Advanced Materials Research Vols. 415-417

Abstract: In order to achieve cost-effective inner electrodes for the multilayer BaTiO₃-based ceramics having a positive temperature coefficient of resistivity (PTCR), we fabricated Ni paste based on Ni powder and investigated the effect of Ni electrode on the performance of semiconducting BaTiO₃ ceramics. We adjusted the particle size of Ni powder (0.2μm, 0.6μm and 1μm) and incorporated them as the electrodes into both single-layer and laminated BaTiO₃ PTCR devices. The device samples were sintered at 1200oC for 30min in reducing atmosphere consisting of N₂ and H₂ (97:3 by volume ratio), and went through a post-sintering in-air heat treatment at 700-900oC in air which is necessary for the PTCR effect. The results indicate that Ni powder with lager particle size are more stable against post-sintering heat treatment, and the heating temperature needs to be optimized to overcome the trade-off between ohmic behaviors of Ni electrodes and the PTCR effect of BaTiO₃-based semiconducting ceramics.

Abstract: As a lead-free positive temperature coefficient of resistivity (PTCR) material, [Ba_0.95-x (K_0.5Bi_0.5)_0.05Ca_x]_1-yNb_yO₃ system was prepared by the conventional solid-state reaction method. All samples sintered in air at 1300°C possess PTC characteristics as well as semi-conductivity characteristics, especially they show high Tc(130°C~160°C) value and the jump of the resistivity (maximum resistivity ρ_max / minimum resistivity ρ_min ) is four orders of magnitude. Samples with the composition of 0.3mol% Nb₅₊ have low room-temperature resistivity (ρ25°C) of ~10³Ω.cm.

Abstract: Porous quartz ceramics were produced using river sand from the Yangtze River in China as the raw material via the atmospheric pressure sintering method. The influence of the sintering temperature on the density, the porosity, the porous structure and the outside shape of ceramics were investigated in this paper.The conclusions show that the sintering temperature increased, the microstructure of the samples changed accordingly and the density increased, while the porosity decreased, the micropores edge gradually become smooth. The optimum sintering temperature of porous quartz ceramics was obtained at 1100 °C as determined by an analysis of the performance price ratio of the porous quartz ceramics, the density is 1.25g/cm³, the porosity is 49.5%, the outside shape is regular, the micropore edge are smooth.

Abstract: (K_0.5Na_0.5)(Nb_1−xV_x)O₃ (KNNV) (x=0.02-0.16) lead-free piezoelectric ceramics have been prepared by a traditional sintering technique. The effect of V on the crystallographic structure, microstructure, dielectric and piezoelectric properties has been investigated. XRD studies showed the formation of perovskite-type structure with orthorhombic symmetry. Dielectric properties as a function of temperature were carried out. The Curie temperature T_C and phase transition temperature of orthorhombic–tetragonal (T_O–T) increased with the increase in V content. In contrast, the remanent polarization decreased with the increase in V substitution.

Abstract: Abstract. The subject is mainly about making metallic lustre glaze at a low temperature with the basic glaze of lead frit and the nucleation agent of metallic oxides of CuO-MnO₂-TiO₂-NiO. It makes a study on the effect on the metallic lustre glaze through observing the process factors like the formula of glaze, the content of additive, the thickness of the glaze and the firing system. The results show that the optimum formula is Mn and Cu,The mass ratio of TiO₂ ,NiO and CeO₂ is respectively 4, 16%, 4.5% and 4.5%.

Abstract: A simplified method with much lower time and energy costs is presented for the rapid synthesis of low thermal expansion materials of CaZr₄P₆O₂₄, SrZr₄P₆O₂₄ and their solid solution Ca_0.5Sr_0.5Zr₄P₆O₂₄. The coefficients of thermal expansion of CaZr₄P₆O₂₄, SrZr₄P₆O₂₄ and Ca_0.5Sr_0.5Zr₄P₆O₂₄ are measured to be -1.45×10^-6, 2.1×10^-6 and 0.26×10^-6, respectively. Raman spectroscopic study confirms the formation of the solid solution of Ca_0.5Sr_0.5Zr₄P₆O₂₄ though its symmetric and asymmetric stretching modes are obviously broadened with respect to those of CaZr₄P₆O₂₄ and SrZr₄P₆O₂₄ due to the lattice deformation by incorporation of Ca²⁺ and Sr²⁺ with different cation size. The shifts of the asymmetric stretching Raman modes and the librational/translational modes with temperature in Ca_0.5Sr_0.5Zr₄P₆O₂₄ are between those in CaZr₄P₆O₂₄ and SrZr₄P₆O₂₄, suggesting a cancelling effect of Ca²⁺ and Sr²⁺ cations in the thermal expansion of Ca_0.5Sr_0.5Zr₄P₆O₂₄.

Abstract: The technology of aquifer thermal energy storage(ATES) is an energy-saving technology which can provide a solution to energy shortages and resources expasion. The first key point of this technology is whether the aquifer can be use to store energy. In this paper, taking Sanhejian Coal Mine as an example, we choose Quaternary upper loose sandy porosity confined aquifer to bottom clayed glavel porosity confined aquifer as aquifers thermal energy storage, to discuss whether the aquifers can be used to store energy. The simulation results of aquifer temperature field show that the selected aquifers reach the goal of energy storage. And with the same irrigation flow, the lower the temperature, the more the cold water and the larger the low temperature region in aquifers thermal energy storage. With the same irrigation temperature, the lager the irrigation flow the more the cold water and the larger the low temperature region in aquifers thermal energy storage.

Abstract: Electrical properties, positive temperature coefficient of resistivity (PTCR), and microstructures of (Ba_m-0.007Sm_0.007)TiO₃ (BST) with different Ba-site/Ti-site (A/B) ratio sintered in a reducing atmosphere and reoxidized in air are investigated. The results reveal that the room temperature resistivity of the semiconducting BST ceramics first decreases and then increases with increasing of A/B ratio (m), particularly when m is equal to 1.006, the semiconducting BST ceramics which have been sintered in a reducing atmosphere and reoxidized at 800°C exhibit significant PTCR effect with a resistance jumping ratio of 3 orders magnitude, and achieve a lower room temperature resisitivity of 80.8 Ω∙cm, in addition, the grain size distribution of the Ti-excess specimens is much better than that of the Ba-excess ones.

Abstract: The high-temperature resistance compression material of lightweight porous ceramics and fiber joining is becoming a kind of promising seal parts in high-temperature industries and aerospace field. A combination of the lightweight mullite matrix porous ceramics and the elastic 3-D silica woven fibre, a novel joining material was studied. The low cost fly ash cenosphere as raw materials, mullite porous ceramics with density 0.92 g/cm³, and the thermal conductivity 0.13 w/m.K, were prepared. Using microwave selective heating properties, designing the interlayer composition, the bonding materials were attained by microwave sintering. The flexural strength of joint materials was about 23 MPa, which was higher than porous ceramics matrix.

Abstract: The effect of the Fe₂O₃ dopant on the electronic densities and the electrical properties has been studied in a ZnO-Bi₂O₃-SnO₂-Co₂O₃-MnO₂-TiO₂-Ni₂O₃-Fe₂O₃ system by the measurements of positron lifetime spectra, coincidence Doppler broadening spectra and current-voltage characteristics. The results show that the 3d electron signal in the spectrum of the varistor increases with the Fe₂O₃ content. The addition of small amount of Fe₂O₃ into the ZnO-based varistor leads to an increase in the donor concentration in the bulk and the defects in the varistor. As the Fe₂O₃ content increased, the threshold voltage (V_T) and the nonlinear coefficient (α) of the varistor decreased monotonously.