Molecular Hydrogen in Natural Mayenite

• Main Authors: Evgeny Galuskin, Irina Galuskina, Yevgeny Vapnik, Mikhail Murashko
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Minerals
• Subjects: mayenite; fluorkyuygenite; Raman spectroscopy; molecular hydrogen; H₂; pyrometamorphic rocks
• Online Access: https://www.mdpi.com/2075-163X/10/6/560

In the last 15 years, zeolite-like mayenite, Ca₁₂Al₁₄O₃₃, has attracted significant attention in material science for its variety of potential applications and for its simple composition. Hydrogen plays a key role in processes of electride material synthesis from pristine mayenite: {Ca₁₂Al₁₄O₃₂}²⁺(O²) → {Ca₁₂Al₁₄O₃₂}²⁺(e⁻)₂. A presence of molecular hydrogen in synthetic mayenite was not confirmed by the direct methods. Spectroscopy investigations of mayenite group mineral fluorkyuygenite, with empirical formula (Ca_12.09Na_0.03)_∑12.12(Al_13.67Si_0.12Fe³⁺_0.07Ti⁴⁺_0.01)_∑12.87O_31.96 [F_2.02Cl_0.02(H₂O)_3.22(H₂S)_0.15□_0.59]_∑6.00, show the presence of an unusual band at 4038 cm⁻¹, registered for the first time and related to molecular hydrogen, apart from usual bands responding to vibrations of mayenite framework. The band at 4038 cm⁻¹ corresponding to stretching vibrations of H₂ is at lower frequencies in comparison with positions of analogous bands of gaseous H₂ (4156 cm⁻¹) and H₂ adsorbed at active cation sites of zeolites (4050–4100 cm⁻¹). This points out relatively strong linking of molecular hydrogen with the fluorkyuygenite framework. An appearance of H₂ in the fluorkyuyginite with ideal formula Ca₁₂Al₁₄O₃₂[(H₂O)₄F₂], which formed after fluormayenite, Ca₁₂Al₁₄O₃₂[□₄F₂], is connected with its genesis. Fluorkyuygenite was detected in gehlenite fragments within brecciaed pyrometamorphic rock (Hatrurim Basin, Negev Desert, Israel), which contains reduced mineral assemblage of the Fe-P-C system (native iron, schreibersite, barringerite, murashkoite, and cohenite). The origin of phosphide-bearing associations is connected with the effect of highly reduced gases on earlier formed pyrometamorphic rocks.