Papers by Keyword: Tape Casting

Abstract: In this work aqueous-based tape casting was used to produce Ni-GDC substrates. Rheological properties of the slurries were measured at room temperature. The acrylic-based suspensions showed a pseudoplastic behavior and remained stable and homogeneous. Tapes with thickness between 100 and 220 um were produced and showed smooth and homogeneous surfaces and good flexibility. Sintered tapes showed good density and porosity values.

Abstract: The aim of this work was to fabricate glass-ceramic substrates using aqueous tape casting technique of the parent glass powder in the SiO₂-Al₂O₃-MgO-Li₂O system with addition of ZrO₂ and B₂O_3. The powder mixture was melted at 1650°C/1h and the obtained glass (frit) was milled and processed by tape casting in thin substrates with 700 μm thickness. Suspensions were prepared by aqueous medium and latex emulsion binder. Flexible green tapes with few defects were obtained using suspensions prepared with 7 and 10 wt% of binder in relation to glass powder. Substrates were submitted to burn out at 700 °C and thermal treatment at 950 oC/30min, 950 oC/4h and 1000 °C/1h. The green density of the substrates was around 1.55 g/cm³ and 2.10 g/cm³ after sintering/crystallization. Microstructure in all treatments showed high porosity. The major crystalline phases identified by XRD were Li_0,6Al_0,6Si_2,4O₆, ZrO₂ and ZrSiO₄.

Abstract: An aqueous tape casting process was employed to produce hydroxyapatite (HA) sheets. The effects of viscosity of slurry, blade height and speed on flexural strength and density of the sintered HA sheets were studied using central composite design (CCD). The flexural strength and the density were measured using a three-point bending test and Archimedes method, respectively. Results suggested that all parameters and the interaction between viscosity and speed had significant effects on both flexural strength and density. Under the conditions studied, the optimal conditions for the maximum flexural strength and density of the sintered HA sheet were obtained with the viscosity of 1532 mPa.s, the blade height of 3.34 mm and the speed of 6.27 mm/s.

Abstract: The composite formation of steel and ceramics is especially for medical applications of great interest. By use of the multicomponent tape casting metal-ceramic composite components like bipolar scissors and other surgical instruments can be produced. A coating technology that comes from the paper industry, allows to apply a very thin insulating layer of a few microns between the electrodes consisting of stainless steel. Until now bipolar surgical instruments are produced by mechanical joining of steel and ceramic parts or by spraying a ceramic layer on the steel instruments. This joining steps can lead to stresses in the sensitive ceramic material and leave fine interstices or pores that are not only avoidable with a force and / or tight fit. Both factors are reasons for premature failure of the instrument, even if the materials are not yet at the limits of their resistance. Through the joint shaping by the tape casting and subsequent co-sintering of both materials, a material bond is achieved in addition to the previously existing mechanisms of force and form fit. This optimizes the composite properties and increases the usage time of metal-ceramic layered composites. Special focus is given to the formation of the interface and the associated changes in properties of the individual components of the laminate. These investigantions illustrate the influence of co-manufacturing on the texture of the laminate materials and the formed interface between them. By x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), x-ray fluorescence analysis (RFA) and thermodynamic calculations (FactSage) of the material bond at the metal-ceramic interface is investigated. In various application areas where steel and zirconia should occur as integral partners, this material combination may be established.

Abstract: This paper focuses on an iterative algorithm for setting and attaining particle packing densities by means of different concentrations of a matrix material. The mechanical properties of a product, such as fracture toughness, bending strength and thermal conductivity are directly dependent on the amount of matrix material present. A tape cast friction layer was developed, in order to investigate the dependence of the parameters of the RRSB distribution on concentration of matrix material. The results verify the calculation method of a solid mixture and show a linear dependence of the RRSB particle-parameter n on the concentration of matrix material (SiC-content).

Abstract: Tape casting process was used to produce Al₂O₃ substrates in an aqueous system with acrylic latex emulsion as binder. The present work studied the slurry formulations in aqueous medium of Al₂O₃ powders with different particle size distribution and made correlation to the green and sintered tapes. Two commercial alumina powders, one sub-micrometric and other micrometric were used. Compositions of Al₂O₃ slurries with 80 and 83 wt% of solids were prepared by dispersing the powders in water with a dispersant with subsequently additions of 7 and 10 wt% of binder. Sub-micrometric Al₂O₃ resulted in a high densification tapes regardless solid concentration and binder amount in the slurry, though green density was affected. For micrometric alumina, increasing the solid concentration resulted in a little higher final density.

Abstract: It has been known for many years that the incorporation of metallic particulates into a ceramic matrix can bring about the improvement of the mechanical properties of ceramics. Alumina/copper composites are well-known for their good frictional wear resistance, high resistance to thermal fatigue, high thermal conductivity as well as high absorption and dissipation of heat. The combination of the properties offered by alumina-copper composites makes them particularly interesting for wear applications in both automobile and aerospace industries. In the present paper we report on the design and production of a new class of alumina-copper functionally graded materials (FGM) which have technological potential for application in automotive brake disks. More specifically, this work deals with the development of the interpenetrating network structure of the FGM material. The manufacturing procedure was based on the gas-pressure infiltration of graded porous alumina preforms by liquid copper. The graded porous ceramic preforms with porosity ranging between 20 and 60% were made by casting foils made from slurries, the main components of which were alumina powder and rice starch powder (a pore forming agent), laminating these foils, subsequently burning-out the starch and last but not least performing a sintering process. A fundamental part of the presented investigations was to correlate the grain size of the alumina powders (Almatis, HVA FG and CT 1200 SG) and the pore size distribution, microstructure and selected mechanical and thermal properties of the porous ceramic preforms.

Abstract: The Solid Oxide Fuel Cell Roll (SOFCRoll) is a novel design based on a double spiral. Combining structural advantages of tubular geometries with processing advantages of thick film methods, it utilises a single cofiring process. The initial concept used separate tape cast layers which were laminated before rolling. To optimise layer thickness to function, thinner screen printed layers were combined into the tape cast structure in 2^nd generation cells. This presented several processing challenges, such as achieving dense electrolyte layers, maintaining porous electrode and current collecting layers and incorporation of integral gas channels. Performance has been promising with open circuit voltages close to 1V and cell power of over 400mW at 800°C, however cracking is still evident. Therefore further iterations are in development where thinner layers are sequentially cast, aiming to improve interfacial bonding and better match plasticity and burn out to reduce cracking. This paper reviews key aspects of understanding and development of the SOFRoll , the challenges that have been tackled and what challenges remain, along with future directions for development and potential applications for this device.

Abstract: CaCu_{(3+ x)}Ti₄O₁₂ (x = 0, 0.001, 0.002, 0.004 and 0.008) ceramics with variation in copper micro-scale excess were prepared via solid-state reaction, Aqueous technology of tape casting was applied to obtain thick films of, about 100 μm in thickness. Crystal phases of the samples were identified by XRD. SEM of samples revealed that copper micro-scale excess can accelerate some important solid phase reactions in the sintering process, most because of liquid phase sintering mechanism. EDX analysis indicated that copper micro-scale excess could compensate for a lack of copper in sintering process. The Cu_3.004 sample exhibited the best dielectric properties with a very low dielectric loss (0.029), while retaining a very high dielectric constant (91,536), and the Cu_3.002 and Cu_3.004 samples exhibited a well frequency and temperature stability which was of significant industrial relevance. In this work, it was concluded that a certain amount of Cu micro-scale excess could improve dielectric properties, frequency stability and temperature stability of CCTO ceramics.

Abstract: M-type barium hexaferrite (BaM) is a promising gyromagnetic material for self-biased microwave\millimeter wave devices because of its large uniaxial magnetocrystalline anisotropy and low microwave loss in high frequency. Due to the limitation of growth conditions, it is difficult to deposit BaM films with enough thickness by PLD, MBE and Magnetron Sputtering for practical application. However, it is demonstrated in present experiment that large area polycrystalline BaM thick films (500μm) with self-biasing (high remanence) and low microwave loss can be successfully fabricated by tape casting. X-ray diffraction and Scanning electron microscopy results indicate that these BaM thick films have highly c-axis oriented crystallographic texture with hexagonal morphology. Magnetic hysteresis loops reveal that samples exhibit excellent properties with a saturate magnetization (4πMs) of 3606G, a high squareness ratio (Mr/Ms) of 0.82. In addition, ferromagnetic resonance (FMR) measurement shows that the FMR linewidth is as small as 431Oe at 48GHz. These parameters ensure these BaM thick films are potentially useful for self-biased microwave\millimeter wave devices such as circulator, phase shifter and filter.