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Ceramic cores are essential for manufacturing hollow mechanical parts, such as impellers and blades, in the casting process. High temperature heat treatment, which causes dimensional deformation and breakage, is required to reveal the effective strength of ceramic cores. Therefore, in this study, a new 3D printing-based process, combined with an organic-inorganic binder conversion process, is proposed to fabricate a ceramic core with high dimensional stability using dual polymers with different chemical properties. The ceramic core was prepared using an extrusion-type 3D printer with a slurry prepared by mixing a starting powder with hydrophilic and hydrophobic polymers. The extruded samples molded from the heterogeneous polymers were immersed in water at 60 °C for 3 min to remove the hydrophilic polymer to create space for impregnating an inorganic binder. The core samples were then dipped in an inorganic binder solution composed of tetraethyl orthosilicate and sodium methoxide and then dried at 80 °C for 1h, followed by a heat treatment at 1000 °C for 1h. Using dual polymers, the amount of inorganic binder coating converted into the glass phase during heat treatment was increased, which resulted in improved core strength. These results confirm that the dual polymer can be used to manufacture ceramic cores with excellent dimensional stability and firing strength through 3D printing combined with the organic-inorganic binder conversion process.

3D printing technologies using photo polymerization of photo-curable monomer and oligomers as an organic binder have been studied to fabricate ceramics with a complicated shape. For minimizing distortion of ceramics during the manufacturing process and fast 3D printing of ceramic green body, high mechanical strength of ceramic green body and fast photo polymerization of the photo-curable resin are required, respectively. In this study, the ceramic green bodies with various compositions were fabricated by photo radical polymerization of the slurry-type resin composed of fused silica bead, and tri- or (and) mono-functional acrylate. Photo radical polymerization behaviors of mono-, tri-functional acrylate monomer, and blend of two monomers were analyzed by photo-DSC and FT-IR measurements. The structure analysis of photo-cured polymers made by each monomer was performed by thermo-mechanical analysis. Through mixing of mono- and tri-functional acrylate monomer, we confirmed that polymerization rate more increased compared with those of only mono-, tri-functional monomer. Unreacted vinyl groups in the polymers prepared with blend of two monomers decreased by an addition of mono-functional monomer in tri-functional monomer. The polymers prepared with the blend showed higher storage modulus and broader viscoelastic behavior compared to those fabricated with tri-functional monomer. Thus, to achieve high fracture strength of the green body, we verified that the photo-cured polymer in the green body should have high crosslinking density and low free volume based on reduction of unreacted vinyl groups in the polymer. Additionally, through analysis of cross-sectional SEM of the green body, we confirmed that acrylate monomer should include proper content in the slurry-type resin to maximize the fracture strength of the body regardless of the type of the used acrylate monomer. This was because low content of acrylate monomer in the slurry-type resin makes it difficult to form neckings composed with photo-cured polymers between the silica beads.

A ceramic core employed in a single-crystal casting process should endure for a long time at casting temperatures above 1500 °C. Therefore, in this work, an inorganic binder was applied to a conventional injection-molding method to produce a core having enough strength during the casting process. The starting powders for the ceramic core used a mixture of three kinds of fused silica with particle sizes of 117 μm, 33 μm, and 17 μm, zircon flour of 10 μm, and silicon carbide of 16 μm. The mixed ceramic powder was coated with a silica precursor and then dried at 80 °C for 1 h. The dried powder was mixed with wax and injection molded. The injected ceramic core was heat-treated at 1200 and 1500 °C for 1 h,and then reheated at 1550 °C for 3 h. The heat treatment at 1550 °C was conducted to investigate the applicability of the core coated with the inorganic binder in the casting process. The inorganic binder-coated core with a superior firing strength had no cracks or surface defects after the heat treatment, compared with the core without the inorganic binder. In addition, the turbine blade of 150 mm length was well cast as a single crystal and the internal core was completely eluted.

In a large-scale reverse electrodialysis (RED) system comprising several hundreds of cell pairs, the contribution of electrode resistance to total resistance is very small compared to that in typical electrochemical cells (e.g., fuel cell and battery). This feature indicates the low susceptibility to both electrocatalytic ability of the electrode and solution conductivity, and to the geometrical area of the electrode as well. Therefore, in this work, we introduce an asymmetrical electrode system, where the geometrical area of the cathode is smaller than that of the anode. Since the cathode is highly vulnerable to significant inorganic scaling due to the high pH conditions during water reduction and crossover of multivalent ions in the natural feed solution, it is expected that minimizing the contact area between the electrode and feed solution by reducing the geometrical area of the cathode can afford more stable electrode reaction and electric power during long-term operation of RED. We measured the changes in electric power as a function of various areas of the cathode in lab- (100 cell pairs) and large-scale (1000 cell pairs) RED systems, which confirmed that even though the cathode area corresponds to 60% of the individual area of the ion-exchange membrane (IEM), the maximum power was obtained with only 3% power loss. In addition, the surface properties and permselectivity of a shielding membrane at the cathode were analyzed by X-ray photoelectron spectroscopy (XPS) and membrane potential measurement to verify the stability of the IEM under higher current density. We recommend the use of the asymmetric electrode system with a bipolar membrane (BPM) to suppress inorganic scaling around the cathode. The high current density achieved by reducing the size of the cathode can induce vigorous water splitting in the BPM, which leads to more effective blocking crossover of the multivalent and hydroxide ions. It can hence be used to design a highly stable electrode system for the long-term operation of a pilot-scale RED system fed with natural feed solutions.

Pore-filling ion exchange membranes are fabricated by complicated and energy-inefficient processes, use of large amounts of polar organic solvents, and optionally post-modification using acid or base. For green fabrication of pore-filling anion exchange membranes (PAEMs), we optimized the process parameters such as pretreatment time, impregnation time, water amount, and photo-polymerization rate of each step using roll to roll (R2R) equipment. Based on these optimized process parameters, a PAEM of 57.5 cm width and 39 μm thickness completely filled with a photo-cured electrolyte polymer was fabricated by aqueous pretreatment and by using an impregnation solution without toxic organic solvents. The impregnation step was conducted along with photo-polymerization at a line speed of 0.3 m/min without repeated impregnation with R2R equipment. The IEC, resistance, and permselectivity of this PAEM were similar to those of handmade PAEMs. The PAEM exhibited chemical stability in the pH range of 0–12. In addition, the reverse electrodialysis stack assembled with these PAEMs exhibited a higher power density than a stack of commercial ion exchange membranes. These results demonstrate that industrial-scale PAEM can be fabricated through a rapid, simple, environmentally friendly, and energy-efficient R2R process.

It is generally accepted that the effect of electrode resistance is not predominant in determining the performance of reverse electrodialysis (RED), because the contribution of electrode resistance to total internal resistance decreases as the number of cell pairs increases. However, this is not true under the condition in which gas is continuously produced by water electrolysis owing to the large stack voltage in pilot-scale applications. We verified that the bubble resistance of the electrode spacer in a conventional endplate causes the electric power of a RED system with 1000 cells to decrease by more than 20% under the specific condition in which the outermost feed solution (OFS) at both electrodes and the electrode solution (ES) are river water. This configuration, called OFS(river)/ES(river), is the best for minimizing inorganic scaling and toxic gas evolution. Another problem associated with the conventional endplate is fluid congestion owing to very narrow spaces, which causes sudden pH changes and deteriorates further with inorganic scaling. To address these issues, we removed the electrode spacer from the electrode system and utilized an open-type endplate with interconnected open spaces. This endplate maintained high electric power without the bubble resistance and suppressed the abrupt changes in the pH around the electrodes and the shielding membranes. We believe that our approach will be useful in the search for an optimum electrode design for RED systems on the industrial scale.

The utilization of large amounts of volatile organic solvents and the complicated process required for industrial manufacturing of ion-exchange membranes necessitate the development of simple, rapid, and environmentally friendly fabrication methods such as those based on photopolymerization. We employed hydrolytic sol–gel reactions between ammonium- and acrylamide-functionalized silane coupling agents to synthesize water-soluble siloxane resins that exhibit high condensation levels (>80%) and comprise oligomers with molecular weights below 2000 Da. These resins were then mixed with a hydrophilic monomer bearing ammonium and acrylamide groups, and porous polyethylene substrates were impregnated with the resulting mixtures and then irradiated with ultraviolet light. The hydrophilicity, mechanical strength, and other properties of the resulting membranes depended on the resin composition, indicating that the substrate pores were efficiently filled with the prepared resins and further suggesting that the membrane performance could be effectively altered by varying the resin composition. Moreover, the obtained membranes exhibited chemical stability in the pH range between 0 and 11 and in hot water at 60 °C. The reverse electrodialysis stack consisting of these membranes showed higher power density than a stack of commercial membranes. Therefore, it can be concluded that without employing volatile organic solvents for reverse electrodialysis, the developed technique is well-suited for the fabrication of ion-exchange membranes.

The solid-phase reaction method for preparing forsterite (Mg2SiO4) using the MgO and SiO2 powders has the disadvantages of high reaction temperature, long reaction time, and inhomogeneous reaction depending on the particle size of MgO. Therefore, MgO-based powders with a high reactivity were synthesized using a coprecipitation method with substitutional elements (Mn or Ni), and the effects of processing parameters on synthesizing MgO-based binary composition powders were investigated through the particle characteristics. The crystal structure was changed continuously with the contents and species of substitutional elements, showing the same trend as the atomistic simulation results. The MgO-based powders showed a higher reactivity than the conventional MgO powder, which could be confirmed in the particle characteristics, such as particle size and crystallinity, obtained in a short reaction time and at a relatively low temperature. The optimum composition ratio in the binary composition powder for forming the Mg2SiO4 depended on the type of substitutional element, and the reaction mechanism was identified based on the particle characteristics.

The direct integration of two-dimensional nanostructures into macroscopic porous carbon substrates is essential for their practical use in potential applications, which is a big challenge due to the difficulty of securing uniform coating layers. In this work, we demonstrate a very simple and effective method for the direct coating of MoS2 onto the surface of porous carbon structures having nano-sized pores, such as vertically aligned carbon nanotube arrays. A uniform coverage of MoS2 over carbon substrates was achieved by chemical vapor deposition of gaseous species derived from starting precursors in a closed reactor. Transmission electron microscopy images, X-ray diffraction data, and Raman spectra confirmed the formation of highly crystalline MoS2 layers. X-ray photoelectron and energy dispersive X-ray spectroscopies revealed highly uniform MoS2 layers over the whole surface of the carbon substrates. Our approach is also applicable for the synthesis of MoS2/carbon fiber paper (CFP) hybrid structures. The electrochemical tests showed that the as-synthesized MoS2/CFP structures can serve as highly active cathodes for reverse electrodialysis.

We have successfully exploited the Michael-type addition reaction between catechol and DABCO (1,4-diazabicyclo-[2,2,2]octane) molecules under alkaline conditions for the formation of new quaternary ammonium (QA) groups in an anion-exchange membrane. The anion-exchange membranes (AEMs) were prepared using the pore-filling method by addition of electrolytes (vinyl benzyl trimethylammonium chloride (VBTMA), dopamine methacrylamide (DMA) bearing a catechol group, and ethylene glycol diacrylate as a cross-linker) to a porous substrate. The formation of new QA groups by the reaction of DABCO with catechol components was confirmed by characterization of new peaks in the Fourier transform infrared spectra of the AEMs. The DABCO-bound AEM demonstrated a significant decrease in area resistance (0.4 Ω·cm2) and increase in permselectivity (94%). Furthermore, the electrochemical properties of the AEMs could be controlled by altering the concentrations of VBTMA and DMA and the formation of new bonds between DMA and DAB...

Flow-electrode capacitive deionization (FCDI) is a desalination process designed to overcome the limited desalination capacity of conventional CDI systems due to their fixed electrodes. Such a FCDI cell system is comprised of a current collector, freestanding ion-exchange membrane (IEM), gasket, and spacer for flowing saline water. To simplify the cell system, in this study we combined the membrane and spacer into a single unit, by coating the IEM on a porous ceramic structure that acts as the spacer. The combination of membrane with the porous structure avoids the use of costly freestanding IEM. Furthermore, the FCDI system can be readily scaled up by simply inserting the IEM-coated porous structures in between the channels for flow electrodes. However, coating the IEM on such porous ceramic structures can cause a sudden drop in the treatment capacity, if the coated IEM penetrates the ceramic pores and prevents these pores from acting as saline flow channels. To address this issue, we blocked the larger microscale pores on the outer surface with SiO2 and polymeric multilayers. Thus, the IEM is coated only onto the top surface of the porous structure, while the internal pores remain empty to function as water channels.

In this study, we investigated the effects of partial condensation on the heat and mass transfer rates during ethanol–water binary distillation based on a laminar boundary layer theory applied to a wetted-wall column, as well as the characteristics of the boundary layer behavior on the vapor phase. The thickness of the thermal and concentration boundary layers were shown to decrease with an increase in partial condensation, whereas the heat and mass transfer rates were demonstrated to increase. The results of this study show that the dimensionless rates considered for the convective fluxes Sh/(1 + αM) and Nu/(1 + αH) can be determined through a combined application of the laminar boundary layer theory and function g(β) of a partial condensation ratio β (mole basis), where β is linearly proportional to υs/u∞ (dimensionless velocity), which is a term for the boundary condition at a vapor–liquid interface. A numerical analysis of the experiment data show that both Sh/(1 + αM) and Nu/(1 + αH) are approximately proportional to the Reynolds number (Re), and not to Re1/2, as is generally the case, under the condition υs = 0. Therefore, we established the functional relationship g(β′) = 0.4288–0.2844eβ″, i.e., the exponential function of β′, which was converted into a mass basis. The modified boundary layer theory was found to be completely self-consistent.

Flow-electrode capacitive deionization (FCDI) has been studied for its ability to perform continuous deionization; however, there are no reports on the degradation of the desalting performance of FCDI under short-circuited closed cycle operation (SCC) mode. In this study, we observed a gradual decrease in FCDI desalting performance and weight increase of the flow-electrode under SCC mode, which mixes the cathode and anode flow-electrodes. Through an analysis of NaCl and water accumulation rates obtained from the weight variation of the flow-electrode, the gradual decline in the desalting performance was caused by a decrease in the content of activated carbon (AC) with ion adsorption sites in the flow-electrodes. This was driven by water transfer from the feed stream to the flow-electrodes through the ion exchange membrane attributed to hydrated ions and osmosis. We calculated the salt adsorption capacity (SAC) and salt adsorption rate (SAR) based on the variable weight of the flow-electrode. The maximum SAC (mSAC) and average SAR (ASAR) values of the FCDI were higher and lower than those of conventional capacitive deionization systems, respectively. This was likely due to the repetitive use of the flow-electrode and long ion transport pathways in the flow-electrode, respectively.

We herein report the synthesis of electrolyte-filled activated carbon (AC) coated with an ion-conducting polymer (AC-N) to achieve a electrode material exhibiting enhanced capacitive properties. The successful formation of the polymer layer was confirmed by X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) analysis. In addition, electrochemical characterization was performed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) at a range of concentrations (i.e., 0.25, 0.5, and 0.75 M NaCl or Na2SO4). The specific capacitance obtained for the 0.75 M Na2SO4-filled AC-N was 13.5% higher than the bare AC-N at a scan rate of 100 mV/s, while the interfacial resistance was reduced by 94.6%. We therefore expect that the electrolyte-filled AC reported herein can improve the performance of the electrosorption based system by reducing cell resistance.

Pore-filling ion-exchange membranes have been produced via complex, low energy efficient, and toxic processes, including repetitive impregnation to fully fill the porous substrates with polymer ele...

A highly compact and scalable three-dimensional desalination cell was realized by utilizing honeycomb-shaped porous lattice scaffolds. It did not require a free-standing ion exchange membrane and a thick current collector. Furthermore, the porous structure can act as a structural scaffold. Therefore, it can be readily scaled-up in three dimensions allowing enhanced salt removal capacity. This provides great potential for scale-up and commercialization of desalination using the capacitive deionization technology.

Flow electrodes have recently been studied for use in capacitive deionization applications because of their continuous and high desalting efficiency. The production capacity of desalinated water in the flow-electrode capacitive deionization (FCDI) system is limited compared to infinite ion capacity of the flow electrodes due to restrictions in the flow rate of the influent/effluent. Therefore, we designed and fabricated an FCDI stack with five unit cells in order to increase the production capacity of desalinated water. Through inlet pressure measurements of the flow electrodes in the FCDI stack, we confirmed that the flow electrodes were uniformly segmented from the manifold formed in the FCDI stack into the flow channels of each unit cell. We also confirmed that there was no pressure increase at the flow electrode in the flow channel caused by an increase in the number of unit cells in the FCDI stack. Also, the FCDI stack showed a similar desalting efficiency when compared to that of the FCDI unit cell....

Reverse electrodialysis (RED) emerged as a promising membrane-based technology due to an increased interest in salinity gradient energy. We report on the fabrication and characterization of ion-exchange membranes wave-patterned with non-conductive materials and supported by thin (16-μm-thick) pore-filling membranes. These membranes, which are double-sided or single-sided, are designed to secure stable electrolyte channels based on wave lines with mirror images. Cross-flow RED stacks were evaluated as functions of cell pairs and flow rates. The non-conductive material increases the membrane resistance for anion and cation exchange, maintaining permselectivity approximately constant. The gross power density of a flat stack is higher than that of a single-sided patterned membrane stack; however, the latter exhibits superior net power density, particularly at high flow rates. The pressure drop of the single-sided wave-patterned membrane is significantly lower (~3 × ) than that of the flat membrane. The maximum gross power density was 1.39 W/m2 for 10-cell pairs, and the optimum cell pairs were 30, with the highest net energy efficiency of 9.4%. The net energy efficiency can be maximized by optimizing the design and operating conditions of the RED stack and net power density, via the addition of an ionic conductivity function to the patterned structure.

Reverse electrodialysis (RED) is an emerging electrochemical process for harnessing salinity gradient power. For the commercialization of the RED process, the development of a highly efficient RED stack at a given flow rate is crucial. For this purpose, we first evaluated the performance of a RED stack according to the number of cell pairs at a given flow rate to improve the net power and specific energy (SE). Integrating the number of cell pairs at a given flow rate caused an increase in the electrical potential, and the net power was converged to the limiting value. The net SE was 0.06 kWh/m3 with 100 cell pairs at a flow rate of 100 mL/min. The levelized cost of electricity (

The hot corrosion behavior of plasma-sprayed Yb2O3-Gd2O3-Y2O3 co-doped ZrO2 (YGYZ) coating against Na2SO4 + V2O5 molten salts was investigated and its detailed hot corrosion mechanism was suggested. The chemical reactivity order between the stabilizers was proposed based on the electronic structure and Lewis acid-base mechanism. After hot corrosion, the YGYZ coating exhibited the maintenance of tetragonality ratio and relatively lower extent of destabilization less than 40% of conventional yttria-stabilized ZrO2 coating. These great chemical and phase stabilities imply that YGYZ is promising candidate for high-temperature thermal barrier material.

Here we describe the development and testing of a hybrid system that combines microbial electrolysis and reverse electrodialysis (RED) to benefit energy production from seawater. A tubular, continuous-flow, microbial electrolysis cell (MEC) was used prior to RED to remove multivalent ions (Ca2+ and Mg2+) that are known to decrease RED power generation due to high electric membrane resistance. When a membrane electrode assembly was applied to reduce external resistance in the MEC, Ca2+ and Mg2+ were effectively removed with efficiencies of 84 ± 5% and 99 ± 5% (current density of 4.0 ± 0.2 A/m2), respectively, and H2 was simultaneously generated. A high H2 (purity > 99.5%) production rate (2.00 ± 0.09 m3/m3·d) at an applied voltage of 1.5 V, and maximum electrical energy efficiency (169 ± 4%) was accomplished at an applied voltage of 0.9 V and with an anode hydraulic retention time of 6 h. Effluent (47 mS/cm) from the MEC was fed to the RED stack as a high-concentration solution and the conductivity of treated seawater was lower than untreated seawater (53.7 mS/cm) due to Ca2+ and Mg2+ elimination from the seawater. Despite its lower conductivity, treated seawater produced higher power (0.29 W/m2, 26% increase) compared to untreated seawater due to the removal of Ca2+ and Mg2+. Therefore, the MEC is superior to other energy-consuming seawater pretreatment system as it produces energy during seawater pretreatment and successfully integrates with RED to enhance power generation.

This work was supported by "Human Resources Program in Energy Technology (No. 20194030202450)" and "Power Generation & Electricity Delivery (No. 20181110100310 & 20193310100090)" of the Korea Institute of Energy Technology Evaluation and Planning from the Ministry of Trade, Industry and Energy, Republic of Korea.

We have synthesized a new type of activated carbon (AC) containing ion-selective functional groups, trimethylammonium (AC-N) for anodes and sulfonate (AC-S) for cathodes, for high carbon loading of flow-electrodes. The AC-N and AC-S were partially covered with a 50 nm-thick polymer layer and their surfaces became more hydrophilic than that of bare AC. In the case of bare AC, the maximum carbon concentration in the flow electrodes was 10%, while in the case of the surface-modified AC (AC-N and AC-S), it increased to a maximum of 35% and decreased the viscosity due to the electrostatic repulsion. Moreover, with the increase in carbon concentration, the salt removal efficiencies were improved from 8.2% to 27.7%. This increase in efficiency was attributed to the formation of percolating networks, which occurred because of high carbon loading. The resulting improvement in electronic conductivity at higher loading led to a higher current, and thus an improved salt removal efficiency. Therefore, we expect that the surface-modified AC electrode can be used as a dispersant for hydrophobic AC particles in aqueous solution, as well as in flow electrodes to improve desalting performance in FCDI systems.

Molybdenum disulfide (MoS2) is considered to be promising two-dimensional material in potential applications because of its superior properties. Herein, our work suggests another important application as an inexpensive and highly active cathode material in reverse electrodialysis (RED). The MoS2 (8, 36, 76, 100 nm)/rutile-phase TiO2/Ti (MoS2/rpTiO2/Ti) heterostructures were successfully prepared with the randomly layered and oblique 1T/2H-MoS2 by one-step chemical vapor deposition of starting precursors in a closed reactor. The MoS2/rpTiO2/Ti reveals a thickness-dependent RED performance. Moreover, the MoS2 synthesis after sulfur modification of Ti surface (MoS2/smrpTiO2/Ti) increases the gross power density and reduces internal resistance of RED stack, indicating that the interfacial engineering between MoS2 and rpTiO2 improves both the catalytic activity and charge transfer efficiency. As a result, the highest gross power density of approximately 270 W/m2electrode was achieved using a RED stack mounted with 50-cell-pair of ion exchange membranes, which is comparable to that of platinum. Our work not only suggests that the MoS2/smrpTiO2/Ti heterostructure shows grate potential in RED stack, but also provides the importance of interface engineering between MoS2 and TiO2 through sulfate-bridge and sulfur-doping in MoS2-based electrocatalytic devices.

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.