Calorimetric and Positron Lifetime Measurements οf Hydrogenated Carbon Nanocones

Abstract

Two carbon nanostructured samples containing 5 and 20% of carbon nanocones in their volume were investigated. Using the Sieverts apparatus the hydrogen was loaded into the samples. The measurements of heat capacity in the temperature range from 100 K to 320 K and the positron lifetime measurements at the room temperature were performed for hydrogenated and non-hydrogenated carbon nanocones. The desorption of hydrogen at the temperature of 230 K is deduced from the heat capacity measurements. The detection of the positronium, the bound state of positron and electron, in the measured samples reveals the presence of open volume defects of ca. 0.198 ± 0.002 nm.

Spectroscopic and positron lifetime measurements of hydrogenated single walled carbon nanohorns

“…The values obtained in our case are in agreement with those reported by others for fine grained nuclear graphite samples, i.e., 362 ps (AXF-5Q1), 369.2 ps (IG-110), and glass carbon (GC-10) 370.2 ps [24]. Positron lifetime for pristine multi-walled carbon nanotubes and cup-stacked carbon nanotubes is close to 360 ps [11,25].…”

“…This value is not exceeded by the other carbon nanomaterials, CNC ($0.25 wt.%) [6], ANPC, MWNB ($0.3 wt.% and $0.4 wt.%, respectively) [11,20]. Obtained results (both at 77 and 300 K, and equilibrium pressure of hydrogen of 10 bar) are roughly comparable.…”

“…This result is in opposition to the observation for CNC studied by PALS in the identical conditions. The hydrogenated CNC exhibited a significant, about four times, reduction of the intensity of the second lifetime component responsible for the annihilation at pores [11]. The reduction of the value of this lifetime component was also observed.…”

“…However, if we compare the shapes of the isotherms (especially at 77 K) we can observe some differences. Among all carbon nanomaterials discussed here ANPC stands out with the steepest isotherm in the lowest hydrogen pressure (below 2 bar); smaller slopes were shown for SWNH and MWNB, and the mildest slope was observed for CNC [11,20]. This observations suggest that the morphology of the carbon nanomaterial exerts weak influence on the amount of hydrogen adsorption at 10 bar but at the same time the ANPC demonstrates the greatest easiness of the adsorption of hydrogen at lower pressures, the slope of the isotherm is the highest (steepest).…”

Positron Spectroscopy of Nanodiamonds after Hydrogen Sorption

“…Positron annihilation (PA) techniques, such as positron lifetime spectroscopy (PLS) and Doppler broadening spectroscopy (DBS), are promising nuclear-physical methods for investigating structural defects in different materials, including ultrafine-grained and nanostructured materials [ 10 , 11 , 12 , 13 ]. The efficiency of PA methods for studying carbon based materials was demonstrated in [ 14 , 15 ]. These methods allow the solution to such problems as the study of the mechanisms and dynamics of the occurrence, transformation, and disappearance of defects during hydrogenation.…”