Quantification of thaumasite in cementitious materials by 29Si {1H} cross-polarization magic-angle spinning NMR spectroscopy
| Autor: | H. J. Jakobsen, L. Hjorth, J. Skibsted |
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| Rok vydání: | 1995 |
| Předmět: | |
| Zdroj: | Advances in Cement Research. 7:69-83 |
| ISSN: | 1751-7605 0951-7197 |
| DOI: | 10.1680/adcr.1995.7.26.69 |
| Popis: | 29Si {1H} cross-polarization (CP) magic-angle spinning (MAS) nuclear nagnetic resonance (NMR) is shown to be a valuable tool for detection and quantification of thaumasite in cementitious systems. A 29Si {1H} CPIMAS NMR method for quantitative analysis of thaumasite employing 1H and 29Si rotating-frame relaxation times TH1p and TSi1p and the 1H—29Si CP time TSiH is introduced. The method is illustrated by determination of the thaumasite content in five laboratory samples containing carbonates and sulphates from different sources. The use of 29Si{lH} CP/MAS rather than 29Si MAS NMR for the detection of thaumasite is shown to reduce the instrument time by up to a factor of IOOO because of the large difference in 1H and 29 spin-lattice relaxation times (TH1 and TSi1) and the 29Si intensity gain by CP for this mineral. The non-standard behaviour of the 1H and 29 spin-lattice relaxation processes observed for some samples is shown to follow a decay exponential in t with time t. 27Al MAS NMR is used to quantify ettringite for some of the samples. In contrast to previous proposals on the mechanism for the formation of thaumasite, it is demonstrated using 29Si{lH} CP/MAS and 27Al MAS NMR that considerable quantities of thaumasite can be produced in virtually aluminium-free materials. 13C {lH} CP/MAS NMR of pure thaumasite shows its potential in characterizing the carbonate anions in this mineral. |
| Databáze: | OpenAIRE |
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