Different route of hydroxide incorporation and thermal stability of new type of water clathrate: X-ray single crystal and Raman investigation

摘要

Chlormayenite Ca12Al14O32[♦4Cl2] (♦-vacancy) is partially hydrated micro porouss mineral with hydroxide groups situated at various crystallographic sites. There are few mechanisms describing its hydration. The first one assumes Cl⁻ substitution by OH⁻ at the center of the structural cages (W-site). The second one determines the converting a T1O4 tetrahedron to a T1O3(OH)3 octahedron due to the replacement of oxygen at the O2 site by three OH-groups according to the scheme: (^O2O²⁻ + ^WCl⁻) → 3 × ^O2aOH. The third mechanism, not considered so far in the case of zeolite-like minerals, includes the hydroxide incorporation in form of hydrogarnet defect due to the arrangement of tetrahedral (OH)4 in vacant cages. This yields a strong hydrated phase containing even up to 35% of water more than in any currently known mineral applicable to Portland cement. Moreover, water molecules present in different structural cages are stable up to 355 K while dehydroxylation linked to the gradual loss of only 8% of OH⁻ groups according to 3^O2aOH⁻ → ^O2O²⁻ +^WOH⁻ + ^gH2O occurs at temperature range from 355 K to 598 K.