Publications (30)34.71 Total impact

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    ABSTRACT: We introduce a new and effective method for improving the fracture toughness of Al2O3-based composites through the addition of a nonstoichiometric material. Al2O3-TiN0.3 composites were sintered by spark plasma sintering with different TiN0.3 content at temperatures between 1300 and 1600°C for 10min and a micro-region diffusion phenomenon was observed at the Al2O3-TiN0.3 interface. Ti atoms from TiN0.3 diffused into Al2O3 to occupy Al sites, which led to the formation of Al vacancies that enabled the transport of aluminum by a vacancy mechanism. The optimal densification temperature of the Al2O3-30vol% TiN0.3 composite was approximately 1400°C. The maximum fracture toughness measured was 6.91MPam1/2, from the composite with 30vol% TiN0.3 sintered at 1500°C.
    No preview · Article · Nov 2015
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    ABSTRACT: The diffusion behavior and solid solution formation in the binary system TaC-TiN0.3 were investigated. TaC, TiN, and TiN0.3 were used as raw materials; TiN0.3 was synthesized through mechanical alloying. Two groups of the prepared samples were spark plasma sintered at 1300-1700 °C for 10 min. TaC-TiN0.3 and TaC-TiN diffusion couples were used for the study of diffusion behavior with an energy dispersive spectrometer. Solid solution formation in the TaC-TiN0.3 system with varying compositions and heat treatment temperatures was characterized by X-ray diffraction. Ta, Ti, C, and N atoms show faster diffusion and higher dissolution rate in the TaC-TiN0.3 system than in the TaC-TiN system because of the vacancy effect.
    No preview · Article · May 2015 · Ceramics International
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    ABSTRACT: Highly nitrogen-deficient non-stoichiometric TiNx powders within nitrogen vacancy defects (0.3<x<0.5) were prepared by mechanical alloying and consolidated by high pressure sintering. The effects of nitrogen vacancy defects, sintering temperature and pressure on densification and grain growth of TiNx were investigated for improving sintering ability and mechanical properties. Increasing nitrogen vacancy defects promoted densification and grain growth of TiNx. Nitrogen vacancies accelerated material transport and diffusion during sintering and altered strong covalent bonding nature was believed to result in enhanced sintering ability. Densification of TiNx was enhanced by increasing temperature and elevating pressure, grain growth was promoted by increasing temperature, whereas restrained by elevating pressure. TiNx (x=0.32) ceramic with relative density of 99.4% and average grain size of 21 nm was obtained at 1200 °C, 5 GPa and 10 min. Vickers hardness of 22.6 GPa and fracture toughness of 5.0 MPa·m1/2 were achieved.
    No preview · Article · Apr 2015 · Ceramics International
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    ABSTRACT: Titania-coated ultrafine diamond (UFD/TiO2) composites had been prepared successfully, which were the core/shell structures with amorphous titania shells of approximately 4 nm thickness using tetrabutyl titanate (TBOT) as the precursor of titania in acidic condition via sol-gel process. It had a great influence on the synthesis of UFD/TiO2 composites to control the hydrolysis and polymerization of TBOT. Contrasting to the pristine ultrafine diamond powders (UFDs), the coated UFDs could be kept dispersed in the multi-component inorganic salts aqueous solution at least 12 h without aggregation. More importantly, the oxidation resistance temperature of the coated UFDs was enhanced nearly 150 °C than the pristine, improving greatly the sintering temperature of UFD-vitrified bond composite powers obtained by polyacrylamide gel (P-G) method.
    No preview · Article · Feb 2015 · Materials Letters
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    ABSTRACT: Silica-coated ultrafine diamond (UFD/SiO2) composites were prepared, which were core/shell structures with amorphous silica shell of approximately 5 nm thickness. Contrasting to the pristine UFDs, the dispersion stability of the UFD/SiO2 composites was improved greatly in the multi-component inorganic salts aqueous solution, and the chemical compositions of the ceramic matrix were introduced by multicomponent inorganic salts. Meanwhile, the oxidation resistance temperature of the coated UFDs was also increased by around 101.0 degrees C. Furthermore, by using the polyacrylamide gel method and hot-press sintering process, ceramic composites were fabricated with the UFD/SiO2 aqueous suspension containing multi-component inorganic salts. The results indicated that the UFDs coated with silica could be dispersed uniformly in ceramic matrix, where no obvious UFD agglomerates were observed.
    No preview · Article · Dec 2013 · Materials Letters
  • Q. Zou · M.Z. Wang · Y.G. Li · L.H. Zou
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    ABSTRACT: The ageing effect on the field emission (FE) reproducibility of multiwalleded carbon nanotubes (MWCNTs) synthesised by plasma enhanced chemical vapour deposition was investigated by scanning electron microscopy. To investigate the ageing effect on the physical state of the MWCNTs, a scanning electron microscope (SEM), a Raman spectrometer, an X-ray photoelectron spectroscope and an X-ray diffractometer were used to characterise the MWCNTs comprehensively before and after the ageing. Through ageing, the FE reproducibility became better because the larger number and more evenly distributed shorter MWCNTs – (resulted from the local vacuum breakdown of higher MWCNTs due to Joule heating and oxidisation) – became the dominating emitters.
    No preview · Article · Jun 2011 · Journal of Experimental Nanoscience
  • Q. Zou · M. Z. Wang · Y. G. Li · B. Lv · Y. C. Zhao
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    ABSTRACT: Onion-like carbon (OLC) was synthesised by annealing detonation nanodiamond for 1.5 h at temperatures from 500 to 1400°C and at a vacuum of 1 Pa. The results showed that the nanodiamond was transformed into the amorphous carbon (a-C) at first and then the a-C was transformed into the OLC gradually with the increase in annealing temperature. Moreover, at the annealing temperature of 600°C, the nanodiamond started transforming into a-C from the edge of the nanodiamond particle (1 1 1) crystal plane. At the annealing temperature of 750°C, the nanodiamond was transformed into the a-C completely. At the annealing temperature of 850°C, the a-C began transforming into the OLC at the edge area. At the annealing temperature of 1000°C, the OLC particle with a size smaller than 5 nm was synthesised. However, in the centre of the OLC particle, untransformed a-C coexisted. At the annealing temperature of 1100°C, the microstructure of the OLC particle with a size smaller than 5 nm became optimised. At the annealing temperature of 1200°C, the OLC particle with a size larger than 5 nm was fabricated. There was also untransformed a-C coexisting in the centre of the OLC particle. At the annealing temperature of 1350°C, all the a-C was transformed into the OLC. The average size of the OLC was approximately 5 nm, which was the same as that of the nanodiamond. The layers of the OLC were varied from several to 12.
    No preview · Article · Dec 2010 · Journal of Experimental Nanoscience
  • Q. Zou · M.Z. Wang · Y.G. Li
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    ABSTRACT: The onion-like carbon (OLC) was synthesised by annealing the nanodiamond fabricated by detonation for 1 h at the temperature of 1150°C in the low vacuum of 2 Pa. The OLC particles were characterised using a high-resolution transmission electron microscope (HRTEM) for observing its microstructure, an X-ray diffractometer (XRD) for determining its crystal structure and component, and a Raman spectrometer for confirming its content. The results showed that the OLC particles exhibited similar shape to that of the original nanodiamond particles. The average size of the OLC was found to be approximately 5 nm. The transformation mechanism of the OLC from the nanodiamond by annealing at lower temperature and lower vacuum was also discussed.
    No preview · Article · Oct 2010 · Journal of Experimental Nanoscience
  • Q. Zou · M. Z. Wang · Y. G. Li · B. Lu
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    ABSTRACT: The onionlike carbon (OLC) was fabricated by annealing nanodiamond synthesized by detonation at the annealing temperatures from 500 to 1400 °C and at the pressure of approximate 2 Pa. A high-resolution transmission-electron microscope was used to characterize the microstructures of the OLC as-fabricated. The results showed that at the annealing temperature of 500 °C, nanodiamond began transforming into amorphous carbon. At the annealing temperature of 800 °C, nanodiamond was transformed into amorphous carbon completely. At the annealing temperature of 900 °C, OLC began appearing and the size of the OLC particles was smaller than 5 nm. At the annealing temperature of 1000–1200 °C, the OLC particle with larger size than 5 nm was fabricated. Moreover, the amorphous carbon untransformed and coexisted in the center of the OLC particle became fewer and fewer with the annealing temperature increase. At the annealing temperature of 1400 °C, all the amorphous carbon was transformed into the OLC. The OLC particles exhibited similarity to the original nanodiamond particles in shape. The formation process of the OLC included formation of amorphous carbon, formation of graphite fragment, connection of graphite fragment, connection and curvature of graphite sheets, and closure of graphite layers.
    No preview · Article · Sep 2010 · Journal of Vacuum Science & Technology B Microelectronics and Nanometer Structures
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    ABSTRACT: Onion-like carbon (OLC) was fabricated by annealing nanodiamond at 1000°C for 2 h in low vacuum ∼1 Pa. The OLC was characterised by a high resolution transmission electron microscope, an X-ray diffractometer and a Raman spectrometer. The results show that the OLC exhibits similarity to the original nanodiamond particles in shape. The average size of the OLC particle is found to be ∼5 nm. The nanodiamond particles are transformed into OLC completely after annealing. The transformation mechanism of the OLC from the nanodiamond by annealing at lower temperature is reported.
    No preview · Article · Sep 2010 · Material Research Innovations
  • Qin Zou · Ming Zhi Wang · Yan Guo Li
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    ABSTRACT: Onion-like carbon (OLC) was fabricated by annealing nanodiamond at temperatures ranging from 500 degrees C to 1400 degrees C. At 800 degrees C, nanodiamond was completely transformed into amorphous carbon. At 900 degrees C, OLC began appearing. As the annealing temperature increased from 1000 degrees C to 1200 degrees C, OLC particles size became larger and larger and the amorphous carbon coexisted in the center of the OLC particle became less and less. At 1400 degrees C, all the amorphous carbon was transformed into the OLC.
    No preview · Article · Aug 2010 · Advanced Materials Research
  • Q. Zou · M. Z. Wang · Y. G. Li
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    ABSTRACT: In order to comprehensively analyse the structures and the surface states of the nanodiamond particles fabricated by detonation, various apparatus were used to investigate the nanodiamond powder including a high-resolution transmission electron microscope, an energy diffraction spectrometer, an X-ray diffractometer, a Raman spectrometer, a Fourier transform infrared spectrometer and differential scanning calorimeter. The grain size of the nanodiamond particles was in the range of 2-12 nm. However, the average grain size of the nanodiamond was approximately 5 nm. Moreover, the shapes of the nanodiamond particles were spherical or elliptical. The nanodiamond as fabricated was very pure, containing almost only the element of carbon. The contents of the impure element including O, Al and S were very small, which came from the synthesis and purification processes when fabricating the nanodiamond. The surfaces of the nanodiamond particles absorbed many functional groups, such as hydroxy, carbonyl, carboxyl and ether-based resin. The initial oxidation temperature of the nanodiamond powder in the air was about 520°C, which was lower than that of the bulk diamond. However, the oxidation temperature of the nanographite existing in the nanodiamond powder was about 228°C. The graphitisation temperature of the nanodiamond powder in the Ar gas was approximately 1305°C.
    No preview · Article · Aug 2010 · Journal of Experimental Nanoscience
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    ABSTRACT: The Ti2AlC was synthesized by laser-induced self-propagating high-temperature sintering (SHS) using 2Ti/Al/C powders as raw material. Several additives were added in the raw materials including TiC, Sn and excess Al in order to improve the reaction. The results showed that the Ti2AlC was synthesized by means of laser-induced SHS. The majority compounds were Ti2AlC and TiC in the sample. The content of the Ti2AlC in the sample was approximate 83%. The TiC or excess Al additives did not improve the synthesis of Ti2AlC. However, the Sn additive improved the synthesis of Ti2AlC obviously. For the raw material of 2Ti/Al/C/0.3Sn, the content of Ti2AlC in the sample attained approximate 95%.
    No preview · Article · Jul 2010 · Journal of Alloys and Compounds
  • F.C. Zhang · B. Lv · C.L. Zheng · Q. Zou · M. Zhang · M. Li · T.S. Wang
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    ABSTRACT: The microstructure in the worn surfaces of a failed bainitic steel railway crossing was investigated using optical microscopy, SEM, TEM, nanoindentation and Mössbauer spectroscopy. The results indicated that a nanocrystalline layer had formed in the surface of a worn crossing during service. The formation of the nanocrystalline layer was due to the severe plastic deformation (SPD) caused by the repeated heavy loading in service by high speed train wheels. The mechanism of formation of the nanocrystalline layer was strain induced dynamic recrystallization, and the nanocrystalline grains were nucleated from the original crystals of the steel directly. The alloying elements in the worn surfaces of the steel segregated slightly by diffusion during the process of recrystallization. The nanocrystalline layer does not display the white etching layer commonly observed in ordinary railway rails, the reason may be the differences of its microstructure and carbon content with the ordinary rail steel.
    No preview · Article · May 2010 · Wear
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    ABSTRACT: SiC/Ti3SiC2/TiC composites were fabricated by means of pressureless sintering using the 3TiC/2.2Si/0.2Al as raw materials. At the temperatures from 1000 degrees C to 1200 degrees C, the main phase of the composite synthesized was Ti3SiC2. At the same time, there was a small amount of TiC and SiC existing. The composite had loose microstructure. At the temperature of 1300 degrees C, the TiC and Ti3SiC2 were the primary phases. And the SiC was the second phase. The SEM images showed that there were two kinds of microstructures in the composite. One was the Ti3SiC2 and the TiC platelets on its surface, another one was the TiC and the SiC equixed grains in its interior.
    No preview · Article · Apr 2010 · Advanced Materials Research
  • Q. Zou · Y. G. Li · B. Lv · M. Z. Wang · L. H. Zou · Y. C. Zhao
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    ABSTRACT: Onion-like carbon (OLC) was synthesized by annealing nanodiamond in low vacuum (1 Pa) at the temperatures from 500 to 11400°C. The high-resolution transmission electron microscope images, X-ray diffraction patterns and Raman spectra showed that, when the annealing temperatures were lower than 900°C, there was no OLC fabricated. The amorphous carbon and the nanodiamond coexisted. The graphitization started from the surfaces of the nanodiamond particles. When the annealing temperatures were higher than 900°C, the OLC was fabricated. At 900°C, OLC began appearing and the size of the OLC particles was smaller than 5 nm. At the annealing temperature of 1400°C all the nanodiamond particles were transformed into OLC. The OLC particles exhibited similarity to the original nanodiamond particles in shape. Based on these results, a mechanism for the OLC synthesis by the method of annealing in vacuum was provided.
    No preview · Article · Feb 2010 · Inorganic Materials
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    ABSTRACT: The properties of the field emission (FE) from multi-walled carbon nanotubes (CNTs) in air used to generate the microplasma at near-atmospheric pressure were investigated in a removable gas cell built into a scanning electron microscope. The gaps between the electrodes were adjusted from 5 to 100 μm and the pressure was changed from 0 to 100 kPa. The obtained results have shown that the FE properties of the CNTs at 10 kPa and lower pressures were the same as those in vacuum. At a pressure more than 10 kPa, the FE threshold voltage in air was higher than those in vacuum, and increased with increasing atmospheric pressure. When the FE threshold voltage became higher than that of the gas breakdown, the microplasma was ignited before the FE initiation. Thus, the FE properties of the CNTs in air were stable when the FE potential was lower than the voltage of conventional gas discharge with CNT cathode.
    No preview · Article · Dec 2009 · Plasma Devices and Operations
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    ABSTRACT: Onion-like carbon (OLC) was synthesized by annealing nanodiamond in low vacuum of 1 Pa and at annealing temperatures from 500°C to 1400°C. The high-resolution transmission electron microscope (HRTEM) images, X-ray diffraction (XRD) and Raman spectrum of the OLC showed that there was no OLC when the annealing temperature was lower than 900°C. Moreover, the fragment amorphous carbon existed on the surfaces of the nanodiamond particles. At the annealing temperature of 900°C, the OLC particles began appearing and the size of the OLC particles was smaller than 5 nm. When the annealing temperature was increased from 900°C to 1400°C, the nanodiamond was transformed into OLC gradually. At the annealing temperature of 1400°C, all the nanodiamond particles were transformed into OLC completely. The OLC exhibited similarity to the original nanodiamond particles in shape. A mechanism for the OLC synthesis by annealing was provided. The graphitization started at the surfaces of the nanodiamond particles. The formation process of the OLC includes formation of graphite fragments, connection and curvature of graphite sheets between diamond (111) planes and closure of the graphite layers.
    No preview · Article · Dec 2009 · Science in China Series E Technological Sciences
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    ABSTRACT: Onion-like carbon (OLC) was fabricated by annealing nanodiamond at 1000 °C for 2 hours in low vacuum (1 Pa). The OLC was characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and differential scanning calorimetry (DSC). The experimental results show that the OLC exhibits similarity to the original nanodiamond particles in shape. The size of the OLC is found to be approximately 5 nm. The transformation mechanism of the OLC from nanodiamond was discussed also.
    No preview · Article · Dec 2009 · Journal of Wuhan University of Technology-Mater Sci Ed
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    ABSTRACT: Field emission (FE) properties of carbon nanotubes (CNTs) in vacuum, Ar gas or air were investigated by scanning electron microscopy. The gas pressures were changed from 0.2 to 1 kPa. The results showed that when the gap was smaller than 20 μm, the FE properties of CNTs were the same in vacuum and in Ar. The FE properties in original vacuum and in air were the same, which were different from that in vacuum after FE measurement in air. When the gap was changed from 20 to 100 μm, there was a discharge at 200-300 V. After the Ar discharge, the FE properties were the same in vacuum. After the air discharge, there was damage on the surface of the CNTs and the turn-on voltage in vacuum was higher than that in original vacuum. The stability of the CNTs experiments results showed that the CNTs were more stable in Ar than that in air during 300 s measurement.
    No preview · Article · Dec 2009 · Material Research Innovations