Modification of nano and micro-phase diamond powder for enhancement of hydrogen storage
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Micron and nano-phase diamond powders were doped with boron in order to change their various chemical properties. Diamond possesses several technologically important properties including extreme hardness, high electrical resistance, chemical inertness, high thermal conductivity, high electron hole mobilities, and optical transparency. Boron-doping of diamond powders via Thermal Diffusion Process was used in this study. Natural boron contains 80.1% ¹¹B and 19.9% ¹⁰B. ¹⁰B has large neutron capture cross section with the reaction ¹⁰B(n, [alpha])⁷Li. The energy release in the reaction is rather high (2.71 MeV), facilitating radiation defects in the sample. The introduction of boron atoms also changed the structure and properties of the diamond powder including resistance to oxidation. Following doping with boron, the diamond powders were irradiated by thermal neutrons by fluence values of 3x10¹⁵, and 4.3x10¹⁸ n/cm² at the Missouri University Research Reactor (MURR). The creation of micro-porous structure in diamond powders for storage of hydrogen is discussed. Prompt Gamma Neutron Activation Analysis was used to determine the concentration of boron in the diamond powder. Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and Thermogravimetric Analysis (TGA) were also employed to study the morphology and structure of the diamond particles. Raman spectroscopy showed that glassy and microcrystalline carbon structures were formed on irradiation. A significant amount of boron was diffused into both nano and micron size diamond powders. The boron concentration before and after irradiation suggested that about 35% ¹⁰B interacted with neutrons. Hydrogen was diffused into both micron and nano size diamond powder before and after boron-doping, and also after irradiation on to evaluate the feasibility of the proposed technique for enhancement of hydrogen storage capacity of diamond powders. Hydrogen storage capacity of undoped-nontreated micron size diamond powder was 0.51 wt% H₂. Hydrogen storage capacity of diamond power when treated in hydrogen plasma was about 1.47 wt% H₂. Surprisingly hydrogen was not detected in boron-doped, irradiated diamond powders by PGNAA. One of the reasons could be the sample amount since the lower limit of detection of total H₂ by PGNAA is 3.93 ug/g of sample. The Raman spectrum showed the existence of CH bonds suggesting the presence of hydrogen in the sample.
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