Non-aqueous Tape Casting Research Articles

Direct tape casting of Al2O3/AlN slurry for AlON transparent ceramic wafers via one-step reaction sintering

In this work, transparent aluminate oxynitride (AlON) ceramic wafers were successfully fabricated by the direct non-aqueous tape casting of Al2O3/AlN slurry and the one-step reaction sintering for the first time. The reaction sintered AlON ceramic wafer exhibits high transmittance of 73.2 % at the wavelength of 1600 nm. This fabricating route realizes smooth and flexible tape without cracks or pinholes in Al2O3/AlN system and efficiently shortens the preparation cycle of transparent AlON wafers, which is a feasible way to prepare high-quality transparent AlON ceramics with large lateral sizes and thin thicknesses by reaction sintering, might also promote the application of transparent AlON ceramic wafers.

Rapid fabrication of extremely thin Nano-Al2O3 transparent ceramic wafers through nonaqueous tape casting

Al2O3 transparent ceramics have important applications in electronics, solid-state lighting, military and 5G industries. At present, thin and large-size Al2O3 ceramics are urgently required by enterprises. Tape casting method has emerged as a powerful tool in producing transparent ceramics, but the preparation of the slurries is generally very time consuming. In this study, a one-step ball milling process was proposed to fabricate Al2O3 transparent ceramics through non-aqueous tape casting, in which green tapes were obtained with uniform texture and no distortion. Thickness of the Al2O3 transparent ceramics approached 0.1 mm. The effects of dry pressing on single and double-layer tapes were also compared. It was found that dry pressing has essentially no effect on monolayer samples, but contributed to improve the densification and promoted grain growth of the bilayer samples. Our results could be used as reference for the preparation of extremely thin Al2O3 transparent ceramic wafers.

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.

Preparation and characterization of sintered bioactive borate glass tape

Non-aqueous tape casting was used to prepare flexible green tapes from borate glass (1393B3) particles. The tapes were sintered at 550, 575, 600 °C: dense tapes were prepared at 600 °C. In-vitro bioactivity in simulated body fluid (SBF) of tapes sintered at different temperatures was evaluated. SEM, FTIR and XRD results showed slow degradation of dense borate glass tape in SBF compared to the non-dense tapes sintered at different temperatures. Formation of HCA (hydroxy carbonated apatite) on sample surfaces was confirmed after 7D in SBF.

Development of the Environmental Friendly Non-Aqueous Tape Casting Process for High-Quality Si3N4 Ceramic Substrates

A cheap and environmental friendly non-aqueous tape casting process for preparing high quality Si3N4 ceramic substrates was explored. A ternary solvent mixture of ethanol, ethyl acetate and butyl acetate-based formula was developed by using castor oil, polyvinyl butyral and dibutyl phthalate as the dispersant, binder and plasticizer, respectively. The influence of dispersant content, binder content and solid loading on the rheological properties of Si3N4 slurries was firstly investigated. It was found that the optimized formulation for dispersant, binder and solid loading was 1.6 wt%, 12 wt% and 51 wt%, respectively. The flat, flexible and uniform green tapes with a thickness of 400–500 μm and high-quality including high bulk density, uniform pore distribution and low porosity were obtained. After drying and debinding, the green sheets were sintered at 1900 °C for 2 h, where Si3N4 ceramics with a thermal conductivity being 85.79 W·m−1·K−1 can be achieved. The sintered samples were one of the most attractive substrate materials for high power electronics applications.

Pump coupling optimization of a native inhomogeneous planar waveguide laser

Abstract Planar waveguide laser is a promising candidate for high power solid state lasers. Normally the native inhomogeneous refractive index exists during fabrication process, this will apparently affect power scaling and beam quality. Few quantitative works have been reported to the optimization of this behavior and in practice, try and error routine is needed to set pump conditions. In this work, we manufactured a miniature composite Yb:YAG ceramic waveguide laser via non-aqueous tape casting method, refractivity index gradience is natively generated via border diffusion between the Yb:YAG and YAG layers. We found a simple and effective criterion to treat pump optimization by combining wave optics model and laser rate equations. Guided by this criterion, we obtained an experimental slope-efficiency about 66% with optimized pumping beam parameters. This method could be forward applied in similar designs and much higher power planar waveguide lasers.

Generation of 70 fs broadband pulses in a hybrid nonlinear amplification system with mode-locked Yb:YAG ceramic oscillator

We demonstrate the passively mode-locked laser performances of bulk Yb:YAG ceramic prepared by non-aqueous tape casting, which generates initial pulses in temporal width of 3 ps and spectrum width of 3 nm without intra-cavity dispersion management. The ceramic laser is further used as seeding oscillator in a fiber nonlinear amplification system, where ultrashort pulses in maximum output power of ∼100 W and pulse duration of 70 fs are achieved. Moreover, the laser spectrum is broadened to be ∼41 nm due to self-phase modulation effects in the gain fiber, overcoming the narrow spectrum limitations of ceramic materials. Our approach opens a new avenue for power-scaling and spectrum-expanding of femtosecond ceramic lasers.

Optimization of the tape casting slurries for high-quality zirconia substrates

A cheap and environmental friendly non-aqueous tape casting process for preparing high density ZrO2 ceramic substrates was explored. A binary solvent mixture of ethanol and ethyl acetate -based formula was developed by using castor oil, polyvinyl butyral and dibutyl phthalate as the dispersant, binder and plasticizer, respectively. The influence of dispersant content, binder content and solid loading on the rheological properties of ZrO2 slurries was firstly investigated. It was found that the optimized formulation for dispersant, binder and solid loading was 1wt%, 4wt% and 60wt%, respectively. The flat, flexible and uniform green tapes with a thickness of 200–280µm and high-quality including high bulk density, uniform pore distribution and low porosity were obtained. After drying and debinding, the green sheets were sintered at 1480℃ for 1h, where ZrO2 ceramics with a relative density of 98% and a dielectric constant being 32 can be achieved. The sintered samples could satisfy the use requirement of the fingerprint identification cover plate.

Demonstration and CW laser performances of composite YAG/Nd:LuAG/YAG transparent laser ceramic

Composite YAG/Nd:LuAG/YAG transparent ceramics with sandwich structure were fabricated by a non-aqueous tape casting method and vacuum solid-state sintering technology. The cations' (Y3+, Lu3+, Nd3+) diffusion behaviors across the contact interfaces between the pure YAG and Nd3+-doped LuAG layers were determined by Fick's second law. The refractive indices for various wavelengths were determined by fitting with an equation derived from Sellmeier's dispersion equation. Finally, CW laser performances under 808 nm diode-laser pumping were studied with two different ways of pumping, namely the perpendicularly and longitudinally pumping methods. For perpendicular pumping, the variation of CW laser output power with incident pump power was investigated, for which a maximum output power of 1.13 W was observed, whereas in the case of longitudinal pumping, the CW laser output power increased linearly with incident pump power and the opt-to-opt efficiency was estimated to be 0.4%.

Tape casting fabrication and properties of planar waveguide YAG/Yb:YAG/YAG transparent ceramics

Highly transparent YAG/10at.%Yb:YAG/YAG planar waveguide ceramics were fabricated by the non-aqueous tape casting and solid-state reactive sintering technology. The tapes are relatively homogeneous and the green body shows a dense structure without distinct interfaces after the treatment of debinding and cold isostatic pressing. YAG/10at.%Yb:YAG/YAG ceramics with almost full dense structure were obtained by vacuum-sintering at 1760 °C for 30 h. For the mirror-polished sample with the thickness of 3.5 mm, the In-line transmittance was measured to be 83.6% at the visual wavelength of 400 nm. The diffusion distance of the Yb3+ ions was about 215 μm along the thickness direction of the ceramics. In the lasing experiments, the YAG/10at.%Yb:YAG/YAG planar waveguide ceramics were end-pumped by a 976 nm semiconductor diode laser and enabled efficient continuous-wave lasers, which resulted in a maximum output power of 1.6 W and a slope efficiency of 34.4% at 1030 nm.

Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK−1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK−1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm−1K−1 (thermal conductivity of alumina is about 24.5 Wm−1K−1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates.

Ceramic planar waveguide laser of non-aqueous tape casting fabricated YAG/Yb:YAG/YAG.

Ceramic YAG/Yb:YAG/YAG planar waveguide lasers were realized on continuous-wave and mode-locked operations. The straight waveguide, fabricated by non-aqueous tape casting and solid state reactive sintering, enabled highly efficient diode-pumped waveguide continuous-wave laser with the slope efficiency of 66% and average output power of more than 3 W. The influence of the waveguide structure on the wavelength tunability was also experimentally investiccgated with a dispersive prism. Passively mode-locked operation of the ceramic waveguide laser was achieved by using a semiconductor saturable absorber mirror (SESAM), output 2.95 ps pulses with maximum power of 385 mW at the central wavelength of 1030 nm.

Preparation of B<sub>4</sub>C-ZrB<sub>2 </sub> Laminated Composites by Non-Aqueous Tape Casting and Hot-Press Sintering

B4C and ZrB2 ceramic tapes were prepared by non-aqueous tape casting with B4C and ZrB2 as main materials, xylene and n-butanol as binary solvent, castor oil as dispersant, polyvinyl butyral (PVB) as binder and dioctyl phthalate (DOP) as plasticizer. B4C-ZrB2 laminated composites were prepared by cutting, laminating, dumping and hot-press sintering. The experiment results indicated that ZrB2 ceramic tapes with high solid content of 48 wt.% could be prepared with 0.8 wt.% castor oil, 3.4 wt.% PVB and 6.8 wt.% DOP. Ceramic tapes have smooth surface, no crack and good ductility. B4C-ZrB2 laminated composites with high relative density of 97.8% were prepared by hot-press sintering under 2020°C sintering temperature, 30MPa pressure, 35 min hold temperature and pressure time. Their bending strength and fracture toughness were 488.6 MPa and 5.85 MPa·m1/2 respectively.

Spectral and Laser Properties of Yb:LuAG Transparent Ceramics Fabricated by Tape Casting Method

Yb3+‐doped LuAG laser ceramics with different Yb3+‐doping concentrations were successfully fabricated by nonaqueous tape casting method and vacuum sintering technology. XRD patterns and SEM morphologies of the ceramics were presented. The optical in‐line transmittance of the Yb‐doped LuAG ceramics was about 83% at 1030 nm. The fluorescence lifetime of annealed and unannealed ceramic samples was compared. From the spectroscopic properties, it can be seen that the ceramics had a large emission cross section of 2.9 × 10−20 cm2 with a FWHM of about 7.2 nm at 1030 nm. Under 100% population inversion, the maximum gain coefficient was estimated to be 12.4 cm−1 at 1030 nm. With a fiber‐coupled diode laser as pump source, CW laser at 1030 nm was demonstrated and the maximum output power of 338.9 mW was achieved with a slop efficiency of 19%. A tuning range from 1028 to 1036 nm was obtained.

Diode-pumped tape casting planar waveguide YAG/Tm:YAG/YAG ceramic laser at 201376 nm

We demonstrated the efficient guided laser action in a diode-pumped YAG/Tm:YAG/YAG ceramic planar waveguide fabricated by nonaqueous tape casting and solid-state reactive sintering technology for the first time, to the best of our knowledge. In the experiment, a maximum output power of 173 mW at a center wavelength of 2013.76 nm was obtained under an incident pump power of 10.3 W, corresponding to a slope efficiency of 3.0%. The beam quality M2=1.5 in a horizontal direction was measured at the highest output power.

Diode-pumped composite ceramic Nd:YAG planar waveguide amplifier with 327 mJ output at 100 Hz repetition rate

We present a diode-pumped high-energy ceramic Nd:YAG planar waveguide that is demonstrated as a record in output energy for the ceramic planar waveguide fabricated by nonaqueous tape casting and solid-state reactive sintering. Under a repetition rate of 100 Hz and a pulse width of 250 μs, a maximum output pulse energy of 327 mJ is obtained with a beam quality factor of =2.6×7.0. The corresponding peak power is 1308 W. The extraction efficiency of the system is about 56%.

Properties of compositionally graded (1−x)(Bi0.85La0.15)FeO3-xPbTiO3 ceramics fabricated by tape casting

Three types of (1−x)(Bi0.85La0.15)FeO3-xPbTiO3 (BLF–PT) compositionally graded ceramics (x = 0.38, 0.40, 0.415 and 0.43) were fabricated using a lamination process based on the non-aqueous tape casting method. Scanning electron microscope images showed that the compositionally graded ceramics possessed dense microstructures without obvious cracks. The dielectric, ferroelectric and piezoelectric properties of the BLF–PT ceramics were sensitive to the composition distributions in the thickness direction. The BLF–PT ceramics with monotonic variation of PT content (in the thickness direction) exhibited the best piezoelectric properties. The tip displacement of compositionally graded piezoelectric ceramics reached up to ∼13.5 μm, which is about ten times higher than that of BLF–PT ceramics with single composition.

Investigation of the (1−x)(Bi0.85La0.15)FeO3–xPbTiO3 multilayered ceramics by tape casting

The compositionally graded (Bi0.85La0.15)FeO3–PbTiO3 (BLF–PT) multilayered ceramics were fabricated by a lamination process based on a non-aqueous tape casting method. For the multilayered structure, the PbTiO3 content reveals a monotonously increased from the composite on side to the other. Specimens exhibited a mixed phase structure and dense microstructures. The dielectric, ferroelectric properties and field-induced strain of the samples were systematically investigated. The results showed that the compositionally graded BLF–PT ceramics had homogenized dielectric constant, loss, remnant polarization but enhanced field-induced strain of 0.3% at 60kV/cm, 1Hz.

Comparison of aqueous and non-aqueous tape casting of fully stabilized ZrO2 suspensions

Laminated and subsequently sintered samples were prepared via aqueous (W_YSZ) and non-aqueous (E_YSZ) tape casting technique from fully stabilized zirconia ceramic powder. Preparation conditions optimised for the E_YSZ were implemented in a varied form to the W_YSZ and compared with each other. Namely the homogenisation time, rheological behaviour and density of the prepared green and sintered samples were investigated and described. Fully sintered samples with ~99.5% of theoretical density after sintering were prepared from 15 sheets pressed together via ethanol based suspension. The water based process leads to ~54.9% and 94.2% of theoretical density after lamination and sintering, respectively. The SEM analysis of the green sheets provides an evidence of entrapped air bubbles in both systems. For the W_YSZ it was ~0.7μm diameter and ≤0.2μm by E_YSZ, which was the reason of differences in obtained final densities of prepared materials.

Continuous-wave laser performance of non-aqueous tape casting fabricated Yb:YAG ceramics

We report on the continuous-wave and tunable laser operation of a transparent Yb:YAG ceramic which is prepared by non-aqueous tape casting method with vacuum sintering at 1750 °C for 10 h. The Yb:YAG ceramic is dense and with excellent optical in-line transmittance characteristics. In the lasing experiment, the Yb:YAG is end-pumped by a high-brightness 974 nm diode pump in fiber core of 50 μm and numerical aperture of 0.22, which results in a maximum output power of 7.01 W and a slope efficiency of 60.2% at 1050 nm. A smooth tunable curve from 1022 nm to 1058 nm is achieved in tunable laser testing, revealing the broadband lasing spectra over 30 nm.