Browsing by Subject "Porosity"

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  • Voutilainen, Mikko; Miettinen, Arttu; Sardini, Paul; Parkkonen, Joni; Sammaljärvi, Juuso; Gylling, Björn; Selroos, Jan-Olof; Yli-Kaila, Maarit; Koskinen, Lasse; Siitari-Kauppi, Marja (2019)
    The spatial porosity and mineral distribution of geological materials strongly affects transport processes in them. X-ray micro computed tomography (X-mu CT) has proven to be a powerful tool for characterizing the spatial mineral distribution of geological samples in 3-D. However, limitations in resolution prevent an accurate characterization of pore space especially for tight crystalline rock samples and 2-D methods such as C-14-polymethylmethacrylate (C-14-PMMA) autoradiography and scanning electron microscopy (SEM) are needed. The spatial porosity and mineral distributions of tight crystalline rock samples from Aspo, Sweden, and Olkiluoto, Finland, were studied here. The X-mu CT were used to characterize the spatial distribution of the main minerals in 3-D. Total porosities, fracture porosities, fracture densities and porosity distributions of the samples were determined using the C-14-PMMA autoradiography and characterization of mineral-specific porosities were assisted using chemical staining of rock surfaces. SEM and energy dispersive X-ray spectroscopy (EDS) were used to determine pore apertures and identify the minerals. It was shown that combination of the different imaging techniques creates a powerful tool for the structural characterization of crystalline rock samples. The combination of the results from different methods allowed the construction of spatial porosity, mineral and mineral grain distributions of the samples in 3-D. These spatial distributions enable reactive transport modeling using a more realistic representation of the heterogeneous structure of samples. Furthermore, the realism of the spatial distributions were increased by determinig the densities and porosities of fractures and by the virtual construction heterogeneous mineral distributions of minerals that cannot be separated by X-mu CT.
  • Voutilainen, Mikko; Kekäläinen, Pekka; Poteri, Antti; Siitari-Kauppi, Marja; Helariutta, Kerttuli; Andersson, Peter; Nilsson, Kersti; Byegård, Johan; Skålberg, Mats; Yli-Kaila, Maarit; Koskinen, Lasse (2019)
    In some countries the spent nuclear fuel produced by nuclear power plants will be deposited in crystalline granitic rock formations. In Finland, a repository for the spent nuclear fuel is being built at Olkiluoto. The safety assessment of the repository requires a careful determination of the transport properties of the bedrock. The porosity of the bedrock and the effective diffusion coefficients and distribution coefficients of different radio-nuclides for the bedrock are used as the main parameters in the safety assessment calculations. It has been questioned whether the parameters determined using laboratory experiments can be used to estimate the parameters in the in situ conditions. In this study, laboratory and in situ water phase diffusion experiments (WPDEs) were performed to resolve the issue. In the experiments, the transport of tritiated water (HTO), Cl-36, and Na-22 was studied using similar experimental setups. Mathematical models were constructed and solved to determine the transport parameters from the measured breakthrough curves. On average, the in situ WPDEs resulted in 20 (+/- 6)% smaller porosities and 32 (+/- 10)% smaller effective diffusion coefficients for HTO and Cl-36 than the laboratory WPDEs. It was also found that in veined gneiss, the most dominant rock type of the Olkiluoto bedrock, anion exclusion reduced the retention parameters of Cl-36 compared with those of HTO. Furthermore, the distribution coefficient of Na-22 for veined gneiss was about one order of magnitude smaller in the in situ conditions than in previous laboratory batch sorption experiments. The effects of the results on the safety assessment were evaluated and discussed.
  • Kohout, Tomas; Kallonen, Aki Petteri; Suuronen, Jussi-Petteri; Rochette, Pierre; Hutzler, A.; Gattacceca, Jerome; Badjukov, Dmitry D.; Skala, Roman; Bohmova, Vlasta; Čuda, Jan (2014)
    X-ray microtomography (XMT), X-ray diffraction (XRD) and magnetic hysteresis measurements were used to determine micrometeorite internal structure, mineralogy, crystallography, and physical properties at ~μm resolution. The study samples include unmelted, partially melted (scoriaceous) and completely melted (cosmic spherules) micrometeorites. This variety not only allows comparison of the mineralogy and porosity of these three micrometeorite types, but also reveals changes in meteoroid properties during atmospheric entry at various velocities. At low entry velocities, meteoroids do not melt, and their physical properties do not change. The porosity of unmelted micrometeorites varies considerably (0-12%) with one friable example having porosity around 50%. At higher velocities, the range of meteoroid porosity narrows, but average porosity increases (to 16-27%) due to volatile evaporation and partial melting (scoriaceous phase). Metal distribution seems to be mostly unaffected at this stage. At even higher entry velocities, complete melting follows the scoriaceous phase. Complete melting is accompanied by metal oxidation and redistribution, loss of porosity (1 ± 1%), and narrowing of the bulk (3.2 ± 0.5 g/cm3) and grain (3.3 ± 0.5 g/cm3) density range. Melted cosmic spherules with a barred olivine structure show an oriented crystallographic structure, whereas other subtypes do not.
  • Puukko, Esa; Lehto, Jukka; Lindberg, Antero; Voutilainen, Mikko (2018)
    This study aims to determine upscaling factors for the radionuclides' distribution coefficients (Kd) on crushed rocks to intact rock for the safety analysis of radionuclide migration from spent nuclear fuel in bedrock towards biosphere. Here we report the distribution coefficients for intact rock determined by electromigration sorption experiments and compare the results with those from recently performed batch sorption experiments. In total 34 rock samples, representing three typical rock types from Olkiluoto Finland, were studied in order to determine distribution coefficients, effective diffusion coefficients and porosities using the electromigration sorption experiments, formation factor experiments and porosity measurement. The parameters determined represent the three main parameters of geosphere used in the safety assessment of spent nuclear fuel disposal. The distribution coefficients of cesium and strontium on intact rock varied between (0.12–26.2) × 10−3 m3/kg and (1.4–13.3) × 10−3 m3/kg, respectively, whereas recent results for crushed rock varied between (2–57) × 10−3 m3/kg and (17–40) × 10−3 m3/kg, respectively. This implies that crushing increases the distribution coefficient significantly and upscaling factors from 3 to 33 were determined for scaling the distribution coefficients of crushed rock to ones of intact rock. The determined distribution coefficients of cesium and strontium for intact rock can be directly applied in the safety assessment whereas the upscaling factors can be used to convert distribution coefficients determined for crushed rock into ones for intact rock. Based on the results for porosities and effective diffusion coefficients it was concluded that they do not seem to correlate with sorption parameters. However, an alteration state, heterogeneity and mineral content seem to be important factors affecting the distribution coefficients and upscaling factors.
  • Rahikainen, Jenni; Mattila, Outi; Maloney, Thaddeus; Lovikka, Ville; Kruus, Kristiina; Suurnäkki, Anna; Grönqvist, Stina (2020)
    Fibre reactivity is essential for cellulose dissolution and derivatisation and a porous fibre structure is one key determinant for a highly reactive pulp. Mechanical and enzymatic treatments are known to improve fibre reactivity and more recently, the combination of mechano-enzymatic treatment has been shown to synergistically enhance the beneficial effect. The aim of this work was to do a systematic study on the effect of dry matter content during enzymatic modification of fibres and define the conditions that optimally improve fibre porosity. The combined mechano-enzymatic treatments at 15-25 w% consistency had the most pronounced effect on fibre porosity and morphology analysed by solute exclusion technique, nitrogen sorption and scanning electron microscopy. Light microscopy imaging confirmed that the combined mechano-enzymatic treatment at high consistency (> 10 w%) resulted in extensive fibrillation of the treated fibres which was not observed after sole mechanical or enzymatic treatments.
  • Karme, Aleksis; Kallonen, Aki; Matilainen, Ville-Pekka; Piili, Heidi; Salminen, Antti (2015)
    Laser additive manufacturing is an established and constantly developing technique. Structural assessment should be a key component to ensure directed evolution towards higher level of manufacturing. The macroscopic properties of metallic structures are determined by their internal microscopic features, which are difficult to assess using conventional surface measuring methodologies. X-ray microtomography (CT) is a promising technique for three-dimensional non-destructive probing of internal composition and build of various materials. Aim of this study is to define the possibilities of using CT scanning as quality control method in LAM fabricated parts. Since the parts fabricated with LAM are very often used in high quality and accuracy demanding applications in various industries such as medical and aerospace, it is important to be able to define the accuracy of the build parts. The tubular stainless steel test specimens were 3D modelled, manufactured with a modified research AM equipment and imaged after manufacturing with a high-power, high-resolution CT scanner. 3D properties, such as surface texture and the amount and distribution of internal pores, were also evaluated in this study. Surface roughness was higher on the interior wall of the tube, and deviation from the model was systematically directed towards the central axis. Pore distribution showed clear organization and divided into two populations; one following the polygon model seams along both rims, and the other being associated with the concentric and equidistant movement path of the laser. Assessment of samples can enhance the fabrication by guiding the improvement of both modelling and manufacturing process.
  • Nenonen, Ville; Dick, P.; Sammaljärvi, Juuso; Johansson, B.; Voutilainen, Mikko; Siitari-Kauppi, Marja (EAGE, 2019)
    The porosity distribution and mineralogical changes in a clay-rich fault core from the Tournemire underground research laboratory are analyzed to determine the mechano-chemical processes in a small-scale vertical strike-slip fault. The results display significant spatial variations in porosity and mineralogy along different gouge zones due to a polyphased tectonic history combined with complex paleo-fluid migrations. Porosity values increase from the center of the gouges to their borders indicating diffusive sealing/healing effects and past hydrothermal activities. The healing and thus the strengthening of the fault is marked by an increase of calcium content, which is concurrent with lower porosities around the gouge zone. Chemical mapping in the gouges reveal clay alteration, iron zonality and the presence of zinc sulphide as well as barium sulphate inside the gouge, further suggesting past hydrothermal activity. Finally, even though the observed porosity variations only occur in subcentimeter-thick gouge bands, the higher porosity sections are pathways for fluid flow during fault activity. © 5th International Conference on Fault and Top Seals 2019. All Rights Reserved.
  • Kaasalainen, Martti; Aseyev, Vladimir; von Haartman, Eva; Karaman, Didem Ş; Mäkilä, Ermei; Tenhu, Heikki; Rosenholm, Jessica; Salonen, Jarno (Springer US, 2017)
    Abstract Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles’ properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.
  • Kaasalainen, Martti; Aseyev, Vladimir; von Haartman, Eva; Şen Karaman, Didem; Mäkilä, Ermei; Tenhu, Heikki Juhani; Rosenholm, Jessica M.; Salonen, Jarno (2017)
    Silicon-based mesoporous nanoparticles have been extensively studied to meet the challenges in the drug delivery. Functionality of these nanoparticles depends on their properties which are often changing as a function of particle size and surrounding medium. Widely used characterization methods, dynamic light scattering (DLS), and transmission electron microscope (TEM) have both their weaknesses. We hypothesize that conventional light scattering (LS) methods can be used for a rigorous characterization of medium sensitive nanoparticles’ properties, like size, stability, and porosity. Two fundamentally different silicon-based nanoparticles were made: porous silicon (PSi) from crystalline silicon and silica nanoparticles (SN) through sol-gel process. We studied the properties of these mesoporous nanoparticles with two different multiangle LS techniques, DLS and static light scattering (SLS), and compared the results to dry-state techniques, TEM, and nitrogen sorption. Comparison of particle radius from TEM and DLS revealed significant overestimation of the DLS result. Regarding to silica nanoparticles, the overestimation was attributed to agglomeration by analyzing radius of gyration and hydrodynamic radius. In case of PSi nanoparticles, strong correlation between LS result and specific surface area was found. Our results suggest that the multiangle LS methods could be used for the size, stability, and structure characterization of mesoporous nanoparticles.
  • Aromaa, Hanna; Voutilainen, Mikko; Ikonen, Jussi; Yli-Kaila, Maarit; Poteri, Antti; Siitari-Kauppi, Marja (2019)
    The spent nuclear fuel in Finland will be deposited in crystalline granitic rock in Olkiluoto, Finland. As a part of the safety assessment of the repository, series of extensive in-situ sorption and diffusion experiments and supplementary laboratory work has been done in the Olkiluoto site. Through Diffusion Experiment in a laboratory (TDElab) aims to provide applicable data for the ongoing in-situ experiment in Olkiluoto. This laboratory scale experiment resembles the in-situ experiment and aims to gain information on possible effects in values of distribution coefficients, effective diffusion coefficient and porosity that are caused by differences in laboratory and in-situ conditions. The through diffusion and sorption of tracer solution with known activities of HTO, 36Cl, 133Ba and 134Cs were studied in a decimeter scale sample of veined gneiss, which is one of the main rock types in Olkiluoto. The measured breakthrough curves were modeled taking into account the porosity of the rock and diffusion and sorption of the radionuclides using Time-Domain Random Walk (TDRW) simulations. The porosities of 0.7–0.8% were determined for the rock and effective diffusion coefficients of (3.5 ± 1.0) × 10−13 m2/s and (3.0 ± 1.0) × 10−13 m2/s were determined for HTO and 36Cl, respectively. The porosity and effective diffusion coefficients were found to be in agreement with previous results for veined gneiss. Furthermore, distribution coefficients of (1.0 ± 0.3) × 10−4 m3/kg and (2.0 ± 0.5) × 10−3 m3/kg were determined for 133Ba and 134Cs, respectively, using information about the effective diffusion coefficient determined for HTO. The distribution coefficients were found to be significantly smaller than the ones determined for crushed rock in previous studies and slightly smaller than the ones from previous in-diffusion experiments.