Synthesis of cobalt oxide aerogels and nanocomposite systems containing single‐walled carbon nanotubes

The synthesis and characterization of porous nanostructured cobalt oxide (Co₃O₄) aerogels using epoxide addition method is described. Cobalt‐containing monoliths were obtained by sol–gel processing of an alcoholic cobalt chloride solution with propylene oxide as the gelation agent. The alcogels were dried by supercritical CO₂ fluid extraction to obtain the highly porous amorphous cobalt (II) aerogels. To enhance and control the structural properties of the aerogels, single‐walled carbon nanotubes (SWCNT) were incorporated into the cobalt (II) aerogel network to form a homogenous composite material. The resulting materials were characterized using powder X‐ray diffraction and nitrogen adsorption/desorption analysis. The detailed microstructure of aerogel networks was investigated using scanning and transmission electron microscopy, which showed significant structural changes induced by the incorporation of SWCNT to the cobalt aerogel. Annealing of the aerogel materials at 600°C yields a highly crystalline well‐faceted Co₃O₄ network SCANNING 31: 132–138, 2009. © 2009 Wiley Periodicals, Inc.     

Study of two tungstates Ca0.5Cd0.5WO4 and Ca0.2Cd0.8WO4 by transmission electron microscopy

To better understand the role of crystal structures and local disorder in the photonic properties of the system (1 ? x)CaWO₄ ? xCdWO₄ with 0 < x < 1, two specific phases with compositions x = 0.5 (scheelite phase) and 0.8 (wolframite phase) have been studied by scanning and transmission electron microscopies. High‐resolution electron microscopy images and image simulations, associated with X‐ray diffraction data, allowed confirming the lattices and space groups I4₁/a and P2/c of the two scheelite and wolframite phases, at the local scale. The electron microscopy data show the existence of a high degree of crystallization associated with statistical distribution of Ca or Cd atoms on a Ca_1?xCd_x site in each lattice.     

Electron and light microscopy studies on the domain structures of Zn3B7O13Cl, Zn3B7O13Br and Zn3B7O13I ferroic boracites

The domain structures of Zn₃B₇O₁₃Cl, Zn₃B₇O₁₃Br and Zn₃B₇O₁₃I boracite single crystals were studied by means of polarized light in conjunction with electron microscopy. Single crystals of the three compositions were grown by chemical transport reactions in closed quartz ampoules, at a temperature of 900 °C and were examined by polarizing optical microscopy (PLM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For both PLM and SEM, the same as‐grown samples were used without having to resort to metallization of the crystal faces. For TEM the single crystals were crushed and mounted on holey carbon films. Comparative electron microscope images were useful for revealing the domain structure of these ferroelectric/ferroelastic materials previously observed between the crossed polars of an optical microscope. X‐ray diffraction analysis of the pulverized crystals was performed for this triad of halogen boracites containing zinc as a common metal.     

The effect of an Ni–Cr protective layer on cyclic oxidation of Ti3Al

The effect of an 80Ni?20Cr (at.%) metallic coating on the cyclic oxidation behaviour of a Ti₃Al‐based alloy with the composition Ti?25Al?11Nb (at.%) was investigated in this study. Cyclic oxidation tests were carried out in air at 600 °C and 900 °C for 120 h. For one cycle test, the specimens were held for 24 h at test temperature and then furnace‐cooled to room temperature. The oxidation rate was determined by plotting the mass gain per unit surface area of the specimen vs. exposure time. The morphology and composition of the oxidation products were characterized on the cross‐section of the specimens by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and atomic force microscopy. The oxidation scale forms during exposure at both 600 °C and 900 °C. TiO₂ is the main oxide component, whereas the Al₂O₃ layer appears only discontinuously. The remarkable improvement in oxidation resistance at 900 °C was attributed to the chemical composition and structure of the scale formed on the 80Ni?20Cr coating.     

TEM and HREM study of Al3Zr precipitates in an Al-Mg-Si-Zr alloy

The structure of Al₃Zr precipitates in Al‐1.0Mg‐0.6Si‐0.5Zr (in wt.%) alloy was investigated using conventional transmission electron microscopy (TEM) and high‐resolution TEM (HREM). After annealing of the alloy in the temperature range 450–540 °C, spherical precipitates of metastable L1₂‐Al₃Zr phase appeared nearly homogeneously within the matrix, and elongated particles were found at grain boundaries. L1₂‐structured Al₃Zr were about 20–30 nm in diameter and coherent with the matrix. Inside some of them, planar faults parallel to {100} planes were revealed by use of HREM. Most probably, these faults are an indication of the transition stage of transformation to the stable D0₂₃‐type Al₃Zr phase. The elongated precipitates (about 100 nm) were identified as D0₂₂‐type Al₃Zr. Energy‐dispersive X‐ray analysis showed that they contain, apart from Al, mainly Zr with small amounts of Si. The substitution of Al by Si increased the stability of the D0₂₂‐Al₃Zr as compared with D0₂₃‐Al₃Zr.     

Independent trafficking of flavocytochrome b558 and myeloperoxidase to phagosomes during phagocytosis visualised by energy‐filtering and energy‐dispersive spectroscopy‐scanning transmission electron microscopy

When polymorphonuclear leukocytes (PMNs) phagocytose opsonised zymosan particles (OPZ), free radicals and reactive oxygen species (ROS) are formed in the phagosomes. ROS production is mediated by NADPH oxidase (Nox), which transfers electrons in converting oxygen to superoxide (O₂^?). Nox‐generated O₂^? is rapidly converted to other ROS. Free radical‐forming secretory vesicles containing the Nox redox center flavocytochrome b558, a membrane protein, and azurophil granules with packaged myeloperoxidase (MPO) have been described. Presuming the probable fusion of these vesicular and granular organelles with phagosomes, the translation process of the enzymes was investigated using energy‐filtering and energy‐dispersive spectroscopy‐scanning transmission electron microscopy. In this work, the primary method for imaging cerium (Ce) ions demonstrated the localisation of H₂O₂ generated by phagocytosing PMNs. The MPO activity of the same PMNs was continuously monitored using 0.1% 3,3′‐diaminobenzidine‐tetrahydrochloride (DAB) and 0.01% H₂O₂. A detailed view of these vesicular and granular structures was created by overlaying each electron micrograph with pseudocolors: blue for Ce and green for nitrogen (N).     

Transmission electron microscopy characterization of the erbium silicide formation process using a Pt/Er stack on a silicon-on-insulator substrate

Very thin erbium silicide layers have been used as source and drain contacts to n‐type Si in low Schottky barrier MOSFETs on silicon‐on‐insulator substrates. Erbium silicide is formed by a solid‐state reaction between the metal and silicon during annealing. The influence of annealing temperature (450 °C, 525 °C and 600 °C) on the formation of an erbium silicide layer in the Pt/Er/Si/SiO₂/Si structure was analysed by means of cross‐sectional transmission electron microscopy. The Si grains/interlayer formed at the interface and the presence of Si grains within the Er‐related layer constitute proof that Si reacts with Er in the presence of a Pt top layer in the temperature range 450–600 °C. The process of silicide formation in the Pt/Er/Si structure differs from that in the Er/Si structure. At 600 °C, the Pt top layer vanishes and a (Pt–Er)Si_x system is formed.     

Defects formed within hardness indenter interaction zone in Al2O3–ZrO2 composite

The Al₂O₃?10 wt% ZrO₂ composites were subjected to hardness tests using a Vickers diamond indenter up to 98.1 N. The microstructure observation using a transmission electron microscopy technique helped to identify up to four zones differing in defect level and character. The densest dislocation tangles, twins accumulation and frequent presence of three slip systems were found in regions that were in contact with the sides of the diamond pyramid. The second zone, characterized by two, or at least one, active slip systems, started at the bottom of the indentation mark and extended up to a distance comparable with the depth of indentation. In the third zone, with a thickness comparable to that above, only some α‐Al₂O₃ crystallites showed the presence of dislocations, whereas other crystallites were defect free. In the last zone the alumina crystals were left unaffected but the ZrO₂ crystallites showed twinning characteristic of strain‐induced transformation.     

Friction and wear behaviour of Sialon/ (Ca,Mg)‐Sialon with lubrication by coated PbS nanoparticles as oil additives

The friction and wear behaviour of Sialon/(Ca,Mg)‐Sialon with lubrication by liquid paraffin containing PbS nano‐particles coated with dialkyldithiophosphate or oleic acid as additives was investigated using an SRV ball‐on‐disc test rig. It was found that the addition of such nanoparticles reduced the friction coefficient of the friction couple irrespective of the concentration of the additive and the wear volume of (Ca,Mg)‐Sialon, especially under relatively high loads such as 150 N or more. X‐ray photoelectron spectroscopy and electron probe microanalysis revealed that a tribochemical film composed of PbSO₄, PbS₂O₃, PbSO₃, etc., was formed on the worn surface, and contributed to the lubricity of the PbS nanoparticles.     

In situ high temperature microscopy study of the surface oxidation and phase transformations in titanium alloys

Two popular commercial titanium alloys, Ti‐6Al‐4V and Ti‐6Al‐2Sn‐4Zr‐2Mo‐0.08Si, were used for in situ high temperature microscopy study. The experiments were performed on an optical microscope equipped with high temperature stage using both normal and florescence lights. Two kinds of experiments were performed, at continuous heating/cooling with different rates and in isothermal conditions at different temperatures. The changes taking place on the sample surface during the experiments were monitored. The morphology of the α?β?α phase transformation was recorded at different heat treatment conditions using the effect of thermal etching. An effect of sample surface oxidation and deoxidation was observed during continuous heating. The appearance and disappearance of ordered titanium oxides Ti₃O and Ti₂O are discussed based on the phase equilibrium diagram. The kinetics of the surface oxidation was monitored in both isothermal and continuous cooling conditions.     

Chemical reactions and morphological stability at the Cu/Al2O3 interface

The microstructures of diffusion‐bonded Cu/(0001)Al₂O₃ bicrystals annealed at 1000 °C at oxygen partial pressures of 0.02 or 32 Pa have been studied with various microscopy techniques ranging from optical microscopy to high‐resolution transmission electron microscopy. The studies revealed that for both oxygen partial pressures a 20–35 nm thick interfacial CuAlO₂ layer formed, which crystallises in the rhombohedral structure. However, the CuAlO₂ layer is not continuous, but interrupted by many pores. In the samples annealed in the higher oxygen partial pressure an additional reaction phase with a needle‐like structure was observed. The needles are several millimetres long, ～10 µm wide and ～1 µm thick. They consist of CuAlO₂ with alternating rhombohedral and hexagonal structures. Solid‐state contact angle measurements were performed to derive values for the work of adhesion. The results show that the adhesion is twice as good for the annealed specimen compared to the as‐bonded sample.     

Toughening and dry sliding wear resistance of Co3Mo2Si alloys

The MgZn₂ type Laves phase of Co₃Mo₂Si has very attractive super high hardness and covalent dominated bonding nature for wear resistance applications. To make it feasible for real application, its inherent brittleness was effectively balanced by toughening it with the ductile cobalt solid solution (Co_ss) by the laser melting process. The toughening effect was evaluated qualitatively by the observation of the indentation behaviors and the micro-hardness variations of the alloys. The wear properties of the Co_ss toughened Co₃Mo₂Si alloys were evaluated in the dry sliding wear test condition at room temperature. Results indicated that the Co_ss toughened Co₃Mo₂Si alloys have excellent combination of strength and ductility, and display exceptional wear property.     

Stoichiometry and valence measurements of niobium oxides using electron energy-loss spectroscopy

Qualitative and quantitative electron energy‐loss spectroscopy analyses have been performed on niobium and stable niobium oxides (NbO, NbO₂ and Nb₂O₅). At integration windows (Δ) greater than 75 eV, k‐factor analysis can be used to distinguish between the stoichiometry of the three oxides within 5.7% error. As seen in other metal oxides, with increasing oxidation state the metal ionization edges shift to higher energies relative to the O‐K edge. Normalized M_2,3 white‐line intensities show a strong correlation with 4d occupancy for each compound. The data are in correspondence with that observed in the literature for 4d transition metals using normalized L_2,3 white lines. Lastly, a distinctive energy‐loss near‐edge, structure of the O‐K edge was observed for each oxide, which could be used as a fingerprint for analysis of unknowns.     

Structural analyses of Nd-doped CeO2 thin films deposited by pulsed laser deposition

CeO₂ thin films doped with neodymium oxides for application to gas sensors have been elaborated by the pulsed laser deposition technique. The films were deposited on orientated Si (100) substrates with variable deposition times (t = 90, 180 and 360 s) and molar fractions of Nd₂O₃ (0, 6.5, 15, 21.5 and 27 at.%). The resulting Nd–CeO₂ thin films were characterized by means of X‐ray diffraction analysis, scanning electron microscopy and transmission electron microscopy equipped with EDS (Energy Dispersive Spectrometer) microanalysis. From X‐ray diffraction analyses, it is clearly established that the texture is modified by Nd additions. The preferred (111) orientations of the CeO₂ crystals change into the (200) orientation. The morphology of the CeO₂ grains changes from triangles, for pure CeO₂ thin films, to spherical grains for Nd‐doped films. In addition, cell parameter analyses from X‐ray diffraction data show that a partial chemical substitution of Ce by Nd should occur in the face‐centred cubic lattice of ceria: this should give rise to Ce_1‐xNd_xO_2?z phases with oxygen non‐stoichiometry.     

Interfacial reactions and silicate formation in highly dispersed Lu2O3– SiO2 system

Solid state interface reactions in highly dispersed Lu₂O₃– SiO₂ binary oxide system were studied at 600–1100 °C with X‐ray powder diffraction (XRD), high‐resolution transmission electron microscopy (HRTEM) and Fourier Transform Infrared spectroscopy (FTIR). The results show that at 600–900 °C an amorphous, nanometer thick Lu‐O‐Si layer covering SiO₂ particles exists in the system. At higher temperatures the breakage of the layer into amorphous islands occurs and crystalline silicates with various structures are formed. In particular, Lu₄[Si₃O₁₀][SiO₄] silicate, analogue of B‐type Dy – Tm disilicates, forms at 1000 °C.     

Real‐space observation of strong metal‐support interaction: state‐of‐the‐art and what's the next

The real‐space resolving of the encapsulated overlayer in the well‐known model and industry catalysts, ascribed to the advent of dedicated transmission electron microscopy, enables us to probe novel nano/micro architecture chemistry for better application, revisiting our understanding of this key issue in heterogeneous catalysis. In this review, we summarize the latest progress of real‐space observation of SMSI in several well‐known systems mainly covered from the metal catalysts (mostly Pt) supported by the TiO₂, CeO₂ and Fe₃O₄. As a comparison with the model catalyst Pt/Fe₃O₄, the industrial catalyst Cu/ZnO is also listed, followed with the suggested ongoing directions in the field.     

Properties and structures of Co-based metallic glasses

A fundamental study on Co-based metallic glasses has been conducted. The study focused on understanding the changes of the properties and structures of an Fe-B-Si glass as a function of Co, Co-Ni, Co-Mn, and Co-Ni-Mo additions. The separate addition of Co, Co-Ni, Co-Mn, and Co-Ni-Mo elements was successful in such a way that four new metallic glasses were produced. The compositions of the new glasses are Fe₆₆Co₁₈B₁₅Si₁, Co₆₆Fe₄B₁₄Si₁₅, Co₇₆Fe₂Mn₄B₁₂Si₆, and Co₆₉Fe₄Mo₂B₁₂Si₁₂. Consequently, an evaluation of the physical and magnetic properties was determined. Furthermore, the internal and surface structures of the glasses have been characterized by a transmission electron microscope (TEM), and a scanning tunneling microscope (STM), respectively. A comparison between the internal and surface structures of the glasses was carried out on both amorphous and crystalline forms. As a result, a correlation between the properties and structures of the glasses is established.     

A controlled atmosphere specimen holder for transmission electron microscopy

A controlled atmosphere specimen holder (CASH) has been developed for transmission electron microscopy (TEM) experiments. It is designed for studying the specimen's microstructure before and after treatments in various gases (H₂, O₂, N₂, Ar, etc.) at temperatures up to 600°C. The experiments are carried out without exposing the specimen to the ambient atmosphere. No modification of the electron microscope itself is needed. The same area of the specimen can be easily located after each gas treatment, thus the changes in the microstructure can be studied directly. Preliminary results on the cyclic oxidation and reduction of a model cobalt catalyst are presented.     

Dislocations in nanostructured two‐phase Fe30Ni20Mn20Al30

In a previous study, the dislocations in Fe₃₀Ni₂₀Mn₂₅Al₂₅ (at. %), which consist of 50 nm wide alternating b.c.c. and B2 phases, were shown to have a/2<111> Burgers vectors after room temperature deformation. The dislocations were found to glide in pairs on both {110} and {112} slip planes and were relatively widely separated in the b.c.c. phase, where the dislocations were uncoupled, and closely spaced in the B2 phase, where the dislocations were connected by an anti‐phase boundary. In this article, we analyze the dislocations in the two ～5 nm‐wide B2 phases in a related two‐phase alloy Fe₃₀Ni₂₀Mn₂₀Al₃₀, with compositions Fe‐23Ni‐21Mn‐24Al and Fe‐39Ni‐12Mn‐34Al, compressed to ～3% strain at a strain rate 5 × 10^?4 s^?1 at 873 K (the lowest temperature at which substantial plastic flow was observed). It is shown that slip occursby the glide of a<100> dislocations. A review of the literature suggests that the differences in the observed slip vector between these B2 phases could be due to the differences in composition, differences in deformation temperature, or possibly both. Microsc. Res. Tech. 76:263–267, 2013. © 2013 Wiley Periodicals, Inc.     

Pecularities of nanocrystal formation in rapidly quenched (FeCo)MoCuB amorphous alloys

The effect of the substitution of Fe by Co on the enhancement of glass‐forming ability limits and subsequent nanocrystallization was studied in a rapidly quenched amorphous system (Fe_xCo_y)₇₉Mo₈Cu₁B₁₂ for y/x ranging from 0 to 1. The effect of Cu on nanocrystallization was investigated by comparison with Cu‐free amorphous Fe₈₀Mo₈B₁₂. Systems partially crystallized at the surface layer were prepared for y/x = 0 using different quenching conditions. The effect of heat treatment of master alloys used for ribbon casting was also assessed. The microstructure and surface/bulk crystallization effects were analysed using transmission electron microscopy and electron and X‐ray diffraction in relation to the expected enhancement of high‐temperature soft magnetic properties, drastically reduced grain sizes (～5 nm) and Co content. Unusual surface phenomena were observed, indicating the origin of possible nucleation sites for preferential crystallization in samples with low Co content.