| 1. |
|
|
| 2. |
|
|
| 3. |
- Aas, Wenche
(författare)
-
Constitution, dynamics and structure of binary and ternary actinide complexes
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stoichiometry, ligand exchange reactions, coordinationgeometry and stability of complexes of type UO2LpFq(H2O)3-n(p= 1–2,q= 1-3), where L is one of the bidentate ligandspicolinate, oxalate, carbonate or acetate have beeninvestigated using single crystal X-ray diffraction, an arrayof19F-,13C-,17O- and1H-NMR techniques and potentiometric titration usingboth F-and H+selective electrodes. The experiments wereperformed in a 1.00 M NaClO4medium. The equilibrium constants were determinedat 25°C while most of the kinetic experiments were done at- 5°C. The equilibrium constants for the stepwise additionof F-to UO2L and UO2L2indicates that the prior coordination of L toU(VI) has a fairly small effect on the subsequent bonding offluoride, except for a statistical effect determined by thenumber of available coordination sites. This indicates thatternary complexes might be important for the speciation andtransport of hexavalent actinides in ground and surface watersystems. A single crystal structure of UO2(picolinate)F32-has been determined showing the same pentagonalbipyramidal symmetry as in aqueous solution studied by NMR. Theexchangeable donor atoms are situated in a plane perpendicularto the linear uranyl group. The complexes show a variety ofdifferent exchange reactions depending on the ligand used. Ithas been possible to quantify external fluoride and the otherligands exchange reactions as well asintra-molecular reactions. This type of detailedinformation has not been observed in aqueous solution before.Water takes a critical part in the exchange mechanism, and whenit is eliminated from the inner coordination sphere a muchslower kinetics can be observed.19F-NMR has showed to be a powerful technique tostudy these reactions, both because of the sensitivity of thisNMR nucleus and also the possibility to observe reactions wherefluoride is not directly involved in the mechanism. TernaryTh(edta)F1-2and (UO2)2(edta)2F1-4have been investigated using1H and19F-NMR. The fluoride complexation to Cm(III) wasstudied using time resolved fluorescence spectroscopy (TRLFS)and the stability constant for the CmF2+complex was determined at 25°C in 1.0 mNaCl.Keywords. Ternary complexes, actinides,dioxouranium(VI), curium(III), thorium(IV), ligand exchange,isomers, NMR, potentiometric titrations, aqueous solution,oxalate, picolinate, acetate, EDTA.
|
|
| 4. |
- Aastrup, Teodor
(författare)
-
In situ investigations of the metal/atmophere interface
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a new experimental setup for surfaceanalysis studies, incorporating chemical information frominfrared reflection absorption spectroscopy (IRAS) andquantitative information from quartz crystal microbalance(QCM). The integrated IRAS/QCM surface analysis system enablesin situstudies to be conducted of the metal/atmosphereinteraction on a sub-monolayer level. In combination withtopographical information from tapping mode atomic forcemicroscopy (TM-AFM), it was possible to follow the formation ofcorrosion products providing information about chemicalidentity, quantity and lateral distribution. The newlydeveloped system was used to study the influence of relativehumidity (RH) and levels of sulfur dioxide (SO2), ozone (O3)and nitrogen dioxide (NO2) down to concentrations of subparts-per-million (ppm), on the initial stages of atmosphericcorrosion of copper.Exposure to RH led to the formation of small grains ofcuprous oxide (Cu2O), with an average diameter of approximately40 nm. The grain nucleation rate increased with increasing RHdue to the increasing amount of physisorbed water on thesurface.Exposure to RH and SO2 led to the formation of coppersulfite (CuSO3•xH2O) species as well as reduction in therate of Cu2O formation. The formation of CuSO3•xH2Ooccurred through the dissolution and consecutive precipitationof surface-bound copper sulfite complexes.The roles of O3 and NO2 in the SO2-induced atmosphericcorrosion of copper was also investigated. O3 was found to havea two-fold effect, resulting in the oxidation of the coppersulfite species to copper sulfate and the enhancement of Cu2Oformation. NO2 promoted the oxidation of copper sulfitespecies, though less efficiently than O3, and reduced Cu2Oformation. In addition, copper nitrate formation wasobserved.IRAS was also used to investigate the interaction betweenSO2 and surfaces made of platinum and palladium. Sulfuric acidformation was observed on both metals, showing the importanceof the surface on the formation of the metal/atmospherereaction products.Keywords:Atmospheric corrosion, IR-spectroscopy, IRAS,QCM, AFM, SO2, O3, NO2, Cu.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Ahlberg Tidblad, Annika
(författare)
-
Surface characterization of the chromium hydroxide and basic calcic deposition layers formed on the steel cathode in the chlorate production process
- 1999
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During technical service, the surface of the steel cathodein the chlorate production process changes with respect tochemical composition and morphology. Deposition of insolublespecies from the electrolyte and corrosion products from thebase metal accumulate and form surface layers that influencethe cathode activity with regards to hydrogen evolution, theprimary reaction, as well as to various parasitic reactions.Improving the activity on the cathode side could reduce theproduction cost of chlorate significantly. Surface analysis hasbeen performed on the thin film formed by reduction of chromateand the layer consisting of basic calcium and magnesiumspecies.Small amounts of sodium chromate are added to the chloratebrine in order to improve the current efficiency of theprocess. Chromate is reduced and forms a thin film withselective permeability that hinders parasitic reduction ofhypochlorite and chlorate ions.Ex situsurface analysis with ESCA and GD-OES were usedin combination within situspectroscopic ellipsometry. Several experimentaldifficulties had to be overcome in order to performellipsometric measurements. The surface film was identified asa hydrated chromium(III) hydroxide, Cr(OH)3*x H2O. The film grows homogeneously on the substrateand attains a maximum thickness of 1-10 nm, depending onchromate concentration, cathodic polarization and substratematerial. The thickness of a monolayer is approximately 0.5 nm.The chemical composition and structural arrangement areconstant during growth and dissolution of the surface productsignificant.Industrial brine contains ppm levels of calcium andmagnesium impurities and carbonate and sulfate ions,<1 g l-1Na2CO3and 10-20 g l-1Na2SO4. Hydrogen gas evolution produces hydroxide ionsand a steep gradient with elevated pH forms in the vicinity ofthe cathode, where various calcium and magnesium saltsprecipitate and form a thick surface layer, 1-1000 µm. Thecalcic deposit is nonconductive and causes cathodicoverpoteniallosses. Characterization using SEM/EDS shows thatthe layer consists of a mixture of calcium hydroxide/carbonate,magnesium hydroxide and sodium sulfate species, which wasconfirmed by an independent kinetic model. The model treatscomplex chemical processes in great detail and employsliterature data for model parameters. To the author'sknowledge, this is the first published attempt at modeling thechemical aspects of the formation of the calcic layer. Thecalcium/magnesium ratio is 3-5, which is higher than predictedby the model, due to the superior ability of calcium to formsoluble complexes and precipitate close enough to beincorporated in the surface layer. High calcium concentrationspromote distinct crystals and dense deposits. Magnesium reducesparticle size and increases the insulating properties of thelayer. Carbonate and sulfate ions contribute to increasingstructural disorder. Precipitation of sodium sulfate onlyoccurs above a critical concentration of sulfate, estimated to25 g l-1Na2SO4. Sodium sulfate precipitates as Na2SO4or as NaClO3*3Na2SO4at high chlorate concentrations.Key words: chlorate cathode processes,chromium(III)hydroxide film, calcic deposit, ESCA, GD-OES,SEM/EDS, spectroscopic ellipsometry, kinetic modeling
|
|
| 9. |
- Ahlblad, Gustav
(författare)
-
Imaging chemiluminescence applied to oxidation of rubber materials and polyamide
- 1998
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the heterogeneous nature of thermal oxidationof polymer materials have been investigated by imagingchemiluminescence (KL). The issues of oxidation depth profilesand physical spreading of oxidation in rubbers materials andpolyamide have been addressed.For this purpose an ICL instrument was designed showing thefollowing unique features: high sensitivity - particularly highsignal to noise ratio for small samples, high spatialresolution and a high accuracy of the in-plane temperature.With these characteristics, the spatial distribution of the CLemission from various polymer materials can be obtained inoxygen and, which has not previously been reported, in nitrogenatmosphere.An experimental method was developed to estimate theoxidation depth in HTPB tubber duringin situoxidation. Thein situoxidation depth data were correlated to oxidation depthprofiles of pre-aged samples from measurements in nitrogenatmosphere. Oxidation depth profiles in nitrogen were alsodetermined for pre-aged PA 6,6 and correlated to carbonyl indexdepth profiles obtained by FlTR microscopy. By subjetting HTPBrubber samples to static as well as dynamit-mechanical load at100°ree;C different oxidation depth profiles could beidentified.Experiments on oxidation in populations of EPDM particlesdemonstrated the presence of two separate distributions ofinitiation times for the individual particles, suggesting twodifferent initiation mechanisms. Further experiments showed acorrelation of the initiation times of adjacent particles. Thecorrelation was improved in populations with closerinterparticle distances. The results were interpreted in termsof a physical spreading of the oxidation from particle toparticle. Results from GC-MS and TG measurements indicated thepresence of volatile species released on oxidation of theparticles.A mechanism is proposed for the physical spreading ofoxidation observed, involving infectious spreading in the gasphase from heterogeneously distributed initiation sites.Keywords:Imaging chemiluminescence, oxidation, depthprofiles, physical spreading, HTPB rubber, EPDM, PA 6,6.
|
|
| 10. |
|
|
