Crystal Structure of Thaumasite, a Mineral containing [Si(OH)6]2− Groups

Edge, R.A.; Taylor, H. F. W.

doi:10.1038/224363a0

Cited by 37 publications

(7 citation statements)

References 3 publications

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“…The precise nature of thaumasite structure can be better understood if the coordination number of silicon 4 or 6 with the hydroxyl group is clarified. However, this is still an unresolved issue at this moment since 6‐coordinated Si is rare in silicates or silicon nitrides. This might happen for some minerals under pressure, but thaumasite is formed at atmospheric pressure.…”

Section: Structures and Model Constructionmentioning

confidence: 99%

Understanding the atomic and electronic origin of mechanical property in thaumasite and ettringite mineral crystals

San

Tao

et al. 2018

J Am Ceram Soc

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Ettringite and thaumasite are 2 of the relevant secondary products in portland cement minerals. They are rare crystals with high water content. Two density functional theory based ab initio packages VASP and the OLCAO were used for exploring the geometry structure, electronic, and mechanical properties of ettringite and thaumasite. The calculations focus on the comparison of their structures and properties to gain insights that can reveal the minute difference in properties due to differences in their structure, composition and water content. Detailed analysis of interatomic bonding shows the similarities and subtle difference between them even though thaumasite has the Si tetrahedron as the backbone unit in contrast to ettringite with Al‐columns and no Si atoms. Moreover, thaumasite has strong C–O bonds that are absent in ettringite, and ettringite has far more water molecules with a substantial contribution from the hydrogen bonding. It is shown that the role played by relatively strong S–O bonds in both crystals has a large impact on the hydration in these crystals. On the basis of calculated total bond order density, it is concluded that thaumasite is slightly more cohesive than ettringite consistent with the calculated mechanical properties. The detailed comparative results for these 2 important minerals we obtained in this paper, many of them for the first time, will pave the way to understanding the structure and electronic structure origin of other more complex cement crystals.

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Section: Structures and Model Constructionmentioning

confidence: 99%

Understanding the atomic and electronic origin of mechanical property in thaumasite and ettringite mineral crystals

San

Tao

et al. 2018

J Am Ceram Soc

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“…Thaumasite is the only mineral known to contain silicon in six-coordination with hydroxyl groups. First single-crystal X-ray diffraction evidence for this has been obtained by Edge and Taylor [37,38]. These authors found that thaumasite crystallizes in the hexagonal, P6 3 , S.G. (a = 11.04, c = 10.39 Å, Z = 2) and that its structure is "based on columns of empirical composition [Ca 3 Si(OH) 6 .12H 2 O] 4+ running parallel to c, between which occur the [CO 3 ] 2− , [SO 4 ] 2− groups and H 2 O molecules.…”

Section: Crystal Structure Drawmentioning

confidence: 92%

TG/DTG-DSC and high temperature in-situ XRD analysis of natural thaumasite

et al. 2021

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This paper investigated thermal properties of natural thaumasite, such as phase composition and reaction mechanism of thermal decomposition using simultaneous TG/DTG-DSC in Ar and Air medium up to 1673 K, coupled with masspectrometer for analysis of evolving gases, and in-situ powder X-ray diffraction measurements. The transitional solid phases, grown with increasing of temperature at thaumasite thermal decomposition, are calcium hydrogen carbonate (Ca(HCO 3) 2) and hydrogen sulphate (Ca(HSO 4) 2), calcite, anhydrite, calcium silicates (wolastonite and larnite), calcium silico-carbonate (spurrite), and calcium silico-sulphate (ternesite). The thermal decomposition in both gaseous media includes the stages of dehydration, dehydroxylation, dacarbonation and desulphuration with obtaining a solid residue of varying degrees of crystallinity. The main solid phase, grown at the highest temperatures, is larnite. Based on the obtained results it was proposed the scheme of chemical reactions, which presents the reaction mechanism of thaumasite thermal decomposition. The defined scheme has both fundamental importance by adding new details of reference data, and practical application for thaumasite identification in chemical archaeology, and in the chemistry of cement and cement-based materials.

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“…To make the matter even more complex, a second mineral, thaumasite may develop through the isostructural transformation of ettringite at temperatures below about 15 o C in the presence of soluble silica and carbonate. The result of the formation of ettringite can be considerable expansion, while the formation of thaumasite will result in a loss of strength and is normally preceded by the formation of ettringite [1,3,10,11,12].…”

Section: Sulfate-induced Heavementioning

confidence: 99%