Tape Casting Procedure Research Articles

Fabrication of flat stainless steel substrates with improved oxidation behavior for metal-supported solid oxide cells using aqueous tape casting

An aqueous tape casting procedure was developed and optimized to fabricate thick, flat tapes for use as porous stainless-steel substrates for metal-supported solid oxide cells (MS-SOCs). Curling tape is one of the main challenges when using aqueous based slurry formation. This work demonstrated that the sedimentation problem can be solved by increasing solid loading rather than adding excessive binder to raise viscosity. The effect of various casting surfaces on tape curling was also investigated. Materials that allow easy tape release resulted in flatter tapes once the water was evaporated. In addition, substrate oxidation resistance at high temperature was evaluated with respect to starting powder size, sintering extent, and pore former types. High sintering extent that removes or encloses the porosity between steel particles while retaining porosity left by pore formers can effectively prevent breakaway oxidation due to local chromium depletion. Carbon residue in the steel substrates from the slurry organic content can be decreased when formulating the slurry to prevent Cr-rich phase formation in the steel, which severely compromises the substrate oxidation resistance and ductility. By dwelling the substrate in high purity hydrogen, the sensitization can be reversed, but more detailed investigation of the reaction dynamics is needed. By combining the strategies described, this work produced crack-free, flat, 400–500 μm thick stainless steel substrates with 28.7 vol% porosity and improved oxidation resistance compared to previous substrates fabricated by dry pressing of fine powders.

Effect of aluminum titanate on the fracture mechanism of the nickel–zirconia system under uniaxial and biaxial strength testing conditions

Solid Oxide Fuel Cell (SOFC) anodes were fabricated with NiO–YSZ and 0–10 wt% aluminum titanate (Al2TiO5, ALT) addition. Samples were manufactured using a tape casting procedure to a thickness of approximately 500 µm. A remarkable enhancement of the mechanical strength, up to 166%, was found when compared to the samples without ALT addition. The development of secondary phases was observed proportional to the amount of aluminum titanate. Mechanical properties evaluation was conducted using uniaxial and biaxial strength testing. Weibull statistics was used for mechanical properties analysis and an advanced statistical analysis was employed to identify the existence of multiple flaw populations. Fractography was performed on selected samples to elucidate the fracture mechanisms. Biaxial testing was characterized by high mechanical strength with lower Weibull moduli; whereas, uniaxial testing showed lower mechanical strength and higher Weibull moduli. It was found that the addition of 0%, 5% and 10% ALT to Ni–YSZ samples exhibit a fracture mechanism that is dependent on one flaw population namely porosity and mechanical strength of secondary phases, respectively. Samples without the addition of ALT were characterized by intergranular fracture while transgranular fracture was found for the addition of 5% and 10% ALT to Ni–YSZ samples. For the addition of 1% ALT to Ni–YSZ samples both flaw populations were identified. Analysis of the fracture surfaces revealed the simultaneous presence of intergranular and transgranular features. It is proposed that secondary phases, developed by ALT addition, increase the mechanical strength of the material shifting the fracture mechanism from intergranular to transgranular.

ULTCC Glass Composites Based on Rutile and Anatase with Cofiring at 400 °C for High Frequency Applications.

The article presents the very first materials to the ultralow temperature cofired ceramic (ULTCC) technology with the sintering temperature of 400 °C. The dielectric composites are based on a rutile and anatase with commercial GO17 sealing glass. In addition to the bulk samples, the tape casting procedure is also introduced to show its feasibility to cofiring with commercial Ag electrodes at 400 °C. The structural, microstructural, thermal, and microwave dielectric properties in the green and sintered samples were investigated. The optimum amount of glass to fabricate substrates was found to be 30 vol %. The ULTCC substrates with the anatase TiO2A-30GO17 and rutile TiO2R-30GO17 that were sintered at 400 °C showed a relative permittivity of 9.9 and 15 and a dielectric loss of 0.006 and 0.003, respectively, at the measurement frequency of 9.9 GHz. The temperature dependences of the relative permittivity were +70 and −400 ppm/°C, respectively. Moreover, the coefficients of the thermal expansion of the substrates were 7.4 and 8.3 ppm/°C in the measured temperature range of 50–300 °C. A preliminary test to study the feasibility of the anatase TiO2A-30GO17 for a dual band antenna was performed due its relatively stable temperature behavior.

Development of an all-solid-state lithium battery by slurry-coating procedures using a sulfidic electrolyte

All-solid-state batteries (ASSBs) are promising candidates to significantly exceed the energy densities of today's lithium-ion batteries. However, for their successful commercialization, an easily scalable production procedure is needed. The tape casting procedure herein described allows to process a composite cathode by using an inert (polyoleophine) binder, conductive carbon, β-Li3PS4 and Li1+x[Ni0.6Mn0.2Co0.2]1-xO2. The inorganic electrolyte β-Li3PS4 layer is either coated onto the composite cathode or applied as a self-standing tape. In both cases a pressing step at room temperature is used to remove the porosity. Finally, a polymer electrolyte layer is added prior to the lithium metal anode to avoid the reaction between the latter and the inorganic solid electrolyte. Such dual-electrolyte, solid-state cells demonstrate good cycle performance and specific capacity. The type of conductive carbon in the composite cathode is seen to play a crucial role.

A new binder-free and conductive-additive-free TiO2/WO3-W integrative anode material produced by laser ablation

Although transition metal oxides anodes have attracted lots of attention, there are still many problems to be resolved. Complicated fabrication process, high cost and poor electrochemical performances are the most important ones, together hindering transition metal oxides anodes for practical use. Herein, we provide a new approach to fabricate a binder-free and conductive-additive-free TiO2/WO3-W integrative anode material through the nanosecond laser ablation and dip-coating technology, which simplifies the entire anode preparation process with no need for a conventional tape-casting procedure. Using this method, great time cost, machine cost and labor cost related to mixing and tape-casting process can be saved on the basis of good electrochemical performances. The prepared TiO2/WO3-W integrative anode realizes a first Coulombic efficiency of 75.6% and attains to a stable capacity within the first five cycles. It can still maintain a capacity of 600 mAh g−1 in the range of 0.01–3 V vs. Li+/Li at a current rate of 0.2 C after 500 cycles. This work offers a new way to achieve a fast fabrication of the integrative anode for lithium ion battery, which is universal for other transition metals (such as Fe, Cu, Ni, Co, Mo, W etc.).

Multilayer tape-casting method for anode-supported planar SOFCs

We have developed a multilayer tape-casting and co-sintering process to fabricate a large-area, anode-supported electrolyte film, which is critical for planar-type, reduced-temperature solid oxide fuel cells (SOFCs). Nickel/yttria-stabilized zirconia (Ni/YSZ), nickel/scandia-stabilized zirconia (Ni/ScSZ) cermets, ScSZ, Ce0.8Gd0.2O1.9 (CGO), and La0.6Sr0.4Co0.2Fe0.8O3δ (LSCF)–CGO were used as materials for anode substrate, anode functional layer, electrolyte, interlayer and cathode, respectively. The powders of these functional layers were ball-milled with organic additives to form slurries, which were assembled together with the multilayer tape-casting procedure to get the green tapes. After drying, the green tape was co-sintered at 1400°C for 4 h in air to get the large-area, anode-supported electrolyte film (thickness 15 μm). For cell preparation, the LSCF–CGO composite cathode was deposited by the screen-printing method and sintered at 1100°C for 3 h. The area-specific resistance (ASR) of the obtained single cell was found to be 0.99 ωcm2 at 850°C with H2/O2 as the operating gases, and the maximum power density achieved was 0.63 W/cm2. The thickness of the (Zr,Ce)O2-based solid solution formed at the ScSZ/CGO interface during high-temperature sintering was investigated. The results illustrate that fabrication of an anode-supported electrolyte film for planar SOFCs with a CGO interlayer is possible by the multilayer tape-casting procedure, which is both cost-effective and feasible.

Tape Casting of Ba0.7Sr0.3TiO3 for Tunable Microwave Devices

In this work, tape-casting technique was employed to prepare Ba0.7Sr0.3TiO3 films for lens antenna system. Effects of slurry properties on the tape casting procedure were investigated and the thickness, tensile strength and the surface roughness of the tapes were studied. The structure, morphology and the dielectric properties of the films were analyzed.

A study of multilayer tape casting method for anode-supported planar type solid oxide fuel cells (SOFCs)

In the present work, we have developed a multilayer tape casting and co-sintering process to fabricate large area anode-supported electrolyte film, which is critical for planar type reduced temperature solid oxide fuel cells (SOFCs). Nickel/yttria-stabilized zirconia (Ni/YSZ), nickel/scandia-stabilized zirconia (Ni/ScSZ) cermets, ScSZ, Ce 0.8Gd 0.2O 1.9 (CGO), and La 0.6Sr 0.4Co 0.2Fe 0.8O 3− δ (LSCF)–CGO were used as materials of anode substrate, anode functional layer, electrolyte, interlayer and cathode, respectively. The powders of these functional layers were ball milled with organic additives to form slurries, which were assembled together with the multilayer tape casting procedure to get the green tapes. After dryness, the green tape was co-sintered at 1400 °C for 4 h in air to get the large area anode-supported electrolyte film (thickness ∼ 15 μm). For cells preparation, LSCF–CGO composite cathode was deposited by screen-printing method and sintered at 1100 °C for 3 h. The area-specific resistance (ASR) of the obtained single cell was found to be ∼0.99 Ω cm 2 at 850 °C with H 2/O 2 as the operating gases, and the maximum power density achieved ∼0.63 W cm −2. The thickness of the (Zr,Ce)O 2-based solid solution formed at the ScSZ/CGO interface during high temperature sintering was investigated. The results illustrate that fabrication of anode-supported electrolyte film for planar SOFCs with a CGO interlayer is possible by multilayer tape casting procedure, which is both cost-effective and feasible.

Al 2O 3/Y-TZP and Y-TZP materials fabricated by stacking layers obtained by aqueous tape casting

A processing method for production of multilayer ceramics by laminating stacked green ceramic tapes with help of adhesive layer and pressing at room temperature was extended. Ceramic tapes with two compositions within the system alumina/yttria stabilized zirconia (Y-TZP) (alumina–40 vol.% Y-TZP and 100 vol.% Y-TZP), obtained from aqueous ceramic slurries by tape casting procedure were employed in this work. The optimum conditions to fabricate pieces made of six tapes with same composition, and to obtain defect free sintered materials, by varying the level of pressure applied, was investigated. For this purpose, previously selected composition of adhesive layer and type of pre-treatment of tapes were used. The analysis of engineering stress–apparent strain curves recorded during the lamination process was done to control the formation of cracks within the pieces under pressure. Optimization of the pressure range was performed by the analysis of the green density change as a function of pressure. The cross section observation by optical and scanning electron microscopy of sintered ceramic pieces was carried out to assure the control of the process. Fabricated pieces were subjected to testing by Impulse Excitation Technique (IET) and Vickers indentation in order to evaluate the adequacy of the fabrication procedure and to analyse the possible effects of interfaces. Dense pieces with maximum sizes of the defects of the same level as those of the microstructural ones and without interface effects on the elastic and mechanical behaviour were obtained.

BST powder with sol-gel process in tape casting and firing

Ferroelectric films such as Barium Strontium Titanate (BST) films are potential candidates for several microwave applications. In this work, the suitability of fine BST powder prepared by the sol-gel process for tape casting and firing were studied and compared with one commercial BST powder. The particle size of the sol-gel powder was 0.05–0.1 μm. The effects of different powders and slurry properties on the tape casting procedure, the thickness and tensile strength of the final tapes and their surface roughness were investigated. Furthermore, the sintering properties of different powders were measured using a dilatometer. The tapes made with sol-gel powder were sintered at 1250 °C and had large shrinkage.

Ba 0.7Sr 0.3TiO 3 powders with B 2O 3 additive prepared by the sol–gel method for use as microwave material

Ferroelectric films based on barium strontium titanates have been widely investigated in microwave devices, such as tunable filters and phase shifters. Recent trends include integration of ferroelectric layers into multilayer dielectric modules by a tape casting procedure. The sintering temperature of BST prepared by the conventional oxide mixing method is, however, very high (1350°C), and only platinum or refractory metals can be used for conductors and electrodes in the co-sintering process of tapes. Decrease of the sintering temperature of BST below 1000°C would result in good compatibility of the ferroelectric layers with embedded electrodes made of highly conductive metals, such as silver. The effects of B 2O 3 addition and powder properties on the sintering behavior and the dielectric properties were investigated. The sol–gel method was used to prepare all powders because of its high purity and homogeneity control and its ability to produce fine powders. The BET results showed that all powders had high specific surface areas, but in dilatometric studies, only boron addition produced the desired shrinkage and dense microstructure at low temperatures (<1000°C). This was also verified in sintered microstructures. The XRD showed an appearing of two secondary phases caused by boron addition. This decreased permittivity and thus set a limit on boron addition.

Alkali resistance of tape-cast SiC porous ceramic membranes

The possibility to limit the alkali poisoning of the internal reforming catalyst in a direct internal reforming-molten carbonate fuel cell (DIR-MCFC) has been investigated by testing porous ceramic membranes in a reactor which simulated DIR-MCFC operative conditions. Silicon carbide (SiC) has been chosen as starting material for the membranes; they have been prepared by adopting the tape-casting procedure, and the reproducibility of this preparative has been verified through several morphological characterizations. Some tests at different lifetimes (150, 700 and 1500 h) have been carried out and it has been found that the membranes are able to retain 50–65% of the potassium after 150 h and this capability decreases at 32% after 1500 h. Because of no variations on the porous ceramic membranes characteristics, before and after the tests, have been evidenced from porosimetric and SEM analyses, we have supposed that the adsorbed K gradually covers the SiC grains surface by forming a thin film without modification of the structure of the samples.

Modified Tape Casting Method for Ceramic Joining: Application to Joining of Silicon Carbide

A simple modified tape casting procedure has been developed for application to ceramic joining when the joining materials are in powder form. The method involves preparation of a slurry from the powder, solvent, and thermoplastic binder, and then casting directly onto the joining surface using a moving doctor blade. Handling of the tape prior to joining is not necessary: therefore, binder content is minimized, plasticizers are not required, and viscosity is controlled by solvent content. The utility of this technique for producing joints with thin, uniform interlayers is demonstrated for silicon carbide materials joined with TiC + Ni and SiC + Si.