ChemInform Abstract: ²⁹Si Magic Angle Spinning NMR Study of Local Silicon Environments in Amorphous and Crystalline Lithium Silicates.

Sol–Gel Preparation and Characterization of Lithium Disilicate Glass–Ceramic

“…However, while Q 4 species may be present to a small extent, there is no clear evidence in the NMR spectra for Q 2 , which should give rise to a signal at −74 ppm. A similarly wide distribution has been reported for Li 2 SiO 3 glass prepared by a melting method 6,7,24,25 . The bond angle and bond length distribution may be increased for sol–gel derived materials because of residues incorporated into the major phases and a less disordered network structure.…”

“…In addition, in the Li 2 O–SiO 2 binary system, immiscibility extends to 33% Li 2 O 2 . Intensive studies have been carried out on the network structure and nucleation/crystallization behavior of lithium silicates (including Li 2 Si 2 O 5 ) synthesized by glass melting methods, with the finding that Q 2 , Q 3 , and Q 4 species were always coexisting in the glasses, 3–7 and Li 2 Si 2 O 5 and metastable lithium silicate (Li 2 SiO 3 ) simultaneously nucleate and coexist in the early stages of heat treatment (∼454°C) 8–14 . By contrast, there have been considerably fewer studies on lithium silicates (including Li 2 Si 2 O 5 ) prepared by sol–gel processes 15–22 …”

Effect of sulphur on the structure of silicate melts under oxidizing conditions

“…Lippmaa et al, 1979;Smith et al, 1983;Emerson et al, 1989;Maekawa et al, 1991;Stebbins, 1995). For fully polymerized melt like HPG, the silicate framework is mostly composed of Q 4 units (NBO = 0 and BO = 4) and will show low frequency position (<-100 ppm) in the 29 Si NMR peak as established in previous studies (Schramm et al, 1984;Brandiss and Stebbins, 1988;Maekawa et al, 1991;Kummerlen et al, 1992;Schmidt et al, 2001).…”

Sol–Gel Route to Nanocrystalline Lithium Metasilicate Particles

“…found that for glasses containing more than approximately 36 mol% Li 2 O, lithium metasilicate becomes the primary nucleating phase, and the nucleation rates increase sharply as the glass composition approaches equal proportions of Li 2 O and SiO 2 . In addition, an NMR study revealed that in lithium silicate glasses prepared by either glass‐melting methods or sol–gel methods, Q 2 structural units always coexist with Q 3 units 21–25 . Furthermore, X‐ray diffraction (XRD) revealed that in most cases lithium metasilicate preferentially crystallizes in lithium silicate glass–ceramics prepared by sol–gel processes, regardless of the composition 21,26,27 .…”