Novel opportunities of structural investigations of glasses by 2D NMR, multiple quantum NMR and ²⁷Al MAS NMR lineshape analysis

Abstract

The recent progress in NMR of glasses is demonstrated using both traditional and improved two‐dimensional (2D) NMR techniques. A novel approach for measuring connectivities Qn units in amorphous and polycrystalline solids is explained. Several examples of phosphate samples are presented to show e.g. how chain end groups can be distinguished from pyrophosphate units. Additionally, novel results of 27Al NMR investigations in mullites and Na2O‐SiO2‐Al2O3 glasses were obtained using a careful lineshape analysis. In mullites three different AlO4 units can be found including an estimation of the relative Al occupancy of the various groups. In ternary Na2O‐Al2O3‐SiO2 glasses we could prove the presence of two AlO4 sites with Al being surrounded by four Q3 units or possibly one terminal oxygen instead of a Q3 unit (60 ppm) and by four Q4 groups (53 ppm). Finally, two different Na sites have been detected for the first time using 23Na MQ NMR in a glass 22.7 Na2O 0.7 B2O 69.8 SiO2.

Effect of substituting CaO with BaO on the viscosity and structure of CaO‐BaO‐SiO2‐MgO‐Al2O3 slags

“…The Al‐related structural units can be quantified after deconvoluting the 27 Al MAS‐NMR spectra into separate AlO 4 and AlO 5 characteristic peaks. The AlO 4 structural units can be fitted by two distinct Gaussian peaks corresponding to the AlO 4 (A) and AlO 4 (B) with different quadrupole coupling constants at approximately 55 ppm and 40 ppm, respectively . The AlO 4 (A) represents the AlO 4 structural units surrounded by four Q 3 units or possibly O − substituting one Q 3 structural unit, and AlO 4 (B) represents the AlO 4 structural units surrounded by four Q 4 structural units .…”

“…The AlO 4 structural units can be fitted by two distinct Gaussian peaks corresponding to the AlO 4 (A) and AlO 4 (B) with different quadrupole coupling constants at approximately 55 ppm and 40 ppm, respectively . The AlO 4 (A) represents the AlO 4 structural units surrounded by four Q 3 units or possibly O − substituting one Q 3 structural unit, and AlO 4 (B) represents the AlO 4 structural units surrounded by four Q 4 structural units . The AlO 5 structural units can be fitted with one Gaussian peak at approximately 25 ppm .…”

“…The AlO 4 (A) represents the AlO 4 structural units surrounded by four Q 3 units or possibly O − substituting one Q 3 structural unit, and AlO 4 (B) represents the AlO 4 structural units surrounded by four Q 4 structural units . The AlO 5 structural units can be fitted with one Gaussian peak at approximately 25 ppm . Thus, the 27 Al MAS‐NMR spectra of all slag samples were deconvoluted using the Gauss‐Deconvolution method with a minimum correlation coefficient of r 2 ≥ .99.…”

Influence of Small Additions of Al2O3 on the Properties of the Na2O·3SiO2 Glass

“…Therefore, they hypothesized that the observed anomalies in the experimental properties of these glasses might be a result in the shift of the percolated alkali diffusion channels from NBO-rich regions to AlO 4 rich regions. 16,19 Detailed information on short-range structure of aluminosilicate glasses may be obtained by 27 NMR at the magic angle (MAS). 20 Early 29 Si NMR studies on sodium-modified glasses were reported by Maekawa et al 21 They found that aluminum tends to be coordinated to SiO 4 -4 tetrahedra of most polymerized states, in agreement with the Loewenstein's rule (the so-called Al-O-Al avoidance rule).…”

Structure and solubility behaviour of zinc containing phosphate glasses

“…DQ experiments under MAS allow for determination of through space connectivities between neighbouring Q n species which have dipole-dipole coupling. [45][46][47][48] Peaks on the diagonal (auto-correlated peaks) represent DQ coherences between adjacent units of the same kind, whereas off-diagonal (cross-correlated) pairs correspond to DQ coherences between chemically different groups. 49,50 For the x = 0 glass composition, a single broad auto-correlated peak at ca.…”