Discrepancies in Thorium Oxide Solubility Values: a New Experimental Approach to Improve Understanding of Oxide Surface at Solid/Solution Interface

Accepted for publication in Radiochimica ActaThe solubility of ThO2(cr) was studied since many years but a large discrepancy in solubility values is noticed in the literature. The present work suggests that this discrepancy is related to differences in the surface properties of thorium oxide. To understand the role of surface properties on solubility values, we conducted experiments with ThO2(cr) spheres with reproducable surface properties. Batch dissolution experiments were conducted in 0.01 M NaCl solution at pH = 3.0 and 4.0 for periods of time up to 270 days. The solutions were spiked with 229Th to determine precipitation (sorption) rates of thorium, while dissolution rates were determined by measuring 232Th released from ThO2(cr) spheres. We assume that 229Th atoms are exchanged only with active sites involved in Th-dissolution. Using 229Th as local sensor of attachement and detachment processes at the ThO2(cr) surface under close-to-equilibrium conditions, allows to assess surface reactivity of the solid during solubility experiments

IMPACT OF WATER RADIOLYSIS ON URANIUM DIOXIDE CORROSION

International audienc

Alpha localized radiolysis and corrosion mechanisms at the iron/water interface: Role of molecular species

This paper is devoted to the iron corrosion phenomena induced by the α (4He2+) water radiolysis species studied in conjunction with the production/consumption of H2 at the solid/solution interface. On one hand, the solid surface is characterized during the 4He2+ ions irradiation by in situ Raman spectroscopy; on another hand, the H2 gas produced by the water radiolysis is monitored by ex situ gas measurements. The 4He2+ ions irradiation experiments are provided either by the CEMHTI (E = 5.0 MeV) either by the ARRONAX (E = 64.7 MeV) cyclotron facilities. The iron corrosion occurs only under irradiation and can be slowed down by H2 reductive atmosphere. Pure iron and carbon steel solids are studied in order to show two distinct behaviors of these surfaces vs. the 4He2+ ions water irradiation: the corrosion products identified are the magnetite phase (Fe(II)Fe(III)2O4) correlated to an H2 consumption for pure iron and the lepidocrocite phase (γ-Fe(III)OOH) correlated to an H2 production for carbon steel sample. This paper underlined the correlation between the iron corrosion products formation onto the solid surface and the H2 production/consumption mechanisms. H2O2 species is considered as the single water radiolytic species involved into the corrosion reaction at the solid surface with an essential role in the oxidation reaction of the iron surface. We propose to bring some light to these mechanisms, in particular the H2 and H2O2 roles, by the in situ Raman spectroscopy during and after the 4He2+ ions beam irradiation. This in situ experiment avoids the evolution of the solid surface, in particular phases which are reactive to the oxidation processing

Radiolytic Corrosion of Uranium Dioxide: Role of Molecular Species

n.a

Combined investigation of water sorption on TiO2TiO_2 rutile (1 1 0) single crystal face: XPS vs. periodic DFT

XPS and periodic DFT calculations have been used to investigate water sorption on the TiO2 rutile (1 1 0) face. Two sets of XPS spectra were collected on the TiO2 (1 1 0) single crystal clean and previously exposed to water: the first set with photoelectrons collected in a direction parallel to the normal to the surface; and the second set with the sample tilted by 70°, respectively. This tilting procedure promotes the signals from surface species and reveals that the first hydration layer is strongly coordinated to the surface and also that, despite the fact that the spectra were recorded under ultra-high vacuum, water molecules subsist in upper hydration layers. In addition, periodic DFT calculations were performed to investigate the water adsorption process to determine if molecular and/or dissociative adsorption takes place. The first step of the theoretical part was the optimisation of a dry surface model and then the investigation of water adsorption. The calculated molecular water adsorption energies are consistent with previously published experimental data and it appears that even though it is slightly less stable, the dissociative water sorption can also take place. This assumption was considered, in a second step, on a larger surface model where molecular and dissociated water molecules were adsorbed together with different ratio. It was found that, due to hydrogen bonding stabilisation, molecular and dissociated water molecules can coexist on the surface if the ratio of dissociated water molecules is less than ≈33%. These results are consistent with previous experimental works giving a 10–25% range

M & L Jaargang 27/2

Marjolijn Van Damme en Dieter Nuytten Luchtvaartexperimenten uit de avontuurlijke pionierstijd: de betonnen paddenstoelen van Hardy en de Grimbergse compenseerinrichting. [Pioneering experiments in aviation: the concrete mushrooms by Hardy and the compensation installation in Grimbergen.]Je zou ze als curiosa kunnen bestempelen, de reusachtige betonnen paddenstoelen die self-made ingenieur Alfred Hardy in de nadagen van WO II uit de tarmac van Grimbergen liet opschieten, ware het niet dat zij als loods voor kleine vliegtuigen ruim vijftig jaar na datum onwrikbaar standhouden.Op hun ligging en contouren na hebben ze met de nabijgelegen compenseerinrichting weinig uitstaans, behalve dan hun pas erkend belang als erfgoed.Hun uniciteit lijkt Marjolein Van Damme en Dieter Nuytten voldoende reden voor een gebalde terugblik.Hugo Vandenborre en Linda Wylleman De restauratie van de Egyptische eetzaal van het kasteel Moeland in Sint-Niklaas. [Restoration of the egyptian dining room of the Moeland castle in Sint-Niklaas.]De veelheid aan faraos, goden en godinnen die de Egyptische eetzaal tooien van kasteel Moeland in Sint-Niklaas kent als gelijke slechts de complexiteit van de interventies, nodig om dit afgeleefde werkstuk van het duo Bonnefoy-de Castro een tweede leven te verzekeren.De cultuurhistorische duiding van dit merkwaardig 19de-eeuws ensemble kreeg eerder reeds in M&L verdiende aandacht.Hugo Vandenborre en Linda Wylleman liggen ditmaal dan ook de klemtoon op de diagnose van de kwalen en de toegepaste therapie.Johan Lagae Bouwen in Le Katanga Moderne: koloniaal architecturaal erfgoed in Lubumbashi, democratische republiek Congo. [Building in Le Katanga Moderne. Colonial architectural heritage in Lubumbashi, Democratic Republic of Congo.]Koloniale architectuur en stedenbouw is voor Johan Lagae, met Congo in het algemeen en Lubumbashi in het bijzonder, allesbehalve terra incognita.Tentoonstellingen, publicaties en initiatieven zoals lokale Open Monumentendagen vestigden recent de aandacht op de waarde van een emotioneel geladen, soms bevreemdend erfgoed, dat het - niet onbedreigd - bestaat een weinig zekere toekomst uit te dagen. Whose heritage? is derhalve een terecht door de auteur gestelde slotvraag.Chris De Maegd Tuinen inventariseren: nodig, nuttig, boeiend, leerrijk. [A garden inventory: necessary, fascinating and educational.]Spijts de verschijning in het voorjaar van een 7de M&L Cahier Historische tuinen en parken van Vlaanderen raakt de nog forse achterstand op het zuiden van het land maar node bijgebeend. Dat in de Tuin van Eden geen appelen met citroenen vergeleken moeten worden is voor Chris De Maegd nochtans een vanzelfsprekendheid. Geconfronteerd met tuinen in hun alsmaar wisselende gedaanten, pleit ze derhalve niet toevallig voor het exhaustief documenteren van de ongrijpbare momentopnamen.Summar

CORI TASK 2 : Organic Degradation cement-organic-radionuclide-interaction

International audienc

CORI TASK 2 : Organic Degradation cement-organic-radionuclide-interaction

International audienc