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

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: (^O2O^2- + ^W Cl^-) → 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^- → ^O2O^2- + ^W OH^- + ^gH₂O occurs at temperature range from 355 K to 598 K.