Diffusion Layer Thickness Research Articles

Structure of Zinc Coating on Steels Formed by Diffusion Saturation in Nitrogen-Containing Atmosphere

Diffusion technique of metallization is applied for receiving of zinc coatings on low-carbon steel with transitional zone. Structure of diffusion zinc layers after saturation of 09Mn2Si steel in ammonia at different temperatures is examined. Effects on saturation temperature on thickness of diffusion layers are discovered. Process at 600⁰C forms diffusion layers with high strengthening level and with smooth microhardness profiles. Elements (Fe, Zn, N) spectrums are analyzed, and phase composition of zinc coating and of transitional zone is determined.

Effect of Gas Diffusion Layer Thickness and Rib-Channel Width on Liquid Water and Oxygen Transport in Polymer Electrolyte Fuel Cells: A Hybrid Pore-Network/Continuum Model

Effect of Gas Diffusion Layer Thickness and Rib-Channel Width on Liquid Water and Oxygen Transport in Polymer Electrolyte Fuel Cells: A Hybrid Pore-Network/Continuum Model

Effect of electrolyte concentration on electrochromic performance of sputtered tungsten oxide film: Experiments and simulation

Tungsten oxide (WO3) thin films are of critical importance in electrochromic devices as positive electrodes. However, the effect of electrolyte properties on the electrochromic properties of these films is not well ascertained. Herein, we demonstrate the effect of various LiClO4 salt concentrations in propylene carbonate (PC) on the switching speed and coloration efficiency of RF sputtered tungsten oxide film via experiments and simulation. The model developed for simulating the electrochromic performance of the WO3 thin films is based on dilute solution theory. The model is flexible enough to account for variable physical properties: lithium salt concentrations, film thickness and thickness of electrolyte diffusion layer. Relevant model parameters are obtained by fitting the model predicted cyclic voltammogram to experimental data obtained from a three-electrode cell composed of sputtered tungsten oxide, platinum, and Ag/AgCl. The switching time strongly depends on thickness of WO3 thin film and the electrolyte diffusion layer while the depth of coloration depends on concentration of the salt and operating voltage. Our simulated and experimental results provide an insight into the design of electrochromic devices with excellent switching speed and coloration efficiency.

Electrochemical Impedance Spectroscopy of Anion-Exchange Membrane AMX-Sb Fouled by Red Wine Components.

The broad possibilities of electrochemical impedance spectroscopy for assessing the capacitance of interphase boundaries; the resistance and thickness of the foulant layer were shown by the example of AMX-Sb membrane contacted with red wine from one side and 0.02 M sodium chloride solution from the other side. This enabled us to determine to what extent foulants affect the electrical resistance of ion-exchange membranes, the ohmic resistance and the thickness of diffusion layers, the intensity of water splitting, and the electroconvection in under- and over-limiting current modes. It was established that short-term (10 h) contact of the AMX-Sb membrane with wine reduces the water-splitting due to the screening of fixed groups on the membrane surface by wine components. On the contrary, biofouling, which develops upon a longer membrane operation, enhances water splitting, due to the formation of a bipolar structure on the AMX-Sb surface. This bipolar structure is composed of a positively charged surface of anion-exchange membrane and negatively charged outer membranes of microorganisms. Using optical microscopy and microbiological analysis, it was found that more intense biofouling is observed on the AMX-Sb surface, that has not been in contacted with wine.

Two-phase developing laminar mixing layer at supercritical pressures

Numerical analysis of a shear layer between a cool liquid n-decane hydrocarbon and a hot oxygen gas at supercritical pressures shows that a well-defined phase equilibrium can be established. Variable properties are considered with the product ρμ in the gas phase showing a nearly constant result within the laminar flow region with no instabilities. Sufficiently thick diffusion layers form around the liquid-gas interface to support the case of continuum theory and phase equilibrium. While molecules are exchanged for both species at all pressures, net mass flux across the interface shifts as pressure is increased. Net vaporization occurs for low pressures while net condensation occurs at higher pressures. For a mixture of n-decane and oxygen, the transition occurs around 50 bar. The equilibrium values at the interface quickly reach their downstream asymptotes. For all cases, profiles of diffusing-advecting quantities collapse to a similar solution (i.e., function of one independent variable). Validity of the boundary layer approximation and similarity are shown in both phases for Reynolds numbers greater than 239 at 150 bar. Results for other pressures are also taken at high Reynolds numbers. Thereby, the validity of the boundary layer approximation and similarity are expected. However, at very high pressures, the similar one-dimensional profiles vary for different problem constraints.

Effects of pore density on microstructure and mechanical properties of porous SiC ceramic foam/Zr-based metallic glass interpenetrating phase composites

The porous SiC ceramic foam/Zr-based metallic glass interpenetrating phase composites were prepared by water quenching after pressure infiltration. Effects of pore density on microstructure and mechanical properties of interpenetrating phase composites are reported. Microstructural investigations show that the metallic glass is completely infiltrated into the open pores of the SiC ceramic foams and a typical interconnected amorphous phase is formed. A ~10 µm thick diffusion layer in which the reactant ZrC is generated can be found between the ceramic phase and the glassy phase. The average size of the metallic glass phase decreases with increasing the pore density. The results of the quasi-static compression tests indicate that the compressive strength of the composites increases with the pore density of the SiC foams due to the formation of more high-quality interfaces. The brittle fracture of the composites is mainly attributed to the premature destruction of the SiC foams. The results of friction tests imply that compared with monolithic Zr-based BMG samples, the reinforcement of SiC retards the adhesive wear and plastic deformation of Zr-based BMG, and reduces the friction coefficient of the composites.

Flow-Driven Release of Molecules from a Porous Surface Explored Using Dynamical Density Functional Theory

We investigate the release of hard-sphere-like molecules from a porous medium to a continuum fluid using dynamical density functional theory. The hard-sphere interactions are employed on the basis of the weighted density approximation. The model porous medium is assumed as a planar wall and molecules are loaded in the medium at an effective density. An equivalent surface density of molecules is applied to determine the surface flux taking into account both the effective medium density and near-wall density fluctuations in the fluid. In the presence of an external flow field which is parabolic near wall, a diffusion layer similar to the mass transfer boundary layer is developed downstream. We compare the effects of various physical parameters including molecular diffusivity, velocity field, interfacial mass transfer resistance, interfacial normal velocity, and effective medium density. We demonstrate that wall-mediated hard-sphere interactions impact the density distribution of released molecules such that the diffusion layer thickness is increased and the near-wall density fluctuation is observed. Moreover, for transient release with a finite amount of loaded molecules, the maximum concentration of the released molecules at different times is identified as a function of distance from the surface. The information gained in this study would be useful to predict the desorption or release efficiency of molecules from a given porous material subjected to various physically-relevant conditions.

Transport-Based Modeling of Bubble Nucleation on Gas Evolving Electrodes.

Bubble nucleation is ubiquitous in gas evolving reactions that are instrumental for a variety of electrochemical systems. Fundamental understanding of the nucleation process, which is critical to system optimization, remains limited as prior works generally focused on the thermodynamics and have not considered the coupling between surface geometries and different forms of transport in the electrolytes. Here, we establish a comprehensive transport-based model framework to identify the underlying mechanism for bubble nucleation on gas evolving electrodes. We account for the complex effects on the electrical field, ion migration, ion diffusion, and gas diffusion arising from surface heterogeneities and gas pockets initiated from surface crevices. As a result, we show that neglecting these effects leads to significant underprediction of the energy needed for nucleation. Our model provides a non-monotonic relationship between the surface cavity size and the overpotential required for nucleation, which is physically more consistent than the monotonic relationship suggested by a traditional thermodynamics-based model. We also identify the significance of the gas diffuse layer thickness, a parameter controlled by external flow fields and overall electrode geometries, which has been largely overlooked in previous models. Our model framework offers guidelines for practical electrochemical systems whereby, without changing the surface chemistry, nucleation on electrodes can be tuned by engineering the cavity size and the gas diffuse layer thickness.

Secondary Reduction of Refractory Metal near Smooth Cathode during the Salt Melt Electrolysis. 3. Numerical Reproducing of Natural Experiment with the Nb Cathodic Reduction in KNaCl2–NaF–K3NbF7 Melt

In terms of the model of steady-state process of a refractory-metal ion secondary reduction with an alkali (or alkali-earth) metal formed on a smooth cathode during salt melt electrolysis, numerical reproducing of a natural experiment is carried out. The model calculations are based on the polarization measured during the cathodic reduction of Nb in chloride―fluoride melt: [Nb] = 2.4 mol %, 800°C, current density i up to 5.4 A/cm2. On a smooth cathode in the overvoltage range from 0.21 to 0.41 V (i = 0.75―1.17 A/cm2), the reduction mechanism is shown to completely change from primary to the secondary reduction. The secondary reduction zone is located inside the diffusion layer and moves away from the cathode with increasing i. Even at maximal i, this zone remains inside δ (δ is the thickness of the diffusion layer): with i = 0.96 A/cm2, the coordinate of the maximum of the secondary reduction rate xm = 0; with i = 5.4 A/cm2, xm = 0.93δ (in the experiment, the value of i at which xm ≥ δ was not achieved). At i = 5.4 A/cm2, the fraction of secondary reduction in the bulk is insignificant, ≈10−5 A/cm2. The δ vs. E curve is calculated: when E is shifted from the equilibrium value toward the negative values, |i| increased from zero and higher, whereas δ first decreased by an order of magnitude and then increased. Correspondingly, the limiting diffusion current is not constant at a constant Nb concentration in the bulk. This is the reason of uncertain limiting current on steady-state cathodic polarization curves during the electrolysis of metals in melts. A hypothesis is proposed on the dependence of the Nernst diffusion layer thickness near the cathode on the current density exceeding the limiting diffusion current density under the conditions of secondary reduction.

High temperature diffusion behavior between Ta-10W coating and CP-Ti and TC4 alloy

To improve high temperature properties of Titanium alloy, Ta-10W coating was deposited by multi-arc ion plating (MAIP) technique on commercial pure titanium (CP-Ti) and TC4 (Ti-6Al-4V) titanium alloy respectively. The microstructures and high temperature diffusion behavior of Ta-10W coating on CP-Ti and TC4 alloy were investigated by XRD, SEM and EDS. The results showed that the obtained Ta-10W coatings consisted of α-Ta, exhibiting an integrated and compact surface as well as excellent interface bonding. For the Ta-10W/Ti samples, a TiTa solid solution diffusion layer formed and gradually became thicker and thicker over time. After diffusion for 50 h, massive titanium element even diffused to the surface of the coating. During cooling, the β-Ti → α′-Ti martensitic phase transformation occurred, and the martensitic relief morphology appeared on the surface of the coatings. Meanwhile, α-Ta precipitated along the laminate boundary of α-Ti, which leads to the formation of white stripe-like structure in the diffusion layer. Dissimilarity, the Ta-10W/TC4 samples possessed relative high diffusion rate, but the Ti didn't reach the surface of the sample after 50 h. There was a thick diffusion layer which contained two layers formed between Ta-10W and TC4 after heat treatment of 10h, and the Kirkendall voids appeared near the interface of Ta-10W/TC4. This work is helpful to understand the high-temperature performance of refractory coating and provides a new idea for the further study of protective coatings on Titanium alloy.

(Invited) Short Introduction of Brenner’s Paradigm on the Steady State Diffusion Layer Model of Alloy Electrodeposition Composition Control, and Its Possible Extensions

Understanding the composition control of alloy electrodeposition is the prerequisite of pursuing fundamental understandings of phase and morphology evolution in the deposit. It is well known that a constant electrolyte concentration boundary, called diffusion layer, will form when the system is under forced convection or natural convection.[1] Given enough time, the thickness of diffusion layer, which in the beginning follows the Cottrell equation, will reach a steady state value, and thus a steady state deposition flux rate and deposition current could be estimated using the ionic diffusivity and diffusion layer length. For alloy electrodeposition, using the steady state deposition flux rate, ideally, the composition of the deposit could be predicted by the concentration ratio in the electrolyte and the mass-transfer coefficient ratio of the depositing ions.Despite being proposed by Essin in the 1930s and systematically documented in Brenner’s famous alloy electrodeposition book in the 1960s,[2, 3] nowadays, this behavior seems to be set aside when investigating the alloy electrodeposition properties. We decided to summarize the recent evidence for the composition control at the limiting case of diffusion layer control (limiting current condition) and discuss the confusions we are facing when applying this paradigm of alloy electrodeposition composition control at steady state.In this presentation, we will tentatively present the following topics: Levich in the 1960s has estimated the diffusion layer thickness of the electrodeposition on a vertical plate without any forced convection: when depositing in low viscosity electrolytes without forced convections, the natural convection will be induced by the tiny variation of local electrolyte density of the electrolyte and lead to the formation of diffusion layer.[4, 5] We will briefly present his model and derivation. From this model, the diffusion layer thickness due to 0.01mM Ni(II) at the height of 1 cm on the vertical electrodecould be as much as 0.21 cm. The time for reaching the steady state diffusion layer thickness and the initial layer thickness of the deposit (assuming two elements start to be deposited simultaneously) is estimated using the Cottrell equation.Expansion of mass-transfer coefficient to higher orders with respect to concentration, under the circumstances of multi-component, multi-element alloy electrodeposition. The matrix for multicomponent system could be fitted from the experimental data with a designated order of approximation on the mass-transfer coefficient. We will give the example for fitting the simplest case: binary system with linear behavior, based on data mentioned in our AgFe DMH-citrate work, where both ions are complexed as anions and deposited under limiting current condition. Meanwhile, a tentative construction of multi-element electrodeposition is given from the tabulated ionic diffusivities and a fixed diffusion layer thickness.Non-linear behaviors of deposit composition ratio - electrolyte concentration ratio sometimes happen in the alloy electrodeposition comparing with the prediction from the diffusion layer model. We will conceptually discuss the several possible causes for this non-linear behavior: the existence of homogeneous reaction inside the diffusion layer due to the pH and ligand concentration variation,[6] the transition from laminar flow to turbulent flow of the electrolyte near the electrode due to hydrogen bubbles and high deposition rate,[1] the formation of extended charge region at the cathode under overlimiting current,[7] and the situations where charge transfer kinetics governs the overall deposition rate.

(Invited) Magnetoelectrochemistry – New Way to Control Morphology of Cathodic Deposit

Magneto-electrochemistry is a domain where three disciplines interact: electrochemistry, fluid mechanics and magnetism. These three fields are individually well established, but recently there has been a surge in interest in magneto-electrochemistry, since in combination with electrodeposition, it offers an opportunity to advance both fundamental as well as practically-relevant issues. There is great potential in several industrial areas to improve the efficiency of electrochemical processes by magnetic fields, such as plating, electropolishing and electrolysis of water. Further application areas are related to lab-on–the-chip technology, electrolysis, fuel cells and electrochemical machining.Following issues will be discussed:- The influence of magnetic field and its gradients on the mass transfer rate, diffusion layer thickness and consequently the control of mass-transfer process based on the electric current distribution (via the Lorentz force) or on the magnetic susceptibility of the electrolyte (via the field-gradient force).- The electric and magnetic forces on ions modifying near-wall hydrodynamics and interface interaction, kinetics and physical properties as surface tension or viscosity.- Improving deposit quality and properties such as surface smoothening, homogeneity, composition and texture.- Improving energy efficiency of large-scale processes such as electrowinning and in devices such as fuel cells- Mask-free structured deposition using spatially-inhomogeneous magnetic fields.- Using tailored transport of ions or charged species to control separation, mixing, and reaction occurring in microchannels in lab-on-the-chip technologies, fuel cells, gas evolving processes, metal recycling, etc.

Aggregate-Free Deposition of Highly Organized Nanocomposite Silica Thin Films on Conductive Substrates By Electrochemically Induced Templated Sol-Gel Synthesis

The synthesis of ordered nanocomposite or nanoporous silica thin films by template-assisted sol-gel processes offers interesting applications in various fields including catalysis, sensors, membranes and energy. The electrochemically assisted self-assembly method allows the growth of highly ordered vertically aligned nanoporous silica thin films on conductive substrates. This orientation, optimized for high mass-transport capabilities, is difficult to obtain by classical approaches. The method involves submerging the conductive substrate in a pre-hydrolyzed precursor liquid followed by the application of a cathodic potential, thereby causing the electrogeneration of hydroxide ions. The pH increase in the diffusion layer near the electrode surface catalyzes the sol-gel formation and the result is a silica thin film that grows on the conductive substrate. The addition of cetyltrimethylammonium bromide (CTAB) micelle templates leads to the formation of a highly ordered nanostructure.A fundamental limitation of the method as reported in the literature is that the maximum layer thickness which can be obtained is rather limited due to the formation of aggregate by-products. In our contribution we show that diffusion layer thickness control is essential to obtain aggregate-free layers. Silica formation is catalyzed by OH- formed in the electrode’s diffusion layer, which quickly grows up to hundreds of microns under stationary conditions, thereby leading to composite thin films as well as precipitation of aggregates. By using a rotating disc electrode, the hydrodynamic layer is controlled, enabling aggregate-free film growth over a wide thickness range. Additionally, thin film coatings on high aspect ratio micropillar structures were demonstrated. Parameters such as precursor age, deposition temperature and deposition current were systematically investigated and the deposits were characterized using SEM, ellipsometry, TEM, FT-IR and an electrochemical redox probe. Using these techniques, we demonstrated the controlled growth of aggregate-free, uniform and nanostructured thin films with high mass-transport capabilities and thicknesses of 20 nm up to 15 µm, thereby significantly expanding the range of 50-150 nm as reported in literature. These results are explained using a single hydrodynamic layer model. Figure 1

Experiments and Simulations on the Turbulent, Rarefaction Wave Driven Rayleigh–Taylor Instability

AbstractExperiments were performed to observe the growth of the turbulent, Rayleigh–Taylor unstable mixing layer generated between air and SF6, with an Atwood number of A=(ρ2−ρ1)/(ρ2+ρ1)=0.64, where ρ1 and ρ2 are the densities of air and SF6, respectively. A nonconstant acceleration with an average value of 2300g0, where g0 is the acceleration due to gravity, was generated by interaction of the interface between the two gases with a rarefaction wave. Three-dimensional, multimode perturbations were generated on the diffuse interface, with a diffusion layer thickness of δ=3.6 mm, using a membraneless vertical oscillation technique, and 20 experiments were performed to establish a statistical ensemble. The average perturbation from this ensemble was extracted and used as input for a numerical simulation using the Lawrence Livermore National Laboratory (LLNL) Miranda code. Good qualitative agreement between the experiment and simulation was observed, while quantitative agreement was best at early to intermediate times. Several methods were used to extract the turbulent growth constant α from experiments and simulations while accounting for time varying acceleration. Experimental, average bubble and spike asymptotic self-similar growth rate values range from α=0.022 to α=0.032 depending on the method used, and accounting for variable acceleration. Values found from the simulations range from α=0.024 to α=0.041. Values of α measured in the experiments are lower than what are typically measured in the literature but are more in line with those found in recent simulations.

Effects of benthic hydraulics on sediment oxygen demand in a canyon-shaped deep drinking water reservoir: Experimental and modeling study

Sediment oxygen demand (SOD) is a major contributor to hypolimnetic oxygen depletion and the release of internal nutrient loading. By measuring the SOD in experimental chambers using in both dissolved oxygen (DO) depletion and diffusional oxygen transfer methods, a model of SOD for a sediment bed with water current-induced turbulence was presented. An experimental study was also performed using near-sediment vertical DO profiles and correlated hydraulic parameters stimulated using a computational fluid dynamics model to determine how turbulences and DO concentrations in the overlying water affects SOD and diffusive boundary layer thickness. The dependence of the oxygen transfer coefficient and diffusive boundary layer on hydraulic parameters was quantified, and the SOD was expressed as a function of the shear velocity and the bulk DO concentrations. Theoretical predictions were validated using microelectrode measurements in a series of laboratory experiments. This study found that flow over the sediment surface caused an increase in SOD, attributed to enhanced sediment oxygen uptake and reduced substances fluxes, i.e., for a constant maximum biological oxygen consumption rate, an increased current over the sediment could increase the SOD by 4.5 times compared to stagnant water. These results highlight the importance of considering current-induced SOD increases when designing and implementing aeration/artificial mixing strategies.

Effect of annealing temperature and time on the microstructure, mechanical properties and conductivity of cold-rolled explosive Cu/Al composite sheets

The 1.5 mm thick Cu/Al composite sheet was obtained after explosive-welding and 6 passes cold rolling. The effects of annealing temperature and time on the microstructure, mechanical properties, and conductivity of cold-rolled Cu/Al composite sheets were investigated. The results show that the thickness of the interface diffusion layer with compounds of Al2Cu, AlCu, and Al4Cu9 increases with the increase in annealing temperature and holding time, and the total activation energy is 108 kJ mol−1. The tensile strength of composite sheets decreases and the fracture elongation increases with the increase of annealing temperature. Especially when the annealing temperature increased from 300 ℃ to 350 ℃, the tensile yield strength decreased from 225 MPa to 77 MPa, and the elongation increased from 16% to 37.5%. The tensile-shear strength of composite sheets reaches to 117 MPa after annealing at 400 ℃ for 2 h. The conductivity of composite sheet is greatly affected by the annealing time. At the annealing temperature of 350 ℃ and time of 4 h, the composite sheets show a better conductivity of 96.4% IACS.

Optimization study of the produced electric power by planar PEMFC-SCG

In this paper, the mathematical equations that govern the physical phenomena produced during the operation of a single cell of a planar Proton Exchange Membrane Fuel Cell with straight channel geometry for the counter- and co-flow arrangements have been solved. A three-dimensional, non-isothermal, steady-state and single-phase model is employed in order to locate the optimal dimensions of the studied fuel cell that deliver the optimum performance. Numerous dimensions such as channels’ width/height, thickness of the gas diffusion layercatalyst layer and membrane thicknesses are investigated. The graphical method is employed to optimize the produced power density versus the operating voltage and current density. From the obtained results, it is found that decreasing the channels’ width/height increases the produced power density and leads to an optimum range dimension. Added to that, the thickness of the gas diffusion layer, catalyst layer and membrane thicknesses have a significant effect on the performance of the PEMFC. The membrane thickness has the biggest impact on this last one’s performance, which can be improved by 181.84 % considering only the studied geometric parameters.

Dominated flow parameters applied in a recirculation microbial fuel cell

Scaling up of microbial fuel cells is a challenge for practical applications in wastewater treatment. In addition, the flow control is an important aspect for the electrochemical reactions occurring at the electrodes are influenced by fluid motions. By using dimensionless parameter analysis fluid regimes can be investigated in different scales of reactors. In this study, four important dimensionless flow parameters such as Reynolds number, Péclet number, Schmidt number, and Sherwood number were used for systematic analysis of hydrodynamic effects and power performance of recirculation mode microbial fuel cells together with computational fluid dynamics method. Results showed that the higher value of Reynolds number enhanced the convective flow of anolyte due to the dominant inertial forces in the flow field. Therefore, Reynolds number of 1.6 × 101 were obtained high mass transfer coefficient of 4.76 × 10−7 m s-1 and thin diffusion layer thickness of 2.52 × 10-3 m. Maximum power density and limited current density of 2422.8 mW m-2 and 4736.4 mA m-2 were obtained respectively which were higher than Reynolds number of 0 by 1.61 and 1.69 times. These findings shall be useful for effective recirculation flow mode MFCs power production and have a great possibility for large scale applications.

Theoretical description of the ligand function for ionoselective electrodes reversible to metal anion complexes. 1. Lower detection limit and its determining factors

Within the framework of the steady-state diffusion model, the theoretical description for the thiocyanate ion lower detection limit (LDL) by the tetrathiocyanatozincate selective electrode, has been presented. The main assumptions of this model are constancy of the ion exchanger concentration along the membrane, traditionally used in various phaseboundary potential diffusion models, and linear profiles of components’ concentrations in diffusion layers. Simple quantitative expressions have been obtained, connecting thiocyanate ion concentration in the solution surface layer (responsible for LDL value) with phase boundary extraction equilibria constants, stability constants for zinc thiocyanate complexes, and diffusion parameters in the membrane and solution phases. Calculated LDL values are in good agreement with experimental data provided in the literature. It has been shown that LDL can be reduced substantially by controlling such easily regulated diffusion parameters as diffusion layer thickness in the membrane phase, which is a function of time, and diffusion layer thickness of the sample solution, which is governed by stirring regime.

Theoretical description of the ligand function for ionoselective electrodes reversible to metal anion complexes. 2. Selectivity to foreign ions

Within the framework of the steady-state diffusion model, the equations have been obtained explicitly describing the selective electrode selectivity coefficient to the ligand ion in relation to foreign ions not forming complexes with zinc ions, as a function of fundamental thermodynamic characteristics (exchange constants of tetrathiocyanatozincate for thiocyanate and foreign ion, concentrations of ion exchanger in the membrane and zinc ion in the sample solution), as well as controllable diffusion parameters (thicknesses of solution and membrane phase diffusion layers, governed by stirring mode and measuring time, respectively). Separate attention is given to cases of measurements in presence and in absence of constant background concentration of zinc ions in the sample solution. It has been shown that selectivity of tetrathiocyanatozincate selective electrode to thiocyanate ion in relation to anions not forming complexes with zinc, is several orders of magnitude higher than selectivity of an ordinary thiocyanate-selective electrode containing higher quaternary ammonium thiocyanate as an ion exchanger, and increases regularly with the background concentration of zinc ions. The results obtained are in general agreement with the experimental data given in the literature. It has been shown that variability of selectivity coefficients caused by variations of diffusion parameters within the limits corresponding to real measuring conditions, can be up to 0.3–0.4 orders of magnitude.