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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.

The aim of the present paper was to investigate microstructure and texture evolution of two single crystals and polycrystal of Cu-8.5%at.Al material. All of mentioned samples were deformed by HE to achieve true strain ε = 1.17. For microstructure analyzes observations by transmission electron microscope (STEM) were done. Crystalline size for samples after SPD were determine using XRD method. The global texture measurements were done using Bruker D8 Discover diffractometer equipped in Cr radiation. Microstructure investigations revealed nanocrystalline structure in single crystals with initial orientations and and polycrystalline Cu-8.5%at.Al material after SPD. The global texture measurements have shown the stability of initial orientation of Cu-8.5%at.Al single crystal after HE, whereas the same SPD process strongly brakes up the orientation Cu-8.5%at. Al single crystal.

The influence of different types of precipitation on the corrosion behavior was investigated in three aluminum-siliconmagnesium alloys. The microstructures of the alloys were studied through optical (OM) and scanning electron microscopy (SEM). The structures consisted of an α-Al solid solution matrix, Si eutectic crystals, secondary phases AlFeSi and AlMgFeSi (Chinese script), as well as Mg2Si. The corrosion behavior was examined with the use of a potentiodynamic polarization test followed by a SEM surface analysis. The results indicate that all the analyzed samples were in the passive state and AlSi10Mg was less reactive in the corrosive environment.

The study investigated the properties of selected certified mixtures used to make wax patterns for the production of precision castings for the aerospace industry. In addition, an assessment of the recycled mixtures consisting of certified wax materials recovered during autoclaving was carried out. Hardness was tested via a proposed method based on penetration, creep related deformation, bending strength and linear contraction. The hardness was studied on laboratory specimens and patterns made with the use of injection molding equipment. For these patterns, linear contraction was estimated at variable pressure and for different temperature injection parameters. Deformations connected with creep and resistance were evaluated on cylindrical specimens. Differences in creep resistance in relation to the hardness were observed depending on the type of pattern mixtures. Recycled mixture has a greater resistance and smaller linear contraction than certified mixtures used for making sprue, raisers and other parts of filler system.

In this work technological properties of ceramic slurries based on silicon carbide were characterized. Silicon carbide and poly(vinyl alcohol) in an amount 6%, 10% and 15 wt. % as a solution were added to prepare the ceramic slurries. Solid phase content in ceramic slurries was 62, 5 wt.%. Plate weight test, pH, density, viscosity (measured by the Zhan 4# cup) and dynamic viscosity were investigated. Dipping test on wax model was done to measure adhesive properties. Characterization of SiC fillers powder was made by determination of grain size, density, chemical composition, Zeta potential and by use of scanning electron microscopy. Obtained results of ceramic slurries based on SiC meet standard specification in industrial investment casting and its properties are very promising for future application in investment casting of superalloys.

β-Fesi2 with the addition of b4C nanoparticles was manufactured by sintering mechanically alloyed Fe and si powders with Mn, Co, Al, p as p and n-type dopants. The consolidated samples were subsequently annealed at 1123 k for 36 ks. XRD analysis of sinters after annealing confirmed nearly full transformation from α and ε into thermoelectric β-Fesi2 phase. sem observations of samples surface were compliant with the diffraction curves. Tem observations allowed to depict evenly distributed b4C nanoparticles thorough material, with no visible aggregates and establish grain size parameter d2 < 500 nm. all dopants contributed to lower thermal conductivity and seebeck coefficient, with Co having strongest influence on increasing electrical conductivity in relation to reference FeSi2. Combination of the addition of Co as dopant and b4C nanoparticles as phonon scatterer resulted in dimensionless figure of merit ZT reaching 7.6 x 10-2 at 773 k for Fe0.97Co0.03 compound. Comparison of the thermoelectric properties of examined sinters to the previously manufactured of the same stoichiometry but without B4C nanoparticles revealed theirs overall negative influence. [ABSTRACT FROM AUTHOR]

The revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) is used for calculating the formation and migration energies of the vacancy in Ge, and the results are compared with those previously obtained using the local density approximation with the on-site Coulomb interaction U (LDA+U) approach and with other published results. It is demonstrated that using HSE06 gives a much more accurate electronic description of the vacancy and yields an excellent estimate of the activation energy of self-diffusion in Ge consistent with experimental data. The migration energies of the vacancy in different charge states calculated with the HSE06 approach agree well with the results of low-temperature infrared-absorption measurements. In contrast to previous results, the HSE06 calculations suggest that vacancies in Ge are multiple-level acceptors with levels located in the upper half of the bandgap. This can explain the observed high density of acceptor-like interface traps near the conduction band, pinning the Fermi level and inhibiting the formation of an inversion layer in n-channel devices in Ge. [ABSTRACT FROM AUTHOR]

Density functional theory with local density approximation including on-site Coulomb interaction has been used to calculate the formation energy of the neutral and charged vacancy in germanium as a function of the Fermi level. The calculations suggest that vacancies in germanium are multiple-level acceptors with a first level at 0.02 eV and a second level at 0.26 eV above the valence band maximum in agreement with published experimental data. The formation energies of the neutral and charged vacancies line up well with the experimental values estimated from quenching experiments. [ABSTRACT FROM AUTHOR]

ABSTRACT: In this paper, we show that using different concentrations of reagents, it is possible to produce gold nanoparticles with different morphology (size, shape). The color of obtained colloidal gold change from pink, violet to blue, and it corresponds to the shape change. The pink color corresponds to spherical nanoparticles and the blue one to a star shape. The mixture of those two types of nanoparticles result in a violet tone. It was also shown that kinetics of nucleation and growth process is controlled by the reaction on the gold atoms surface, i.e., comproportionation of Au(III) and Au(0) to Au(I), which can be inhibited by varying precursor and reductant concentration. [ABSTRACT FROM AUTHOR]

Background: The one of the most recent imaging technology is X-ray microtomography which allows non-invasive three-dimensional visualisation of structures. It also offers the opportunity to conduct a comprehensive quantitative analysis of the tested objects such as measuring the shares of the various phases, determining the material density and distribution of the size of pores and particles. The aim of the paper was to present an overview on the applicability and relevance of X-ray microtomography in the study of mineralised tissues of the teeth.Materials and Methods: The article is based on the most recent and significant literature and own observations.Results: The use of X-ray microtomography in dentistry has recently increased and includes, inter alia, the assessment of the density of minerals in enamel and dentin, the detection of demineralisation in an artificially and a naturally induced caries, the automatic measurement of the depth of cavities in dentin, the measurement of the amount of removed dentin in preparation of carious lesions by various methods, the assessment of microleakage around fillings and fissure sealants, cortical bone density measurement, evaluation of root canal morphology, comparison of the accuracy of root canal working and filling by various methods.Conclusions: X-ray microtomography offers within the analysis of mineralised tissues - complex structures of bone, teeth and biomedical materials, turn out to be indispensable since it opens new opportunities for cognitive and implementation research. [ABSTRACT FROM AUTHOR]

The aim of study was to investigate the effects of static magnetic fields [1 mT (miliTesla), 5 and 10 mT] on Saprolegnia parasitica growth, development, and cytotoxicity in the infection of trout eggs in hatcheries under laboratory and industrial conditions. The egg envelope (SEM) structures resulting from infection with and development of S. parasitica are also presented. S. parasitica mycelium was cultured on a microbiological medium SDA in Petri dishes (4 ± 0.2°C, 97% humidity) exposed to a magnetic field and in a control, to assess the mycelium growth rate. Effects of the magnetic field on cytotoxicity of S. parasitica after a 21-day incubation on SDA medium were analyzed using the colorimetric cytotoxicity test MTT. Eggs of brown trout Salmo trutta were infected with S. parasitica by inoculum and incubated in glass vessels (4 ± 0.2°C) in a magnetic field and a control. The degree of mycelium invasion of the egg envelopes and the percentage of egg mortality were recorded daily thoughout the period of embrionic development. The magnetic field effects on brown trout eggs infected by wild strains of fungus-like organisms (FLO) in the hatchery (4°C ± 0.1) were also investigated. Changes in the structure of brown trout egg envelopes as a result of infection and development of S. parasitica were examined in a FIB/SEM. The effects of magnetic fields of 5 and 10 mT on slowing the growth of mycelium of S. parasitica in vitro were also observed. Determining biochemical properties of S. parasitica also showed the effects of the magnetic field in differentiating the cytotoxicity. All magnetic field values showed a distinct decrease from medium to low values of S. parasitica cytotoxicity; the most effective reduction was observed at 5 mT. Magnetic fields in all tested levels slowed development of the mycelium on the incubated trout eggs, resulting in a decrease in the number of eggs infected by S. parasitica and thus permitting a greater hatching success. Similar effects were observed in other hatching conditions where eggs were also exposed. No negative effects of magnetic field treatment on the condition of the newly-hatched larvae were observed. The SEM and FIB (Focused Ion Beam) analyses revealed penetration of S. parasitica via radial canals of the envelope. The magnetic field had no effect on the structure of hyphae or sporangia of S. parasitica, but did affect the growth rate of mycelium on the egg surface. [ABSTRACT FROM AUTHOR]

Surface functionalisation of carbon nanotubes (CNTs) provides possibility of employing them in the biomedical industry as drug/growth factor carriers improving healing of a patient after injury. Carbon nanotubes are also very perspective nanomaterials as reinforcement in composites because of their mechanical properties. In the present work, single wall CNTs (SWCNTs), single wall/double wall (SW/DWCNTs) and multiwall CNTs (MWCNTs) functionalised with -COOH, -OH and -NH2 groups were tested as ion carriers in electrodeposition and as reinforcements in the composite calcium phosphate coatings. In our research, new composite coatings with Ca/P ratios ranging from 1·0 to 1·50 were obtained during electrodeposition in electrolytic solutions containing -COOH functionalised SWCNTs and MWCNTs. Amorphous calcium phosphates were fabricated in electrolytic solutions containing -NH2 functionalised MWCNTs, while no coating was fabricated in electrolytes containing -OH functionalised SW/DWCNTs. The structure and kind of functionalised groups of CNTs had an influence on the type, morphology and thickness of electrodeposited calcium phosphate coatings. [ABSTRACT FROM AUTHOR]

The differences in the microstructure and texture of two Ni single crystals, with different initial orientations (100 and 110), and of polycrystalline nickel, before and after severe plastic deformation (SPD) produced by hydrostatic extrusion (HE), have been investigated. The crystals were deformed by a two-step HE process with a total deformation value of ε=1.2. The global texture, mechanical properties, and microstructure were examined after the deformation. In every investigated sample, the presence of 111 fibre texture was noted, while the starting orientation of a 100 Ni single crystal was preserved in 50% of the volume. The results obtained were compared with the relevant literature data. [ABSTRACT FROM AUTHOR]

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Synchrotron radiation micro-X-ray fluorescence and micro-X-ray diffraction analysis, micro-computed tomography and transmission electron microscopy were used to investigate the microstructure of turbine blades made of a second generation nickel based superalloy CMSX-4 manufactured by investment casting process via Bridgman technique. The dependence of microstructure on process parameters, among others, on the withdrawal rate was analysed. The results set the stage for optimising the microstructure of the blades in terms of their mechanical properties. [ABSTRACT FROM AUTHOR]

In this paper, we report the results of investigation of 9.5 µm AlGaAs/GaAs and strain compensated 4.7 µm AlInAs/InGaAs/InP QCLs. We also show the results for 9.5 µm lasers based on lattice matched AlInAs/InGaAs/InP structures. The developed GaAs/AlGaAs lasers show the record pulse powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the MBE growth process and by applying a high reflectivity metallic coating to the back facet of the laser. The 9.5 µm AlInAs/InGaAs/InP lasers utilize AlInAs waveguide and were grown exclusively by MBE without MOCVD regrowth. The short wavelength, strain compensated QCLs were grown by MOCVD. They represent state-of-the-art parameters for the devices of their design. For epitaxial process control, the atomic-force microscopy (AFM), high resolution X-ray diffraction (HR-XRD) and transmission electron microscopy (TEM) were used to characterize the morphological and structural properties of the layers. The basic electro-optical characterization of the lasers is provided. We also present results of Green's function modeling of mid-IR QCLs and demonstrate the capability of non-equilibrium Green's function (NEGF) approach for sophisticated but still computationally effective simulation of laser's characteristics. [ABSTRACT FROM AUTHOR]

SUMMARY The favourable scaffold for bone tissue engineering should have desired characteristic features, such as adequate mechanical strength and three-dimensional open porosity, which guarantee a suitable environment for tissue regeneration. In fact, the design of such complex structures like bone scaffolds is a challenge for investigators. One of the aims is to achieve the best possible mechanical strength-degradation rate ratio. In this paper we attempt to use numerical modelling to evaluate material properties for designing bone tissue engineering scaffold fabricated via the fused deposition modelling technique. For our studies the standard genetic algorithm was used, which is an efficient method of discrete optimization. For the fused deposition modelling scaffold, each individual strut is scrutinized for its role in the architecture and structural support it provides for the scaffold, and its contribution to the overall scaffold was studied. The goal of the study was to create a numerical tool that could help to acquire the desired behaviour of tissue engineered scaffolds and our results showed that this could be achieved efficiently by using different materials for individual struts. To represent a great number of ways in which scaffold mechanical function loss could proceed, the exemplary set of different desirable scaffold stiffness loss function was chosen. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The relationship between the activation energy and enthalpy, either in the presence or absence of a catalyst, is of particular importance. If a catalyst is present, the energy required for a given chemical reaction to go into transition state decreases, thereby decreasing the energy required to initiate the reaction. The dynamics of heterogeneous catalysis is still under discussion. The same applies to tribochemistry and/or tribocatalysis. It has been assumed that heterogeneous solid catalysts decrease the activation energy, reflected as apparent activation energy. The model presented elsewhere has been theoretically evidenced for the first time by reviewing the existing literature data concerning anisotropy features of the angular distribution of exoelectrons emitted from perturbed surfaces. Metal-insulator-metal thin film sandwich structures are of particular interest in this paper. Other evidence supporting the model is also discussed such as the anisotropic desorption emission from a surface during catalytic processes. The conclusions of this work have been applied in practice to design specific measurement techniques and devices for estimating the angular distribution of electrons triboemitted from solid catalyst materials under sliding contact in a high-vacuum tribometer. [ABSTRACT FROM AUTHOR]

The paper presents results of studies of structure and properties of the NiAl + FeAl type diffusion layers fabricated on 316L steel (00H17N14M2) by the chemical vapour deposition using aluminium chloride (AlCl3) in a hydrogen atmosphere as a carrier gas. The layers were examined using light and scanning electron microscopy. Chemical composition analyses were carried out by EDS and phase content was investigated by XRD. Corrosion resistance was tested using the potentiodynamic method in 0.5 M NaCl, and layer/structure adhesion was tested by the scratch test. The results obtained indicate that the 50 µm thick layers fabricated on the 316L steel substrate show very good adhesion combined with very good corrosion resistance. [ABSTRACT FROM AUTHOR]

Decomposition of ethane over cobalt nanoparticles was studied in isothermal conditions in the temperature range 375-500 °C. The obtained products were examined using XRD and HR-TEM techniques. Carbon deposit was reduced by a flow of hydrogen in the temperature range 500-575 °C. The kinetics of hydrocarbon decomposition and carbon deposit hydrogenation were investigated using the thermogravimetry method. The values of apparent activation energies of these processes have been determined. [ABSTRACT FROM AUTHOR]

Identification of the elastoplastic material model for C–Mn steel, using finite element model of micro-indentation test developed by the authors and proposed algorithm of inverse analysis, is one of the objectives of the project. The micro-indentation experiment is widely described in the present paper, especially those parts, which are meaningful in getting input data for direct, further application in the numerical model of micro-indentation test and in the inverse procedure. Finite element solution connected with the inverse algorithm, which is based on the simplex method, is used to search for the unknown parameters of material model. Validation of the developed inverse algorithm is the particular objective of the present work. The present paper shows that material model determined using the inverse analysis is in agreement with that obtained from the tensile test. The results coincide also with the data available in the literature. [ABSTRACT FROM AUTHOR]

Application of the phase imaging and force modulation SPM techniques for description of the dispersion of multiwalled carbon nanotubes (MWCNTs) in polyol (polyester diol- PED) matrix is presented. The MWCNTs-PED mixture is used to prepare polyurethane (PUR) nanocomposites. Dispersion of MWCNTs in PUR depends on the dispersion of carbon nanotubes in polyol. It is very important to evaluate the degree of homogeneity of the investigated materials. The phase imaging and force modulation microscopy connected with tapping mode allow collecting not only topography images but also images of mechanical properties of a material (hardness, adhesion, friction). By using these SPM modes, it is possible to distinguish structural elements of the mixture and hence to obtain direct information about the distribution of MWCNTs in PED matrix. [ABSTRACT FROM AUTHOR]

The corrosion resistance of Type 316 (UNS S31600) austenitic stainless steel in an aggressive environment containing Cl[sup−] ions in the as-received state and after nanostructuralization caused by severe plastic deformation by hydrostatic extrusion (HE) was investigated. Transmission electron microscopy (TEM) was used to examine the structural changes introduced by the HE process. The effects of the surface oxide film on the corrosion resistance of Type 36 stainless steel in a borate buffer + 0.1 M sodium chloride (NaCl) solution and in a saline solution of 0.15 M NaCl were investigated using potentiodynamic polarization. Surface analytical techniques such as scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to characterize the morphology and chemistry of the surface before and after HE. [ABSTRACT FROM AUTHOR]

Nickel and copper were subject to severe plastic deformation at room temperature, using hydrostatic extrusion (HE) and equal-channel angular pressing (ECAP). The maximum deformation was 13.5 in nickel and 22.3 in copper. These deformations were obtained by each of the techniques separately and by their combination. It has been found that the combined HE and ECAP deformation greatly increases the homogeneity of the microstructure and improves considerably its mechanical properties comparing with a single technique. After the combined treatment, the grain size of both copper and nickel was of the order of 100 nm. The experiments have shown that the combination of HE and ECAP techniques permits producing homogeneous nanocrystalline materials of large volumes. [ABSTRACT FROM AUTHOR]

The paper reports on finite element method (FEM) analysis of Cu--SiC composites behaviour under cyclic loading conditions. In order to emphasise the influence of materials description on following results, there were two hardening rules used to describe the plastic behaviour of the matrix: (a) simple isotropic and (b) combined isotropic-kinematic. Reinforcing ceramics was assumed to be perfectly elastic. The analysis was carried out for Cu--SiC fibre--reinforced lamina composite. The fibre volume fracture was assumed to be 20%. The modelling was based on representative volume element (RVE) geometry. Additionally, the effect of thermal residual stresses was taken into account and its influence upon the Cu--SiC composite mechanical behaviour was clarified. [ABSTRACT FROM AUTHOR]

Samples of nanocrystalline iron were carburised with ethylene and next reduced with hydrogen. Both carburisation and reduction were monitored by the thermogravimetry. The obtained samples were characterised using X-ray diffraction, high-resolution transmission electron microscopy and ferromagnetic resonance. The samples after carburisation contained cementite (Fe3C) and carbon deposit (nanofibres and nanotubes). As the result of reduction with hydrogen at 450 or 500 °C cementite was reduced to iron. A major part of carbon was also hydrogenated, only thin carbon nanotubes remained. The FMR spectra of the prepared samples were recorded at room temperature. The sample after carburisation has shown a wide FMR line with weak intensity while the resonance field has been shifted to lower magnetic field. This spectrum has been attributed to the presence of cementite. The FMR lines corresponding to samples after reduction are more intense and are connected with the presence of a-Fe nanoparticle conglomerates. [ABSTRACT FROM AUTHOR]

The structural parameters and the elastic stiffness coeffcients of Ni3Al and TiAl under a pressure P were computed by the ab initio pseudopotential method with the plane-wave basis set and the generalized gradient approximtion (GGA). The pressure dependence of the elastic constants is an important characteristics for both Ni3Al and TiAl as these materials are frequently subject to varying pressures during processing. The bulk modulus was also calculated. Stress-strain relationships were used to obtain the elastic constants. The results are in good agreement with the available experimental data. [ABSTRACT FROM AUTHOR]

The goal of the present work is to demonstrate that a bulk, ultra-fine grained microstructure can be obtained by the hydrostatic extrusion process of a 99.5% technical purity of nickel. Deformation with the total true strain of 3.8 was performed at room temperature to a wire 3 mm in diameter. Microstructure was characterized by light microscopy, TEM, XRD and mechanical properties. Hydrostatic extrusion was shown to be an effective method of severe plastic deformation, which allows ultra-fine grained structures to be obtained within the deformed material. After cumulative hydrostatic extrusion, the yield stress tripled, reaching a maximum of 812 MPa with a moderate elongation of 13%. A mean subgrain size of 200 nm was observed, with a considerable diversity in the size of individual grains. For the final passes of hydrostatic extrusion, a slight decrease in the mechanical properties was observed, accompanied with an increase in crystallite size. This is explained in terms of thermal softening processes activated by the heat generated during hydrostatic extrusion. [ABSTRACT FROM AUTHOR]

The present study was concerned with multilayer composites of the .../Al2O3/Al2O3 + x vol. % Mo/Al2O3 type produced by tape casting. Molybdenum content in individual layers of the composites varied from 4 to 28 vol. %. The densities, porosities, Young moduli, bending strengths, and fracture toughnessess of the composites were measured. The residual stress in the layers was analysed by FEM. Investigations of the composite microstructures revealed: α-Al2O3, Mo, and Mo2C. After sintering, the composites had a high relative density (the porosity Pc did not exceed 10%). As the volumetric content of molybdenum increased, the densities of the composites increased, whereas their Young moduli E decreased. The highest values of the bending strength σb (819 MPa), stress intensity factor K1C (7.75MPa⋅m1/2), and cracking energy γ (102 J/m²) were obtained in the composite with the 14 vol. % molybdenum content. The strength σb and fracture toughness of this composite were more than two times higher than those of Al2O3, and the cracking energy six times. These values can be partly explained in terms of the compressive residual stress in the composite layers. [ABSTRACT FROM AUTHOR]