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1
Content available remote Effect of anode porosity on the performance of molten carbonate fuel cell
EN
Nickel anodes, for molten carbonate fuel cell (MCFC), of various porosities were fabricated using tape casting and firing processes. The same slurry composition but different sintering temperatures, 700 and 900°C, were used to obtain different anode porosities. Combined experimental and computational techniques were used to study the influence of anode porosity on the performance of molten carbonate fuels cell. The power generated by the 20.25 cm2 class MCFC single cell was experimentally measured at 650°C in humidified hydrogen with respect to the porosity of the anodes. The computational aspect involved the modeling of the microstructure of the sintered porous anodes which included measured size distribution of Ni powder used and porosities of the manufactured materials. For the best performing single cell, the optimal porosity for the nickel MCFC anode was experimentally determined to be 55%. Computations revealed that the specific surface area, which is a determining factor in electrochemical reactions, reaches a maximum at a porosity of 52%.
EN
The study employs numerical calculations in the characterization of reservoir sandstone samples based on high-resolution X-ray computed microtomography. The major goals were to determine porosity through pore size distribution, permeability characterization through pressure field, and structure impact on rock strength by simulation of a uniaxial compression test. Two Miocene samples were taken from well S-3, located in the eastern part of the Carpathian Foredeep. Due to the relation between sample size and image resolution, two X-ray irradiation series with two different sample sizes were performed. In the first approach, the voxel side was 27 µm and in the second it was up to 2 µm. Two samples from different depths have been studied here. Sample 1 has petrophysical features of conventional reservoir deposits, in contrast to sample 2. The approximate grain size of sample 1 is in the range 0.1–1.0 mm, whereas for sample 2 it is 0.01–0.1 mm with clear sedimentation lamination and heterogenic structure. The porosity, as determined by µCT, of sample 1 is twice (10.3%) that of sample 2 (5.3%). The equivalent diameter of a majority of pores is less than 0.027 mm and their pore size distribution is unimodal right-hand asymmetrical in the case of both samples. In relations to numerical permeability tests, the flow paths are in the few privileged directions where the pressure is uniformly decreasing. Nevertheless, there are visible connections in sample 1, as is confirmed by the homogenous distribution of particles in the pore space of the sample and demonstrated in the particle flow simulations. The estimated permeability of the first sample is approximately four times higher than that of the second one. The uniaxial compression test demonstrated the huge impact of even minimal heterogeneity of samples in terms of micropores: 4–5 times loss of strength compared to the undisturbed sample. The procedure presented shows the promising combination of microstructural analysis and numerical simulations. More specific calculations of lab tests with analysis of variable boundary conditions should be performed in the future.
EN
In the present paper we present the approach for modeling of the elastic behavior of open-cell metallic foams concerning non-uniform pore size distribution. This approach combines design of foam structures and numerical simulations of compression tests using finite element method (FEM). In the design stage, Laguerre-Voronoi tessellations (LVT) were performed on several sets of packed spheres with defined variation of radii, bringing about a set of foam structures with porosity ranging from 74 to 98% and different pore size variation quantified by the coefficient of pore volume variation, CV(V), from 0.5 to 2.1. Each structure was numerically subjected to uni-axial compression test along three directions within the elastic region. Basing on the numerical response, the effective Young’s modulus, Eeff, was calculated for each structure. It is shown that the Eeff is not only dependent on the porosity but also on the pore size variation.
EN
The main current of publication is focused around the issues and problems associated with the formation of composite materials with Cu matrix and reinforcing phases in the various carbon nanoforms. The core of the research has been focused on thermal conductivity of these composites types. This parameter globally reflects the state of the structure, quality of raw materials and the technology used during the formation of composite materials. Vanishingly low affinity of copper for carbon, multilayered forms of graphene, the existence of critical values of graphene volume in the composite are not conducive to the classic procedures of composites designing. As a result, the expected, significant increase in thermal conductivity of composites is not greater than for pure copper matrix. Present paper especially includes: (i) data of obtaining procedure of copper/graphene mixtures, (ii) data of sintering process, (iii) the results of structure investigations and of thermal properties. Structural analysis revealed the homogenous distribution of graphene in copper matrix, the thermal analysis indicate the existence of carbon phase critical concentration, where improvement of thermal diffusivity to pure copper can occur.
EN
This paper addresses the issue of the quantitative characterization of the structure of the calibration model (phantom) for b-matrix spatial distribution diffusion tensor imaging (BSD-DTI) scanners. The aim of this study was to verify manufacturing assumptions of the structure of materials, since phantoms are used for BSD-DTI calibration directly after manufacturing. Visualization of the phantoms’ structure was achieved through optical microscopy and high-resolution computed microtomography (µCT). Using µCT images, a numerical model of the materials structure was developed for further quantitative analysis. 3D image characterization was performed to determine crucial structural parameters of the phantom: porosity, uniformity and distribution of equivalent diameter of capillary bundles. Additionally calculations of hypothetical flow streamlines were also performed based on the numerical model that was developed. The results obtained in this study can be used in the calibration of DTI-BST measurements. However, it was found that the structure of the phantom exhibits flaws and discrepancies from the assumed geometry which might affect BSD-DTI calibration.
EN
This paper presents for the first time X-ray computed microtomography (μCT) analysis as a technique for Silurian graptolite detection in rocks. The samples come from the Jantar Bituminous Claystones Member of the Opalino core, Baltic Basin, northern Poland. Images were obtained with spatial resolution of 25 μm, which enabled the authors to create a 3-D visualization and to calculate the ratio of fissure and graptolite volume to the total sample volume. A set of μCT slices was used to create a 3-D reconstruction of graptolite geometry. These μCT slices were processed to obtain a clearly visible image and the volume ratio. A copper X-ray source filter was used during exposure to reduce radiograph artifacts. Visualization of graptolite tubaria (rhabdosomes) enabled Demirastrites simulans to be identified. Numerical models of graptolites reveal promising applications for paleontological research and thus for the recognition and characterization of reservoir rocks.
EN
The present study concerns numerical simulations and experimental measurements on the influence of inlet gas mass flow rate on the growth rate of aluminum nitride crystals in Metalorganic Vapor Phase Epitaxy reactor model AIX-200/4RF-S. The aim of this study was to design the optimal process conditions for obtaining the most homogeneous product. Since there are many agents influencing reactions relating to crystal growth such as temperature, pressure, gas composition and reactor geometry, it is difficult to design an optimal process. Variations of process pressure and hydrogen mass flow rates have been considered. Since it is impossible to experimentally determine the exact distribution of heat and mass transfer inside the reactor during crystal growth, detailed 3D modeling has been used to gain insight into the process conditions. Numerical simulations increase the understanding of the epitaxial process by calculating heat and mass transfer distribution during the growth of aluminum nitride crystals. Including chemical reactions in the numerical model enables the growth rate of the substrate to be calculated. The present approach has been applied to optimize homogeneity of AlN film thickness and its growth rate.
8
Content available remote Design of open-porous materials for high-temperature fuel cells
EN
Microstructure is one of the major factors influencing material properties. It is especially important for open-porous materials dedicated to catalytic applications, where fraction of pores, their size distribution and specific surface influence the diffusion of reactants and the kinetics of catalytic reactions. In these studies the numerical models of the microstructure of open-porous electrodes for molten carbonate fuel cell (MCFC) are presented. The models presented here simulate fabrication routes for real materials, including mixing of powders, tape casting and sintering processes. The substrate powders are represented by spheres with defined size distribution. Mixing and compaction of powders with polymeric binder is simulated by a granular model implemented in LAMMPS code. In the next step the polymeric phase represented by fine particles and larger porogen addition is removed to form pores. The sintering process is simulated by geometry smoothing, which results in sphere aggregation. The models presented here were compared with micro computed tomography (µCT) 3D images of real MCFC materials. Quantitative analysis of µCT images was performed and it was demonstrated that algorithms used in these studies make it possible to design materials with the desired porous microstructure.
PL
W artykule przedstawiono metodykę badań próbek z horyzontów perspektywicznych dla eksploatacji łupków gazonośnych z polskiej części basenu bałtyckiego. Do badań wykorzystano wysokorozdzielczą mikrotomografię komputerową (µCT) oraz pomiar czasu przejścia fal ultradźwiękowych przez próbki. Uzyskany rozmiar piksela obrazu µCT dla próbek o większych rozmiarach wynosił 25 µm, natomiast dla niewielkich fragmentów próbek było to 5 µm. W badaniach ultradźwiękowych czynnikiem o dominującym wpływie na uzyskiwane wyniki okazała się szczelinowatość, która oddziaływała tłumiąco na propagację fal. Na podstawie analizy µCT określono procentowy udział szczelin w próbkach (średnia 0,82%) oraz przekroje przedstawiające strukturę wewnętrzną próbek z morfologią szczelin. Na podstawie prędkości propagacji fal ultradźwiękowych przez próbki obliczono dynamiczne parametry modułu Younga (zakres wyników 22÷57 GPa) oraz współczynnika Poissona (0,21÷0,40). Otrzymane wyniki wskazują na wysoką przydatność stosowania analiz ultradźwiękowych oraz wysokorozdzielczej tomografii komputerowej jako badań uzupełniających się.
EN
The article presents the methodology of characterization research of samples from prospective horizons for the exploitation of shale gas from Polish part of the Baltic Basin. High-resolution computed microtomography (μCT) and ultrasonic technique were used for the analysis. The resulting pixel size of μCT image for larger samples were 25 microns, while for small fragments of samples pixel size were 5 microns. In ultrasonic tests, fissures had a dominant impact on acoustic waves propagation. Extensive fissures surface resulted in attenuation of ultrasonic waves. Based on the μCT analysis, percentage content of fissures in the samples (average 0.82%) were determined. Furthermore a cross-section of specimens revealed the internal structure and morphology of fissures. Dynamic parameters of Young’s modulus (range 22÷57 GPa) and Poisson’s ratio (0.21÷0.40) were calculated, by converting the process of propagation velocity of ultrasonic waves through the samples. Results indicate the suitability of the use of ultrasonic analysis and μCT as complementary tests.
PL
Artykuł przedstawia wyniki wykorzystania wysokorozdzielczej mikrotomografii komputerowej w analizie strukturalnej oraz ilościowej przestrzeni porów i szczelin w piaskowcach mioceńskich. Dodatkowo wykonano badanie przepuszczalności analizowanych skał. Próbki zostały pobrane z odwiertu S-3, zlokalizowanego we wschodniej części zapadliska przedkarpackiego. W celu przeprowadzenia badania wykonano dwie serie naświetlania rentgenowskiego próbek. Pierwszy zestaw próbek został wytypowany dla uzyskania przestrzennego rozkładu ziaren, porów oraz szczelin. Długość boku woksela (tzn. najmniejszego elementu objętości) w tym etapie badań wynosiła około 26 μm. Drugi zestaw naświetlania został wykonany dla zobrazowania elementów strukturalnych o wielkościach od około 3 μm do 26 μm oraz cech petrofizycznych. Wynikiem przeprowadzonych badań jest charakterystyka analizowanych skał, która umożliwia podział próbek na dwie grupy. Pierwsza grupa próbek posiada cechy strukturalne oraz petrofizyczne typowe dla skał złóż konwencjonalnych, natomiast druga grupa – dla skał złóż typu niekonwencjonalnego. Właściwe rozpoznanie parametrów petrofizycznych każdego typu złoża stanowi kluczowy element optymalizacji procesu jego udostępniania.
EN
The article presents results of high-resolution computed microtomography use in the structural analysis and quantification of pores and fractures in Miocene sandstones. Furthermore, the permeability studies of rocks were performed. Miocene samples were taken from well S-3, located in the eastern part of the Carpathian Foredeep. For the aforementioned analysis two series of X-ray irradiation were performed. The first set of samples was selected to obtain the spatial distribution of grains, pores and fractures. At this stage of the study, the length of the voxel side amounted to approx. 26 μm. The second set of X-ray exposure was performed to reveal structural elements and petrophysical characteristics of sizes ranging from approx. 3 μm to 26 μm. The result of performed characteristics is the division of samples into two groups. The first group of samples has structural and petrophysical features of rocks typical for conventional reservoir deposits, while the second – for the unconventional type. Appropriate identification of petrophysical parameters of the formation is a key element for the optimization of the reservoir development.
EN
In the present paper the quantitative relationship between the heat and mass transfer in the Aixtron VP508 hot wall CVD reactor and the epitaxial growth of silicon carbide is determined. The aim of this study was to estimate optimal process conditions for obtaining monocrystalline silicon carbide epi-layers with the most homogenous thickness. Since there are many parameters influencing reactions on the crystal area, such as temperature, pressure, gas flow and reactor geometry, it is difficult to design an optimal process. Detailed 3D modeling was used to gain insight into the process conditions, as it is problematic to experimentally determine the exact distribution of heat and mass transfer inside the reactor during epitaxial growth. Numerical simulations allow one to understand the process by calculating the heat and mass transfer distribution during the epitaxial growth of silicon carbide. The present approach was applied to enhance the performance of the Aixtron VP508 reactor.
EN
The paper presents the spectrum of methods and results for design of structures, which are frequently applied in numerical simulations of properties and processes taking place in cellular materials. The methods described here are universal for many applications at various length-scales. They can be efficiently applied for complex cellular structures such as polycrystals or foams, where the elements (grains or pores) are distributed and shaped in a controlled way. The digital material representations created by these methods can be used for a number of numerical techniques such as: Molecular dynamics (MD), Monte Carlo (MC), Cellular Automaton (CA), Finite Element Method (FEM) or Finite Volume Method (FVM). The examples of structures consisting of atoms, fields or finite elements are presented in this paper. The applications of such structures are demonstrated by the properties and processes relevant to the specific length scales.
PL
W artykule przedstawiono metody oraz wyniki projektowania struktur, które są stosowane do numerycznej symulacji własności i procesów występujących w materiałach komórkowych. Zaprezentowane metody mają charakter uniwersalny dla zastosowań w różnych skalach wymiarowych. Mogą być stosowane do takich materiałów jak polikryształy lub pianki, w których elementy (ziarna lub pustki) są rozłożone i ukształtowane w sposób kontrolowany. Cyfrowe reprezentacje materiału utworzone za pomocą zaproponowanych w pracy rozwiązań mogą stanowić podstawę dla takich numerycznych metod jak Dynamika Molekularna (ang. Molecular Dynamics - MD), Monte Carlo (MC), Automaty Komórkowe (ang. Cellular Automaton -CA), Metoda elementów Skończonych (ang. Finite Element Method - FEM) lub Metoda Objętości Skończonych (ang. Finite Volume Method - FVM). W artykule zaprezentowano przykłady struktur składających się z atomów, pól lub elementów skończonych. Przedstawiono również zastosowania tych struktur do opisu własności i procesów charakterystycznych dla różnych skal wymiarowych.
EN
The aim was to compare size readings for the same ceramic nanopowders as reported by different characterization methods. Capabilities of TEM, XRD and BET characterization techniques, such as size vs. size distribution output, crystalline phase resolution, ability of error estimation of the size as well as dispersion of size readings are briefly described.
PL
Celem prezentowanej pracy było porównanie odczytów wielkości cząstek dla takich samych nanoproszków ceramicznych otrzymanych za pomocą różnych metod charakteryzujących tę cechę. Zwięźle opisano możliwości technik charakteryzujących takich jak TEM, XRD i BET w odniesieniu do pomiaru wielkości i uzyskiwanego rozkładu wielkości ziaren, rozdzielania faz krystalicznych, zdolności oceny błędu oznaczenia wielkości ziarna i rozrzutu jej odczytów.
EN
The mechanical properties of materials depend on their structure. The significant influence of the grain size and grain distribution on flow stress in the polycrystalline materials (e.g. metals) has been observed. The value of yield point is usually predicted by the Hall-Petch relationship which was established experimentally for grain size from macro- to microscale level. However when the grain size reaches the nanometric size the relationship between grain size and flow stress is changing due to activation of grain boundary sliding mechanism. The grain boundaries have the considerable role for plastic deformation of the polycrystalline nano-materials which are characterized by a significant volume fraction of atoms at the grain boundaries. In order to model this influence quantitatively, two-phase finite element model was developed in which the generalized Hill potential theory for modeling the anisotropic plasticity of grain boundaries was used. The results of numerical simulations show the influence of different parameters on plastic deformation of nano-polycrystalline materials. The simulations were also applied to study grain size homogeneity effect on mechanical properties of nanometals.
PL
Właściwości mechanicznre materiałów są ściśle związane z ich budowa wewnętrzną. Wpływ wielkości ziaren i niejednorodności struktury na odkształcenie plastyczne materiałów polikrystalicznych (zwłaszcza metali) jest często rozważany w literaturze. Zmiana wartości granicy plastyczności określana zazwyczaj zależnością halla-Petcha (h-P0, jest zgodna z danymi eksperymentalnymi dla mikrometrycznych wielkości ziaren. W przypadku kiedy wielkość ziarna osiąga poziom nanometryczny zależność H-P przestaje obowiązywać, co wiąże się między innymi z aktywacją mechanizmu odkształcenia, jakim jest poślizg po granicach ziaren. Znaczący udział objętościowy atomów umieszczonych w obszarach pomiędzy poszczególnymi ziarnami powoduje, że granice ziaren pełnią decydującą rolę w odkształceniu nanomateriałów. W celu ilościowego opisu wpływu właściwości granic ziaren. Wyniki symulacji ilustrują wpływ szeregu parametrów na odkształcenie materiałów nanokrystalicznych.
15
Content available remote Image based analysis of complex microstructures of engineering materials
EN
The paper presents various methods for quantitative description of material structures. The main focus is on direct methods of description based on image analysis. In particular, techniques for the estimation of the size, shape and spatial distribution of structural elements observed by different microscopic techniques are described. The application of these methods for the characterization of the structures of engineering materials is demonstrated on a stainless steel used in petrochemical installations. It is shown that the methods applied are useful for the assessment of service degradation of materials.
16
Content available remote Application of image analysis for characterization of powders
EN
A number of currently developed and produced modern multi-functional materials are to a large extent based on the use of powders. Powders with precisely characterized size, size distribution, shape and surface are used directly (e.g. catalysis) or to fabricate novel ceramics, metals and composites. Description of morphology of powders, both in micro- and nano-scale, could be obtained by the means of modern stereological methods supported by computerized image analysis. These methods can be used to describe size, shape, surface topography for both the aggregates and agglomerates and single crystallites. Stereological methods supported by computerized image analysis of high-resolution electron microscope images are becoming an important tool of modern powder-related materials science. The present work demonstrates the possibility of using such methods in determining the basic stereological parameters characterizing the morphology of the ceramic powders in micro- and nano-scale.
17
Content available remote Wpływ rozkładu wielkości ziarna na właściwości mechaniczne nanometali
PL
Właściwości mechaniczne materiałów zależą od mechanizmów odkształcenia plastycznego, które z kolei determinowane są przez ich strukturę. W przypadku metali istotnym elementem struktury są granice ziaren, które w przeszłości traktowane były jako defekty dwuwymiarowe. Nanomateriały wyróżniają się na tle konwencjonalnych materiałów dużym udziałem atomów znajdujących się na granicach ziaren. Oznacza to, że ich opór przy odkształceniu plastycznym należy analizować w kategorii odkształcenia akomodowanego przez granice i wnętrza ziaren. W artykule przedstawiono (na przykładzie metali) wpływ wielkości ziaren na właściwości mechaniczne nanomateriałów. Na podstawie rozważań biorących pod uwagę "kompozytową" budowę nanometali oraz stochastyczne cechy procesu odkształcenia plastycznego, wykazano możliwość wystąpienia odwrotnej zależności Halla-Petcha. Omówiono także efekt rozproszenia wielkości ziaren w nanomateriałach otrzymanych różnymi metodami rozdrobnienia struktury i konsolidacji proszków.
EN
Mechanical properties of engineering materials are controlled by mechanisms of plastic deformation. These mechanisms are, to the high degree, determined by the microstructure of materials. In the case of metals grain boundaries are important structural elements, which in the past were considered as two-dimensional defects. In nanomaterials the fraction of atoms at grain boundaries is much higher than in traditional polycrystals. It implies that, plastic deformation must be studied in terms of its accommodation by the grain boundaries and grain interiors. In this work the influence of grain size on mechanical properties of nanometals has been investigated. The occurrence of the inverse Hall-Petch relation is explained on the basis of the assumption of the composite-like character of grain boundaries and grain interiors. The grain size dispersion effect on the flow stress in nanometals, subjected to severe plastic deformation (SPD) is also addressed.
EN
The present paper shows the possibility of fabrication, under high pressure, of composites with percolated structure from alumina powder coated with nanoparticles of Ni-P to electroless nickel plating process. This process leads to either uniformly dispersed nanoparticles of Ni-P (size range of 10-100 nm) or thin nanometric layers covering the entire grain surface of the ceramic powder. By high pressure sintering one can obtain two types of nanocomposites from coated powders: (a) Al2O3/Ni-P particulate system and (b) ceramic metal percolated structure. Three kinds of composites with percolated structures were fabricated at different temperatures and investigated by SEM and TEM. The results were compared with model structures for percolated structures.
PL
Przedmiotem niniejszej pracy była struktura i właściwości żelaza po dużym odkształceniu plastycznym (epsilon log=10) realizowanym metodą przeciskania przez kanał kątowy ECAP (Equal Channel Angular Pressing). W pracy uzyskano opis jakościowy i ilościowy mikrostruktury dzięki wykorzystaniu metod stereologii i komputerowej analizy obrazów, oraz przeprowadzono badania właściwości mechanicznych w skali nano-, mikro-- i makroskopowej. Zastosowana metoda odkształcania doprowadziła do uzyskania żelaza o mikrostrukturze nanokrystalicznej. Towarzyszył temu kilkakrotny wzrost parametrów wytrzymałościowych w stosunku do stanu wyjściowego. Wykazano jednocześnie występowanie charakterystycznej niejednorodności struktury w skali mikro- i makroskopowej, która powoduje istotny rozrzut wartości parametrów opisujących właściwości mechaniczne.
EN
The aim of this study was to characterize microstructure and properties of iron after severe plastic deformation (epsilon log=10) via ECAP (Equal Channel Angular Pressing). The qualitative and quantitative description of microstructure was obtained using stereology and image analysis. Strength of the material was measured in the nano-, micro- and macro- scale. The results show that ECAP method used in this investigation brought about nanocrystalline microstructure in iron. This was accompanied by a significant increase in the strength of this material. Also characteristic, non-homogeneous structure in the micro- and macro-scale was revealed which influences the mechanical properties of the nano-iron obtained by ECAP.
EN
Transmission Electron Microscopy is an essential technique for imaging the microstructures at the nanometer scale. However, quantitative analysis of such images is not easy due to the nature of TEM contrast based on diffraction phenomena. A quantitative description of the microstructure of melt-spun AlY ribbons has been carried out in the present work. TEM observations have revelated randomly distributed and oriented spherical nanometer crystals. In order to describe quantitatively their size and shape, images under different diffraction conditions were recorded. These images have been analyzed using software for image analysis. the data have been compared to the results obtained by other techniques, such as X-ray diffractometry and differential scanning calorimetry.
PL
Transmisyjna Mikriskopia Elektronowa jest podstawową techniką obrazowania mikrostruktury materiałów w skali nanometrycznej. Jednakże analiza ilosciowa obrazów jest trudna ze względu na naturę kontrastu mikroskopowego opierającego się na zjawisku dyfrakcji elektronów w sieci krystalicznej materiału. W niniejszej pracy przedstawione są wyniki analizy ilościowej mikrostruktury stopu AlY w postaci taśmy otrzymanej na drodze przechodzenia ze stanu ciekłego. Obserwacje przeprowadzone za pomocą transmisyjnego mikroskopu elektronowego ujawniły przypadkowo rozmieszczone i zorientowane kryształy o wymiarach nanometrycznych. w celu ich ilościowego opisu zarejestrowano obrazy mikrostruktury przy różnych orientacjach preparatu wzgledem wiązki elektronów. Analizę obrazów przeprowadzono za pomocą programu komputerowego. Wyniki przeprowadzonych pomiarów porównano z wynikami otrzymanymi za pomoca dyfraktometru rengenowskiego oraz kalorymetru różnicowego.
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