Co-reporter:Abdelkhalek Henniche, Jia-Hu Ouyang, Yong-Hui Ma, Zhi-Gang Wang, ... Zhan-Guo Liu
Ceramics International 2017 Volume 43, Issue 9(Volume 43, Issue 9) pp:
Publication Date(Web):15 June 2017
DOI:10.1016/j.ceramint.2017.02.125
An efficient and flexible chemical co-precipitation method has been used to synthesize nanoscale Al2O3-GdAlO3 powders with eutectic composition. The as-synthesized powders exhibit a highly dispersive and homogeneous distribution with an average particle size of 50 nm. The phase transition in the resulting powders strongly depends upon the calcination temperature. GdAlO3 undergoes complete crystallization after calcination at 1050 °C, however, the diffraction peaks of α-Al2O3 are found at a relatively high calcination temperature of at least 1300 °C. The fully-densified Al2O3-GdAlO3 ceramic with eutectic composition obtained by hot pressing the nanoscale powders at 1500 °C exhibits a room temperature flexural strength of 556 MPa, a Vickers hardness of 17.3 GPa and a fracture toughness of 7.5 MPa m1/2. The high temperature flexural strength of the as-sintered Al2O3-GdAlO3 ceramic is measured to be 515 MPa after bending tests at 1000 °C.
Co-reporter:Abdelkhalek Henniche, Jiahu Ouyang, Yonghui Ma, Zhigang Wang, ... Xinyu Liu
Progress in Natural Science: Materials International 2017 Volume 27, Issue 4(Volume 27, Issue 4) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.pnsc.2017.08.002
•Large scale Al2O3-GdAlO3-ZrO2 nanopowders with eutectic composition were successfully synthesized via chemical co-precipitation method.•The as-synthesized Al2O3-GdAlO3-ZrO2 nanoparticles show high homogeneity and uniform particle size distribution.•The phase evolution and morphology of Al2O3-GdAlO3-ZrO2 powders as a function of calcination temperature are disclosed.•The Al2O3-GdAlO3-ZrO2 specimen sintered at 1500°C displays a competitive thermo-mechanical properties.A low cost chemical co-precipitation method was employed to fabricate nanoscale Al2O3-GdAlO3-ZrO2 powder with eutectic composition. A careful control of reaction conditions was required during the preparation. The synthesized nanopowders exhibited a particle size of 20–200 nm, and were highly dispersive and uniform. The results showed that calcination temperature had an important influence on the phase constituents of the nanopowders. With increasing the calcination temperature, a phase transformation from Ɵ-Al2O3 to α-Al2O3 and a thermal decomposition from Gd3Al5O12 (GdAG) to GdAlO3 and α-Al2O3 occurred in sequence. A calcination temperature of 1300 °C was needed for the crystallization of α-Al2O3. These nanosized powders were consolidated via hot pressing to produce a fully densified ceramic composite with eutectic composition. The Al2O3-GdAlO3-ZrO2 ceramic hot-pressed at 1500 °C exhibited a relative density of 99.4%, a flexural strength of 485 MPa and a fracture toughness of 6.5 MPa m1/2. The ceramic had a thermal conductivity of 1.9 W m K−1 at 1200 °C and a thermal expansion coefficient of 9.49 × 10−6 K−1 at 1100 °C.
Co-reporter:Zhan-Guo Liu, Kai-Jun Hu, Jia-Hu Ouyang, Yu-Jun Jin
Journal of Alloys and Compounds 2016 Volume 683() pp:470-473
Publication Date(Web):25 October 2016
DOI:10.1016/j.jallcom.2016.05.128
•The Ho3+-doped La2Zr2O7 nanoparticles exhibit a defect fluorite-type structure.•The Ho3+-doped La2Zr2O7 nanoparticles show the uniform particle size of 50 nm.•The emission intensity has a maximum for the (La0.95Ho0.05)2Zr2O7 nanoparticles.(La1−xHox)2Zr2O7 (x = 0, 0.025, 0.05, 0.075, 0.1) nanoparticles have been successfully synthesized by a facile chemical co-precipitation and calcination method, and were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. (La1−xHox)2Zr2O7 nanoparticles calcined at 900 °C for 5 h in air exhibit a single phase of defect fluorite-type structure and have a particle size of about 50 nm. The emission bands centered at 542 nm and 553 nm are identified as the 5F4, 5S2 → 5I8 transitions. The emission intensity increases with the increase of the Ho3+ ion content, and reaches the maximum for the (La0.95Ho0.05)2Zr2O7 nanoparticles, and then decreases with further increasing Ho3+ ion content.
Co-reporter:Yong-Hui Ma, Zhan-Guo Liu, Jia-Hu Ouyang, Yu-Jun Jin
Ceramics International 2016 Volume 42(Issue 13) pp:14749-14753
Publication Date(Web):October 2016
DOI:10.1016/j.ceramint.2016.06.102
Abstract
Sm2(Zr1–xTix)2O7 (0≤x≤0.15) ceramics have been fabricated by pressureless-sintering method at 1973 K for 10 h in air. The influence of TiO2 doping on microstructure and thermo-optical properties of Sm2(Zr1–xTix)2O7 ceramics is investigated by X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The partial substitution of Ti4+ for Zr4+ results in a significant increase in emissivity at low wavelengths contrasted with undoped Sm2Zr2O7. Sm2(Zr0.85Ti0.15)2O7 ceramic exhibits a high emissivity of above 0.70 at 1073 K in a wavelength range of 3–16 µm, where the highest value at this temperature is more than 0.90 especially in the wavelength range of 9–14 µm. FT-IR spectra and optical absorption spectra unveil the mechanisms of enhanced emissivity in Sm2(Zr1–xTix)2O7 (0.05≤x≤0.15) ceramics in the intermediate infrared range, especially at the wavelengths of 3–8 µm, due to Ti4+ ion substitution for Zr4+ ion.
Co-reporter:Jiao-Jie Cui, Jia-Hu Ouyang, Zhan-Guo Liu
Journal of Alloys and Compounds 2016 Volume 685() pp:316-321
Publication Date(Web):15 November 2016
DOI:10.1016/j.jallcom.2016.05.272
•The hot-corroded products at 1250 °C vary with prolonging the corrosion time.•The corrosion products at 1250 °C for 2 h are Ca(Mg,Al)(Al,Si)2O6 and CaAl2Si2O8.•The corrosion product at 1250 °C for 4 h or 16 h consists mainly of CaAl2Si2O8.•The corrosion mechanisms are proposed according to the phase diagram.Hot corrosion is one of the significant failure mechanisms in hot-section components, especially when molten CaO–MgO–Al2O3–SiO2 (CMAS) deposits attack the thermal barrier coating and facilitate its degradation at elevated temperatures. This work concentrates on the hot corrosion behavior of LaMgAl11O19 ceramic as a promising candidate for TBCs after exposure to CMAS at 1250 °C for 1–16 h in air. The phase constituents and morphologies of the hot corrosion products were investigated by X-ray diffraction and scanning electron microscopy, respectively. Energy-dispersive X-ray spectroscopy was employed for elemental and microstructure analysis. The corrosion products are identified to be CaAl2Si2O8 and Ca(Mg,Al)(Al,Si)2O6 due to the interaction between LaMgAl11O19 ceramic and melt-CMAS by dissolution-reprecipitation. The hot corrosion mechanism was further proposed based on the phase diagram.
Co-reporter:Jun Xiang, Jia-Hu Ouyang, Zhan-Guo Liu
Journal of Power Sources 2015 Volume 284() pp:49-55
Publication Date(Web):15 June 2015
DOI:10.1016/j.jpowsour.2015.03.006
•La10Si5.9W0.1O27.1 ceramic has the highest total conductivity of 4.45 × 10−2 S cm−1 at 1073 K.•The solid solubility of W6+ in the lattice of apatite-type La10Si6−xWxO27+δ phase is 0.1.•Some fine non-conducting La6W2O15 particles are found at grain boundaries.•Doping with W6+ is beneficial to the removal of La2SiO5 impurity phase.Different compositions of apatite-type La10Si6−xWxO27+δ ceramics are prepared successfully by the high-temperature solid state reaction route. Crystal structure and electrical properties of La10Si6−xWxO27+δ ceramics are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and electrochemical impedance spectroscopy (EIS). La10Si6−xWxO27+δ (x = 0.1, 0.2, 0.3, 0.4, 0.5) ceramics consist of a hexagonal apatite-type structure and a small amount of La6W2O15 phase of orthorhombic structure but no La2SiO5 phase. The diffraction peaks of the hexagonal apatite-type structure shift to the low angle side with doping the W6+. When the content of hexavalent tungsten is beyond 0.1, rod-like grains of La10Si6−xWxO27+δ ceramics are replaced gradually by equiaxed apatite-type grains, and some fine particles of La6W2O15 are observed at grain boundaries. These La6W2O15 particles are non-conducting materials and lead to the increase in grain impedance and grain boundary impedance of La10Si6−xWxO27+δ ceramics gradually when the content of hexavalent tungsten is beyond 0.2. However, the solid solubility of W6+ in the lattice of apatite-type structure reaches the maximum when the W6+ content is at 0.1, and correspondingly the La10Si5.9W0.1O27.1 ceramic has the highest total conductivity of 4.45 × 10−2 S cm−1 at 1073 K.
Co-reporter:Jun Xiang, Jia-Hu Ouyang, Zhan-Guo Liu, Guo-Chao Qi
Electrochimica Acta 2015 Volume 153() pp:287-294
Publication Date(Web):20 January 2015
DOI:10.1016/j.electacta.2014.12.017
Oxy-apatite type La10Si6–xNbxO27+δ ceramics doped with different pentavalent niobium contents are synthesized via the high-temperature solid state reaction method. Crystal structure and electrical properties of La10Si6–xNbxO27+δ ceramics are investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectroscopy and complex impedance measurements. La10Si6O27 ceramic sintered at 1923 K consists of hexagonal oxy-apatite phase and a small amount of La2SiO5. Pentavalent niobium can partially substitute for tetravalent silicon to form a Nb-doped oxy-apatite structure. However, La2SiO5 phase disappears with increasing the pentavalent niobium content. Some fine La3NbO7 particles are found at grain boundaries of oxy-apatite phase in La10Si6–xNbxO27+δ ceramics when the pentavalent niobium content is beyond 0.1. Raman spectra of La10Si6–xNbxO27+δ ceramics generates three new characteristic modes at 710 cm−1, 342 cm−1 and 136 cm−1 with the addition of different pentavalent niobium contents, which are significantly enhanced especially at x = 0.1 and x = 0.5. These new modes are from NbO bonds of La3NbO7 phase and obstruct the interstitial oxide-ion O(5) from conducting in dry atmosphere, thus the grain boundary impedance of La10Si6–xNbxO27+δ ceramics increases correspondingly. La10Si5.9Nb0.1O27.05 ceramic exhibits the highest total conductivity among all the compositions above 873 K.
Co-reporter:Xiu-Ping Zhang, Jia-Hu Ouyang, Zhan-Guo Liu, Yu-Jin Wang, Ya-Ming Wang, Yu Zhou
Materials & Design (1980-2015) 2015 67() pp: 324-329
Publication Date(Web):
DOI:10.1016/j.matdes.2014.11.053
Co-reporter:Xiu-Ping Zhang, Jia-Hu Ouyang, Zhan-Guo Liu, Yu-Jin Wang, Ya-Ming Wang
Materials Science and Engineering: A 2015 Volume 648() pp:299-304
Publication Date(Web):11 November 2015
DOI:10.1016/j.msea.2015.09.041
Crack-healing behavior and strength recovery of ZrO2(Y2O3)–Al2O3–MoSi2 (TZ3Y20A–MoSi2) ceramics have been investigated. Heat treatment in air enhances distinctly the flexural strength of TZ3Y20A–MoSi2 ceramics. Si–O oxide and ZrSiO4 are found after heat treatment, in which the former heals the cracks and recovers the strength, however, the latter is one kind of brittle materials that reduces mechanical performance of ceramics. The TZ3Y20A–10 vol% MoSi2 ceramic has a complete crack-healing effect and strength recovery by suitable heat treatment at 1373 K for 3 h in air, however, the strength does not recover completely under other heat treatment conditions. With further increasing the MoSi2 contents to 20 vol%, the flexural strength of as heat-treated TZ3Y20A–MoSi2 ceramics is higher than that of pre-cracked specimens, but remains lower than that of smooth specimens. Crack closure and rebonding of the crack walls are due to the formation of Si–O glassy phase by oxidation reaction.
Co-reporter:Jun Xiang, Zhan-Guo Liu, Jia-Hu Ouyang, Fu-Yao Yan
Journal of Power Sources 2014 Volume 251() pp:305-310
Publication Date(Web):1 April 2014
DOI:10.1016/j.jpowsour.2013.11.074
•La10Si6−xInxO27−δ is synthesized via high-temperature solid state reaction.•La10Si5.8In0.2O26.90 has a total conductivity of 3.14 × 10−2 S cm−1 at 1073 K.•La10Si5.8In0.2O26.90 has a higher conductivity than undoped La10Si6O27.•La10Si5.6In0.4O26.80 has a thermal expansion coefficient of 9.01 × 10−6 K−1 at 1073 K.Oxy-apatite type La10Si6−xInxO27−δ (x = 0.1, 0.2, 0.3, 0.4, 0.5) ceramics are synthesized via the high-temperature solid state reaction method to obtain dense bulk ceramics. Crystal structure and properties of La10Si6−xInxO27−δ ceramics are investigated by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, complex impedance analysis and thermal expansion coefficient measurement. All the compositions of La10Si6−xInxO27−δ ceramics doped with In3+ consist of a hexagonal apatite structure with a space group P63/m. The diffraction peaks of La10Si6−xInxO27−δ ceramics shift to the low angle side with increasing the content of In3+. Lanthanum silicates doped with trivalent In3+ have a higher total conductivity than those without trivalent In3+ at the Si4+ site. La10Si5.8In0.2O26.90 ceramics has the highest total conductivity of 3.14 × 10−2 S cm−1 at 1073 K, which is considerably higher than that of undoped La10Si6O27. La10Si5.6In0.4O26.80 has the highest thermal expansion coefficient of 9.01 × 10−6 K−1 at 1073 K.
Co-reporter:Fu-Yao Yan, Zhan-Guo Liu, Jia-Hu Ouyang, Mu-Fu Yan
International Journal of Hydrogen Energy 2014 Volume 39(Issue 3) pp:1457-1462
Publication Date(Web):16 January 2014
DOI:10.1016/j.ijhydene.2013.11.018
•We model the interaction between H2O and LaNbO4(010) surface via first-principles.•We take H2O respectively over oxygen vacancy and the Nb atom into considerations.•The new tetrahedron is regular if H2O is over the oxygen vacancy, or is flattened.•H2O is more favorable to dissociate over the oxygen vacancy than at other sites.The water-containing atmosphere plays an important role in the improvement of proton conductivity of LaNbO4. The interaction between the water molecule and the oxygen-deficient (010) surface of LaNbO4 crystal has been investigated via first-principles calculations. The water molecule is set at different heights over the oxygen vacancy and the exposed niobium atom in Nb–O tetrahedron. The adsorption and dissociation behavior of the water molecule to the surface are illustrated and analyzed by the total and localized density of states (DOS) plots. By finely adjusting the heights of the water molecule from the surface, the relatively stable position for the water molecule is determined by free energies of the hydrated slabs. The water molecule prefers to adsorb onto LaNbO4 (010) surface and then to dissociate into one proton and one hydroxyl over the oxygen vacancy rather than over the exposed niobium atom in Nb–O tetrahedron.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Yu Zhou
Journal of Power Sources 2013 Volume 228() pp:1-6
Publication Date(Web):15 April 2013
DOI:10.1016/j.jpowsour.2012.11.072
The effect of nickel oxide addition on the sintering behavior and electrical properties of the GdSmZr2O7 ceramic has been investigated. The crystal structure, microstructure and electrical properties of the GdSmZr2O7 ceramic incorporated with or without 1 wt.% nickel oxide are characterized by the X-ray diffraction, field-emission scanning electron microscopy and electrochemical impedance spectroscopy, respectively. The GdSmZr2O7 ceramic exhibits a single phase of the pyrochlore-type structure. No chemical reaction between GdSmZr2O7 and NiO is found in the sintered samples. The grain, grain boundary, and total conductivity of the GdSmZr2O7 ceramic with or without NiO addition obey the Arrhenius relation. The addition of a small amount of NiO to the GdSmZr2O7 ceramic greatly promotes the densification process, achieving 93% of the theoretical density after sintering at 1773 K in air. This reduces the sintering temperature by about 200 K, without adversely affecting the total conductivity of the GdSmZr2O7 ceramic. The GdSmZr2O7 ceramic with 1 wt.% NiO addition is an oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels.Highlights► The GdSmZr2O7 ceramic exhibits a single phase of the pyrochlore-type structure. ► 1 wt.% of NiO to GdSmZr2O7 promotes sintering densification. ► 1 wt.% of NiO to GdSmZr2O7 reduces sintering temperature by about 200 K. ► Total conductivity of GdSmZr2O7 was not adversely affected by the addition of NiO.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou
Journal of Power Sources 2013 Volume 243() pp:836-840
Publication Date(Web):1 December 2013
DOI:10.1016/j.jpowsour.2013.06.093
•The 1 wt.% ZnO-modified GdSmZr2O7 exhibits a single cubic pyrochlore-type phase.•1 wt.% ZnO to GdSmZr2O7 promotes sintering densification.•1 wt.% ZnO to GdSmZr2O7 reduces the sintering temperature by about 200 K.•The total conductivity of GdSmZr2O7 is improved by the addition of 1 wt.% ZnO.The effects of zinc oxide (ZnO) additive on the crystal structure, densification, and electrical conductivity of the GdSmZr2O7 ceramic have been examined. The GdSmZr2O7 ceramic with and without the addition of 1 wt.% ZnO sintered at temperatures between 1773 and 1973 K exhibits a single cubic pyrochlore-type phase. ZnO is very effective as a sintering aid for the GdSmZr2O7 ceramic, and it reduces the sintering temperature by about 200 K with a positive effect on the total conductivity. The total conductivity of the ZnO-modified GdSmZr2O7, as measured by A.C. impedance spectroscopy under an air atmosphere, is higher than that of the unmodified GdSmZr2O7 at identical temperature levels. At 1173 K, the highest total conductivity of the ZnO-modified GdSmZr2O7 is about fifteen percent higher than that of the unmodified GdSmZr2O7. The 1 wt.% ZnO-modified GdSmZr2O7 is one of good oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at different test temperatures.
Co-reporter:Yi-Jing Gu, Zhan-Guo Liu, Jia-Hu Ouyang, Fu-Yao Yan, Yu Zhou
Electrochimica Acta 2013 Volume 105() pp:547-553
Publication Date(Web):30 August 2013
DOI:10.1016/j.electacta.2013.05.034
BaCe0.85Ln0.15O3−δ (Ln = Gd, Y, Yb) ceramics are synthesized by the solid state reaction method. All of BaCe0.85Ln0.15O3−δ ceramics are composed of a single perovskite-type phase. The grain size of BaCe0.85Ln0.15O3−δ (Ln = Gd, Y, Yb) ceramics decreases with decreasing the ionic radius of doped cations. BaCe0.85Y0.15O3−δ ceramic has the highest total conductivity at 1073 K in both 4% H2O-saturated H2 and air among three kinds of BaCe0.85Ln0.15O3−δ ceramics. Total conductivities of BaCe0.85Gd0.15O3−δ and BaCe0.85Y0.15O3−δ ceramics exceed 0.01 S cm−1 in both 4% H2O-saturated H2 and air above 773 K. The pre-exponential factors and activation energies of BaCe0.85Ln0.15O3−δ ceramics are similar both in 4% H2O-saturated H2 and in air. The crystal structure, relative density and grain boundary area are the main influencing factors on electrical conductivity of doped barium cerates.
Co-reporter:Sa Li, Zhan-Guo Liu, Jia-Hu Ouyang
Applied Surface Science 2013 Volume 276() pp:653-659
Publication Date(Web):1 July 2013
DOI:10.1016/j.apsusc.2013.03.149
Highlights
- •
YbVO4 evolved from hot corrosion of V2O5-coated Yb2Zr2O7 is particle-shaped.
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YbVO4 exhibits rod-like crystal from hot corrosion of (Na2SO4 + V2O5)-coated Yb2Zr2O7.
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The mechanism is explained by a model based on dissolution–precipitation process.
Co-reporter:XIAO-MING LIU;YI-JING GU;ZHAN-GUO LIU
Bulletin of Materials Science 2013 Volume 36( Issue 3) pp:395-401
Publication Date(Web):2013 June
DOI:10.1007/s12034-013-0485-9
BaCe0·8 − xAxGd0·2O3 − δ (A = In, Zr, Ta; x = 0, 0·1) ceramics were synthesized by solid-state reaction method. Microstructure and electrical properties of BaCe0·8 − xAxGd0·2O3 − δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 573–1073 K in different atmospheres. BaCe0·8Gd0·2O3 − δ, BaCe0·7In0·1Gd0·2O3 − δ and BaCe0·7Zr0·1Gd0·2O3 − δ ceramics exhibit a single cubic perovskite structure. BaCe0·7In0·1Gd0·2O3 − δ ceramic has the highest conductivity of 4·6 × 10 − 2 S·cm − 1 in air at 1073 K. BaCe0·7In0·1Gd0·2O3 − δ and BaCe0·7Zr0·1Gd0·2O3 − δ ceramics exhibit an excellent chemical stability against boiling water. Indium is a suitable doping element to promote the sintering densification and to enhance both electrical conductivity and chemical stability of Gd-doped BaCeO3 at operating temperatures.
Co-reporter:Zhen-Lin Yang, Jia-Hu Ouyang, Zhan-Guo Liu, Xue-Song Liang, Yu-Jin Wang
Wear 2013 Volume 301(1–2) pp:641-647
Publication Date(Web):April–May 2013
DOI:10.1016/j.wear.2013.01.012
TiN–TiB2 composites incorporated with or without MoSi2 have been prepared by the reactive hot pressing method, using Ti, BN or MoSi2 powders as the starting materials. The influence of MoSi2 addition on tribological properties of TiN–TiB2 composites have been evaluated by using a ball-on-disk friction and wear tester in sliding against alumina ball from room temperature to 800 °C. The wear performance depends mainly upon temperature as well as the applied load. At room temperature and 10 N load, the TiN–TiB2 ceramic has a wear rate of 1.6×10–6 mm3 N–1 m–1, however, the TiN–TiB2–MoSi2 composite exhibits a wear rate of 1.5×10–4 mm3 N–1 m–1 under identical wear condition. At room temperature, the material removal of composites results from brittle fracture and abrasive wear during wear tests. The addition of MoSi2 can improve the oxidation resistance of TiN–TiB2 ceramic at high temperatures as it oxidizes to produce a protective SiO2 layer, which forms an effective barrier layer to restrain from further oxidation. At 800 °C and 10 N load, the wear rate of TiN–TiB2–MoSi2 composite is 1.7×10–6 mm3 N–1 m–1, which is only one fifth as much as the TiN–TiB2 ceramic. The low wear rate of TiN–TiB2–MoSi2 composite at 800 °C is attributed to high oxidation resistance, the formation of dense SiO2 scale and self-healing of microcracks.
Co-reporter:Zhen-Lin Yang, Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Yu-Jin Wang, W.G. Sloof
International Journal of Refractory Metals and Hard Materials 2013 Volume 41() pp:54-59
Publication Date(Web):November 2013
DOI:10.1016/j.ijrmhm.2013.02.001
Reaction process and phase formation mechanisms in reactive hot pressing (RHP) of titanium and boron nitride blend powders have been investigated in vacuum. In temperatures of up to 1300 °C, chemical reactions in the Ti–BN blend powder proceed via a solid-state diffusion process. Intermediate phases of hexagonal α-TiN0.3, tetragonal Ti2N, nonstoichiometric cubic TiN0.9 and orthorhombic TiB are found before they finally transform to the stoichiometric cubic TiN and hexagonal TiB2. Both the TiN–TiB2 ceramics reactive hot-pressed at 1600 and 1800 °C represent intragranular/intergranular distributions of TiB2 in TiN. In contrast with monolithic TiN and TiB2 ceramics, the reactive hot-pressed TiN–TiB2 exhibits a significant enhancement on flexural strength and fracture toughness. TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a Vickers hardness of 17.8 GPa, an elastic modulus of 475 GPa, a flexural strength of 732 MPa and a fracture toughness of 8.5 MPa·m1/2.Highlights► Intermediate phases of α-TiN0.3, Ti2N, TiNx and TiB are found in TiN–TiB2 ceramics. ► TiN–TiB2 ceramics show intra-granular/inter-granular distributions of TiB2 in TiN. ► TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a high flexural strength of 732 MPa. ► TiN–TiB2 ceramics reactive hot-pressed at 1800 °C have a high fracture toughness of 8.5 MPa·m1/2.
Co-reporter:Xiao-Liang Xia, Zhan-Guo Liu, Jia-Hu Ouyang, Yi Zheng
Journal of Power Sources 2012 Volume 217() pp:316-321
Publication Date(Web):1 November 2012
DOI:10.1016/j.jpowsour.2012.06.034
SmDy1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics are prepared by solid state reaction method at 1973 K for 10 h in air. The crystal structure and microstructure of SmDy1−xGdxZr2O7 ceramics are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the SmDy1−xGdxZr2O7 ceramics (x = 0.2, 0.4, 0.6, 0.8, 1.0) exhibit a pyrochlore structure except for SmDyZr2O7 ceramic. SmDyZr2O7 ceramic has a defective fluorite structure. The incorporation of Gd3+ facilitates a structural evolution from a defective fluorite into an ordered pyrochlore-type structure. Electrical conductivity of SmDy1−xGdxZr2O7 ceramics has been investigated by impedance spectroscopy over a frequency range of 1 Hz to 8 MHz from 673 to 1173 K. The grain conductivity of SmDy1−xGdxZr2O7 ceramics follows the Arrhenius behavior. The grain conductivity of SmDy1−xGdxZr2O7 ceramics increases obviously with increasing Gd3+ content in the temperature range of 673–1073 K, and the optimal grain conductivity value is 1.90 × 10−2 S cm−1 in the composition of SmGdZr2O7 ceramic at 1173 K. All the SmDy1−xGdxZr2O7 ceramics are purely oxide ionic conductors in the test temperature range.Highlights► Phase transition from fluorite to pyrochlore occurs in SmDy1−xGdxZr2O7 ceramics. ► Electrical conductivity of Sm2Zr2O7 is significantly improved by codoping strategy. ► The grain conductivity of SmGdZr2O7 ceramic is 1.90 × 10−2 S cm−1 at 1173 K. ► SmDy1−xGdxZr2O7 ceramics are purely oxide-ion conductors in test temperature range.
Co-reporter:Yi-Jing Gu, Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Fu-Yao Yan
Electrochimica Acta 2012 Volume 75() pp:332-338
Publication Date(Web):30 July 2012
DOI:10.1016/j.electacta.2012.05.002
Dy3+-doped barium zirconate ceramics, BaZr1–xDyxO3–δ (x = 0, 0.05, 0.10, 0.15, 0.20), have been synthesized by pressureless-sintering method at 1973 K for 10 h in air. The structure and electrical conductivity of BaZr1–xDyxO3–δ ceramics were investigated by means of X-ray diffraction, scanning electron microscopy and complex impedance spectroscopy. BaZr1–xDyxO3–δ ceramics exhibit a cubic perovskite structure. The total conductivity of BaZr1–xDyxO3–δ ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1073 K. The BaZr0.90Dy0.10O3–δ ceramic exhibits the highest total conductivity at 1073 K. The measured total conductivities of the BaZr0.90Dy0.10O3–δ ceramic in wet hydrogen (4% H2O/H2) and in air are 7.90 × 10−3 S cm−1 and 7.31 × 10−3 S cm−1 at 1073 K, respectively. The activation energy of BaZr1–xDyxO3–δ (x = 0.10, 0.15, 0.20) ceramics is clearly lower than that of undoped BaZrO3 ceramic in both wet hydrogen and air atmospheres, and it can be concluded that the Dy3+-doped BaZr1–xDyxO3–δ (x = 0.10, 0.15, 0.20) ceramics are potential proton conductors.
Co-reporter:Xiao-Ming Liu, Zhan-Guo Liu, Jia-Hu Ouyang, Yi-Jing Gu, Jun Xiang, Fu-Yao Yan
Electrochimica Acta 2012 Volume 59() pp:464-469
Publication Date(Web):1 January 2012
DOI:10.1016/j.electacta.2011.11.004
BaCe0.7In0.1A0.2O3−δ (A = Gd, Y) ceramics were synthesized by solid state reaction method. The microstructure and electrical properties of BaCe0.7In0.1A0.2O3−δ ceramics were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis at intermediate temperatures of 773–1073 K in different atmospheres. All BaCe0.7In0.1A0.2O3−δ ceramics exhibit a cubic perovskite structure. Relative densities of BaCe0.7In0.1A0.2O3−δ ceramics are above 92%. BaCe0.7In0.1Gd0.2O3−δ and BaCe0.7In0.1Y0.2O3−δ ceramics exhibit an excellent chemical stability against boiling water. The conductivity values of BaCe0.7In0.1Gd0.2O3−δ are higher than those of BaCe0.7In0.1Y0.2O3−δ in both air and dry hydrogen atmospheres. The highest conductivity is 4.6 × 10−2 S cm−1 for BaCe0.7In0.1Gd0.2O3−δ ceramic in air at 1073 K. BaCe0.7In0.1Gd0.2O3−δ ceramic with a conductivity value of 1.0 × 10−2 S cm−1 at 823 K in both air and dry hydrogen atmospheres is considered as a promising alternative for electrolytes of SOFC in view of decreasing the operating temperature and keeping both high conductivity and good chemical stability.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Yu Zhou
Ceramics International 2012 Volume 38(Issue 4) pp:2935-2941
Publication Date(Web):May 2012
DOI:10.1016/j.ceramint.2011.11.070
Abstract
Polycrystalline GdSm1−xCaxZr2O7−x/2 (0 ≤ x ≤ 0.20) ceramics have been prepared by the solid-state reaction method. The effects of CaO addition on the microstructure and electrical properties of the pyrochlore-type GdSmZr2O7 ceramic were investigated. GdSm1−xCaxZr2O7−x/2 (x ≤ 0.05) ceramics exhibit a pyrochlore-type structure; however, GdSm1−xCaxZr2O7−x/2 (0.10 ≤ x ≤ 0.20) ceramics consist of the pyrochlore-type structure and a small amount of CaZrO3. The total conductivity of GdSm1−xCaxZr2O7−x/2 ceramics follows the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. GdSm1−xCaxZr2O7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4–1.0 atm at each test temperature. The highest total conductivity is about 1.20 × 10−2 S cm−1 at 1173 K for the GdSm0.9Ca0.1Zr2O6.95 ceramic.
Co-reporter:Yuan-Hong Wang, Zhan-Guo Liu, Jia-Hu Ouyang, Ya-Ming Wang, Yu Zhou
Applied Surface Science 2012 Volume 258(Issue 22) pp:8946-8952
Publication Date(Web):1 September 2012
DOI:10.1016/j.apsusc.2012.05.125
Abstract
Microarc oxidation (MAO) was used to produce oxide ceramic coatings on Ti2AlNb alloy. The influences of NaOH and NaF additives in the electrolyte on microstructure and high-temperature oxidation resistance of MAO ceramic coatings were investigated. MAO ceramic coatings formed on Ti2AlNb alloy exhibit a volcanic-like porous structure, and consist of Al2TiO5, R-TiO2, γ-Al2O3 and small amounts of α-Al2O3, Nb2O5. NaOH additive in the electrolyte enhances the densification of ceramic coatings and the relative content of Al2TiO5. NaF additive in the electrolyte not only increases the thickness of coatings, but also promotes the formation of Al2TiO5. In the case of static oxidation at 800 °C for 100 h, MAO coatings improve high temperature oxidation resistance of Ti2AlNb alloy. The oxidized products after thermal exposure to 800 °C for 100 h in air exhibit a multiple-layered oxide structure, and are main composed of R-TiO2, γ-Al2O3 and Al2TiO5.
Co-reporter:Kai-Jun Hu, Zhan-Guo Liu, Jun-Yao Wang, Tao Wang, Jia-Hu Ouyang
Materials Letters 2012 Volume 89() pp:276-278
Publication Date(Web):15 December 2012
DOI:10.1016/j.matlet.2012.08.138
A facile chemical co-precipitation and calcination method has been used to prepare (Gd1−xEux)2Zr2O7(0≤x≤0.100) ceramic particles. (Gd1–xEux)2Zr2O7 ceramic particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. (Gd1–xEux)2Zr2O7 ceramic particles exhibit a single phase of defect fluorite-type structure. PL spectra show that the characteristic peaks correspond to the f–f transition 5D0–7FJ (J=1, 2, 3, and 4) of Eu3+. The relationship between the structure of the PL spectra and the host lattice is discussed to identify the changes in intensity for different activation mechanisms.Highlights► Eu3+-doped Gd2Zr2O7 is synthesized by a facile chemical method. ► The excitation peaks are divided into two wavelength groups by different mechanisms. ► PL spectra of Eu3+-doped Gd2Zr2O7 are intense and have a clear rule. ► Eu3+-doped Gd2Zr2O7 can be considered as a red light material.
Co-reporter:Jun Xiang, Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Fu-Yao Yan
Solid State Ionics 2012 220() pp: 7-11
Publication Date(Web):20 July 2012
DOI:10.1016/j.ssi.2012.05.033
Co-reporter:Xue-Song Liang;Zhan-Guo Liu;Zhen-Lin Yang
Tribology Letters 2012 Volume 47( Issue 2) pp:203-209
Publication Date(Web):2012 August
DOI:10.1007/s11249-012-9984-x
In this article, friction and wear characteristics of BaCr2O4 ceramics have been investigated using a high-temperature friction and wear tester from room temperature to 800 °C in dry sliding against sintered alumina ball. At room temperature, the friction coefficient and wear rate of BaCr2O4 ceramics are quite high. BaCr2O4 ceramics exhibit low friction coefficients and small wear rates with temperature increasing up to 400–600 °C. The oxidation reaction of BaCr2O4 during high-temperature wear tests is responsible for the tribological properties. The oxidized product of BaCr2O4 is BaCrO4, which forms a smooth self-lubricating film on the worn surface to effectively reduce friction and wear. However, at 800 °C, severe oxidation reduces the relative density of sintered BaCr2O4 ceramics, and further expedites the materials removal process.
Co-reporter:Xiao-Liang Xia, Zhan-Guo Liu, Jia-Hu Ouyang
Journal of Power Sources 2011 Volume 196(Issue 4) pp:1840-1846
Publication Date(Web):15 February 2011
DOI:10.1016/j.jpowsour.2010.09.056
(Sm1−xDyx)2Zr2O7 (0 ≤ x ≤ 1) ceramics are prepared by a solid state reaction process at 1973 K for 10 h in air. (Sm1−xDyx)2Zr2O7 (0 ≤ x ≤ 0.3) ceramics exhibit a single phase of pyrochlore-type structure, while (Sm1−xDyx)2Zr2O7 (0.5 ≤ x ≤ 1.0) possess a defective fluorite-type structure. The full width at half-maxima in the Raman spectra increases with increasing Dy content, which indicates that the degree of structural disorder increases as the Dy content increases. The ionic conductivity of (Sm1−xDyx)2Zr2O7 ceramics is investigated by impedance spectroscopy over a frequency range of 0.2 Hz to 8 MHz in the temperature range of 873–1173 K in air and hydrogen atmospheres, respectively. The ionic conductivity has a maximum near the phase boundary between the pyrochlore- and the defective fluorite-type phases under identical temperature levels. The ionic conductivity is determined by the degree of structural disorder or unit cell free volume, which is depending on the Dy content. As the ionic conductivity in the hydrogen atmosphere is almost the same as that obtained in air, the conduction of (Sm1−xDyx)2Zr2O7 is purely ionic with negligible electronic conduction.
Co-reporter:Zhan-Guo Liu, Xian-Zhong Xiong, Jia-Hu Ouyang, Jun Xiang
Electrochimica Acta 2011 Volume 56(Issue 7) pp:2837-2841
Publication Date(Web):28 February 2011
DOI:10.1016/j.electacta.2010.12.067
SmYb1−xMgxZr2O7−x/2 (0 ≤ x ≤ 0.15) ceramics are pressureless-sintered at 1973 K for 10 h in air. The structure and electrical conductivity of SmYb1−xMgxZr2O7−x/2 ceramics are investigated by the X-ray diffraction, scanning electron microscopy and impedance spectroscopy measurements. SmYb1−xMgxZr2O7−x/2 ceramics exhibit a defect fluorite-type structure. The measured electrical conductivities of SmYb1−xMgxZr2O7−x/2 ceramics obey the Arrhenius relation, and electrical conductivity of each composition increases with increasing temperature from 673 to 1173 K. At identical temperature levels, the electrical conductivity of SmYb1−xMgxZr2O7−x/2 ceramics gradually increases with increasing magnesia content. SmYb1−xMgxZr2O7−x/2 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The electrical conductivity obtained in SmYb1−xMgxZr2O7−x/2 ceramics reaches the highest value of 2.72 × 10−3 S cm−1 at 1173 K for the SmYb0.85Mg0.15Zr2O6.925 ceramic.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Yu Zhou, Jun Xiang
Electrochimica Acta 2011 Volume 56(Issue 20) pp:7045-7050
Publication Date(Web):1 August 2011
DOI:10.1016/j.electacta.2011.06.001
A novel series of Gd1−xEu2xSm1−xZr2O7 (x = 0, 1/3, 1/2, 2/3, 1) ceramics with a constant lattice parameter are prepared by solid-state reaction, and are then evaluated as possible solid electrolytes. The microstructure and electrical properties of Gd1−xEu2xSm1−xZr2O7 ceramics have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis. Gd1−xEu2xSm1−xZr2O7 ceramics exhibit a single phase of pyrochlore-type structure. The total conductivity of Gd1−xEu2xSm1−xZr2O7 ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. At 973–1173 K, the composition has little effect on electrical conductivity of Gd1−xEu2xSm1−xZr2O7 ceramics. Gd1−xEu2xSm1−xZr2O7 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The maximum total conductivity of Gd1−xEu2xSm1−xZr2O7 ceramics is about 1.01 × 10−2 S cm−1 at 1173 K in air.Highlights► Dense Gd1−xEu2xSm1−xZr2O7 were firstly prepared by pressureless-sintering. ► The total conductivity of Gd1−xEu2xSm1−xZr2O7 increases with temperature. ► Gd1−xEu2xSm1−xZr2O7 are oxide-ion conductors in low oxygen partial pressure. ► The composition has little effect on the total conductivity of Gd1−xEu2xSm1−xZr2O7.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Jun Xiang, Xiao-Ming Liu
Materials & Design (1980-2015) 2011 Volume 32(8–9) pp:4201-4206
Publication Date(Web):September 2011
DOI:10.1016/j.matdes.2011.04.036
A series of zirconate compounds with the general formula Sm2–xLaxZr2O7 (0 ⩽ x ⩽ 1.0) were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, structure and electrical conductivity of Sm2–xLaxZr2O7 ceramics were investigated by the Archimedes method, X-ray diffraction and impedance spectroscopy measurements. Sm2–xLaxZr2O7 (0 ⩽ x ⩽ 1.0) ceramics exhibit a pyrochlore-type structure. The measured electrical conductivity of Sm2–xLaxZr2O7 ceramics obeys the Arrhenius relation and gradually increases with increasing temperature from 673 to 1173 K. Sm2–xLaxZr2O7 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The electrical conductivity of Sm2–xLaxZr2O7 ceramics decreases with increasing lanthanum content at identical temperature levels.Highlights► Dense Sm2–xLaxZr2O7 ceramics were prepared by pressureless-sintering at 1973 K. ► Sm2–xLaxZr2O7 ceramics have a single phase of pyrochlore-type structure. ► The electrical conductivity of Sm2–xLaxZr2O7 increases with increasing temperature. ► Sm2–xLaxZr2O7 ceramics are oxide-ion conductors in low oxygen partial pressure. ► The electrical conductivity of Sm2–xLaxZr2O7 decreases with increasing La content.
Co-reporter:Zhen-Lin Yang, Jia-Hu Ouyang, Zhan-Guo Liu
Materials & Design 2011 Volume 32(Issue 1) pp:29-35
Publication Date(Web):January 2011
DOI:10.1016/j.matdes.2010.06.041
Isothermal oxidation behavior of reactive hot-pressed TiN–TiB2 ceramics with various TiN/TiB2 molar ratios of 2/1, 1/1 and 1/2 was evaluated in the temperature range of 500–800 °C in air. TiN–TiB2 ceramics have a relative density of 97–98.6%. The oxidation weight gains of TiN–TiB2 ceramics depend upon the composition, oxidation temperature and exposure time. The structure and morphology of oxidized layers of TiN–TiB2 ceramics were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). During isothermal oxidation of TiN–TiB2 ceramics, anatase and rutile-TiO2 form as the oxidized products at 500 °C. However, phase transformation from anatase to rutile occurs at temperatures between 500 and 600 °C, and therefore rutile-TiO2 becomes the only crystalline phase after oxidation at temperatures of 600–800 °C for 10 h. The oxidation mechanism was proposed with reference to thermodynamically feasible oxidation reactions. The influence of composition on oxidation behavior of TiN–TiB2 ceramics varies with temperature.
Co-reporter:Hong-Zhi Liu, Zhan-Guo Liu, Jia-Hu Ouyang, Ya-Ming Wang
Materials Letters 2011 Volume 65(17–18) pp:2614-2617
Publication Date(Web):September 2011
DOI:10.1016/j.matlet.2011.05.093
LaMg1 − xNixAl11O19 (x = 0, 0.25, 0.5, 0.75, 1) ceramics are fabricated by pressureless-sintering method at 1700 °C for 10 h in air. The microstructure and thermo-optical properties of LaMg1 − xNixAl11O19 ceramics are investigated by the X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The influence of NiO doping on structure and thermo-optical properties of LaMg1 − xNixAl11O19 ceramics is investigated. The partial substitution of Ni2+ for Mg2+ results in a significant increase in emissivity at low wavelengths as compared with unmodified LaMgAl11O19. When the Ni2+ content increases to x = 0.75 or above, LaMg1 − xNixAl11O19 ceramics have a high emissivity value above 0.70 at low wavelengths at 500 °C. The measured emissivity of all LaMg1 − xNixAl11O19 ceramics shows a similar trend in the wavelength range of 6 to 14 μm.Research highlights► LaMg1 − xNixAl11O19 ceramics were fabricated by pressureless-sintering at 1700 °C. ► LaMg0.25Ni0.75Al11O19 has the highest emissivity value above 0.70 at low wavelengths. ► LaMg1 − xNixAl11O19 ceramics have the similar trend in the emissivity from 6 to 14 μm.
Co-reporter:Xiao-Liang Xia, Zhan-Guo Liu, Jia-Hu Ouyang, Shuai Gao, Xiao-Ming Liu
Solid State Sciences 2011 Volume 13(Issue 6) pp:1328-1333
Publication Date(Web):June 2011
DOI:10.1016/j.solidstatesciences.2011.04.001
Gd2(Zr1−xCex)2O7 (0 ≤ x ≤ 0.3) ceramics are prepared via a solid-state reaction process at 1973 K for 10 h in air. Gd2(Zr1−xCex)2O7 (0 ≤ x ≤ 0.3) ceramics exhibit a defective fluorite-type structure. XPS analysis indicates the oxidation state of Ce cations is mainly Ce4+. The electrical property of Gd2(Zr1−xCex)2O7 ceramics is investigated by impedance spectroscopy over a frequency range of 10 Hz to 8 MHz from 623 to 1173 K. The activation energy of grain conductivity increases with increasing cerium content, whereas the pre-exponential factor of grain conductivity for doped-Gd2(Zr1−xCex)2O7 (0.1 ≤ x ≤ 0.3) ceramics is lower than that of undoped-Gd2Zr2O7. The grain conductivity of Gd2(Zr1−xCex)2O7 ceramics follows the Arrhenius-type behaviour. The grain conductivity of Gd2(Zr1−xCex)2O7 ceramics slightly decreases with increasing cerium content. Gd2(Zr0.9Ce0.1)2O7 is an oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm in the test temperature region.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Yu Zhou
Materials Letters 2011 Volume 65(Issue 2) pp:385-387
Publication Date(Web):31 January 2011
DOI:10.1016/j.matlet.2010.10.032
Co-reporter:Sa Li, Zhan-Guo Liu, Jia-Hu Ouyang
Materials Chemistry and Physics 2011 130(3) pp: 1134-1138
Publication Date(Web):
DOI:10.1016/j.matchemphys.2011.08.044
Co-reporter:J.H. Ouyang, Z.L. Yang, Z.G. Liu, X.S. Liang
Wear 2011 Volume 271(9–10) pp:1966-1973
Publication Date(Web):29 July 2011
DOI:10.1016/j.wear.2010.11.057
TiB2–TiN composites with different TiB2:TiN molar ratios of 2:1 and 1:1 were synthesized by the reactive hot-pressing process using Ti, B and BN powders as raw materials. Friction and wear properties of reactive hot-pressed TiB2–TiN composites were evaluated in sliding against Al2O3 ball from room temperature to 700 °C in air. For TiB2–TiN composites, typical break-in stage in evolution of friction coefficients is observed at room temperature. At 700 °C, the friction coefficient of TiB2–TiN composites is relatively low and steady, as contrasted with the data obtained at room temperature and 400 °C. Under all testing conditions, TiB2–TiN composites exhibit small wear rates, which range in the order of 10−6–10−7 mm3/Nm. The specific wear rates of TiB2–TiN composites and the coupled ball decrease with testing temperature. Wear mechanisms of TiB2–TiN composites depend mainly upon testing temperature. At room temperature, mild abrasion is the dominated wear mechanism of TiB2–TiN composites. However, tribo-oxidation as well as mild abrasion plays an important role during wear test at 400 °C. At 700 °C, continuous oxidized films comprised of rutile form on the surface by thermal oxidation, and provide excellent lubrication and protection.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Xiao-Liang Xia
Journal of Power Sources 2010 Volume 195(Issue 21) pp:7225-7229
Publication Date(Web):1 November 2010
DOI:10.1016/j.jpowsour.2010.05.064
SmYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics were pressureless-sintered at 1973 K for 10 h in air. The relative density, structure and electrical conductivity of SmYb1−xGdxZr2O7 ceramics were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance spectroscopy measurements. SmYb1−xGdxZr2O7 (0 ≤ x ≤ 0.5) ceramics exhibit a defect fluorite-type structure, while SmYb1−xGdxZr2O7 (0.7 ≤ x ≤ 1.0) ceramics have a pyrochlore-type structure. The measured values of the electrical conductivities obey the Arrhenius relation. The grain conductivity of each composition in SmYb1−xGdxZr2O7 ceramics increases with increasing temperature from 723 to 1173 K. The grain conductivity of SmYb1−xGdxZr2O7 ceramics gradually increases with increasing gadolinium content at identical temperature levels. An increase of about one order of magnitude in grain conductivity is found at all temperature levels when the gadolinium content increases from 0.5 to 0.7. SmYb1−xGdxZr2O7 ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 2.69 × 10−2 S cm−1 at 1173 K for SmGdZr2O7 ceramic.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Journal of Power Sources 2010 Volume 195(Issue 10) pp:3261-3265
Publication Date(Web):15 May 2010
DOI:10.1016/j.jpowsour.2009.11.135
(Nd1−xYbx)2Zr2O7 (0 ≤ x ≤ 1) ceramics were prepared by pressureless-sintering to obtain dense bulk materials. The electrical conductivity of (Nd1−xYbx)2Zr2O7 was investigated by complex impedance spectroscopy over a frequency range of 20 Hz to 2 MHz from 723 to 1173 K in air. A high-temperature dilatometer was used to analyze thermal expansion coefficient of (Nd1−xYbx)2Zr2O7 in the temperature range of 373–1523 K. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of each composition in (Nd1−xYbx)2Zr2O7 gradually increases with increasing temperature. A decrease of about one order of magnitude in grain conductivity is found at all temperature levels when the Yb content increases from x = 0.3 to x = 0.5. The highest electrical conductivity value obtained in this work is 9.32 × 10−3 S cm−1 at 1173 K for (Nd0.7Yb0.3)2Zr2O7 ceramic. (Nd1−xYbx)2Zr2O7 ceramics are oxide-ion conductors in the oxygen partial pressure range from 1.0 × 10−4 to 1.0 atm at all test temperature levels. Thermal expansion coefficients of (Nd1−xYbx)2Zr2O7 gradually decrease with increasing ytterbium content at identical temperature levels.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Ke-Ning Sun, Xiao-Liang Xia
Electrochimica Acta 2010 Volume 55(Issue 28) pp:8466-8470
Publication Date(Web):1 December 2010
DOI:10.1016/j.electacta.2010.07.060
Several compositions of NdYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, microstructure and electrical conductivity of NdYb1−xGdxZr2O7 ceramics were analyzed by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance plots measurements. NdYb1−xGdxZr2O7 (0 ≤ x ≤ 0.3) ceramics have a single phase of defect fluorite-type structure, and NdYb1−xGdxZr2O7 (0.7 ≤ x ≤ 1.0) ceramics exhibit a single phase of pyrochlore-type structure; however, the NdYb0.5Gd0.5Zr2O7 composition shows mixed phases of both defect fluorite-type and pyrochlore-type structures. The measured values of the grain conductivity obey the Arrhenius relation. The grain conductivity of each composition in NdYb1−xGdxZr2O7 ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb1−xGdxZr2O7 ceramics are oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 1.79 × 10−2 S cm−1 at 1173 K for NdYb0.3Gd0.7Zr2O7 composition.
Co-reporter:Xiao-Liang Xia, Shuai Gao, Zhan-Guo Liu, Jia-Hu Ouyang
Electrochimica Acta 2010 Volume 55(Issue 19) pp:5301-5306
Publication Date(Web):30 July 2010
DOI:10.1016/j.electacta.2010.04.086
Gd2(Zr1−xNbx)2O7+x (0 ≤ x ≤ 0.2) ceramics are prepared via the solid state reaction process at 1973 K for 10 h in air. Gd2(Zr1−xNbx)2O7+x (x = 0.1, 0.2) ceramics exhibit an ordered pyrochlore-type structure, whereas Gd2Zr2O7 has a defective fluorite-type structure. The electrical property of Gd2(Zr1−xNbx)2O7+x ceramics is investigated by electrochemical impedance spectroscopy over a frequency range of 10 Hz to 8 MHz from 623 to 923 K. The electrical conductivity obeys the Arrhenius equation. The grain conductivity of Gd2(Zr1−xNbx)2O7+x ceramics varies with doping different Nb contents, and exhibits a maximum at the Nb content of x = 0.1 in the temperature range of 623–923 K. The conductivity in hydrogen atmosphere is a little bit higher than in air in the temperature range of 723–923 K, which indicates that the doping of Zr4+ by Nb5+ can increase the proton-type conduction and reduce the oxide-ionic conduction. The conduction of Gd2(Zr1−xNbx)2O7+x is not a pure oxide-ionic conductor.
Co-reporter:Yuan-Hong Wang, Jia-Hu Ouyang, Zhan-Guo Liu
Materials & Design (1980-2015) 2010 Volume 31(Issue 7) pp:3353-3357
Publication Date(Web):August 2010
DOI:10.1016/j.matdes.2010.01.058
Co-reporter:Xiao-Liang Xia, Jia-Hu Ouyang, Zhan-Guo Liu
Journal of Power Sources 2009 Volume 189(Issue 2) pp:888-893
Publication Date(Web):15 April 2009
DOI:10.1016/j.jpowsour.2008.12.136
(Sm1−xCax)2Zr2O7−x (0 ≤ x ≤ 0.100) ceramics were prepared by a solid state reaction process at 1973 K for 10 h in air, and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). (Sm1−xCax)2Zr2O7−x (0 ≤ x ≤ 0.025) ceramics have a single phase of pyrochlore-type structure; however (Sm1−xCax)2Zr2O7−x (0.050 ≤ x ≤ 0.100) consist of pyrochlore phase and a small amount of perovskite-like CaZrO3. The electrical conductivity of (Sm1−xCax)2Zr2O7−x ceramics was investigated by complex impedance spectroscopy over a frequency range of 0.1 Hz to 20 MHz in the temperature range of 573–873 K. The measured electrical conductivity obeys the Arrhenius relation. Both the activation energy and pre-exponential factor for grain conductivity increase with increasing the CaO content; however, electrical conductivity of (Sm1−xCax)2Zr2O7−x decreases with increasing the CaO content, which is due to the increase in structural disordering at 0 ≤ x ≤ 0.025 and the presence of the poorly conducting CaZrO3 phase at 0.050 ≤ x ≤ 0.100, respectively.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Electrochimica Acta 2009 Volume 54(Issue 15) pp:3968-3971
Publication Date(Web):1 June 2009
DOI:10.1016/j.electacta.2009.02.017
(Sm1 − xYbx)2Zr2O7 (0 ≤ x ≤ 1.0) ceramic powders were prepared by chemical-coprecipitation and calcination method, and were pressureless-sintered at 1973 K for 10 h to fabricate dense bulk materials. (Sm1 − xYbx)2Zr2O7 has a single phase with a pyrochlore or defect fluorite structure, depending mainly upon the Yb content. They are found to be pyrochlores for 0 ≤ x ≤ 0.1, and defect fluorites for 0.3 ≤ x ≤ 1.0. The electrical conductivity of (Sm1 − xYbx)2Zr2O7 was investigated by complex impedance spectroscopy over a frequency range of 200 Hz to 20 MHz from 723 to 1173 K in air. The measured electrical conductivity obeys the Arrhenius relation. The grain conductivity of (Sm1 − xYbx)2Zr2O7 ceramics gradually increases with increasing temperature. A decrease of about one order of magnitude in grain conductivity is found at all temperature levels when the Yb content increases from x = 0.1 to x = 0.3. The electrical conductivities of defect fluorite-type materials are lower than those of pyrochlore-type materials in (Sm1 − xYbx)2Zr2O7 system, whereas activation energies for the conduction process increase monotonically as the structure becomes disordered.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Materials & Design (1980-2015) 2009 Volume 30(Issue 5) pp:1845-1849
Publication Date(Web):May 2009
DOI:10.1016/j.matdes.2008.07.019
The phase stability and thermal expansion property of ZrO2–NdO1.5–AlO1.5 ceramics from 50 to 1550 °C were investigated for potential high-temperature structural and functional applications. All ZrO2–NdO1.5–AlO1.5 ceramics consist mainly of perovskite-like NdAlO3 and pyrochlore or fluorite (F–ZrO2) structures, and have relatively stable thermal expansion coefficients from 200 to 1400 °C. However, ZrO2–NdO1.5 (Nd2Zr2O7) ceramics have a single pyrochlore-type lattice, and exhibit a distinct decreasing tendency of thermal expansion coefficients from 400 to 1550 °C. The thermal expansion coefficients of ZrO2–NdO1.5–AlO1.5 ceramics are within the range of 10.3–11.5 × 10−6 K−1 at 1400 °C, which are of the same order of magnitude as 7 wt.% yttria stabilized zirconia.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Materials & Design 2009 Volume 30(Issue 9) pp:3784-3788
Publication Date(Web):October 2009
DOI:10.1016/j.matdes.2009.01.030
Gd2(Zr1−xTix)2O7 (0 ⩽ x ⩽ 1.00) solid solutions were synthesized by solid state reaction at 1550–1650 °C for 10 h in air. The relative density, microstructure and thermal expansion property of Gd2(Zr1−xTix)2O7 were investigated by the Archimedes method, X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy and high-temperature dilatometry. Gd2Zr2O7 exhibits a defect fluorite-type structure; however, Gd2(Zr1−xTix)2O7 (0.25 ⩽ x ⩽ 1.00) solid solutions have an ordered pyrochlore-type structure. Gd2Zr2O7 and Gd2Ti2O7 are completely soluble. The degree of structural order for Gd2(Zr1−xTix)2O7 solid solutions increases with increasing Ti content. The thermal expansion coefficients of Gd2(Zr1−xTix)2O7 increase with increasing temperature from 30 to 1250 °C. The thermal expansion coefficients of Gd2(Zr1−xTix)2O7 gradually decrease with increasing Ti content at identical temperature levels.
Co-reporter:Zhan-Guo Liu;Yu Zhou
Bulletin of Materials Science 2009 Volume 32( Issue 6) pp:603-606
Publication Date(Web):2009 December
DOI:10.1007/s12034-009-0092-y
YbxGd2−xZr2O7 (x = 0, 1, 2) ceramics were pressureless-sintered using ceramic powders acquired by chemical-coprecipitation and calcination methods. Heat capacities of YbxGd2−xZr2O7 were measured with a heat flux-type differential scanning calorimetry in the temperature range of 298–1200 K. At 298 K, the heat capacities of Gd2Zr2O7, YbGdZr2O7 and Yb2Zr2O7 were 214, 221 and 230 J·K−1 mol−1, respectively.
Co-reporter:Jia-Hu Ouyang, Shinya Sasaki, Takashi Murakami, Yu Zhou, Jian Zhang
Wear 2009 Volume 266(1–2) pp:96-102
Publication Date(Web):5 January 2009
DOI:10.1016/j.wear.2008.05.002
Titanium-containing diamond-like carbon (Ti-DLC) coatings were deposited on steel with a close-field unbalanced magnetron sputtering in a mixed argon/acetylene atmosphere. The morphology and structure of Ti-DLC coatings were investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Nanoindentation, nanoscratch and unlubricated wear tests were carried out to evaluate the hardness, adhesive and tribological properties of Ti-DLC coatings. Electron microscopic observations demonstrated the presence of titanium-rich nanoscale regions surrounded by amorphous carbon structures in Ti-DLC coating. The Ti-DLC coatings exhibit friction coefficients of 0.12–0.25 and wear rates of 1.82 × 10−9 to 4.29 × 10−8 mm3/Nm, depending on the counterfaces, sliding speed and temperature. The Ti-DLC/alumina tribo-pair shows a lower friction coefficient than the Ti-DLC/steel tribo-pair under the identical wear conditions. Increasing the test temperature from room temperature to 200 °C reduces the coefficient of friction and, however, clearly increases the wear rate of Ti-DLC coatings. Different wear mechanisms, such as surface polishing, delamination and tribo-chemical reactions, were found in the tribo-contact areas, depending on different wear conditions.
Co-reporter:J.H. Ouyang, Y.F. Li, Y.M. Wang, Y. Zhou, T. Murakami, S. Sasaki
Wear 2009 Volume 267(9–10) pp:1353-1360
Publication Date(Web):9 September 2009
DOI:10.1016/j.wear.2008.11.017
In this paper, spark plasma sintering is employed to synthesize a variety of self-lubricating ZrO2(Y2O3) matrix composites by tailoring the chemical compositions. The additives of BaF2, CaF2, Ag, Ag2O, Cu2O, BaCrO4, BaSO4, SrSO4 and CaSiO3 were incorporated into the ceramic matrix to evaluate their potentials as effective high-temperature solid lubricants from room temperature to 800 °C by using a ball-on-block friction and wear tester in sliding against alumina ball. For a comparative study, ZrO2(Y2O3) matrix composites incorporated with and without graphite or MoS2 were also investigated under the identical test conditions. The relationships among composition, microstructure and tribological properties of the composites are investigated to identify their self-lubrication mechanisms. The unlubricated ZrO2(Y2O3)–Al2O3 (TZ3Y20A) ceramics have a friction coefficient of 1.15 and a wear rate in the order of 10−4 mm3/Nm at 800 °C, while the TZ3Y20A–SrSO4 composites exhibit a steady-state friction coefficient of less than 0.2 and a wear rate in the order of 10−6 mm3/Nm from room temperature to 800 °C. Surface fatigue and brittle fracture are considered as the dominating wear mechanism of unmodified TZ3Y20A ceramics at 800 °C. However, for self-lubricating TZ3Y20A–SrSO4 composites, the formation, plastic deformation and effective spreading of SrSO4 lubricating films are the most important factor to reduce friction and wear rate over a wide temperature range.
Co-reporter:Yu-Feng Li;Yu Zhou;Xue-Song Liang
Bulletin of Materials Science 2009 Volume 32( Issue 2) pp:149-153
Publication Date(Web):2009 April
DOI:10.1007/s12034-009-0022-z
A facile aqueous solution route has been employed to synthesize BaxSr1−xSO4 (0 ≤ x ≤ 1) solid solution nanocrystals at room temperature without using any surfactants or templates. The as-synthesized products were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscopy (SEM), and differential scanning calorimetry-thermogravimetry (DSC-TG). The BaxSr1−xSO4 solid solution nanocrystals exhibit an orthorhombic structure and an ellipsoidal-shaped morphology with an average size of 80–100 nm. The lattice parameters of BaxSr1−xSO4 solid solution crystals increase with increasing x value. However, they are not strictly coincident with the Vegard’s law, which indicates that the as-obtained products are non-ideal solid solutions. The BaxSr1−xSO4 solid solution nanocrystals have an excellent thermal stability from ambient temperature to 1300°C with a structural transition from orthorhombic to cubic phase at about 1111°C.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Journal of Power Sources 2008 Volume 185(Issue 2) pp:876-880
Publication Date(Web):1 December 2008
DOI:10.1016/j.jpowsour.2008.09.005
Gd2−xSmxZr2O7 (x = 0, 0.2, 0.6, 1.0, 1.4, 1.8, 2.0) ceramic powders synthesized with the chemical-coprecipitation and calcination method were pressureless-sintered at 1873 K for 10 h in air. The electrical conductivity of Gd2−xSmxZr2O7 ceramics was investigated by complex impedance spectroscopy over a frequency range of 0.01 Hz to 15 MHz. Gd2−xSmxZr2O7 is an oxide-ion conductor in the oxygen partial pressure range from 1.0 × 10−15 to 1.0 atm and in the temperature range of 623–873 K. The measured electrical conductivity obeys the Arrhenius relation. The activation energy and pre-exponential factor for grain-interior conductivity gradually decrease with increasing Sm content. The grain-interior conductivity varies with the Sm substitution for Gd, and reaches the maximum at the equal molar of Sm3+ and Gd3+ in Gd2−xSmxZr2O7 ceramics. A significant increase in the grain-interior conductivity is obtained by isovalent rare-earth element like Sm substitution for Gd in the temperature range of 623–873 K.
Co-reporter:Yu-Feng Li, Jia-Hu Ouyang, Yu Zhou, Xue-Song Liang, Ji-Yong Zhong
Materials Letters 2008 Volume 62(Issue 29) pp:4417-4420
Publication Date(Web):30 November 2008
DOI:10.1016/j.matlet.2008.07.053
A facile aqueous solution route has been employed to prepare SrSO4 nanocrystals with different crystallographic morphologies at room temperature without using any surfactants or templates. The SrSO4 products were characterized by X-ray diffraction and scanning electron microscopy. The morphology of SrSO4 nanocrystals varies from a needle-like to a plate-like feature with increasing the molar ratio (R) of Sr2+ cations to SO42− anions from R = 1:2 to R = 2:1. The morphological evolution process of SrSO4 nanocrystals is discussed. This simple method is also useful for the synthesis of other nanostructured sulfates.
Co-reporter:Zhan-Guo Liu, Jia-Hu Ouyang, Yu Zhou, Xiao-Liang Xia
Materials Letters 2008 Volume 62(Issue 29) pp:4455-4457
Publication Date(Web):30 November 2008
DOI:10.1016/j.matlet.2008.07.050
The Gd2(TixZr1 − x)2O7 (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd2(TixZr1 − x)2O7 were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd2(TixZr1 − x)2O7 from room temperature to 1400 °C was measured by a laser-flash method. The Gd2Zr2O7 has a defect fluorite-type structure; however, Gd2(TixZr1 − x)2O7 (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd2Zr2O7 and Gd2Ti2O7 are infinitely soluable. The thermal conductivity of Gd2(TixZr1 − x)2O7 increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd2(TixZr1 − x)2O7 first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd2(TixZr1 − x)2O7 is within the range of 1.33 to 2.86 W m− 1 K− 1 from room temperature to 1400 °C.
Co-reporter:Z.-G. Liu;J.-H. Ouyang;Y. Zhou;J. Li ;X.-L. Xia
Advanced Engineering Materials 2008 Volume 10( Issue 8) pp:754-758
Publication Date(Web):
DOI:10.1002/adem.200800079
Co-reporter:Yu-Feng Li, Jia-Hu Ouyang, Yu Zhou
Materials Chemistry and Physics 2008 Volume 111(2–3) pp:508-512
Publication Date(Web):15 October 2008
DOI:10.1016/j.matchemphys.2008.05.008
Novel monodispersed peanut-type SrSO4 (celestine) particles have been prepared using a facile precipitation reaction of Sr-EDTA chelating precursors at ambient temperature. The as-formed products were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen absorption–desorption and differential scanning calorimetry–thermogravimetry (DSC–TG) measurement. The monodispersed SrSO4 particles with an average length of 1.7 μm and an aspect ratio of 1.4 appear unusual peanut-type morphology. These SrSO4 particles have a relatively large Brunauer–Emmett–Teller (BET) surface area of about 20.9 m2 g−1 and contain mesopores with a mean pore size of about 34.3 nm. The SrSO4 particles exhibit an excellent thermal stability from room temperature to 1400 °C with a structural transformation at 1158.3 °C. The growth mechanism of the monodispersed peanut-type celestine particles was discussed to obtain a better understanding on their formation process.
Co-reporter:J.H. Ouyang, T. Murakami, S. Sasaki
Wear 2007 Volume 263(7–12) pp:1347-1353
Publication Date(Web):10 September 2007
DOI:10.1016/j.wear.2006.12.031
The high-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating have been investigated with a SRV high-temperature friction and wear tester. After heating in air at temperatures above 500 °C, V2O5 and TiO2 phases were identified on surfaces of (V,Ti)N coating with V2O5-type platelets as the major oxidized product. (V,Ti)N coatings exhibit a friction coefficient in the range of 0.53–1.08 and a wear rate in the range of 1.69 × 10−7–1.31 × 10−5 mm3/Nm, depending on test temperature used. At low temperatures, the presence of oxide debris induced by tribological stressing on the load-bearing regions reduces direct contact between (V,Ti)N coating and Al2O3, and generates a mild wear, however, adherent and compacted wear-protective oxide layers are not developed. At temperature of 500 °C or above, the wear-protective oxide layers containing thermally-oxidized V2O5 platelets deform plastically to produce a lubricious and smooth appearance to reduce friction. Raman spectroscopy was used to identify the structures of wear debris and coating surfaces after wear tests. Tribochemical reactions are the dominating wear phenomena at low temperatures. The wear debris generated during the wear process consists mainly of the V2O5-type tribo-oxides.
Co-reporter:Yu-Feng Li, Jia-Hu Ouyang, Yu Zhou, Xue-Song Liang, T. Murakami, S. Sasaki
Journal of Crystal Growth (15 May 2010) Volume 312(Issue 11) pp:1886-1890
Publication Date(Web):15 May 2010
DOI:10.1016/j.jcrysgro.2010.03.007
Novel dumbbell-like SrSO4 with hierarchical architecture was fabricated with a facile template-free aqueous solution method at room temperature. The crystallographic morphology of SrSO4 products depends mainly on the pH value of the reaction solution. The SrSO4 products exhibit a dumbbell-like hierarchical architecture at pH=3 and 5, and have a tablet-like crystallographic morphology at pH=1 when keeping other reaction parameters unchanged. The dumbbell-like SrSO4 synthesized at pH=3 has a length of 8–14 μm, and is composed of numerous well-aligned single crystalline nanoplates with an average width of 140 nm and a length of 0.7–1 μm. The Brunauer–Emmett–Teller (BET) surface area of the crystallized SrSO4 products is about 2.8 m2 g−1. A formation mechanism is proposed for the evolution process of dumbbell-like SrSO4 with hierarchical architecture.
