Simultaneous Quantification of Hydride Ions and Electrons Incorporated in 12CaO·7Al₂O₃ Cages by Deuterium-Labeled Volumetric Analysis

Abstract

An extended volumetric method, combined with quadrupole mass spectroscopy (QMS), is proposed. This method enables us to distinguish and simultaneously quantify hydride (H–) ions and electrons (e–) incorporated in cages of 12CaO·7Al2O3 (C12A7), which is accomplished upon annealing with CaH2. When a sample is dissolved in a deuterium chloride solution, most of the H– ions and electrons released from cages react to form HD and D2 molecules, respectively. These isotope-labeled molecules are then detected by QMS. We have used this method to follow the concentrations of H– ions and electrons in C12A7-treated CaH2 over the thermal treatment time. We found that during the initial seven days of treatment, both concentrations increased. Thereafter, the electron concentration begins to decrease, while the H– ion concentration continues to increase toward the theoretical maximum. This diverging behavior is due to differences in their diffusion ratios and thermodynamic stabilities.

Hydride ions in oxide hosts hidden by hydroxide ions

“…were observed for the electron concentration range of 2 × 10 19 −8 × 10 20 cm −3 (ref. 18 ; Supplementary Fig 1 ). Thus, chemical shielding has the dominant effect on the δ iso (H − ) value.…”

“…The structural formula of mayenite is [ M 24 Al 28 O 64 ] 4+ ·4 X − , where the brackets correspond to the lattice framework of a unit cell with a space group I 3 d , and M is Ca (refs 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25) or Sr (ref. 26).…”

“…These questions frequently arise in connection to the chemical shifts of 1 H nuclear magnetic resonance (NMR) spectroscopy in non-metals, which exhibit values that are typical for H + , for example, ~+5 p.p.m. with respect to tetramethylsilane (TMS)111718, whereas ‘metallic’ hydrides, such as TiH 2 , exhibit large negative shifts28.…”

“…13 )) may not only be useful for employing H − as a reductant in organic and electrochemical reactions 14 but may also facilitate redox reactions inside materials containing H − ions. An example of the latter has been reported for H − ion-doped mayenite 15 16 17 18 19 20 21 22 23 24 25 26 , in which H − ions are photochemically converted to protons by releasing carrier electrons 15 16 17 . A similar photochemical conversion process is also found on the surface of MgO (ref.…”

New chemistry of transition metal oxyhydrides

“…Another approach to quantification has been acid digestion of the sample, and volumetric/mass spectrometric analysis of the evolved gases. For example Yoshizumi et al and Kobayashi et al dissolved their C12A7:H – [ 43 ] and BaTiO 3– x H x samples [ 12 ] in DCl/D 2 O or D 2 SO 4 , and collected the evolved gases to prove and quantify the existence of lattice hydride.…”