Proton-exchange membrane fuel cells are one of the most promising energy conversion technologies for both automotive and stationary applications. Scientists are testing a number of solutions to increase the durability of cells, especially catalysts, which are the most expensive component. These solutions include, among others, the modification of the composition and morphology of supported nanoparticles, the platinum–support interface, and the support itself. A detailed understanding of the mechanism of platinum degradation and the subsequent improvement of the durability of the entire cell requires the development of methods for effectively monitoring the behavior of catalytic nanoparticles under various cell operating conditions. The Identical-Location Transmission Electron Microscopy (IL-TEM) method makes it possible to visually track structural and morphological changes in the catalyst directly. Because the tests are performed with a liquid electrolyte imitating a membrane, they provide better control of the degradation conditions and, consequently, facilitate the understanding of nanoparticle degradation processes in various operating conditions. This review is primarily intended to disseminate knowledge about this technique to scientists using electron microscopy in the study of energy materials and to draw attention to issues related to the characterization of the structure of carbon supports.

The study investigated the microstructures, residual stress and mechanical properties of double carbides cermet coatings manufactured on AZ31 magnesium alloy substrate by high-velocity oxy-fuel spraying (HVOF). The HVOF spraying was carried out using a JP 5000 TAFA spray system and the commercially available powder WC-20Cr3C2-7Ni was used to manufacture coatings. The variable process parameter was spray distance (320, 360 and 400 mm). The top surfaces of the manufactured coatings are typical for HVOF coatings and is relatively smooth. Nevertheless, some irregularities and voids are observed. All coatings exhibit dense structure with relatively low porosity level (below 3 vol.

In this paper, three commercial cermet powders, WC-Co-Cr, WC-Co and WC-Cr3C2-Ni, were sprayed by the High Velocity Oxy Fuel (HVOF) method onto magnesium alloy AZ31 substrate. The coatings were investigated in terms of their microstructure, phase analysis and residual stress. The manufactured coatings were analyzed extensively using optical microscopy (OM), X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM). Based on microstructure studies, it was noted that the coatings show satisfactory homogeneity. XRD analysis shows that in WC-Co, WC-Co-Cr and WC-Cr3C2-Ni coatings, main peaks are related to WC. Weaker peaks such as W2C, Co0.9W0.1, Co and W for WC-Co and W2C, Cr3C2 and Cr7C3 for WC-Cr3C2-Ni also occur. In all cermet coatings, linear stress showed compressive nature. In WC-Co and WC-Cr3C2-Ni, residual stress had a similar value, while in WC-Co-Cr, linear stress was lower. It was also proved that spraying onto magnesium substrate causes shear stress in the WC phase, most likely due to the low elastic modulus of magnesium alloy substrate.

Cermet double carbide coatings (WC-Cr3C2-Ni) were HVOF sprayed onto magnesium substrate. The variable parameter was spray distance (320, 360 and 400 mm). The microstructure of the coatings has been characterized by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). Additional, porosity and residual stress have been estimated. Phase composition of WC-Cr3C2-Ni cermet coatings consists of hexagonal WC carbide, as well as the Cr3C2 and Cr7C3 carbides. For the longest spray distance, minor presence of WC6O6 was detected, most likely as an effect of higher spraying distance, leading to partially oxidation of WC at powders particles boundaries. Comparing lattice parameters with model data it should be noted that no significant contribution of stress is present, due to minor changes in WC lattice parameters in comparison to ICDD data. It also should be noted that Cr7C3 carbide in WC-Cr3C2-Ni coating has different lattice parameters than ICDD data what shows its reactive nature. In obtained results it is clearly seen, that residual stress have the lowest values for coating sprayed from the shorter distance. This tendency is visible for both, linear and shear stress. The crystallite sizes are also the smallest for the shorter spray distance. Such fine structure shows a tendency to good redistribute of the thermal stress in the sprayed coating and also on the coating-substrate interface.

Soot is characterized by a multiscale structural organization; the only diagnostic tool that can give access to it is the transmission electron microscope (TEM). However, as it is a diffraction-based technique, TEM images only conjugate aromatic systems and, thus, it is particularly useful to combine it with electron energy-loss spectroscopy (EELS), which is able to provide quantitative information about the relative abundance of sp3 and sp2 hybridized carbon. In this paper, a method for the EELS spectrum analysis of carbonaceous materials, recently developed for electron-irradiated graphite and glassy carbon composition analysis, has been applied for the first time on soot samples, in order to test its performance in soot nanostructure study in combination with TEM and high-resolution TEM (HRTEM). Soot samples analyzed were collected in the soot inception region of premixed flames of different hydrocarbon fuels. EELS, in agreement with TEM and HRTEM, showed a quite disordered and heterogeneous structure for young soot, with a relatively low sp2 content and slight presence of fullerene-like structures, more evident in the case of methane soot hinting to the effect of more saturated aliphatic fuels on soot characteristics at soot inception.

Purpose: of this paper is to determine the effect of manufacturing conditions, especially milling time, on the microstructure and phase composition of CoFe2O4 cobalt ferrite. Design/methodology/approach: Cobalt ferrite (CoFe2O4) has been synthesised from a stoichiometric mixture of CoCo3 and α-Fe2O3 powders in a high energy planetary mill. Annealing at 1000°C for 6 hours after milling was used to improve the solid-state reaction. Calcinated samples were analysed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). The relationship between the milling time of powders, their microstructure, as well as their properties were evaluated. Particles size distribution and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) examination were also made. Findings: CoFe2O4 ferrites were successfully synthesized by mechanical alloying of α-Fe2O3 and CoCO3 powders. The powder particles had undergone morphological changes with the increasing milling time. However, the milling time does not affect the ferrite formation rate. It is expected that the improvement of fabrication parameters can further enhance the properties of cobalt ferrite presented in this work. Research limitations/implications: Contribute to research on the structure and properties of cobalt ferrites manufactured by mechanical alloying. Practical implications: The reactive milling and subsequently annealing is an efficient route to synthesise cobalt ferrite powder. However, using steel milling equipment risks powder contamination with iron and chromium from the vials and balls. Originality/value: The results of the experimental research of the developed ferrite materials served as the basis for determining material properties and for further investigation.

The paper presents the results of research studies involving the ceramic-metal tool materials with the deposited nitride coatings on the basis of aluminium, titanium and silicon. The cathodic arc evaporation with lateral rotating cathodes method was used for deposition of nanocrystalline, wear resistant nitride coatings - AlTiSiN type. Structural examinations are presented of the applied coatings and their support material made on the scanning electron microscope (SEM) and the scanning/transmission electron microscope (STEM). Chemical composition analysis as a function of the distance from the specimen surface, the so-called profile analysis, were carried out also. The structural analysis confirms that deposited multilayer coatings have dense microstructure without any visible porosity and delamination. It was found that the investigated coatings have nanocrystalline structure and consisting of fine crystallites even less than 6nm. Lattice deformations and numerous structural defects were also observed in the nanolayers. Depositing the AlTiSiN coatings results in the significant hardness increase within the range of 2252 +/- 256 to 2908 +/- 295 HV0.01.

This paper presents the results of the tests using high-resolution transmission electron microscopy (HRTEM) with both transmission and scanning modes, as well as energy-dispersive-spectroscopy (EDS) investigation of the AlSi9Cu alloy after laser surface remelting.The possibility of using a computer simulation to identify precipitates in the analysed alloy was also explored.The obtained results and computer simulations were compared.Moreover, this article presents the advantages of the computer aid in solving the diffraction patterns and precipitates in supercell simulations.

The advantages of giant magnetostrictive materials (GMMs) include the contactless energy supply, short‐time response to the signal, and a high value of the magnetomechanical coupling factor. This paper presents the variation of the magneto‐mechanical properties in the composite materials with a polyurethane matrix reinforced with Terfenol‐D particles. The particle size distribution of Terfenol‐D powders, the impact of initial stress on the composite' materials magnetostriction value, and the compression modulus under various magnetic field intensities were analyzed. It was found that the optimization of composite materials with polyurethane matrix reinforced with Terfenol‐D particles is possible, with particular consideration of the Terfenol‐D particles' size and share in the polyurethane matrix. POLYM. COMPOS., 38:797–802, 2017. © 2015 Society of Plastics Engineers

The paper presents the results of the crystallisation process of cast magnesium alloys based on the thermal-derivation analysis.The effects of aluminium content and cooling rate on the characteristic parameters of the evaluation of magnesium dendrites during solidification at different cooling rates were investigated by thermal-derivative analysis (TDA). Dendrite coherency point (DCP) is defined with a new approach based on the second derivative cooling curve. Solidification behaviour was evaluated via one thermocouple thermal analysis method. Microstructural evaluations were characterised by light microscope, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. This research revealed that utilisation of d(2)T/dt(2) versus the time curve methodology allows for analysis of the dendrite coherency point.

The paper presents the results of the crystallisation process of cast magnesium alloys based on the thermal-derivation analysis. The effects of aluminium content and cooling rate on the characteristic parameters of the evaluation of magnesium dendrites during solidification at different cooling rates were investigated by thermal-derivative analysis (TDA). Dendrite coherency point (DCP) is defined with a new approach based on the second derivative cooling curve. Solidification behaviour was evaluated via one thermocouple thermal analysis method. Microstructural evaluations were characterised by light microscope, X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy. This research revealed that utilisation of d2T/dt2 versus the time curve methodology allows for analysis of the dendrite coherency point.

The aim of this work was to observe the changes in the magnetomechanical properties of composite materials with different Tb 0.3 Dy 0.7 Fe 1.9 (Terfenol-D) powder particle-size distributions and varying volume fractions in the polyurethane matrix. The results show a direct relationship between the properties and the particle size of the Tb 0.3 Dy 0.7 Fe 1.9 powder: the increases in the particle-size distribution of the Tb 0.3 Dy 0.7 Fe 1.9 powder in the matrix amplify the magnetostrictive responses and the compressive modulus values. Moreover, it was found that the key role in efficiency of the transformation of magnetic energy into mechanical plays the initial compressing pre-stress.

The purpose of this work is the development of the aluminium alloy matrix composite materials using powder metallurgy technologies, including mechanical alloying and hot extrusion with the required properties and structure of the designed material. In this work halloysite nanotubes, was used as alternative reinforcement of metal matrix composites. Halloysite is a clayey mineral of volcanic origin, characterised by high porosity, high ion exchange, large specific surface and easy chemical, as well as mechanical treatment. High energy ball milling leads to uniform distribution of the halloysite reinforcing particles throughout the AlMg1SiCu matrix and simultaneously reduces the particle size. Proved microstructural changes influence the mechanical properties, especially microhardness, and compression yield, as well as wear resistant. The tribological analysis reveals that composite materials – irrespective of the measuring cycles number and load – are characterised by much smaller wear volume in comparison to the matrix material. The MMCs obtained as a result of mechanical alloying, cold compacting and hot extrusion are characterised with the microstructure of homogeneous distribution of halloysite particles in fine-grain matrix of AlMg1SiCu alloy, facilitate the obtainment of higher values of mechanical properties, compared to the base alloy. The composite materials reinforced with nanoparticles with 15% mass share are characterised by more than 180% higher yield strength and almost twice as higher microhardness compared to the matrix material. The analysis of the investigation results has confirmed that halloysite nanotubes can be applied as effective reinforcement in the MMCs.

Purpose: The paper presents a numerical model for the analysis of magnetostriction in composite materials in polymer matrix reinforced by Tb0.3Dy0.7Fe1.9 particles. The properties were determined by taking into account the applied stresses and magnetic field intensity. Design/methodology/approach: The finite element method for simulation the magnetostriction phenomenon was established by theoretical analysis based on experimental results. Findings: Thanks to the finite element method the numerical model has been formulated, enabling to simulate behavior of dynamically exciting rod with the nonlinear constituted model of magnetostrictive effect. The results received from experiments and simulations confirmed accuracy of this model for operating conditions, enabling a selection of magnetostrictive composite material with polymer matrix reinforced with Tb0.3Dy0.7Fe1.9 particles for specific application. Research limitations/implications: It was confirmed that using the finite element method can be a way for reducing the investigation cost. This paper proposes analysis which is efficient with respect to the number of simplifications in numerical model and accuracy of results. Practical implications: The proposed method could be helpful in the design process of magnetostrictive composite materials. Originality/value: Modelling based on the finite element method allows to simulating behavior of dynamically exciting rod with the nonlinear constituted model of magnetostriction phenomenon.

Purpose: The purpose of this study was to determine the thermal and electrical conductivity of composite materials with the polyurethane matrix reinforced with Tb0.3Dy0.7Fe1.9 particles with different particle size distributions and varying volume concentration. Design/methodology/approach: The investigated samples were obtained by casting of the composite materials with the polyurethane matrix reinforced with Tb0.3Dy0.7Fe1.9 particles. There were determined the samples density, electrical properties (by a resistivity measurements), thermal conductivity (by Physical Property Measurement System with thermal transport option), as well as the metallographic investigations (by stereo microscope). Findings: It was found from obtained results that the resistivity value for composite materials filled with larger particle size Tb0.3Dy0.7Fe1.9 was lower than the smaller particles size filled composites. Moreover, it may be noticed that thermal conductivity has an approximate value for different Tb0.3Dy0.7Fe1.9 particle size and the same its volume fraction in matrix. Simultaneously it was also observed that the thermal conductivity of the composite materials did not depend on the temperature within the tested range from 293 to 333 K. Research limitations/implications: Contributes to research on structure and physical properties of magnetostrictive composite materials with the polyurethane matrix reinforced with Tb0.3Dy0.7Fe1.9 particles. Practical implications: The polyurethane matrix in investigated composite materials causes growth of resistivity, limiting this way losses for eddy currents at the high operating frequency of the transducers. Originality/value: The obtained results show the possibility of manufacturing the magnetostrictive composite materials based on the Tb0.3Dy0.7Fe1.9 particles, with desired physical properties (including thermal and electrical one) in cost effective way in comparison to conventional giant magnetostrictive materials (GMM).

Purpose: The aim of this work is to obtain functional composite materials and to observe changes of magnetic properties of samples with different particle size distributions of magnetostrictive Terfenol-D (Tb0.3Dy0.7Fe1.9) powder. The influence of the concentration and particles size of the Tb0.3Dy0.7Fe1.9 on magnetic properties were investigated as function of applied magnetic field intensity, temperature and frequency. Design/methodology/approach: The investigated samples were obtained by casting of the composite materials with the polyurethane matrix reinforced with Tb0.3Dy0.7Fe1.9 particles. Magnetizations versus applied field curves were registered using the Oxford Instruments Ltd. vibrating sample magnetometer (VSM). Volume magnetic susceptibility was determined as temperature function on the Cahn RG automatic electrobalance (Ventron Instrumens, USA). Testing of the magnetic permeability in function of frequency was made using the Maxwell-Wien bridge system and the electrical properties were made by the resistivity measurements. Findings: Analysis establishes a direct connection between physical properties and structural characteristics of the Tb0.3Dy0.7Fe1.9 powder size: the increases of particle size distribution of Tb0.3Dy0.7Fe1.9 powder in composite materials amplify the magnetic responses and at the same time causing growth of resistivity values also. Moreover, in the investigated frequency range, no effect was observed of frequency on the susceptibility value for the particular material, which suggests possibility of using these materials in the high-frequency magnetic fields. Practical implications: The polyurethane matrix in investigated composite materials causes growth of resistivity, limiting these way losses for eddy currents at the high operating frequency of the transducers. Originality/value: The obtained results show the possibility of manufacturing the magnetostrictive composite materials based on the Tb0.3Dy0.7Fe1.9 particles, with desired physical properties (including electrical one) in cost effective way in comparison to conventional giant magnetostrictive materials (GMM).