ABSTRACT
In this work, we aim to study the hydrogen adsorption in several kinds of carbon nanotubes grown under different process conditions and to correlate the findings with the morphological microstructure and physical properties of these materials. The growth conditions and the behaviour with respect to hydrogen interaction of various carbon nanotubes are discussed, to establish microstructure-process-property relationships. In particular, we have analyzed several types of carbon nanotubes, namely one single-walled and five multi-walled having different tube diameter (due to different deposition techniques and conditions), different defectiveness and submitted to different surface treatments. To better understand the differences among the various samples, they have been investigated using field emission scanning electron microscopy and high resolution transmission electron microscopy for the morphological and structural characteristics, thermo-gravimetric analysis for the sample purity and Brunauer-Emmett-Teller analysis for the surface area. The experimental measurements on the ability of the different types of carbon nanotubes to adsorb and/or releasing hydrogen have been performed at 77 K with a volumetric Sievert analytical tool. Our findings clearly demonstrate a direct correlation between the exposed surface area and adsorbed hydrogen capacity, which confirms their linear relationship observed previously. For instance, single-walled nanotubes with surface area density of approximately 800 m2/g have showed hydrogen storage of approximately 1.7 wt% at a pressure of 35 atm. Adsorption process seems to be perfectly reversible. The adsorption values have been compared with a simple model, in order to evaluate the potentialities for carbon-based nanomaterials in future hydrogen storage applications.
ABSTRACT
In this work, we aim to study the hydrogen adsorption in several kinds of carbon nanotubes grown under different process conditions and to correlate the findings with the morphological microstructure and physical properties of these materials. The growth conditions and the behaviour with respect to hydrogen interaction of various carbon nanotubes are discussed, to establish microstructure-process-property relationships. In particular, we have analyzed several types of carbon nanotubes, namely one single-walled and five multi-walled having different tube diameter (due to different deposition techniques and conditions), different defectiveness and submitted to different surface treatments. To better understand the differences among the various samples, they have been investigated using field emission scanning electron microscopy and high resolution transmission electron microscopy for the morphological and structural characteristics, thermo-gravimetric analysis for the sample purity and Brunauer-Emmett-Teller analysis for the surface area. The experimental measurements on the ability of the different types of carbon nanotubes to adsorb and/or releasing hydrogen have been performed at 77 K with a volumetric Sievert analytical tool. Our findings clearly demonstrate a direct correlation between the exposed surface area and adsorbed hydrogen capacity, which confirms their linear relationship observed previously. For instance, single-walled nanotubes with surface area density of approximately 800 m2/g have showed hydrogen storage of approximately 1.7 wt% at a pressure of 35 atm. Adsorption process seems to be perfectly reversible. The adsorption values have been compared with a simple model, in order to evaluate the potentialities for carbon-based nanomaterials in future hydrogen storage applications.
ABSTRACT
The electronic structure of LaNiSn and NdNiSn compounds and their hydrides has been studied by first principles calculations and variable temperature 119Sn Mossbauer spectroscopy and the nature of the hydrogen-metal bond is discussed. The analysis of the electronic density of states (DOS) in both compounds before and after hydrogenation indicates an hybridization of the Sn, Ni, and H orbitals. The partial Sn-p DOS of LaNiSnH2 gives evidence for a lower symmetry of electron density around tin atoms compared to LaNiSn, according to the larger quadrupole splitting in the corresponding Mossbauer spectrum. Theoretical and experimental Mossbauer parameters agree very well for all samples.
ABSTRACT
Spontaneous renal and perirenal hematomas are heavy clinical events and, even if rare, they need an early diagnosis in order to plan therapy. A spontaneous renal hematoma should be suspected in case of acute lumbar pain because in more than 60% of cases it is due to a neoplastic lesion. In the other cases it is due to vascular and infectious kidney diseases while in 5 to 15% of cases the cause of the hematoma can not be found. In this paper 4 cases of spontaneous renal hematomas quite interesting both for their rarity and the imaging features are reported. All cases have been treated by medical therapy. According to personal experience and to the literature reports, the primary imaging diagnostic methods are ultrasonography and CT, while renal angiography should be employed when a vascular disease is suspected. In fact, US can provide the diagnosis of spontaneous renal hematoma but only CT can accurately assess its extension and moreover detect the cause of the hemorrhage. In personal experience, MR did not add significative diagnostic information if compared with CT.
