Studies of Inorganic Layer and Framework Structures Using Time-, Temperature- and Pressure-Resolved Powder Diffraction Techniques

This thesis is concerned with in-situ time-, temperature- and pressure-resolved synchrotron X-ray powder diffraction investigations of a variety of inorganic compounds with twodimensional layer structures and three-dimensional framework structures. In particular, phase stability, reaction kinetics, thermal expansion and compressibility at non-ambient conditions has been studied for 1) Phosphates with composition MIV(HPO4)2·nH2O (MIV = Ti, Zr); 2) Pyrophosphates and pyrovanadates with composition MIVX2O7 (MIV = Ti, Zr and X = P, V); 3) Molybdates with composition ZrMo2O8. The results are compiled in seven published papers and two manuscripts. Reaction kinetics for the hydrothermal synthesis of α-Ti(HPO4)2·H2O and intercalation of alkane diamines in α-Zr(HPO4)2·H2O was studied using time-resolved experiments. In the high-temperature transformation of γ-Ti(PO4)(H2PO4)·2H2O to TiP2O7 three intermediate phases, γ'-Ti(PO4)(H2PO4)·(2-x)H2O, β-Ti(PO4)(H2PO4) and Ti(PO4)(H2P2O7)0.5 were found to crystallise at 323, 373 and 748 K, respectively. A new tetragonal three-dimensional phosphate phase called τ-Zr(HPO4)2 was prepared, and subsequently its structure was determined and refined using the Rietveld method. In the high-temperature transformation from τ-Zr(HPO4)2 to cubic α-ZrP2O7 two new orthorhombic intermediate phases were found. The first intermediate phase, ρ-Zr(HPO4)2, forms at 598 K, and the second phase, β-ZrP2O7, at 688 K. Their respective structures were solved using direct methods and refined using the Rietveld method. In-situ high-pressure studies of τ-Zr(HPO4)2 revealed two new phases, tetragonal ν-Zr(HPO4)2 and orthorhombic ω-Zr(HPO4)2 that crystallise at 1.1 and 8.2 GPa. The structure of ν-Zr(HPO4)2 was solved and refined using the Rietveld method. The high-pressure properties of the pyrophosphates ZrP2O7 and TiP2O7, and the pyrovanadate ZrV2O7 were studied up to 40 GPa. Both pyrophosphates display smooth compression up to the highest pressures, while ZrV2O7 has a phase transformation at 1.38 GPa from cubic to pseudo-tetragonal β-ZrV2O7 and becomes X-ray amorphous at pressures above 4 GPa. In-situ high-pressure studies of trigonal α-ZrMo2O8 revealed the existence of two new phases, monoclinic δ-ZrMo2O8 and triclinic ε-ZrMo2O8 that crystallises at 1.1 and 2.5 GPa, respectively. The structure of δ-ZrMo2O8 was solved by direct methods and refined using the Rietveld method.

Preparation and characterisation of refractory whiskers and selected alumina composites

A whisker is a common name of single crystalline inorganic fibre of small dimensions, typically 0.5-1 μm in diameter and 20-50 μm in length. Whiskers are mainly used as reinforcement of ceramics. This work describes the synthesis and characterisation of new whisker types. Ti0.33Ta0.33Nb0.33CxN1-x, TiB2, B4C, and LaxCe1-xB6 have been prepared by carbothermal vapour–liquid–solid (CTR-VLS) growth mechanisms in the temperature range 900-1800°C, in argon or nitrogen. Generally, carbon and different suitable oxides were used as whisker precursors. The oxides reacted via a carbothermal reduction process. A halogenide salt was added to form gaseous metal halogenides or oxohalogenides and small amount of a transition metal was added to catalyse the whisker growth. In this mechanism, the whisker constituents are dissolved into the catalyst, in liquid phase, which becomes supersaturated. Then a whisker could nucleate and grow out under continuous feed of constituents. The syntheses of TiC, TiB2, and B4C were followed at ordinary synthesis conditions by means of mass spectrometry (MS), thermogravimetry (TG), differential thermal analysis (DTA) and quenching. The main reaction starting temperatures and reaction time for the different mixtures was revealed, and it was found that the temperature inside the crucible during the reactions was up to 100°C below the furnace set-point, due to endothermic nature of the reactions. Quench experiments showed that whiskers were formed already when reaching the temperature plateau, but the yield increased fast with the holding time and reached a maximum after about 20-30 minutes. Growth models for whisker formation have been proposed. Alumina based composites reinforced by (2-5 vol.%) TiCnano and TiNnano and 25 vol.% of carbide, and boride phases (whiskers and particulates of TiC, TiN, TaC, NbC, (Ti,Ta)C, (Ti,Ta,Nb)C, SiC, TiB2 and B4C) have been prepared by a developed aqueous colloidal processing route followed by hot pressing for 90 min at 1700°C, 28 MPa or SPS sintering for 5 minutes at 1200-1600°C and 75 MPa. Vickers indentation measurements showed that the lowest possible sintering temperature is to prefer from mechanical properties point of view. In the TiNnano composites the fracture mode was typically intergranular, while it was transgranular in the SiCnano composites. The whisker and particulate composites have been compared in terms of e.g. microstructure and mechanical properties. Generally, additions of whiskers yielded higher fracture toughness compared to particulates. Composites of commercially available SiC whiskers showed best mechanical properties with a low spread but all the other whisker phases, especially TiB2, exhibited a great potential as reinforcement materials.

Spark Plasma Sintering of Si3N4-based Ceramics : Sintering mechanism-Tailoring microstructure-Evaluationg properties

Spark Plasma Sintering (SPS) is a promising rapid consolidation technique that allows a better understanding and manipulating of sintering kinetics and therefore makes it possible to obtain Si3N4-based ceramics with tailored microstructures, consisting of grains with either equiaxed or elongated morphology. The presence of an extra liquid phase is necessary for forming tough interlocking microstructures in Yb/Y-stabilised α-sialon by HP. The liquid is introduced by a new method, namely by increasing the O/N ratio in the general formula RExSi12-(3x+n)Al3x+nOnN16-n while keeping the cation ratios of RE, Si and Al constant. Monophasic α-sialon ceramics with tailored microstructures, consisting of either fine equiaxed or elongated grains, have been obtained by using SPS, whether or not such an extra liquid phase is involved. The three processes, namely densification, phase transformation and grain growth, which usually occur simultaneously during conventional HP consolidation of Si3N4-based ceramics, have been precisely followed and separately investigated in the SPS process. The enhanced densification is attributed to the non-equilibrium nature of the liquid phase formed during heating. The dominating mechanism during densification is the enhanced grain boundary sliding accompanied by diffusion- and/or reaction-controlled processes. The rapid grain growth is ascribed to a dynamic ripening mechanism based on the formation of a liquid phase that is grossly out of equilibrium, which in turn generates an extra chemical driving force for mass transfer. Monophasic α-sialon ceramics with interlocking microstructures exhibit improved damage tolerance. Y/Yb- stabilised monophasic α-sialon ceramics containing approximately 3 vol% liquid with refined interlocking microstructures have excellent thermal-shock resistance, comparable to the best β-sialon ceramics with 20 vol% additional liquid phase prepared by HP. The obtained sialon ceramics with fine-grained microstructure show formidably improved superplasticity in the presence of an electric field. The compressive strain rate reaches the order of 10-2 s-1 at temperatures above 1500oC, that is, two orders of magnitude higher than that has been realised so far by any other conventional approaches. The high deformation rate recorded in this work opens up possibilities for making ceramic components with complex shapes through super-plastic forming.

Structural investigation of Nb-based layer sulfides

In this work we have investigated the intercalation of electron-donors between NbS2 slabs in Nb-based layer sulfides. Two series of Sr substituted Nb-based misfit sulfides belonging to the 1.5Q/1H and 1Q/1H series of misfit layer compounds have been synthesised. For large lanthanides (Ln=La, Ce), only the 1Q/1H compounds formed whereas for smaller lanthanides and yttrium, both types of phases can be obtained. The crystal structure of misfit sulfide (Pr0.55Sr0.45S)1.15NbS2 has been refined using the composite approach. In the Q-slab, Pr-atoms are partly replaced by Sr with a random distribution over one cation position. The crystal structure of misfit sulfide [(Sm1/3Sr2/3S)1.5]1.15NbS2 belonging to the 1.5Q/1H series have also been determined. The obtained results suggest a preferred occupancy of the cation positions in the slab where Sr atoms mainly occupy positions on the exterior of the slab while Sm atoms are in the center of the slab. The (La1-xSrxS)1.15NbS2 solid solution (0.1<x<0.9) has also been studied. It was found that the maximum value of Sr substitution is 40-50% and therefore, the minimal value of charge transfer to stabilize this structure type is about 0.6ē per Nb atom. An attempt to synthesize SrxNbS2 (0.1≤x≤0.5) intercalates was made but single phases were not obtained and increasing the temperature from 1000оС to 1100оС leads to the decomposition of these intercalates. Single crystals of Sr0.22Nb1.05S2 and Sr0.23NbS2 were found and their structures were determined. The structures belong to two different types of packings with statistical distribution of Sr between layers. A new superconducting sulfide, "EuNb2S5", was investigated by ED and HREM and its structure model consisting of Nb7S14 and (Eu3S4)2 slabs alternating along the c-axis is suggested. An attempt to suggest a model for the structure of "SrNb2S5" by means of X-ray single crystal diffraction was made. The proposed structure consists of two types of slabs: a Nb7S14 and a [Sr6(NbS4)2S] slab with niobium in tetrahedral coordination. It is shown that "SrNb2S5" and "EuNb2S5" are have similar structures. For the first time, single crystals of the complex sulfide BaNb0.9S3 have also been studied by means of X-ray single crystal diffraction. The single crystal refinement and EDX analysis showed the existence of cation vacancies at the niobium position. BaNb0.9S3 has also been studied by ED and no superstructure was found which implies that and the vacancies are statistically distributed. No improvement of the magnetic properties of the studied compounds was observed in comparison to NbS2.

Synthesis and properties of substituted Hg-based superconductors

This thesis is focused on studies of substituted Hg-based superconducting copper oxides ((Hg1-xMx)Ba2Can-1CunO2n+2+δ). These compounds are promising objects of investigation, not only from a fundamental point of view but also because of their high values of superconducting transition temperature (Tc) and irreversibility field (Hirr). The first part of the thesis is devoted to optimization of the synthesis procedure for Hg-based cuprates. The influence of different parameters (T, t, p(Hg), p(O2)) on the synthesis of these compounds in sealed silica tubes was studied. Optimal conditions yielded samples containing up to 95% of HgBa2Ca2Cu3O8+δ (Hg-1223). The formation of solid solutions with the formula (Hg1-xCux)Ba2Ca2Cu3O8+δ (where x <= 0.5) was also established. Another technique was developed, using LiF as a flux, for synthesis of samples containing up to 90% of the HgBa2CaCu2O6+δ (Hg-1212) phase. The second part concerns synthesis and studies of oxyfluorides using Hg-1212 and Hg-1223 as starting materials together with XeF2 as a fluorinating agent. It was found that oxyfluorides of both phases have a parabolic dependence of Tc vs. a parameter as well as enhanced Tc values (ΔT ≈ 3-4 K) in comparison with optimally doped non-fluorinated analogues. The crystal structure of Hg-1223 oxyfluoride was studied by X-ray powder and neutron diffraction methods. It is suggested that chemical modification of the crystal structure leads to a decrease in Cu-O distance without noticeable change in Cu-O-Cu angle (in the (CuO2) layers), which may be the significant factors influencing this Tc increase. Hg-1223 oxyfluoride was also studied under high pressure for first time. It was found that this compound has a record-high Tc value (≈ 166 K) at P ≈ 23 GPa. The last part describes the investigation of substituted Hg-based superconductors in the series (Hg0.9M0.1)Ba2CuO4+δ {(Hg,M)-1201}, where M = Tl, Pb, W, Mo, Nb and V. A comprehensive study of these compounds by various methods (X-ray powder diffraction, EDX, IR-, EXAFS- and XANES -spectroscopy) indicated that the change of charge carrier doping level is a crucial factor determining the irreversibility line. (Hg0.9Mo0.1)Ba2CuO4+δ showed the most improved irreversibility line position among the (Hg,M)-1201 compounds studied in this series.

Computational chemistry studies of UV induced processes in human skin

This thesis presents and uses the techniques of computational chemistry to explore two different processes induced in human skin by ultraviolet light. The first is the transformation of urocanic acid into a immunosuppressing agent, and the other is the enzymatic action of the 8-oxoguanine glycosylase enzyme. The photochemistry of urocanic acid is investigated by time-dependent density functional theory. Vertical absorption spectra of the molecule in different forms and environments is assigned and candidate states for the photochemistry at different wavelengths are identified. Molecular dynamics simulations of urocanic acid in gas phase and aqueous solution reveals considerable flexibility under experimental conditions, particularly for for the cis isomer where competition between intra- and inter-molecular interactions increases flexibility. A model to explain the observed gas phase photochemistry of urocanic acid is developed and it is shown that a reinterpretation in terms of a mixture between isomers significantly enhances the agreement between theory and experiment , and resolves several peculiarities in the spectrum. A model for the photochemistry in the aqueous phase of urocanic acid is then developed, in which two excited states governs the efficiency of photoisomerization. The point of entrance into a conical intersection seam is shown to explain the wavelength dependence of photoisomerization quantum yield. Finally some mechanistic aspects of the DNA repair enzyme 8-oxoguanine glycosylase is investigated with density functional theory. It is found that the critical amino acid of the active site can provide catalytic power in several different manners, and that a recent proposal involving a SN1 type of mechanism seems the most efficient one.

Local Structure of Hydrogen-Bonded Liquids

Ordinary yet unique, water is the substance on which life is based. Water seems, at first sight, to be a very simple molecule, consisting of two hydrogen atoms attached to one oxygen. Its small size belies the complexity of its action and its numerous anomalies, central to a broad class of important phenomena, ranging from global current circulation, terrestrial water and CO2 cycles to corrosion and wetting. The explanation of this complex behavior comes from water's unique ability to form extensive three-dimensional networks of hydrogen-bonds, whose nature and structures, in spite of a great deal of efforts involving a plethora of experimental and theoretical techniques, still lacks a complete scientific understanding. This thesis is devoted to the study of the local structure of hydrogen-bonded liquids, with a particular emphasis on water, taking advantage of a combination of core-level spectroscopies and density functional theory spectra calculations. X-ray absorption, in particular, is found to be sensitive to the local hydrogen-bond environment, thus offering a very promising tool for spectroscopic identification of specific structural configurations in water, alcohols and aqueous solutions. More specifically, the characteristic spectroscopic signature of the broken hydrogen-bond at the hydrogen side is used to analyze the structure of bulk water, leading to the finding that most molecules are arranged in two hydrogen-bond configurations, in contrast to the picture provided by molecular dynamics simulations. At the liquid-vapor interface, an interplay of surface sensitive measurements and theoretical calculations enables us to distinguish a new interfacial species in equilibrium with the gas. In a similar approach the cluster form of the excess proton in highly concentrated acid solutions and the different coordination of methanol at the vacuum interface and in the bulk can also be clearly identified. Finally the ability of core-level spectroscopies, aided by sophisticated density functional theory calculations, to directly probe the valence electronic structure of a system is used to observe the nature of the interaction between water molecules and solvated ions in solution. Water around transition metal ions is found to interact with the solute via orbital mixing with the metal d-orbitals. The hydrogen-bond between water molecules is explained in terms of electrostatic interactions enhanced by charge rehybridization in which charge transfer between connecting molecules is shown to be fundamental.

Landshövding Uuno Hannula 10.4.1963 Kemi

Kirje

Magister Raoul Palmgren 21.12.1958 Kemi

Kirje

Magister Raoul Palmgren 11.11.1961 Kemi

Kirje

Magister Raoul Palmgren 18.1.1962 Kemi

Kirje

Fleuve de Kemi : dessiné par A. F. Skjöldebrand ; gravé par J. F. Martin

Digitoitu valokuvasta, joka on julkaistu kirjassa: R. Knapas & P. Koistinen, Historiallisia kuvia, 1993.

Prostens och kyrko-herdens i Tornå mag. Johannis J. Tornæi Beskrifning, öfwer Tornå och Kemi lappmarker. Författad. År 1672

Foreword by Sam. S. Loenbom.

Geografisk och ekonomisk beskrifning om Kemi lappmark i Vesterbottens höfdingdöme. Med geografisk karta. På bergs-rådet friherre S. G. Hermelins anmodan : författad af Göran Wahlenberg ...

Digital reproduction, The National Library of Finland, Centre for Preservation and Digitisation, Mikkeli

Physico-chemical characterization of nanoparticle coated paper

Förståelse av olika ytors vätningsegenskaper är viktig i många pappers-relaterade industriella processer eftersom vätningen påverkar materialbeteendet, t.ex. vid bestrykning, tryckning och laminering. Förmågan att kontrollera vätningen är av intresse, därför att den ger nya möjligheter till modifikation av ytor. Vätningen styrs av ytans struktur och kemi. Kunskap om dessa egenskaper krävs både i fundamentala studier och för industriella applikationer. Nanopartiklar används ofta för att skapa funktionella ytor med mångsidiga egenskaper. Detta arbete strävar till att förstå de fysikalisk-kemiska egenskaperna hos papper och kartong som är bestrukna med nanopartiklar, för att sedan kunna förklara de observerade förändringarna i ytornas vätningsförmåga. Funktionella ytor med justerbar vätningsförmåga tillverkades genom att deponera nanopartiklar i en rulle-till-rulle vätskeflammasprutningprocess (LFS). TiO2 -nanopartikelbeläggningen skapar en superhydrofob yta som har över 160° kontaktvinkelmed vatten, medan SiO2-nanopartikelbeläggningar skapar mycket hydrofila ytor med kontaktvinklar så låga som 21° med vatten. Superhydrofobiciteten eller hydrofiliteten är ett resultat av den kombinerade effekten hos ytstrukturen och ytkemin, såsom nanopartiklarnas oxidationsnivå eller karbonatiseringsnivå. Kartongytor som är bestrukna med TiO2-nanopartiklar kan vara såväl superhydrofoba som hydrofila. Hydrofilitet kan induceras genom UVA-strålning, medan behandling i hög temperatur i ugn resulterar i en superhydrofob yta. Ett mål med arbetet var att förstå mekanismerna hos de kemiska för ändringar som sker under UVA-bestrålning och värmebehandling av ytor, bestrukna med TiO2-nanopartiklar. Ytornas abrasions- och kompressionsmotstånd samt relaterade förändringar i funktionella egenskaper undersöktes. Resultaten skapar en bättre förståelse för potentiell användning av LFS-nanopartikelbeläggningar i pappersrelaterade applikationer. En förståelse för stabiliteten hos nanopartikelbeläggningarna när de exponeras för externa krafter är viktig för att försäkra deras funktionalitet i industriella applikationer och för att garantera beläggningarnas miljö-, hälso- och säkerhetsaspekter. ------------------------------------------ Pinnan kastumisominaisuuksien hallinta on tärkeää monissa paperiteollisuuden prosesseissa, sillä pinnan kastuminen vaikuttaa esimerkiksi päällystämiseen, painamiseen ja laminointiin. Pinnan kastuvuuden säätäminen avaa mielenkiintoisia uusia mahdollisuuksia pintojen ominaisuuksien hallintaan. Pinnan kastuvuus määräytyy pinnan rakenteesta ja kemiasta, ja näiden ominaisuuksien ymmärtäminen on tärkeää sekä perustutkimuksessa että teollisissa sovelluksissa. Nanopartikkeleita käytetään usein toiminnallisten ja hallitusti kastuvien pintojen aikaansaamiseksi. Tässä työssä on tarkasteltu nanopartikkelipinnoitetun paperin ja kartongin fysikaalis-kemiallisia pintaominaisuuksia, jotka selittävät havaittuja muutoksia pinnan kastuvuudessa. Toiminnalliset pinnat säädettävillä kastuvuusominaisuuksilla valmistettiin nesteliekkiruiskutus (LFS) nanopartikkelipinnoituksella rullalta rullalle-menetelmällä. TiO2-nanopartikkelipäällystys saa aikaan superhydrofobisen pinnan, jonka veden kontaktikulma on suurempi kuin 160°. Toisaalta SiO2-nanopartikkelipäällystys muuttaa pinnan hyvin hydrofiiliseksi, veden kontaktikulman ollessa vain 21°. Pinnan superhydrofobisuus tai hydrofiilisyys riippuu nanopartikkelipinnan rakenteesta ja pintakemiasta kuten pinnan hapettumisasteesta ja hiilipitoisuudesta. TiO2-nanopartikkelipinnoitetun kartonkipinnan kastumista voidaan säätää superhydrofobisen ja hydrofiilisen välillä. Pinnan hydrofiilisyys saadaan aikaan UVA-valolla, kun taas superhydrofobinen pinta voidaan palauttaa korkeassa lämpötilassa uunissa. Tämän työn tavoitteena oli selvittää, millaisia muutoksia TiO2-nanopartikkelipäällystetyn pinnan kemiassa tapahtuu UVA-valon ja lämpökäsittelyn vaikutuksesta. Työssä tarkasteltiin myös pinnan mekaanisen hankauksen ja kokoonpuristuksen vaikutusta toiminnallisiin ominaisuuksiin. Työssä saavutetut tulokset auttavat ymmärtämään LFS-nanopartikkelipäällystettyjen pintojen soveltuvuutta paperiin liittyvissä sovelluksissa. Nanopartikkelipäällystettyjen pintojen stabiilius ulkoisten voimien alaisena on tärkeää toiminnallisten päällystysten ympäristö-, terveys- ja turvallisuusnäkökulmia tarkasteltaessa.