Off-Resonance Nutation Nuclear-Magnetic-Resonance Study of Framework Aluminosilicate Glasses with Li, Na, K, Rb or Cs as Charge-Balancing Cation

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Solid-State Mas NMR-Study of Pentameric Aluminosilicate Groups wiht 180-Degrees Intertetrahedral AL-O-SI Angles in Zunyite and Harderite

The minerals zunyite, AL(13)Si(5)O(20)(OH,F)(18)Cl, and harkerite, Ca24Mg8[AlSi4(O,OH)(16)](2)- (CO3)(8)(BO3)(8)(H2O,Cl), have been studied by means of solid-state Al-27 MAS NMR. Zunyite contains Si5O16 pentamers and harkerite contains AlSi4(O,OH)(16) pentamers. These pentameric groups are unique because their T-O-Si angles are almost 180 degrees. Chemical analysis of the zunyite sample shows that it has excess Al: the A-Si ratio is 2.9, compared with the ideal of 2.6. High-speed spinning Al-27 MAS NMR spectra (11-13 kHz) showed two more signals than the spectra obtained by Kunwar et al. (1984). The signal with delta(iso) = 46.8 +/- 0.5 ppm represents the excess Al, which enters the central Si1 site of the Si5O16 pentamer. This assumption is confirmed by the fact that delta(iso) of Al in the AlSi4(O,OH)(16) pentamer in harkerite is 44 +/- 1 ppm. Additional proof comes from comparing the electrostatic energy and the quadrupole interaction of Al in either a Si1 or Si2 configuration. The Al site in the pentamers of zunyite and harkerite can be considered as a q(4)(4Si) site. In this case, Al-O-Si angles are correlated with the Al-27 chemical shift (Lippmaa et al., 1986). This correlation holds well for the Al-27 data for harkerite. The value for zunyite indicates that the structure adapts to the incorporation of Al in the Si1 site by a narrowing of the A1-O-Si angle to 171 +/- 2.5 degrees. The lower limit of the chemical shift range for Al in framework aluminosilicates is decreased by 12 ppm, from 55.8 ppm for mordenite to 44 ppm for harkerite

Interactions of Fullerenes and Calixarenes in the Solid-State Studied with C-13 Cp-Mas Nmr

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Changes in structural and electronic properties of the zeolite framework induced by extraframework Al and La in H-USY and La(x)NaY: A Si-29 and Al-27 MAS NMR and Al-27 MQ MAS NMR study

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Changes in Structural and Electronic Properties of the Zeolite Framework Induced by Extra-Framework Al and La in H-USY and La(x)NaY : A 29Si and 27Al MAS NMR and 27Al MQ MAS NMR Study

A 27Al 3Q MAS, a quantitative 27Al MAS, and a 29Si MAS NMR study has been carried out on La(x)NaY and H-USY. Assignment of the different types of Al coordinations has been done using the results of the MQ MAS experiments. The 29Si MAS and 27Al MAS NMR results obtained at high fields (14.1 T) and fast MAS up to 27 kHz made a quantitative assignment possible of the framework and nonframework Al coordinations. It is shown that highly charged octahedrally coordinated extraframework Al causes a polarization inducing a quadrupolar broadening of part of the framework Al in ultrastable Y. A similar interaction is found for the framework of La(x)NaY due to the La3+ cations. In both cases, charged extraframework species polarize the framework Al. In La(x)NaY, La3+ in a cation position and in H-USY extraframework octahedral Al are the origin of the polarization. Besides this short-range polarization effect, an additional long-range effect is observed in La(x)NaY. This long-range geometrical effect causes an increase in both Si-O-Al and Si-O-Si angles depending on the La content

29 Si-Nuclear magnetic resonance on the etching products of silicon in potassium hydroxide solutions

We present results of 29Si-nuclear magnetic resonance experiments on a large number of KOH solutions in which silicon has been dissolved. The goal of the experiments is to clarify the chemical composition of concentrated alkaline solutions after etching of silicon. It is confirmed that the initial etching product of wet-chemical etching of silicon in KOH is a silicate monomer. Increasing the silicon content of the solution gives rise to silicate polymerization products. The often reported aging of etching solutions is due to silica in the etchan

Multiple quantum Al-27 magic-angle-spinning nuclear magnetic resonance spectroscopic study of SrAl12O19: Identification of a Al-27 resonance from a well-defined AlO5 site

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