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Plank H.,University of Graz | Plank H.,Graz Center for Electronic Microscopy
Nanotechnology | Year: 2015

During the last decade, focused ion beam processing has been developed from traditionally used Ga+ liquid ion sources towards higher resolution gas field ion sources (He+ and Ne+). Process simulations not only improve the fundamental understanding of the relevant ion-matter interactions, but also enable a certain predictive power to accelerate advances. The historic 'gold' standard in ion-solid simulations is the SRIM/TRIM Monte Carlo package released by Ziegler, Ziegler and Biersack 2010 Nucl. Instrum. Methods B 268 1818-23. While SRIM/TRIM is very useful for a myriad of applications, it is not applicable for the understanding of the nanoscale evolution associated with ion beam nano-machining as the substrate does not evolve with the sputtering process. As a solution for this problem, a new, adapted simulation code is briefly overviewed and finally addresses these contributions. By that, experimentally observed Ne+ beam sputter profiles can be explained from a fundamental point of view. Due to their very good agreement, these simulations contain the potential for computer aided optimization towards predictable sputter processes for different nanotechnology applications. With these benefits in mind, the discussed simulation approach represents an enormous step towards a computer based master tool for adaptable ion beam applications in the context of industrial applications. © 2015 IOP Publishing Ltd. Source


Kovacic S.,University of Graz | Matsko N.B.,Graz Center for Electronic Microscopy | Ferk G.,University of Maribor | Slugovc C.,University of Graz
Journal of Materials Chemistry A | Year: 2013

The high internal phase emulsion (HIPE) templating approach to macroporous poly(dicyclopentadiene) γFe2O3/Fe3O 4 nanocomposite foams via ring opening metathesis polymerisation was elaborated and the influence of the formulation of the HIPE on structural and mechanical properties of the magnetic composite foams of 80% nominal porosity was studied. HIPEs solely stabilized with the nanoparticles resulted in considerably shrunken monolithic specimens characterized by an open cellular morphology with cavities bigger than 265 μm. Nanoparticles were situated in the bulk and on the surface of the polymeric foam skeleton. Precise control over the feature sizes could not be obtained in this case. In contrast, HIPE formulations co-stabilized with a surfactant yielded samples of good casting quality characterized by a fully open cellular morphology in all cases. The cavity and the window size could be controlled by the amount of surfactant in the emulsion. A low surfactant loading of 1.5 v% with respect to the monomer yielded diameters of the cavities of the order of 20 μm interconnected with windows with diameters in the order of 4 μm, while 10 v% surfactant resulted in smaller cavities (10 μm) and windows (2 μm). All these feature sizes are hardly affected by the nanoparticle loading which was varied from 1 to 30 wt%. Surfactant stabilized and cured HIPEs featured the nanoparticles predominantly on the surface of the cavities. Mechanical properties of the composite foams were assessed by stress-strain tests and revealed a strengthening of the foams prepared with 10 v% surfactant upon addition of the nanoparticles. Indicative of the strengthening is an increase of the Young's modulus from 13 ± 2 MPa in the case of a sample without nanoparticles to 104 ± 4 MPa in the case of the composite foam with 15 wt% nanoparticles. This trend was accompanied by a decrease of the elongation at break from 21 ± 4 to less than 1%. Specimens prepared with 1.5 v% surfactant are ductile and gave the same high Young's modulus (104 ± 9 MPa) irrespective of the nanoparticle loading and became stronger upon raising the nanoparticle amount reaching an ultimate strength of 3.4 ± 0.4 MPa at an elongation at break of 13 ± 4%. © 2013 The Royal Society of Chemistry. Source


Voitic G.,University of Graz | Nestl S.,University of Graz | Lammer M.,University of Graz | Wagner J.,Graz Center for Electronic Microscopy | And 2 more authors.
Applied Energy | Year: 2015

Fuel cell cars powered by hydrogen enable CO2-emission free mobility. A main requirement for the success of this technology is the availability of an area-wide and affordable hydrogen supply. A significant cost factor in the hydrogen supply chain is the multi-stage gas compression to provide the mandatory filling pressure for the pressurized tanks. One way to address this issue is to perform the hydrogen production process at elevated pressure. In this paper the feasibility of compressed hydrogen production without additional gas compression based on the steam iron process is discussed. Experiments were performed in a lab-scale test rig using fixed bed reactor technology. The focus was to evaluate the influence of pressurized hydrogen production on the cycle stability, on the conversion efficiency and on the structural integrity of a Fe2O3-Al2O3 (90 + 10 wt%) oxygen carrier. The oxidations were performed at different pressure levels of 7-22 bar (g) at a temperature of 750 °C with steam. The steady steam supply was ensured by a HPLC pump which delivered 0.03 g min-1 (at room temperature) of water, which was evaporated in the heated inlet section. The water was introduced for approximately 100 min until the oxygen carrier was fully oxidized. The iron oxide was reduced in the subsequent reaction steps at 750 °C and ambient pressure with 25 Nml min-1 H2 as reducing agent. The reduction reactions were analyzed to evaluate possible influences of its prior oxidations. The results revealed no signs of negative repercussions. The oxygen carrier conversion of initially 84% remained at a steady behavior between the 15 performed cycles. Only small losses of 0.8% per cycle caused by thermal sintering of the contact mass were observed, which was independent from the different pressure levels of the prior oxidations. The evaluation of the pressurized oxidations did not reveal any performance decrease as well. The rise of pressure in each oxidation showed a consistent characteristic throughout the complete test series. Scanning electron microscopy analysis of the oxygen carrier sample after the experiment revealed some structural changes, which are related to thermal sintering but the structural integrity of the sample stayed intact. The oxidations yielded an average of 18 mmol gFe -1 hydrogen with a maximum hydrogen pressure of 22 bar (g). The conducted experiments showed that the steam iron process is very suitable for the production of compressed hydrogen and that the process is not negatively influenced by the elevated system pressure. © 2015 Elsevier Ltd. Source


Kovacic S.,University of Graz | Matsko N.B.,Graz Center for Electronic Microscopy | Jerabek K.,Czech Institute of Chemical Process Fundamentals | Krajnc P.,University of Maribor | Slugovc C.,University of Graz
Journal of Materials Chemistry A | Year: 2013

Reducing the surfactant amount below generally accepted values in polyHIPE chemistry allowed for distinctly improving the mechanical properties of ROMP derived HIPE templated poly(dicyclopentadiene) without compromising the open cellular structure of the scaffold rendering the preparation of a ductile polymer foam with 80% porosity and a Young's modulus of 110 MPa possible. This journal is © 2013 The Royal Society of Chemistry. Source


Mittal V.,The Petroleum Institute | Luckachan G.E.,The Petroleum Institute | Matsko N.B.,Graz Center for Electronic Microscopy
Macromolecular Chemistry and Physics | Year: 2014

The microstructure of high-density polyethylene (PE) and chlorinated polyethylene (CPE) blends, as well as their composites with graphene oxide (GO) is characterized. The filler dispersion improves as the extent of chlorination is enhanced. The platelets are also observed to be covered with a harder phase by atomic force microscopy (AFM), due to the stronger nucleating action of the graphene clusters, along with the alignment or ordering of the CPE phase at the interface with the filler. The filler and the CPE phases are observed to undergo chemical interaction during solution mixing, which enhances during melt mixing of the CPE-GO masterbatch with the PE matrix. The majority of the Cl atoms in the CPE chains are observed to be depleted during chemical reaction or thermal degradation at the melt compounding temperature, resulting in chlorine-free materials. The microstructure of high-density polyethylene (PE) and chlorinated polyethylene (CPE) blends, as well as their composites with graphene oxide (GO) are characterized. The filler dispersion improves as the extent of chlorination is enhanced. The majority of the Cl atoms in the CPE chains are observed to be depleted during chemical reaction or thermal degradation at the melt compounding temperature, resulting in chlorine-free materials. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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