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  • 1.
    Alam, Md. Minhaj
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Barsoum, Z.
    Royal Institute of Technology.
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Kaplan, Alexander
    Häggblad, Hans-Åke
    The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 265, no 6, p. 1936-1945Article in journal (Refereed)
    Abstract [en]

    Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by four point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

  • 2.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 21, p. 8917-8925Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.

  • 3.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shaer, M. El
    Department of Engineering Physics and Mathematics, Faculty of Engineering, Zagazig University.
    Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 14, p. 4633-4641Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism.

  • 4.
    Bergström, David
    et al.
    Mid Sweden University.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    The absorptance of steels to Nd:YLF and Nd:YAG laser light at room temperature2007In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 253, no 11, p. 5017-5028Article in journal (Refereed)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modelling of laser-material interactions. Unfortunately, most of the absorptance data presently available considers only polished pure metals rather than the commercially available (unpolished, oxidised) alloys, which are actually being processed in manufacturing. This paper presents the results of absorptance measurements carried out at room temperature on as-received engineering grade steels including hot and cold rolled mild steel and stainless steels of various types. The measurements were made using an integrating sphere with an Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified; for all materials studied, the absorptance was considerably higher than the previously published values for the relevant pure metals with polished surfaces. For all 15 samples the absorptance was higher for the green than for the infrared wavelength. No clear trend correlating the absorptance with the roughness was found for mild steel in the roughness range Sa 0.4-5.6 μm. A correlation between absorptance and roughness was noted for stainless steel for Sa values above 1.5 μm.

  • 5.
    Chen, Y
    et al.
    Chinese Academy of Sciences, Beijing.
    Gan, C.H.
    Chinese Academy of Sciences, Beijing.
    Wang, L.X.
    Chinese Academy of Sciences, Beijing.
    Yu, G.
    Chinese Academy of Sciences, Beijing.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Laser surface modified ductile iron by pulsed Nd:YAG laser beam with two-dimensional array distribution2005In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 245, no 1-4, p. 316-321Article in journal (Refereed)
    Abstract [en]

    A novel modification layer on the surface of pearlite-ferrite matrix ductile iron was fabricated under irradiation of Nd:YAG laser beam equipped with self-designed diffractive optical element (DOE) which produces a 5×5 two-dimensional array distribution at the focal plane. The microstructure of the layer along the surface and the direction of the layer depth had obvious gradient distribution, and therefore the two-dimensional microhardness map of the layer alternated higher hardness with lower hardness. The results showed that the novel modification layer is expected to have excellent combination of strength and toughness

  • 6.
    Concina, Isabella
    et al.
    Department of Information Engineering, University of Brescia and SENSOR Laboratory, CNR-INO.
    Comini, Elisabetta
    University of Brescia, CNR IDASC SENSOR Lab.
    Kacilius, S.
    CNR-ISMN, Institute for the Study of Nanostructured Materials, Rome.
    Sberveglieri, Giorgio
    SENSOR Lab, Department of Information Engineering, University of Brescia.
    Quantum dots as mediators in gas sensing: A case study of CdS sensitized WO3 sensing composites2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 290, p. 295-300Article in journal (Refereed)
    Abstract [en]

    In this study the proof of principle of the use of naked semiconductor directly generated on metal oxide surface as mediators in gas sensing is provided. Successive ionic layer absorption and reaction (SILAR) technique has been applied to sensitize a WO3 thin film with CdS quantum dots. Response to gases of bare WO3 is deeply modified: quantum dots dramatically increase the metal oxide conductance, otherwise rather poor, and modify the capability of detecting environmental pollutants, such as CO and NO2. A modified sensing mechanism is proposed to rationalize the mediation exerted by the semiconducting active layer on the interaction between gaseous species and WO3 surface.

  • 7.
    Edelbro, R.
    et al.
    Luleå tekniska universitet.
    Sandström, Åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Paul, Jan
    Full potential calculations on the electron band structures of Sphalerite, Pyrite and Chalcopyrite2003In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 206, no 1-4, p. 300-313Article in journal (Refereed)
    Abstract [en]

    The metal contents of ore can be as low as 0.4%m This means sophisticated methods of enrichment have to be applied. Better understanding of the processes of flotation and leaching may lead to higher yields and less damage to the environment. The bulk electronic structures of Sphalerite, Pyrite and Chalcopyrite have been calculated within an ab initio, full potential, density functional approach. The exchange term was approximated with the Dirac exchange functional, the Vosko-Wilk-Nusair parameterization of the Cepler-Alder free electron gas was used for correlation and linear combinations of Gaussian type orbitals were used as basis functions. The Sphalerite (zinc blend) band gap was calculated to be direct with a width of 2.23 eV. The Sphalerite valence band was 5.2 eV wide and composed of a mixture of sulfur and zinc orbitals. The band below the valence band located around -6.2 eV was mainly composed of Zn 3d orbitals. The S 3s orbitals gave rise to a band located around -12.3 eV. Pyrite was calculated to be a semiconductor with an indirect band gap of 0.51 eV, and a direct gap of 0.55 eV. The valence band was 1.25 eV wide and mainly composed of non-bonding Fe 3d orbitals. The band below the valence band was 4.9 eV wide and composed of a mixture of sulfur and iron orbitals. Due to the short inter-atomic distance between the sulfur dumbbells, the S 3s orbitals in Pyrite were split into a bonding and an anti-bonding range. Chalcopyrite was predicted to be a conductor, with no band-crossings at the Fermi level. The bands at -13.2 eV originate from the sulfur 3s orbitals and were quite similar to the sulfur 3s bands in Sphalerite, though somewhat shifted to lower energy. The top of the valence band consisted of a mixture of orbitals from all the atoms. The lower part of the same band showed metal character. Computational modeling as a tool for illuminating the flotation and leaching processes of Pyrite and Chalcopyrite, in connection with surface science experiments, is discussed.

  • 8.
    Frostevarg, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Olsson, Rickard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development. Laser Nova AB, Östersund, Sweden.
    Powell, John
    Laser Nova AB, Östersund, Sweden.
    Palmquist, Anders
    Department of Biomaterials, University of Gothenburg, Gothenburg, Sweden.
    Brånemark, Rickard
    Department of Orthopaedic Surgery, University of California, San Francisco, USA.
    Formation mechanisms of surfaces for osseointegration on titanium using pulsed laser spattering2019In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 458, p. 158-169Article in journal (Refereed)
    Abstract [en]

    Accelerated bone grow (osseointegration) can be achieved by modifying the surface of medical implants. For this purpose, pulsed lasers can be used to successfully texture such beneficial surfaces on titanium, e.g. a BioHelix™ structure. This surface typically includes ridges and droplets with a size range between 1 and 20 μm. This paper presents the results of an experimental program where a range of laser parameters was used to create different surface textures on titanium substrates, using pulsed laser spattering. The resultant surfaces are analysed by scanning electron microscope and X-ray Micro Computer Tomography. It is shown that optimisation of the laser parameters results in a robust process which produces a surface that has proven to be beneficial for osseointegration. The results are also deeper analysed, explaining how different types of surface are created by the laser-material interaction under different conditions. Further, droplet flight distances and the formation of the spongeous nano-scale surface that characterizes the surface structure depends on very fast cooling and is also evaluated.

  • 9. Hirschauer, B.
    et al.
    Söderholm, S.
    Paul, Jan
    Flodström, A.S.
    Large area synthesis of thin alumina films by laser ablation1996In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 99, no 4, p. 285-291Article in journal (Refereed)
    Abstract [en]

    Al2O3 has been ablated on commercially available 3″ silicon wafers at different distances between the target and the substrate and laser fluencies. ‘Amorphous' Al2O3 (γ-alumina with grain size <20 nm) was grown by pulsed laser deposition at room temperature. The structure, the morphology, the profile and the composition of the produced films have been investigated. Fully oxidised thin films (thickness ≤5 μm) with high uniformity and smoothness were synthesised without additional oxygen gas during the ablation. The quality of the films was independent of the ablation fluency and of the distance between target and substrate.

  • 10.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Absorption homogenization at wavy melt films by CO2-lasers in contrast to 1 micron-wavelength lasers2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 328, p. 229-234Article in journal (Refereed)
    Abstract [en]

    For wavy metal melts, across a wide range of their topology parameters, lasers with about 1 μm wavelength experience the highest Fresnel absorption around the shoulders of the waves. Calculations show that this induces a strong peak of the absorbed power density of the laser beam. The high temperature gradients have the potential to cause very local boiling and growth of the valleys. In contrast, for a certain parameter category the small Brewster angle for the CO2-laser partially homogenizes the temperatures by elevated absorption at domains of grazing incidence. This has the potential to cause opposite consequences on the process, like wave smoothing.

  • 11.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Fresnel absorption of 1 μm- and 10 μm-laser beams at the keyhole wall during laser beam welding: Comparison between smooth and wavy surfaces2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 8, p. 3354-3363Article in journal (Refereed)
    Abstract [en]

    The angle-dependent absorption of laser beams at metal surfaces is described by the Fresnel-equations. During keyhole laser welding the essential interaction takes place at very striping angles of incidence of the order of 1-8 degrees at the front of the vapour capillary, called the keyhole. For a smooth vapour capillary, laser beams with a wavelength of about 1 μm operate in a Fresnel-regime where the absorptance increases with the angle of incidence at the wall, towards the weak Brewster-angle maximum. In contrast, for 10 μm-lasers high absorptance around the more pronounced Brewster-angle peak takes place. From high speed imaging keyhole surface waves were observed. Mathematical modelling of the laser-keyhole interaction demonstrates that already relatively little waviness of the melt surface at the keyhole strongly modulates the angles of incidence and in turn the Fresnel-absorption due to varying angles of incidence, soon also leading to shadow zones. Due to this local variation of the angle of incidence the absorptance tends towards the angle-averaged value, with the consequence that for 1 μm-lasers the direct absorptance and in turn the penetration depth increases, particularly at low welding speed, while for 10 μm-lasers it generally decreases.

  • 12.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Local absorptivity modulation of a 1 μm-laser beam through surface waviness2012In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 258, no 24, p. 9732-9736Article in journal (Refereed)
    Abstract [en]

    In laser materials processing operations such as deep penetration laser welding, the laser beam often interacts with a wavy, molten surface. This wavy topology strongly modulates the local angle of incidence of the laser rays across the surface and in turn the local absorptivity, which is described by the Fresnel-equations. In this paper this modulation of the absorptivity is modelled over a two-dimensional steel surface for prescribed wavy topology for high power lasers with a wavelength of about 1 μm, like disc, fibre, Nd:YAG or diode lasers. It has become apparent that even a topology with regular peaks and valleys causes a complex absorptivity distribution at the surface, including significant shadowing domains due to the grazing angle of incidence during processes like laser welding, drilling or cutting. In contrast to a smooth melt, the waviness tends towards an angle-averaged absorptivity, of 33% for 1 μm-lasers and steel. The high sensitivity of the absorptivity and of shadowing on the surface topology significantly modulates the local absorptivity of the beam power density and in turn the local process mechanisms, such as boiling accompanied by recoil pressure

  • 13.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Model of the absorption variation during pulsed laser heating applied to welding of electronic Au/Ni-coated Cu-leadframes2005In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 241, no 3-4, p. 362-370Article in journal (Refereed)
    Abstract [en]

    C. Absorption is an essential mechanism during laser materials processing, affecting the process efficiency and reliability, but is studied little due to its complex nature. A mathematical model was developed to calculate the absorptivity and the resulting temperature field as a function of space and time during pulsed laser heating of a plane surface, based on modelling the temperature dependence of the absorptivity, here for Au/Ni-galvanized Cu-substrate as an electronic material. For this extremely reflecting case, the absorptivity can increase by a factor of seven during the process. Beside sensitivity analysis of process parameter variations, a process theory can be stated for a variety of effects like the absorption dependence on surface pollutions, diffusion of the coating during melting, acceleration of heating during melting, saturation when the melt exceeds the beam size and onset of evaporation, etc

  • 14.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Analysis of a fibre laser welding case study, utilising a matrix flow chart2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 9, p. 4113-4122Article in journal (Refereed)
    Abstract [en]

    For fibre laser welding of an eccentric corner joint, the quality of the resulting weld cross section was studied with respect to the dependence on process parameters like lateral laser beam alignment, beam inclination, focal plane position or welding speed. The complex load situation of the support beamer was simplified to bending of one corner. Due to fatigue load, the weld properties causing the peak stress are essential, in particular the top and root shape of the weld cross section. For the parameters varied, the resulting shapes were categorized into different top and root classes, determined by certain key dimensions, considering also welding defects like undercuts. The shapes are boundary conditions for Finite Element Analysis of the joint under load for quantitative comparative analysis of the maximum stress. As two high strength steel grades were joined, the hardness transition across the weld was of interest, too. High speed imaging of the weld pool surface shape provided additional information on the relation between the parameter input and quality output. The different trends identified were discussed and guidelines were derived. As the systematic documentation of results is unsatisfactory in welding, a new method was developed and applied for the first time, called the Matrix Flow Chart. It enables an illustrative view on the resulting welding trends in a combined manner and is extendable by other researchers

  • 15.
    Karlsson, Jan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Norman, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Rubin, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lamas, Javier
    Centro Tecnolóxico do Naval Galego, Ferrol.
    Yañez, Armando
    Universidade da Coruña, Ctr Invest Tecnol.
    Observation of the mechanisms causing two kinds of undercut during laser hybrid arc welding2011In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 257, no 17, p. 7501-7506Article in journal (Refereed)
    Abstract [en]

    Two different kinds of undercut were identified when laser hybrid welding hot rolled HSLA-steel in either the as-rolled condition or with the top surface mill scale removed. The presence of mill scale on the steel surface was found to give a sharp angled undercut combined with a sharp oxide inclusion at the edge of the weld which would have the same mechanical effect as a crack in this position. Removal of the surface oxides before welding resulted in the elimination of the oxide inclusions and a more rounded undercut geometry indicative of superior mechanical properties, particularly fatigue life. The mechanisms of the formation of both types of undercut have been analysed by high speed photography and SEM.

  • 16.
    Liedl, G.
    et al.
    Forschungsinstitut für Hochleistungsstrahltechnik, University of Technology, Vienna.
    Schröder, K.
    Forschungsinstitut für Hochleistungsstrahltechnik, University of Technology, Vienna.
    Kaplan, Alexander
    Excimer laser processing of ferrite video heads1996In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 106, no 2, p. 374-378Article in journal (Refereed)
    Abstract [en]

    The technology of pulsed excimer laser ablation for processing ferrite video heads at 248 nm KrF laser radiation was studied. Using the mask imaging technique two trapezoids were projected onto the surface of the samples producing laser-etched grooves with a depth of approximately 45 μm. A sufficiently sharp contour of the trapezoids was achieved at the workpiece. Since the variations of the critical dimensions with respect to depth were outside the tolerance range the sample was slightly tilted to compensate for the beam divergence and to obtain parallel edges of the trapezoidal grooves with an error of less than 5 μm over the whole depth of the cavities. Micrographs of the samples showed that the surfaces of the laser-etched video heads were covered with ablated material and small droplets of resolidified material. These sediments can be removed easily by a slight polishing of the surface. For the experiments a typical fluence of 5 J/cm2 was used which allowed etch rates of 50 nm per pulse. The work showed that excimer lasers are useful tools for the precise micromachining of ferrite video heads.

  • 17.
    Malysheva, L.
    et al.
    Bogolyubov Institute for Theoretical Physics, Kiev.
    Onipko, Alexander
    Valiokas, R.
    Division of Sensor Science and Molecular Physics, Department of Physics and Measurement Technology, Linköping University.
    Liedberg, B.
    Division of Sensor Science and Molecular Physics, Department of Physics and Measurement Technology, Linköping University.
    First-principles modeling of oligo(ethylene glycol)-terminated and amide group containing alkanethiolates2005In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 246, no 4, p. 372-376Article in journal (Refereed)
    Abstract [en]

    Recently, self-assemblies of HS(CH2)15CONH(CH2CH2O)6H were found to undergo a reversible temperature-driven conformational transition from the helical to all-trans state [R. Valiokas, M. Östblom, S. Svedhem, S.C.T. Svensson, B. Liedberg 104 (2000) 7565]. The transition reveals distinctive signatures in the reflection-absorption (RA) spectrum associated with different conformations of the OEG portion of the SAM [R. Valiokas, M. Östblom, S. Svedhem, S.C.T. Svensson, B. Liedberg 104 (2000) 7565]. Here we report an extensive ab initio modeling of infrared RA spectra of molecular constituents of OEG-terminated amide-containing SAMs. The model spectra for this type of molecules (with large OEG and alkyl portions) are obtained, for the first time, by using DFT methods with gradient corrections. The position and relative intensities of all characteristic bands, observed in the fingerprint region of the SAM RA spectrum, are shown to be well reproduced by the single-molecule model spectrum calculated for a certain relative orientation of the alkyl- and OEG portions and the amide bridge. This provides us additional information about actual structure, particularly, molecular orientation within the OEG-containing SAMs in focus

  • 18.
    Matti, Ramiz
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Analysis of moving surface structures at a laser-induced boiling front2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 317, p. 560-567Article in journal (Refereed)
    Abstract [en]

    Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

  • 19.
    Matti, Ramiz
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Post-modelling of images from a laser-induced wavy boiling front2015In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 357, no B, p. 2277-2284Article in journal (Refereed)
    Abstract [en]

    Processes like laser keyhole welding, remote fusion laser cutting or laser drilling are governed by a highly dynamic wavy boiling front that was recently recorded by ultra-high speed imaging. A new approach has now been established by post-modelling of the high speed images. Based on the image greyscale and on a cavity model the three-dimensional front topology is reconstructed. As a second step the Fresnel absorptivity modulation across the wavy front is calculated, combined with the local projection of the laser beam. Frequency polygons enable additional analysis of the statistical variations of the properties across the front. Trends like shadow formation and time dependency can be studied, locally and for the whole front. Despite strong topology modulation in space and time, for lasers with 1 μm wavelength and steel the absorptivity is bounded to a narrow range of 35–43%, owing to its Fresnel characteristics.

  • 20.
    Rodríguez Ripoll, Mane
    et al.
    AC2T research GmbH, Wiener Neustadt.
    Totolin, Vladimir
    AC2T research GmbH, Wiener Neustadt.
    Gabler, Christoph
    AC2T research GmbH, Wiener Neustadt.
    Bernardi, Johannes
    USTEM, Technische Universität Wien.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Diallyl disulphide as natural organosulphur friction modifier via the in-situ tribo-chemical formation of tungsten disulphide2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 428, p. 659-668Article in journal (Refereed)
    Abstract [en]

    The present work shows a novel method for generating in-situ low friction tribofilms containing tungsten disulphide in lubricated contacts using diallyl disulphide as sulphur precursor. The approach relies on the tribo-chemical interaction between the diallyl disulphide and a surface containing embedded sub-micrometer tungsten carbide particles. The results show that upon sliding contact between diallyl disulphide and the tungsten-containing surface, the coefficient of friction drops to values below 0.05 after an induction period. The reason for the reduction in friction is due to tribo-chemical reactions that leads to the in-situ formation of a complex tribofilm that contains iron and tungsten components. X-ray photoelectron spectroscopy analyses indicate the presence of tungsten disulphide at the contact interface, thus justifying the low coefficient of friction achieved during the sliding experiments. It was proven that the low friction tribofilms can only be formed by the coexistence of tungsten and sulphur species, thus highlighting the synergy between diallyl disulphide and the tungsten-containing surface. The concept of functionalizing surfaces to react with specific additives opens up a wide range of possibilities, which allows tuning on-site surfaces to target additive interactions.

  • 21. Roonasi, Payman
    et al.
    Holmgren, Allan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) study of oleate adsorbed on magnetite nano-particle surface2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 11, p. 5891-5895Article in journal (Refereed)
    Abstract [en]

    Magnetite nano-particles were coated with sodium oleate and the spectral behaviour of the coating layer was studied by FTIR spectroscopy after the particles had been heated in air and argon. Magnetite was synthesized by controlled co-precipitation and subsequently coated with sodium oleate. Thermal analysis in combination with mass spectroscopy was carried out to support the FTIR spectroscopic interpretations, but also to monitor the decomposition and surface reaction of oleate adsorbed on the magnetite surface. It was deduced from FTIR and TGA results that the oleate molecules are bonded to iron atoms by a bidentate mononuclear complex and form essentially a single layer with a distance between oleate molecules of ∼36 Å2. It was shown by IR as well as Raman spectroscopy that oleic acid, when heated in air, undergoes decomposition implying that new carbon-oxygen bonds are formed. Heating the iron oxide-oleate system in air also implies oxidation of the double bond at the C:9 position of the alkyl chain and formation of intermediate oxygen-rich molecules. An enthalpy change of ΔH = 49.86 J/g was obtained for oleate desorption/decomposition at ∼350 °C under argon atmosphere and a carbonaceous graphitic species resulted from this decomposition.

  • 22.
    Serrano, Noelia Saurin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Sanes, J.
    Grupo de Ciencia de Materiales e Ingeniería Metalúrgica. Departamento de Ingeniería de Materiales y Fabricación. Universidad Politécnica de Cartagena. Campus de la Muralla del Mar.
    Bermúdez, Juan
    Grupo de Ciencia de Materiales e Ingeniería Metalúrgica. Departamento de Ingeniería de Materiales y Fabricación. Universidad Politécnica de Cartagena. Campus de la Muralla del Mar.
    Study of the effect of tribo-materials and surface finish on the lubricant performance of new halogen-free room temperature ionic liquids2016In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 366, p. 464-474Article in journal (Refereed)
    Abstract [en]

    The present work evaluates different materials and surface finish in the presence of newly designed, hydrophobic halogen-free room temperature ionic liquids (RTILs) as lubricants. A reciprocating tribo-tester was employed with steel-ceramic and steel-thermosetting epoxy resin contacts under boundary lubrication conditions. Four different tetraalkylphosphonium organosilanesulfonate RTILs provided excellent lubricating performance, with friction coefficients as low as 0.057, and non-measurable wear for the higher roughness machine-finish stainless steel flat against sapphire balls, in the case of the lubricants containing the 2-trimethylsilylethanesulfonate anion. Higher friction coefficients of the order of 0.1 and wear volumes of the order of 10-4 mm3, were observed for the lower roughness fine-finished flat stainless steel surface. All RTILs prevent wear of epoxy resin against stainless steel balls, with friction coefficients in the range of 0.03-0.06. EDX analysis shows the presence of RTILs on the stainless steel surfaces after the tribological tests. Under the experimental conditions, no corrosive processes were observed.

  • 23. Shao, Y.
    et al.
    Paul, Jan
    TPD studies of the interaction of D2O and Na with clean and oxidized Al(100) surfaces1993In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 72, no 2, p. 113-124Article in journal (Refereed)
    Abstract [en]

    Temperature-programmed desorption spectra of D2O and Na adsorbed on aluminum and aluminum oxide are presented. D2O adsorbs associatively as well as dissociatively on the Al(100) surface, except at low exposures (<0.5 L) when no molecular species are observed. At these low exposures only dissociative adsorption is observed. High exposures of D2O result in ice formation on both Al and Al2O3. Molecular water desorbs at around 180 K for the metal surface. Ice sublimation takes place at 185 K. D2 has a broad desorption peak between 120 and 150 K possibly from several overlapping peaks and a small peak at around 640 K. Sodium adsorbs on the clean Al(100) surface in two forms: a monolayer strongly interacting with the substrate and multilayers, characterized by Na-Na bonds

  • 24.
    Vomiero, Alberto
    et al.
    Consiglio Nazionale delle Ricerche, CNR.
    Ferroni, Matteo
    Consiglio Nazionale delle Ricerche, Pisa.
    Natile, Marta Maria
    Consiglio Nazionale delle Ricerche, Pisa.
    Fischer, Thomas
    Universität zu Köln.
    Fiz, Raquel
    Universität zu Köln.
    Mathur, Sanjay
    Universität zu Köln.
    Sberveglieri, Giorgio
    Consiglio Nazionale delle Ricerche, Pisa.
    Sequential physical vapor deposition and chemical vapor deposition for the growth of In2O3-SnO2 radial and longitudinal heterojunctions2014In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 323, no 30, p. 59-64Article in journal (Refereed)
    Abstract [en]

    Heterostructures of In2O3 and SnO2 were produced by sequential application of the physical- and chemical-vapor deposition techniques usually adopted for nanowire fabrication. In2O3 nanowires exhibit a single crystal body-centered cubic structure oriented along the [1 0 0] direction and grow epitaxially on α-sapphire substrate by means of a transport and condensation method assisted by Au nanoparticles. Nucleation and growth occurred via direct vapor solid (VS) mechanism competing with catalyst-mediated vapor-liquid-solid (VLS). SnO2 nanowires were obtained in a single crystal tetragonal (cassiterite) structure and oriented along the [1 0 1] direction, the growth being promoted by the gold particle at the apex of the In2O3 nanowires. The size of the catalyst thereby determines the main morphological features of SnO2 wires. CVD deposition allows precise control of the geometrical features of the heterojunction, also limiting detrimental nucleation of SnO2 on the lateral sides of In2O3 nanowires due to lower longitudinal growth rate. These results can help in improving the ability of finely tuning the morphological and structural properties of heterostructured oxide nanocrystals. © 2014 Elsevier B.V. All rights reserved.

  • 25.
    Zsirka, Balázs
    et al.
    University of Pannonia, Institute of Environmental Engineering, Hungary.
    Horváth, Erzsébet
    University of Pannonia, Institute of Environmental Engineering, Hungary.
    Szabó, Péter
    University of Pannonia, Department of Analytical Chemistry, Hungary.
    Juzsakova, Tatjána
    University of Pannonia, Institute of Environmental Engineering, Hungary.
    Szilágyi, Róbert K.
    Department of Chemistry and Biochemistry, Montana State University, USA.
    Fertig, Dávid
    University of Pannonia, Department of Analytical Chemistry, Hungary.
    Makó, Éva
    University of Pannonia, Institute of Materials Engineering, Hungary.
    Varga, Tamás
    University of Szeged, Department of Applied and Environmental Chemistry, Hungary.
    Kónya, Zoltán
    University of Szeged, Department of Applied and Environmental Chemistry, Hungary; MTA-SZTE Reaction Kinetics and Surface Chemistry Research Group, Hungary .
    Kukovecz, Ákos
    University of Szeged, Department of Applied and Environmental Chemistry, Hungary; MTA-SZTE “Lendület” Porous Nanocomposites Research Group, Hungary.
    Kristóf, János
    University of Pannonia, Department of Analytical Chemistry, Hungary.
    Thin-walled nanoscrolls by multi-step intercalation from tubular halloysite-10 Å and its rearrangement upon peroxide treatment2017In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 399, p. 245-254Article in journal (Refereed)
    Abstract [en]

    Surface modification of the halloysite-10 Å mineral with tubular morphology can be achieved by slightly modified procedures developed for the delamination of kaolinite minerals. The resulting delaminated halloysite nanoparticles have unexpected surface/morphological properties that display, new potentials in catalyst development. In this work, a four-step intercalation/delamination procedure is described for the preparation of thin-walled nanoscrolls from the multi-layered hydrated halloysite mineral that consists of (1) intercalation of halloysite with potassium acetate, (2) replacement intercalation with ethylene glycol, (3) replacement intercalation with hexylamine, and (4) delamination with toluene. The intercalation steps were followed by X-ray diffraction, transmission electron microscopy, N2adsorption-desorption, thermogravimetry, and infrared spectroscopy. Delamination eliminated the crystalline order and the crystallite size along the ‘c’-axis, increased the specific surface area, greatly decreased the thickness of the mineral tubes to a monolayer, and shifted the pore diameter toward the micropore region. Unexpectedly, the removal of residual organics from intercalation steps adsorbed at the nanoscroll surface with a peroxide treatment resulted in partial recovery of crystallinity and increase of crystallite size along the ‘c’-crystal direction. The d(001) value showed a diffuse pattern at 7.4–7.7 Å due to the rearrangement of the thin-walled nanoscrolls toward the initial tubular morphology of the dehydrated halloysite-7 Å mineral.

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