No abstract

a b s t r a c t 17 O MQMAS NMR was used to characterize the influence of zirconium on the structural organization of soda-lime borosilicate glasses. A new method of quantitative analysis of the 17 O MQMAS spectra is presented, by a direct fit of the two-dimensional MQMAS spectrum which provides the resolution of all the structural groups in glasses containing up to five oxides. Additional data were also obtained from the quantitative deconvolution of the 11 B MAS NMR spectra, with the help of the direct fit of MQMAS data as well. Excess of non-bridging oxygen is clearly identified in these glasses. Sixfolded zirconium is preferentially compensated rather than the tetrahedral boron and calcium only partially compensate the tetrahedral boron. Alteration gels arising from glass leaching were probed by oxygen-17 supplied by the alteration solution. Most of the zirconium is inserted in the silicate network forming Si-O-Zr bonds with the same configuration in the glass and in the gel. During leaching, calcium clearly remains in the alteration gel, either near non-bridging oxygen or as a zirconium charge compensator. This quantitative approach applied to 17 O MQMAS spectra demonstrates its potential for investigating the structure of increasingly complex glass and gel compositions.

No abstract

The positions of nu8a and nu*(NH) bands in the spectrum of protonated 2,6-dimethylpyridine vary with the strength of Brønsted acidity: the higher the nu*(NH) wavenumber and the lower the nu8a wavenumber, the stronger the acidity. The results obtained with 2,6-dimethylpyridine adsorption correlate with those obtained by CO adsorption experiments on a series of faujasite zeolites (LiHNaY, KHNaY, HY, HY(SA), HNaX). These relations were extended to gamma-Al2O3 having weak Brønsted acidity, not detected by pyridine and hardly detected by CO. The number (0.1 per nm2) and the strength (corresponding to delta nu (OH) by CO = 155 cm(-1)) of the most acidic OH groups of Al2O3, as well as the position of the corresponding nu (OH) band (<3700 cm(-1)) are deduced from 2,6-dimethylpyridine adsorption experiments.

No abstract

No abstract