Papers by Author: Tie Cheng Lu

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Authors: Ji Cheng Zhou, Zhi Jun Liao, Jian Qi Qi, Wei Pang, Ya Wen, Jin Song Wen, Hai Ping Wang, Jun Feng He, Deng Xue Wu, Tie Cheng Lu
Abstract: Transparent AlON ceramics are prepared with single-phase AlON powder synthesized from micron-sized aluminum and nano-sized alumina. The ceramics are prepared through sintering at the temperature of 1880°C for 10, 20 and 40 hours in flowing-nitrogen atmosphere, respectively. The effects of powder and temperature holding-time on transparent ceramic preparation and microstructure and transparency are investigated. The results show that all samples are transparent and of a single-phase AlON and, with increasing holding-time, the average pore size and porosity decreases and consequently, the ceramics are dense and their transparency is improved.
Authors: Cun Bing Huang, Tie Cheng Lu, Li Bin Lin, Mu Yun Lei, Cun Xin Huang
Abstract: Transparent Mg-Al spinel ceramics of four different nonstoichiometries were obtained utilizing two-stage sintering technique of vacuum sintering and post hot isostatic pressing using MgO·nAl2O3 powders with n of 1, 1.3, 1.5 and 1.8, respectively, as raw materials. The mechanical properties of the ceramics were measured and indentation shapes and radial crack propagations were observed. The results showed that change of molar ratio of Al2O3 to MgO leads to variation of indentation shapes and crack propagations of the ceramics, resulting in the change of mechanical properties of the ceramics. The flexural strengths of the ceramics increase first then decrease with increasing n. However, the hardness and fracture toughness of the ceramics increase with increasing n. As a result, an optimal n for high performance ceramic is suggested to be 1.5. In addition, mechanisms of toughening and strengthening of the transparent ceramics have also been discussed.
Authors: Jie Zhang, Deng Xue Wu, Xiang Hui Chang, Tie Cheng Lu, Yi Hang Jiang, Jian Guo Zhu
Abstract: Dielectric constant and dielectric dissipation of MgAl2O4 transparent nano-ceramics were measured at different frequencies. The results indicated that the transparent nano-ceramic has a very low dielectric constant and low dielectric dissipation in frequency range of 1K~9MHz, but the dissipation of is independent of frequency. The dielectric constant of the transparent nano-ceramic does not vary signifycantly with temperature.
Authors: Xiang Hui Chang, Duan Wei He, Jie Zhang, Yong Tao Zou, Jiang Hua Wang, Tie Cheng Lu
Abstract: Nano-sized MgAl2O4 powders were treated at 500~1000 oC in a vacuum of 10-3Pa for 2 h, and then sintered at 500~900 oC under 1~6 GPa. The powders with and without vacuum-heat-treatment were investigated by means of Transmission Electron Microscope (TEM) and Sedimentation Test. It was found that the vacuum-heat-treatment of nano powder could effectively get rid of the absorbed gas on the surface of nano-particles. Bulk nanostructured transparent ceramics without cracks were sintered easily with the treated nano-sized powder. The success rate of nano-sinterning of bulk transparent ceramics was greatly increased when a suitable vacuum-heat-treatment process was used for the starting nano-sized powder.
Authors: Xue Jun Wang, Tie Cheng Lu, Yue Feng Sun
Abstract: To determine the optimal doping concentration, a series of Mn:MgAl2O4 were successfully prepared through vacuum-sintering with the highest doping concentration up to 35%. Samples with a low doping concentration exhibit a light green color. When the doping concentration increases, its color becomes deeper and deeper and when the doping concentration reaches 14%, their colors become brown and deeper brown when their concentrations further increase. The crystal phases of the samples were manifested by XRD measurements and their photoluminescence properties were studied. Combined with phase analysis, optimal doping concentration of transparent ceramics has been determined. In addition, the mechanism for fluorescence of Mn:MgAl2O4 transparent ceramics has also been discussed.
Authors: Hai Ping Wang, Deng Xue Wu, Wei Pang, Jian Qi Qi, Ji Cheng Zhou, Jin Song Wen, Zi Meng Cheng, Ya Wen, Zhi Jun Liao, Tie Cheng Lu
Abstract: Aluminum oxynitride powders were synthesized by carbothermal reduction, using nano-sized alpha-alumina, gamma-alumina and carbon as raw materials. Effects of the weight percentages of alpha-alumina in alumina (R) and synthesizing temperatures (T) on the preparation of single-phase AlON powders have been studied. The results showed that proper R can reduce the shrinkage and increase the formation rate of AlON phase, but a high R will reduce the formation rate of AlON phase, because the activity of alpha-alumina was lower than that of gamma-alumina. Single-phase AlON powder with excellent properties can be obtained under the condition of R=0.15, T=1700°C. Moreover, this single-phase AlON powder was well-dispersed with an average size of about 2 μm.
Authors: Xiang Hui Chang, Tie Cheng Lu, Jian Qi Qi, Xiang Jie Luo
Abstract: Transparent MgAl2O4 nano-ceramics were prepared by ultrahigh-pressure-sintering method, using improved nano-sized powder synthesized by high-temperature calcination. The synthesis temperatures were exactly measured by nichrome-NiSi thermocouple passing through the samples. The micromorphology of the ceramics was observed by means of dynamic force microscopy (DFM), and the relation between transparency and micro-morphology was investigated. The results show that, the sintering temperatures, now calibrated, of transparent nano-ceramics are just 540~700°C, which are much lower than those of conventional nano-ceramics and transparent ceramics, and the uniformity of grain sizes and orderliness of the grain array are beneficial to the transparency and integrity of the ceramics.
Authors: Xiang Hui Chang, Tie Cheng Lu, Ying Zhang, Xiang Jie Luo, Qiang Liu, Cun Bing Huang, Jian Qi Qi, Mu Yun Lei, Cun Xin Huang, Li Bin Lin
Abstract: The first experimental work to produce transparent MgAl2O4 nano-ceramics was reported in this paper. The sintering characteristics of transparent nano-ceramics were investigated at relatively low temperature (800 ~ 1100°C) under ultrahigh pressure (2 ~ 5 GPa) using hydrostatic equipment. The morphologies and phases of ceramics were observed by means of SEM and XRD, respectively. The grain sizes of the ceramics are shown to be less than one hundred nanometers, far smaller than the sizes of common transparent ceramics. Furthermore, the higher the sintering temperature and pressure are, the greater the extent of densification is. At the same temperature, the higher the pressure is, the smaller the average grain size is. Under the same pressure, the higher the temperature is, the larger the average grain size is. The optimal sintering condition for preparing transparent nano-ceramics was also determined.
Authors: Tie Cheng Lu, Xue Jun Wang, Bing Xun Cheng, Qiang Hu, Shao Bo Dun
Abstract: In this paper, transparent ceramics Mn:MgAl2O4, which are potentially applicable in visibleband laser field, were prepared and their light transmission and photoluminescence properties were investigated. In experiment, Mn:MgAl2O4 powders with two kinds of doping concentrations of 0.5 and 1.0 at% were synthesized through a high-temperature calcination method with NH4Al(SO4)2·12H2O and MgSO4·7H2O as raw materials, and with MnSO4·H2O as dopant. Transparent ceramics Mn:MgAl2O4 were prepared through vacuum hot-pressing sintering at 1750oC for 1 h, and subsequent vacuumannealing at 1700oC for 2 h. The samples were measured by means of light transmission and photoluminescence. The results show that transparent ceramics Mn:MgAl2O4 can be prepared by a low-cost powder technique and vacuum hot-pressing sintering. Two channels of visible-band luminescence, one peak around 520nm and one wideband centered at 650nm, respectively, can be shown. The intensity of their luminescence increases with increasing doping concentration. Obviously, it possesses a potential application in the field of visible-band solid tunable laser material with high doping concentration.
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