FORMATION OF ND2FE14B HYDRIDE BY MILLING OF ANHYDRIDE PARTICLES IN TOLUENE IN A CLOSED REACTOR

When milling micrometer thin Nd2Fe14B platelets, of an average 1-2 mm diameter, in toluene in a closed reactor, part of the toluene decompos es at the surface of the platelets and yields nascent hydrogen and car bon/low hydrocarbons. The hydrogen diffuses into the Nd,Fe,,B platelet s and the carbon forms a thin surface passivation layer of the platele ts, forming the stable Nd2Fe14BHx, x less than or equal to 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. A n N-2 gas atmosphere, if used during the heating, facilitates the H-de sorption process with the modified kinetic parameters. For example, th e enthalpy of the H-desorption Delta H and the related activation ener gy E-a have the measured values Delta H=153J/g and E-a = 58.2 kJ/mol i n argon and Delta H = 256 J/g and E-a = 41.6 kJ/mol in N-2. It is argu ed that N-2 gas has a fast reaction with the H atoms desorbing off the thin sample platelets and forms NH3 gas with an instantaneous decreas e 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 N-2 gas.