Formation of Nd2Fe14B hydride by milling of anhydride particles in toluene in a closed reactor |
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Authors: | S Ram H D Banerjee S Haldar P Ramachandrarao |
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Affiliation: | (1) Materials Science Centre, Indian Institute of Technology, 721 302 Kharagpur, India;(2) National Metallurgical Laboratory, 831 007 Jamshedpur, India |
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Abstract: | When milling micrometer thin Nd2Fe14B platelets, of an average 1–2 mm diameter, in toluene in a closed reactor, part of the toluene decomposes at the surface
of the platelets and yields nascent hydrogen and carbon/low hydrocarbons. The hydrogen diffuses into the Nd2Fe14B platelets and the carbon forms a thin surface passivation layer of the platelets, forming the stable Nd2Fe14BH
x
,x ≤ 5, hydride at room temperature. On heating in a calorimeter, the hydrogen desorbs off the sample with a well-defined endotherm
between 370 and 425 K. An N2 gas atmosphere, if used during the heating, facilitates the H-desorption process with the modified kinetic parameters. For
example, the enthalpy of the H-desorption ΔH and the related activation energyE
a have the measured values ΔH = 153 J/g andE
a = 58·2 kJ/mol in argon and ΔH = 256 J/g andE
a = 41·6 kJ/mol in N2. It is argued that N2 gas has a fast reaction with the H atoms desorbing off the thin sample platelets and forms NH3 gas with an instantaneous decrease of the total external gas pressure at the sample. This supports the fast desorption of
H atoms in the sample with the modified desorption kinetics in N2 gas. |
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Keywords: | Nd2Fe14BH x x ≤ 5 hydrides hydrogen intercalation hydrogen desorption stable metal hydride thermal desorption mechanical attrition |
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