Dataset of Mechanically stimulated gas emission from pellets of sodium alanate subjected to rubbing at room temperature under vacuum and related surface, structural, mechanical, and tribological characterization of the pellets

The pellets were subjected to reciprocating rubbing under vacuum (10-7 mbar range) using an alumina sphere, 3 mm in diameter. A specially designed friction cell with nearly zero own gas emission was used. The motion frequency was 1 Hz. One motion cycle consisted of one forth and one back stroke, each of which lasted for about 40 ms. The indenter stood still for around 50 ms after the forth stroke and 870 ms after the back one. The stroke length was la = 7 mm, the mean sliding speed was Vs = 0.18 m s-1 and the normal load was in the range 0.22 ??? 0.88 N. The total and partial gas pressures were measured in the experimental vacuum chamber, where the pellets were rubbed, using an ionization Bayard-Alpert type vacuum gauge and a quadrupole mass-spectrometer, correspondingly. To quantify minute gas emission rates (<1 nmol/s) the experimental chamber was connected to a gas-expansion chamber through a diaphragm, which conductance under molecular gas flow was carefully measured. Before starting the experiments, the chamber was pumped out for at least 48 hours to achieve stable background pressure (the rate of change of low-pass filtered pressure signal ???10-11 mbar s-1). The gas emission was evaluated from the pressure time series during the mechanical action and benchmarked against the stable background. The gas composition and the emission rates were determined using a previously developed statistical matrix method. X-ray diffraction (XRD) with Cu K?? (?? = 0.15418 nm) radiation was employed for the structural characterization of NaAlH4. To assess the thermal stability of NaAlH4 Temperature-Programmed Desorption Mass-Spectrometry (TPD-MS) was used. A portion of NaAlH4 powder was placed into an alumina crucible in a glove box under Ar atmosphere (MBraun, <1 ppm H2O, <10 ppm O2). Alumina crucible was used instead of a Pt one to avoid possible decomposition of NaAlH4 due to the catalytic effect of Pt. The crucible was transferred to the TPD-MS system, where it was set into another Pt crucible. During the transfer, the sample was briefly exposed to the atmospheric air (about 5 min). The test was carried out under an Ar flux of 50 ml/s and a heating rate of 5 ??C/min. The mechanically affected zones were characterized using FTIR spectrometry, Raman confocal spectroscopy (incident laser wavelength ??? = 532 nm and power 5.6 mW) and Scanning Electron Microscopy (Hitachi S 800) to contrast possible structural and chemical variations induced in the material by the mechanical action. All the results were benchmarked against the measurements on the pristine zones of the same pellets.