu
Precursors with different nitrogen contents were synthesised using hafnium (IV) chloride (HfCl 4 ), dicyandiamide (DICY) and triethylamine (Et 3 N) as raw materials and were used for preparing Hf-based nanocomposites. The synthesis, ceramic conversion and microstructural evolution of HfC-based nanocomposites derived from precursors with different nitrogen contents were investigated. The results indicate that the composition of the synthesised precursors can be controlled by adjusting the molar ratio of HfCl 4 and dicyandiamide. Pyrolysis of the precursors at 1200 °C led to the formation of Hf 2 CN or HfN-based ceramics. As the nitrogen content of the synthesised precursors increased, the Hf 2 CN crystallites present in the ceramics annealed at 1200 °C gradually transformed to HfN. Furthermore, at 1600 °C, the HfN and Hf 2 CN phases gradually converted to HfC(N). The results also indicate that nitrogen favours the sintering of the obtained nanocomposites. The HfC-based ceramics should be promising for application as high-performance composite ceramics.
研究领域:
材料科学
·
陶瓷工程
✓ 已验证
产品关联
DOI
高影响因子
JOURNAL OF SOLID STATE CHEMISTRY
·
2023
·
IF 3.3
Bowen Zhang,Fugang Zhong,Xinchao Qiu,Jianbo Xu,Mengchen Hu,Jun Ou-Yang,Yue Zhang,Benpeng Zhu,Xiaofei Yang,Shi Chen
Hafnium carbide (HfC) whiskers were successfully synthesized by combining hydrothermal and carbothermal reduction. The precursor of HfC whiskers was prepared by the hydrothermal method, subsequently pyrolyzed, and reduced to HfC whiskers at 1500–1700 °C. The synthesis parameters of HfC whiskers at various temperatures, C/Hf molar ratios, and NaF concentrations were investigated in detail. The whiskers with diameters of 1–3 μm and lengths of 50–90 μm were prepared by pyrolyzing the precursors with a C/Hf molar ratio of 6 at 1700 °C. The experimental results and thermodynamic analysis demonstrated that the growth of HfC whiskers was governed by the vapor-liquid-solid (VLS) mechanism. Furthermore, the prepared HfC whiskers were added to the ZrB 2 -HfO 2 coatings on the surface of tungsten-rhenium substrates in different ratios to toughen the coatings. The thermal shock test results indicated that the coatings toughened with HfC whiskers had better thermal shock resistance. In particular, the maximum number of thermal shock cycles that 6%HfC W -ZH could withstand was five times higher than that of W–Re alloy and about one time higher than that of ZH coatings without HfC whiskers. The thermal shock resistance of the ZrB 2 -HfO 2 coatings was significantly improved by adding HfC whiskers.
研究领域:
材料科学
·
陶瓷材料
·
表面工程
✓ 已验证
产品关联
DOI
高影响因子
CERAMICS INTERNATIONAL
·
2023
·
IF 5.2
Pengju Chen,Tian Tian,Chenzhuo Zhang,Xian Tang,Zhuan Li
A series of Ce-doping nanograin Gd 2 Ce x Hf 2- x O 7 (0.0 ≤ x ≤ 2.0) ceramic samples as nuclear waste forms were prepared, and their microstructure, phase evolution, and aqueous durability were systematically studied. The results revealed that the original Gd 2 Hf 2 O 7 sample comprised a single pyrochlore structure after sintering at 1673 K, but all the Gd 2 Ce x Hf 2- x O 7 (0.5 ≤ x ≤ 2.0) samples assumed defective fluorite structures with Ce-doping. As the x Ce value increased from 0.0 to 2.0, the average grain size of the samples gradually increased from 162 nm to 599 nm, whereas the relative density (measured density/theoretical density) of the samples gradually increased from 91.12% to 93.93%. The normalized release rates of Ce element in the Gd 2 Ce 2 O 7 sample after 42 days were slightly lower than those of Hf element in the Gd 2 Hf 2 O 7 sample owing to the lower porosity of the Gd 2 Ce 2 O 7 sample, and the bond dissociation energy of Ce–O (∼795 kJ/mol) was slightly higher than that of Hf–O (∼791 kJ/mol). Moreover, the normalized release rates of all considered elements were lower than 10 −5 g m −2 d −1 , indicating that the samples had excellent chemical stability.
研究领域:
材料科学
·
核能工程
✓ 已验证
产品关联
DOI
高影响因子
CATALYSIS TODAY
·
2018
·
IF 4.667
Hu Li,Yan Li,Zhen Fang,Richard L. Smith
An acid-base bifunctional nanohybrid phenylphosphonic acid (PhP) - hafnium (1:1.5) was synthesized through assembly of PhP with HfCl 4 for catalytic transfer hydrogenation of furfural (FUR) to furfuryl alcohol (FFA) using 2-propanol as both reaction solvent and hydrogen donor source. An FFA yield of 97.6 % with formation rate of 9760 μmol g −1 h −1 at 99.2 % FUR conversion was obtained with the reaction system at 120 °C for 2 h reaction time. Activation energy (Ea) was estimated to be 60.8 kJ/mol with respect to FUR concentration, which is comparable with or even lower than Ea values attained over metal catalysts. The pronounced catalytic activity of PhP-Hf (1:1.5) is attributed to its moderate acidity and relatively strong basicity. The PhP-Hf (1:1.5) catalyst was demonstrated to maintain its activity for five consecutive reuse cycles.
研究领域:
化学工程
·
催化科学
✓ 已验证
DOI
高影响因子
IONICS
·
2022
·Vol. 28
·期 9
·4273-4282
·
IF 2.961
Gao Jiayi,Yang Yujie,Ren Yujie,Zhu Wenjie,Li Jin,Liu Yongguang,Dai Lei,Wang Ling,He Zhangxing
Vanadium redox flow batteries have the advantages of long life, flexible design, safety, and reliability, so they have broad development prospects in the field of energy storage. Borides are extensively used in electrochemistry due to their excellent electrical conductivity. In this program, HfB 2 was used as catalyst for the V 3+ /V 2+ pair. The catalytic effect was verified by electrochemical impedance spectroscopy and cyclic voltammetry. The result shows that the cell using HfB 2 as negative catalyst can exhibit excellent rate capability when the current density is 50 ~ 125 mA cm −2 . At 125 mA cm −2 , the discharge capacity of the modified cell is 68.7 mA h, which is much higher than pristine cell (22.8 mA h). And the energy efficiency of pristine cells is 11.2% lower than that of modified cells. These consequences suggest that HfB 2 is a catalyst with promising prospects to enhance electrochemical activity of V 3+ /V 2+ redox reaction in VRFB.
研究领域:
材料科学
·
电化学
✓ 已验证
DOI
高影响因子
MATERIALS CHARACTERIZATION
·
2024
·
IF 4.8
Shuai Ma,Di Dong,Mengyao Zhang,Ye Gao,Zhuangzhi Wu,Dezhi Wang
W-Re-HfC alloys have been extensively applied in the field of high-temperature structural parts. To ensure high temperature reliability, it is essential to enhance creep resistance ability. In this study, the microstructures of forged W-Re-HfC alloys were adjusted using different heat treatment processes . The corresponding tensile creep properties were also measured at 2000 °C with 40 MPa. Furthermore, a possible creep fracture mechanism was also explored. The forged W-Re-HfC sample annealed for 2 h exhibited the best creep performances with a steady-state creep rate of 3.28 × 10 −6 and a creep life of 5.6 h. Generally, a larger grain size indicates a lower steady-state creep rate; however, the precipitation of carbides at the grain boundaries (GBs) deteriorates the bonding strength of interfaces, thus reversing the former trend. The dominant creep mechanism is diffusion creep , in which the voids nucleate perpendicular to the GBs, grow and connect into cracks, ultimately leading to fractures.
研究领域:
材料科学
·
金属学与热处理
·
高温结构材料
·
固态物理
·
力学性能
✓ 已验证
DOI
高影响因子
危险品化学品经营许可证（带存储）