Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles.

Non-oxidative ethanol dehydrogenation is a renewable source of acetaldehyde and hydrogen. The reaction is often catalyzed by supported copper catalysts with high selectivity. The activity and long-term stability depend on many factors, including particle size, choice of support, doping, etc. Herein, we present four different synthetic pathways to prepare Cu/SiO2 catalysts (∼2.5 wt % Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometer clusters), dry impregnation (A̅ = 3.4 nm; σ = 0.9 nm and particles up to 32 nm), strong electrostatic adsorption (A̅ = 3.1 nm; σ = 0.6 nm), and solvothermal hot injection followed by Cu particle deposition (A̅ = 4.0 nm; σ = 0.8 nm). All materials were characterized by ICP-OES, XPS, N2 physisorption, STEM-EDS, XRD, RFC N2O, and H2-TPR and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol-gel exhibited high Cu dispersion and, accordingly, the highest catalytic activity. Its acetaldehyde productivity (2.79 g g-1 h-1 at 255 °C) outperforms most of the Cu-based catalysts reported in the literature, but it lacks stability and tends to deactivate over time. On the other hand, the sample prepared by simple and cost-effective dry impregnation, despite having Cu particles of various sizes, was still highly active (2.42 g g-1 h-1 acetaldehyde at 255 °C). Importantly, it was the most stable sample out of the studied materials. The characterization of the spent catalyst confirmed its exceptional properties: it showed the lowest extent of both coking and particle sintering.

Influence of Fe on the Hydrogen Storage Properties of LaCeNi Alloys.

LaNi5 intermetallic compounds with a hexagonal CaCu5 type structure can react reversibly with hydrogen. The element substitutions in LaNi5 can significantly change the hydrogenation properties, allowing to tune them to a large extent. It could be very advantageous to partially replace Ni or La with other elements to reduce the cost of this alloy as well as the equilibrium pressure of absorption and desorption. The hydrogen storage properties of ball-milled AB5 alloys containing the elements La, Ce (A-rare elements) and Ni, Fe (B-transition metals) were studied in this paper. Although the substitution of Ni (atomic radius 1.49 Å) with Fe atom (atomic radius 1.56 Å) increased the unit cell volume from 86.4149 to 87.947 5 Å3 of the LaNi5 phase, its hydrogen storage capacity was still close to the value 1.4 wt %. The enthalpy (ΔH) of hydride formation for hydrogen absorption and desorption of the experimental alloys was in the range of 29-32.6 kJ/mol. A very favorable effect of Fe on the sorption properties was found in the significant reduction of the equilibrium pressure of absorption and desorption. These studied experimental Fe-containing alloys were able to store hydrogen at 300 K and with pressure under 0.1 MPa. The fastest sorption kinetics of hydrogen was found in alloys with FeNi phase particles located on the surface of the powder. However, if the FeNi phase was segregated at the grain boundaries, it acted as a barrier limiting the growth of the hydride phase. This led to a decrease of the hydride sorption kinetics.

Creep Resistance of S304H Austenitic Steel Processed by High-Pressure Sliding.

Sheets of coarse-grained S304H austenitic steel were processed by high-pressure sliding (HPS) at room temperature and a ultrafine-grained microstructure with a mean grain size of about 0.14 µm was prepared. The microstructure changes and creep behavior of coarse-grained and HPS-processed steel were investigated at 500-700 °C under the application of different loads. It was found that the processing of S304H steel led to a significant improvement in creep strength at 500 °C. However, a further increase in creep temperature to 600 °C and 700 °C led to the deterioration of creep behavior of HPS-processed steel. The microstructure results suggest that the creep behavior of HPS-processed steel is associated with the thermal stability of the SPD-processed microstructure. The recrystallization, grain growth, the coarsening of precipitates led to a reduction in creep strength of the HPS-processed state. It was also observed that in the HPS-processed microstructure the fast formation of σ-phase occurs. The σ-phase was already formed during slight grain coarsening at 600 °C and its formation was enhanced after recrystallization at 700 °C.

Influence of Processing Techniques on Microstructure and Mechanical Properties of a Biodegradable Mg-3Zn-2Ca Alloy.

New Mg-3Zn-2Ca magnesium alloy was prepared using different processing techniques: gravity casting as well as squeeze casting in liquid and semisolid states. Materials were further thermally treated; thermal treatment of the gravity cast alloy was additionally combined with the equal channel angular pressing (ECAP). Alloy processed by the squeeze casting in liquid as well as in semisolid state exhibit improved plasticity; the ECAP processing positively influenced both the tensile and compressive characteristics of the alloy. Applied heat treatment influenced the distribution and chemical composition of present intermetallic phases. Influence of particular processing techniques, heat treatment, and intermetallic phase distribution is thoroughly discussed in relation to mechanical behavior of presented alloys.

Towards near-permanent CoCrMo prosthesis surface by combining micro-texturing and low temperature plasma carburising.

An advanced surface engineering process combining micro-texture with a plasma carburising process was produced on CoCrMo femoral head, and their tribological properties were evaluated by the cutting-edge pendulum hip joint simulator coupled with thin film colorimetric interferometry. FESEM and GDOES showed that precipitation-free C S-phase with a uniform case depth of 10µm was formed across the micro-textures after duplex treatment. Hip simulator tests showed that the friction coefficient was reduced by 20% for micro-metre sized texture, and the long-term tribological property of microtexture was enhanced by the C-supersaturated crystalline microstructure formed on the surface of duplex treated CoCrMo, thereby enhancing biotribological durability significantly. In-situ colorimetric interferometry confirmed that the maximum film thickness around texture area was 530nm, indicating that the additional lubricant during sliding motion might provide exceptional bearing life.

Heat-induced spinodal decomposition of Ag-Cu nanoparticles.

Solvothermal synthesis was used for Ag-Cu nanoparticle (NP) preparation from metallo-organic precursors. The detailed NP characterization was performed to obtain information about nanoparticle microstructure and both phase and chemical compositions. The resulting nanoparticles exhibited chemical composition inside a FCC_Ag + FCC_Cu two-phase region. The microstructure study was performed by various methods of electron microscopy including high-resolution transmission electron microscopy (HRTEM) at an atomic scale. The HRTEM and X-ray diffraction studies showed that the prepared nanoparticles form the face centred cubic (FCC) crystal lattice where the silver atoms are randomly mixed with copper. The CALPHAD approach was used for predicting the phase diagram of the Ag-Cu system in both macro- and nano-scales. The predicted spinodal decomposition of the metastable Ag-Cu nanoparticles was experimentally induced by heating on an X-ray powder diffractometer (HT XRD). The nucleation of the Cu-rich phase was detected and its growth was studied. Changes in the Ag-rich phase were observed in situ by X-ray diffraction under vacuum. The heat treatment was conducted at different maximum temperatures up to 450 °C and the resulting particle product was analysed. The experiments were complemented by differential scanning calorimetry (DSC) measurements up to liquidus temperature. The start temperatures of the spinodal phase transformation and particle aggregation were evaluated.