Aqueous Tape Casting Process Research Articles

Free-Standing Garnet-Type Solid Electrolyte Separators Fabricated By Water-Based Tape-Casting

The garnet-type Li-ion-conductor Li7La3Zr2O12 (LLZO) is regarded as a promising oxide-ceramic based solid electrolyte (SE) material for all-solid-state lithium ion battery (Li-ASB) owing to its wide electrochemical stability window, chemical stability versus Li metal and excellent conductivity. However, one of the challenges regarding the fabrication of such ASBs is the industrial scalability of manufacturing methods. Tape-casting of ceramic components is known e.g. from SOFC manufacturing to enable the large-scale production of free-standing ceramic components and cells with low thickness. Additionally, in conventional tape-casting, organic solvents are usually employed, which give rise to health and safety issues and lead to high cost for solvent recovery. Hence, development of a green, water-based processing route is favorable.Herein, we report an aqueous tape-casting process of LLZO separators using a water-soluble biopolymer as binder. A lattice expansion of LLZO is observed by X-ray diffraction in aqueous green tape due to the partial replacement of Li+ by H+, whereas the lattice parameter of LLZO in sintered sheet decreases to the same value of pristine LLZO powder, indicating the Li-recovery in the LLZO structure after sintering. This observation confirms that the Li+/H+-exchange reaction is reversible during the aqueous processing. The obtained free-standing LLZO sheet after sintering shows high ionic conductivity observed by impedance spectrometry in Li/LLZO/Li symmetric cell at room temperature, which is comparable with reported thin garnet separators fabricated by conventional non-aqueous tape-casting.In summary, we successfully fabricate self-supporting LLZO sheet with high ionic conductivity by aqueous tape-casting process, which is enabled by reversible Li+/H+-exchange. This free-standing LLZO sheet can be later used as separator in the Li-ASBs having an electrolyte-supported configuration.

Optimization of Lithium Content and Sintering Additives in Tape Cast Lithium Garnet Electrolyte Sheets

The lithium garnet (LLZO) remains one of the most promising electrolyte materials for producing solid state batteries. Tape casting is one method for producing the thin ceramic electrolyte layer required for a high-performance solid state battery. Processing of LLZO is complicated by several factors including lithium volatilization, abnormal grain growth and phase instability. Many of these issues are exacerbated in tape cast sheets by the sheets’ higher surface area to volume ratio, when compared to pellet processing methods. We report on an environmentally friendly aqueous tape casting process for LLZO using methylcellulose as a binder and compare final sheet properties to other, solvent-based, options. Solids loading, binder content, dispersant composition, and wetting agent type are varied to improve ease of casting and enhance properties of the as-cast tape. Lithium content in sintered LLZO sheets is controlled by the inclusion of excess Li2CO3 as lithium source in the ceramic tape itself and by a novel method of producing a lithium-saturated furnace atmosphere. Sintering time and temperature are optimized, and rapid thermal processing is investigated as a method of reducing lithium loss. Al2O3 and MgO are examined for use as sintering additives. Characterization of LLZO sheets is performed with XRD, EIS and SEM. Li2CO3 and sintering additive levels are optimized for ionic conductivity and density. The optimization effort improved the conductivity and density of 100µm thick sintered sheets to greater than 3x10-4 S/cm conductivity and 90% density. Figure 1

Optimal Conditions for Aqueous Tape Casting of Hydroxyapatite

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.

Effect of Bismuth Oxide as Sintering Aid for Gadolinia-doped Ceria at 1050°C

Dense GDC electrolytes can work as high ion-conducting material for innovative IT-SOFCs. These electrolytes will be used as a base to develop sulfur resistant anodes using copper oxide and GDC, in order to avoid the use of nickel oxide. An aqueous tape casting process to produce dense gadolinia-doped ceria (GDC) electrolyte was developed. The study developed in three main steps. First, the dispersant concentration was idealized for slurries consisting of only distilled water, an ammonium polyacrylate (PAA) dispersant and ceramic powder (commercial Ce0.9Gd0.1O1.95). By examining the rheological behavior of the slurry, the ideal ratio between the active part of dispersant and powder surface was found to be between 0.15 and 0.30 mg/m2 . Second, starting with the dispersed slurry, fixed amounts of acrylic binder and plasticizer were added and the pH was varied in order to identify the optimum pH interval in which the suspension is stable and no agglomerates form. The ideal pH was found to be between 8 and 9. Finally, the amounts of binder and plasticizer were varied and the suspensions were tape casted (thickness 200 µm) to produce a defect free, smooth and high relative green density (about 50%) tape. SEM observations of samples sintered at 1500 °C showed satisfactory dense section profile (about 95%). Figure 1

A route to increase fracture toughness of layered Si3N4/SiC composite using interlocked interfaces

Multilayer Si3N4/SiC composite with interwoven interfaces was designed and prepared via the aqueous tape casting and gas pressure sintering process. This composite had relatively uniform layer thickness, high strength (~564MPa), toughness (~16.8MPam1/2) and work-of-fracture (~4411J/m2). The first-level toughening mechanism started from the fracture surface of the multilayer composite. Obvious crack deflection was found in the Si3N4 and SiC layers. At the same time, the pullout and fractured rodlike β-Si3N4 grains were detected along the interfaces of the composite. The growth of the rodlike β-Si3N4 grains (the grain size>50μm) along the interfaces was determined by the vapor phase transport mechanism. Both rich SiO2 on the surfaces of the SiC/Si3N4 particles and high porosity of the SiC layers were contributed to the growth of β-Si3N4 grains.

Aqueous tape casting and mechanical properties of La2NiO4+δ dense membranes

An environmentally friendly aqueous tape casting process for the fabrication of La 2 NiO 4+ δ membranes was developed using fine powders synthesized by spray pyrolysis. Green tapes with a thickness of 30–300 μm were obtained and dense and homogeneous membranes were prepared by lamination of green tapes followed by sintering in the temperature range 1300–1420 °C. The bi-axial fracture strength of the sintered materials increased from ∼108 to ∼155 MPa decreasing the average grain size of the membranes from about 9.6 to 4.2 μm. The hardness and fracture toughness, measured by the Vickers indentation technique, also decreased with increasing grain size. The mechanical properties of La 2 NiO 4+ δ ceramics are discussed with focus on micro-cracking/residual stresses due to the strong crystallographic anisotropy of La 2 NiO 4+ δ .

Aqueous tape casting of boron carbide ceramic

An environmental friendly aqueous tape casting process has been introduced to fabricate B4C green tapes. Tetramethylammonium hydroxide (TMAH) and a mixture of waterborne epoxy emulsions and anionic aliphatic urethanes emulsions were selected as the dispersant and binder, respectively. The influence of pH value on the zeta potential of ceramic suspensions has been investigated, and the dispersant content added has been optimized based on the rheological behaviors of B4C slurries. The green sheets showed homogeneous microstructure with high flexibility and enough strength for the subsequent cutting and lamination. After sintering at 2100°C, dense B4C ceramics can be achieved. The relative density and the flexural strength of the sintered samples were 96.8% and 636±70MPa, respectively.

Preparation of Thin Cordierite Sheets by Aqueous Tape Casting

Aqueous tape casting process was used to prepare the thin cordierite sheets, the influences of dispersant (PAAS), the rate of plasticizer (PEG),and binder (PVA),content (R) and drying temperature on the tape casting process were investigated, the sintering character of the sheets were studied after drying. It was showed that when the content of PAAS was 1wt%, the slurries were stable uniform and the shear thinning was reversible. The green sheets with the thickness of 177μm showed good flexibility, lubricious surface and compact microstructure when R was 0.7 and the drying temperature was 25°C. A compact α-cordierite sheet was obtained at 1000°Csintering for 2h.

수계 테이프 케스팅 법에 의한 봉상 γ-LiAlO2입자 강화 MCFC 매트릭스 제조 공정의 최적화

Rod-shaped particle reinforced LiAlO₂ matrices for MCFC were fabricated by an aqueous tape-casting technique. The hydrolysis reaction and agglomeration of γ-LiAlO₂ particles in aqueous slurries were inhibited by additions of LiOH·H₂O and glycerin to the aqueous γ-LiAlO₂ slurry. The tape-casting, performed using the aqueous slurry containing protein albumin, was fast and led to an effective drying at casting temperature range of 60~65℃. The strength of the particle reinforced matrix was improved about 4 times compared to that of matrix without reinforcement. Pore size distribution (0.1~0.4 ㎛) and porosity (50~60%) of the reinforced matrices were determined to be appropriate for the MCFC matrix. The aqueous tape casting process is not only environmental-friendly but also efficient for fabricating MCFC matrices compared to non-aqueous tape casting.

Aqueous tape casting process for SiC

The condition for the preparation of stable SiC slurries by aqueous tape casting was identified. To acquire stable uniform slurries, the influences of dispersant, solid loading, sintering additives, binder and plasticizer on the rheological properties and viscosity were investigated. The conditions for preparing stable SiC slurries were studied and optimized. After tape casting and drying, the green SiC sheets showed smooth surface and homogeneous microstructure. The SiC ceramic can be densified to 98.89% after hot-pressing at 1850 °C (at 25 MPa in Ar for 30 min). The flexural strength, hardness, and toughness are 779.5 ± 39.2 MPa, 21.51 ± 0.70 GPa and 5.54 ± 0.26 MPa m 1/2, respectively. SEM shows a fine microstructure with few pores in the sintered samples. The fracture surface exhibited predominantly intergranular fracture type.

Preparation of the Pb(Mg 1/3Nb 2/3)O 3 films by aqueous tape casting

Lead magnesium niobate (PMN) is a relaxor ferroelectric material. Because of its high dielectric constant and superior electrostrictive properties it is commonly used in the manufacture of multilayer electronic devices which is typically produced by tape casting. However, preparation of PMN slurry formulations to use in aqueous tape casting process is not investigated in detail yet. Therefore, in this study aqueous PMN formulations were developed for tape casting and its relation with the final properties of PMN films were investigated. The slurries were prepared using poly(acrylic acid)-based comb polymer as the dispersant, nonionic acrylic latex as the binder and the hydroxypropyl methyl cellulose as the wetting agent. The results showed that it is possible to prepare flexible, crack-free PMN films using highly concentrated suspensions without using any plasticizer. The study gives guidelines for the aqueous tape casting of PMN and can be adapted to processing of other multi-component metal oxides.

Fabrication and characterization of Li1+x−yNb1−x−3yTix+4yO3 substrates using aqueous tape casting process

An aqueous system for tape casting Li1+x−yNb1−x−3yTix+4yO3 (LNT) ceramics was developed using poly(vinyl alcohol) (PVA) binder, ethylene alcohol (EG) plasticizer and ammonium salt of polycarboxylate (PCA-NH4) dispersant. The zeta potential measurement showed that the isoelectric point of the LNT particles moved slightly toward more acid region after the dispersant absorbed on the particles, while the zeta potential increased significantly. The rheological test indicated that the ceramic slurry exhibited a typical pseudoplastic behavior without thixotropy. The effect of solid loading on the properties of the green tapes was investigated. The increase in the solid loading increased the tensile strength and the green density of the tapes. TGA analysis indicated that the organic additives in the green tapes can be completely removed by heat treatment at 600 °C. SEM micrographs showed that the microstructure of the green and sintered tapes was homogeneous.

Production of cordierite ceramic by aqueous tape casting process

Tape-casting process was used to produce cordierite ceramics in an aqueous system with polyvinylalcohol (PVA), and polyethyleneglicol (PEG), as binder and plasticizer, respectively. Before starting to tape-casting studies, optimum amount of sodium tripolyphosphate (STPP, Na 5 P 3 O 10 ) was used by sedimentation method for dispersing the powders. The sedimentation of raw materials (Kaolin, Al 2 O 3 and Talc) with STPP, as a dispersant for 20 wt.% solid content was performed. Various tape slips with different solid content (50–55–60 wt.%) and 10–12 wt.% PEG + PVA were prepared. The influence of the solid content on the rheological properties of slips and the resultant green tapes were studied. The increase in the PVA + PEG content deteriorated the slip properties and fostered the formation of bubbles in the slip. In addition, the properties of the sintered tapes were investigated. The slip composition, 10 wt.% PVA + PEG for 55 wt.% solid content produced green tapes with good surface properties and flexibility that had higher sintered density.

Aqueous tape casting process for hydroxyapatite

The condition for the preparation of stable hydroxyapaptite (HA) slurries by aqueous tape casting was identified. To acquire stable low-viscosity slurries, the influences of dispersant, binder and plasticizer on the rheological properties were investigated. The slurries of submicron sized HA behaved as near Newtonian up to a solid loading of 56.1 vol%. Films of HA had very good qualities, such as homogeneity, surface quality, and so on. Results indicated that slurries at selected conditions met the needs of tape casting process.

Reactivity and diffusion between La 0.8Sr 0.2MnO 3 and ZrO 2 at interfaces in SOFC cores by TEM analyses on FIB samples

In this paper, we investigate the diffusion and reactivity at the interface between the electrolyte (YSZ) and the cathode (LSM) of planar SOFC single cells by Analytical and High Resolution Transmission Microscopy. Cells were obtained via an aqueous tape-casting process allowing casting the three layers (cathode, electrolyte, anode [Ni-YSZ]) in a single operation. To allow the cell to function at intermediate temperatures (750–850 °C), the final electrolyte thickness after co-sintering at 1350 °C must range between 40 μm and 50 μm. As-sintered cells as well as cells that have been operated at 850 °C have been considered here; it is shown that the electrical performances were one order of magnitude less than expected and that they deteriorated quickly under operating conditions. In order to explain this behavior, we carried out analytical transmission electron microcopy. To obtain precisely located chemical and structural information, we used the “H-Shape” as well as the Lift Out FIB (Focused Ion Beam) techniques to extract 5 × 10 × 0.1 μm TEM samples; additional High Resolution characterization was carried out at interfaces between LSM and YSZ grains on standard ion-milled samples. We showed that the co-sintering temperature (1350 °C) was responsible for some diffusion of manganese through the electrolyte and the cathode, leading then to the rise of a significant electronic conduction and to the drop off of the ionic conductivity, and accounts for the germination and growth of the resistive pyrochlore phase La 2Zr 2O 7. Operating the cell at 850 °C do not aggravate these phenomena, but rather alters the anode microstructure.

Aqueous tape casting of 10 mol%-Gd 2O 3-doped CeO 2 nano-particles

The aqueous tape casting process was systematically developed and investigated for the tape casting of 10 mol%-Gd 2O 3-doped CeO 2 nano-particles. This study focused on obtaining the optimum slurry formulations and on the effects of the processing parameters such as the stability, the rheology and the wetting properties on the tape characteristics. High solid loading (55 vol.%) and stable slurries of 10GDC nano-particles were achieved using poly(acrylic acid) (PAA) as a dispersant; poly(vinyl alcohol) (PVA) as a binder; poly(ethylene glycol) (PEG) as a plasticizer; octanol as a defoamer and 2,4,7,9-tetramethyl-5-decyne-4,7-diol ethoxylate as a surfactant. The pH values of the slurries were maintained in the range of 9.0–10.0. Homogeneous, defect-free green tapes (thickness 150–200 μm) with smooth surface and high relative green density (51.5%) were thus successfully obtained.

Aqueous tape casting process with styrene-acrylic latex binder

A commercial styrene-acrylic latex binder has been investigated as a good binder for aqueous Al2O3 suspensions tape-casting process. This paper focuses on the forming film mechanism of latex binder, the rheological behaviors of the suspensions, physical properties of green tapes and drying process of aqueous slurries with latex binder system. The drying process of the alumina suspensions is shown to follow a two-stage mechanism (the first stage: evoporation controlled process; and the second stage: diffusion controlled process). During the drying stage of the suspensions, the compressive force presses the latex particles and makes them be distorted, which results in cross-linking structure in contacted latex particles of the solidified tapes. A smooth-surface and high-strength green tape was fabricated by aqueous tape casting with latex binder system. The results from the SEM images of the crossing section microstructure of green tapes show that the latex is a very suitable binder for aqueous tape casting.

Guidelines for the Scale-Up of an Aqueous Ceramic Process: a Case Study of Statistical Process Control

Process-scale up is the change from a feasibility study in a laboratory to a full-scale prototype production process. It is an important issue for the ceramics industry, but has been the subject of relatively little systematic research. This paper will show how certain manufacturing concepts used in a number of industries - can be applied to the scale up of a feasibility study level, aqueous tape casting process. In particular, it examines the elements of process standardisation using the example of the Statistical Process Control (SPC) technique applied to a sub process of an aqueous powder process. It illustrates that these elements are an essential step in moving from conceptual design to the process prototype.

Aqueous processing of SiC green sheets II: Binder and plasticizer

Well-dispersed SiC slurries in the presence of binder and plasticizer were prepared and investigated in this series of work. In this part, poly(vinyl alcohol) (PVA) 1788 was investigated as a potential binder for aqueous tape casting process. The minimum amount of binder was determined through a primary calculation. Effects of the binder on SiC slurries properties were analyzed in term of zeta potential measurement and rheological test. Coupled with PEI as dispersant and glycerol as plasticizer, they lead to homogeneous systems which seem compatible. The suspensions (formulated with 47.9 wt% SiC powder, 1 wt% dispersant, 3.5 wt% binder, and 3.5 wt% plasticizer) exhibited a shear-thinning behavior with a very limited time-dependent character. After tape casting and drying process, the properties of green tapes were evaluated in term of solid content and gap height. The optimal solid content of SiC was found to be near 22.25 vol%, and the gap height, near 200 μm. The microstructure of green tape was characterized by TEM. Results showed that preparation of homogeneous green tapes with relative densities at about 51 vol% was feasible.

Influence of slip preparation and casting conditions on aqueous tape casting of Al 2O 3

In this work the influence of the slip preparation on manufacturing alumina tapes through an aqueous tape-casting process is studied. For this purpose deflocculated slips with 80 to 87 wt% of solids have been prepared and rheologically characterized. Ceramic tapes were produced following two different preparation routes, (1) starting from deflocculated suspensions with a fixed final solid concentration of 80 wt% after binders addition, and (2) starting from deflocculated slips with 84 wt% solid loading to produce tape casting slurries with different final solid concentration after binders addition. A mixture of two acrylic emulsions with different T g values has been used as binding system with total concentrations of 10, 15, and 20 wt% with respect to solids. It has been found that tapes produced by route 1 have a maximum green density (56% of theoretical density) when adding 15 wt% of binder system and 95% of relative final density, while tapes produced by route 2 give a similar relative green density (∼58.5% Th.) for any binder system additions. The final density of tapes obtained from route 2 have a maximum density of 97% for slips with 15 wt% of binder system. Additionally, the influence of tape casting parameters on green and final density was also studied. From this it was found that it is possible to increase the green density values from 60 to 62% and from 97 to 98% for fired density from tapes which were cast at 400 μm gap and 5 mm/s.