![]() Computer simulation of γ-Al 2O 3 microscrystal. Álvarez LJ, Leon LE, Sanz JF, Capitáno MJ, Odriozola JA. Observation and accurate quantification of 27A1 MAS NMR spectra of some Al 2SiO 5 polymorphs containing sites with large quadrupole interactions. J Solid State Chem 62(3):402–404.Īlemany LB, Massiot D, Sherriff BL, Smith ME, Taulelle F. Crystal structure of a new digermanate: Al 2Ge 2O 7. Other allophanes with Al/Si < 2, and which are poor in octahedra relative to tetrahedra, may also have significant Al in 5-coordinate sites.Īgafonov V, Kahn A, Michel D, Perez y Jorba M. We suggest that 5-coordination in Silica Springs allophane is associated with the edges of fragments of incomplete octahedral sheets that are bonded to disordered, though more complete, curved tetrahedral sheets in the primary particles of this allophane. The “true” chemical shift (after a small correction for quadrupolar shift) observed for 5-coordinate Al in Silica Springs allophane is 36 ± 1 ppm, which is consistent with shifts reported for 5-coordination in well-characterized crystalline structures. Use of 2 instruments and 2 field strengths allowed the integrity of the spectra and the assignment of 5-coordinate Al to be verified. For 1 sample, the peak for 5-coordinate Al is dominant. Spectra for all samples show peaks for 6- and 4-coordinate Al and also for 5-coordinate Al. Samples of Silica Springs allophane from Tongariro National Park, New Zealand, having Al/ Si atomic ratios in the range 1.1-1.9, were studied by 27Al nuclear magnetic resonance (NMR) spectroscopy with high field strength (9.4 and 11.7 T) and fast magic-angle spinning (MAS) (9-13 kHz).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |