High-Performance Ceramics III

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Authors: Ting Fang, Jenq Gong Duh, Sue Yueh Tsai
Abstract: Mn3O4 hausmannite, which is a normal spinel with the Mn2+ in the tetrahedral site and the Mn3+ in the tetrahedral site, is one of the most stable manganese oxides. Variation in the valence of Mn ions (2+, 3+ and 4+) contributes to several different structures of manganese oxides. The autoxidation of precipitated manganese hydroxide in an alkaline solution is a practical approach to synthesize hausmannite (Mn3O4) at low temperature. During the process, the particle size and morphology of derived products were totally different from the precursors even though nanometer-sized Mn(OH)2 crystals were fabricated at first. It was observed that the variation was resulted from the accumulation of produced Mn3O4 crystallites which departed from the original crystals. This study has not only discussed the influence of reactant concentrations on the particle size and morphology of derived powders, but also revealed the morphological transformation of crystals involved in autoxidation with the aid of electron micrographs
Authors: Jun Shou Li, Yu Jun Yin, Jun Yan, Bao Cai Xu
Abstract: A new method, named the thermal explosive deforming synthesis (TEDS), for producing SnO2 nano-fibers is reported. The optimal condition for forming SnO2 nano-fibers is also discussed. The resulting SnO2 fibers have diameters in the range of 20 ~ 100 nm and are expected as the matrix materials for gas sensor, humidity sensor and piezoresistive pick-up.
Authors: Kenichi Sodeyama, Yoshio Sakka
Abstract: Hollow glass microspheres named expanded perlite have been prepared from perlite, but the size is usually above 20 µm. In the conventional preparation method, it is difficult to produce fine expanded perlite with particle size under 20 µm because the water contained in finely milled perlite particle, which is the origin of foaming, is evolved during heating process. A new fluidized sand-bedfurnace has developed and fine expanded perlite particles with particle size less than 15 µm and bulk density under 0.5 g/cm3 are prepared successfully. Using the fine expanded perlite, lightweight composites with alumina and lightweight pottery are successfully prepared by colloidal processing and subsequent heating.
Authors: Yun Han Ling, Jun Jie Qi, X.F. Zou, X.M. Zhao, Xin De Bai, Qing Ling Feng
Abstract: Antibacterial titanate nanotubes were synthesized by alkali digesting of metatitanic acid via hydrothermal route, following by cation-exchanged and immobilized with Ag+, Zn2+ and Cu2+. The conditions for nanotube synthesis and ion exchange were investigated; the microstructures of as-synthesized nanotubes were characterized by XRD, SEM, XPS and DTA/TG. The antibacterial performance of cation-doped titanate nanotubes was tested and evaluated by Escherichia Coli. and staphylococcus aureus.
Authors: Juan Yang, S. Quaresma, Sen Mei, José Maria F. Ferreira, P. Norby
Abstract: Mono-dispersed free-standing Co3O4 single crystals were synthesized by hydrothermally treating Co(NO3)2·6H2O aqueous solutions with addition of NaNO3 and tetraethylammonium hydroxide (TENOH). For comparison, samples were prepared using sodium hydroxide (NaOH) instead of TENOH. The obtained phases were greatly dependent on the types of alkalis and their concentrations. TEM images of TENOH-derived samples showed that the formation of free standing spinel Co3O4 nanocubes with sizes of 40-60 nm dominate over all the observation ranges for the samples with lower TENOH concentrations. While brucite-like Co(OH)2, Co3O4 and rod-like CoOOH appeared in the NaOH-derived sample, TENOH favoured the formation of Co3O4 nanocubes compared with NaOH.
Authors: Fa Gui Qiu, Xi Peng Pu, Rui Zhang, Jing Kun Guo
Abstract: Ultrafine yttrium aluminum garnet (Y3Al5O12, YAG) powders were synthesized by sol-gel combustion process from a mixed solution containing aluminum and yttrium nitrates. The precursor and powders were characterized using X-ray diffraction, thermogravimetry-differential scanning calorimetry-mass spectrometry, and transmission electronic microscope. Mono-phase cubic powders were obtained at 900oC by directly crystallizing from amorphous materials and no intermediate phase was observed. The powders processed at 900oC were uniform and in good dispersity with average particle size of about 20 nm.
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: Süleyman Tekeli, Metin Gürü
Abstract: To achieve improvements in the mechanical properties, fine grain size, homogeneous microstructure and high density are desirable. The poor dispersion of the powders produce difficulties in the densification and the presence of agglomerates is responsible for poor mechanical properties. Slurry casting is an important colloidal processing method for the ceramic industry and helps to prevent the agglomeration of fine particles. In the present study, the effect of processing parameters, namely solid content, dispersing agent concentration, slurry viscosity and milling time on slurry casting of 8YSCZ ceramics were investigated and optimum values were determined. The results showed that ceramic powder used was castable under limited conditions. The effect of shaping processon sintering behaviour and microstructure was also investigated for slurry-cast and die-pressed specimens. The results showed that specimen processed by slurry-casting had a faster sintering rate and lower sintering temperatures, compared to die-pressed specimen. The reason for better sintering was due to the homogeneous dispersion of the powder and elimination of agglomerates in slurry-cast specimen.
Authors: Xi Xin Wang, Jian Ling Zhao, Xiao Hui Wang
Abstract: Dispersing barium titanate (BT) in aqueous media has received special attention due to economic and environmental considerations. A new kind of dispersant named poly (acrylic acid-co-itaconic acid) has been synthesized in our study. By adjusting reactant ratio and reactant condition poly (acrylic acid-co-itaconic acid) with different average molecular (2000~10000) and different content of itaconic acid (10% ~ 30%) have been obtained. Dispersing effects of poly (acrylic acid-co-itaconic acid) have been studied through zeta potential, sediment experiments, rheological behavior. It can be concluded from our study poly (acrylic acid-co-itaconic acid) containing 20% itaconic acid with Mw between 3000 and 5000 show the best dispersing effect.
Authors: Jin Long Yang, Chun Lei Dai, Liang Su, Yong Huang
Abstract: Colloidal injection moulding of ceramics (CIMC) is a new ceramic forming technique that combines the advantages of gelcasting and injection moulding. It can inject nonplastic slurry into the mould and solidification course of ceramics slurry can be controlled by both temperature and pressure. Quick mixing technique ensures that ceramic slurry will not be solidified before casting. The equipment of CIMC was designed and developed. High performance ceramic components with complex shape have been manufactured by this equipment.

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