Papers by Author: Tai Qiu

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Authors: Lei Yu, Jian Yang, Tai Qiu
Abstract: Fully dense (ZrB2+ZrC)/Zr3[Al (Si)]4C6 composites with ZrB2 content varying from 0 to 15 vol.% and fixed ZrC content of 10 vol.% were successfully prepared by in situ hot-pressing in Ar atmosphere using ZrH2, Al, Si, C and B4C as raw materials. With the increase of ZrB2 content, both the bending strength and fracture toughness of the composites increase and then decrease. The synergistic action of ZrB2 and ZrC as reinforcements shows significant strengthening and toughing effect to the Zr3[Al (Si)]4C6 matrix. The composite with 10 vol.% ZrB2 shows the optimal mechanical properties: 516 MPa for bending strength and 6.52 MPa·m1/2 for fracture toughness. With the increase of ZrB2 content, the Vickers hardness of the composites shows a near-linear increase from 15.3 GPa to 16.7 GPa. The strengthening and toughening effect can be ascribed to the unique mechanical properties of ZrB2 and ZrC reinforcements, the differences in coefficient of thermal expansion and modulus between them and Zr3[Al (Si)]4C6 matrix, fine grain strengthening and uniform microstructure derived by the in situ synthesis reaction.
Authors: Zhi Lan Tang, Chun Ying Shen, Zhao Xi Li, Jian Yang, Tai Qiu
Abstract: Ba4Sm9.33Ti18O54 (BST) ceramics were prepared by conventional solid-state reaction method. The effect of CuO-Bi2O3 co-doping on the sintering behavior and microwave dielectric properties of BST ceramics has been investigated. The results indicated that when the total addition of CuO-Bi2O3 doping agent was 1.0wt%, the sintering temperature of BST ceramics was reduced to 1240°C as a result of liquid-phase sintering effect derived from CuBi2O4. When the total addition of CuO-Bi2O3 was fixed at 1.0wt%, the microwave dielelctric properties of BST were improved by adjusting the mass percentage of Bi2O3. With the increase of Bi2O3 amount from 20wt% to 80wt%, the dielectric constant (εr) decreased, the quality factor (Q•f) increased and the temperature coefficient of resonant frequency (τf) shifted from negative value to positive value. The excellent microwave dielectric properties of εr=82.51, Q•f=7878GHz and τf=+6.02ppm/ were obtained for the sample with Bi2O3 amount of 80wt% when sintered at 1240°C for 3h.
Authors: Yin Liu, Fan Fei Min, Tai Qiu, Jin Bo Zhu, Ming Xu Zhang
Abstract: Nanocrystalline CoFe2O4 ferrite have been synthesized by a spraying-coprecipitation method. X-ray diffraction (XRD) and Transmission electron microscope (TEM) confirmed the formation of single-phase CoFe2O4 ferrite nanoparticles in the range 10 nm ~ 100 nm depending on the calcining temperature. The magnetic measurements show that specific saturation magnetization of nanocrystalline CoFe2O4 ferrite increases from 36.1 A•m2•kg-1 to 88.6 A•m2•kg-1 as grain size increases from 12 nm to 98 nm. The coercivity shows a peak with grain size, peaking at around 43 nm. The magnetic behaviour of nanocrystalline CoFe2O4 ferrite might be attributed to the effects of surface and random anisotropy.
Authors: Wen Bo Bu, Tai Qiu, Jian Lin Shi, Jie Xu
Authors: Wen Bo Bu, Tai Qiu, Jie Xu, Xiao Yan Li
Authors: Bao Xiang Jiao, Tai Qiu, Chun Cheng Li, Chun Ying Shen
Abstract: Microstructure and mechanical properties of zirconia-toughened alumina (ZTA) composite ceramics prepared by gelcasting process were investigated. The results indicated that Al2O3-ZrO2 composites have high bending strength and fracture toughness for the solid loading of the suspension ³ 50vol.%. The bending strength and fracture toughness of sintered ZTA ceramics reach values as high as 631.5 MPa and 7.64 MPa·m1/2, respectively, with solid loading of suspension being 55vol.%. The t-ZrO2 content is increased, and the uniformity of ZrO2 particle distribution is improved in sintered samples prepared by gelcasting compared with those by dry pressing.
Authors: An Guo Lu, Tai Qiu
Abstract: Calcium borosilicate (CaO-B2O3-SiO2, CBS) glass based glass-ceramic composites were prepared by introducing borosilicate glass. The effects of borosilicate glass and firing temperature on the microstructure and properties of the glass-ceramic composites were investigated. The results showed that the composites containing 0~40% (in mass fraction, the same below) borosilicate glass can be sintered at 850°C. The dielectric constant (εr) decreases with the increase of borosilicate glass content and can be adjusted in the range of 5.6~6.6. The coefficient of thermal expansion (CTE) increases with the increase of borosilicate glass content. Increasing sintering temperature favors the precipitations of crystal phases, which have lower εr than CBS glass, resulting in the decrease of εr for the composites.
Authors: Chun Ying Shen, Tai Qiu, Yu Ming Lu
Abstract: AlN fibers were synthesized by carbothermal reduction using Al2O3 fibers as starting material. The N content of AlN fibers synthesized at 1780°C was more than 31%. The morphology and microstructure of AlN fibers were studied with XRD, SEM and TG-DSC. The fibers containing small AlN grains were pipe-shaped, in which the particle size is about 1µ, diameter 4 ~ 6µ, length/diameter ratio 20 ~ 30. The main reaction process is as follows: Firstly, alumina is reduced by carbon to lower-valent aluminum oxide, which further reacts with nitrogen and forms AlN. Secondly, when the alumina fibers are coated by AlN layer, the reaction takes place simultaneously on both interfaces of the AlN layer.
Authors: Jian Yang, Xiang Xin Xue, Li Mei Pan, Mei Wang, Tai Qiu
Abstract: TiO2/(O′+β′)-Sialon multiphase ceramics with different phase composition of TiO2 were prepared by pressureless sintering under high-purity N2 atmosphere with (O′+β′)-Sialon powder and nano TiO2 (anatase) powder as raw materials, Yb2O3 or Tb2O3 as additive. For each sample, the weight percentage of anatase in TiO2 was calculated from XRD data and the kinetics of anatase-rutile transformation was investigated, wherein the emphasis was placed on the influence of Yb2O3 and Tb2O3. The results indicate that the added Tb2O3 and Yb2O3 serve the significant function of inhibition and promotion on the phase transformation, and the effects are enhanced and attenuated with increasing additive content, respectively. For the sample without additive, the transformation process follows apparent first-order kinetic model. The addition of Yb2O3 or Tb2O3 results in completely different transformation kinetic law. For the samples with Yb2O3 added, the transformation is an apparent second-order reaction, whereas a unique kinetic model, CA=kt1/2+C, is valid for the samples containing Tb2O3. In the two cases, the effect of the additive content on the transformation can be perfectly reflected by the apparent rate constant.
Authors: Jia Mao Li, Tai Qiu
Abstract: Microstructures and microwave dielectric properties of Ca(Sm0.5Nb0.5)O3 ceramics, prepared by a conventional solid-state reaction method, were systematically investigated by varying calcining temperature, sintering temperature and cooling rate. The XRD result showed that a single Ca(Sm0.5Nb0.5)O3 phase could be synthesized at a calcining temperature of 1200 °C. Optimized combination of microwave dielectric properties of εr = 22.36, Q×f = 18030 GHz and τf = -31.2 ppm/°C was obtained for furnace-cooled Ca(Sm0.5Nb0.5)O3 ceramics sintered at 1550 °C for 4 h. However, some microcracks were found from the microstructures of the furnace-cooled specimens. Further, the Q×f value could be increased by controlling the cooling rate during the sintering process due to the disappearance of microcracks in the final material. With a cooling rate of 2 °C/min, Ca(Sm0.5Nb0.5)O3ceramics exhibited an enhanced Q×f value of 37130 GHz.
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