Stane Pejovnik - Academia.edu (original) (raw)
Papers by Stane Pejovnik
International Journal of Materials Research
ABSTRACT
Chemischer Informationsdienst
Solid State Ionics, 1995
A new measuring principle to study interfacial effects using a displacement current through a die... more A new measuring principle to study interfacial effects using a displacement current through a dielectric coating is presented. It enables the scanning of the electric response from the core of the interface up to the bulk by changing the frequency. In contrast to traditional impedance measurements, the interfacial effects appear at higher frequencies than the bulk and can be measured with a corresponding high sensitivity. The investigations of the Ag/AgCI interface can be consistently explained by a depletion of silver vacancies due to injection of silver ions from the silver electrode. The perpendicular interfacial impedance is discussed in a new approach by using the Sturn-Liouville form of transport equation. The computational results are analysed on the basis of perturbed defect density in the system.
Acta chimica Slovenica, 2016
The electrochemical characteristics of sulfurized polyacrylonitrile composite (PAN/S) cathodes we... more The electrochemical characteristics of sulfurized polyacrylonitrile composite (PAN/S) cathodes were compared with the commonly used carbon/S-based composite material. The difference in the working mechanism of these composites was examined. Analytical investigations were performed on both kinds of cathode electrode composites by using two reliable analytical techniques, in-situ UV-Visible spectroscopy and a four-electrode Swagelok cell. This study differentiates the working mechanisms of PAN/S composites from conventional elemental sulphur/carbon composite and also sheds light on factors that could be responsible for capacity fading in the case of PAN/S composites.
Carbon, 1998
The adsorption of cationic surfactant cetyltrimethylammonium bromide (CTAB) from aqueous solution... more The adsorption of cationic surfactant cetyltrimethylammonium bromide (CTAB) from aqueous solution onto carbon black was studied using charge-compensating polyelectrolyte titration for quantitative determination of the surfactant content in solution and X-ray powder diffraction analysis of air-dried dispersions. Sharp saturation was observed. The saturated surface concentration of the adsorbed CTAB was found to be the same in the dispersed and air-dried product. Fourier transformed infrared spectroscopy and extended X-ray absorption fine structure (EXAFS) analyses suggest -CTA+ and Br- ion sites in the dried product.
AIP Conference Proceedings, 2001
We report on the structure and electronic properties of single wall carbon nanotube (SWNTs) tips ... more We report on the structure and electronic properties of single wall carbon nanotube (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structures; these include round, conical, as well as tips with a messy shape. Standing wave pattern of the charge density is observed at the tube cap
AIP Conference Proceedings, 2002
ABSTRACT It is shown that the (MoS2)n nanotube bundles are capable of reversible lithium insertio... more ABSTRACT It is shown that the (MoS2)n nanotube bundles are capable of reversible lithium insertion. Comparing its properties with layered MoS2, which has been used as a positive material in the Li-ion batteries in the past [1], the new material shows promising improvements. The intercalation takes place close to the metallic lithium potential and during the insertion process, the potential decreases linearly with the amount of inserted lithium. In all, the system's characteristics indicate that (MoS2)n nanotubes may be used as a negative electrode in rechargeable lithium batteries with some potential advantages over other systems currently in use.
Electrochimica Acta, 2003
Sintering Processes, 1980
Construction and Building Materials, 2015
ABSTRACT The subject of this paper is the extent to which, during wetting-drying cycles, chloride... more ABSTRACT The subject of this paper is the extent to which, during wetting-drying cycles, chloride ions penetrate into fly ash modified concrete. Detailed chloride profiles were recorded which show how the total and water-soluble chloride contents vary with the depth of penetration of these ions into the concrete. In order to study the effect of exposure time, fly ash content, and fly ash composition on such penetration, two different types of fly ash were used as a partial replacement of Portland cement, their proportions amounting to 0%, 20% and 50% by weight of the binder.
Processing of Crystalline Ceramics, 1978
Rearrangment in ceramic-glass systems was studied on models. When Al203-spheres of 50/um diameter... more Rearrangment in ceramic-glass systems was studied on models. When Al203-spheres of 50/um diameter are sintered in the presence of an alkali-borate glass which does not dissolve any appreciable amount of Al203, large pores form during the early sintering stage and persist even after prolonged sintering at high temperatures. Contrary, sintering with anorthite glass, which in the molten state rapidly dissolves kore than 5 wt. % Al203, leads to particle disintegration and increased densification. Similarly, using Al203-agglomerates instead of solid spheres leads to increased densification. It is shown that the solubility of Al203 in the glass-pharse is more important for densification by arrangement than large changes in the viscosity of the liquid phase.
Materials Science Forum, 1995
Progress in Colloid and Polymer Science, 2001
The gelatin content in graphite—gelatin composites was determined from the difference in the mass... more The gelatin content in graphite—gelatin composites was determined from the difference in the mass of graphite particles before and after the treatment with gelatin and by thermogravimetric analysis. It was found that the content of gelatine has a maximum at those pH values of gelatin solution which correspond to the isoelectric point of gelatin. The result is correlated with previous findings concerning gelatin adsorption on various substrates as a function of pH. The “hairy” structure of gelatin allows deposition of different types of small particles (e.g. carbon black) and, under appropriate conditions, may lead to the formation of thick (0.3 μm) and dense layers. On the basis of the good adsorption of gelatin on graphite surfaces, we prepared anodes for lithium accumulators. In graphitic anodes, gelatin serves both as a binder between particles and as a surface modifier, which leads to lower irreversible losses of charge owing to anode passivation.
Sintering’85, 1987
Microstructural evolution during sintering of BaTiO3 with 0–16 Mole % CaTiO3 in the presence of T... more Microstructural evolution during sintering of BaTiO3 with 0–16 Mole % CaTiO3 in the presence of TiO2 — rich liquid phase was examined. It was observed that 8 Mole % CaTiO3 addition causes coarsening of microstructure, whereas 16 Mole % addition produces fine grain structure, as compared with the undoped BaTiO3. The irregular behaviour of average grain size vs. amount of CaTiO3 added is explained as a consequence of discontinuous grain growth during sintering.
MRS Proceedings, 2001
We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips... more We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. At low bias voltage, topographic STM images show standing wave pattern of the charge density in the vicinity of nanotube ends. The patterns originate from constructive interference between the electronic states and its reflection on the nanotube tips. The modulations extend along 6-8 nm away from the cap. Atomically resolved images show asymmetry in the charge density that smears out as the bias voltage increases. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.
International Journal of Materials Research
ABSTRACT
Chemischer Informationsdienst
Solid State Ionics, 1995
A new measuring principle to study interfacial effects using a displacement current through a die... more A new measuring principle to study interfacial effects using a displacement current through a dielectric coating is presented. It enables the scanning of the electric response from the core of the interface up to the bulk by changing the frequency. In contrast to traditional impedance measurements, the interfacial effects appear at higher frequencies than the bulk and can be measured with a corresponding high sensitivity. The investigations of the Ag/AgCI interface can be consistently explained by a depletion of silver vacancies due to injection of silver ions from the silver electrode. The perpendicular interfacial impedance is discussed in a new approach by using the Sturn-Liouville form of transport equation. The computational results are analysed on the basis of perturbed defect density in the system.
Acta chimica Slovenica, 2016
The electrochemical characteristics of sulfurized polyacrylonitrile composite (PAN/S) cathodes we... more The electrochemical characteristics of sulfurized polyacrylonitrile composite (PAN/S) cathodes were compared with the commonly used carbon/S-based composite material. The difference in the working mechanism of these composites was examined. Analytical investigations were performed on both kinds of cathode electrode composites by using two reliable analytical techniques, in-situ UV-Visible spectroscopy and a four-electrode Swagelok cell. This study differentiates the working mechanisms of PAN/S composites from conventional elemental sulphur/carbon composite and also sheds light on factors that could be responsible for capacity fading in the case of PAN/S composites.
Carbon, 1998
The adsorption of cationic surfactant cetyltrimethylammonium bromide (CTAB) from aqueous solution... more The adsorption of cationic surfactant cetyltrimethylammonium bromide (CTAB) from aqueous solution onto carbon black was studied using charge-compensating polyelectrolyte titration for quantitative determination of the surfactant content in solution and X-ray powder diffraction analysis of air-dried dispersions. Sharp saturation was observed. The saturated surface concentration of the adsorbed CTAB was found to be the same in the dispersed and air-dried product. Fourier transformed infrared spectroscopy and extended X-ray absorption fine structure (EXAFS) analyses suggest -CTA+ and Br- ion sites in the dried product.
AIP Conference Proceedings, 2001
We report on the structure and electronic properties of single wall carbon nanotube (SWNTs) tips ... more We report on the structure and electronic properties of single wall carbon nanotube (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structures; these include round, conical, as well as tips with a messy shape. Standing wave pattern of the charge density is observed at the tube cap
AIP Conference Proceedings, 2002
ABSTRACT It is shown that the (MoS2)n nanotube bundles are capable of reversible lithium insertio... more ABSTRACT It is shown that the (MoS2)n nanotube bundles are capable of reversible lithium insertion. Comparing its properties with layered MoS2, which has been used as a positive material in the Li-ion batteries in the past [1], the new material shows promising improvements. The intercalation takes place close to the metallic lithium potential and during the insertion process, the potential decreases linearly with the amount of inserted lithium. In all, the system's characteristics indicate that (MoS2)n nanotubes may be used as a negative electrode in rechargeable lithium batteries with some potential advantages over other systems currently in use.
Electrochimica Acta, 2003
Sintering Processes, 1980
Construction and Building Materials, 2015
ABSTRACT The subject of this paper is the extent to which, during wetting-drying cycles, chloride... more ABSTRACT The subject of this paper is the extent to which, during wetting-drying cycles, chloride ions penetrate into fly ash modified concrete. Detailed chloride profiles were recorded which show how the total and water-soluble chloride contents vary with the depth of penetration of these ions into the concrete. In order to study the effect of exposure time, fly ash content, and fly ash composition on such penetration, two different types of fly ash were used as a partial replacement of Portland cement, their proportions amounting to 0%, 20% and 50% by weight of the binder.
Processing of Crystalline Ceramics, 1978
Rearrangment in ceramic-glass systems was studied on models. When Al203-spheres of 50/um diameter... more Rearrangment in ceramic-glass systems was studied on models. When Al203-spheres of 50/um diameter are sintered in the presence of an alkali-borate glass which does not dissolve any appreciable amount of Al203, large pores form during the early sintering stage and persist even after prolonged sintering at high temperatures. Contrary, sintering with anorthite glass, which in the molten state rapidly dissolves kore than 5 wt. % Al203, leads to particle disintegration and increased densification. Similarly, using Al203-agglomerates instead of solid spheres leads to increased densification. It is shown that the solubility of Al203 in the glass-pharse is more important for densification by arrangement than large changes in the viscosity of the liquid phase.
Materials Science Forum, 1995
Progress in Colloid and Polymer Science, 2001
The gelatin content in graphite—gelatin composites was determined from the difference in the mass... more The gelatin content in graphite—gelatin composites was determined from the difference in the mass of graphite particles before and after the treatment with gelatin and by thermogravimetric analysis. It was found that the content of gelatine has a maximum at those pH values of gelatin solution which correspond to the isoelectric point of gelatin. The result is correlated with previous findings concerning gelatin adsorption on various substrates as a function of pH. The “hairy” structure of gelatin allows deposition of different types of small particles (e.g. carbon black) and, under appropriate conditions, may lead to the formation of thick (0.3 μm) and dense layers. On the basis of the good adsorption of gelatin on graphite surfaces, we prepared anodes for lithium accumulators. In graphitic anodes, gelatin serves both as a binder between particles and as a surface modifier, which leads to lower irreversible losses of charge owing to anode passivation.
Sintering’85, 1987
Microstructural evolution during sintering of BaTiO3 with 0–16 Mole % CaTiO3 in the presence of T... more Microstructural evolution during sintering of BaTiO3 with 0–16 Mole % CaTiO3 in the presence of TiO2 — rich liquid phase was examined. It was observed that 8 Mole % CaTiO3 addition causes coarsening of microstructure, whereas 16 Mole % addition produces fine grain structure, as compared with the undoped BaTiO3. The irregular behaviour of average grain size vs. amount of CaTiO3 added is explained as a consequence of discontinuous grain growth during sintering.
MRS Proceedings, 2001
We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips... more We report on the structure and electronic properties of single wall carbon nanotubes (SWNTs) tips with atomically spatial resolution. Scanning tunneling microscopy (STM) show topographic images of closed tips with a variety of geometrical structure; these include round, conical, as well as tips with a messy shape. At low bias voltage, topographic STM images show standing wave pattern of the charge density in the vicinity of nanotube ends. The patterns originate from constructive interference between the electronic states and its reflection on the nanotube tips. The modulations extend along 6-8 nm away from the cap. Atomically resolved images show asymmetry in the charge density that smears out as the bias voltage increases. These distinctive tip states do not exist elsewhere on the tube and are related to the presence of topological defects at tube ends.