29Si and 17O NMR investigation of the structure of some crystalline calcium silicate hydrates

✍ Scribed by Xiandong Cong; R.James Kirkpatrick

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 1021 KB
• Volume: 3
• Category: Article
• ISSN: 1065-7355
• DOI: 10.1016/s1065-7355(96)90045-0

✦ Synopsis

This paper presents the results of a systematic investigation of the structure of 170-enriched, hydrothermally synthesized 1.1-nm tobermorite, 1.4-nm tobermorite, jennite, calciochondrodite, xonotlite, and hillebrandite, using 29Si magic angle spinning (MAS) NMR, 1H-29Si cross-polarization magic angle spinning (CPMAS) NMR, and 170 MAS NMR. The I70 and most of the 1H29Si CPMAS results are the first reported for these phases. Six types of oxygen sites were observed in tobermorite and jennite, including both Si-OH and Ca-OH linkages. The structure of 1.4-nm tobermorite is similar to that of 1.1-nm tobermorite with about 26% of the Ca2+'s in the interlayers. The results support the proposed jennite structure in which silicate chains and rows of OH groups alternately occur along the CaO layers [1]. Jennite contains long, single silicate chains similar to those in 1.4-nm tobermorite, with Si-OH sites primarily occurring on bridging tetrahedra, and there seems to be no interlayer Ca2*'s. Although the Si sites in xonotlite and calciochondrodite cross-polarize well, neither contains Si-OH linkages. AD-VANCED CEMENT BASED MATERIALS 1996, 3, 133--143 KEY WORDS: Jennite, NMR, Tobermorite, Xonotlite C rystalline calcium silicate hydrates are important minerals to cement science, some having compositions similar to that of calciumsilicate-hydrate (C-S-H) gel, and occurring in cement materials heated at moderate temperatures. The structure of C-S-H has been thought to be similar to those of 1.4-nm tobermorite and jennite [2]. Unfortunately, the structures of the phases of greatest interest to cement science have not been fully determined. Even for 1.1-nm tobermorite, whose structure has been solved [3], there is still controversy about the polymerization and the assignments of the 29Si magic angle spinning (MAS) NMR peaks [4--6].