Hydrogen storage in liquid hydrogen carriers: recent activities and new trends

Efficient storage of hydrogen is one of the biggest challenges towards a potential hydrogen economy. Hydrogen storage in liquid carriers is an attractive alternative to compression or liquefaction at low temperatures. Liquid carriers can be stored cost-effectively and transportation and distribution can be integrated into existing infrastructures. The development of efficient liquid carriers is part of the work of the International Energy Agency Task 40: Hydrogen-Based Energy Storage. Here, we report the state-of-the-art for ammonia and closed CO2-cycle methanol-based storage options as well for liquid organic hydrogen carriers

Metalik cam alaşımlarında lokal ve kimyasal yapı

In this thesis structural and corresponding mechanical properties of marginal metallic glass-forming alloys were studied. Al90Tb10 system exhibits unique devitrification features due to their exceptional primary crystallization products of Al nanocrystals with populations reaching up to 1024 m−3 . A full agreement on how this abnormal nucleation event occurs is still lacking. Our previous studies on Al-RE (RE: rareearth element) have shown that two different amorphous precursors prepared using melt-spinning and magnetron sputtering techniques showed clear differences in phase selection hierarchy upon continuous heating. It is considered that this difference is originated from the medium range ordered structure, exist in as-quenched melt-spun ribbon which is inherited from its molten state. In this study the local structure, chemistry and any possible higher order correlations were investigated by performing critical high energy synchrotron X-ray Diffraction (HEXRD),Extended X-ray Absoprtion Fine Structure (EXAFS), ab-initio and Reverse Monte Carlo (RMC) modelling. RE atoms were found to be highly correlated with Al atoms which results in formation of network dividing the amorphous matrix which in turn result in abnormal crystallization behavior. Afterwards, effects of these nanocrystals on mechanical properties are investigated via micropillar compression tests and transmission electron microscopy (TEM). Embedding nanocrystals on amorphous matrix increased the fracture stress and ductility at the same time where as increasing heat treatment temperature beyond first crystallization event temperature caused formation of intermetallic compound which decreased the ductility while further increasing fracture stressMarjinal metalik cam oluşturan alaşımlar yapısal ve mekanik olarak incelenmiştir. Al90Tb10 sisteminin kendine özgü devitrifikasyon özellikleri vardır. Bu özellikler sistemin ilk kristallenme reaksiyonu olan Al nanokristallerinin 1024 m−3 popülasyonu ile oluşmasından kaynaklanır. Günümüze kadar bu anormal kristallenme reaksiyonunun nedeni konusunda uzlaşmaya varılamamıştır. Al-NTE (NTE=Nadir Toprak Elementleri) üzerine çalışmalarımızda iki farklı üretim yöntemi olan eriyik savurma ve manyetron saçılma yöntemleri ile üretilen aynı alaşımların faz seçilimi hiyerarşisinde farklılıklara rastlanmıştır. Bu farklılıgın sıvı fazda olan orta erim düzeninden kaynak- ˘ landıgı ve katı faza iletildi ği düşünülmektedir. Bu çalışmada lokal yapıkimya ve üst ˘ seviye düzen ilintileri kritik sinkrotron X-ışını kırınımı, uzamış X-ışınları sogurumlu ˘ ince yapı, ab-initio ve reverse monte carlo modellemeleri ile incelenmiştir. NTE atomlarının Al atomları ile yüksek oranda ilintili oldugu ve bunun sonucunda bir a ğ oluştu- ˘ rarak matrixi böldügü gözlenmiştir. Sonrasında bu bölünmenin etkisiyle ortaya çıkan ˘ anormal seviyede yüksek sıklıkta oluşan naokristallerin mekanik özelliklere etkisi nanoçentik testleri ve transmisyon elektron mikroskopu ile incelenmiştir. Incelemenin sonunda matrixin kısmi kristallendirilmesinin kopma stresini ve aynı zamanda yumuvii şaklıgı artırdı ğı gözlenirken ısıl işlem sıcaklı ğının artırılması ile oluşan metallerarası ˘ bileşiklerin kopma stresini artırmaya devam ederken yumuşaklıgı düşürdü ğü gözlen- ˘ miştir.M.S. - Master of Scienc

Fabrication of metallic anisotropic particles

Having the capability to fabricate programmable and advanced materials with designed properties and new functions has been of significant attention for the broad scientific community. One of the recent approaches to developing such capability in nano- and micro-materials is to introduce a spatial distribution of at least two components and benefit from the multifunctionality stemmed from this anisotropy for programmability or synergetic effects. Synthesis of anisotropic metallic particles at nano- or microscale is a challenging task due to the size-dependent limitations and the complex chemistry. In this presentation, we will introduce a novel technique for fabrication of metallic anisotropic structures that is simple, robust, scalable and environmentally friendly. The topological (Scanning Electron Microscopy), chemical (Back Scattering Electron Microscopy) and crystallographic (X-Ray Crystallography) characterization of fabricated particles will be presented. The capabilities of anisotropic particles depend also on the distribution of components throughout the particle. The focused ion beam is used in scanning electron microscopy to slice off the anisotropic particle for complete characterization. The results show that the fabricated particles do not have the core-shell structure (the core of the particle is same, but the components are distributed on the shell), but it is coreless (the anisotropy is throughout the particle). To conclude, in this presentation, the novel technique for fabrication of anisotropic particles will be introduced and its capabilities will be demonstrated on the model Bi-Sn system. The findings can be elaborated on the other systems as the technique allows easy adjustments over other combinations