Browsing by Subject "Kemia"

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  • Seppälä, Sanni (Helsingin yliopisto, 2019)
    This thesis focuses on the development of new atomic layer deposition processes for zirconium oxide and rare earth oxides. Atomic layer deposition (ALD) is a chemical thin film deposition method that is capable of generating films with excellent properties including conformality, uniformity, high density and pinhole free structure. Because of these film properties, ALD has become the best and often the only method capable of fulfilling the demands of many applications, microelectronics being the best example. The unique properties of ALD films are enabled by the self-limiting growth mechanism of these films. Traditionally, ALD metal precursors have been homoleptic, meaning that the compound contains only one type of ligands. In the search of precursors with higher thermal stability, growth rate and uniformity, heteroleptic precursors with more than one type of ligands have gained interest. However, properties of different ligand combinations are hard to predict which means that comprehensive studies on the precursors with different oxygen sources are needed. In this work, heteroleptic precursors for rare earth oxides and zirconium oxide were studied. ZrO2 and rare earth oxides are so called high-κ materials with a wide variety of applications ranging from microelectronics to fuel cells, optics and catalysis. For the ALD of ZrO2, three metal precursors, Zr(Me5Cp)(TEA), Zr(MeCp)(TMEA) and ZrCp(tBuDAD)(OiPr) were evaluated with water or ozone as the oxygen source. Self-limiting growth processes typical for ALD were found for two Zr precursors with ozone. The deposition temperature for the self-limiting Zr(Me5Cp)(TEA)/O3 process was as high as 375 °C making Zr(Me5Cp)(TEA) one of the most thermally stable precursors for zirconium. ZrO2 films with high purity were deposited with the three precursors especially when ozone was used as the oxygen source. Heteroleptic cyclopentadiene-amidinate precursors RE(iPrCp)(iPramd) were studied for Y, La, Pr, Gd and Dy. Water and ozone were studied as oxygen sources. In addition to these common oxygen sources, also ethanol as well as water and ozone in the same deposition process separated by a purge period were tested for the La2O3 deposition. Self-limiting growth was confirmed for Y2O3, La2O3 and Gd2O3.
  • Häkkinen, Riina (Helsingin yliopisto, 2020)
    The utilization of renewable biomass and development of greener technologies are in high demand. Especially, cellulose is a desired component in many applications, but the insolubility in most solvents limits its use. The currently used methods have also environmental issues and other concerns. To overcome these problems, ionic liquids were discovered to be able to dissolve cellulose and other renewable biomass fairly effectively. However, ionic liquids cannot be considered as “innocent” solvents, as their synthesis is not green, and they are often toxic and expensive. Deep eutectic solvents are recognized as promising green alternatives for ionic liquids and petroleum-based solvents, and are now widely used in biomass processing. Generally, deep eutectic solvents are binary mixtures formed by mixing cheap components together: a hydrogen bond donor with a hydrogen bond acceptor. The strong hydrogen bonding between the components is believed to be responsible of the reduced melting point of the mixture. As deep eutectic solvents were introduced quite recently, these novel solvents are still lacking the knowledge and understanding of their fundamentals. In this thesis, the introduction section covers the background on basic carbohydrate chemistry, ionic liquids which are able to dissolve cellulose, and deep eutectic solvents with their applications in biomass treatment. The characteristics of ionic liquids and deep eutectic solvents are compared. Generally, ionic liquids have better dissolution capability towards polysaccharides than deep eutectic solvents, but very little research has been done to explain why. The aim of this thesis is to understand and explain the fundamentals of deep eutectic solvents. Therefore, the properties affecting carbohydrate solubility, including cellulose (publication I), physicochemical properties of a new DES (publication III), solvent-solute interactions (publication I, II) and phase behavior of different alcoholic solutes in a DES (publication II) are studied in more detail. Furthermore, the unique properties of DESs are utilized in a novel way: as a green binder for Lithium-ion batteries (publication IV).
  • Hyväkkö, Uula (Helsingin yliopisto, 2020)
    This thesis explores novel applications which utilize ionic liquids and electrolyte solutions in treatment of biomass for obtaining high-quality value-added products, such as cellulose, hemicelluloses and lignin as relatively pure fractions, which can be further processed into useful materials and chemicals. Albeit ionic liquids have been described as chemically and thermally highly stable solvents, the potential drawbacks of ionic liquids and electrolyte solutions regarding to their possible degradation in common processing temperatures are discussed in detail in this thesis. The potential of a highly hydrophilic aqueous organic electrolyte solution tetra-n-butylphosphonium hydroxide [P4444][OH] was studied in fractionation of wheat straw. Lignin from the biomass was extracted with varying concentations of [P4444][OH] in water. The carbohydrate rich fractions were isolated and finally all collected fractions were analyzed. The results showed that 40 w/w% aqueous solutions of [P4444][OH] were found stable. The irreversible decomposition kinetics were assessed at for 60 w/w% solution and it was not possible to obtain 70 w/w% concentrations or higher because of the decomposition at during evaporation at 25 °C. The next project was to assess the hydrolytic stability of 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] using HPLC. The [DBNH][OAc] can rapidly dissolve large quantities of cellulose and can be utilized in the IONCELL-F process to convert cellulose pulp into strong cellulosic man-made fibers. In addition, synthesis routes were studied for the superbase precursors 9-methyl-1,5-diazabicyclo(4.3.0)non-5-ene (9-mDBN) which was assumed to lead to increased hydrolytic stabilities of the final ionic liquid. In the last research, aqueous solution of triethylammonium hydrogensulphate [TEAH][HSO4] was studied for fractionation of wheat straw and aspen in comparison with non-sulfate NaOH pulping and various recently discovered pulping methods utilizing a microwave reactor in all procedures. All fractions were analyzed with GPC and spectroscopic methods in order to evaluate their potential for further refining.
  • Heikkinen, Harri (Helsingin yliopisto, 2019)
    There are many chemical analytical techniques available to probe molecular structures. Nuclear Magnetic Resonance (NMR) spectroscopy is an analytical spectroscopy technique that exploits strong external magnetic field and is capable of elucidating and quantifying molecular structures at the atomic level. NMR spectrum is typically measured from dissolved materials or directly from solid materials. The influence of magnetic interactions in solution and solid-state define the information that is obtainable from the NMR spectrum. The molecular motion and mobility play a key role. The obtainable spectral resolution in solid-state is usually lower than in the liquid state due to the presence of anisotropic interactions, which are not averaged out like in solution state. In NMR this means that the spectra, which contain the structural information, can be visually very different. These phenomena, combined with the need to obtain quantitative information, need to be addressed with proper considerations when acquiring and interpreting NMR data. This thesis focuses on the impact of relevant magnetic interactions in NMR via selected chemical structure studies of materials such as lignin, Ziegler-Natta (ZN) and aluminosilicate catalysts and cellulose.
  • Muuri, Eveliina (Helsingin yliopisto, 2019)
    Käytetyn ydinpolttoaineen loppusijoituksen turvallisuusanalyysin sorptio- ja diffuusioparametrit on pääasiassa määritetty laboratorio-olosuhteissa. Ilmiöiden fysikaalinen käyttäytyminen voi kuitenkin olla erilaista eri mittakaavoissa, esimerkiksi laboratorio-olosuhteissa verrattuna luonnonolosuhteisiin. Tämä tunnetaan skaalaefektinä. Skaalaefektit voivat olla merkittäviä ja niillä voi olla merkitystä suuren mittakaavan mallinnuksissa, jotka käyttävät laboratoriokokeissa määritettyjä tietoja. Tämän väitöskirjan tavoitteena oli tutkia, kuinka laboratoriossa määritetyt sorptio- ja diffuusiotulokset voidaan skaalata in situ -olosuhteisiin. Tämä tehtiin määrittämällä 133Ba:n sorptio- ja diffuusioparametrit laboratoriokokeissa ja vertaamalla tuloksia Sveitsin Grimselissä toteutetun pitkäaikaisen in situ -diffuusiokokeen tuloksiin. Bariumin sorptiokäyttäytymistä tutkittiin tässä väitöskirjassa laboratoriossa tehdyissä eräsorptiokokeissa ja ohuthiesorptiokokeissa. Bariumin diffuusiota tutkittiin myös laboratoriodiffuusiokokeissa kivikuutioilla. Laboratoriokokeet tehtiin Grimselin ja Olkiluodon pääkivityypeille sekä pohjavesisimulanteissa, jotka tehtiin muistuttamaan Grimselin ja Olkiluodon pohjavesiolosuhteita. Bariumin sorptiotuloksia mallinnettiin PhreeqC-ohjelmalla ja diffuusiotulokset mallinnettiin PhreeqC-ohjelmalla sekä COMSOL Multiphysics -ohjelmalla. Lisäksi työssä kehitettiin uutta kvantitatiivista mittausmenetelmää bariumin aktiivisuuden jakautumisen mittaamiseen kivikuutioissa sekä ohuthieissä uudella elektronisella autografiamenetelmällä, BeaQuantTM:lla. Lopuksi 133Ba:n diffuusioprofiilit Grimselin in situ -diffuusiokokeesta määritettiin gammamittauksella ja autoradiografialla, ja tulokset mallinnettiin COMSOL Multiphysics -ohjelmalla. Tässä työssä selvitettiin, että bariumin laboratorio-olosuhteissa määritetyt sorptioparametrit ovat noin kaksikymmentäkertaiset verrattuna tuloksiin in situ -olosuhteissa. Tämä on tärkeää tietoa käytetyn ydinpolttoaineen loppusijoittamisen turvallisuusanalyysille, kun muunnetaan laboratoriokokeissa määritettyjä arvoja vastaamaan in situ- olosuhteita. Lisäksi työssä kehitettiin uutta elektronista autoradiografiamenetelmää, jotta sillä voitiin mitata 133Ba:n aktiivisuuden jakautumista graniittisissa kivissä kvantitatiivisesti.
  • Kakko, Tia-Annette (Helsingin yliopisto, 2019)
    The separated wood components cellulose, hemicelluloses, and lignin allow for the production of various materials via chemical modifications. In addition to modifications, understanding the structural features of these products is important for enabling tailored processes for commodities. In this thesis, the introduction covers background information concerning cellulose chemistry. The dissolution of cellulose in various solvent systems is compared, and the usability of these solvents in acetylation of polysaccharides is assessed. Typically, the solvents used in Viscose or Lyocell processes are not suitable for chemical modifications, mainly due to their reactivity with either cellulose hydroxyls or used reagents. Furthermore, in current industrial cellulose acetate (CA) processes, the degree of polymerization (DP) of the product decreases. The results and discussion present the possibility of using ionic liquids as a reaction media for homogeneous acetylation of hemicelluloses and cellulose. The aim is to produce new methods in ionic liquids, in which tunable substitution is possible for acetylated hemicelluloses and CAs without substantial losses in DP. Furthermore, the procedure is upscaled and acetate fibers are produced with good spinnability and fiber characteristics in collaboration with Aalto University. Another issue under study is lignin chemistry, especially the structural characterization of hydrothermally (HT) treated Kraft lignin. The results demonstrate that diphenyl methanes are formed during HT treatment of Kraft lignin.
  • Hatanpää, Timo (Helsingin yliopisto, 2019)
    Precursors have a critical role in depositing thin films using chemical vapor phase methods, including atomic layer deposition. In these methods, precursor molecules are transported through the gas phase to the substrate where thin films of solid material are formed as a result of chemical reactions on the surface or in the vicinity of the surface. While a right choice of the precursor or precursor combination is needed to make the film growth possible, the choice will also, together with growth parameters, affect the structure, morphology, purity, electrical, optical, mechanical, and other properties of the forming films. New precursors are needed for new materials and to make better processes for known materials, or to make known materials in a way that fulfills the requirements of a specific application. Essential requirements for ALD precursors are volatility, thermal stability, and sufficient reactivity. Because of the different properties of the elements, finding precursors fulfilling all the requirements is easy for some elements and extremely difficult for some others. The required properties are pursued by molecular design, i.e., by choosing or tailoring the right kind of ligands and compounds. This dissertation is about ALD precursors. The general requirements for ALD precursors, factors affecting those, and ways to pursue them are first assessed. Then the design and development process and the methods typically used for studying the precursors are dealt with. The experimental part of this dissertation is divided into five parts. Each part deals with a selected case of process-driven precursor development. Compounds developed in the work are 1) β-diketonates of alkaline-earth metals, especially magnesium, 2) cyclopentadienyl compounds of alkaline earth metals as precursors for oxide materials, 3) various bismuth compounds as precursors for oxide materials, 4) various silver compounds as precursors for silver thin films, and 5) alkylsilyl compounds of chalcogens and pnictogens as precursors for chalcogenides and pnictides The invented and synthesized precursors have enabled ALD of many materials of technological interest. Among these thin film materials are, e.g. (Sr,Ba)TiO3, Bi4Ti3O12, and Ge2Sb2Te5 that may be used in memory applications, and metallic silver that can be used, e.g. in substrates for surface-enhanced Raman spectroscopy.