Mattias Olsson

Macroscopic pressure–volume–temperature properties versus free-volume characteristics of isotropic pressure-densified amorphous polymer glasses

We made a series of isotropic pressure-densified (0–200 MPa) amorphous homopolymer [atactic polystyrene (a-PS)] and copolymer [poly(styrene-co-acrylonitrile) (SAN) and poly(styreneco-maleic anhydride) (SMA)] glasses and studied their macroscopic pressure–volume–temperature (PVT) properties vs their free-volume characteristics from the Simha–Somcynsky equation-of-state (EOS) theory and from positron annihilation lifetime spectroscopy (PALS). The glass densities lie in the range of 1.0403–1.0535 g/cm3 (PS), 1.0573–1.0759 g/cm3 (SAN), and 1.0989–1.1196 g/cm3 (SMA). With increasing formation pressure, all pressure-densified glasses exhibit decreasing volume and free-volume characteristics such that the changes in specific volume (1.26%–1.85%) are <ortho-positronium (o-Ps) lifetime τ3 (5.5%–9.1%) <free-volume hole size V(τ3) (10.3%–17.1%) <free-volume fraction h (25.1%–30.5%). We find, furthermore, that the o-Ps formation probability I3 is independent of formation pressure. Likewise, the glasses’ thermal expan...

Sorption of Pu(VI) onto TiO2

The sorption of Pu(VI) onto TiO(2) was studied as a function of pH (2-10) and Pu concentration (10(-8)-10(-4) M) under an N(2) atmosphere, in 0.016 and 0.1 M NaClO(4). A batch-wise method was used, in which pH was measured in separate experimental containers after removal of a sample to determine the amount of Pu that had been sorbed. As Pu is radioactive, it was used as a tracer and measured by liquid scintillation counting. No ionic strength dependence was discerned, which was taken as an indication of inner sphere complex formation. In the interval of pH 2-7 the system could be described by the formation of two positively charged surface complexes using a 1-pK Stern model. Sorption of the plutonyl ion (PuO(2)(2+)) and the first hydrolysis species (PuO(2)(OH)(+)) was estimated using FITEQL to logK(1)=6.9 and logK(2)=1.4, respectively.

Sorption of trivalent plutonium onto UO2 and the effect of the solid phase on the Pu oxidation state

Summary A problem with plutonium in sorption studies is its tendency to occur in a mix of oxidation states. This work was a study of the sorption of plutonium on the solid phase UO2 — in a perchlorate medium as a function of pH — where plutonium is kept in its trivalent oxidation state. Experiments also showed that uranium(IV) oxide can reduce Pu(IV) to Pu(III) in an acidic solution and maintain it in that state. It was observed at the same time that the chemically inert solid phases TiO2 and ThO2 possibly increase the rate of disproportionation of Pu(IV) at a pH of about 0.5. In accordance with previous studies MnO2 was found to have an oxidizing effect, converting Pu(IV) into Pu(VI). A comparison is made between the sorption of Th(IV), Pu(III) and Co(II) on UO2 and TiO2, and Pu(VI) on TiO2.

On the stability of Pu(III) at different pH under non-inert conditions

A glove-box in contact with the lab atmosphere has been used in a test to see whether trivalent plutonium can be kept in this oxidation state at different pH. The box hosted a vessel of Pu(III) solution through which a hydrogen/argon gas mix was bubbled in the presence of a Pd/Pt catalyst. The results of solvent extractions and UV-Vis spectra for this system show that such conditions should not be considered sufficient to keep plutonium trivalent at a pH above two. The solvent extraction method was not found to affect the oxidation state composition of the samples.

Sorption of Pu(III-IV) onto TiO2: A Preliminary Study

A preliminary study of the sorption of reduced plutonium (III-IV) onto TiO2 has been done under anoxic conditions at varying pH and ionic strength. The first approach was to study tetravalent Pu, but the sorption decreases with time in this case. This is probably due to disproportionation of Pu(IV) at the TiO2 surface, which then acts as a catalyst. A further observation that supports this explanation is that the sorption of Pu(IV) onto the walls of the experimental equipment is in some cases higher than the sorption of (disproportioned) Pu onto the oxide. Pu(III) sorption onto the oxide was also investigated and showed similarities with the previously investigated sorption of Pm(III) in a similar system.