| 1. |
- Abbas, Zareen, 1962, et al.
(författare)
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Monte Carlo simulation of the dissociation constants of CO2 in 0 to 1 molal sodium chloride between 0 and 25 °C
- 2013
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 150:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Stoichiometric dissociation constants of the carbon dioxide system in NaCl solution between 0 and 1 mol and 0 to 25 °C were estimated by Monte Carlo (MC) simulations, and compared with Pitzer calculations and experimental measurements. The MC simulations used experimentally determined dielectric constants of water at different temperatures, and optimal agreement with the experimental data and Pitzer calculations was achieved by adjusting the ionic radii. This simple procedure resulted in effective ionic radii which were further used to simulate the activity coefficients of salt mixtures. The first and second stoichiometric dissociation constants of carbonic acid in NaCl solution (pK1⁎ and pK2⁎) were estimated from the MC-derived activity coefficients of mixed salts in NaCl. The MC results are in good agreement with the experimental data as well as with the Pitzer calculations. This study shows that Monte Carlo simulations in the temperature and ionic strength range relevant to seawater can provide pK values of the same quality as Pitzer calculations, and constitutes the first step in developing a temperature-dependent MC model for seawater. While MC calculations require greater computing resources, the number of parameters derived by fitting to thermodynamic data is substantially smaller than for Pitzer calculations.
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| 2. |
- Abbas, Zareen, 1962, et al.
(författare)
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Synthesis, characterization and particle size distribution of TiO2 colloidal nanoparticles
- 2011
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 384:1-3, s. 254-261
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles of controlled size, well defined shape, pure phase and of clean surfaces are ideal model systems to investigate surface/interfacial reactions. In this study we have explored the possibility of synthesizing TiO2 nanoparticles in the size range of 7–20 nm under well controlled experimental conditions. A simple method based on the hydrolysis of TiCl4 was used to obtain particles having surfaces free from organics. Stable dispersions of TiO2 nanoparticles of various sizes were obtained by optimizing the reaction/dialysis time and temperature. The synthesized TiO2 particles were found to be predominantly of anatase phase and narrow particle size distributions were obtained. The TiO2 particles were characterized with respect to their phase, size and shape by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Particle size distribution in a colloidal dispersion was obtained by the electrospray scanning mobility particle sizer (ES-SMPS) method and compared with an average particle size determined from dynamic light scattering (DLS). The average particle sizes obtained by the DLS and ES-SMPS methods were in good agreement, while a primary particle size of 4 nm was found in X-ray diffraction irrespective of the particle size in solution. Early stages of the nucleation process were monitored by the ES-SMPS method. These results show that small particles of 4–5 nm are initially formed and it is highly likely that large particles are formed due to aggregation of primary particles.
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| 3. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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A study of the accelerated ageing process of cementitious materials
- 2011
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Ingår i: Advances in Construction Materials through Science and Engineering. ; RILEM PRO 79
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Konferensbidrag (refereegranskat)abstract
- This paper presents part of a study in a research project called “Ageing of the cementitious materials for storage of nuclear waste”. The goal is to establish a mechanistic model for predicting longevity of concrete in storage facilities for nuclear waste. As deposition of low and intermediate level radioactive waste (LILW) needs up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Laboratory methods are, therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. Chemical and electrochemical acceleration approaches were tried in this study. Chemical acceleration involves leaching of samples under conditions of actual groundwater. Electrochemical migration is also applied to accelerate leaching process. Chemical and XRD analysis is carried out to identify the compositions before and after the acceleration tests. The results indicate a possibility to produce aged specimens for further mechanical tests and other physical tests, such as porosity and diffusivity.
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| 4. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Ageing of cementitious materials for storage of nuclear waste
- 2011
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Ingår i: Nordic Concrete Research. ; Publication No. 43, s. 429-432
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Konferensbidrag (refereegranskat)abstract
- This paper presents an on-going research project dealing with ageing process of cementitious materials in a perspective of hundreds and thousands years. As it is risky to use empirical models for extrapolation of performance data from relatively short term experiments, a mechanism-based (chemo-mechanical coupled) model for safer prediction of longevity of concrete in storage facilities for nuclear waste is needed. The project work involves thermodynamic modeling, development of accelerated aging tests, physical, chemical and mineralogical characterization of young and aged cementitious materials, including mechanical, transport (diffusivity) properties, binding (adsorption) capacities and surface complexation (charging) behavior.
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| 5. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Ageing process of cementitious materials: Ion transport and diffusion coefficient
- 2012
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Ingår i: Concrete Repair, Rehabilitation and Retrofitting III - Proceedings of the 3rd International Conference on Concrete Repair, Rehabilitation and Retrofitting, ICCRRR 2012. - 9780415899529 ; , s. 369-374
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Konferensbidrag (refereegranskat)abstract
- Risk assessment analysis concerning service life predictions of concrete structures in nuclear waste repositories requires broad knowledge about long-term concrete deterioration processes. It is well known that the degradation process of cementitious materials involves diffusion of internal and external ions, interaction between these ions and re-deposition of the interacted products. However, although diffusion properties play an important role in the deterioration process, there is a lack of reliable data on ion diffusivity in concrete, especially co-existing ions rather than chloride. The aim of this study is to further analyze multi-component ionic diffusion accompanied with surface complexation and selective adsorption. Natural diffusion cell and field immersion tests are used to analyze transport properties of ions present in groundwater surrounding nuclear waste repositories such as chloride, sodium, lithium and calcium ions, through cement paste. Analytical techniques such as Ion chromatography, potentiometric titration, inductively coupled plasma mass spectrometry and X-ray fluorescence methods are used. Results indicate that the ionic diffusion coefficients differ between different ions and the higher the concentration of the ions, the lower the diffusion coefficient will be.
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| 6. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Chloride Penetration Resistance of Calcium Depleted Concrete Specimens
- 2014
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Ingår i: Proceedings of XXII Nordic Concrete Research Symposium, 13 - 15 August 2014, Reykjavik Iceland. ; , s. 487-490
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Konferensbidrag (refereegranskat)abstract
- To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are used. However, in order to reach an efficient leaching rate small sample sizes have been used which limits further testing. In this study an electro-chemical migration method to accelerate leaching of calcium from concrete specimens of size 50×100Ø is presented. Rapid chloride migration test is utilized to account for the changes in chloride diffusion coefficient of concrete specimens due to calcium depletion. The results indicate up to at least 70% of increase of chloride diffusion coefficient as a result of decalcification.
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| 7. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Electrochemical migration technique to accelerate ageing of cementitious materials
- 2013
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759810468 ; 56
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Konferensbidrag (refereegranskat)abstract
- Durability assessment of concrete structures for constructions in nuclear waste repositories requires long term service life predictions. As deposition of low and intermediate level radioactive waste (LILW) takes up to 100 000 years, it is necessary to analyze the service life of cementitious materials in this time perspective. Using acceleration methods producing aged specimens would decrease the need of extrapolating short term data sets. Laboratory methods are therefore, needed for accelerating the ageing process without making any influencing distortion in the properties of the materials. This paper presents an electro-chemical migration method to increase the rate of calcium leaching from cementitious specimens. This method is developed based on the fact that major long term deterioration process of hardened cement paste in concrete structures for deposition of LILW is due to slow diffusion of calcium ions. In this method the cementitious specimen is placed in an electrochemical cell as a porous path way through which ions can migrate at a rate far higher than diffusion process. The electrical field is applied to the cell in a way to accelerate the ion migration without making destructions in the specimen's micro and macroscopic properties. The anolyte and catholyte solutions are designed favoring dissolution of calcium hydroxide and compensating for the leached calcium ions with another ion like lithium.
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| 8. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
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Mineralogical, Physical and Chemical Characterization of Cementitious Materials Subjected to Accelerated Decalcification by an Electro-Chemical Method
- 2014
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Ingår i: Nordic Concrete Research. - 0800-6377. ; 1/2014:49, s. 181-198
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Tidskriftsartikel (refereegranskat)abstract
- To facilitate the service life predictions regarding durability of nuclear waste repositories acceleration methods enhancing the decalcification process are needed. In this study an electro-chemical migration method to accelerate leaching of calcium from cementitious specimens of sizes 50×100Ø and 75×50Ø mm is presented. The mineralogical, physical and chemical properties of degraded samples are characterized. The results demonstrate that up to 70% decrease in strength, 50 % decrease in E-modulus, 90 % increase in gas permeability, at least 70% increase in chloride diffusion coefficient and 70 % increase in pore volume could be expected due to leaching of portlandite from concrete.
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| 9. |
- Brown, Matthew A, et al.
(författare)
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Measure of Surface Potential at the Aqueous-Oxide Nanoparticle Interface by XPS from a Liquid Microjet
- 2013
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Ingår i: Nano letters. - 1530-6984 .- 1530-6992. ; 13:11, s. 5403-5407
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Tidskriftsartikel (refereegranskat)abstract
- We show that the surface potential at a water–oxide nanoparticle (NP) interface, long considered an immeasurable direct quantity, can be measured by X-ray photoelectron spectroscopy (XPS) from a liquid microjet. This new method does not require a priori knowledge of the particles’ surface structure or of the ion distribution throughout the electrical double layer for its interpretation and can be applied to any colloidal suspension independent of composition, particle size and shape, and solvent. We demonstrate the application for aqueous suspensions of 9 nm colloidal silica (SiO2) at pH 0.3 and 10.0, where the surface potential changes from positive to negative. The experimental results are compared with calculated surface potentials based on Guoy–Chapman theory and are shown to be in good agreement.
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| 10. |
- Brown, Matthew, et al.
(författare)
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Effect of Surface Charge Density on the Affinity of Oxide Nanoparticles for the Vapor–Water Interface
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:16, s. 5023-5029
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Tidskriftsartikel (refereegranskat)abstract
- Using in-situ X-ray photoelectron spectroscopy at the vapor–water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye–Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups (≡Si–O–) by counterions in the condensed ion layer. The increased negative surface charge density results in an electrostatic repulsion from the vapor–water interface that is seen to a lesser extent for larger particles that have a reduced charge density in the XPS measurements. We compare the results and interpretation of the in-situ XPS and corrected Debye–Hückel theory for surface complexation calculations with traditional surface tension measurements. Our results show that controlling the surface charge density of colloid particles can regulate their adsorption to the interface between two dielectrics.
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