Synthesis, thermal evolution and magnetic investigations of SBA-15 silica functionalized with anchored iron phosphonate molecules.

In the current work, we report on the synthesizing of a series of novel nanocomposite materials obtained by functionalizing the SBA-15 silica matrix with anchored iron phosphonate molecules and the following thermal treatment. The obtained results reveal the formation of a unique amorphic layer of Fe-based compounds on the surface of silica walls of SBA-15 channels as a result of the organic groups' decomposition after moderate thermal treatment. Due to their unique structure, represented in an active Fe-containing amorphous coating spread over a large surface area, these materials are of great interest for their potential applications in fields such as catalysis, adsorption, and non-linear optics. The obtained materials remain amorphous, preserving the SBA-15 mesoporous structure up to temperatures of approximately 800 °C, after which the partial melting of the silica backbone is observed with the simultaneous formation of nanocrystals inside the newly-formed glassy mass. All obtained materials were characterized using such techniques as thermogravimetry, transmission and scanning electron microscopy combined with energy dispersive x-ray spectroscopy mapping, Raman spectroscopy, N2sorption analysis, x-ray diffraction, x-ray photoelectron spectroscopy, Mössbauer spectroscopy, and SQUID measurements.

Mechanical Properties and Microstructure of Inconel 718 Lattice Structures Produced by Selective Laser Melting Process.

This article presents the results of an analysis regarding the microstructure, mechanical strength, and microhardness of two kinds of samples built through selective laser melting with Inconel 718, the most frequently used alloy in metal additive manufacturing due to its excellent mechanical properties. The sample geometry was made up of two types of lattice structures with spherical and hyperbolical stiffness elements. The goals of these studies are to determine how homogenization heat treatment influences the microhardness and the mechanical properties of the specimens and to identify the structure with the best mechanical properties. The analysis showed that heat treatment was beneficial because the regular dendritic structure disappears, the δ phase precipitates at the grain boundaries, and both the γ and γ″ phases dissolve. It has also been shown that the structures with hyperbolical stiffness elements have better compressive strength than the structures with the elliptical structures, with a 47.6% increase for the as-fabricated structures and an approximate 50% increase for the heat-treated structure.

Effect of Size on the Formation of Solid Solutions in Ag-Cu Nanoparticles.

Modern technologies stimulate the quest for multicomponent nanosized materials with improved properties, which are ultimately defined by the atomic arrangement and interphase interactions in the nanomaterial. Here, we present the results of the experimental study of the formation of solid solutions in Ag-Cu nanoparticles in a wide size and temperature range using in situ TEM techniques. The Ag-Cu nanoparticles with a eutectic ratio of components were formed on an amorphous carbon film by the physical vapor deposition technique. Electron diffraction, HAADF-STEM imaging, energy-dispersive X-ray spectroscopy, chemical element mapping, and electron energy loss spectral imaging were used for the characterization of mixing patterns and composition of phases in AgCu nanoparticles down to the atomic level. As a result, we constructed the solid-state part of the Ag-Cu phase diagram for nanoparticles with a size down to 5 nm. We found a highly asymmetric behavior of the solvus lines. Thus, the content of Cu in Ag gradually increased with a size reduction and reached the ultimate value for our configuration of 27 wt % Cu at a nanoparticle size below ∼8 nm. At the same time, no Cu-rich solid solution was found in two-phase AgCu nanoparticles, irrespective of the size and temperature. Moreover, a quasi-homogeneous solid solution was revealed in AgCu nanoparticles with a size smaller than 8 nm already at room temperature. A size dependence of the terminal temperature T term, which limits the existence of AgCu alloy nanoparticles in a vacuum, was constructed. Evaporation of the AgCu phase with the composition of 86 wt % Ag was observed at temperatures above T term. We show the crucial role of the mutual solubility of components on the type of atomic mixing pattern in AgCu nanoparticles. A gradual transition from a Janus-like to a homogeneous mixing pattern was observed in Ag-Cu nanoparticles (28 wt % Cu) with a decrease in their size.

Multiscale Characterization of an Oxide Scale Formed on the Creep-Resistant ATI 718Plus Superalloy during High-Temperature Oxidation.

The ATI 718Plus® is a creep-resistant nickel-based superalloy exhibiting high strength and excellent oxidation resistance in high temperatures. The present study is focused on multiscale 2D and 3D characterization (morphological and chemical) of the scale and the layer beneath formed on the ATI 718Plus superalloy during oxidation at 850 °C up to 4000 h in dry and wet air. The oxidized samples were characterized using various microscopic methods (SEM, TEM and STEM), energy-dispersive X-ray spectroscopy and electron diffraction. The 3D visualization of the microstructural features was achieved by means of FIB-SEM tomography. When oxidized in dry air, the ATI 718Plus develops a protective, dense Cr2O3 scale with a dual-layered structure. The outer Cr2O3 layer is composed of coarser grains with a columnar shape, while the inner one features fine, equiaxed grains. The Cr2O3 scale formed in wet air is single-layered and features very fine grains. The article discusses the difference between the structure, chemistry and three-dimensional phase distribution of the oxide scales and near-surface areas developed in the two environments. Electron microscopy/spectroscopy findings combined with the three-dimensional reconstruction of the microstructure provide original insight into the role of the oxidation environment on the structure of the ATI 718Plus at the nanoscale.

Pore shape and size dependence on cell growth into electrospun fiber scaffolds for tissue engineering: 2D and 3D analyses using SEM and FIB-SEM tomography.

Electrospun nanofibers have ability to boost cell proliferation in tissue engineered scaffolds as their structure remind cells extra cellular matrix of the native tissue. The complex architecture and network of nanofibrous scaffolds requires advanced characterization methods to understand interrelationship between cells and nanofibers. In our study, we used complementary 2D and 3D analyses of electrospun polylactide-co-glycolide acid (PLGA) scaffolds in two configurations: aligned and randomly oriented nanofibers. Sizes of pores and fibers, pores shapes and porosity, before and after cell culture, were verified by imaging with scanning electron microscopy (SEM) and combination of focus ion beam (FIB) and SEM to obtain 3D reconstructions of samples. Using FIB-SEM tomography for 3D reconstructions and 2D analyses, a unique set of data allowing understanding cell proliferation mechanism into the electrospun scaffolds, was delivered. Critically, the proliferation of cells into nanofibers network depends mainly on the pore shape and pores interconnections, which allow deep integration between cells and nanofibers. The proliferation of cells inside the network of fibers is much limited for aligned fibers comparing to randomly oriented fibers. For random fibers cells have easier way to integrate inside the scaffold as the circularity of pores and their sizes are larger than for aligned scaffolds. The complex architecture of electrospun scaffolds requires appropriate, for tissue engineering needs, cell seeding and culture methods, to maximize tissue growth in vitro environment.

A bottom-up process of self-formation of highly conductive titanium oxide (TiO) nanowires on reduced SrTiO3.

Reduced titanium oxide structures are regarded as promising materials for various catalytic and optoelectronic applications. There is thus an urgent need for developing methods of controllable formation of crystalline nanostructures with tunable oxygen nonstoichiometry. We introduce the Extremely Low Oxygen Partial Pressure (ELOP) method, employing an oxygen getter in close vicinity to an oxide during thermal reduction under vacuum, as an effective bottom-up method for the production of nanowires arranged in a nanoscale metallic network on a SrTiO3 perovskite surface. We demonstrate that the TiO nanowires crystallize in a highly ordered cubic phase, where single nanowires are aligned along the main crystallographic directions of the SrTiO3 substrate. The dimensions of the nanostructures are easily tunable from single nanometers up to the mesoscopic range by varying the temperature of reduction. The interface between TiO and SrTiO3 (metal and insulator) was found to be atomically sharp providing the unique possibility of the investigation of electronic states, especially since the high conductivity of the TiO nanostructures is maintained after room temperature oxidation. According to the growth model we propose, TiO nanowire formation is possible due to the incongruent sublimation of strontium and crystallographic shearing, triggered by the extremely low oxygen partial pressure (ELOP). The controlled formation of conductive nanowires on a perovskite surface holds technological potential for implementation in memristive devices, organic electronics, or for catalytic applications, and provides insight into the mechanism of nanoscale phase transformations in metal oxides. We believe that the ELOP mechanism of suboxide formation is suitable for the formation of reduced suboxides on other perovskite oxides and for the broader class of transition metal oxides.

Combinatorial Study of Gradient Ag-Al Thin Films: Microstructure, Phase Formation, Mechanical and Electrical Properties.

A combinatorial approach is applied to rapidly deposit and screen Ag-Al thin films to evaluate the mechanical, tribological, and electrical properties as a function of chemical composition. Ag-Al thin films with large continuous composition gradients (6-60 atom % Al) were deposited by a custom-designed combinatorial magnetron sputtering system. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), nanoindentation, and four-point electrical resistance screening were employed to characterize the chemical composition, structure, and physical properties of the films in a time-efficient way. For low Al contents (<13 atom %), a highly (111)-textured fcc phase was formed. At higher Al contents, a (002)-textured hcp solid solution phase was formed followed by a fcc phase in the most Al-rich regions. No indication of a µ phase was observed. The Ag-Al films with fcc-Ag matrix is prone to adhesive material transfer leading to a high friction coefficient (>1) and adhesive wear, similar to the behavior of pure Ag. In contrast, the hexagonal solid solution phase (from ca. 15 atom %Al) exhibited dramatically reduced friction coefficients (about 15% of that of the fcc phase) and dramatically reduced adhesive wear when tested against the pure Ag counter surface. The increase in contact resistance of the Ag-Al films is limited to only 50% higher than a pure Ag reference sample at the low friction and low wear region (19-27 atom %). This suggests that a hcp Ag-Al alloy can have a potential use in sliding electrical contact applications and in the future will replace pure Ag in specific electromechanical applications.