Papers by Keyword: Textured Ceramics

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Authors: Xin Wen Zhu, Tetsuo Uchikoshi, Yoshio Sakka
Abstract: Recently, textured microstructure has received particular interest in the processing of advanced Si3N4 ceramics because of significant improvement in the mechanical properties and thermal conductivity. This work will report a highly textured β-Si3N4 ceramic by aqueous slip casting in a magnetic field and subsequent pressureless sintering, using commercial α-Si3N4 raw powder and a mixture of Y2O3 and Al2O3 as sintering aids. To obtain the well-dispersed Si3N4- Y2O3-Al2O3 slurries, polyethylenimine (PEI) was chosen as a dispersant. Effects of the sintering aids, PEI amount, pH and stirring time on the stability of the Si3N4 slurries were studied. It is shown that PEI is an effective dispersant for stabilizing the Si3N4-Y2O3-Al2O3 slurries that does not show a time-dependent behavior at an optimum pH ≈ 10, compared to the case in the absence of PEI. Using the 30 vol% Si3N4-Y2O3-Al2O3 slurries stabilized with 1.5 dwb% PEI at pH 10, the highly textured β-Si3N4 with 97 % relative density could be obtained by slip casting in a magnetic field of 12 T and subsequent sintering at 1800 oC for 1 h. The textured microstructure is featured by the alignment of c-axis of β-Si3N4 crystals perpendicular to the magnetic field, and the Lotgering orientation factor, f, is determined to be 0.8.
Authors: Cun You Wu, Shu Qin Li, Yuichiro Murakami, Kensuke Sassa, Shigeo Asai
Abstract: A new technology relating to crystal orientation and structure alignment has emerged by the development of superconducting technologies. Now, a high magnetic field covering a rather large space is available even in small-scale laboratories. Under this circumstance it has been found that the crystal orientation in materials can be controlled by imposition of the high magnetic field. This principle due to a magnetization force can be applied not only to magnetic materials but also to non-magnetic materials with asymmetric unit cells. In this paper, three novel processes for the crystal orientation of ceramics and metals are described.
Authors: Huan Bei Chen, Jin Bao Xu, Ji Wei Zhai
Abstract: The bismuth layered structure materials (BLSFs) with general formula of the (Bi2O2)2+(Am-1BmO3m+1)2-, have attracted considerable attention for high-temperature piezoelectric applications. Hot pressing is a useful densifying and texture technique for enhancing the piezoelectric properties. In this present study, four different types (m=1, 2, 3, 4) of ceramics with Aurivillius structure were prepared and the influential factors of textured degree was investigated systematically by hot pressing method. The result indicates that the value of m is larger, the BLSFs ceramics is easier to get high degree of texture and high piezoelectric properties in the parallel of the hot pressing direction.
Authors: Yoshio Sakka, Tohru Suzuki, Tetsuo Uchikoshi
Abstract: Recently to improve properties, highly microstructure controlled ceramics such as fine-grained, textured and laminated structures are required. We have demonstrated a new processing of textured ceramics with a feeble magnetic susceptibility by colloidal processing in a high magnetic field and subsequent heating. As colloidal processing, slip casting and electrophoretic deposition (EPD) have been conducted successfully. Colloidal processing is known to be a powerful method for consolidating fine particles with a high density and homogeneous microstructure. The degree of orientation strongly depends on the particle dispersion and some processing factors, such as particle size, applied magnetic field, concentration of the suspension, sintering temperature, etc. Crystalline-textured controlled laminated composites can be fabricated using EPD by varying the angle between the vectors of electric field and magnetic field. Also textured ceramics with complicated structure can be fabricated by reaction sintering. The colloidal processing in a high magnetic field confers several advantages and it is possible for this type of processing to be applied to non-cubic ceramics, such as alumina, titania, zinc oxide, tin oxide, hydroxy apatite, aluminium nitride, silicon carbide, silicon nitride, etc. The textured ceramics showed anisotropic properties depending on the crystal plane.
Authors: Tomoyuki Endo, Yamato Hayashi, Jun Fukushima, Hirotsugu Takizawa
Abstract: Various (ZnO)5In2O3 ceramics were fabricated by microwave heating. Density, XRD pattern and microstructure were examined and those of Al-doped (ZnO)5In2O3 were almost the same as Al-free one. Highly textured (ZnO)5In2O3 ceramic was also fabricated by reactive templated grain growth (RTGG) method. The electrical conductivity was not improved by Al-doping; however it was improved slightly by microwave heating compared with conventional heating and especially improved by texturing using RTGG method. On the other hand, the absolute Seebeck coefficient in microwave heating was improved about 25% by Al-doped. Maximum electric power factor of textured specimen fabricated by RTGG method along ab-plane showed 5.76×10-4 WK-2m-1 (at 873K), which was attributed to high electrical conductivity.
Authors: Anatoly Yu. Zakharov, Mirza I. Bichurin, Yong Ke Yan, Shashank Priya
Abstract: The algorithm for fast evaluation of the hysteresis loops of uniaxial or textured ferroelectric microcrystal or grains with long-range interactions is developed. Two types of ceramic microstructures are considered: 1. Random ceramics with complete isotropic distribution function of the crystallographic orientations of grains; and 2. Textured ceramics with anisotropic distribution function of the crystallographic orientations of grains. The qualitative analysis of the hysteretic behavior in terms of the grain distribution function is successfully demonstrated. Comparison of the calculated results with experimental data for Pb (Mg1/3Nb2/3)O3 PbTiO3 ceramics is presented.
Authors: Yoshio Sakka, Tohru Suzuki
Abstract: The controlled development of texture is one of the ways for effective in improving the physical and mechanical properties. We’ll demonstrate new processing of textured ceramics as an example of alumina by slip casting in a high magnetic field and subsequent heating. Susceptibility of diamagnetic α-alumina is very small, but the orientation energy of alumina particle by a high magnetic field becomes larger than the thermal energy. α-alumina of a rhombohedral structure shows anisotropic susceptibility, but this anisotropy has up to now been more or less ignored due to its very low value. However, in a high magnetic field the energy of crystal anisotropy becomes comparable to or larger than the energy of thermal motion. The degree of orientation depends on processing factors such as heating temperature, particle size, magnetic field and concentration of suspension, etc. This process technique confers several advantages and it is possible for this type of processing to be applied to other non-cubic ceramics, such as TiO2, ZnO, SnO, HAP, AlN, SiC, etc.
Authors: Yukio Higuchi, Hirozumi Ogawa, Daisuke Kuroda, Masahiko Kimura, Hiroshi Takagi, Yukio Sakabe
Abstract: Ceramic materials based on lead titanate, lead niobate and bismuth layer-structured ferroelectrics (BLSF) were studied to develop piezoelectric ceramics for high temperature sensor applications. Compositional modification enabled lead titanate and lead niobate type ceramics to exhibit good piezoelectric properties at 500°C . The Curie temperature for one BLSF, CaBi4Ti4O15 was close to 800°C, though the piezoelectric constant was smaller than those of lead titanate and lead niobate ceramics. These ceramics seem to be good candidates for use as high temperature sensor materials. In addition, textured SrBi2Nb2O9 (SBN), another BLSF, ceramics with various orientation factors were fabricated through the templated grain growth (TGG) method. The resonant frequency of 76% textured SBN varied linearly with temperature and exhibited stable temperature characteristics. The temperature coefficient of the resonant frequency was –0.85 ppm/°C from –50 to 250°C, and was smaller than that of a quartz oscillator. Therefore, textured SBN ceramics are suitable for use as a resonator material when stable resonant frequency is needed in a high temperature range.
Authors: Ender Suvacı, Gary L. Messing
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