Browsing by Department "Department of Materials Science and Engineering"

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  • Adhesion Testing of Atomic Layer Deposited TiO2 on Glass Substrate by the Use of Embedded SiO2 Microspheres
    (2014) Lyytinen, Jussi; Berdova, Maria; Franssila, Sami; Koskinen, Jari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Alkaline leaching of iron and steelmaking dust
    (2012) Stafanova, Anna; Aromaa, Jari
     School of Chemical Technology | D4 Julkaistu kehittämis- tai tutkimusraportti tai -selvitys
    Steel production generates significant quantities of dust and sludge in blast furnaces (BF),basic oxygen furnaces (BOF), and electric arc furnaces (EAF). These dusts contain toxicelements, such as heavy metals, and are thus classified as harmful waste making the disposalof them expensive. In addition, direct recycling of dust back to steel production is hindered dueto the presence of zinc. In this literature survey the alkaline leaching of zinc from iron and steelmaking dusts isreviewed. The characteristics of EAF, BOF and BF dust and their processing based on causticsoda (NaOH) leaching is described. Also some methods, e.g. pre-treatments, to enhanceleaching are introduced. Dusts from iron and steel production consist mainly of ferrous oxides. In addition, theycontain zinc, lead and cadmium oxides as well as minor amount of many other elements. Thezinc content in EAF dust can run up 30 %, when it is usually lower in BOF and BF dusts, around1-3 % and 1.5 %, respectively. Zinc is present mainly as zinc oxide, ZnO (50-80 %), and rest is aszinc ferrite, ZnFe2O4. The dusts are very fine (usually < 0.01 mm) and have tendency to agglomerate. Metal extraction from the dusts is difficult due to their complex composition and finding asuitable process is complicated as each dust is unique. The advantage of caustic soda leachingis its selectiveness in leaching zinc compared to iron compounds. Thus a relatively clean andiron-free solution is obtained and the complicated iron removal processes is avoided. Somefacilities using NaOH leaching have been constructed for dissolving zinc from the steelmakingdusts, but they have been closed as inefficient and expensive. For the optimal leaching conditions 6-10 M NaOH solution, liquid to solid ratio of around 10,and temperature of 80 – 95 °C has been presented. Zinc recoveries of 80-85 % can be reachedbut part of zinc is not dissolved and recovered. ZnO dissolves easily in caustic soda, butZnFe2O4 is highly stable compound and is the major obstruction in the hydrometallurgicalextraction of zinc. Pressure leaching, and microwave or ultrasound assisted leaching has notimproved significantly zinc recovery. For breaking the zinc ferrite structure, pyrometallurgicalprocesses, such as roasting, can be used prior to leaching. By roasting with caustic soda priorto alkaline leaching zinc ferrites can be decomposed and leaching of zinc could be improved.
  • Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties
    (2017-01-01) Ylivaara, Oili M E; Kilpi, Lauri; Liu, Xuwen; Sintonen, Sakari; Ali, Saima; Laitinen, Mikko; Julin, Jaakko; Haimi, Eero; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo-Pekka; Ronkainen, Helena; Puurunen, Riikka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Atomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al2O3) and titanium dioxide (TiO2) films on silicon were explored as a function of growth temperature (110-300 °C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO2 content (0%-100%). Al2O3 was grown from Me3Al and H2O, and TiO2 from TiCl4 and H2O. According to wafer curvature measurements, Al2O3/TiO2 nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO2 fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon.
  • Axonal Kainate Receptors Modulate the Strength of Efferent Connectivity by Regulating Presynaptic Differentiation
    (2016-01-20) Sakha, Prasanna; Vesikansa, Aino; Orav, Ester; Heikkinen, Joonas; Kukko-Lukjanov, Tiina-Kaisa; Shintyapina, Alexandra; Franssila, Sami; Jokinen, Ville; Huttunen, Henri J.; Lauri, Sari E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Kainate type of glutamate receptors (KARs) are highly expressed during early brain development and may influence refinement of the circuitry, via modulating synaptic transmission and plasticity. KARs are also localized to axons, however, their exact roles in regulating presynaptic processes remain controversial. Here, we have used a microfluidic chamber system allowing specific manipulation of KARs in presynaptic neurons to study their functions in synaptic development and function in vitro. Silencing expression of endogenous KARs resulted in lower density of synaptophysin immunopositive puncta in microfluidically isolated axons. Various recombinant KAR subunits and pharmacological compounds were used to dissect the mechanisms behind this effect. The calcium permeable (Q) variants of the low-affinity (GluK1-3) subunits robustly increased synaptophysin puncta in axons in a manner that was dependent on receptor activity and PKA and PKC dependent signaling. Further, an associated increase in the mean active zone length was observed in electron micrographs. Selective presynaptic expression of these subunits resulted in higher success rate of evoked EPSCs consistent with higher probability of glutamate release. In contrast, the calcium-impermeable (R) variant of GluK1 or the high-affinity subunits (GluK4,5) had no effect on synaptic density or transmission efficacy. These data suggest that calcium permeable axonal KARs promote efferent connectivity by increasing the density of functional presynaptic release sites.
  • Behavior of gallium and germanium associated with zinc sulfide concentrate in oxygen pressure leaching
    (2017) Liu, Fupeng; Liu, Zhihong; Li, Yuhu; Wilson, Benjamin P.; Lundstrom, Mari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The Fankou zinc concentrate (Guangdong province, China) was mineralogically characterized and results showed that the main germanium-bearing minerals in the sample comprised of zinc sulfide and galena, whereas gallium-bearing minerals were pyrite, sphalerite and silicate. Oxygen pressure leaching of zinc sulfide concentrate was carried out in order to investigate the effect of pressure, leaching time, sulfuric acid and copper concentrations on the leaching behavior of gallium and germanium. Under optimum conditions, leaching of Zn, Fe, Ge and Ga reached 98.21, 90.45, 97.45 and 96.65%, respectively. In the leach residues, it was determined that some new precipitates, such as PbSO4, CaSO4 and SiO2, were formed, which co-precipitated a certain amount of Ga and Ge from the leach solution. The results clearly indicated that Ga and Ge were much more difficult to leach than Zn, and provided answers to why the leaching efficiency of Ga is 10% lower when compared to Ge.
  • Carbon nanomaterials and carbon coatings in lubrication - "MINIMA MAXIMA SUNT"
    (2015) Elomaa, Oskari
     School of Chemical Technology | Doctoral dissertation (article-based)
    Controlling the friction and wear properties of mechanical contacts under high loads by liquid lubrication enables energy savings, provides better efficiency and increases component lifetime. Lubricant performance can be improved by use of additives, for example nanomaterials or protective coatings. Carbon has many allotropic forms which include diamond with sp3-structure, graphite with sp2-structure or amorphous carbons with mixed sp2/sp3 structures, among others. These allotropes have properties which are potential for lubrication purposes such as high hardness and strength, high thermal conductivity, low friction surfaces and chemical activity.  In this work nanodiamonds (NDs), graphene oxide (GO) and silica/graphene oxide (SiO2/GO) composites were used to improve the friction and wear performance of high-load steel-steel and carbon-steel contacts in ethylene glycol (EG) or water lubrication by Pin-On-Disc (POD). The SiO2/GO composites used as lubricant additives were reported in this thesis for the first time. The carbon nanomaterials were dispersed into the lubricants or deposited directly on contact surfaces by spray or agglomeration methods. The effect of carbon coatings and steel surface finishing methods on friction performance was studied in oil lubrication by Twin Disc (TD) testing. The coatings used for TD testing were tetrahedral amorphous carbon (ta-C) and tungsten containing carbon (WC-C). The carbon nanomaterials in EG reduced friction coefficient 19 % (GO), 31 % (NDs), and 38 % (SiO2/GO composite), respectively, in comparison to pure EG in steel-steel contacts. All nanomaterials in EG reduced the wear rate of steel surfaces.   GO dispersions in water reduced friction 57 % in comparison to pure water in ta-C-steel contact. Optimized combination of surface roughness and WC-C coatings in oil lubrication reduced the friction coefficient 27 % in comparison to reference steel surfaces.  According to the results, the improved friction and wear performance of carbon nanomaterials was due to incorporation of particles into the tribolayer and embedding onto the contact surfaces, respectively. Furthermore, carbon coatings deposited on steel with optimized surface roughness both prohibited metal asperity contacts and improved lubrication by acting as lubricant reservoir.  The results here suggest that the use of carbon nanomaterials and carbon coatings in liquid lubrication can significantly improve the friction and wear performance of high-load mechanical contacts and provide longer lifetime for many industrial applications such as gears and bearings.
  • Carbon thin films as electrode material in neural sensing
    (2014-11-25) Kaivosoja, Emilia; Sainio, Sami; Lyytinen, Jussi; Palomäki, Tommi; Laurila, Tomi; Kim, Sung I.; Han, Jeon G.; Koskinen, Jari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • CFD procedure for studying dispersion flows and design optimization of the solvent extraction settler
    (2007-11-23) Kankaanpää, Timo
     Doctoral dissertation (monograph)
    Computational fluid dynamics (CFD) modelling has been applied to study the behaviour of organic-aqueous dispersion and flow patterns in the copper solvent extraction settler with the aim of developing a complementary method for traditional physical experiments in settler design work. The simulations have been carried out with an Eulerian-Eulerian two-phase model of the commercial CFX-4.4 software in conjunction with the incorporated MUSIG model, which is based on a population balance equation and takes into account the break-up and coalescence models of droplets. Due to the complicated process phenomena of the phase separation including droplets deformation, variable collision forces, the drop-drop and drop-interface coalescences, film thinning of the continuous phase between droplets or a droplet and its homophase, high-volume fractions of the separated phases and numerical convergence difficulties, a new six-item CFD calculation procedure and the specified boundary conditions were developed. During the developing work, the relative velocity of the phases versus drag force correlations, the dispersed droplet size range, inner iteration of the MUSIG model, the drag force in a dense dispersion, the calibration coefficient of the coalescence model, the discretisation schemes, and steady-state versus transient simulation were tested. The developed calculation procedure and the temperature-related phase separation correlation coefficient, together with the specified boundary conditions, were applied to the pilot settler with the aim of testing and showing the possibilities of the CFD in the settler design, and gaining new information about dispersion flows and force balances on the droplet level in the settler. The simulation cases took into account the thickness of the dispersion layer versus the specific volume flow rate, temperature and number of picket fences. Furthermore, the pressure drop over the picket fence, the droplet size distribution, the linear velocity of the organic phase, and the hydrodynamic force balances between the viscous, inertia, surface and buoyancy forces were studied. The developed new calculation procedure proved to be very useful in complicated multiphase modelling. It ensures that all simulation cases can be carried out in the same way, and thus the obtained results are comparable. In addition, use of the procedure improves the overall trust of CFD simulations. The simulated results agree well with experimental data obtained with a pilot settler. The model predicts that the phase separation is achieved more effectively when the picket fences are set into the settler, the temperature is increased or the specific volume flow rate is decreased. These phenomena could also be obtained from the results of the force balances. The inertia forces decrease and, respectively, the buoyancy and surface forces increase when the picket fences are set, and when the dispersion disengages and flows from the front end of the settler towards the rear end. Furthermore, an effective separation requires that the buoyancy forces become stronger than the surface forces. It can be concluded that settler operations with picket fences can be optimized with the aid of CFD modelling.
  • Characterization of Gas Atomized Ni-Mn-Ga powders
    (2015) Nilsén, Frans; Aaltio, Ilkka; Ge, Yanling; Lindroos, Tomi; Hannula, Simo-Pekka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Gas atomization is a well-known process for obtaining high quality metallic powders. It produces spherical high-density particles with a controllable particle size distribution. We used gas atomization to obtain two different Ni-Mn-Ga powders and investigated their microstructure, transformation temperatures and magnetic properties as well as the effects of heat treatment on those. The phase and magnetic transformation temperatures of the powders were considerably lower as compared to similar conventionally prepared alloys. Nevertheless, heat treatment of the atomized powder was found to recover the magnetic properties of the materials, probably by releasing the residual strains generated by the rapid solidification during the gas atomization process. Sintering of powders seemed to start at a significantly lower temperature when compared to the powder prepared by ball milling of bulk Ni-Mn-Ga-alloys.
  • Characterization of thin film adhesion by MEMS shaft-loading blister testing
    (2013) Berdova, Maria; Lyytinen, Jussi; Grigoras, Kestuti; Baby, Anu; Kilpi, Lauri; Ronkainen, Helena; Franssila, Sami; Koskinen, Jari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Comparison of collection schemes of municipal solid waste fraction: The impacts on global warming potential for case of Helsinki Metropolitan Area
    (2012) Kuusiola, T.; Wierink, Maaria; Heiskanen, Kari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this research article the sustainability of different practices to collect the metal fraction of household waste in the Helsinki metropolitan area, Finland is examined. The study is carried out by calculating and comparing the greenhouse gas reduction potential of optional practices for collecting the metal fraction of household waste in the Helsinki metropolitan area, Finland. In order to locate the greenhouse gas reduction potential of the separate collection of the metallic fraction of municipal solid waste (MSW) collected from residential sources, a comparative carbon footprint analysis using Life Cycle Assessment (LCA) on six different waste management scenarios is carried out. The modeled system consisted of a waste collection system, transportation, and different waste management alternatives, including on-site separation, separation at the waste management facility as well as metallurgical recovery of separated scrap. The results show that, in terms of greenhouse gas emissions, separate collection and recycling of the metallic fraction of solid MSW at residential properties is the preferable option compared to a scenario with no source sorting and incineration of everything. According to this research scenario where the metal fraction of solid household waste was not source-separated or collected separately have clearly higher greenhouse gas emissions compared to all the other scenarios with separate collection for metals. In addition, metal recycling by regional collection points has considerably lower greenhouse gas emission potential than metal recycling by collection directly from residential properties
  • Comparison of conventional and lignin-rich microcrystalline cellulose
    (2016-05-01) Vanhatalo, Kari; Maximova, Natalia; Perander, Anna Maija; Johansson, Leena Sisko; Haimi, Eero; Dahl, Olli
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Three microcrystalline cellulose (MCC) samples were manufactured from bleached and unbleached softwood kraft pulp, and their properties were compared to those of the commercial MCC, Avicel PH-101. One of the produced samples retained a large portion of lignin (10.3%), while the two others retained only some. The physical, chemical, thermogravimetric, and molecular properties were analyzed. The presence of lignin caused a substantial effect on the thermogravimetric and chemical properties of the MCC, as well as on its surface characteristics. The lignin-containing sample degraded at lower temperatures, and its UV Raman spectra had a high intensity aromatic band (1600 cm-1) arising from the lignin. X-ray photoelectron spectroscopy confirmed a high surface lignin coverage (40%) in this specimen only. Particle size and BET surface area measurement results varied in some limits between MCCs, while the cellulose crystallinity index showed almost equal values between 0.82 and 0.84. This work introduces a new wood-based product, the lignin-containing MCC, comparable in properties to the wide-marketed Avicel.
  • A compilation of thermodynamic properties measured with an advanced EMF arrangement
    (2016) Aspiala, Markus
     School of Chemical Technology | Doctoral dissertation (article-based)
    Experimental thermodynamic studies are nowadays rare, but the need for thermodynamic data has increased as the metal industry has been obligated to use the low-grade ores resulting from the intensive mining and the high consumption of metals. Furthermore, thermodynamic data obtained by the EMF method has impact in materials science and, for example, concerning thermoelectric generators. In this study, an advanced EMF method has been developed and a compilation of thermodynamic data has been measured by applying improved practices and arrangements. Not only was experimental apparatus developed, but also the sample preparation method and measurement procedures were improved. During the development of the experimental arrangement, the studied chemical assemblages were selected from well-known systems in order to compare the impact of the modifications to the measured EMF with reliable reference data presented in the literature. A number of different approaches were tested and the modifications with a beneficial outcome were combined in the final experimental procedure. Different solid electrolytes were applied to measure chemical oxide systems as well as systems with silver content. Yttria stabilized zirconia was implemented as an O2- conducting electrolyte whereas AgI was used in silver systems as a Ag+ conducting solid electrolyte. The experimental temperature ranges as well as the capability to measure volatile test electrodes were improved by the use of ion exchanged B''-alumina as a solid Ag+ conducting electrolyte together with AgI. Finally, the improvements were applied to study the thermodynamic properties of a number of intermetallic compounds and oxides with little or no previously measured thermodynamic data but a notable practical importance in many areas. Particularly, the studied alloys and compounds have been selected to respond to the specific needs of the metal industry and to support the development of thermoelectric materials.All in all, the advanced EMF method has been applied to measure the thermodynamic properties of the following compounds: Ag3Sb, Ag6Sb, SbxTe1-x, AgSbTe2, AgSbS2, Ag3SbS3, Bi2O3, Sb2O3, TeO2, Ca4Fe9O17. Also, the thermodynamics of the virtual cell reactions, taking place in the experimental cells, have been experimentally measured. The determined values include Gibbs energies of reactions and formations as well as enthalpies and entropies. Third law analysis has been applied to calculate standard thermodynamic properties of the oxide compounds measured at high temperatures if the specific heat capacity as function of temperature is known.
  • A computational framework for coupled modelling of three-phase systems with soluble surfactants
    (2012) Wierink, Gijsbert Alexander
     School of Chemical Technology | Doctoral dissertation (monograph)
    Bubble-particle interaction is a key phenomenon in many industrial applications, for example in mineral froth flotation. Flotation systems are typically characterised by high void fraction of dispersed phases and often multiple surface active compounds are present. The complexity of bubble-particle interaction has lead researchers to develop simplified models for dilute systems and typically physical and physico-chemical aspects are left out. This work discusses a modelling framework for analysis of bubble-particle interaction in the presence of soluble surfactants. The model includes full momentum coupling between gas, liquid, and solid phases using a coupling between Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM) named CFDEM. CFDEM is an open source modelling framework where the CFD code OpenFOAM and the DEM code LIGGGHTS interact. To accommodate topological changes of the bubble surface during break-up and coallescence the Volume Of Fluid (VOF) method was used. Solid particles are tracked in a Lagrangian frame of reference and experience forces due to collisions and the presence of the gas-liquid interface. A comprehensive model has been developed where particle-interface forces are modelled as a hyperbolic function of the gradient of the phase fraction. Particles can be captured within the interfacial region and can detach from the bubble when the balance of forces so dictates. DLVO and non-DLVO forces, as well as inertial forces, form part the total stress balance and contribute to the momentum equation of all phases. Variable interfacial tension is taken into account by implementation of a volumetric transport equation for soluble surfactant in the bulk fluid and within the interfacial gas-liquid region. The method is fully mass conservative and combines higher order physical momentum coupling with physico-chemical momentum. The sub-models used need further study, but to the authors knowledge the model presented is the first to couple all momenta in a comprehensive modelling framework for bubble-particle interaction. The main value of this work is that the computational framework is modular and easily extensible to include more accurate sub-models. The Lagrangian particles are in fact dynamic lists that can be populated by the properties appropriate to the system. These properties accommodate further development and help to identify future research needs in the field of flotation modelling.
  • Conditions for forming composite carbon nanotube - diamond like carbon material that retain the good properties of both materials
    (2015) Ren, Wei; Iyer, Ajai; Koskinen, Jari; Kaskela, Antti; Kauppinen, Esko I; Avchaciov, Konstantin; Nordlund, Kai
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
  • Correlation of material characteristics and wear of powder metallurgical metal matrix composites
    (2006-12-01) Kivikytö-Reponen, Päivi
     Doctoral dissertation (monograph)
    The wear of materials is a major and widely recognised industrial problem. The direct costs of wear failures, i.e., wear part failures and replacements, increased work and time, loss of productivity, as well as indirect losses of energy and the increased environmental burden, are real problems in everyday work and business. In this study, the materials of interest are wear-resistant powder metallurgical metal matrix composites, MMCs. Powder metallurgical, P/M, production of material, involving, for example, hot isostatic pressing (HIPing), offers considerable potential for enhanced wear resistance because it has a larger capacity to modify microstructures than conventional production technologies. Martensitic- and tool-steel-based composites were studied with reference to the needs of the mineral industry, while the wear of austenitic- or duplex-steel-based composites was evaluated with reference to those of the energy industry. The wear was studied both in functional wear tests involving a small-scale cone crusher, as well as in laboratory tests, such as the dry sand rubber wheel and erofuge tests. The correlation between the wear behaviour and the material-related parameters of the steel-based metal matrix composites was investigated. The material-related parameters were microstructural parameters, such as the volume fraction of the reinforcements and hard particles, the size of the reinforcements, the true carbide size of the hard particles and spacing between the reinforcement particles. These parameters are evaluated by varying the matrix material of the composite and by varying the reinforcements in the fixed matrix material. The significantly important parameters that have an effect on the material wear rate were identified. The most important reinforcement-related parameters in these wear environments were the total volume fraction of the hard phase, the spacing between hard particles and the type of the hard phase.
  • Corrosion protection of steel with multilayer coatings: Improving the sealing properties of physical vapor deposition CrN coatings with Al2O3/ TiO2 atomic layer deposition nanolaminates
    (2017-04) Leppäniemi, Jarmo; Sippola, Perttu; Broas, Mikael; Aromaa, Jari; Lipsanen, Harri; Koskinen, Jari
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Atomic Layer Deposition (ALD) of Al2O3/TiO2 nanolaminatewas applied to improve the sealing properties of CrN coating deposited with Physical Vapor Deposition (PVD) on high speed steel (HSS). The corrosion protection propertieswere explored with Linear Sweep Voltammetry and visual estimation. Nearly two orders of magnitude decrease in corrosion current density was obtained by applying plasma pre-treatment prior to ALD coating. Sealing of CrN pinholes was shown with Focused Ion Beam/Scanning Electron Microscope technique. The effect of the ALD deposition parameters to adhesion of the ALD coatings was investigated with Rockwell indentation and microscope analysis. Thickness and refractive index of the ALD coatings were measured with ellipsometry, and density and roughness of the ALD coatingswere investigatedwith X-Ray Reflectivity measurements. Neutral Salt Spray testing was used to investigate the corrosion resistance of PVD/ALD nanolaminates on HSS dental curettes.
  • Crack growth of 10M Ni-Mn-Ga material in cyclic mechanical loading
    (2010) Aaltio, I.; Ge, Yanling; Pulkkinen, H.; Sjöberg, A.; Söderberg, O.; Liu, X.W.; Hannula, S.-P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The 10M martensitic Ni–Mn–Ga single crystal materials are usually applied in the magneto-mechanical actuators. Therefore, it is important to know the possible effect of the long-term cyclic shape changes on their structure and behavior. This can be evaluated with the mechanical fatigue testing. In the present study, the single crystal 10M Ni–Mn–Ga samples of different compositions were applied to strain-controlled uniaxial mechanical cycling in the multivariant state at ambient temperature. The experiments revealed distinctive changes of the twin variant structure, especially in the mobile twin area, density of twin boundaries, and in the tendency for fatigue crack growth. Characterization of the crack surface showed that the cracks in the microscale grow in a step-wise manner on specific crystallographic planes, i.e, twin boundary planes, but that the macroscopic crack does not occur only along crystallographic directions.
  • The crystal and magnetic microstructure of Ni-Mn-Ga alloys
    (2007-04-13) Ge, Yanling
     Doctoral dissertation (article-based)
    The crystal structure and magnetic domain patterns of Ni-Mn-Ga alloys are studied in the present thesis work. The crystal structure of the martensitic phases in these alloys is highly dependent on the chemical composition. Single crystal X-ray diffraction shows that five-layered martensite is approximately a tetragonal phase with c < a, seven-layered martensite is orthorhombic and non-modulated martensite is a tetragonal type with c > a. Powder X-ray diffraction refinement suggests that five-layered martensite is a modulated structure with its basic structure having a monoclinic lattice, with the lattice parameter a being slightly different from the parameter b. Two-dimensional X-ray scattering distribution and electron diffraction confirmed that there are two shuffling systems with two modulation wave vectors. The interface, i.e. the macrotwin boundary, is formed between these two domains, which have a nearly orthogonal microtwin plane. This interface consists of two constituent elements, a step and a crossing. The layered martensite, which can be viewed as a periodic microtwin sequence, is not perfect; aperiodic plane faults and other-than nominal periodic microtwins are definitely present. In a multi-variant martensite, each martensitic band consists of internal twins. The 180° magnetic domains arise from the major internal twin variant, which is observed both by Type I and Type II magnetic contrast with a scanning electron microscope. The minor internal twin variants show a zigzag pattern when the c-axis is out of plane. In a two-variant state sample, the 180° magnetic domains follow the c-axis in each twin variant and continue to the neighbouring twin variant by a 90° domain wall, which coincides with the twin boundary. In a single-variant state the 180° magnetic domains are parallel to the c-axis and run through the whole observed surface. Optical observation of the magnetic domain pattern reveals that there is a surface relief associated with the magnetic domains. This surface relief causes the (011) twins to appear as a zigzag pattern when projected on the (010) plane. Such magnetic domain associated surface relief is due to the less strained surface as compared to the bulk during the magnetic shape memory phenomenon. In this thesis work it is also found that the application of an excitation voltage of 20-30kV and the Kα line for Ga are critical factors for obtaining a reliable chemical composition for Ni-Mn-Ga alloys using energy-dispersive spectrometer and wavelength-dispersive spectrometer analysis. It is discovered that there are two shuffling systems and the interface between them consists of step and crossing elements in five-layered martensite. It is revealed for the first time in Ni-Mn-Ga alloys that surface relief is associated with the magnetic domains. This provides a new opportunity to observe the magnetic domain patterns with an optical microscope.
  • Decision making towards sustainability in process industry – drivers, barriers and business opportunities
    (2015) Pajunen, Nani
     School of Chemical Technology | Doctoral dissertation (article-based)
    The present economy is based on growth and technical superiority. In a market-based economy companies play a critical role in adoption of sustainable business practices by demonstrating economic benefits and sustainable competitiveness. Environmental impacts are connected to flows of materials and energy, with the most important flows, at least for manufacturing companies, being closely linked to products. Greening of production is forcing companies to reconsider sustainable sourcing and supplier relationships because their total environmental impact is strongly influenced by the supply chain. Social, economic and ecological thinking can be an opportunity for all actors in the production and consumption cycle where saving raw-materials, increasing energy efficiency, using by-products and reducing waste might be win-win situations for companies and their employees, shareholders, consumers, communities and the environment. Sustainable production and consumption is also one of the key aims of the European Union's environmental policy. Legislation is one of the main drivers in improving material efficiency, but it may also become one of the main barriers. Legal systems are effective in achieving their objectives once the most difficult step of determining the right objectives is achieved. On the other hand one must ask whether there is any other way to achieve the same objectives without legislation or of even defining the targets from a systemic point of view. In this respect it is often unclear at to which is the most optimum approach to control a system. The short-term thinking encouraged by normal financial reporting and the time horizons over which financial returns are generally expected and or are acceptable to businesses and investors, does not go easily hand in hand with life cycle thinking and sustainability. In research and development work the time frame is counted in years and not months. This goes for greening business benefits as well as progress towards sustainability. One of the most important practicalities is a question of our values: every decision should change the world towards a more sustainable future. The aim of this study is to bring out and assess existing, especially market-based, drivers for effective industrial material use and their influence on environmental friendly business strategy and decision-making, especially in process industry. The ambitious target is to determine positive incentives to change the everyday working culture in companies and in society towards sustainability with the idea that every decision has a consequence. In this study, the target is to show the importance of new ways of thinking and how to break the silos in our minds and in society. This study rests on qualitative material, based on co-operation with Finnish process industry companies.