The bonding environment of chlorine in silicate melts

The local bonding environment of chlorine in silicate melts has a profound influence over the thermodynamic properties and structure melt, affecting viscosity, rheology, volatile degassing potential. To constrain Cl natural melts, we have determined K-edge X-ray absorption fine (XAFS) spectra for 44 experimentally produced glasses both near edge (XANES) extended (EXAFS) regions. In pre-edge region, presence peak indicates covalent with silicon. Addition divalent cations suppresses this feature, its centroid shifts to higher energy, indicating change increasingly more ionic bonding. XANES region main E0, energy maximum intensity, EMax, are also compositionally dependent. SiO2- rich relatively low values E0 EMax while addition 2+ ions increases close those found end-member chlorides CaCl2, MgCl2, FeCl2. two Na-rich glasses, corresponding energies NaCl. It appears, therefore that is closely related simple chlorides. This may be due clustering which generates CaCl, MgCl, FeCl NaCl linkages either themselves or rearrangements during quenching. EXAFS parts glass confirm conclusions derived from region. These show that, as expected Ca Fe2+ leads R-space peaks anhydrous CaCl2 FeCl2 respectively. order determine if depend on pressure, temperature fugacity synthesis, 9 experiments were conducted using single starting composition (Fe-free haplobasalt, An50Di28Fo22) across range temperatures (1300–1400 °C), pressures (5–20 kbar), fugacities (f(Cl2)) (1.38E−03 1.66E−06), water contents (expected 0–8 wt% H2O). results there almost no regions, independent intensive parameters experiment all quench same around atoms.