| 1. |
- Rubensson, J. E., et al.
(författare)
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Soft X-ray Spectroscopic Characterization of Montmorillonite
- 2009
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Konferensbidrag (refereegranskat)abstract
- Soft X-ray spectroscopy was applied to study a calcium bentonite from the Kutch area in India. We recorded the X-ray absorption spectra from the L-edge of calcium, silicon, and aluminum, and from K-edge of oxygen. The Ca absorption spectrum shows a quasi-atomic behavior, while the Si spectrum closely simulates the absorption spectrum of a pure silicon oxide The O K spectrum shows a pre-peak, which is absent in the spectra of both the pure, bulk aluminum and silicon oxides. The At L spectrum is complex and shows almost no resemblance to the absorption spectrum of aluminum oxides. The chemical state of the At atoms (in octahedral coordination) must, thus, be quite different from what is common in the oxides. The obtained data show that soft X-ray spectroscopy is a promising technique for studying clay minerals. It is capable of supplying unique information that is complementary to information accessible using other techniques; especially, it can be used to determine the local electronic structure at various atomic sites in the complex samples.
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| 2. |
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| 3. |
- Rosborg, Bo, et al.
(författare)
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Real-time monitoring of copper corrosion at the Äspö HRL
- 2004
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Konferensbidrag (refereegranskat)abstract
- In Sweden the principal strategy for high-level radioactive waste disposal is to enclose the spent nuclear fuel in tightly sealed copper canisters that are embedded in bentonite clay about 500 m down in the Swedish bed-rock. Initially, a limited amount of air will be left in a repository after emplacement. The entrapped oxygen will be consumed through reactions with minerals in the rock and the bentonite and also through microbial activity. After the oxygen has been consumed in the repository, after a few hundred years at the very most, corrosion will be controlled completely by the supply of dissolved sulphide to the canister. The present work concerns the oxic period after emplacement. The main hypothesis is that the average corrosion rate of the canister under oxic conditions will be less than 7 μm/year, and that pitting will only be possible under these conditions. The Äspö Hard Rock Laboratory offers a realistic environment for different experiments and tests under the conditions that will prevail in a deep repository. Real-time monitoring of copper corrosion is presently performed with polarization resistance, harmonic distortion analysis and electrochemical noise techniques. The first two techniques are used to derive information regarding the general corrosion rate and the third to derive information regarding localized corrosion. In order to support these measurements at Äspö, laboratory work is also performed at the Royal Institute of Technology in Stockholm using the very same corrosion monitoring equipment and also other equipment and techniques. Copper coupons are also exposed at Äspö. Results from the work at Äspö and in Stockholm are presented with an emphasis on the gained information concerning localized corrosion. The recorded corrosion rates at Äspö are well below the value given above, and the recorded localization factors are interpreted as indicating only a slight tendency to local attack.
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| 4. |
- Rosborg, Bo, et al.
(författare)
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The corrosion rate of copper in a test parcel at the Äspö Hard Rock Laboratory
- 2004
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Ingår i: Mater Res Soc Symp Proc. ; , s. 489-494
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Konferensbidrag (refereegranskat)abstract
- Cylindrical copper electrodes have been installed in a test parcel at the Äspö Hard Rock Laboratory and real-time corrosion monitoring was initiated in May 2001. The test parcel was emplaced on October 29, 1999, and will be retrieved in 2004. The three electrodes, each of about 100 cm 2 surface area, are installed in bentonite block 36, where the temperature is about 24°C. The corrosion monitoring is performed with linear polarization resistance (LPR), harmonic distortion analysis (HDA) and electrochemical noise techniques. A value on the Stern-Geary coefficient is required to calculate the corrosion rate from the measured LPR data. A default value of 10.3 mV has been used, but an actual value can in fact be obtained from the HDA. The corrosion rate will be overestimated if the frequency of the voltage perturbation for the LPR measurements is not low enough. Electrode impedance measurements have been performed to verify this. Two and a half year after emplacement the recorded corrosion rate of copper in the above bentonite block amounts to about 2.2 μm per year (using a default value of 10.3 mV for the Stern-Geary coefficient and a 0.01 Hz voltage perturbation frequency). The actual corrosion rate is estimated to less than 0.7 μm per year (considering a measured Stern-Geary coefficient of 6.5 mV and the findings from the electrode impedance measurements).
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| 5. |
- Thuresson, A., et al.
(författare)
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Anomalous temperature behavior in clay swelling due to ion-ion correlations
- 2016
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075. ; 114:3
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Tidskriftsartikel (refereegranskat)abstract
- We show, experimentally and theoretically, that swelling of both natural and refined clays has an anomalous temperature behavior depending on counterion valency. In an aqueous clay dispersion dominated by monovalent counterions the swelling pressure increases with temperature as expected from entropic arguments. In a clay with predominantly divalent counterions, the opposite behavior is found. The explanation is due to the fact that ion-ion correlations increase with temperature. Ion-ion correlations are important at strong electrostatic coupling and in an aqueous solution the dielectric permittivity, ϵr, drops with increased temperature, T, in such a way that the product ϵrT also decreases. Thus, the net effect is an increased coupling.
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