Papers by Author: Erika Kálmán

Abstract: The nanoindentation behaviours of single crystalline silicon samples has gained wide attention in recent years, because of the anomaly effects in the loading curve, caused by the pressure induced phase transformation of silicon. To further enlighten the phenomenon bulk, ion-implanted, single crystalline Si samples have been studied by nanoindentation and by atomic force microscopy. The implantation of Si wafers was carried out by P+ ions at 40 KeV accelerating voltage and 80 ions/cm2 dose, influencing the defect density and structure of the Si material in shallow depth at the surface. Our experiments provide Young’s modulus and hardness data measured with Berkovich-, spherical- and cube corner indenters, statistics of the pop-in and pop-out effects in the loading- and unloading process, and interesting results about the piling-up behaviour of the Si material.

Abstract: Protective, chromate substitute thin layers on roughened galvanized surfaces produced at OCAS (Arcelor, Belgium) were characterized and compared using Scanning Electron Microscopy (SEM+EDS), Atomic Force Microscopy (AFM), Nanoindentation and X-ray Photoemission Spectroscopy (XPS). EDX maps, line scans and point analyses obtained at various places of the surfaces have shown differences between the CVD and silane nanolayers in the matter of thickness distribution and composition. At cross-section specimens the thickness of the layers could be shown. The hardness differences caused by layer thickness variations are hard to follow by nanoindentation as the penetration depth of the indenter is much larger than the thickness of the coatings. XPS measurements can distinguish between the chemical states of silicon in CVD and silane coatings.

Abstract: The layer formation of phosphonic acids on mica surface as a model system, from aqueous and ethanol solutions has been investigated. The aggregation behavior (critical micelle concentration, cmc) of molecules in the solution phase has been determined by surface tension measurements in order to select the appropriate concentration for the layer formation experiments. Layer formation of self-assembling molecules of alkyl-phosphonic acids has been followed by atomic force microscopy (AFM). Nucleation, growth and coalescence of densely packed islands of phosphonates from ethanol solution have been recorded on mica surface. The structure of islands depends on the length of alkyl-chains. Self-assembly of phosphonates has been also observed from aqueous solution, as presented by octyl-phosphonic acid (OcPA). The height of OcPA islands is 1.46 􀁲 0.22 nm, which is practically equal with the length of molecule (1.4 nm). This shows that OcPA molecules form monolayer height domains on the mica surface.

Abstract: New chemical synthesis procedure for the preparation of nickel zinc doped W-type hexagonal barium ferrite and aluminium doped yttrium-iron garnet nanoparticles has been developed, using the nitrate-citrate sol-gel auto-combustion method (NCSAM). The crystalline phase attributes, microstructure, morphology, specific surface area, Curie temperature (TC), permeability, thermal behavior of the as-burnt phase and the heat treated powders were characterized using XRD, SEM, FT-IR, BET, TG-DTA and AC magnetic permeability with frequency shift. In the case of the hexaferrite, the pure W-type ferrite phase is formed during 4 hour annealing at a temperature of 1200 °C, the garnet phase is formed at a lower temperature i.e. 1000 °C. Furthermore it has been confirmed, that the AC magnetic permeabilities of the garnet materials are strongly depending on the chemical composition.

Abstract: The objective of our studies was to investigate the layer formation of 1, 5-diphosphonopentane (DPP) on zinc surface from aqueous solution. For surface treatment, water based solutions of 1, 5-diphosphono-pentane was applied with different treatment times. Evidence of the adsorption of the diphosphonic acid on the zinc surface was obtained using the Infrared Reflection Absorption Spectroscopy (IRRAS).

Abstract: In order to alter the physical/chemical characteristics of multi-walled carbon nanotubes (MWNTs) we modified them by different organic reactions (Diels-Alder and Sand-Meyer reaction, oxidation) and their d properties were characterized by thermogravimetry/mass spectrometry, photoelectron spealterectroscopy, and nuclear magnetic resonance spectroscopy, as well as by dispersion. The results proved that, depending on the groups built in the MWNTs, the modified carbon nanotubes are more dispersible either in polar or apolar solvents and the suspensions are stable for long time. The presence of the substituents in the MWNTs was proved by methods listed above, e.g. high concentration of sulfur was detected when SO3H groups were inserted onto the MWNTs. The enhanced thermal stability of the modified carbon nanotubes allows their further application.

Abstract: The aim of the present work is to produce new types of solid nanomaterials for different purposes (coatings, fillers, foams, bulk pieces, etc.). Technologies such as RS Al flake production, high energy mechanical milling and high energy rate forming technology (HERF) for compacting are used. The products are analyzed mainly by XRD, SEM and TEM methods. It was shown that the new-type of RS Al “flake” material is suitable not only for pigments but also for powder metallurgical purposes, i.e. Al based nanocomposites. By choosing suitable parameters for mechanical alloying with the Fritsch Planetary mill 4, very fine, alloyed and composited nanostructures can be produced (Al-4.5w%Cu- 10w%Al2O3, Al-15w%Pb) Dynamic compaction (HERF) using explosive techniques seems to offer a good way for the compaction of Al (metal) matrix nanostructured composites.

Abstract: Radical reduction of sulphur content in diesel fuel from the mid 90’s had disastrous impact on diesel fuel’s lubricity. Due to the desulphurization process the lubricity of diesel fuel dropped significantly and got crucial nowadays. The lubricity performance of the diesel fuel is evaluated by the HFRR test in Europe. The HFRR value is determined by measuring the equivalent wear scar diameter occurred on the steel ball specimen during the test. The topographies of these wear scars were investigated by AFM and correlation between the morphology of the worn surfaces and the different HFRR values has been found.

Abstract: The ZrO2 coatings were deposited by sol-gel techniques on copper and steel. The film morphology has been investigated by AFM technique. The performance of ZrO2 films as protective layers was investigated by electrochemical techniques and optical microscopy. Firstly, the electrochemical behaviour of the uncoated copper and steel substrates was investigated by cyclic voltammetry in HCl (1 M) and NaOH (0.4 M) solutions having various pH values. Secondly, the anticorrosion protective effect of sol-gel ZrO2 coatings was evaluated by potentiodynamic measurements in degrading media in which substrates were immersed for 1-90 days. The comparisons of electrochemical parameters allow an explanation of the role of the ZrO2 coatings in the increased resistance of steel and copper against corrosion in moderately aggressive environments..

Abstract: Phosphonate layer formation on passive iron surface has been investigated by electrochemical and atomic force microscopy techniques. It was found that phosphonate groups bond more strongly to oxide surface, while metallic iron surface is disadvantageous for phosphonate layer formation in aqueous solutions. The rate of anodic dissolution is continually decreasing due to the time-dependent formation of protective phosphonate layer. The kinetics of phosphonate layer formation on passive iron is determined by the potential applied for preceding passive film formation. The size and shape of iron oxide grains depends slightly on the potential of passivation. Changes in morphology due to the phosphonate layer formation have been recorded by AFM.