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Minerals in cement chemistry: a single-crystal neutron diffraction and Raman spectroscopic study of thaumasite, Ca3Si(OH)6(CO3)(SO4)o12H2O. (Articolo in rivista)
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- Label
- Minerals in cement chemistry: a single-crystal neutron diffraction and Raman spectroscopic study of thaumasite, Ca3Si(OH)6(CO3)(SO4)o12H2O. (Articolo in rivista) (literal)
- Anno
- 2012-01-01T00:00:00+01:00 (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#doi
- 10.2138/am.2012.4058 (literal)
- Alternative label
G. DieGo Gatta,
Garry J. Mcintyre,
Julia G. SwanSon,
anD Steven D. JacobSen (2012)
Minerals in cement chemistry: a single-crystal neutron diffraction and Raman spectroscopic study of thaumasite, Ca3Si(OH)6(CO3)(SO4)o12H2O.
in The American mineralogist
(literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#autori
- G. DieGo Gatta,
Garry J. Mcintyre,
Julia G. SwanSon,
anD Steven D. JacobSen (literal)
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- Pagina fine
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- http://dx.doi.org/10.2138/am.2012.4058 (literal)
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- Scopus (literal)
- Google Scholar (literal)
- Http://www.cnr.it/ontology/cnr/pubblicazioni.owl#affiliazioni
- Dipartimento di Scienze della Terra, Universita' degli Studi di Milano, Via Botticelli 23, I-20133 Milano, Italy
CNR-Istituto per la Dinamica dei Processi Ambientali, Milano, Italy
The Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001,
Kirrawee DC, New South Wales 2232, Australia
Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A. (literal)
- Titolo
- Minerals in cement chemistry: a single-crystal neutron diffraction and Raman spectroscopic study of thaumasite, Ca3Si(OH)6(CO3)(SO4)o12H2O. (literal)
- Abstract
- Thaumasite, Ca3Si(OH)6
(CO3
)(SO4
)?12H2O, is recognized as a secondary-alteration mineral and
indicator of sulfate attack in Portland cement in contact with sulfate-rich groundwater, especially in
cold regions. The hydrogen positions in thaumasite have been determined from single-crystal neutron
diffraction structure refinements at 300 and 22 K. No phase transitions occur within the temperature
range investigated. The structure of thaumasite is largely held together by hydrogen bonding. The
major structural units [CO3
groups, SO4
tetrahedra, Si(OH)6
octahedra, and Ca(OH)4
(H2O)4
polyhedra] are interconnected via 10 distinct hydrogen bonds. Analysis of the difference-Fourier maps of
the nuclear density reveals the positions of all 10 hydrogen atoms in the structure, and the hydrogen
bonding becomes shorter (stronger) upon decreasing temperature to 22 K. The SO4
tetrahedron expands upon decreasing temperature (i.e., negative thermal expansion at the molecular level), driven
by shortening of the hydrogen bonding between [Ca3Si(OH)6
(H2O)12
]
4+
columns. Polarized Raman
spectra of thaumasite show that the ?1
symmetric stretching modes of Si(OH)6
, SO4
, and CO3
occur at
658, 983, and 1066 cm-1
, respectively. In addition, the out-of-plane bending mode (?2
) and asymmetric
stretching mode (?3
) of the carbonate group are tentatively assigned to bands at 887 and 1400 cm-1
,
respectively. Bands at 418 and 455 cm-1
(and possibly at 477 cm-1
) are attributed to the symmetric
bending modes (?2
) of the sulfate group, and we observe a possible asymmetric stretching mode (?3
)
of SO4
at 1090-1100 cm-1
. Splitting of some sulfate and carbonate vibrational modes may occur due
to hydrogen bonding on all the oxygen sites. At 1685-1710 cm-1
we observe the H2O bending modes
(H-O-H), and from 2900-3600 cm-1
there are 13 distinct bands associated with bending overtones
and the O-H stretching vibrations corresponding to H-positions determined in the neutron diffraction
study. The effect of the low-temperature stability of thaumasite on the pronounced \"thaumasite sulfate
attack\" of Portland cements observed in cold regions is discussed. (literal)
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