Eski mektuplar

Ahmet Mithat'ın Tercüman-ı Hakikat'te tefrika edilen Eski Mektuplar adlı roman

Economic Manganese-Oxide-Based Anodes for Efficient Water Oxidation: Rapid Synthesis and In Situ Transmission Electron Microscopy Monitoring

Earth-abundant, environmentally friendly, and low-cost manganese oxide materials are promising resources for water oxidation catalysts in clean solar fuel applications. We here introduce a convenient and economic method for manufacturing stable and highly efficient manganese-oxide-based anodes for electrochemical water oxidation under neutral conditions. The electrodes were fabricated through thermal decomposition of acidic KMnO4 solution. The phase transitions of the manganese oxide film during calcination and thermal decomposition of KMnO4 were monitored with in situ heating transmission electron microscopy (TEM), in situ heating scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM/EDX), and in situ heating powder X-ray diffraction (PXRD). In-depth monitoring of formation pathways and phase transformations by in situ techniques under high temperatures shed light upon the fabrication of efficient manganese oxides for energy conversion applications. After parameter optimizations, the best-performing manganese oxide catalyst was applied for water electrolysis for 100 h with a stable current density of 1.0 mA/cm2 at an overpotential of 490 mV in neutral pH. Post operando characterizations of key oxide film properties showed no significant changes. The readily commercially available precursor enables a simple and rapid fabrication method, and the promising stability and high performance of the herein developed electrodes render them quite promising for technological water splitting systems

On The Plate-Like Τ-Phase Formation In Mnal-C Alloys

A detailed description of the displacive transformation mode of the formation of plate-like τ-phase in MnAl (containing a small amount of carbon) is given. The plate-like τ-phase forms in a stepwise mode from the ε-phase. Crystallographic correspondence is transmitted from the ε- to the τ-phase during the whole transformation sequence. The intermediate long-range ordered ε′-phase nucleates within the ε-matrix. As ε′-domains evolve, elastic strains increase at the ε′-interfaces until shear occurs in ε′-domains to reduce the transformation strains. Stacking faults appear between ε′-domain boundaries. Polytypes are the result of a shuffling of the stacking faults within ε′-domains. Finally, the ε′-domain boundaries are overcome by the collective motion of transformation dislocations which form twinned τ-plates. The ε′-domain boundaries are nucleation sites for successive transformation steps and limit the spatial extension of the transformation for the intermediate steps

Copper thin films by ion beam assisted deposition: Strong texture, superior thermal stability and enhanced hardness

Nanocrystalline metals generally exhibit exceptionally high strength. However, their susceptibility to grain growth restricts their applications in high temperature environments. The current study presents that nanocrystalline Cu thin films produced by ion beam assisted deposition (IBAD) are able to sustain their as-deposited microstructure and high hardness upon annealing at high temperatures. IBAD-Cu films exhibit a strong (111) fiber texture, which is caused by the ion beam induced effects of substrate cleaning, preferential damage and preferential sputtering. The microstructure of the IBAD-Cu films is stable at temperatures up to 800°C (80% of the melting point of Cu). The hardness of the as-deposited IBAD-Cu films can reach a maximum value of 3.85 GPa. Even after annealing, their hardness is still much higher than that of the normally deposited (without ion beam) films as well as their bulk nanocrystalline counterparts before heat treatment. The excellent thermal stability of microstructure is attributed to the formation of nanometer-sized voids and their pinning effect on grain boundary migration. The kinetics of void formation, the contribution of twin boundaries and ion beam induced defects to the hardness are analyzed and discussed. The findings in this study demonstrate that IBAD is an effective method for the stabilization of microstructure and mechanical properties of nanocrystalline metal thin films.The authors also acknowledge financial support by the Swiss National Science Foundation under contract no. 200021_140532 and 200021_143633

Size-dependent strengthening in multi-principal element, face-centered cubic alloys

Multi-principal element (MPE) alloys, sometimes also known as high entropy, complex concentration or multicomponent alloys, have attracted significant attention due to their remarkable mechanical properties, especially face-centered cubic (fcc) CrCoNi-based alloys. In this study, the size effect and strain rate dependence of the strength of equiatomic ternary (CrCoNi), quaternary (CrFeCoNi), and quinary MPE (CrMnFeCoNi) alloys were investigated using in situ strain rate jump (SRJ) micropillar compression tests. No obvious correlation is found between size dependence of strength and the number of elements in these alloys, but an inverse relation is observed between size effect exponent and the Peierls' stress. The single arm source strengthening model was successfully applied on the entire range of samples from the fcc pure elements to fcc equiatomic MPE alloys. Moreover, the activation volumes (~10 b3 to ~100 b3) are consistent among the MPE alloys, indicating the main deformation mechanism is similar in these alloys: dislocation-solute and dislocation-dislocation interactions.ISSN:0264-1275ISSN:1873-419