Flow properties of PLZTN aqueous suspensions for tape casting

Several aqueous suspensions of lead zirconate titanate powder doped with lanthanum and niobium (PLZTN) were prepared, tape cast and characterized by rheological measurements in steady shear flow. Experimental data were fitted by some viscous models available on literature and the model parameters compared in order to obtain information about the effects of the composition on suspension viscosity. Such approach represents a necessary step in the desirable optimization of tape casting process, which includes also the analysis by flow simulations. Five viscous models have been considered: from the classic plastic models of Bingham and Herschel–Bulkley, to the modified plastic model of Papanastasiou, up to the pseudoplastic models of Cross and Roberts–Barnes–Carew. The parameter-based comparison was carried on with the latter, resulting, with its eight parameters, the best-fit model, while for flow simulation purposes the ones with few parameters, as the Cross and Herschel–Bulkley models, resulted the more appropriate from some simple considerations.     

Eco-friendly tape casting of borosilicate glass/Al2O3 sheets for LTCC applications

This work reports the innovative development of a borosilicate glass/Al₂O₃ tape for LTCC applications using an eco-friendly aqueous tape casting slurry. Polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA) were the respective dispersants, while carboxymethyl cellulose (CMC) and styrene acrylic emulsion (SA) were the respective binders. The results showed that PVP was more suitable than PAA as the dispersant for the aqueous casting slurry, and that 1.5 wt% PVP would achieve well dispersion of CABS glass/Al₂O₃ powder in the aqueous slurry. Moreover, a small amount of 2.0 wt% CMC binder could yield smooth CABS glass/Al₂O₃ tapes crack free. A high-quality CABS glass/Al₂O₃ tape with a smooth surface was made from an aqueous slurry containing 1.5 wt% PVP dispersant, 2.0 wt% CMC binder, and 2.0 wt% PEG-400 plasticizer. The density, tensile strength, and surface roughness of the green tape were 2.05 g/cm³, 0.87 MPa, and 148 nm, respectively. The resulting CABS glass/Al₂O₃ composites sintered at 875 °C exhibited a bulk density of 3.14 g/cm³, a dielectric constant of 8.09, a dielectric loss of 1.0 × 10^?3, a flexural strength of 213 MPa, a thermal expansion coefficient of 5.30 ppm/^°C, and a thermal conductivity of 3.2 W m^?1 K^?1, thus demonstrating its broad prospects in LTCC applications.     

Porous asymmetric microfiltration membranes shaped by combined alumina freeze and tape casting

An assembled asymmetric alumina microfiltration membrane with high performance was prepared by combining freeze and tape casting techniques followed by two sintering steps. Freeze casting was used for manufacturing of the porous support layer with a highly interconnected pore network. Tape casting was applied on the top layer to form a pre-membrane with smaller pore size and controlled thickness, which was set on the sintered support. Morphology influences were investigated for different solid loadings, additives content and the assembled layer membrane structures. No delamination among the layers was observed. The assembled ceramic membrane had an average pore size between 30 and 50 μm together with a top surface layer around 0.35 μm, which is suitable to the microfiltration separation process. Porosity in the range of 26–50 % and water flux of 11–32 m³ m^?2 h^?1 bar^?1 were reached for samples prepared with two sintering steps at 1600 and 1300 °C for 2 h.     

Aqueous tape casting of B4C ceramics

B₄C green tapes are prepared by aqueous tape casting and a spark plasma sintering (SPS) process using polyethylenimine (PEI) as dispersant, hydroxypropyl methyl cellulose (HPMC) as binder and polyethylene glycol (PEG) as plasticiser. The influences of solid content, dispersant content, mass ratio of plasticiser to binder (R value) and milling time on the slurry viscosity are studied. The samples are characterised by means of hardness tester, universal testing machine and scanning electron microscopy. The results indicate that the solid content of B₄C slurry achieves 47.5?wt-% with milling time of 12?h when the content of PEI, HPMC and PEG is 1.5, 5 and 5?wt-%, respectively. The relative density of B₄C ceramics subject to SPS at 1600°C and 50?MPa for 8?min is up to 97.2%. The Vickers hardness, flexural strength and fracture toughness of B₄C ceramics reach 36.5?±?0.7?GPa, 510.3?±?19.4?MPa and 5.04?±?0.29?MPa?m^?1/2, respectively.     

Critical analysis of aqueous tape casting,sintering, and characterization of planar Yttria‐Stabilized Zirconia electrolytes for SOFC

Tape casting is an established forming technique for several industries, however, researches focus more on slurry composition. In this work, the combined use of design of experiment and materials characterization techniques showed tape casting process parameters have great influence on the microstructure and mechanical properties of green tapes. Formulation and processing optimization allowed obtaining YSZ green tapes with good mechanical characteristics and homogeneous microstructure without laminating step. The optimized sintering schedule and sintering load allowed obtaining planar electrolytes with high density, tensile strength, and electrical conductivity. This work provides an environmental friendly procedure for large‐scale production of SOFCs planar electrolytes.     

Properties of phyllosilicate-based porous ceramics shaped by conventional tape casting and freeze tape casting

Silicate ceramics were shaped using tape casting (TC) and freeze tape casting (FTC) processes from three clays labeled HCR, KORS, and KCR. These clays exhibited mass content of 77% halloysite–10 Å, 29% kaolinite, and 98% kaolinite minerals, respectively. After casting the slurries, the dried tapes were sintered at 1200°C. The microstructure changes were characterized before and after sintering using scanning electron microscopy. The apparent porosity of TC samples was lower (36–47 vol.%) compared to values obtained with FTC samples (67–79 vol.%). The latter samples exhibited a highly textured porosity, with micron-sized pores aligned perpendicular to the tape surfaces. Upon sintering, the porosity of TC samples tended to decrease conversely to the case of FTC samples. Such behavior seemed related to the simultaneous effect of organic additives and ice templating. Consequently, the FTC samples showed a relatively low mechanical strength of 3–7 MPa and thermal conductivity of .14– .22 W m⁻¹ K⁻¹. After sintering, the mullite crystallization contributed to strengthen the bulk materials, helping to compensate for the detrimental effect of porosity on the stress to rupture and on thermal conductivity values.     

流延法制备Ni-YSZ/YSZ复合基膜及性能测试

采用传统有机流延法制备NiO-YSZ/YSZ复合基膜,其中包括流延浆料配制及流延工艺过程.采用共烧结方式制备均匀平整的SOFC多孔阳极支撑的致密电解质膜,阳极支撑层厚度1000 μm、阳极功能层20 μm、致密电解质层40 μm左右.并对阳极孔隙率和电解质气体渗透率、显微结构及膨胀系数等进行测试.结果表明通过复合流延的方式可以制备出具有良好组织结构和性能的SOFC阳极支撑系统.     

Five-layer reverse tape casting of IT-SOFC

Tape casting is a well-established method for manufacturing thin ceramic layers with controllable thickness and porosity. This study investigates the potential of 10Sc1CeSZ material for the electrolyte and anode layers for intermediate-temperature solid oxide fuel cells (IT-SOFC) in an anode-supported cell (ASC) geometry. In order to use La_0.6Sr_0.4Co_0.2Fe_0.8 Oxide (LSCF) cathode material, a Gd_0.2Ce_0.8 Oxide (GDC) barrier layer is needed; however, thermal expansion coefficient mismatch results in delamination of the GDC from the electrolyte during high temperature sintering when fabricated by conventional tape casting procedures. For the first time, ASCs have been manufactured by a five-layer tape casting technique; barrier layer, novel composite layer, electrolyte, anode functional layer, and anode substrate. Ni-ScCeSZ composite cells were tested between 650 and 800°C in H₂:N₂ fuel (85% H₂) on the anode and air on the cathode to yield a maximum power density of .46 W/cm². These results demonstrate the feasibility of this new five-layer tape casting technique to produce IT-SOFC.     

Asymmetric porous cordierite ceramic membranes prepared by phase inversion tape casting and their desalination performance

Asymmetric porous cordierite ceramic membranes were fabricated by phase inversion tape casting method. It is shown that the membranes consist of a relatively dense skin layer on the top, a sponge layer at the bottom and a finger-like layer in the middle. The membranes have a hierarchical pore structure, where macrovoids (denoted as dozens-micron-sized (DMS) pores) are present in the finger-like layer and micron-sized (MS) pores are located in the skin layer, sponge layer and the wall of macrovoids. After surface silylation by post-grafting with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS), the sample with a starting powder/polyethersulfone (PESf) weight ratio of 9 (M − 4) becomes hydrophobic, with a water contact angle of 150°. At a NaCl concentration of 3.5 wt%, a feed rate of 18L/h and a feed temperature of 80 °C, the hydrophobic M − 4 membrane exhibits a water permeate flux of 22.33 kg/m²h, which is considerably larger than that of the membranes prepared by dry pressing method previously, and a salt rejection of 99.9%. The higher water permeate flux is attributed to the much lower transport resistance of water vapor in the membranes of the present work.     

Preparation of aluminum nitride green sheets by aqueous tape casting

Aluminum nitride green sheets were prepared by aqueous tape casting. The characteristics of a treated AlN were studied in aqueous ball-milling media. The oxygen content picked up with the increase of ball-milling time. It was noted that the oxygen content of AlN powder with the dispersant DP270 was lower than that of AlN powder without the dispersant DP270. The isoelectric points of the treated AlN with and without DP270 were, respectively, at pH 3.35 and pH 3.90. The dispersant DP270 not only efficiently dispersed AlN powder in water to form a stable suspension, but also formed a coat onto AlN surface to limit hydrolysis of the AlN powder. The tape casting slurry exhibited a typical shear-thinning behavior. Aqueous AlN green tape had a smooth surface and a narrow pore size distribution. Its relative density was 52.6%. No other crystalline phase was detected by XRD except for AlN and sintering aid yttria in AlN green sheet.     

Palygorskite sheets prepared via tape casting for wound healing applications

The main objective was to increase the applicability of palygorskite by palygorskite sheets using a tape casting method. The stability of the suspension was investigated and the tapes were characterized by TGA/DTA, XRD, and SEM-FEG. The antimicrobial activity was analyzed in order to test the applicability of a newly modified drug release system that incorporates neomycin in palygorskite. Preliminary results showed that the palygorskite sheet prepared via the tape casting is promising for wound healing applications.     

Porous Cu/YSZ anodes processed by aqueous tape casting for IT-SOFC

Porous copper/yttria-stabilized zirconia (Cu/YSZ) thin tapes were produced to be used as anodes in intermediate temperature solid oxide fuel cells (IT-SOFC). The use of copper in these cermets promises a better chemical resistance and a lower operating temperature for SOFC. Graphite and cassava starch were used as pore forming agents, which led to porosity values between 30 and 40%. Tapes were obtained by aqueous tape casting with controlled thickness (300–2000 μm). Before casting, CuO/YSZ aqueous suspensions were formulated based on rheological characterization. Sintering was carried out at 1150 °C during 1 h. Cu/YSZ tapes were obtained after redox reaction, performed at 400, 600 and 800 °C.     

Fabrication of Si3N4 ceramics substrates with high thermal conductivity by tape casting and gas pressure sintering

In this paper, high thermal conductivity Si₃N₄ ceramics were successfully fabricated through exploring and optimizing the tape casting process. The impact of various organic additives on the rheological characteristics of Si₃N₄ slurry was explored, and the pore size distribution and microstructure of the green tapes at different solid loadings were investigated, as well as the microstructure of Si₃N₄ ceramics. Green tapes with a narrow pore size distribution, a small average pore size, and a high density of 1.88 g cm⁻³ were prepared by the investigation and optimization of the Si₃N₄ slurry formulation. After gas pressure sintering, Si₃N₄ ceramics with a density of 3.23 g cm⁻³, dimensions of 78 mm × 78 mm, and a thickness of 0.55 mm were obtained. The microstructure of the Si₃N₄ ceramics showed a bimodal distribution and a low content of glassy phases. The thermal conductivity of the Si₃N₄ ceramics was 100.5 W m⁻¹ K⁻¹, the flexural strength was 735 ± 24 MPa, and the fracture toughness was 7.17 MPa m^1/2.     

Rheological properties of nanosized barium titanate prepared by HGRP for aqueous tape casting

The conditions for the preparation of stable nanosized barium titanate suspensions with high solids content for the production of aqueous tape casting are identified. The rheological behavior of colloidal barium titanate suspension with Ammonium polyacrylate (NH₄-PAA) as a dispersant to aid the powder dispersion has been investigated. Nanosized barium titanate powder was synthesized by a continuous high-gravity reactive preparation (HGRP) technique, and then annealed at 900 °C for 2 h. Measuring the zeta potential, the particle size distributions and ball-milling time, assessed the optimum conditions of the suspension with low viscosity and stability. An isoelectric point (IEP) at pH = 2.8 was found. Particle size distribution tests identified an optimum pH value about 10 and an optimum dispersant addition about 1.2 wt.% (based on the dry powder weight). As the ball-milling time was longer than 8 h, the amount NH₄-PAA adsorbed on the barium titanate reached to saturation. The maximum solid content attained during this work was 45 vol.% at pH of 10, with dispersant addition 1.2 wt.%. High green density value (up to ∼55.4% of the theoretical density) in BaTiO₃ sheet was achieved with a solid content 40 vol.%. After sintering at 1200 °C for 2 h a final density of 95% is reached.     

Optimization of non-aqueous tape casting of high solid loading slurry for aluminum nitride ceramic substrates

Aluminum nitride (AlN) ceramic substrates have been fabricated using non-aqueous tape casting and pressureless densification under flowing N₂ atmosphere. Considering the economic and environmental impact, a new strategy of solvent and dispersant system was adopted to prepare AlN slurries with high solid loading. According to the viscosity characteristics of AlN slurries, dispersant content was adjusted to be 0.5 wt% of AlN powder in order to optimize the rheological behavior of AlN slurries. The addition contents of binder and plasticizer were both optimized as 5 wt% of AlN powders by combining the viscosity of slurries and tensile strength of green tapes. Green AlN tapes were fabricated with an optimized tape casting process such as dry temperature. The exclusion process of organic additives was investigated by employing thermogravimetric analysis. Flat and dense AlN ceramic substrates with a relative bulk density over 99.75 % were achieved after being sintered under 1800°C for 6 hours, which had a maximum size of 110 × 110 mm. The thermal conductivity of the AlN substrate could reach 145 Wm⁻¹K⁻¹.     

Application of polypropylene carbonate for the tape casting of silicon nitride ceramics

QPAC40 (polypropylene carbonate), with a little decomposition residue, is commonly used as a binder in aluminum nitride (AlN) tape casting. In this paper, we tried to explore its application in silicon nitride (Si₃N₄) tape casting. By studying the influence of dispersant, binder, plasticizer/binder ratio, and solid loading on slurry and green tape properties, the optimum formulation of the tape casting of Si₃N₄ slurry was determined, and the green tape with a uniform structure and relative density up to 63.16% was prepared. Si₃N₄ ceramics were obtained by debinding at 600°C for 1 h in vacuum and gas-pressure sintering at 1830°C for 2 h in N₂. The thermal conductivity and flexural strength of Si₃N₄ ceramics were 56.28 ± 1.21 W/(m·K) and 1130.67 ± 23.58 MPa, respectively. These results indicated that QPAC40 can be used to prepare Si₃N₄ sheets through tape casting.     

Optimization of the tape casting process for the development of high performance silicon nitride substrate

In this paper, tape casting of Si₃N₄ substrate were investigated and optimized. The effects of dispersant content, binder, plasticizer/binder ratio, and solid loading on the green sheet properties were studied. An optimal formulation for the tape casting slurries was proposed, green tape with homogeneous microstructure and higher relative density of 56.08% was developed. After gas‐pressure sintering and annealing, Si₃N₄ substrate with a relative density of above 99% and thermal conductivity as 58 W/m/K was obtained. Results showed that the combination of tape casting and gas‐pressure sintering is feasible for the development of Si₃N₄ circuit substrates for power electronic devices.     

YAG ceramic processed by slip casting via aqueous slurries

Stable YAG (Y₃Al₅O₁₂) aqueous slurry with ammonium polyacrylate (NH₄PAA) polyelectrolytes as dispersant was prepared by ball mill method. The effects of polyelectrolyte concentration and pH value on the stability of the suspension is described here, and the stability maps are constructed at different pH value and polymer concentration. The rheological behavior of YAG slips of different solid loading (60–70%) has been studied by measuring their viscosity and shear stress as a function of shear rate and pH of the slurry. An optimal amount of dispersant and pH value for the suspension was found. YAG suspension displays a maximum in zeta potential values and a minimum viscosity in pH range of 9–11. Slips behaved as near Newtonian at the pH value up to a solid loading of 60 wt% and as non-Newtonian with thixotropic behaviors above this solid loading value. The density and the green as well as sintered microstructure of the cast products bear a direct relationship to the state of this slips induced by the alternation in the pH and the concentration of the dispersant as well as solid loading.     

The tape casting process for manufacturing low‐temperature co‐fired ceramic green sheets: A review

For low‐temperature co‐fired ceramic technology, the fabrication of high‐performance green sheet is a critical step because of its effect on subsequent operations such as punching, printing, laminating, and firing. Here, we present an overview of the tape casting process for manufacturing high‐performance low‐temperature co‐fired ceramic green sheets. Previous research is reviewed, and the primary materials for preparing the casting slurry, such as powders, solvents, dispersants, binders, and plasticizers, are systematically described. Their functions, application methods, and action mechanisms are described. Suggestions are made for future research into the tape casting process based on recent results.     

Microwave hybrid and conventional sintering of Al2O3 and Al2O3/ZrO2 multilayers fabricated by aqueous tape casting

In this study, microwave hybrid sintering and conventional sintering of Al₂O₃- and Al₂O₃/ZrO₂-laminated structures fabricated via aqueous tape casting were investigated. A combination of process temperature control rings and thermocouples was used to measure the sample surface temperatures more accurately. Microwave hybrid sintering caused higher densification and resulted in higher hardness in Al₂O₃ and Al₂O₃/ZrO₂ than in their conventionally sintered counterparts. The flexural strength of microwave-hybrid-sintered Al₂O₃/ZrO₂ was 70.9% higher than that of the conventionally sintered composite, despite a lower sintering temperature. The fracture toughness of the microwave-hybrid-sintered Al₂O₃ increased remarkably by 107.8% despite a decrease in the relative density when only 3 wt.% t-ZrO₂ was added. The fracture toughness of the microwave-hybrid-sintered Al₂O₃/ZrO₂ was significantly higher (247.7%) than that of the conventionally sintered composite. A higher particle coordination and voids elimination due to the tape casting and the lamination processes, the microwave effect, the stress-induced martensitic phase transformation, and the grain refinement phenomenon are regarded as the main reasons for the mentioned outcomes.