Thickness Of Electrolyte Layer Research Articles

Electrochemical Study of IT-SOFC Unit Cell Prepared By Tape Casting Process and Co-sintering

Anode-supported electrolyte with a large electrode area of 7.5×7.5 cm2 was fabricated using tape casting method aided by co-sintering process, in which the thickness of electrolyte layer is about 10 μm. SEM morphology showed the thin film of electrolyte with dense and crack-free structure which was formed between anode and cathode. As a result, open circuit voltage (OCV) of unit cell was around 1.1 V and its maximum power density was 0.214 W/cm2 at 800{degree sign}C. Impedance results of unit cell indicated that the ohmic resistance was 0.267 Ωcm2 at 800{degree sign}C, which was a suitable for the operation of SOFC at the intermediate temperature. In this study, we demonstrated that the tape casting process aided by co-sintering method is a suitable method for the mass production of planar SOFC unit cell with large electrode area.

Corrosion Multi-Monitoring of Carbon Steel in Coastal Area

The corrosion behavior of carbon steel and the atmospheric corrosiveness were monitored simultaneously by the corrosion multi-monitoring system. The system consists of a temperature and humidity chamber, a corrosion monitor, an ACM data logger, a surface reaction measurement device and a microscope. After installing the corrosion sensor and the ACM sensor in the chamber, the droplet of artificial seawater with different chloride ion concentration was added to the sensor surface, and the relative humidity was changed from 30% to 95% in every 12 hours. As the relative humidity increased, both the corrosion rate and the ACM current increased and the surface potential shifted to less noble. Furthermore, the obtained data was discussed for the average thickness of electrolyte layer calculated thermodynamically. The corrosion behavior was divided into three regions for thickness of electrolyte layer, and the corrosion rate showed a maximum at a thickness of about 100μm.

Computational Modeling of the Stability of Crevice Corrosion of Wetted SS316L

The stability of localized corrosion sites on SS 316L exposed to atmospheric conditions was studied computationally by considering the wetted cathode and the crevice anode separately and linking them via a constant potential boundary condition at the mouth of the crevice. The limitations on the ability of the cathode that are inherent due to the restricted geometry were assessed in terms of the dependence on physical and electrochemical parameters (temperature, electrolyte layer thickness, solution conductivity, and the size of the cathode). An analysis of variance showed that the solution conductivity and the length of the cathode were the most important parameters in determining the total cathodic current capacity of the external surface. A semi-analytical equation was derived for the total current from a restricted geometry held at a constant potential at one end.

A study of the corrosion of aluminum alloy 2024-T3 under thin electrolyte layers

The corrosion of aluminum alloy 2024-T3 (AA2024-T3) under thin electrolyte layers was studied in 3.0 wt% sodium chloride solutions by cathodic polarization and electrochemical impedance spectroscopy (EIS) method. The cathodic polarization measurements show that, when the electrolyte layer is thicker than 200 μm, the oxygen reduction current is close to that of the bulk solution. But in the range of 200–100 μm, the oxygen reduction current is inversely proportional to the layer thickness, which shows that the oxygen diffusion through the electrolyte layer is the rate-determining step for the oxygen reduction process. In the range of 100 μm to about 58 μm, the oxygen reduction current is slightly decreased probably due to the formation of aluminum hydroxide or the change of the diffusion pattern from 2-dimensional diffusion to one-dimensional diffusion. The further decrease in electrolyte layer thickness increase the oxygen reduction current to some extent again, because the diffusion of oxygen plays more important role in thin electrolyte layers. The EIS measurements show that the corrosion is controlled by the cathodic oxygen reduction at the initial stage, showing the largest corrosion rate at the electrolyte layer thickness of 105 μm. But at the later stage of corrosion, the anodic process begin to affect the corrosion rates and the corrosion rates show a maximum at 170 μm, which may be the thickness where the corrosion changes from cathodic control to anodic control. The corrosion rate under the very thin electrolyte layer (62 μm in this study) is even smaller than that in bulk solution, this is due to that the anodic process is strongly inhibited.

AC impedance study on corrosion of 55%Al–Zn alloy-coated steel under thin electrolyte layers

The corrosion behavior of 55%Al–Zn alloy-coated steel under a chloride-containing electrolyte layer ranging from 15 to 888 μm in thickness has been investigated using electrochemical impedance spectroscopy (EIS). The interface of the coating-electrolyte layer can be represented by an equivalent circuit consisting of a solution resistance, a charge transfer resistance, a double layer capacitance and a Warburg element. The corrosion current density estimated from the polarization resistance significantly decreases as the thickness of electrolyte layer increases between 15 and 100 μm and is almost independent of the thickness up to 888 μm. Furthermore, corrosion monitoring of 55%Al–Zn alloy-coated steel has been performed under alternate conditions of 1 h-immersion in solution of 0.05 M NaCl or 0.05 M Na 2SO 4 and 7 h-drying at 298 K and 60% RH. During the wet–dry cycles, the instantaneous corrosion rate was monitored by AC impedance method together with the corrosion potential. The corrosion rate increases at the initial stage of the wet–dry cycles because the native oxide on the coating surface is dissolved into the solution and converted to hydrated zinc and aluminum oxides, and then decreases slowly owing to the accumulation of the corrosion products over the coating surface. The corrosion mechanism of 55%Al–Zn coating is discussed on the basis of the monitoring results.

Corrosion of Iron Under Alternating Wet and Dry Conditions

Abstract In-situ alternating current (AC) and direct current (DC) electrochemical techniques were used to determine the corrosion rate and corrosion potential of high-purity iron under alternate wet and dry conditions. Comparisons between DC electrochemical measurements and weight loss were conducted to verify the validity of the corrosion rate measurements. Identification of the corrosion products was performed using Raman spectroscopy. Corrosion products contained layers of iron oxides and oxyhydroxides. At low Cl− concentrations, corrosion products consisted of lepidocrocite (γ-FeOOH) and magnetite (Fe3O4). At higher Cl− concentrations, the formation of akaganeite (β-FeOOH) was observed. Corrosion rates and corrosion potentials fluctuated throughout the wet cycles depending on electrolyte layer thickness, ionic strength, and wetting cycle. Accelerated corrosion rates of high-purity iron, up to three times those observed under continuously immersed conditions, were the result of Fe(III) reduction in the...

A study of the effect of concentration build-up of electrolyte on the atmospheric corrosion of carbon steel during drying

Impedance and cathodic polarization measurements for carbon steel under a thin layer of Na 2SO 4 solution of varying concentrations were conducted to investigate the effect of concentration build-up on the atmospheric corrosion of carbon steel. Electrolyte thickness was controlled by two methods. One is a microsyringe method which allows a predetermined amount of the electrolyte to be dropped onto the metal surface to make electrolyte layers of different thickness with the same electrolyte concentration; the other is a drying method which controls a water layer thickness through drying, causing concentration build-up of electrolyte during thinning. The concentration build-up has two opposite effects on the atmospheric corrosion rate of carbon steel depending on electrolyte layer thickness. For a comparatively thick electrolyte layer in which the atmospheric corrosion of carbon steel is controlled by a cathodic oxygen reduction reaction, the concentration build-up reduced the corrosion rate. However, it increased the corrosion rate for a very thin electrolyte layer. The critical thickness for maximum corrosion rate also changed by the concentration build-up, which indicates that the concentration build-up is the important factor responsible for determining the critical thickness.

ケルビンプローブによる低合金鋼の乾湿繰り返し腐食過程における薄液膜厚さと腐食電位の計測

ケルビンプローブによる低合金鋼の乾湿繰り返し腐食過程における薄液膜厚さと腐食電位の計測

Influence of Electrolyte Layer Thickness and pH on the Initial Stage of the Atmospheric Corrosion of Iron

Cathodic polarization curves for the reduction of oxygen and protons on platinum and iron electrodes under thin electrolyte layers (Xf: 1 mm to 10 μm) were measured to elucidate the effects of the thickness and the pH of the electrolyte layer on the initial atmospheric corrosion stage of iron. A limiting current was exhibited on the cathodic polarization curves under neutral electrolyte layers containing 0.1 to 2 M NaCl, which was inversely proportional to the thickness of the electrolyte layer down to approximately 20 μm. This result indicates that oxygen diffusion through the electrolyte layer is the rate‐determining step (rds) for the oxygen reduction process. Meanwhile the limiting current under still thinner layers (Xf: 10 to 20 μm) was independent of the thickness, where an oxygen dissolution step at the air/electrolyte interface is the rds because of the considerably higher diffusion rate under such very thin electrolyte layers. AC impedance corrosion monitoring of iron for the period of 4 h was performed under electrolyte layers of different thickness (Xf: 1 mm to 10 μm) and pH (pH 3.0, 4.0, and 5.7). The results indicated that the corrosion rate showed a maximum at an electrolyte thickness of 20 to 30 μm in all cases, and the effect of pH on the atmospheric corrosion rate was negligible, except for cases wherein a relatively thick electrolyte layer (>1 mm) was present for a short exposure period (<1 h). This can be attributed to a neutralization of the electrolyte due to corrosion reaction because of the extremely limited amount of electrolyte present.

Behaviour of the current in a membrane-covered disc microelectrode under steady-state conditions

The inlaid disc electrode covered with a membrane can be modelled as a system with axial symmetry containing several parallel layers with different permeabilities. A recent solution of the steady state under diffusion limited conditions of an electroactive species in such a system is implemented with Mathematica. Computation of the theoretical current becomes an easy and fast procedure, capable of being implemented on any personal computer or workstation. The effects of the membrane permeability, the thickness of the membrane, the electrode radius and the electrolyte layer thickness on the current are analysed. We define an index of edge-effect contribution of each layer to the overall flux, providing their formulae together with the physical interpretation. For many sets of parameters, the edge-effect is responsible for an important contribution of the radial diffusion within the electrolyte and membrane. More accurate determination of the permeabilities of the different media is now possible experimentally, as the functional dependence of the current on the physical parameters is readily available for fitting procedures.

Numerical simulation of the time-dependent current to membrane-covered oxygen sensors: Part I. The switch-on transient

We have examined the nature of the diffusion processes and determined the transient current characteristics of membrane-covered Clark-type oxygen senso Correction for a singularity at the edge of the cathode allows us to achieve a numerical solution which we demonstrate to the accurate to 1%. Earlier o shown to be grossly inadequate for predicting the variation in behaviour with cathode radius and electrolyte layer thickness. The calculated depletion system affect sensitivity and transient response, which is examined more closely as a function of the membrane characteristics. The time dependence of processes involved. The calculations were facilitated by the availability of fast computing on transputers.

An experimental study of oxygen probe linearity and transient characteristics in the high oxygen concentration range

A systematic study was made of the linearity and transient characteristics of oxygen probes with large-surface cathodes ( d K = 0.35–7.0 mm) to elucidate the effects of experimental conditions. The following effects were investigated: electrolyte pH and layer thickness; addition of catalase to electrolyte; membrane material and thickness; cathode material; and the direction and level of concentration changes. The experimental results were so organized as to provide a synoptical pattern of information which would lend itself, as an aid, to the efforts of those seeking oxygen probes of more desirable linearity and transient characteristics.

A spherical model of the clark electrode in a flowing liquid medium

A spherical model has been developed for a Clark electrode immersed in a flowing liquid medium. This model relates the sensitivity of the electrode to cathode radius, to electrolyte layer permeability and thickness, to membrane permeability and thickness and to the concentration boundary-layer thickness established by the flowing medium. The model was tested with sensitivity values obtained from a 1.3 cm diameter Teflon-covered electrode assembly which was placed in a 2.5 cm i.d. flow loop such that the centerline streamline stagnated at the cathode. The data set spanned a range of cathode radii from 65 to 677 μm, membrane thicknesses of 6 μm and 76 μm and a range of mean axial tube velocities ( V) from 0.5 to 62 cm s −1 corresponding to tube Reynolds numbers of 125–16,000. The boundary-layer thickness was assumed to be of the form (γ V − n ) and the constants γ and n were determined by a non-linear least-squares regression of the sensitivity data to the spherical model. For the purposes of this regression, the sensitivity values were grouped into a laminar and a turbulent data set and (γ, n) values were determined for each set separately. The parameters P e/ P m (electrolyte to membrane permeability ratio) and ω e (electrolyte layer thickness) were treated as constants, with their values set at the regressed values previously obtained from fitting the gas-phase sensitivity values. Here, γ and n were both treated as free parameters. The spherical model fits the experimental current values in the laminar and turbulent regions with average relative errors of 8.74% and 13.1% respectively. Residuals were randomly distributed over the range of cathode radii and the two membrane thicknesses used. The final regressed values of γ and n were 0.0307 and 0.518 respectively for the laminar region, and 0.0317 and 0.451 respectively for the turbulent region. The n value for the laminar region is in reasonable agreement with the theoretically predicted value of 0.5. For comparison, a one-dimensional planar model was used to correlate the laminar and the turbulent data sets. Here again the parameters P e/ P m and ω e were assigned those values previously obtained from fitting gas-phase sensitivity values by the planar model. The relative average errors, 34.7% and 37.6% for the laminar and turbulent regions respectively, were excessively large and the final regressed value of n, 0.387 for the laminar data set, was unrealistic with respect to the theoretical prediction.

A spherical model of the clark electrode

A spherical model that relates the sensitivity ( S) of a Clark electrode to cathode radius ( a), to electrolyte layer permeability ( P c) and thickness ( ω c), and to membrane permeability ( P m) and thickness ( ω m) has been developed. This model was used to correlate two different data sets, one obtained from polypropylene-covered ( P m=1.7×10 −11cm 3 O 2/cm.s.Torr) and the other obtained from Teflon-covered ( P m=6.0×10 −11 cm 3 O 2/cm.s.Torr) Clark electrodes. The two data sets spanned a range of cathode radii from 10 to 677.5 μm and a range of membrane thickness from 6.35 to 76.2 μm. The spherical model fits the experimental sensitivity values with average relative errors of 13.3 and 23.9% for the polypropylene and Teflon data sets respectively; individual errors were randomly distributed over the range of membrane thicknesses, membrane permeabilities and cathode radii. The final regressed values of the free parameters ( P c/ P m and ω c) were found to be 69.22 and 27.7 μm, respectively, for the polypropylene data, and 6.13 and 154.6 μm, respectively, for the Teflon data. Although the P c/ P m values are consistent with reported values in the literature, ω c values are larger than expected. For purposes of comparison, a one-dimensional planar model and a pseudo-two-dimensional model were also used to correlate the data sets. The planar model was incapable of fitting sensitivity values corresponding to small cathode radii, and the pseudo-two-dimensional model was incapable of fitting sensitivity values for the Clark electrodes covered with the more permeable (Teflon) membrane. Final regressed values of the two free parameters ( P c/ P m and ω c) were generally unrealistic for these two models.

The Use of Concentrated NaN03in tcPo2Electrodes to Diminish O2Consumption and Dehydration Drift

We investigated: (1) The effects of NaN03 concentration, membrane material and thickness, and electrolyte layer thickness on electrode O2 consumption, stirring effect (O) and response time; (2) The effect of NaNO3 on P(H20) and electrode drift; and (3) The effect of KCl on Ag deposition at the cathode. Electrolytes containing 0–8 m NaN03, 0.01 m KCl, and 0.1 m pH 7 phosphate were tested in a 20 μ cathode tcPo2 electrode at 42dC. Increasing NaNO3 concentration reduced O2 solubility and sensitivity by a factor: e-(C/4.6). Thus, sensitivity was a linear function of solubility. Without cellophane, sensitivity with 12 μm polypropylene was 50% that of 25 μm Teflon; 7 m NaNO3 reduced sensitivity for both membranes by about 60%. 12 μ cellophane, by increasing the thickness of the electrolyte layer, minimized the difference between the membranes and exaggerated the effects of increasing NaNO3 concentration on sensitivity. O was a linear function of sensitivity. Cellophane decreased the ratio of O to sensitivity. Response times of electrodes were almost unaffected by addition of NaNO3, but were increased as expected by use of thicker membranes, and by addition of cellophane spacers. Electrolyte vapour pressure was decreased 67% by addition of 7 m NaNO3. When electrolyte vapour pressure differed significantly from that of skin or calibration solutions, water crossed the polypropylene or Teflon membranes, changing the O2 sensitivity, and causing drift both on skin and in calibration solutions. With KCl containing electrolytes, silver deposition occurs at the cathode, the rate of deposition increasing greatly as KCl concentration approaches saturation. Thus addition of NaNCO3 to O2 electrolytes lowers vapour pressure, delays dehydration, reduces O2 sensitivity by reducing permeability of the electrolyte layer to O2, and thereby reduces the gas/skin correction factor O, without significantly delaying response time, and without increasing silver deposition.