Electrolyte Mass Transfer Research Articles

Modeling of Lithium-Ion Convection Cell Effects on Reaction Distribution and Different Cathode Active Materials

Li-ion batteries (LIBs) could play a substantial role in mitigating climate change if they become more widely adopted in transportation and stationary energy storage applications. Increasing this adoption requires improvement in both power density and energy density. At the cell level, this dual requirement calls for designs and active materials that overcome challenging trade-offs in nominal cell voltage, rate capability, and loaded capacity.In our previous research,1,2 we simulated that a convection cell with liquid electrolyte flow, using LCO, can overcome the trade-offs by enhancing accessed capacity under high-rate operation. Electrolyte flow achieves this enhancement by effectively addressing both bulk electrolyte mass transfer and thermal limitations. The flow of electrolyte raises cell voltage by promoting a uniform Li+ salt concentration and regulates temperature by removing heat and lowering heat-producing overpotentials.In our current work, we extend our macrohomogeneous modeling analysis of a Li-ion convection cell to explore the impact of concentration uniformity on charge-transfer reaction distribution and the flexibility of this approach to work with different active materials. Concentration uniformity evens the reaction distribution, facilitating spatially consistent and full utilization of the active material in the electrodes. Additionally, the use of flow enables the cell to maintain rate capability across various electrode thicknesses and areal capacity loadings. At high C rates, a convection cell with flow exhibits significantly higher output capacity than a closed cell without flow. The degree of increase in running voltage and delivered capacity depends on the choice of positive electrode active material—LFP, LCO, NCA, NMC, or LMO.Finally, simulations of net power density and net energy density account for pumping energy loss across the cell. The improvement in net energy density with flow becomes substantial at high power density. W. Gao, M.J. Orella, T.J. Carney, Y. Román-Leshkov, J. Drake, F.R. Brushett, J. Electrochem. Soc., 167, 140551 (2020).W. Gao, J. Drake, F.R. Brushett, J. Electrochem. Soc. 170, 090508 (2023).

Elucidation of Mass Transport Phenomena in Highly Concentrated Electrolytes during Current Cycling Using In-Situ Interferometry and Finite Difference Method

Understanding electrolyte mass transfer during charge–discharge reactions is essential for developing next-generation storage batteries with high energy densities. In this study, we investigated Li+ transport in a highly concentrated electrolyte (HCE) consisting of an equimolar mixture of lithium bis(fluorosulfonyl)amide (LiFSA) and tetraglyme (G4) under current reversal and re-reversal. Concentration profiles of the electrolyte at a distance of 0–600 μm from the Li electrodes were obtained using in situ laser interferometry. The Li+ transference numbers and LiFSA diffusion coefficients were calculated from these profiles. Raman spectroscopy suggested that the coordination structure surrounding Li+ ions in the electrolytes mainly contributed to the transference number. A one-dimensional unsteady diffusion equation and the finite difference method were employed to simulate the concentration profiles. The maximum error percentage between the measured and simulated values was only 3%, confirming the accuracy and validity of the interferometric measurements. Our findings on Li-ion transfer in HCEs could promote the rational design of high-energy-density Li-ion batteries with higher cation transference numbers of electrolytes and charge–discharge rates.

Designing High‐mass Loading 2D Ni‐TiO2/graphene Pellet Electrodes for Lithium Metal Batteries

AbstractHigh conductivity and mass transfer channels of electrode materials with high mass loadings are the fundamental requirements for achieving high‐rate performance and high‐volume energy density. In this study, we investigated the method of constructing high‐mass loading pellet electrodes and their applications in lithium metal batteries from three different perspectives: selecting active electrode materials, designing the mass transfer porous structure, and constructing a conductive network. The three‐dimensional conductive network with porous structures provides the electrolyte's mass transfer channels and convenient charge transfer paths. The resulting pellet electrode demonstrates Young's modulus of 511 MPa under 44 % porosity, achieving satisfactory rate performance under mass loadings of 37.7 mg cm−2. After 200 cycles at the current density of 2.83 mA cm−2, it can maintain 56 % initial capacity, and the volume expansion is only 8.04 %. This study provides reference values for exploring and preparing high‐mass loading electrodes and the future design of solid‐state battery electrodes.

Biomass wood-derived efficient Fe–N–C catalysts for oxygen reduction reaction

Efficient and low-cost electrocatalysts for oxygen reduction reaction (ORR) were the key for scalable application of metal–air batteries and fuel cells. Herein, iron-based nitrogen-doped carbon catalysts (Fe–N–Cwood) were prepared, using hydrothermal-pyrolysis-treated wood-derived nitrogen-doped carbon as the support. This support possessed large specific surface area and macro–meso–micro hierarchical porous networks, ensuring fluent mass transfer of electrolyte and oxygen species. In the ORR electrochemical test, Fe–N–Cwood catalyst showed an excellent activity, with a half-wave potential of 0.90 V in 0.1 M KOH, and a half-wave potential of 0.70 V in 0.1 M HClO4. Moreover, durability tests illustrated that Fe–N–Cwood possessed high stability and methanol tolerance. The Fe–N–Cwood-based Zn–air battery delivered a peak power density of 231 mW cm−2, suggesting its potential applications in sustainable energy conversion systems. A highly efficient ORR electrocatalyst was obtained by embedding iron nanoparticles with hydrothermal-pyrolysis-treated wood-derived carbon.

Development of Porous Electrode Theory to Accommodate Voltage Gradients and Nonlinearity

Simulations of ionic and solvent mass transfer in electrolytes are typically based upon either i) the Poisson-Nernst-Plank equations with Fickian diffusion (Poisson-Fickian), or ii) the Newman-type porous electrode equations with Stefan-Maxwell transport (Newman-Stefan-Maxwell). Computational expense usually limits the Poisson-Fickian-type simulations to simple systems with only one or two phases, and one or two dimensions. Meanwhile the Newman-Stefan-Maxwell-type equations are explicitly only one-dimensional but are much easier to execute and can crudely handle more phases. This ease and flexibility made the Newman-Stefan-Maxwell approach popular over the past thirty years, and the Newman-type model continues to be popular with modern usage at current date.The work presented here shows a further development of the Newman-Stefan-Maxwell equations that extend the Newman theory to i) simulate voltage and pressure gradients in the electrolyte that are significant when ionic concentrations are below ~2 Molar, and ii) include more accurate thermodynamics when describing the chemical potential of the species. The new equations are shown and justified. No significant increase in computational expense or model complexity is necessary for these improvements.An additional predictor-corrector modelling scheme is shown for calculating the chemical composition at the particle-liquid interface, which allows for the overall model to be solved with explicit time-differencing without requiring extremely small time steps. The explicit time-differencing is advantageous because it discards the requirement to linearize all equations, and therefore allows for fully nonlinear charge-transfer equations to be tested with an arbitrary complexity desired.The new model is capable of simulating one-dimensional full battery operation (anode, cathode, separator, electrolyte) with improved accuracy over the classical Newman-Stefan-Mawell model regarding spatio-temporal patterns of electrochemical potential, concentrations, and reaction rate. Some example applications are shown for CV cycling and galvanostatic cycling of: i) a 1 Molar Zn-MnO2 battery, ii) a EMImCl:AlCl3 aluminum-graphite battery. Additional systems are proposed for study where the voltage and pressure gradients are important to simulate.

Carbon-nanotube-grafted and nano-Co3O4-doped porous carbon derived from metal-organic framework as an excellent bifunctional catalyst for zinc–air battery

In this study, carbon-nanotube (CNT)-grafted and nano Co3O4-doped porous carbon was prepared by the carbonization of a synthesized zeolitic imidazolate framework compound (ZIF-67/ZIF-8) followed by an oxidation treatment. The novel catalyst demonstrated excellent ORR and OER because of the Co3O4 nanoparticles and nitrogen-doped in the carbon framework (NC). In addition, the carbon nanotube grafted on the framework provided a good electrical conductivity while the carbon framework matrix provided a porous skeleton which is beneficial for the mass transfer of electrolyte. In the ORR study, the novel catalyst, CNT-Co3O4/NC, showed a half-wave potential of −0.124 V at 0.1 M KOH (Pt/carbon: −0.152 V) while the limited current density is 4.84 mA/cm2 (Pt/carbon: 4.9 mA/cm2). In terms of OER performance, the potential is 0.819 V at current density of 10 mA/cm2 (Ir/carbon: 0.771 V). The CNT-Co3O4/NC catalyst shows a specific capacitance of 814 mAh/g (1.19 V at 50 mA/cm2), which is very close to the theoretical capacitance (820 mAh/g) and the maximum power density was 267 mW/cm2 (0.746 V at 385 mA/cm2) while 255 mW/cm2 (0.711 V at 360 mA/cm2) was obtained using Pt/carbon catalyst. We believe that the novel CNT-Co3O4/NC can be used as an excellent catalyst in the zinc-air battery.

The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

AbstractAdvanced chlor‐alkali electrolysis with oxygen depolarized cathodes (ODC) requires 30 % less electrical energy than conventional hydrogen‐evolution‐based technology. Herein, we confirm that the activities of hydroxide and water govern the ODC performance and its dynamics. Experimental characterization of ODC under varying mass transfer conditions on the liquid side reveals large differences in the polarization curves as well as in potential step responses of the electrodes. Under convective transport in the liquid electrolyte, the ODC is not limited by mass transfer in its current density atj>3.9 kA m−2, whereas transport limitations are already reached atj≈1.3 kA m−2with a stagnant electrolyte. Since gas phase conditions do not differ significantly between the measurements, these results are in contrast the common assumption that oxygen supply determines ODC performance. A dynamic model reveals the strong influence of the electrolyte mass transfer conditions on oxygen availability and thus performance. Dynamic responses of the current density to step‐wise potential changes are dominated by the mass transport of water and hydroxide ions, which is by orders of magnitude faster with convective electrolyte flow. Without convective liquid electrolyte transport, a high accumulation of hydroxide ions significantly lowers the oxygen solubility. Thus, a fast mass transport of water and hydroxide is essential for high ODC performance and needs to be ensured for technical applications. The predicted accumulation of ions is furthermore validated experimentally by means of scanning electrochemical microscopy. We also show how the outlined processes can explain the distinctively different potential step responses with and without electrolyte convection.

Mass Transfer Mechanisms in Solid Electro Deposition

Copper plating is generally used for the fabrication of printed circuit boards of electronic devices. The patterning is carried out by masking with insulator for the partial plating on the substrate. It is desirable to develop a new alternative technology that takes environmental issues into consideration because the partial plating with a mask involves very complicated processes and wastewater treatment. Solid Electro Deposition (SED) method with the solid electrolyte membrane was reported by Yanagimoto et al.1) as the way to resolve the problem. The SED can be performed by a simple electrochemical cell in which the solid electrolyte membrane is sandwiched by counter and working electrodes. Imposition of voltage between two electrodes enables electrodeposition on the working electrode. The advantages of SED are written as follows. ・The electrochemical cell is very simple because the electrolyte is solid. ・The post-processing is also simple． ・It can be high-rate plating because the driving force of mass transfer of reactant is migration. Among these advantages, the principle for high-rate plating by SED is explained below. Figure 1 shows the conceptual diagrams of mass transfer of cupric ions on electrode surface in two electrolytes. The charge transfer rate increases depending on the overvoltage in the case of plating in liquid electrolyte. However, the concentration polarization occurs on the electrode surface when the charge transfer rate is higher than the mass transfer rate of reactant. In this case, the driving force of mass transfer in electrolyte is normally diffusion. On the other hand, the mass transfer of reactant is dominated by migration in the SED if the transport ratio of metal ions in the solid electrolyte is unity. In this condition, the charge transfer rate becomes equal to the migration rate and the concentration polarization of reactant in the vicinity of the electrode does not occur, even if the charge transfer rate is increased. Therefore, it is possible to realize high-rate plating because diffusion is not rate-limiting process. We report the relationship between mass transfer mechanisms in solid electrolyte membrane and potential-current curves and establish the theory of high-rate copper plating by the SED. Reference: 1) K. Akamatsu, Y. Fukumoto, T. Taniyama, T. Tsuruoka, H. Yanagimoto, H. Nawafune, Langumuir, 27, 11761-11766 (2011). Figure 1

Effect of magnetic field on anodic dissolution in electrochemical machining

The authors modeled the electrochemical reactions of ECM with magnetic field using COMSOL commercial software. They studied the effect of filed strength and direction on the electrolyte mass transfer rate and the anodic dissolution amount. The mathematical models of the electrolyte rate distribution and the anodic dissolution amount were established. Simulation results indicated that the magnetic field would enhance the mass transfer rate and anodic dissolution amount and that the direction of the field will play a bigger part than the intensity in this connection. Experiments were also conducted to verify the model accuracy. Their experimental results were in good consistency with those of simulations. It is observed that the direction of the magnetic field that has a decisive say in altering the electrochemical machining system and this conclusion will potentially promote the application of magnetic field assisted electrochemical machining. The magnetic field works favorably to electromagnetic anodic dissolution reactions by improving both the mass transport rate and the corrosion rate.

Ternary MnO2/NiCo2O4/NF with hierarchical structure and synergistic interaction as efficient electrocatalysts for oxygen evolution reaction

Ternary metal oxides MnO2/NiCo2O4 supported on nickel foam (NF) as electrocatalysts for oxygen evolution reaction (OER) have been fabricated via a two-step hydrothermal process. NF as support can provide excellent conductivity and 3 dimensional skeleton, which facilitate the utilization of active sites and mass transfer of electrolyte. The ternary MnO2/NiCo2O4/NF also possess the advantage of synergistic effect between MnO2 and NiCo2O4, implying the enhanced intrinsic activity for OER. XRD, EDX and XPS confirm the existence and distribution of each element of MnO2/NiCo2O4/NF. SEM shows the hierarchical structure of MnO2/NiCo2O4/NF with vertically aligned MnO2/NiCo2O4 nanoflakes covering on the surface of NF, which is in favor of the more exposed active sites and the fast dissipation of O2 bubbles. Additionally, to clearly testify the significance of the vertically aligned MnO2/NiCo2O4 nanoflakes, non-vertical MnO2/NiCo2O4/NF sample (MnO2/NiCo2O4/NF-1) is prepared for comparing OER performances in the same condition. OER measurements in alkaline solution show that ternary MnO2/NiCo2O4/NF displays better electrocatalytic activity with a low overpotential of 340 mV at a current density of 10 mA cm−2 than other samples. Therefore, ternary metal oxides with hierarchical structure on NF may be a promising choice for excellent electrocatalysts for OER.

Macroporous ZnO/ZnS/CdS composite spheres as efficient and stable photocatalysts for solar-driven hydrogen generation

Solar-driven hydrogen (H2) generation utilizing photocatalysts has received extensive attention because of its potential to mitigate the global energy crisis and environmental problem. The implementation of efficient H2 production strongly relies on stable, active, and low-cost photocatalysts. In this work, we report the designed synthesis of macroporous ZnO/ZnS/CdS composite spheres as a highly active photocatalyst for H2 production via solar-driven water splitting. The composite spheres were synthesized by a facile solvothermal reaction paired with controllable ion-exchange processes. The resulting material exhibits superior photocatalytic activity, delivering a high H2 production rate of ~11.37 mmol h−1 g−1 under light illumination (250–780 nm, with an ultraviolet light intensity of 34 mW cm−2 and visible light intensity of 158 mW cm−2). Such performance enhancement can be mainly ascribed to the synergic effects of the composite structure: (1) formation of coherent ZnO/CdS and ZnS/CdS heterojunctions at nanoscale, facilitating charge separation of photoinduced electron/hole pairs, (2) highly accessible inner surface of the meso/macroporous ZnO/ZnS/CdS composites for rapid mass transfer of electrolyte, and (3) enhanced visible light scattering capability induced by their large particle size.

Passivation degradation of Alloy 800 on nucleate boiling surface

ABSTRACTIn this work, the passivation degradation of Alloy 800 on nucleate boiling surface was studied by using polarisation curve, electrochemical impedance spectroscopy and secondary ion mass spectrometry. Experimental results indicated that boiling bubble would significantly degrade the passive film, as indicated by a decreased pitting potential and increased passive current density. Under boiling condition, the mass transfer of electrolyte is accelerated and the temperature of Alloy 800 was increased, as a result, the cathodic reaction and the dissolution rate of the passive film were increased. The passive film was Cr-depleted but Ni- and Fe-enriched, and the decreased Cr content in the passive film led to a degraded passive film.

Electrodepositing Ni-TiN nanocomposite Layers with Applying Action of Ultrasonic Waves

Ultrasonic wave was applied to prepare nanocermet Ni–TiN composite layers on steel substrates during electrodeposition. The action of mechanical disturbance by ultrasonic waves on electrolyte mass transfer, the inhibition of nanoparticle aggregation by ultrasonic cavitation and the effect of electric pulse parameters on the nucleation and growth of grains were investigated. Proper utilization of the mechanical disturbance and cavitation effects of ultrasonic waves could improve the mass transfer of the electrolyte and inhibit the aggregation of TiN nanoparticles, leading to homogeneous dispersion of the particles in the plated layer. Electricity pulses of high amplitude, narrow width and low occupancy accelerated the nucleation and inhibited the growth of metal grains, resulting in nano-sized nickel grains of homogeneous size. The nanocermet Ni–TiN composite layer consisted of nanocrystalline nickel (40–60 nm) and TiN nanoparticles was obtained on the surface of common metal substrates using optimum conditions.

Tunable synthesis of nanoporous tin oxide structures on metallic tin by one-step electrochemical anodization

Nanoporous tin oxide structures were synthesized by electrochemical anodization of tin substrates at various anodizing conditions, including electrolyte species and concentration, anodizing potential, anodizing temperature and duration of the process. The influences of anodizing conditions on the structure features of anodized oxide films were investigated in detail. It is worth stressing that the correlation of the morphologies and current density virtue time curves (i-t curves) was analyzed in our work. The structure features of as-prepared tin oxide layers were found to be strongly related to anodizing conditions. Significant increases of average pore diameter occurred with the increase of anodizing potential, temperature and time. In addition, it is noteworthy that strong linear dependences between average steady-state current density and electrolyte concentration, anodizing potential as well as temperature were observed. It indicates the anodizing process is limited by mass transfer in electrolyte. Moreover, growth mechanisms in both kinetics and thermodynamics were established to elaborate the growth process of porous structures during anodization.

Porous TiO2 urchins for high performance Li-ion battery electrode: facile synthesis, characterization and structural evolution

Porous TiO2 urchins have been synthesized by a hydrothermal route using TiO2/oleylamine as precursors with subsequent ion-exchange and calcination. The resultant material consists of porous spherical cores and nanochains-constructed shells with straight channels. Electrochemical measurements indicate the TiO2 urchins deliver superior lithium storage capability in terms of high capacity (206.2mAhg−1 at 0.5C), superior rate performance (94.4mAhg−1 at 20C) and stable cycling stability (94.3% capacity retention over 1000 cycles at 10C versus the third cycle). Such performance enhancement is mainly due to the increased electrode/electrolyte contact interface, reduced Li+ diffusion pathways and improved mass transfer of electrolyte in the unique 3D interconnected hierarchical network. In addition, ex-situ XRD, SEM and TEM analyses further reveal high structure integrity of the porous TiO2 urchins during the electrochemical lithiation, leading to enhanced lithium storage stability. Moreover, we detected that some anatase nanocrystals evolved into electrochemically inactive Li1TiO2 dots (∼10nm in size) during long-term electrochemical cycling. Our findings provide more insights for better understanding of the structure evolution and capacity decay mechanism in porous TiO2 nanostructures.

Preparation and Mechanical Properties of Ni-TiN Composite Layers by Ultrasonic Electrode Position

Ultrasonic electrodeposition was used to prepare nanocermet Ni-TiN composite layers on steel substrates. The action of mechanical disturbance by ultrasonic waves on electrolyte mass transfer, the inhibition of nanoparticle aggregation by ultrasonic cavitation and the effect of electric pulse parameters on the nucleation and growth of grains were investigated. The nanocermet Ni-TiN composite layer consisted of nanocrystalline nickel (30~60 nm). The micro-hardness of the composite layers increases a little when TiN content increases from 0% to 2%. However, micro-hardness increases greatly when V is increased from 2% to 9%. The maximal micro-hardness for Ni-TiN composite layers is 860 HV, 908 HV and 950 HV, respectively.

Turbulent Mass Transfer Simulations of Binary Electrolyte in Parallel-Plate Electrode Channel

Electrochemical mass transfer in turbulent flows and binary electrolytes is investigated. The primary objective is to provide information about mass transfer in the near-wall region between a solid boundary and a turbulent fluid flow at different Schmidt numbers. Based on the computational fluid dynamics and electrochemistry theories, a model for turbulent electrodes channel flow is established. The turbulent mass transfer in electrolytic processes has been predicted by the direct numerical simulation method under limiting current and galvanostatic conditions, we investigate mean concentration and the structure of the concentration fluctuating filed for different Schmidt numbers from 0.1 to 100 .The effect of different concentration boundary conditions at the electrodes on the near-wall turbulence statistics is also discussed.

Influence of Aeration on the Passivation Characteristics of AS/NZS 3679.1-300 Mild Steel in High-Temperature Bayer Liquor Under Conditions of Disturbed Flow

The flow-enhanced corrosion of mild steel has been examined in high-temperature spent Bayer liquor as a function of Reynolds number, fluid flow disturbance, and electrolyte aeration. ne electrochemical characteristics of the steel in this electrolyte was derived using a high-pressure nickel flow loop at 160 degrees C (total gauge pressure = 0. 7 MPa to 0.9 MPa). The influence of both a sudden pipe expansion and a pipe contraction on both corrosion rate and polarization behavior was quantified. Considering the mechanism of the corrosion reaction, electrolyte mass transfer did not directly control the electrochemical rates of either the cathodic or anodic currents at the corrosion potential. It is concluded that chemical modification and/or dissolution/erosion of passivating layers may have a strong influence over the metal loss of the steel observed in some alumina plants. Aeration of the liquor was found to be a significant factor regarding passivation rates and the corrosion characteristics of acid-treated steel, and it caused an overall increase in the rate of active and. passive steel dissolution relative to the deoxygenated state for all but one electrode. However, the time to passivation was relatively low at high fluid velocities (Re congruent to 141,500), which led to a 27016 to 509,6 reduction in metal loss over a caustic exposure time of 19 h. At low velocities (Re congruent to 50,900), time to passivation in the aerated liquor was also lowered, but not to the same order as that observed in the high-velocity area. Therefore, as a result of elevated reaction rates in the presence of oxygen, total corrosive losses over this short operating period were up to 37%, higher than that of the deoxygenated electrolyte. The results were essentially independent of the level off low disturbance.

Streaming effect of single electrolyte mass transfer in nanofiltration: potential application for the selective defluorination of brackish drinking waters

This work deals with electrical properties of nanosurfaces in contact with electrolyte solutions. Single halide ion solutions were studied by streaming potential (SP) measurements and observed retention (R obs) of the F −, Cl −, and Br − ions across nanofiltration (NF) membranes. The detailed understanding of an electrolyte solution mass transfer requires an intimate knowledge of the physicochemical interactions occurring between nanoporous materials and electrolyte solutions across the first-generation composite membranes called NF55, NF70 and NF90. These membranes are composed of a polysulfone mesoporous sublayer and a microporous skin layer in polyamide. In order to get a better understanding of these effects, it seems attractive to compare the mass transfer permeation of the monovalent ions F −, Cl −, and Br − with the electrokinetic characterizations deduced from a properly developed SP apparatus. SP measurements is a very simple method to show the intrinsinc charges on membrane pore walls. The membrane's electrical properties are studied with SP design modeling pH, ionic strength and kind of electrolyte solutions. We have observed that the isoelectric point (IEP) of the membrane materials is both dependent on the ionic strength and on the kind of electrolyte solution. The IEP in the presence of KCl is 4.4 at 0.0001 mol/L and 5.8 at 0.001 mol/L, showing an increasing adsorption of the cation K + by increasing its solution concentration. For a fixed concentration, the effect of the electrolyte solution has shown that a higher adsorption of Ca ++ occurs in comparison to K + and Na +. But the adsorption of these electrolyte solutions is essentially reversible as observed under dilution conditions. Furthermore SP measurements were used for the first time to characterize the transmembrane pressure ranges where a convective and/or a diffusional mass transfer occurs. Such an approach was developed to correlate the R obs of the halide ions F −, Cl − and Br − with the kind of mass transfer (diffusional and/or convective) occurring predominantly under transmembrane pressure variations. Thus the NF70 membrane shows at low pressure (under 3 bar) the order of R obs following the hydrated ionic radius: R obs .( F −)> R obs .( Cl −)> R obs .( Br −). For a higher pressure (> 3 bar) an inversion occurs between Cl − and Br −, but F − was not affected. These results open a new prospective area for selective defluorination of brackish drinking waters using NF membranes under low transmembrane pressure.

Fe/Ni 합금전착에 의한 다공성 그물군조 방열재료의 제조 연구

다공성 그물구조 금속을 반도체 칩 방열재료로써 활용하기 위한 실험을 실시하였다. 이를 위해 다공성 그물구조 구리와 반도체 칩 사이의 열팽창 차이를 최소화하기 위한 시도로써 다공성 구리에 대한 Fe/Ni 합금전착을 수행하였다. Fe/Ni 합금전착 실험으로 표준 Hull Cell을 구성하고 전류밀도 분포에 따른 Fe/Ni 합금층 내의 조성변화를 관찰하였으며, 실험결과 합금전착시 이상공석현상으로 인하여 전해액의 교반정도에 따라 합금층 조성이 크게 영향을 받는 것으로 나타났다. 본 실험에서는 paddle type 교반기를 사용하여 전해질의 확산을 제어하는 방법으로 원하는 조성의 Fe/Ni 합금층을 얻을 수 있었으며, 얻어진 Fe/Ni 후막을 대상으로 TMA 열분석을 실시한 결과 구리에 비해 훨씬 낮은 열팽창율을 보이는 것으로 나타났다. 또한, 본 실험에서 Fe/Ni 합금전착을 통하여 제작한 다공성 그물구조 금속을 대상으로 방열성능을 측정한 결과 구리 평판 대비 최대 2배 이상의 방열성능을 보여 반도체 칩 방열재료로의 활용 가능성을 높여 주었다. An attempt was made for the application of porous reticular metal to a heat dissipation material in semiconductor process. For this aim, the electrodeposition of Fe/Ni alloy on the porous reticular Cu has been performed to minimize the thermal expansion mismatch between Cu skeleton and electronic chip. Preliminary tests for the electrodeposition of Fe/Ni alloy layer were conducted by using standard Hull Cell to examine the effect of current density on the composition of alloy layer. It seemed that mass transfer affected significantly the composition of Fe/Ni layer due to anomalous codeposition in the electrodeposition of Fe/Ni alloy. A paddle type stirring bath, which was employed to control the mass transfer of electrolyte in the work, was found to allow the electrodeposition Fe/Ni with a precise composition. result showed that the thermal expansion of Fe/Ni alloy layer was much lower than that of pure copper. From the tests of heat dissipation by using the apparatus designed in the work the heat dissipation material fabricated in the work showed the excellent heat dissipation capacity, namely, more than two times as compared to that of pure copper plate.