Papers by Keyword: Transparent Ceramic

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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.
441
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.
1207
Authors: Yue Hu, Wei Pan
Abstract: Light scattering caused by pores detrimentally affects the optical transparency of transparent ceramics. Herein, Mie theory has been used to calculate the cross-section of pore scattering in transparent ceramics, and the influence of wavelength, pore size distribution and refractive index has been discussed in detail. For wavelength between 200 nm and 2000 nm, the scattering cross-section decreases with increasing wavelength, which means that pore scattering is more detrimental to short-wavelength transparency. With ZOLD function simulating the pore size distribution inside the ceramic, it has been found that the scattering is strongest when the most-probable diameter dm equals the incident light wavelength λ. And FWHM (full width at half maximum) parameter a also affects the scattering cross-section. a between 0.003 and 0.7 is necessary for obtaining high optical transparency in visible wavelength range. The method presented in this work is available for the estimation of scattering effect in different kinds of materials, which may be useful for future design of high-transparency ceramics.
655
Authors: Fa Hui Li, Jian Bao Li, Hong Lin, Cun Xin Huang, Mu Yun Lei, Hong Bing Du
Abstract: The present paper summarizes the technology and basic process for fabricating transparent ceramic MgAl2O4 spinel and introduces a scalable production technique. Fully transparent polycrystalline spinel has been prepared by combined vacuum sintering, hot-pressing, sintering in H2 atmosphere and hot isostatic pressing(HIP). The optical transmittance of the specimen sintered at 1500°C following HIP at 1800°C was nearly the same as that of single crystal spinel. When radiated by γ-ray and X- ray, colorless spinel became brown due to V-type color centers, which decreased its transmittance. On the other hand, the spinel ceramics’ resistance to radiation improved by doping CeO2.
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Authors: Li Qiong An, D.S. Wang, Run Hua Fan, Li Hua Dong
Abstract: The dielectric response and electrical conduction of Lu3NbO7 transparent ceramic produced by spark plasma sintering were investigated. Lu3NbO7 transparent ceramic exhibited low frequency dielectric dispersion and a peak in dielectric loss, shifting to higher frequency at high temperatures. This indicated space charge polarization and broad relaxation time, confirmed by impedance and modulus spectra. The Nyquist plot shows the dominant grain effect in the electrical conduction. The AC conductivity of Lu3NbO7 transparent ceramic is 4.18×10-2 S m-1 at 1073 K, with an activation energy of 1.30 eV.
1681
Authors: Xiao Juan Zhang, Guan Jun Qiao, Xiao Zhang
Abstract: High purity Al2O3 powder was used as raw material and MgO was used as additive to sinter alumina transparent ceramics in hydrogen atmosphere. EBSD image showed that, with the increase of the MgO content, the grain size decreased from 200μm (when no Mg was doped) to about 20μm (when the Mg doping amount was 1.0wt%), indicating that MgO had an inhibition effect on the grain growth. XRD analysis showed that the doping of MgO did not lead to the formation of new phases. A further refinement of cell parameters revealed that, when the doping amount reached 1.0wt%, lattice distortion occurred and the cell volume increased by about 80%, which was attributed to the formation and diffusion of oxygen vacancies. The Eg mode at ν=575cm-1 revealed by Laser Raman Spectroscopy suggested that AlO6 octahedra were distorted with the increase of the MgO content. And the frequency change of the A1g mode at ν=642cm-1 reflected the combined effect of ion mass and mechanical constant. Measurement of the optical transmittance indicated that, after the doping of MgO, a small amount of MgAl2O4 phase formed at the grain boundary, causing the transmittance to increase first and then decrease with the increase of the MgO content. And analysis of the dielectric properties showed that the change of the dielectric constant and loss with the frequency at room temperature resulted from ion relaxation polarization induced by the weakly bound ions in the AlO6 octahedron.
1264
Authors: Lei Tao Nie, Xi Yun He, Xia Zeng, Ping Sun Qiu, Wen Xiu Cheng, Cheng Kang Chang
Abstract: PLZT (X/70/30) ceramics with different La contents (X=7.45, 7.54, 7.63 mole%) were fabricated by hot-press sintering techniques. The effects of annealing on ferroelectric, optical and electrically controlled light scattering properties of PLZT transparent ceramics were examined and analyzed. The XRD patterns indicated that all the samples were crystallized into a pure perovskite phase without the second phase. The SEM exhibited fully dense, uniform microstructures with well-developed grains. The annealing treatment weakened the degree of squareness of the ferroelectric hysteresis loop, and even the anti-ferroelectric phase occurred as the La content increasing to X=7.63. The remnant polarization (Pr) and coercive electric field (Ec) decreased with the annealing treatment for all samples. The slow annealing treatment resulted in the lager increase of both transmittance and contrast ratio than those of the rapid annealing treatment at λ=632.8nm. The electrically controlled light scattering properties were obviously enhanced by the annealing treatment. Especially, the PLZT (7.63/70/30) ceramics exhibited the different electrically controlled light scattering performance which indicated it could hold high transmittance and symmetry in a wide electric field range with the slow annealing treatment.
1686
Authors: Wei Wei Li, Bing Chu Mei, Xiaonv Li, Jing Hong Song, Guang Lin Zhi
Abstract: Er3+, Na+-co-doped CaF2 transparent ceramics with Er3+ dopant concentration of 5at% and Na+ of 0, 0.5, 1.0 and 1.5at% were fabricated by the vacuum hot pressing method. Absorption spectra, emission spectra and fluorescence lifetimes were measured at room temperature to study the effects of Na+ on the spectral properties of Er3+: CaF2 transparent ceramic. The results showed that after introducing Na ion into Er3+: CaF2 transparent ceramics, charge-neutralized Er3+-Na+ structure formed which prevented Er3+ from clustering, the absorption intensity of ceramics decreased with the increase of Na+ concentration, but the spectroscopy and photoluminescence properties of Er3+ in CaF2 transparent ceramic could be modulated by adjusting the concentration of Na+. Co-doping Na+ to increase fluorescence lifetime should have an optimal value.
307
Authors: Yun Han Li, Qiu Hong Yang, Shen Zhou Lu
Abstract: Yttrium Lanthanum Oxide transparent ceramics were fabricated with (Y0.9La0.1)2O3 powders prepared by different methods. The growth characteristics, physical and chemical properties of the powders were investigated. The wet-chemical composite powders’ particle size was inhibited by La2O3 at high temperature treatment, therefore smaller than that of powders by solid-state reaction method. During the solid-state reaction between La2O3 and Y2O3 at temperature of 700~1100°C, La2O3 may have not effectively hindered the particle growth of Y2O3. (Y0.90La0.10)2O3 ceramic fabricated by both powders own smaller grain size and lower porosity than Y2O3 ceramics. The transmittance and sintering performance of Y2O3 ceramics were also improved after adding of La2O3. The powders prepared by both methods could be used to make high transparency ceramics.
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