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Facile synthesis of high-entropy zirconate nanopowders and their sintering behaviors

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Journal of Advanced Ceramics 2023年第3期12卷 498-509页

作者： Lin Tan Xinghua Su Jingxin Yang Pengchao Ji Fu Sun Qiang Tian Zhenhuan Zhao School of Materials Science and Engineering Chang’an UniversityXi’an 710061China State Key Laboratory of Environment-Friendly Energy Materials Southwest University of Science and TechnologyMianyang 621010China School of Advanced Materials and Nanotechnology Xidian UniversityXi’an 710126China

The challenge in synthesizing high-entropy ceramic(HEC)nanopowders is to suppress severe grain coarsening and particle agglomeration,which occur at elevated temperatures.This challenge could be addressed by the polyacrylamide gel method.In this work,single-phase high-entropy(Lao.2Ndo.2Smo.2Gdo.2 Ybo.2)2Zr2O7 and(Lao.2Ndo.2Yo.2Euo.2Gdo.2)2Zr2O7 nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time.The results showed that phase composition,particle size,and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide(AM)/Zr and calcination temperature.These as-synthesized high-entropy zirconate(HEZ)nanopowders could be sintered into fully dense ceramics at 1500 C for 2 h.These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature.Additionally,two-step sintering of these nanopowders was conducted,and the HEZ ceramics with fine grains were prepared.The polyacrylamide gel method is simple and easily operated,which is a facile approach of producing the HEC nanopowders with excellent sinterability.

关键词： high-entropy ceramics(HECs) nanopowders zirconate acrylamide(AM) sintering

Effect of synthesis conditions and surrounding medium on luminescence properties of YVO_4:Eu^(3+) nanopowders

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Journal of Rare Earths 2015年第2期33卷 129-134页

作者： E.V.Golyeva D.V.Tolstikova I.E.Kolesnikov M.D.Mikhailov St.Petersburg State Polytechnical University St.Petersburg 195251 Russia Scientific and Technological Institute of Optical Material Science VNTs S.I.Vavilov State Optical InstituteSt.Petersburg 192171 Russia St.Petersburg State University St.Petersburg 199034 Russia

Nanocrystalline yttrium vanadate doped with europium ions powders were synthesized via sol-gel method based on decomposition of metal-polymer complex. X-ray diffraction analysis showed that samples had pure tetragonal phase without any impurities. Scanning electron microscopy and static light scattering technique were used to study morphology and size of prepared nanoparticles. Average diameter of the nanoparticles was about 40 nm. The changes in structural and luminescence properties were observed as a function of the first and second calcination temperature. The optimal conditions for synthesis of nanoparticles were determined as Т1=500℃, t1=1 h; Т2=950 ℃, t2=1.5 h. The effect of different media surrounding the nanoparticles on their luminescence properties and lifetime was investigated and discussed in terms of effective refractive index. It was found that the observed lifetime of YVO4：Eu^3＋ 5 at.% nanophosphor was decreased from 0.64 ms in air（nmed=1） to 0.45 ms in chalcogenide glass As39S61（nmed=2.39）.

关键词： nanopowders rare earths luminescence effective refractive index lifetime

Energy transfer and 2 μm emission in Tm^(3+)/Ho^(3+) co-doped(Y_(0.87)La_(0.1)Zr_(0.03))_2O_3 nanopowders

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Journal of Rare Earths 2018年第5期36卷 468-473页

作者： Yaqian Chen Huanping Wang Xiaoting Zhang Zhen Xiao Qinghua Yang Ruoshan Lei Degang Deng Lihui Huang Shiqing Xu College of Materials Science and Engineering China Jiliang University

（Y0.87La0.1Zr0.03）2O3 nanopowders doped with various concentrations of Tm^3＋ and Ho^3＋ were prepared by the citrate method. The standard cubic Y2O3 phase can be matched in the Tm^3＋/Ho^3＋ co-doped（Y0.87La0.1Zr0.03）2 O3 nanopowders. The nanopowders exhibit average particle sizes of 40,60, 80 and 100 nm after calcinated at 900,1000,1100 and 1200℃,respectively. The energy transfer from Tm^3＋ to Ho^3＋ and the optimum fluorescence emission around 2 μm were investigated. Results indicate that the emission bands at around 1.86 and 1.95 μm correspond to 3 F4→3 H6 transition of Tm^3＋ and 5 I7→5 I8 transition of Ho^3＋, respectively.Better spectral properties were achieved in Tm^3＋/Ho^3＋ co-doped（Y0.87La0.1Zr0.03）2O3 nanopowders with the average size of 100 nm obtained at the conditions of the treatment of precursors calcinated at 1200 ℃ for 2 h doped with 1.5 mol% Tm^3＋ and 1 mol% Ho^3＋.

关键词： Emission spectral Tm^3＋/Ho^3＋ Y2O3 La2O3-ZrO2 nanopowders Rare earths

Novel Salt-Assisted Combustion Synthesis of High Surface Area Ceria nanopowders by An Ethylene Glycol-Nitrate Combustion Process

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Journal of Rare Earths 2006年第4期24卷 434-439页

作者：陈伟凡李凤生于吉义李永绣 National Special Superfine Powder Engineering Research Center Nanjing University of Science & Technology Nanjing 210094China Research Center for Rare Earths & Micro/Nano-Functional Materials Nanchang University Nanchang 330047China

A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion synthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ～6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m^2·g^-1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m^2·g^-1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.

关键词： salt-assisted combustion synthesis ceria nanopowders ethylene glycol high surface area rare earths

Preparation of Sr_2Fe_(1-x)Sc_xMoO_(6-δ) nanopowders and its electrical conductivity

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Journal of Rare Earths 2011年第7期29卷 673-677页

作者：葛奔艾德生马景陶邓长生林旭平 State Key Laboratory of New Ceramics and Fine Processing Beijing Key Lab of Fine Ceramics Institute of Nuclear and New Energy Technology Tsinghua University

Double-perovskite Sr2Fe1-xScxMoO6-δ （x=0, 0.05, 0.1, 0.2, 0.3, 0.4） powders applied to the cathode of solid oxide electrolysis cells were synthesized by the sol-gel citrate combustion method. Initial powders were calcined at different temperatures under different atmosphere （air, H2（4 vol.%）/Ar）, and the effects of the preparation process on the structure and the morphology of the powders were investigated by thermal analysis （TG/DSC）, X-ray diffraction （XRD）, scanning electron microscopy （SEM） and surface area analysis. The electric conductiv-ity of the materials was measured by electrochemical work station using wafers prepared by dry pressing. It was found that the formation of perovskite structure was related to the content of Sc and combustion improver （NH4NO3）, pH value, calcining temperature and atmosphere. A single perovskite phase of Sr2Fe1-xScxMoO6-δ could be formed after 3 h calcining in reducing atmosphere of H2 （4 vol.%）/Ar at 1100 oC. The electrical property indicated that, this material had a potential to be used in medium/high temperature solid oxide fuel cells or electrolysis cells.

关键词： nanopowders double-perovskites sol-gel citrate combustion method solid oxide electrolysis cells rare earths

Preparation of Y_2O_3 nanopowders by Sol-Gel Method

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Journal of Rare Earths 2003年第S1期21卷 127-130页

作者：王介强于庆华高新睿郑少华陶珍东 School of Materials Science & Engineering Jinan University School of Materials Science & Engineering Shandong University

Using the inexpensive inorganic salts as the starting materials,pure yttria nanopowders were prepared by sol-gel method. The primary particles are spherical and about 60 nm in diameter with a narrow size distribution. Moderate sulfate ions used as additive were the key to the formation of precursor and the preparation of spherical Y_2O_3 nanopowders. Transformation of the precursor was investigated during the calcining. The influence of calcination temperature on size and purity of production was analyzed. The results show that higher temperature is beneficial to the preparation of pure and complete crystallization of yttria powders under the condition of not making particles excessively grow.

关键词： inorganic nonmetal materials nanopowders yttria inorganic sol-gel sulfate ions calcinations temperature rare earths

Low-agglomerated yttria nanopowders via decomposition of sulfate-doped precursor with transient morphology

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Journal of Rare Earths 2014年第4期32卷 320-325页

作者： R.P.Yavetskiy D.Yu.Kosyanov V.N.Baumer A.G.Doroshenko A.I.Fedorov N.A.Matveevskaya A.V.Tolmachev O.M.Vovk Institute for Single Crystals of NAS of Ukraine State Scientific Institution"Institute for Single Crystals"of NAS of Ukraine

The fabrication peculiarities of low-agglomerated yttria （Y2O3） nanopowders via thermal decomposition of sulfate-doped precursor with transient morphology were studied. It was determined that Y2（OH）5（NO3）x（CO2）y（SO4）z·nH2O （n=1-2） crystalline precursor underwent fragmentation and decomposition into isolated quasi-spherical Y2O3 particles upon calcination. Effect was con-nected with minimizing the free energy of the plate-like crystallites via reducing the contact surface until to the moment of spheroidi-zation and attainment of isolation that occurred atТ=1100 °С. Residual sulfate ions slowed down the surface diffusion during heat treatment thus retaining quasy-spherical morphology and low aggregation degree of Y2O3 nanopowders. Sulfate-doped yttria nanopowders with medium particle size of 53±13 nm possessed improved sinterability in comparison with undoped ones arising from finer particle size, narrower particle distribution and lower agglomeration degree.

关键词： precursor transient morphology sulfate-ions yttria nanopowders particle size sinterability rare earths

Synthesis and microwave absorbing properties of La-doped Sr-hexaferrite nanopowders via sol-gel auto-combustion method

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Rare Metals 2017年第9期36卷 704-710页

作者： Jun-Liang Liu Peng Zhang Xing-Kai Zhang Qing-Qing Xie Dong-Jun Pan Jian Zhang Ming Zhang School of Chemistry and Chemical Engineering Yangzhou UniversityYangzhou 225002China

La-doped Sr-hexaferrite（Sr（1-x）LaxFe（12）O（19））（x=0.05,0.10,0.15,0.20） nanopowders with particle size ranging from 80 to 110 nm were successfully synthesized by sol-gel auto-combustion. The phase formation temperature increases, while the particle size decreases as the Ladoping content goes up. The partial substitution of Sr^（2＋） by La^（3＋） results in the suppression effects on the growth-up of the crystallites and the enhancement of the electron hopping between Fe^（3＋） with different valences, which leads to the improvement in the dielectric loss and magnetic loss.Therefore, both the microwave absorbing abilities and absorbing frequency ranges are tuned by La-doping. The synthesized Sr-hexaferrite nanopowders with doping element content of 0.10 demonstrate the fine broad microwave absorbing properties.

关键词： Ferrite La-doping nanopowders Sol-gelauto-combustion Microwave absorbing properties

Effect of different sol-gel synthesis processes on microstructural and morphological characteristics of hydroxyapatite-bioactive glass composite nanopowders

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Journal of Advanced Ceramics 2014年第3期3卷 207-214页

作者： Mohamadhassan TAHERIAN Ramin ROJAEE Mohammadhossein FATHI Morteza TAMIZIFAR Department of Materials and Metallurgical Engineering Iran University of Science and Technology(IUST)Tehran 16866-13114Iran Biomaterials Research Group Department of Materials EngineeringIsfahan University of TechnologyIsfahan 84156-83111Iran Dental Materials Research Center Isfahan University of Medical SciencesIsfahanIran

The aim of this work was to study the influence of the different synthesis processes on microstructural and morphological characteristics and distribution of hydroxyapatite-bioactive glass(HAp-BG)composite nanopowders obtained by sol-gel method.HAp-BG composite nanopowders with 20 wt%bioactive glass were prepared using a sol-gel method via four routes:(I)mixing the prepared HAp solution with BG solution before aging time;(II)mixing the prepared BG solution with the prepared HAp gel after gelation;(III)mixing the calcined BG nanopowders with the prepared HAp solution;and(IV)mixing the two prepared calcined nanopowders by mechanochemical activation.The prepared nanopowders were evaluated and studied by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray spectrometer(EDS),Fourier transform infrared(FTIR),transmission electron diffraction(TEM)and Brunauer-Emmet-Teller(BET)method to investigate the phase structure,microstructure and morphology,functional groups,and the size and distribution of nanopowders.Results indicated that morphology,crystallinity,crystallite size and specific surface area(SSA)of the powders are highly correspondent to the process and type of synthesis method.These findings suggest that the modified sol-gel derived HAp-BG composite nanopowders are expected to efficiently provide a possibility to produce a good candidate to use for fabrication of a bulk nanostructured HAp-BG composite for bone tissue engineering.

关键词： hydroxyapatite(HAp) bioactive glass(BG) composite nanopowders sol-gel