Papers by Keyword: Tape Casting

Abstract: The paper reports on processing and characterization of multilayer NTC (negative temperature coefficient) perovskite thermistors. Three materials La_0.8Sr_0.2Ti_0.4Fe_0.6O₃, CaTi_.0.8Co_0.2O₃ and CaTi_0.9Y_0.1O₃ with the stable perovskite structure were synthesized by solid state reactions and used for preparation of slurries for tape casting. Green sheets with screen printed internal Pt electrodes were stacked, laminated isostatically and cofired at 1250-1350°C. SEM observations revealed dense, fine-grained microstructure of ceramic layers, lack of delaminations and cracks and a good cooperation between ceramic and Pt electrode layers. Resistance-temperature characteristics of the fabricated multilayer thermistors were measured in the temperature range 20-820°C. The temperature coefficients of resistance were high, ranging from-9.7 to-1%/°C. Two developed compositions CaTi_.0.8Co_0.2O₃ and CaTi_0.9Y_0.1O₃ were found to be suitable for use at a higher temperature range of 150-500°C. The endurance tests showed small resistance changes (below 1%) after long term ageing at 300-400°C.

Abstract: Multilayer ZnO varistors were prepared by aqueous gel tape casting with water-soluble acrylamide as binder. 0.8wt% PAA dispersant was found to be the optimum concentration needed to prepare stable slurry. Plasticizer glycerol has a positive effect on the fluidity of the suspension and oxygen anti-polymerizing inhibitor PEG 2000 deteriorated the fluidity. The addition of 15wt. % PEG2000 eliminates the surface exfoliation absolutely due to the oxygenation of ether units. The solid loading of the slurry was about 71wt% compared to the custom acrylic formulation binder 60wt%. The multilayer ZnO varistors prepared by aqueous gel tape casting display comparable good electrical properties to those prepared by water-based tape casting using custom acrylic formulation binder which is attributed to the high solid loading of slurry.

Abstract: A glass powder of the SiO₂-Al₂O₃-K₂O-Na₂O system was added to fused silica particles to form composite green compacts by tape casting. This procedure was able to lower the sintering temperature of the fused silica particles making the composites suitable for being co-fired with the silver-palladium (Ag-Pd) paste commonly used as a conductive circuit in several microwave applications. The resulting new ceramic composite with the composition of 50 wt% fused silica and 50 wt% glass (brand name: TC-3) had a low dielectric constant and a low loss tangent of 2.7 and 2.5-3.7 x10^-3 , respectively, and was able to be co-fired with the Ag-Pd conductive paste at the temperature of 895 °C, resulting in a potential low temperature co-fired ceramic (LTCC) system for microwave applications.

Abstract: NiO/YSZ (6:4 wt.%) and NiO/SDC (6:4 wt.%) anodes, NiO/YSZ (SDC) anode-supported SDC electrolyte half cell were fabricated by tape casting, laminating and co-sintering technique. The laminating temperature was chosen to be 85¡æ that was above the glass transition temperature of PVA binder. Laminating pressure of 30-70 MPa was tried and it was found that 50 MPa was the best. Some unreacted CeO₂ was decomposed between 1365-1393¡æ and Sm₂NiO₄ compound was formed in NiO-based complexes at about 1445-1448¡æ. The sintering temperature of 1400 ¡æ was selected. The flexural strength of NiO/SDC anode (with an open porosity of 22.7%) and NiO/YSZ anode (with an open porosity of 21.2%) was 68.8 and 165.6 MPa, respectively. The flexural strength of as-fabricated NiO/YSZ anode achieved the requirement of the mechanical property for anode-supported SOFCs. SDC electrolyte with dense, crackfree and uniform structure was successfully adhered to the porous and homogeneous NiO/YSZ anode.

Abstract: The active magnetic regenerator refrigerator is currently the most common magnetic refrigeration device for near room temperature applications, and it is driven by the magnetocaloric effect in the regenerator material. In order to make this efficient, a graded configuration of the magnetocaloric material is needed. Tape casting is a common process in producing functional ceramics, and it has recently been established for producing side-by-side (SBS) functionally graded ceramics (FGCs). The main goal of the present work is to study the multiple material flows in SBS tape casting and analyze the influence of the different material properties, i.e. the density and the viscosity, on the interface between the flows, since this is highly important for the efficiency of the device. The Newtonian flow behavior with relatively high viscosity is assumed for each fluid and used in the simulation with a commercial CFD code (ANSYS FLUENT). The results show that the density change does not affect the interface between the adjacent fluids. The viscosity of the fluids plays the most important role in the behavior of the interface. Moreover, increasing the viscosity difference of the adjacent flows, Δμ, leads to increasing the diffusive region between the two fluids.

Abstract: The M-type hexagonal ferrite thick films are prepared by tape casting . The morphology is investigated by scanning electron microscope (SEM), the phase composition is characterized by X-ray diffraction (XRD) and the magnetic properties are characterized by vibrating sample magnetometer (VSM). The result shows that thick film by tape casting has high remanence as 26.607emu/g, high magnetization as 55.236emu/g, high coercivity as 2323.8Oe, and high squareness ratio and a good morphology which is suitable for small and light-weight microwave and millimeter-wave devices .

Abstract: The Co2Z ferrites noise suppression sheet was prepared by tape casting. Its microstructural characterization was performed by electron microscopy and noise suppression effect was measured by a microstrip line method. Results indicate that as the sinter temperature increases, the imaginary permeability increases leading to the enhancement of the suppression capability, and the thickness of noise suppression sheets also contribute to the noise suppression capability.

Abstract: The use of ceramic processes inducing a microstructural organization at the grain scale favors the improvement of strength and toughness. With layered structures, it is possible to design the microstructural characteristics of materials, leading to increased threshold strength. Layered structures can be arranged to control the local residual stresses causing elastic mismatches between dissimilar materials and crack deflection at interfaces. In this way, multilayer composites from kaolinite and alumina or mullite fibers were shaped by tape casting and staked by thermo-compression, or by centrifugation. During sintering, they show at strong anisotropic behavior, which is in correlation with different activation energy for sintering. Mullite growth is also anisotropic, inducing the formation of an organized micro composite microstructure. The mechanical and elastic properties are correlated with the organization degree of mullite crystals, due to the formation of an interconnected mullite network in the microstructure. It is also shown that variations of mechanical and elastic properties are correlated with the texture index obtained by Quantitative Texture Analysis from X-ray data. The anisotropy of the elastic properties is evidenced by different values of Young’s modulus in directions parallel and perpendicular to the casting direction. Beside, the crack growth resistance is governed by discontinuities along layer boundaries and fiber interfaces.

Abstract: In this work, NASICON-type disks with the formula, Na₃Zr₂Si₂PO₁₂ were prepared by non-aqueous tape casting method. The effect of the dispersant on the slurry viscosity was investigated, triethanolamine was found to be an effective dispersant for NASICON slurry. The correlation between the overall conductivity and the sintering conditions (temperature and time) for the NASICON disk was also studied. Green tapes were calcined at 900°C, 1000°C, 1100°C for 6h and 12h, respectively. Results revealed that the overall conductivity increased with the increasing of the sintering temperature and decreased with the increasing of the sintering time. The segregation of resistive monoclinic ZrO₂ phase was examined to have a negative effect on the overall conductivity. The CO₂ sensor using NASICON disk and Li₂CO₃-BaCO₃ complex thick film was fabricated and evaluated, the sensitivity was about 82.9 mV/decade at 450°C.

Abstract: Triacetin (TAC) was used as plasticizer to improve the ductile of polylactic acid (PLA). A composite film composed of PLA and TCA was therefore Paraed, and the packaging properties of this film were tested including the elongation, tensile strength, tear strength, Transparency and permeability. The results suggest that the film owns superior synthetically packaging properties when the proportion of TAC is 30 % (mass ratio). At the same time, this film has a low gas barrier which is especially for the package of the novel vegetable and fruits.