G. Petkova

Bulgarian Academy of Sciences, Ulpia Serdica, Sofia-Capital, Bulgaria

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Publications (16)59.3 Total impact

  • D. Pavlov · T. Rogachev · P. Nikolov · G. Petkova
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    ABSTRACT: It is known that negative plates of lead-acid batteries have low charge acceptance when cycled at high rates and progressively accumulate lead sulphate on high-rate partial-state-of-charge (HRPSoC) operation in hybrid-electric vehicle (HEV) applications. Addition of some carbon or graphite forms to the negative paste mix improves the charge efficiency and slows down sulfation of the negative plates. The present investigation aims to elucidate the contribution of electrochemically active carbon (EAC) additives to the mechanism of the electrochemical reactions of charge of the negative plates. Test cells are assembled with four types of EAC added to the negative paste mix in five different concentrations. Through analysis of the structure of NAM (including specific surface and pore radius measurements) and of the electrochemical parameters of the test cells on HRPSoC cycling, it is established that the electrochemical reaction of charge Pb2++2e−→Pb proceeds at 300–400mV lower over-potentials on negative plates doped with EAC additives as compared to the charge potentials of cells with no carbon additives. Hence, electrochemically active carbons have a highly catalytic effect on the charge reaction and are directly involved in it. Consequently, the reversibility of the charge/discharge processes is improved, which eventually leads to longer battery cycle life. Thus, charging of the negative plates proceeds via a parallel mechanism on the surfaces of both Pb and EAC particles, at a higher rate on the EAC phase. Cells with EAC in NAM have the longest cycle life when their NAM specific surface is up to 4m2g−1 against 0.5m2g−1 for the lead surface. The proposed parallel mechanism of charge is verified experimentally on model Pb/EAC/PbSO4 and Pb/EAC electrodes. During the charge and discharge cycles of the HRPSoC test, the EAC particles are involved in dynamic adsorption/desorption on the lead sulfate and lead surfaces. Another effect of electrochemically active carbons is also evidenced namely that, above a definite concentration, some EAC forms reduce the mean pore radius of NAM. When it diminishes to less than 1.5μm, access of sulfuric acid into the pores is impeded and PbO forms instead of PbSO4 in the pores of NAM during discharge. Thus, it may be presumed that electrochemically active carbons change the overall electrochemical reaction of charge and discharge of lead-acid cells when operated under HRPSoC cycling conditions.
    No preview · Article · Jun 2009 · Journal of Power Sources
  • E. Lazarova · G. Petkova · T. Iankova · L. Ivan · G. Neikov
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    ABSTRACT: The inhibiting properties and adsorption behaviour of thioacetamide (TAA), thiobenzamide (TBA) and thiocinnamamide (TCA) on mild steel in sulphuric acid solution were studied by gravimetric, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. TBA and TCA were found to be mixed type inhibitors providing good corrosion inhibition. Different mechanisms of adsorption and corrosion inhibition were observed for the tested thioamides. In the cases of TBA and TCA, the adsorption of the compounds is chemical and the values of the activation energy (Ea) and the pre-exponential factor (A) are lower than the corresponding values observed in inhibitor free solution. The adsorption of TAA is physical and the values of Ea and А are higher than the corresponding values in sulphuric acid solution. The adsorption process of TBA and TCA on the mild steel/sulphuric acid solution interface is described by Langmuir’s isotherm. A correlation between the adsorption capability and the inhibiting efficiency of the molecules and their donor–acceptor properties (E HOMO and E LUMO) has been established. It is ascertained that the protection effect of TAA depends on the amount of hydrolysis products.
    No preview · Article · Jan 2008 · Journal of Applied Electrochemistry
  • D. Pavlov · G. Petkova · T. Rogachev
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    ABSTRACT: The influence of sulfuric acid concentration on negative plate performance has been studied on 12V/32Ah lead-acid batteries with three negative and four positive plates per cell, i.e. the negative active material limits battery capacity. Initial capacity tests, including C20 capacity, cold cranking ability and Peukert tests, have been carried out in a wide range of sulfuric acid concentrations (from 1.18 to 1.33sp.gr.). High initial capacity and good CCA performance were registered for batteries with acid concentration between 1.24 and 1.30sp.gr. The charge acceptance depends on acid concentration as well as on battery state of charge. Batteries with high SoC exhibit high charge acceptance at low acid concentrations. The cycle life tests at two discharge rates (10 and 3h discharge) evidence that sulfuric acid concentration exerts a strong effect on negative plate performance. The cycle life of batteries decreases with increase of acid concentration. The obtained results demonstrate the high impact of lead sulfate solubility on the cycle life and charge efficiency of lead-acid batteries.
    No preview · Article · Jan 2008 · Journal of Power Sources
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    V Grigorova · G Petkova · O Bock
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    ABSTRACT: We have observed in a previous study that adaptation to reversed visual feedback in a tracking task is better when subjects are instructed to look at the cursor providing feedback (group C) rather than at the target (group T). Since both groups actually looked at the target, irrespective of their instructions, we suggested that the advantage of group C is not related to their eye movements, but rather to their allocation of spatial attention. The present study scrutinized this view by combining the same adaptation task with a concurrent reaction-time task, designed to spread subjects' attention across the whole display area. Again, subjects were instructed to look at the cursor or at the target, and again, both groups actually looked at the target. Adaptation was similar to group T, and poorer than group C of the previous study. We therefore concluded that adaptation indeed depends on the subjects' allocation of attention: focussing attention mainly on the target, or spreading it across the whole display area, is not as good as distributing attention between target and cursor.
    Full-text · Article · Dec 2006 · Experimental Brain Research
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    ABSTRACT: Lead dioxide obtained by using various methods in combination with particles ranging from nanometric to micrometric size was tested as positive active material in lead-acid cells. The structural and textural properties of the material were determined by using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM), N2 adsorption measurements and thermogravimetric analysis (TGA). Thin lead dioxide positive electrodes were prepared with obtained materials by spray deposition technique and were subjected to cycling tests. The combination of a small particle size (in the nanometric range) and the presence of water strongly bound to the lattice is essential to ensure a high utilization of the active material and good cycling properties of the positive electrode. Therefore, appropriate nanometric materials provide an effective method for increasing the efficiency of the active material in lead-acid batteries.
    Full-text · Article · Aug 2006 · Journal of Power Sources
  • G. Petkova · P. Nikolov · D. Pavlov
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    ABSTRACT: The effect of polyaspartate (PASP) on the performance of the lead-acid negative plate has been investigated. It was established that this polymer additive controls the crystallization process of lead sulphate and modifies the shape and size of PbSO4 crystals. The addition of PASP to the negative paste and to the electrolyte improves the utilization of the negative active material and reduces the internal resistance of the negative plates.The results obtained during cycling of lead-acid cells under simple simulated HRPSoC cycling duty with 2C discharge current show that addition of PASP improves the cycling ability of the negative plates and thus decreases the frequency of equalization charging during operation. A beneficial effect on the performance of lead-acid batteries was observed during HRPSoC cycling of flooded batteries with 0.1% PASP in the electrolyte. The addition of PASP leads to formation of smaller PbSO4 crystals, which are more easily reduced during charge and hence prevents the accumulation of large lead sulphate crystals on the negative plates in HRPSoC duty.
    No preview · Article · Aug 2006 · Journal of Power Sources
  • E. Slavcheva · G. Petkova · P. Andreev
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    ABSTRACT: The influence of chloride ions on the corrosion of AZ91 magnesium alloy in water/ethylene glycol solutions and the inhibiting effect of lactobiono-tallowamide (LTA) were investigated using electrochemical and surface analysis methods. Potentiodynamic polarization curves in aqueous solution of ethylene glycol (50:50w%) containing 0.1 g.L−1 chloride and up to 0.5 g.L−1 LBT were obtained at room and at elevated temperatures. The chloride anions showed a distinct deteriorating effect as they caused pit initiation and accelerated the dissolution of the tested alloy. The selected organic compound demonstrated good protective properties against corrosion of AZ91 magnesium alloy and behaved as inhibitor of mixed type hindering both the cathodic and the anodic partial reactions. It showed inhibition efficiency of 77% at relatively low concentration of 0.2 g.L−1 and was considered as a promising corrosion inhibitor. The mechanism of inhibition was discussed on the basis of the electrochemical impedance spectroscopy (EIS) and XRD analysis of the surface.
    No preview · Article · Feb 2005 · Materials and Corrosion
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    ABSTRACT: Nanostructured PbO2 obtained by hydrolysis of Pb(CH3COO)4 is shown to exhibit an excellent electrochemical activity as a thin electrode in lead-acid cells. This material was characterized by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Brunauer-Teller-Emmett measurements. The electrode was prepared by spray deposition of the nanostructured PbO2 material and showed high utilization ~about 65% of the theoretical capacity and good cycling stability at discharge current of 1 C. It is suggested that the nanostructure is the key factor for the enhanced electrochemical activity of lead dioxide.
    Full-text · Article · Jan 2004 · Electrochemical and Solid-State Letters
  • G. Petkova · D. Pavlov
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    ABSTRACT: The effect of fast and three-step charge mode on the capacity and cycle life of lead–acid battery negative plates was investigated using a model mini electrode (ME). It has been found that the charge algorithm exerts a strong effect on the charge acceptance of the negative electrode. In the two-step charging mode I1, ϕ2 with increase of the current at the first step of charge, the capacity of the negative electrode decreases and the cycle life shortens. This phenomenon is reversible as it is probably due to the incomplete reduction of PbSO4 to Pb. The phenomenon is explained based on the mechanism of the process of reduction of PbSO4. At high initial charge currents, the concentration of H2SO4 in the pores of NAM increases, which decreases the solubility of PbSO4 crystals and limits the charge acceptance of the negative plate. The higher initial charge current influences markedly the formation of smaller Pb crystals that build up the energetic structure of the negative active material. It is essential that a third step with a small constant current, I3 is added to the charge algorithm. The third step of charge in the I1, ϕ2, I3 charge mode decreases the Ohmic resistance and ensures complete charge of the lead electrode.
    No preview · Article · Jan 2003 · Journal of Power Sources
  • E. Lazarova · G. Petkova · R. Raicheff · G. Neykov
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    ABSTRACT: The adsorption of halogen derivatives of aniline on an iron electrode in sulfuric acid medium has been studied in relation to their inhibiting properties using electrochemical a.c. impedance and d.c. polarization techniques, as well as quantum chemical calculations of chemical structure and distribution of electron charges in the organic molecules. It is established that the adsorption process is described by Frumkin's isotherm. The adsorption parameters characterizing the interaction forces between the molecules in the adsorbed layer, the free energy of adsorption, the maximum surface excess of adsorbed species, the area occupied by each molecule etc. have been calculated on the basis of this isotherm. It is shown that the inhibition efficiency, as well as the free energy of adsorption, increases in the sequence: aniline p-Cl-aniline p-Br-aniline p-I-aniline. It was found that the adsorption behaviour of the substances studied is characterized by two adsorption states: vertical and planar orientation of the molecules. Combining data from electrochemical measurements with data from quantum chemical calculations the correlation between the chemical structure of the aniline derivatives and their adsorption capability and inhibition efficiency has been ascertained.
    No preview · Article · Dec 2002 · Journal of Applied Electrochemistry
  • D Pavlov · G Petkova
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    ABSTRACT: The capacity of the positive plate of the lead-acid battery is determined by the number of the active centers in positive active material (PAM) where the reaction PbO2-->PbSO4 proceeds and by the resistance of the interface corrosion layer (CL) 1 AMCL (thin PAM layer interconnecting the PAM and the CL). It was established that the number of the active centers is high if the positive plate discharge is performed with low current and if the charge (at the initial period) is performed with high current. During discharge the active centers from the outer layer of the plate are exhausted and the reaction of the PbO2 reduction approaches the inner part of the plate near the interface and the interface itself. If the pH of the pore solution is low the reduction of the PbO2 proceeds to PbSO4. At the subsequent charge with sufficiently high current a maximum appears on the potential transient. When the H2SO4 flux to the interface is impeded, the pH of the solution in the pores in the interface is high and the reduction of the PbO2 proceeds to PbOn (1 < n < 1.5). As the PbOn has high electrical resistance, during the subsequent charge with high current a peak appears at the beginning of the potential transient. Its height depends on the resistance of the interface. On the basis of the appearance of a maximum or a peak the state of change and the state of health of the positive plate can be determined. (C) 2002 The Electrochemical Society.
    No preview · Article · May 2002 · Journal of The Electrochemical Society
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    ABSTRACT: Quantum chemical SCF calculations of the geometrical and electronic molecular structure of α- and γ-pyrophthalone compounds were performed. The correlation between molecular structure of these compounds and their inhibition efficiency in case of copper corrosion was found. It was established that the decrease of the ionisation potential and the increase of the molecular dipole moment favour the higher inhibition efficiency toward corrosion.
    Full-text · Article · May 2002 · Chemical Physics
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    D. Pavlov · G. Petkova

    Preview · Article · Jan 2002 · Journal of The Electrochemical Society
  • P Gatev · V Koleva · G Petkova · D Dimitrova · L Ilieva
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    ABSTRACT: We studied the influence of stance width and vision on the plantar pressures for the left and right foot during bipedal quiet standing on the pressure-sensitive insoles. The support widening shifted the left and right centers-of-foot-pressure (CFPs) laterally and forward (right foot), diminished SDs of: the left and right mean plantar pressures (MPPs), the anteroposterior and mediolateral displacements of left and right CFPs. It also decreased negative correlations between left and right MPPs and between mediolateral displacements of left and right CFP and increased positive correlation between anteroposterior displacements of left and right CFPs, more expressive with eyes-open. The later results suggested that support widening increased the weight of exploratory behaviour regarding anteroposterior equilibrium and decreased exploratory sway serving mediolateral equilibrium. Eyes' closure lead to a small left bias of the body-weight-bearing and forward shift of the left versus right CFP, thus suggesting that vision increased bilateral symmetry of stance.
    No preview · Article · Feb 2001 · Acta physiologica et pharmacologica Bulgarica
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    D Pavlov · G Petkova · M Dimitrov · M Shiomi · M Tsubota
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    ABSTRACT: A criterion has been found for determination of the factor limiting the discharge of the lead dioxide plate. When on discharge with moderate currents, an arrest or a shoulder appears between 1.0 and 0.7 V (vs. Hg/HgSO4 electrode) in the potential transient, then the charging potential transient features a peak at the beginning of the curve. The capacity is limited by the interface. The life cycle of the battery is short. This phenomenon is known as PCL effect. When a broad maximum occurs in the potential transient on charge, this indicates that the electrode capacity is limited by zones of high resistance in positive active mass (PAM) near the interface. The capacity is determined by the lead dioxide active mass. It has been established that the life of the positive plate is proportional to the current density during the initial charge stage. A sol–gel–crystal mechanism of the charge processes is proposed to explain this effect of fast charge on electrode life. The high rate of the electrochemical reaction leads to high oversaturations of the Pb(OH)4 sol and to fast formation of gel–crystal PbO(OH)2/PbO2 particles, which not only form new agglomerates tightly connected to the PAM skeleton, but also fill in and improve the contacts between the agglomerates. The latter process has the effect of “welding” of the PAM skeleton. Moreover, the higher concentration of the Pb(OH)4 sol affects the macro- and microstructure of the PAM, which in turn has an influence on the electrochemical reaction. Impedance measurements have evidenced different values of the electron transfer resistance in electrodes charged at high and low currents.
    Preview · Article · Apr 2000 · Journal of Power Sources
  • D. Pavlov · M. Dimitrov · G. Petkova · H. Giess · C. Gnehm
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    ABSTRACT: In valve regulated batteries of the adsorbed glass mat type the connecting strap and lugs of the plates (top lead) are covered by a thin liquid film of HâSOâ solution. The HâSOâ is consumed for the formation of a PbSOâ corrosion layer. The liquid film has high ohmic resistance and hence the strap and lugs of the plates are cathodically unprotected. As a result of this, often the life of the battery is limited by corrosion of the negative semiblock top lead. In battery manufacturing practice, Pb-Sn alloys are often used for the straps in the above battery type. The present paper examines creeping of the thin liquid film up a strap electrode, the structure and phase composition of the corrosion layer formed on the electrode surface, as well as the rate of corrosion of Pb-Sn and Pb-Sn-Se electrodes partly immersed in an absorbing glass mat soaked in HâSOâ or HâSOâ + NaâSOâ solutions. It has been established that the potential of that part of the electrode immersed in the solution controls the potential of the electrode up to a height of 1 cm above the solution level. The corrosion layer formed on the electrode surface above the solution (in the air) features zones of different phase compositions. The introduction of NaâSOâ to the HâSOâ solution leads to a sevenfold increase in corrosion rate of Pb-Sn alloys, while the addition of 0.03% Se to the alloy suppresses completely this effect of NaâSOâ. When the Sn content in the alloy is below 1%, the rate of corrosion increases. Selenium suppresses this effect, too, in alloys containing 0.6% Sn. Selenium has an anticorrosion effect and acts as a grain refiner in Pb-Sn alloys decreasing also the size of PbSOâ crystals and facilitating their nucleation.
    No preview · Article · Sep 1995 · Journal of The Electrochemical Society

Publication Stats

307 Citations
59.30 Total Impact Points


  • 1995-2009
    • Bulgarian Academy of Sciences
      • • Institute for Electrochemistry and Energy Systems
      • • Institute of Neurobiology
      Ulpia Serdica, Sofia-Capital, Bulgaria