Secondary Ion Mass Spectrometry of Zeolite Materials: Observation of Abundant Aluminosilicate Oligomers Using an Ion Trap
Oligomeric oxyanions were observed in the secondary ion mass spectra (SIMS) of zeolite materials. The oxyanions have the general composition AlmSinO2(m+n)H(m-1)- (m + n = 2 to 8) and are termed dehydrates. For a given mass, multiple elemental compositions are possible because (Al + H) is an isovalent and isobaric substitute for Si. Using 18 keV Ga+ as a projectile, oligomer abundances are low relative to the monomers. Oligomer abundance can be increased by using the polyatomic projectile ReO4- (~5 keV). Oligomer abundance can be further increased using an ion trap (IT-) SIMS; in this instrument, long ion lifetimes (tens of ms) and relatively high He pressure result in significant collisional stabilization and increased high-mass abundance. The dehydrates rapidly react with adventitious H2O present in the IT-SIMS to form mono-, di-, and trihydrates. The rapidity of the reaction and comparison to aluminum oxyanion hydration suggest that H2O adds to the aluminosilicate oxyanions in a dissociative fashion, forming covalently bound product ions. In addition to these findings, it was noted that production of abundant oligomeric aluminosilicates could be significantly increased by substituting the countercation (NH4+) with the larger alkali ions Rb+ and Cs+. This constitutes a useful tactic for generating large aluminosilicate oligomers for surface characterization and ion-molecule reactivity studies.
- Research Organization:
- Idaho National Lab. (INL), Idaho Falls, ID (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- DE-AC07-99ID-13727
- OSTI ID:
- 912113
- Report Number(s):
- INEEL/JOU-00-00767; TRN: US0800276
- Journal Information:
- Analytical Chemistry, Vol. 73, Issue 2
- Country of Publication:
- United States
- Language:
- English
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