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  • 1.
    Rajczakowska, Magdalena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Hedlund, Hans
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering. Concrete Specialist, Skanska AB, Göteborg.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Autogenous Self-Healing: A Better Solution for Concrete2019In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 31, no 9, article id 3119001Article in journal (Refereed)
    Abstract [en]

    Self-healing can be defined as the ability of a material to repair inner damage without any external intervention. In the case of concrete, the process can be autogenous, based on optimized mix composition, or autonomous, when using additionally incorporated capsules containing a healing agent and/or bacteria spores. The first process uses unhydrated cement particles as the healing material while the other utilizes a synthetic material or bacteria released into the crack from a broken capsule or activated through access of water and oxygen. The critical reviewing of both methods indicates that the autogenous self-healing is more efficient, more cost effective, safer, and easier to implement in full-scale applications. Nevertheless, a better understanding of the mechanism and factors affecting the effectiveness of the process is needed. The main weaknesses of the autonomous method were identified as loss of workability, worsened mechanical properties, low efficiency and low probability of the healing to occur, low survivability of the capsules and bacteria in harsh concrete environment, very high price, and lack of full-scale evaluation.

  • 2.
    Tole, Ilda
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Mechanochemical activation of natural clay minerals: an alternative to produce sustainable cementitious binders – review2019In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 113, no 4, p. 449-462Article in journal (Refereed)
    Abstract [en]

    Mechanochemical activation can be defined as a process able to induce structural disorder through intensive grinding. In certain conditions, it may increase the chemical reactivity of the processed material. The process is extensively utilized in extractive metallurgy, synthesis of nanocomposites or pharmacology. It is also considered an environmentally friendly alternative to activate kaolinitic clay avoiding high calcination temperature. This paper aims to give a comprehensive overview of the process, its evolution, process parameters and applications. The paper focuses on the mechanochemical treatment of natural clay minerals, aiming at their transformation into cementitious or pozzolanic materials. It provides a summarized review of the theories related to the mechanochemistry and discusses commonly used models. The paper also analyzes various key factors and parameters controlling the mechanochemical activation process. The optimization and control of the several factors, as the filling ratio, the grinding media, the velocity, the time of grinding, etc., can promote developments and new research opportunities on different fields of application. Examples of applications, with a special focus on mechanochemically activated clay minerals and their use as cementitious binders, are listed as well.

  • 3.
    Buasiri, Thanyarat
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Krzeminski, Lukasz
    Silesian University of Technology, The Institute of Engineering Materials and Biomaterials, Poland.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Piezoresistive Load Sensing and Percolation Phenomena in Portland Cement Composite Modified with In-Situ Synthesized Carbon Nanofibers2019In: Nanomaterials, ISSN 2079-4991, Vol. 9, no 4, article id 594Article in journal (Refereed)
    Abstract [en]

    Carbon nanofibers (CNFs) were directly synthesized on Portland cement particles by chemical vapor deposition. The so-produced cements contained between 2.51–2.71 wt% of CNFs; depending on the production batch. Several mortar mixes containing between 0 and 10 wt% of the modified cement were produced and the electrical properties at various ages and the load sensing capabilities determined. The percolation threshold related to the electrical conductivity was detected and corresponded to the amount of the present CNFs, 0.271, 0.189, 0.135 and 0.108 wt%. The observed threshold depended on the degree of hydration of the Portland cement. The studied mortars showed a strong piezoresistive response to the applied compressive load reaching a 17% change of the electrical resistivity at an applied load of 3.5 MPa and 90% at 26 MPa. This initial study showed that the studied material is potentially suitable for future development of novel fully integrated monitoring systems for concrete structures.

  • 4.
    Buasiri, Thanyarat
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    State of the Art on Sensing Capability of Poorly or Nonconductive Matrixes with a Special Focus on Portland Cement–Based Materials2019In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 31, no 11Article in journal (Refereed)
    Abstract [en]

    Concrete is a well-established and the most used but also well-characterized building material in the world. However, many old and new-build structures suffer from premature failures due to extensive deterioration and decreased load-bearing capacity. Consequently, structural monitoring systems are essential to ensure safe usage of concrete structures within and beyond the designed life. Traditional monitoring systems are based on metallic sensors installed in crucial locations throughout the structure. Unfortunately, most of them have a relatively low reliability and very short life span when exposed to often very harsh environments. The ideal solution is therefore to develop a smart concrete having itself self-sensing capability. A number of studies show that conductive cementitious matrixes will undergo changes in their electrical resistivity with variations of stresses, strains or, developing microcracking. This can be used as a reliable tool to measure changes. This review provides a comprehensive overview of several non-conductive matrixes, with special focus on Portland cement based materials showing self-sensing capabilities by description of detection mechanisms, sensing capabilities, limitations and potential applications.  

  • 5.
    Tole, Ilda
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Rajczakowska, Magdalena
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Activation of a Raw Clay by Mechanochemical Process: Effects of Various Parameters on the Process Efficiency and Cementitious Properties2018In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 11, no 10, article id 1860Article in journal (Refereed)
    Abstract [en]

    The efficiency of the mechanochemical activation (MCA) is influenced by various process parameters as well as by the properties of the treated material. The main objective of this research was to optimize the MCA process, gaining enhancement of the chemical reactivity of a Swedish raw clay, which is going to be used as an alkali-activated cementitious binder. The effects of the amount of water, the filling ratio, the rotation speed, and the grinding duration on the amorphization degree were evaluated by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Generally, wet and dry processes showed an extensive amorphization of both kaolinite and muscovite minerals present in the studied clay. On the contrary, quartz was amorphized mainly by the wet grinding process. The efficiency of both dry and wet grinding processes was enhanced by the increased number of grinding media versus the amount of the activated material. However, longer processing times caused significant agglomeration while a higher rotational speed enhanced the amorphization. Preliminary tests have shown that alkali activation of the processed clays produced hardened samples. Furthermore, the increased amorphization corresponded to the increased compressive strength values.

  • 6.
    Bohling, Daniel
    et al.
    Aalto University, Helsinki, Finland.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Bond Strength between Glass Fiber Fabrics and Low Water-to-Binder Ratio Mortar: Experimental Characterization2018In: Advances in Civil Engineering / Hindawi, ISSN 1687-8086, E-ISSN 1687-8094, Vol. 2018, article id 8197039Article in journal (Refereed)
    Abstract [en]

    Full utilization of mechanical properties of glass fiber fabric-reinforced cement composites is very limited due to a low bond strength between fibers and the binder matrix. An experimental setup was developed and evaluated to correlate the mortar penetration depth with several key parameters. The studied parameters included fresh mortar properties, compressive and flexural strengths of mortar, the fabric/mortar bond strength, fabric pullout strength, and a single-lap shear strength. Results showed that an average penetration of mortar did not exceed 100 µm even at a higher water-to-binder ratio. The maximum particle size of the used fillers should be below an average spacing of single glass fibers, which in this case was less than 20 µm to avoid the sieving effect, preventing effective penetration. The pullout strength was strongly affected by the penetration depth, while the single-lap shear strength was also additionally affected by the mechanical properties of the mortar.

  • 7.
    Cwirzen, Andrzej
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Metsäpelto, Lari
    MSc, YIT Infra Oy, Helsinki, Finland.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Interaction of Magnesia with Limestone-Metakaolin-Calcium Hydroxide Ternary Alkali-Activated Systems2018In: Advances in Materials Science and Engineering, ISSN 1687-8434, E-ISSN 1687-8442, Vol. 2018, article id 1249615Article in journal (Refereed)
    Abstract [en]

    The effect of magnesia on ternary systems composed of limestone, metakaolin and calcium hydroxide, alkali activated with sodium silicate, sodium hydroxide, and sodium sulphate was studied by determination of the compressive strength, X-ray powder diffraction (XRD), thermogravimetry (TG), and scanning electron microscope (SEM). Pastes activated with sodium silicate and sodium sulphate showed strength regression caused by a formation of an unstable prone to cracking geopolymer gel. The presence of magnesia in sodium hydroxide-activated system hindered this trend by promoting a formation of more stable crystalline phases intermixed with brucide. In general, magnesia densified the binder matrix by promoting a formation of amorphous phases while sodium hydroxide produced the most porous microstructure containing high amount of crystalline phases.

  • 8.
    Blandine, Feneuil
    et al.
    Aalto University, Concrete Technology Laboratory, Department of Civil and Structural Engineering, School of Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Cwircen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Erratum to: Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste2017In: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 11, no 2, p. 255-255Article in journal (Refereed)
  • 9.
    Feneuil, Blandine
    et al.
    Aalto University, Concrete Technology Laboratory, Department of Civil and Structural Engineering, School of Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Contribution of CNTs/CNFs morphology to reduction of autogenous shrinkage of Portland cement paste2016In: Frontiers of Structural and Civil Engineering, ISSN 2095-2430, E-ISSN 2095-2449, Vol. 10, no 2, p. 224-235Article in journal (Refereed)
    Abstract [en]

    In this experimental study, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were dispersed by intensive sonication in water in the presence of superplasticizer and subsequently mixed with Portland cement with water/ cement ratios varying between 0.3 and 0.4. The autogenous shrinkage in the fresh stage was investigated. The CNTs and CNFs were characterized by high resolution scanning electron microscopy (SEM) and the hydrated pastes were studied by X-ray diffraction and SEM. The results showed a reduction of the autogenous shrinkage by 50% for pastes containing small amounts (0.01 wt%) of nanomaterials. Higher additions appeared to be less effective. The highest reduction of shrinkage was observed for carbon nanofibers which were long, rather straight and had diameters of around 200 nm. The result showed that the addition of nanomaterials accelerated the hydration processes especially in the early stages of hydration. The effect was the most pronounced in the case of functionalized nanotubes. The proposed mechanism resulting in the reduction of the autogenous shrinkage was a combination of nano-reinforcing effects, alterations of hydration and microstructure of the hydrated matrix.

  • 10.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Sztermen, P.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Effect of baltic seawater and binder type on frost durability of concrete2014In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 26, no 2, p. 275-282Article in journal (Refereed)
    Abstract [en]

    The effects of Baltic seawater on frost durability of PC concretes using sulfate resistant portland cement and combination of rapid hardening portland cement with silica fume were studied. The freeze-thaw cycles were performed on specimens exposed to the Baltic seawater, 3% sodium chloride solution and deionized water. The freeze-thaw cycles appeared to cause the most extensive internal damage in specimens based on sulfate resistant cement (SR) and exposed to seawater. The most extensive surface scaling was observed in the case of concretes containing silica fume and exposed to deicing salts. Based on the thermo gravimetric and X-ray diffraction analyses it was concluded that extensive internal damage of concrete based on SR was caused by changes of the microstructure due to secondary formation of ettringite, carbonation, and formation of calcite. The results showed also that low C3A content of the SR did not fully mitigate formation of secondary ettringite during freeze-thaw cycles. A combination of rapid hardening portland cement and silica fume appeared to form more frost resistant concrete when exposed to seawater. © 2014 American Society of Civil Engineers.

  • 11.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Engblom, Ronny
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Punkki, Jouni
    Consolis Technology Oy.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Effects of curing: Comparison of optimised alkali-activated PC-FA-BFS and PC concretes2014In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 66, no 6, p. 315-323Article in journal (Refereed)
    Abstract [en]

    The effects of curing on the mechanical properties, chemical composition, microstructure and shrinkage of optimised alkali-activated concretes (AACs) based on ternary mixtures of fly ash (FA), blast-furnace slag (BFS) and Portland cement (PC) were compared. Heat treatment was found to accelerate the early-age strength development of both the PC concrete and the AAC. The long-term strength of AAC was not adversely affected by the heat treatment after 90 d of dry curing. Water curing slightly enhanced the ultimate long-term strength of non-heat-treated AAC specimens but had barely any effect on the heat-treated specimens. Conversely, the dry-cured PC specimens showed a significant decrease in long-term compressive strength. The ultimate drying shrinkage of the PC concrete was lower compared with the AAC, independent of the type of applied curing. In the case of AAC, the drying shrinkage was significantly decreased by the application of heat treatment while water curing did not have any measurable effect. Conversely, the drying shrinkage of AAC cured at ambient temperatures was decreased with the application of water curing. Compared with the PC concrete, the microstructure of the AAC samples was denser and more homogeneous without visible microcracking of the binder matrix. The dominant phases were geopolymer and calcium silicate hydrate (C-S-H) gels intermixed with probably sodium and aluminium ions and crystalline inclusions of zeolitic hydroxysodalite. A large amount of unreacted FA and BFS was observed in the hardened binder matrix of the AAC specimens. At the same time, no anhydrous PC was observed, thus indicating its extensive dissolution and contribution to the formation of the modified C-S-H gel.

  • 12.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Provis, John L.
    Department of Chemical & Biomolecular Engineering, University of Melbourne.
    Penttala, Vesa
    Department of Civil and Structural Engineering, Aalto University.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    The effect of limestone on sodium hydroxide-activated metakaolin-based geopolymers2014In: Construction and Building Materials, ISSN 0950-0618, E-ISSN 1879-0526, Vol. 66, p. 53-62Article in journal (Refereed)
    Abstract [en]

    Blends of metakaolin and limestone can be alkali-activated with NaOH to form solid binders, which show relatively low strength but offer potential as a model system by which the reaction processes of more complex systems can be better understood. The effects of curing procedure, limestone content and alkalinity of the activator are able to be related to the mineralogy, mechanical properties and microstructure of hardened pastes. The presence of limestone enhances the release of Al and Si ions from metakaolin, with the Al released in the early stages of the reaction being bound into AFm-type phases. Dissolution of LS is slightly higher when a lower alkalinity sodium hydroxide activator is used. The heat treatment of pastes activated with 3 M NaOH solution resulted in a lower extent of reaction of limestone, while with 5 M solution, heat-curing at early age resulted in more reaction. The main alkali-activation product in metakaolin-limestone-NaOH pastes is a geopolymer gel with inclusions of unreacted metakaolin, limestone particles, zeolite A, and AFm phases, with different zeolites such as faujasite-like and hydrosodalite phases also identified at higher reaction temperatures. © 2014 Elsevier Ltd. All rights reserved.

  • 13.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Effects of reactive magnesia on microstructure and frost durability of portland cement-based binders2013In: Journal of materials in civil engineering, ISSN 0899-1561, E-ISSN 1943-5533, Vol. 25, no 12, p. 1941-1950Article in journal (Refereed)
    Abstract [en]

    The effects of portland cement (PC) replacement with magnesia (reactive magnesium-oxide) on properties of PC-based pastes, mortars, and concretes were investigated. The research included determination of mechanical properties and frost durability in addition to studies of the microstructure and microchemistry. The mortar and paste mixtures contained from 10-80 weight percent (wt%) replacement of PC by magnesia and had water to cementitious-binder ratios from 0.4-0.7, whereas concretes contained from 5-10 wt% magnesia and had a water to cementitious-binder ratio of 0.53. Replacement of PC by magnesia had adverse effects on the mechanical properties and frost durability. The magnesia reduced microcracking of the binder matrix in comparison with pastes containing only PC. The primary hydration product of magnesia was brucite in addition to regular hydration phases of PC. The amount of formed portlandite was increased. Magnesia caused densification of the microstructure but also increased the capillary porosity, resulting in lower frost-durability. © 2013 American Society of Civil Engineers.

  • 14.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    The effect of carbon nano- and microfibers on strength and residual cumulative strain of mortars subjected to freeze-thaw cycles2013In: Journal of Advanced Concrete Technology, ISSN 1346-8014, Vol. 11, no 3, p. 80-88Article in journal (Refereed)
    Abstract [en]

    The strength and development of residual strain of normal strength mortars subjected to freeze-thaw cycles incorporating carbon nanotubes (CNTs) and carbon microfibers (CMF) were studied. The workability was influenced by the fiber type, the dispersion method, and the amount of fibers. The obtained results showed that the measured flexural strength increased only in the case of mortars incorporating CMFs. The compressive strength remained unchanged in the case of mortars containing CMFs and was slightly lower when CNTs were present. The residual strain due to freeze-thaw cycles was lowered in comparison with reference mortar only when incorporating CMFs. The obtained results confirmed that in order to utilize the outstanding mechanical properties of CNTs the binder matrix must be very homogenous to provide sufficient contact area for stress transfer. The used water to binder ratio was sufficiently low only for long CMFs, which were able to bridge numerous weak inclusions present on the binder matrix. © 2013 Japan Concrete Institute.

  • 15.
    Habermehl-Cwirzen, Karin
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Curtain, Roger
    Bio21 Molecular Science and Biotechnology Institute.
    Penttala, Vesa
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Provis, John
    Geopolymer and Minerals Processing Group, Department of Chemical and Biomolecular Engineering, AUS-University of Melbourne.
    Gordon, Laura
    Geopolymer and Minerals Processing Group, Department of Chemical and Biomolecular Engineering, AUS-University of Melbourne.
    Cwirzen, Andrzej
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Sustainable straw-based cementitious building materials2012In: fib Symposium 2012: Concrete Structures for Sustainable Community - Proceedings / [ed] Dirch H. Bager; Johan Silfwerbrand, Stockholm: Swedish Concrete Association , 2012, p. 477-480Conference paper (Refereed)
    Abstract [en]

    New classes of sustainable cementitious materials are needed to improve the environmental impact of cement-based building materials. This study describes the recent work carried out on cementitious materials made with various straw-fibre based additions. The straw was used as unprocessed and chemically processed. The chemical processing enabled fibre extraction down to the micro and nano scale. The different fibres, before and after processing, as well as the fibre-hydrated cement paste composites were characterized and the mechanical properties of the different materials were determined.

  • 16.
    Nasibulina, Larisa I.
    et al.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Anoshkin, Ilya V.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Shandakov, Sergey D.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulin, Albert G.
    Department of Applied Physics and Center for New Materials, Aalto University.
    Cwirzen, Andrzej
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Mudimela, Prasantha R.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, Karin
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Malm, Jari E M
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Koltsova, Tatiana S.
    Material Science Faculty, State Polytechnical University.
    Tian, Ying
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Vasilieva, Ekaterina S.
    Material Science Faculty, State Polytechnical University.
    Penttala, Vesa
    Laboratory of Building Materials Technology, Aalto University.
    Tolochko, Oleg V.
    Material Science Faculty, State Polytechnical University.
    Karppinen, Maarit J.
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Kauppinen, Esko I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Direct synthesis of carbon nanofibers on cement particles2010In: Transportation Research Record, ISSN 0361-1981, E-ISSN 2169-4052, no 2142, p. 96-101Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes (CNTs) and nanofibers (CNFs) are promising candidates for the next generation of high-performance structural and multifunctional composite materials. One of the largest obstacles to creating strong, electrically or thermally conductive CNT-CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps are required in purifying and functionalizing the carbon nanomaterial. A new approach under which CNTs-CNFs are grown directly on the surface of matrix and matrix precursor particles is proposed. Cement was selected as the precursor matrix, since it is the most important construction material. A novel cement hybrid material (CHM) was synthesized in which CNTs and CNFs are attached to the cement particles by two different methods: screw feeder and fluidized bed reactors. CHM has been proved to increase the compressive strength by two times and the electrical conductivity of the hardened paste by 40 times.

  • 17.
    Cwirzen, Andrzej
    et al.
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Habermehl-Cwirzen, Karin
    Department of Civil and Structural Engineering, Aalto University, School of Engineering, Espoo.
    Enhancement of Frost Durability by Application of Nanomaterials2010In: Additions improving properties of concrete: AdIPoC / [ed] Wolfgang Brameshuber, Bagneux: Rilem publications, 2010, p. 307-313Conference paper (Refereed)
    Abstract [en]

    The effect of carbon nanotubes (CNT), carbon nanofibers (CNF) and nano-sized silica (NS) on the frost durability of mortars was investigated. The test specimens were produced using Portland cement as binder and water to binder ratios of 0.5 and 0.33. CNT and CNF were added as water dispersion with superplasticizers. The NS was intermixed with micro silica and added as slurry. The frost durability was determined by a modified CIF method. The results showed that in the case of addition of nano-sized fibers a positive effect can be only found if the binder matrix is homogenous and dense. The combination of CNTs and NS resulted in the lack of any frost damage even after 180 freeze-thaw cycles.

  • 18.
    Nasibulin, Albert G.
    et al.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Shandakov, Sergey D.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulina, Larisa I.
    Cwirzen, Andrzej
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Mudimela, Prasantha R.
    Department of Applied Physics, Aalto University.
    Habermehl-Cwirzen, Karin
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Grishin, Dmitrii A.
    Mendeleev University of Chemical Technology.
    Gavrilov, Yuriy V.
    Mendeleev University of Chemical Technology.
    Malm, J. E M
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Tapper, Unto
    VTT Biotechnology.
    Tian, Ying
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Penttala, Vesa
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Karppinen, Maarit J.
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Kauppinen, Esko I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    A novel cement-based hybrid material2009In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 11, article id 23013Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purification and fimctionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles. As the matrix we selected cement, the most important construction material. We synthesized in a simple one-step process a novel cement hybrid material (CHM), wherein CNTs and CNFs are attached to the cement particles. The CHM has been proven to increase 2 times the compressive strength and 40 times the electrical conductivity of the hardened paste, i.e. concrete without sand. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

  • 19.
    Cwirzen, Andrzej
    et al.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, Karin
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Nasibulina, Larisa I.
    Department of Applied Physics, Aalto University, Department of Applied Physics and Center for New Materials, Laboratory of Physics, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Shandakov, Sergey D.
    Department of Applied Physics and Center for New Materials, Aalto University, Laboratory of Carbon NanoMaterials, Kemerovo State University, Department of Applied Physics, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulin, Albert G.
    Department of Applied Physics, Aalto University, Department of Applied Physics and Center for New Materials, Centre for New Materials, Laboratory of Physics, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Kauppinen, Esko I.
    Department of Applied Physics, Aalto University, VTT Biotechnology, Laboratory of Physics, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Mudimela, Prasantha R.
    Department of Applied Physics and Center for New Materials, Aalto University, Centre for New Materials, Department of Applied Physics, Laboratory of Physics, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Penttala, Vesa
    Department of Civil and Structural Engineering, Aalto University, Department of Structural Engineering, Laboratory of Building Materials Technology, Laboratory of Building Materials, NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    CHH Cement Composite2009In: Nanotechnology in Construction 3: Proceedings of the NICOM3 / [ed] Zdeněk Bittnar ; Peter J.M. Bartos; Jiří Němeček; Vit Šmilauer; Jan Zeman, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2009, p. 181-185Conference paper (Refereed)
    Abstract [en]

    The compressive strength and electrical resistivity for hardened pastes produced from nanomodified Portland SR cement (CHH- Carbon Hedge Hog cement) were studied. The nanomodification included growing of carbon nanotubes (CNTs) and carbon nanofibers (CNFs) on the cement particles. Pastes having water to binder ratio of 0.5 were produced. The obtained hardened material was characterized by increased compressive strength in comparison with the reference specimens made from pristine SR cement, which was attributed to reinforcing action of the CNTs and CNFs. The electrical resistivity of CHH composite was lower by one order of magnitude in comparison with reference Portland cement paste

  • 20.
    Cwirzen, A.
    et al.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, K.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Shandakov, D.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulina, L. I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulin, A. G.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Mudimela, P. R.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Kauppinen, E. I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Penttala, V.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Properties of high yield synthesised carbon nano fibres/portland cement composite2009In: Advances in Cement Research, ISSN 0951-7197, E-ISSN 1751-7605, Vol. 21, no 4, p. 141-146Article in journal (Refereed)
    Abstract [en]

    The compressive strength and electrical resistivity of hardened pastes produced either from nanomodified Portland sulfate-resistant cement (CHH) or a mixture of nanomodified and pristine sulfate-resistant cements were determined. The nanomodification included grow carbon nanotubes (CNTs) and carbon nanofibres (CNFs) on the cement particles. Pastes having a water-to-binder ratio of 0-5 were produced. The test results revealed that partial replacement of sulfate-resistant cement by CHH cement decreased the electrical resistivity of the 28 day old specimens but worsened the mechanical properties. The lower compressive strength was attributed to a lower degree of hydration of the CHH cement. The addition of a mixture of surfactants enabled the production of specimens consisting entirely of CHH cement. The hardened material obtained was characterised by a nearly doubled compressive strength in comparison with the reference specimens made from pristine sulfate-resistant cement. This was attributed to a high degree of hydration as well as reinforcing action of the CNTs and CNFs. The electrical resistivity was lowered by one order of magnitude classifying this material as a semiconductor.

  • 21.
    Cwirzen, A.
    et al.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, K.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Nasibulin, A. G.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Kaupinen, E. I.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Mudimela, P. R.
    Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Penttala, V.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    SEM/AFM studies of cementitious binder modified by MWCNT and nano-sized Fe needles2009In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 60, no 7, p. 735-740Article in journal (Refereed)
    Abstract [en]

    Several compositions of cement paste samples containing multiwalled carbon nanotubes were produced using a small-size vacuum mixer. The mixes had water-to-binder ratios of 0.25 and 0.3. Sulfate resistant cement has been used. The multiwalled carbon nanotubes were introduced as a water suspension with added surfactant admixtures. The used surfactant acted as plasticizing agents for the cement paste and as dispersant for the multiwalled carbon nanotubes. A set of beams was produced to determine the compressive and flexural strengths. The scanning electron microscope and atomic force microscope studies of fractured and polished samples showed a good dispersion of multiwalled carbon nanotubes in the cement matrix. The studies revealed also sliding of multiwalled carbon nanotubes from the matrix in tension which indicates their weak bond with cement matrix. In addition to multiwalled carbon nanotubes also steel wires covered with ferrite needles were investigated to determine the bond strength between the matrix and the steel wire. These later samples consisted of 15-mm-high cylinders of cement paste with vertically cast-in steel wires. As reference, plain steel wires were cast, too. The bond strength between steel wires covered with nano-sized Fe needles appeared to be lower in comparison with the reference wires. The scanning electron microscope studies of fractured samples indicated on brittle nature of Fe needles resulting in shear-caused breakage of the bond to the matrix. © 2008 Elsevier Inc. All rights reserved.

  • 22.
    Mudimela, Prasantha R.
    et al.
    NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulina, Larisa I.
    NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Nasibulin, Albert G.
    NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Cwirzen, Andrzej
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Valkeapää, Markus
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, Karin
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Malm, Jari E M
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Karppinen, Maarit J.
    Laboratory of Inorganic Chemistry, Department of Chemistry, Helsinki University of Technology, Espoo.
    Penttala, Vesa
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Koltsova, Tatiana S.
    Material Science Faculty, State Polytechnical University.
    Tolochko, Oleg V.
    Material Science Faculty, State Polytechnical University.
    Kauppinen, Esko I.
    NanoMaterials Group, Department of Applied Physics and Center for New Materials, Helsinki University of Technology, Espoo.
    Synthesis of carbon nanotubes and nanofibers on silica and cement matrix materials2009In: Journal of Nanomaterials, ISSN 1687-4110, E-ISSN 1687-4129, Vol. 2009, article id 526128Article in journal (Refereed)
    Abstract [en]

    In order to create strong composite materials, a good dispersion of carbon nanotubes (CNTs) and nanofibers (CNFs) in a matrix material must be obtained. We proposed a simple method of growing the desirable carbon nanomaterial directly on the surface of matrix particles. CNTs and CNFs were synthesised on the surface of model object, silica fume particles impregnated by iron salt, and directly on pristine cement particles, naturally containing iron oxide. Acetylene was successfully utilised as a carbon source in the temperature range from 550 to 750 °C. 5-10 walled CNTs with diameters of 10-15nm at 600 °C and 12-20nm at 750 °C were synthesised on silica particles. In case of cement particles, mainly CNFs with a diameter of around 30nm were grown. It was shown that high temperatures caused chemical and physical transformation of cement particles. © 2009 Prasantha R. Mudimela et al.

  • 23.
    Cwirzen, A.
    et al.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Habermehl-Cwirzen, K.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Penttala, V.
    Laboratory of Building Materials Technology, Faculty of Engineering and Architecture, Helsinki University of Technology, Espoo.
    Surface decoration of carbon nanotubes and mechanical properties of cement/carbon nanotube composites2008In: Advances in Cement Research, ISSN 0951-7197, E-ISSN 1751-7605, Vol. 20, no 2, p. 65-73Article in journal (Refereed)
    Abstract [en]

    The present study investigated the effects of the method of surface decoration on the wetability of multi-walled carbon nanotubes (MWCNTs) and the mechanical properties of the cement paste incorporating these dispersions. The results showed that stable and homogenous dispersions of MWCNTs in water can be obtained by using surface functionalisation combined with decoration using polyacrylic acid polymers. The cement paste specimens incorporating these dispersions revealed good workability and an increase in the compressive strength of nearly 50% even with only a small addition of the MWCNTs, namely 0-045-0-15% of the cement weight. These results indicate the existence of chemical bonds between the OH groups of the functionalised MWCNTs and probably the C-S-H phase of the cement matrix, which enhanced the transfer of stresses. A second method that was studied included decoration of MWCNTs with polyacrylic acid polymers and gum Arabic. These dispersions appeared to be homogeneous only for approximately 2 h after which a progressive sedimentation occurred. Good workability was found for the cement pastes produced with all of the dispersions; the only significant difference being the slower hydration of the cement incorporating gum Arabic. The mechanical properties of the cement pastes incorporating MWCNTs treated with polyacrylic polymers were unchanged.

  • 24.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Coadsorption of CO and C6H6 on Co(0 0 0 1)2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 584, no 1, p. 70-76Article in journal (Refereed)
    Abstract [en]

    We have studied the influence of CO on the adsorption of benzene on the Co(0 0 0 1) surface using LEED, XPS, TDS and work function measurements. CO was found to reduce the benzene adsorption, but even at saturation CO exposure no complete blocking was observed. Thermal desorption of the coadsorbed layer featured CO and H2 peaks indicating partial dehydrogenation of benzene and retaining of the CO bond. Ordered LEED structures were found with all coverages: Pre-adsorption of CO led to patterns already seen for pure carbon monoxide adsorption. Pre-adsorption of benzene showed the known (7×7)R19°structure of pure benzene also with small CO exposures, but higher CO exposures yielded a mixture of (7×7)R19°and (3×3)R30°patterns

  • 25.
    Lahtinen, J.
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Kantola, P.
    Laboratory of Physics, Helsinki University of Technology.
    Jaatinen, S.
    Laboratory of Physics, Helsinki University of Technology.
    Habermehl-Cwirzen, K.
    Laboratory of Physics, Helsinki University of Technology.
    Salo, P.
    Laboratory of Physics, Helsinki University of Technology.
    Vuorinen, J.
    Institute of Physics, Tampere University of Technology.
    Lindroos, M.
    Institute of Physics, Tampere University of Technology.
    Pussi, K.
    Laboratory of Electronics Materials Technology, Lappeenranta University of Technology.
    Seitsonen, A. P.
    Institute of Mineralogy and Condensed Matter Physics, CNRS and University of Pierre and Marie Curie.
    LEED and DFT investigation on the (2 × 2)-S overlayer on Co(0 0 0 1)2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 599, no 1-3, p. 113-121Article in journal (Refereed)
    Abstract [en]

    The geometric surface structure of a (2 × 2)-S layer formed by adsorption of hydrogen sulfide at 185 K on the Co(0 0 0 1) surface has been determined by low energy electron diffraction (LEED) experiments and density-functional theory (DFT) calculations. The favored atomic configuration consists of sulfur atoms residing at the fcc-hollow sites with S-Co distance of 2.2 ± 0.1 Å. Buckling in the first layer is negligible and the three nearest-neighbor Co atoms below the S atom are symmetrically moved by 0.05 ± 0.09 Å along the surface away from the S atom. The DFT calculations confirm the hollow-site adsorption and give further information on the electronic structure of the system. © 2005 Elsevier B.V. All rights reserved.

  • 26.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Laboratory of Physics, Helsinki University of Technology.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    Methanol on Co(0 0 0 1): XPS, TDS, WF and LEED results2005In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 598, no 1-3, p. 128-135Article in journal (Refereed)
    Abstract [en]

    The adsorption and decomposition of methanol on clean Co(0 0 0 1) was studied as a function of temperature and exposure by means of TDS (thermal desorption spectroscopy), XPS (X-ray photoelectron spectroscopy), WF (work function measurements) and LEED (low energy electron diffraction). Methanol was adsorbed by OH-bond scission as methoxide on the cobalt surface. TD and XP spectra revealed that beside a small amount of molecularly desorbing methanol, it decomposed during heating to the final products: CO and H2. Desorption of H2 took place around 356 K and desorption of CO around 390 K. These temperatures are characteristic for desorption of these species on clean cobalt. Work function measurements showed that the adsorption of methanol resulted in a lowering of the WF by 1.1 eV. Heating - and therewith decomposition - led to an increase in the WF of +0.4 eV. After all decomposition products had desorbed, the WF returned to the value for the clean Co(0 0 0 1) surface. LEED exhibited a combination of two ordered structures: p(2 × 2) and (7×7)19.1°. The (7×7)19.1° pattern was formed by methoxide or hydrogen and vanished below 340 K. The p(2 × 2) structure was still found above 380 K and was therefore assigned to CO

  • 27.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Kauraala, K.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology.
    Hydrogen on cobalt: effects of carbon monoxide and sulphur additives on the D-2/Co(0001) system2004In: Physica scripta. T, ISSN 0281-1847, Vol. T108, p. 28-32Article in journal (Refereed)
    Abstract [en]

    Hydrogen reaction on catalytic surfaces is an important field of research in fuel cell science. The adsorption of hydrogen (deuterium) on Co(0001) and the influence of carbon monoxide and sulphur on the adsorption were studied by XPS, TDS, WF measurements and LEED. The WF increased due to D2 adsorption, revealing the electronegative character of deuterium. It was found that the deuterium saturation coverage is similar to 0.17 ML at 320K and similar to 0.27ML at 180 K. The activation energy for desorption was estimated to be 33 kJ/mol. The coadsorption measurements with CO indicated a decrease in the deuterium yield by 50%. A downward shift of 50K in the deuterium desorption temperature was observed as a consequence of coadsorbed CO, but changes in the CO desorption were minimal. At small CO exposures the (2 X 2) LEED structure of deuterium was seen, while at exposures of above 5 L the (2 root 3 x 2 root 3)R30... structure was detected by LEED as with pure CO adsorption. Coadsorption with sulphur led also to a decrease in the D2 yield leading to a complete inhibition of hydrogen adsorption at sulphur saturation. The sulphur (2 X 2) LEED structure did not underwent changes due to deuterium adsorption. As assumed, sulphur worked as a strong poison to the adsorption on Co(0001).

  • 28.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology.
    Sulfur poisoning of the CO adsorption on Co(0001)2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 573, no 2, p. 183-190Article in journal (Refereed)
    Abstract [en]

    CO adsorption on a sulfur covered cobalt surface at 185 K has been studied using XPS, TDS, LEED, and WF measurements. As in the case of CO adsorption on the clean Co(0001) surface, CO adsorbs and desorbs molecularly and no dissociation was observed. The saturation coverage of CO decreases linearly from 0.54 ML to 0.27 ML when the S pre-coverage increases to 0.25 ML. The WF increased during CO adsorption, but did not reach the value obtained for CO adsorption on the clean surface. The smaller work function change is explained by the reduced adsorption of CO on the sulfur-precovered surface. A reduction in the activation energy of desorption for CO from 113 kJ/mol to 88 kJ/mol was observed indicating weaker bonding of the CO molecules to the surface. The behavior of the CO/S/Co(0001) system was explained by a combination of steric and electronic effects.

  • 29.
    Pussi, Katariina
    et al.
    Laboratory of Electronics Materials Technology, Lappeenranta University of Technology, Institute of Physics, Tampere University of Technology.
    Lindroos, Matti
    Institute of Physics, Tampere University of Technology.
    Katainen, Jukka
    Laboratory of Physics, Helsinki University of Technology.
    Habermehl-Cwirzen, Karin
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Seitsonen, Ari Paavo
    Université Pierre et Marie Curie, Physikalisch Chemisches Institut, Universität Zürich.
    The (√7 × √7)R19.1°-C6H6 adsorption structure on Co{0001}: A combined tensor LEED and DFT study2004In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 572, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    The geometric structure of a Co{0001}-(√7 × √7)R19.1°-C6H6 surface formed by adsorption of benzene to the saturation coverage at 170 K has been determined by low energy electron diffraction (LEED). The favored model consists of a flat laying, nearly undisturbed benzene molecule, with the hydrogen-carbon bonds bent away from the substrate by 0.3 ± 0.2 Å. The carbon ring lies at a hcp-site with the two parallel C-C bonds aligned with [1̄100] direction. Buckling between the inequivalent carbon atoms in the molecular ring is within the experimental uncertainty (0.01 ± 0.11 Å). The experimental results are supported by density functional calculations

  • 30.
    Habermehl-Cwirzen, Karin
    et al.
    Laboratory of Physics, Helsinki University of Technology.
    Katainen, Jukka
    Laboratory of Physics, Helsinki University of Technology.
    Lahtinen, Jouko
    Department of Applied Physics, Aalto University School of Science, Laboratory of Physics, Helsinki University of Technology, Laboratory of Physics, Aalto University.
    Hautojärvi, Pekka
    Laboratory of Physics, Helsinki University of Technology.
    An experimental study on adsorption of benzene on Co(0001)2002In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 507, p. 57-61Article in journal (Refereed)
    Abstract [en]

    The adsorption of benzene on Co(0 0 0 1) was studied by X-ray photoelectron spectroscopy, temperature programmed desorption, low energy electron diffraction (LEED) and work function measurements. The adsorption was found to be molecular at room temperature and to saturate at a fractional coverage of 0.125 ML. With LEED a c(2root3 x 4) overlayer structure was seen. Below 220 K at high exposures a p(root7 x root7)R19degrees LEED pattern was observed corresponding to a coverage of 0.143 ML. Temperature programmed desorption measurements stated that benzene starts to decompose around 340 K to hydrogen and a hydrocarbon fragment, most likely C6H5. While the hydrogen desorbed, the hydrocarbon stayed at the surface. The desorption of molecular benzene was negligible. The activation energy for the dehydrogenation was calculated to be about 102 kJ/mol. The work function of Co(0 0 0 1) decreased by 1.3 eV upon saturation with benzene. The induced dipole moment was calculated to be 1.9 Debye/molecule.

1 - 30 of 30
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