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At thermal junctions of aluminium alloy castings and at points where risering proves to be difficult there appear internal or external shrinkages, which are both functionally and aesthetically inadmissible. Applying the Probat Fluss Mikro 100 agent, which is based on nano-oxides of aluminium, results in the appearance of a large amount of fine microscopic pores, which compensate for the shrinking of metal. Experimental tests with gravity die casting of AlSi8Cu3 and AlSi10Mg alloys have confirmed that the effect of the agent can be of advantage in foundry practice, leading to the production of castings without local concentrations of defects and without the appearance of shrinkages and macroscopic gas pores. Also, beneficial effect on the mechanical properties of the metal has been observed.

[ES] Los materiales de sílice mesoporosos ordenados, también llamados OMS, son un grupo de nanomateriales de sílice con poros ordenados, cuyo tamaño puede ser de 2 a 50 nm. Se han utilizado mucho desde 1990 en varios campos, como la administración de fármacos, la adsorción, la separación y la catálisis. El OMS más conocido es el SBA-15, pero el COK-12, que se descubrió en 2010, tiene propiedades análogas y su síntesis muestra algunas ventajas en comparación con el SBA-15. La síntesis de COK-12 tiene lugar a temperatura ambiente y pH casi neutro y es más rápido, más económico y respetuoso con el medio ambiente. En esta tesis se estudiaron dos métodos de síntesis diferentes del material de sílice mesoporoso COK-12 ordenado, con el fin de encontrar el mejor método de síntesis según los requisitos de las propiedades en cada caso. En cada uno de los dos métodos de síntesis hubo algunas variaciones en el proceso y se estudiaron las propiedades cambiantes del producto final, especialmente la morfología de los poros y las características de la superficie. Como el COK-12 tiene aplicaciones en catálisis y adsorción, en este trabajo se produjeron esferas y membranas con COK-12 en diferentes composiciones. Los resultados se muestran en esta tesis., [EN] Ordered mesoporous silica materials, also called OMS, are a groups of silica nanomaterials with ordered pores, which size can be from 2 to 50 nm. They have been used a lot since 1990 in several fields such as drug delivery, adsorption, separation and catalysis. The most widely known OMS is SBA-15, but COK-12, wich was discovered in 2010, has analogous properties and it¿s synthesis shows some advantages in comparison to SBA-15. COK-12 synthesis takes place at room temperature and almost neutral pH and it¿s quicker, more inexpensive and environmetally friendly. In this thesis two different synthesis methods of the ordered mesoporous silica material COK-12 were studied, in order to find the best synthesis method according to the properties requirements in each case. In each of both synthesis methods there were some variations in the process and the changing properties of the final product were studied, specially the pore morfology and the surface characteristics. As COK-12 has applications in catalysis and adsorption, spheres and membranes with COK-12 in different compositions were produced in this work. The results are shown in this thesis.

Shales are the most abundant sedimentary rocks and as such they are important constituents of sedimentary basins. The characterization of the pore space and mi-crostructure of shales is crucial for many applications in geosciences. For example in the reservoir characterization of gas shales, in basin modeling studies, in understanding of sealing behavior and in hydrocarbon generation in organic-rich shales. Because these fine-grained rocks have relatively low porosity and permeability, under-standing of their petrophysical properties is difficult and requires new methods and techniques. One such newly developed method is the combination of Broad-Ion-Beam (BIB) milling and Scanning Electron Microscopy (SEM). This method allows imaging pores with resolution down to 5 nm in equivalent diameter, and quantitative measurement of porosity in representative elementary area on the scale of a few mm2.The aim of the dissertation (Chapter 1) is to investigate the porosity and microstruc-ture in organic-rich shales of the Posidonia Shale, Haynesville Shale and Bossier Shale formations with different maturities, using BIB-SEM. In more detail, the effect of grain size, mineralogy and maturity on pore space is investigated and the connectivity of the pore space is assessed. Chapter 2 describes complementary techniques like Focused Ion Beam (FIB)-SEM, Micro Computed Tomography (MicroCT), Mercury Intrusion Porosimetry (MIP) and Wood’s Metal Injection (WMI). The BIB-SEM method and workflow is explained in detail in Chapter 3.The first BIB-SEM study (Chapter 4) reports on two early mature (VRr = 0.59 and 0.61) samples of Posidonia Shale from the Hils Syncline in Germany. Pore morphologies and pore sizes are clearly related to the mineral phases. The porosity resolvable by BIB-SEM is 2.75 and 2.74 %. Pore size distribution can be described by a power law function. The pores in the carbonate fossils show a dual-power law distribution. By extrap-olating the power-law distribution for a sample, total porosity is estimated and can be compared with values gained by MIP. Comparison between the imaged porosity and the MIP porosity suggest a very high pore body to pore throat ratio. This results in a pore model where large pores, represented mainly by pores in fossils and calcite grains, are connected via a low-porous clay-rich matrix with pore throats below 10 nm.In the following chapter (Chapter 5) four Haynesville Shale and four Bossier Shale samples of different maturity, fabric and mineralogy are described using BIB-SEM. This variability within the samples enabled to study the controls on the porosity distribution in these shales. Pores exist as intraparticle pores mainly in carbonate grains and py-rite framboids and as interparticle pores, mainly in the clay-rich matrix. Pore sizes are power law distributed and a positive trend of organic-matter porosity with maturity was found. Porosities measured by BIB-SEM are significantly lower than porosities obtained by MIP. In Chapter 6 an alternative method of MIP is presented. WMI in combination with BIB-SEM allows imaging of the solid Wood’s Metal (WM)-filled pores. WMI was conducted at 316 MPa. The samples were BIB polished followed by high resolution SEM imaging. SEM investigations showed WM-filled pores down to at least 10 nm and almost full impregnation of the WM in the Boom Clay sample and heterogeneous impregnation in the Bossier Shale sample. The Opalinus Clay and Haynesville Shale samples showed WM mainly in cracks and in larger pores directly adjacent to those cracks. These first results suggest that many published MIP data on mudstones could contain serious methodological artifacts and reliable metal intrusion porosimetry requires a demon-stration that the metal has entered the pores. Moreover, results show that, in particu-lar for the Opalinus Clay, the pore throats are actually smaller than suggested by Mercury data, resulting in higher capillary resistance and thus a higher sealing capacity. Chapter 7 reports on the microstructural characterization of porosity, mineralogy and organic matter in 2 and 3 dimensions of an organic-rich Haynesville Shale sample. Sample size varies from several centimeters down to 10 micrometers in size using op-tical microscopy, BIB/FIB-SEM, MicroCT and WMI. The sample consists of a heterogeneous mineralogy and fabric, uniformly distributed on the centimeter scale except for one millimeter-size carbonate-rich layer. Organic matter shows the largest pore networks, up to 8 μm in length. The organic matter is connected throughout the sample and is therefore the most probable controlling factor for gas transport.In Chapter 8 presents the microstructural characterization of porosity of two organic-rich Posidonia Shale samples with different maturates (VRr = 0.91 and 1.52), using BIB-SEM. Results show that both samples have a similar pore size distribution, but the ma-ture sample contains a lower visible porosity (0.82 % vs. 2.47 %). The postmature sample contains intra-organic-matter pores, which are notably different from the mature sample that contains crack-type porosity at the organic-matter – mineral interface. The latter are interpreted either to be due to shrinkage because of devolatization or hydraulic fracturing because of hydrocarbon generation. The transition from these crack-type porosity into intra-organic-matter pores is interpreted because of thermal maturation. Final concluding remarks are given in the last chapter (Chapter 9).

During the firing of bricks, mineralogical and textural transformations produce an artificial aggregate characterised by significant porosity. Particularly as regards pore-size distribution and the interconnection model, porosity is an important parameter to evaluate and predict the durability of bricks. The pore system is in fact the main element, which correlates building materials and their environment (especially in cases of aggressive weathering, e.g., salt crystallisation and freeze-thaw cycles) and determines their durability. Four industrial bricks with differing compositions and firing temperatures were analysed with “direct” and “indirect” techniques, traditional methods (mercury intrusion porosimetry, hydric tests, nitrogen adsorption) and new analytical approaches based on digital image reconstruction of 2D and 3D models (back-scattered electrons and computerised X-ray micro-Tomography, respectively). The comparison of results from different analytical methods in the “overlapping ranges” of porosity and the careful reconstruction of a cumulative curve, allowed overcoming their specific limitations and achieving better knowledge on the pore system of bricks.

The aim of this study was to micromorphologically analyze modifications in soil porosity due to the occurrence of erosive rainfall events. Three types of soils, Typic Hapludox, Typic Hapludult and Rhodic Kandiudalf, were analyzed to determine their total porosity and the distribution and number of pores. The soils were tilled with a heavy disk and leveling harrow to ensure homogeneity of surface conditions at the beginning of the trial period and to simulate cropping conditions. The soils were kept uncovered during the trial period, and rainfall events with intensities greater than 25 mm h-1were recorded. The results showed that all of the soils presented crust formation, influenced by the soil texture. NVef showed significant changes in total porosity, pore numbers and pore morphology, while LVAd and PVAd did not display marked modifications in these attributes. O objetivo deste trabalho é analisar micromorfologicamente as modificações na porosidade do solo devido a ocorrência de eventos chuvosos considerados erosivos. Foram avaliadas a porosidade total, distribuição e número de poros de um Latossolo Vermelho - Amarelo distrófico típico (LVAd) de textura média, Argissolo Vermelho - Amarelo distrófico típico (PVAd) de textura arenosa/média e Nitossolo Vermelho Eutroférrico típico (NVef) de textura argilosa. Os solos foram preparados com auxílio de grade pesada e niveladora para garantir condições iniciais homogêneas e para simular as condições de plantio adotada em sistemas convencionais de cultivo. O solo foi mantido descoberto e foram contabilizados eventos chuvosos erosivos com intensidade superior a 25 mm h-1. Por meio das análises micromorfológicas conclui-se que os três solos apresentam a formação de crostas superficiais, sendo estas influenciadas pela textura do solo. O NVef apresentou alterações significativas na porosidade total, número e morfologia dos poros, enquanto LVAd e PVAd não sofreram modificações significativas na porosidade total, número e morfologia dos poros.

Metal nanoparticle growth represents a major deactivation mechanism of supported catalysts and other functional nanomaterials, particularly those based on low melting-point metals. Here we investigate the impact of the support porous structure on the stability of CuZnO/SiO2 model methanol synthesis catalysts. A series of silica materials with ordered cagelike (SBA-16 mesostructure) and disordered (SiO2-gel) porosities and varying pore sizes were employed as catalyst supports. Nitric oxide moderated nitrate decomposition enabled the synthesis of catalytically active Cu nanoparticles (3-5 nm) exclusively inside the silica pores with short interparticle spacings. Under relevant reactive conditions, confinement of the Cu particles in cagelike silica pores notably enhances catalyst stability by limiting Cu particle growth as compared to catalysts deposited in SiO2-gel host materials with also 3D and highly interconnected though unconstrained porosity. For both pore morphologies, we find a direct relationship between catalyst stability and support porosity, provided the narrowest characteristic pore dimension is employed as a porosity descriptor. For cagelike porosities this corresponds to the size of the entrances to the nanocages. Our results point to nanoparticle diffusion and coalescence as a relevant growth mechanism under reactive conditions and underscore the significance of the narrowest pore constrictions to mitigate growth and improve catalyst stability. This finding contributes to the establishment of general and quantitative structure-stability relationships which are essential for the design of catalysts and related functional nanostructures with long lifetimes under operation conditions.

Representative elementary volumes (REV) are of major importance for modeling the transport properties of multi-scale porous materials. REVs can be used to schematize heterogeneous microstructures and form the basis of a numerical analysis. In this paper, the most appropriate REV size for numerical modeling for mass transport in hydrating cement paste is investigated. Numerous series (264) of virtual three-dimensional (3D) microstructures with different porosities and pore morphologies were generated using Hymostruc, a numerical simulation model for cement hydration and microstructure development. The influence of the initial particle size distribution, hydration evolution, numerical resolution and type of transport boundary conditions (periodic versus non-periodic) was investigated. The effective diffusivity was obtained by using a 3D finite difference scheme. The connectivity, dead-end porosity, tortuosity and constrictivity of the capillary pore network was evaluated. Based on a statistical chi-square analysis, it was concluded that the REV size largely depends on the complexity of the pore morphology, which in its turn, primarily depends on the degree of cement hydration, i.e. the porosity of the simulated microstructure, the employed numerical resolution as well as on the initial particle size distribution of the unhydrated cement grains. Furthermore, the results proved that employing periodic boundary conditions can effectively decrease the variability of the calculated effective properties and, thus, lower the size of an REV.

Clay rich formations are investigated thoroughly as candidate host rocks for the deep geological storage of radioactive waste. In the Mont Terri Rock Laboratory (Switzerland) Opalinus Clay is investigated with the aim to analyse its hydrological, geochemical and rock mechanical properties. Detailed investigation of the pore morphology and pore space contributes to the understanding of the sealing capacity, coupled flow, and associated deformation in clay. The Opalinus Clay formation is a fine-grained sedimentary rock deposited 180 Ma ago in a shallow sea compacted to a low porosity of 9–25% (depending on the measuring method used) and low permeability. On the regional scale the lateral variability of facies and lithology is low. Opalinus Clay is subdivided in six subfacies where the two end-members are the Shaly and the Sandy facies. To minimize damage of the clays microstructure the samples investigated, in this study, were carefully dried, as described in Chapter 2. After drying samples were imaged using a combination of Broad-Ion-Beam (BIB) milling and Scanning-Electron-Microscope (SEM) imaging. The method allows direct imaging of the clay fabric and porosity down to the nm scale. Visible porosity in the SE-micrographs was than segmented either manually or automatically (Chapter 3). A combination of BIB-milling and SEM imaging allows large representative area investigation of claystones, and a summary on porosity, pore morphology and pore size distribution of undamaged Opalinus Clay Shaly facies microstructures can be found in Chapter 4. This approach is able to provide a qualitative study of porosity as well as quantification of the pores directly from the micrographs at the nm - µm scale. Although the overall micro fabric differs per layer and per facies (Chapter 5), a low variability of the microstructure and porosity has been observed within each mineral phase. For example microstructurally the BIB polished cross-sections, produced in samples that have a high content of clay matrix (> 60%), display comparable microstructures for Sandy and Shaly facies samples of Opalinus Clay. The same is true for the pore size distribution and prominent pore shape per mineral phase, independent of the facies or polished cross-sections investigated; the pores within the clay matrix follow a similar pore size distribution and possess similar pore shapes. The large mineral grains, fossil shells and mineral aggregates are completely surrounded by the clay matrix, where the kind and amount of minerals depend on the facies of Opalinus Clay. The microstructure and porosity of the Shaly facies has also been investigated in 3D using a combination of µ-CT, BIB-SEM and FIB-SEM techniques (Chapter 6). The µ-CT measurements are used to get a 3D microstructural overview down to the µm scale. Afterwards a 2D BIB-polished cross-section was made through the µ-CT sample to examine the 2D microstructure down to the nm scale. FIB-SEM was used to study the 3D pore connectivity on two selected areas (Clay matrix and fossil shell) down to the nm scale. Next to the samples from the undisturbed Shaly and Sandy facies of Opalinus Clay, samples from the ‘Main fault’ (Mont Terri rock laboratory, Switzerland) were investigated, for the details see Chapter 7. Differences in microstructure with the undisturbed samples are the numerous micrometer wide calcite, celestine and pyrite filled veins present in the disturbed samples. Furthermore, damage zones of about 15 µm wide featuring less porosity are present. In order to investigate the pore connectivity Wood’s metal injection experiments were performed (Chapter 8). Preliminary results show that Wood’s metal although present in the bigger cracks and a few pores did not intruded a greater part of the pores present in the sample. This can indicate that that the connecting pore throats are smaller than 9 nm wide.

Ostracods belonging to the genus Bennelongia differ much in valve morphology between adults and juveniles. Adult valves are asymmetrical, characterised by a beak-like feature in the antero-ventral region of the left valve, and, with some notable exceptions, mostly have smooth or weakly-ornamented valves. Juvenile specimens, on the other hand, have valves that are almost symmetrical, with no beak-like feature and are often heavily ornamented. We have examined the last 3 - 4 juvenile stages of 6 Bennelongia species from 5 different lineages, in order to decipher the types of external valve ornamentation and their recurrences during ontogeny and across lineages. It is clear that ornamentation is more prevalent at the early instar stages compared to the last 2 pre-adult stages, and especially when compared to the adult stage itself. We also examined the surprising presence of a calcified inner lamella with a prominent inner list in the pre-adult stages of Bennelongia species, that is usually absent in juveniles of other ostracods, thus questioning if heterochronic processes have provided an intermediate valve morphology between the simple (normal) cypridinid juvenile state and the heavily derived and modified state of adult Bennelongia. We discuss the possible (speculative) functionality of the ornamentation in juveniles.

Research on semiconductor nanostructures is motivated by two key considerations. The first is the continuing call for smaller and more efficient versions of existing semiconductor devices. The second is the characterisation and exploitation of the unique characteristics that are often exhibited by structures at the nano-scale. While a wide variety of semiconductor nanostructures can be produced without difficulty (e.g. by self-assembly or preferential etching), precise control over the morphology of these structures is often much harder to achieve. The electrochemical formation of nano-scale porosity in semiconductors has been studied extensively1-5 and has found some application due to its bulk characteristics e.g. the use of porous silicon as a passivation layer6. However, the exploitation of the nano-scale properties of these structures is unlikely until a comprehensive understanding of the factors affecting pore morphology has been obtained. We have previously demonstrated7-9 the formation of nano-scale porosity in n-type InP anodised in KOH. Pores emerge form pits in the electrode surface10 and grow and branch along the A crystallographic directions9 forming tetrahedral porous domains8. Under certain conditions, current-line oriented pores can also be obtained.11 In order to understand the factors effecting pore morphology, porous InP was formed under a range of different temperatures, electrolyte concentrations, carrier concentrations and current densities. The morphology of the resulting porous layers was analysed in detail. In particular, the pore width, layer thickness and porosity of the layers were all measured. We show that at low current densities, the pore width is dominated by the magnitude of the current density. At higher current densities, we show that both the pore width and the porosity are inversely related to the kinetics of the electrochemical reaction: the pore width being lowest at high temperatures and intermediate KOH concentrations. The pore width decreases with increasing carrier concentration, which is likely due to the associated decrease in the space charge layer thickness. Porosity varies in a similar manner to pore width and the maximum porous layer thickness is correlated to the pore width in all cases. These results support a model9of pore formation based on competition in kinetics between hole supply at the pore tip and the electrochemical reaction at the semiconductor electrolyte interface. It will be shown that this model makes the correct qualitative predictions for the variation of pore morphology with temperature, electrolyte concentration, carrier concentration and current density. Such an understanding of the factors affecting the morphology of these porous layers is an essential step in achieving the process control necessary for them to be integrated into standard semiconductor fabrication techniques. References: 1. P. Schmuki, L. Santinacci, T. Djenizian and D. J. Lockwood, Phys. Stat. Sol., A, 182, 51 (2000). 2. P. Schmuki, U. Schlierf, T. Herrmann and G. Champion, Electrochim. Acta, 48, 1301 (2003). 3. H. Föll, M. Christophersen, J. Carstensen and G. Hasse, Phys. Stat. Sol., A, 182, 7 (2000). 4. H. Föll, J. Carstensen, S. Langa, M. Christophersen and I. M. Tiginyanu, Phys. Stat. Sol., A, 197, 61 (2003). 5. A. M. Goncalves, L. Santinacci, A. Eb, I. Gerard, C. Mathieu and A. Etcheberry, Electrochem. Solid-State Lett., 10, D35 (2007). 6. V. Yakovtseva, L. Dolgyi, N. Vorozov, N. Kazuchits, V. Bondarenko, M. Balucani, G. Lamedica, L. Franchina and A. Ferrari, J. Porous Mater., 7, 215 (2000). 7. C. O'Dwyer, D. N. Buckley, D. Sutton and S. B. Newcomb, J. Electrochem. Soc., 153, G1039 (2006). 8. R. P. Lynch, C. O’Dwyer, N. Quill, S. Nakahara, S. B. Newcomb and D. Noel Buckley, J. Electrochem. Soc., 160, D260 (2013). 9. R. P. Lynch, N. Quill, C. O'Dwyer, S. Nakahara and D. N. Buckley, Phys. Chem. Chem. Phys., 15, 15135 (2013). 10. C. O'Dwyer, D. N. Buckley, D. Sutton, M. Serantoni and S. B. Newcomb, J. Electrochem. Soc., 154, H78 (2007). 11. N. Quill, R. P. lynch, C. O’Dwyer and D. N. Buckley, ECS Trans., 50, 143 (2013). Figure 1

International audience; Water within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicatehydrates (C−S−H). Here, we employed Grand Canonical Monte Carlo simulations to investigate the properties of water confined at ambient temperature within and between C−S−H nanoparticles or "grains" as a function of the relative humidity (%RH). We address the effect of water on the cohesion of cement pastes by computing fluid internal pressures within and between grains as a function of %RH and intergranular separation distance, from 1 to 10 Å. We found that, within a C−S−H grain and between C−S−H grains, pores are completely filled with water for %RH larger than 20%. While the cohesion of the cement paste is mainly driven by the calcium ions in the C−S−H, water facilitates a disjoining behavior inside a C−S−H grain. Between C−S−H grains, confined water diminishes or enhances the cohesion of the material depending on the intergranular distance. At very low %RH, the loss of water increases the cohesion within a C−S−H grain and reduces the cohesion between C−S−H grains. These findings provide insights into the behavior of C−S−H in dry or high-temperature environments, with a loss of cohesion between C−S−H grains due to the loss of water content. Such quantification provides the necessary baseline to understand cement paste damaging upon extreme thermal, mechanical, and salt-rich environments.

Molecular simulations are used to study the adsorption, structure, and dynamics of benzene at 298 K in atomistic models of ordered and disordered nanoporous carbons. The ordered porous carbon is a regular slit pore made up of graphene sheets. The disordered porous carbon is a structural model that reproduces the morphological (pore shape) and topological (pore connectivity) disorder of saccharose-based porous carbons. As expected for pores of a regular geometry, the filling occurs at well-defined pressures which are an increasing function of the pore width H. In contrast, in qualitative agreement with experimental data for activated carbon fibers, the filling of the disordered carbon is continuous and spans over a large pressure range. The structure and dynamics of benzene in the disordered carbon also strongly depart from that for the slit pore geometry. While benzene in the slit graphite nanopores exhibits significant layering, benzene in the disordered porous carbon exhibits a liquid-like structure very close to its bulk counterpart. Both the ordering and self-diffusivity of benzene in the graphite nanopores depend in a complex manner on the pore width. The dynamics is either slower or faster than its bulk counterpart; our data show that the self-diffusivity decreases as the number of confined layers n divided by the pore width H increases (except for very small pore sizes for which benzene crystallizes and is necessarily slower than the liquid phase). The dynamics of benzene in the disordered porous carbon is isotropic and is much slower than that for the graphite slit nanopores (even with the smallest slit nanopore considered in this work). The results above show that the adsorption, structure, and dynamics of benzene confined in disordered porous carbons cannot be described in simple terms using an ideal model such as the slit pore geometry.

Within this work the relationship between the pore morphology and the fatigue properties of sintered pure iron and steel has been investigated. The mechanical properties of P/M are controlled by their microstructure and the porosity. Many parameters are influencing the microstructure and the porosity. A few of these parameters were considered in the investigation, which will have a significant influence on the performance characteristics of the materials. These parameters are the density, the kind of the powder, the sinter temperature and technique of alloying as well as the composition. The density acts as main parameter because it includes all other parameters. Therefore, the density has the maximum potential for optimizing the properties of the sintered components. The above mentioned parameters influence the morphology of the pores. Due to this, the characterizing of the pore characteristics is very important. The mechanical properties and the porosity have been investigated by varying the density, the sintering temperature and basic powder for sintered pure iron and alloyed steel. The investigated materials were Distaloy AE and SE, pure iron ABC 100.30 and MH 65.17. Basic powder was water atomized and pure broken sponge iron. The sintering conditions were 1120°C and 1280°C in an atmosphere of 70% N2 and 30% H2 in industrial equipment. If the relationship between the geometrical features of the pores and the influencing parameters is known, it is possible to optimize the morphology of the pores by the influencing factors. The base characteristics are pore area and perimeter, convex perimeter, maximum and minimum pore dimensions and the intercepts or distances between the pores. From the primary data a huge variety of secondary quantities can be derived which are used to describe the pore size, the pore shape, and pore interpore space. The pore morphology was quantified by image analysis. According to the results of the image analysis, the majority of all pores is small and rather round. Only a few large pores which are automatically also very irregular can act as potential fracture initiation sites. For this reason 98% of all pores were excluded from the further processing. Only 2% of the remaining larger and most irregular pores were evaluated. Pore irregularities are commonly characterized by a shape factor. The bending fatigue strength was investigated for a varying density by different sintering temperatures and basic powders. For each experimental condition 60 specimens were used in fully reversed flat bending tests at 6 stress levels of which 3 occurred in fracture. The endurance limits were determined for 50% probability at 107 cycles. Many properties of porous sintered materials are related to the pore microstructure. An attempt was made to correlate the fatigue behavior of industrially manufactured sintered iron and steels with quantitative pore characteristics. Crack initiation in fatigue tests was restricted to very few large irregular pores. All efforts to correlate average pore size or shape factors with fatigue strength values yield at best tendencies. Powder laws to describe the relationships between the strength, the density, and the shape factor the coefficients were calculated by regression analysis.

eEarth 4(1), 15-22 (2009)., Published by Copernicus Publ., Katlenburg-Lindau

This work deals with the appraisal of the most important microstructural parameters influencing the stain resistance of polished porcelain stoneware tiles. The correlations between the stain resistance on one side and bulk or surface characteristics on the other side were evaluated through a statistical approach, which provided a previsional model of the staining behaviour of tiles, based on the surface roughness as well as the pore amount, size and morphology.

Porosity is one of the major defects in castings because it reduces the mechanical properties of a cast piece [1]. Porosity formation results from the effect of two concomitant mechanisms, namely solidification shrinkage and segregation/precipitation of gases [1]. A model for the prediction of microporosity, macroporosity and pipe shrinkage during the solidification of alloys has been developed at the Computational Materials Laboratory (LSMX-EPFL) [2]. This model has then been improved by taking into account the effect of various alloying elements and gases on porosity formation [3, 4, 5]. However, the modeling of two physical phenomena still needed to be improved: (i) the curvature influence and (ii) the hydrogen diffusion influence on the growth of pores. The effect of pinching, i.e. the pores are forced by the growing solid network to adopt a complex non spherical shape, induces curvature restriction to the pores. This pinching effect can be a limiting factor for the growth of pores and is too simply modeled in the model of Péquet et al. [2]. Several other pinching models exist, but a rigorous experimental study to validate either one of these models is needed. Additionally, Carlson et al. [6] have recently shown that hydrogen diffusion might also be a limiting factor for the growth of pores. In the model of Péquet et al. [2], this effect was not taken into account. This thesis is mainly aimed to (i) provide experimental results that specifically validate the pinching model developed by Couturier et al. [4], (ii) investigate the influence of hydrogen diffusion on the growth of pores and (iii) provide a new model that takes into account the pinching effect and the hydrogen diffusion influence on the growth of pores. At first, pores formed in aluminum-copper (Al-Cu) samples (cast under controlled conditions) have been analyzed using high resolution X-ray tomography. The influence of the alloy inoculant, copper content, cooling rate and initial hydrogen content on the morphology of pores has been investigated. The results show that the curvature of micropores pinched in either non-inoculated or inoculated Al-4.5wt%Cu alloys can be fairly well approximated to that of cylinders. The results also show that the pinching model must be function of (i) the volume fraction of the primary phase gα and (ii) the secondary dendrite arm spacing λ2. However, the influence of the initial hydrogen content appears to be negligible. The pinching model developed by Couturier et al. [4] accounts for these observations and their relation fits fairly well the average mean curvature value of our experimental data. A new model has been developed to calculate an effective hydrogen diffusion coefficient De(gs), that is a function of the volume fraction of solid only. For that purpose, in-situ X-ray tomography has been performed on Al-Cu alloys. For each volume fraction of solid 0.6 ≤ gs ≤ 0.9, a representative volume element of the microstructure has been obtained from the tomography data. Solid and liquid voxels being assimilated to solid and liquid nodes respectively, a hydrogen diffusion equation has then been solved numerically. Calculations have been run until steady-state was reached in order to deduce De(gs) and the simulation results were successfully compared with a new theory based on effective-medium approximations. Both approaches lead to the main conclusion that hydrogen diffusion through the solid phase cannot be neglected, unlike it is assumed in the model of Carlson et al. [6]. Next, using the pinching model of Couturier et al. [4] and the obtained De(gs), a new volume-averaged model has been developed in order to simulate the growth of pores limited by (i) the curvature of the pore phase and (ii) the diffusion of hydrogen. The results show that, although hydrogen diffusion can be a limiting factor for the growth of pores, the pinching effect has a much larger influence. Accordingly, any model for porosity prediction should carefully take into account the influence of curvature and hydrogen diffusion on the growth of pores. In order to ripen this study at a refined scale, a 2D phase-field model has been developed to describe the complex shape of a pore formed within interdendritic liquid channels [7]. The influence of the solid, which can force the pore to adopt a non-spherical shape, is taken into account through the geometry of the domain and appropriate boundary conditions. This model accounts for curvature influence and hydrogen diffusion in the liquid, two of the main aspects governing the growth kinetics of a pore. However, the model still needs to be combined with a description of the liquid flow induced by the pore growth. Basically, this model should serve as a sound basis for further developments that might lead to more sophisticated pinching models. Finally, an experimental study has been conducted in order to track the inoculant influence on the shape of pipe shrinkage. Simultaneously, pipe shrinkage calculations (using the model of Péquet et al. [2]) were performed in order to track the influence of the gs,c parameter on the shape of the pipe shrinkage. This gs,c parameter corresponds to the critical volume fraction of solid at which mass feeding stops. Comparisons between experimental and simulation results show that the gs,c parameter should be set equal to 0.6 or 0.1 for a casting simulation of an inoculated or non-inoculated alloy, respectively.