In Situ Fabrication of B4C–NbB2 Eutectic Composites by Spark–Plasma Sintering

This contribution reports, for the first time, the sintering, microstructure and properties of in situ synthesized/consolidated eutectic composites by spark–plasma sintering (SPS). SPS involves a number of processing parameters that may be used to tailor the composition of eutectic composites. It was shown that pressure may be used as a means of controlling the eutectic formation. By changing the pressure, temperature and composition, we propose a processing route that results in the in situ formation of strengthened eutectic composites, consisting of a matrix (B₄C, and B₄C–NbB₂ composite) and also containing regularly distributed whiskers of NbB₂. The composites with the eutectic composition of 35 mol.% NbB₂ obtained by SPS exhibit a high Vickers hardness (26–27 GPa) and indentation fracture toughness (~6 MPa·m^1/2).     

Effect of Iron Content on Sintering Behavior of Ti-V-Fe-Al Near-β Titanium Alloy

Two near-β Ti-10V-3Fe-3Al and Ti-10V-2Fe-3Al alloys were produced by blended elemental powder metallurgy using hydrogenated titanium and V-Fe-Al master alloy powders. The distributions of the alloying elements were investigated at different stages of transformation of the heterogeneous powder compacts into the final homogeneous alloy product. The influence of iron content on chemical homogenization, densification, microstructure, and mechanical properties of as-sintered alloys was discussed with respect to the fast diffusion mobility of iron in titanium. It was concluded that a 1 pct increase in Fe content, as the alloying element with the fastest diffusivity in titanium, has a positive effect on densification. However, this also results in some grain coarsening of the final material. The attained mechanical properties were comparable with those of cast/wrought near-beta titanium alloys.     

Influence of Cold Forming and Heat Treatment on the Microstructure and Mechanical Properties of an Air‐Hardening Steel

The use of air‐hardening steels in the manufacture of automobile body components shortens the corresponding process chain by means of eliminating the immersion or gas quenching operation since hardening occurs in still air. To choose the optimal forming and heat‐treatment parameters, the development of the microstructure needs to be considered as a consequence of the thermomechanical production processes. The object of this work is to investigate the effects of forming and the subsequent heat‐treating on the changes of the microstructural parameters for the air‐hardening steel LH800. For this purpose, specimens were processed under different forming and heat‐treating conditions and subsequently examined by means of SEM and mechanically tested using tensile tests. Based on this, an empirical equation was derived which describes the influence of both the martensite's bundle thickness and the original austenite's grain size on the yield stress. In this way, microstructural parameters can be identified which lead to good mechanical properties. The measured correlation can thus be used for modeling the LH800 steel's forming and heat‐treatment processes.     

Charge transport characteristics of diarylethene photoswitching single-molecule junctions

We report on the experimental analysis of the charge transport through single-molecule junctions of the open and closed isomers of photoswitching molecules. Sulfur-free diarylethene molecules are developed and studied via electrical and optical measurements as well as density functional theory calculations. The single-molecule conductance and the current-voltage characteristics are measured in a mechanically controlled break-junction system at low temperatures. Comparing the results with the single-level transport model, we find an unexpected behavior of the current-dominating molecular orbital upon isomerization. We show that both the side chains and end groups of the molecules are crucial to understand the charge transport mechanism of photoswitching molecular junctions.     

Phase Equilibria in the ZrO2–MgO–MnOx System

Phase equilibria were experimentally investigated in the MgO–MnO_x and the ZrO₂–MgO–MnO_x systems for different oxygen partial pressures by powder X‐ray diffractometry, scanning electron microscopy, and differential thermal analysis. The formation of two compositionally and structurally different β‐spinel solid solutions was observed in the MgO–MnO_x system in air in the temperature interval 1473–1713 K. Isothermal sections of the ZrO₂–MgO–MnO_x phase diagram were constructed for air conditions ( = 0.21 bar) at 1913, 1813, 1713, 1613, and 1523 K. In addition, isothermal sections at 1913 and 1523 K were constructed for = 10^?4 bar. The β‐spinel and halite phases of the MgO–MnO_x system were found to dissolve up to 2 and 5 mol% ZrO₂. A continuous c‐ZrO₂ solid solution forms between the boundary ZrO₂–MnO_x and ZrO₂–MgO systems. It stabilizes in the ZrO₂–MgO–MnO_x system down to at least 1613 K in air and down to 1506 K at = 10^?4 bar.     

Economic comparison of pressure driven membrane processes to electrically driven processes for use in hydraulic fracturing

Hydraulic fracturing has become a reliable source for oil and natural gas, yet widespread use has led to significant issues with water consumption and sustainable sourcing. Research into the reuse of produced water and flowback water have focused on mitigating water demand in this industry through membrane separation technology. In general, nanofiltration and reverse osmosis have been thought to be more economically viable for the treatment of produced and flowback water at high flowrates. However, electrodialysis and electrodeionization are generally more flexible for production of produced water and brackish water for reuse in fracturing operations when contaminant concentrations in produced water and flowback water are low. Electrodialysis and electrodeionization can also significantly reduce wastewater produced from water treatment, decreasing the amount of water that must be disposed by deep well injection. Thus, there are many cases where electrically driven processes compete well with pressure driven processes due to high water recovery and each case must be analyzed in terms of water quality variability and overall desired water treatment rate. This paper finds that at low ion concentration of inlet water, electrodialysis and electrodeionization are energy-efficient, cost-effective attractive technologies for water recovery.     

Ultrabright Fluorescent Mesoporous Silica Nanoparticles

The first successful approach to synthesizing ultrabright fluorescent mesoporous silica nanoparticles is reported. Fluorescent dye is physically entrapped inside nanochannels of a silica matrix created during templated sol–gel self‐assembly. The problem of dye leakage from open channels is solved by incorporation of hydrophobic groups in the silica matrix. This makes the approach compatible with virtually any dye that can withstand the synthesis. The method is demonstrated using the dye Rhodamine 6G. The obtained 40‐nm silica particles are about 30 times brighter than 30‐nm coated water‐soluble quantum dots. The particles are substantially more photostable than the encapsulated organic dye itself.