Jeong-Gu Yeo

Ion storage and energy recovery of a flow-electrode capacitive deionization process

The ion storage and extraction (or the ion charge and discharge) of a continuous capacitive deionization system were investigated using novel flow-electrode capacitive deionization (FCDI). The flow-electrode, charged by constant voltage, generated about 20% of the supplied energy in an FCDI cell during constant current discharge with NaCl solution (concentration: 35.0 g L−1).

Internal stresses in BaTiO3/Ni MLCCs

Abstract The internal stresses in BaTiO 3 based multilayer ceramic capacitors (MLCCs), showing Y5V characteristics, were estimated with a sharp indentation method using a micro-indenter. The influence of the direction to electrode on the internal stresses, especially residual stresses, was investigated at the three planes ( x , y , and z planes), including the effect of the distance from the electrode on hardness. Hardness is constant to a special distance from the electrode, depending on the plane, and modestly decreases above that distance. The internal stresses at the planes parallel to the electrode, x and y planes, indicate the compressive and tensile stresses in the directions parallel ( x and y directions at x and y planes, respectively) and perpendicular ( z direction) to the electrode, respectively. The internal stresses at the plane perpendicular to the electrode, z plane, are compressive in both directions. The extrinsic stress induced by the fabrication process is tensile, which is much severer than the intrinsic stress by the material constants. The internal stresses created on MLCCs are dependent on the plane with the lamination and the direction to the electrode, parallel and perpendicular directions. Crack formation and damage mode related to the internal stresses are also discussed.

Zirconia-stainless steel functionally graded material by tape casting

Abstract Ceramic/metal functionally graded material (FGM) was fabricated by tape casting. Zirconia (ZrO 2 ) and stainless steel (SUS) were stably dispersed in deionized water (DI-water). An optimal dispersion condition of ZrO 2 was obtained from electrokinetic sonic amplitude (ESA) data, and ZrO 2 particles could be dispersed by electrostatic repulsion. Conversely, a stable SUS slurry was prepared by increasing solution viscosity and using steric hindrance. Monophase and binary slurries were cast at uniform thickness through a doctor blade. ZrO 2 / SUS FGM was sintered at 1350 °C in Ar/H 2 atmosphere. The sintering defects could be controlled by the adjustment of the particle size and phase-type of ZrO 2 . As a consequence, the microstructure and interface showed a compositional gradient continuously.

Design and microstructure of ZrO2/SUS316 functionally graded materials by tape casting

Abstract Zirconia (ZrO 2 ) and stainless steel 316 (SUS316) functionally graded materials (FGM) were fabricated by tape casting from an aqueous system. For the stable dispersion of ZrO 2 and SUS316, we observed the zeta-potential ( ζ ) of each phase with pH variation and investigated the effect of organic additives on dispersion. Tetragonal zirconia polycrystals (TZP) and monoclinic zirconia polycrystals (MZP), which was used to control the shrinkage and sintering behaviors of TZP and SUS316, could be dispersed with addition of polymethacrylic acid (PMAA) as dispersant and SUS316 could be dispersed with carboxymethylcellulose sodium salt (Na–CMC) as suspending agent. Monophase and composite slurries were cast when the optimized conditions were established from the electrokinetic sonic amplitude (ESA) and viscosity data. ZrO 2 /SUS316 FGM was fabricated by sintering at 1350°C in Ar/H 2 atmosphere. As a consequence, the microstructure and the interface of the FGM showed the continuous compositional gradient. It was verified that the sintering defects, such as delamination, cracking and warping, can be reduced or eliminated by the adjustment of the particle size and the phase-type of ZrO 2 .

Flow-Electrode Capacitive Deionization Using an Aqueous Electrolyte with a High Salt Concentration

Flow-electrode capacitive deionization (FCDI) is novel capacitive deionization (CDI) technology that exhibits continuous deionization and a high desalting efficiency. A flow-electrode with high capacitance and low resistance is required for achieving an efficient FCDI system with low energy consumption. For developing high-performance flow-electrode, studies should be conducted considering porous materials, conductive additives, and electrolytes constituting the flow-electrode. Here, we evaluated the desalting performances of flow-electrodes with spherical activated carbon and aqueous electrolytes containing various concentrations of NaCl in the FCDI unit cell for confirming the effect of salt concentration on the electrolyte of a flow-electrode on desalting efficiency. We verified the necessity of a moderate amount of salt in the flow-electrode for compensating for the reduction in the performance of the flow-electrode, attributed to the resistance of water used as the electrolyte. Simultaneously, we confirmed the potential use of salt water with a high salt concentration, such as seawater, as an aqueous electrolyte for the flow-electrode.

Effects of PVB on the gelation behavior of BaTiO3-based dielectric particles and glass suspension

Abstract The effect of polyvinyl butyral (PVB) resins on the gelation behavior of the BaTiO 3 -based dielectric particles and borosilicate glass particulate suspensions was investigated in a system where organic solvents, dispersant, binder and gelation modifier were used as processing additives in a low temperature cofired ceramic fabrication processes. The strong flocculation, gels of the suspension without a modifier was attributed to the reaction and strong linkage between the boron in the borosilicate glass and the functional hydroxyl group of PVB resins, which was confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. When the butyral content of PVB employed in each slurry formulation diminish by approximately 8%, it caused the concentrated suspension to gel. The butyral content of PVB had a much greater impact on gelation than did the molecular weight of PVB. As the molecular weight of PVB was increased, the apparent viscosities of the slurries increased due to the broader chain length of higher molecular weight of PVB. According to the relative viscosity measurement results, both suspensions with high and low PVB molecules had similar viscosity values and it might be regarded as the more viscous feature of PVB polymer solution.

Dissolution and reprecipitation of barium at the particulate BaTiO3-aqueous solution interface

Abstract The electrokinetic behavior of BaTO 3 particles in an aqueous medium exhibited a hysteresis loop with titration direction. As BaTiO 3 suspension was titrated toward acidic pH, the amount of Ba 2+ dissolution strongly increased, and in the subsequent titration toward alkaline pH, Ba 2+ adsorbed and/or reprecipitated on the Ba-depleted BaTiO 3 surface. This dissolution–reprecipitation cycle results in the observed hysteresis behavior. An attempt was made to identify the responsible species of the adsorbed/reprecipitated compound by XPS in conjunction with electrokinetic titrations.

The role of 2-methyl-2,4-pentanediol modifier and its interaction with poly(vinyl butyral) binder in BaTiO3 and Li2O–B2O3–BaO–SiO2 glass suspensions

Abstract The role of the modifier, 2-methyl-2,4-pentanediol (MPD), and its interaction with poly(vinyl butyral) (PVB) binder with BaTiO 3 -based dielectric particles and Li 2 O–B 2 O 3 –BaO–SiO 2 glass suspensions were investigated using viscosity and adsorption isotherm measurements, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). Commercial MPD and PVB commonly serve as a modifier and binder, respectively, in organic suspension media in low-temperature cofired ceramic (LTCC) fabrication processes. In the absence of a modifier, a suspension prepared with PVB behaves as a highly viscous fluid that is readily flocculated to form a gel. This is due to the reaction of PVB hydroxyl groups with boron in the glass, as shown by FT-IR spectra. In suspensions prepared with MPD and PVB, the suspensions did not form a gel, and the BOH peak in FT-IR spectra disappeared. This is because PVB binder interacts with MPD modifier, and this interaction between the binder and the modifier affects the rheology of the suspension and combined adsorption of PVB and MPD. Sequential studies of viscosity and adsorption show that the flow behavior of the suspension was independent of the addition sequence, and was primarily dependent on the presence of the modifier with high affinity and the reaction of the modifier with the binder species.

Effect of Organic Processing Parameters in Non-aqueous Tape-casting on Dispersion Stability of Barium Titanate-Borosilicate Glass Based Suspensions

The effect of organic processing parameters on the dispersion stability of the BaTiO-based dielectric particles and borosilicate glass particulate suspensions was investigated in a system where organic solvents, dispersant, binder and modifier were used as processing additives in a low temperature cofired ceramic fabrication processes. Two- and three-component organic solvents were used to disperse ceramic particles and it was found the better stability in the particulate suspension prepared in a bi-solvent, which was consists of toluene and ethanol in a non-azeotropic composition. The addition amount of organic additives had a great impact on dispersion in the present investigation. The flow curves of the suspensions prepared with binder and modifier were fitted according to the power-law equation, which indicates that the internal structure of the suspension could be disturbed under the applied shear stress. Finally, the LTCC green tapes were successfully tape-cast based upon the optimum formulation of LTCC suspension and its microstructure was compared with that of the hard-agglomerates.