Peep Miidla

Adsorption of pyridine on the (111), (001) and (001) faces of bismuth

The adsorption of pyridine (PY) on Bi(111), Bi(001) and Bi(011) single crystal electrodes has been studied in 0.1 M aqueous NaF solution for concentrations of PY ranging from 1 to 200 mM. In the range of potentials explored, adsorption maximum coverage of the surface and the desorption of PY at E = −1.8 V (SCE) have been observed. At the negative potentials and polarization close to the potential of zero charge, PY molecules at bismuth single crystal planes assume a tilted orientation, with the hydrocarbon ring facing the metal. The saturation coverage Λmax and the limiting capacity C1 decrease, and the shift of zero charge potential EN, due to the displacement of surface water by a monolayer of PY, rises in the sequence of planes Bi(011) < Bi(001) < Bi(111) as the vertical component of the orientation of the PY molecules increases. Adsorption isotherms, values of the attraction constant a and standard Gibbs energy of adsorption ΔGads0 have been determined. As in the case of other organic compounds studied, the activity of Bi planes increases in the sequence of planes Bi(111) < Bi(001) < Bi(011). The partial change transfer from PY to Bi electrodes increases in the same direction of planes. The attractive interaction between the adsorbed molecules in the sequence of planes Bi(011) < Bi(111) < Bi(001) as the superficial density of atoms decreases. The absolute value of the Gibbs energy of adsorption of Py increases in the sequence of electrodes Ag Hg>Bi(001)>Bi(011).

Influence of surface pretreatment of bismuth and cadmium electrodes to the electric double layer and adsorption characteristics of organic compounds

Abstract Influence of the surface structure of electrodes on the electric double layer properties, as well as on the adsorption characteristics of various organic compounds has been investigated by cyclic voltammetry, impedance and electron microscopic methods at variously prepared Bi, Sb and Cd electrodes. The systematic trends of the influence of surface roughness and energetic inhomogeneity on the electric double layer characteristics (value of differential capacity, potential of diffuse minimum, Parsons-Zobel factor, inner layer capacity, roughness function) have been established. The dependencies of the shape of adsorption-desorption maxima of organic compounds and other adsorption parameters (values of attraction interaction, adsorption equilibrium constant, shape of adsorption isotherm) on the electrode surface structure have been investigated. The Debye-length dependent roughness function has been calculated. The approximate values of the linear parameter of homogeneous regions, which prevail at the surface of polycrystalline electrodes have been calculated using various theoretical models. The established values of linear parameters of homogeneous regions have been compared with the characteristics obtained from the electron microscopic studies.

Influence of charge density and electrolyte concentration on the electrical double layer characteristics at rough cadmium electrodes

Abstract A new effective diffuse layer thickness dependent surface roughness model, based on the non-linear Poisson–Boltzmann theory, has been used for the interpretation of impedance data for rough cadmium electrodes. The so-called electrochemical roughness function values at various electrode potentials and surface charge densities have been calculated. It was found that the roughness function values, the inverse value of Parsons–Zobel plot, as well as the fitting coefficient in the Valette–Hamelin approach, obtained from the electrochemical impedance data, are effective (seeming) parameters and do not characterise the real geometrical structure of electrode surface. However, they characterise the deviation of real experimental system from ideally smooth (flat) surface. In the region of moderate rational electrode potentials 0≤| E |≤0.2 V and surface charge densities (1≤| a |≤4 μC cm −2 ) the roughness function rises with the decrease of the effective thickness of diffuse layer. At higher electrode potentials and surface charge densities the surface roughness function levels of to the constant value, i.e. to the so-called geometrical surface roughness value. The new effective diffuse layer thickness dependent surface roughness theory needs future corrections taking into account the role of crystallographic inhomogeneity of the geometrically rough electrode surface, i.e. the dependence of the local surface charge density on the crystallographic structure of energetically homogeneous regions exposed on the macro-polycrystalline electrode surface.

Adsorption of isomers of butanol on bismuth single crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for quantitative study of normal butanol (n-BA), iso-butanol (iso-BA), sec-butanol (sec-BA) and tert-butanol (tert-BA) adsorption at the bismuth single crystal plane¦aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, the surface excess and other adsorption parameters have been determined. As found, the adsorption characteristics of the isomers of butanol depend on the crystallographic structure of the electrodes, as well as on the geometrical structure of hydrocarbon chains of adsorbate. The adsorption characteristics obtained from the impedance and chronocoulometric measurements are in good agreement within the limits of surface charge densities — 24 < σ < 3 μC cm−2. The adsorption of n-BA, sec-BA, iso-BA and tert-BA on Bi single crystal planes is physical and is limited by the rate of diffusion of organic molecules to the electrode surface. The adsorption activity of adsorbates at the bismuth¦solution interface increases in the sequence tert-BA < sec-BA < iso-BA < n-BA as the adsorption at the air¦solution interface increases. In the case of all compounds studied, the adsorption activity of planes increases in the sequence (101) ≤ (001) < (211) < (011) as the superficial density of atoms increases. According to the values of the standard Gibbs energy of adsorption, it was established that the hydrophilicity of electrodes increases in the sequence Sb(111) < Bi(011) < Bi(211¯) < Bi(101) ≤ Hg < Bi(001) < Bi(111) < Cd(0001) < Zn(0001) < Ag(111) < Ag(100) < Ga.

Adsorption of normal hexanol on bismuth single crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for a quantitative study of 1-hexanol (n-HA) adsorption at the bismuth single crystal plane|aqueous Na2SO4 solution interface. The adsorption characteristics obtained from the impedance and chronocoulometric measurements are in reasonable agreement within the limits of surface charge densities −18<σ<5 μC cm−2. The adsorption isotherms, Gibbs energies of adsorption ΔGA0, the limiting surface excess Γmax and other adsorption parameters, dependent on the crystallographic structure of electrodes, have been determined. The adsorption of n-HA on Bi single crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for n-HA with normal propanol (n-PA), normal butanol (n-BA), butyl acetate (BAC), cyclohexanone (CHN), cyclohexane carboxylic acid (CHCA) and cyclohexanol (CH) shows that the adsorption characteristics depend on the structure of the hydrocarbon radical, as well as on the chemical nature of the functional group of the adsorbate. The adsorption activity of adsorbates at the bismuth|solution interface increases in the sequence n-PA<n-BA<n-HA as the adsorption at the air|solution interface increases. In the case of all compounds studied, the adsorption activity increases in the sequence of planes (111)<(001)<(011). According to the values of the standard Gibbs energy of adsorption it was established that the hydrophilicity of electrodes increases in the sequence Sb(211)<Sb(001)<Sb(111)<Bi(011)<Bi(211)<Bi(101)≤Hg≤Bi(001)<Bi(111)<Cd(0001)<Cd(1010)<Cd(1120)<Ag(111)<Ag(100)<Ga<Ag(110)<Zn(0001)<Zn(1010)<Zn(1120).

The efficiency of Estonian central public libraries

Purpose – This paper sets out to describe the results of a four‐year‐long study into the efficiency of Estonian central public libraries.Design/methodology/approach – The study uses data envelopment analysis (DEA), a non‐parametric linear programming‐based tool to determine the relative efficiency of 20 central public libraries of Estonia. Relative efficiency shows the capacity of an organisation to provide the same output for less expenditure.Findings – The study finds that 40 per cent of the libraries investigated used their resources effectively. Efficiency scores of the rest of the libraries varied from 0.74 to 0.98, with staff expenditure slack being the main inefficiency factor for half of inefficient libraries.Originality/value – The results of this research enhance the diagnostic capacity for planning the future activities of Estonian central public libraries and offers insights into using DEA for efficiency measurement and decision‐making in public libraries in general.

A Mathematical Model of Troposphere Water Vapor Tomography

The tomographical contribution of the Global Positioning System (GPS) is possible due to methods of high precision detection of tropospheric delays of navigation signals from the satellites to the receivers. A system of linear equations with rectangular matrices is considered as the mathematical model of troposphere water vapor distribution. The authors use numerical simulation as the most time- and cost-efficient way to study the different processes related to this model to realize the tropospheric water vapor tomography. The possible mathematical approach to construct the virtual ground-based sensors (GPSreceivers) network for a real geographical location and discretization of the troposphere are described. The output of tomographical modeling of the troposphere might be applied to improve the results of large scale numerical weather prediction models but also real-time navigation. The questions of voxel geometry and methods of data processing are expected as further key questions in constructing an effective GPS-receiver network for water vapor tomography.

Simulation of a Twisting-Ball Display Cell

A system of differential equations describing the behavior of a single ball in an elementary cell of the twisting-ball information display is considered. Nonlinear ordinary differential equations describe the ball shift and rotation. For efficient practical implementation of the display, the optimal values of ball and cell parameters are needed. To obtain these, the computer simulations were realized. Results of numerical experiments of modeling the balls with different physical parameters are presented. The numerical experiments show that the movement of the elementary particle of the twisting-ball display is extremely sensitive to the physical parameters of the balls but there exist nearly optimal combinations of these parameters. In this case the ball rotation intends towards some complete rotation cycle: if control voltage changes its polarity, the ball rotates nearly 180∘ and exposes right, black or white, size to the observer and the display works as expected.