V41B-3069
Effect of pressure on the carbon speciation in silicate glasses and melts: Insights from multi-nuclear solid-state NMR
Thursday, 17 December 2015
Poster Hall (Moscone South)
Eun Jeong Kim1, Yingwei Fei2 and Sung Keun Lee1, (1)Seoul National University, Seoul, South Korea, (2)Carnegie Institution for Science Washington, Washington, DC, United States
Abstract:
The pressure-induced structural changes in carbon-bearing silicate glasses and melts is essential to understand the changes in melt properties in the Earth interior and yield atomistic insights into the deep carbon cycle. Despite the extensive pioneering studies on carbon-bearing silicate glasses, spectroscopic and scattering studies at high pressure above ~4 GPa is limited due to the lack of suitable experimental probes. Here, we report the pressure-induced structural changes around C, Si and Al in albite and Na-trisilicate (Na2O:SiO2=1:3, NS3) glasses with varying pressure up to 8 GPa, using 27Al, 29Si and 13C solid-state high-resolution NMR. 27Al 3QMAS NMR spectra for carbon-bearing albite glasses quenched from melts at high pressure up to 6 GPa show only [4]Al environments. The FWHM of [4]Al in albite glasses increases with increasing pressure, indicating that the overall densification of albite glasses at high pressure is accompanied by an increase in the topological disorder around Al. 29Si MAS NMR spectra for NS3 glasses at high pressure up to 8 GPa show the presence of highly coordinated Si, [5,6]Si, which contributes to an increases in the total configurational disorder in the NS3 glasses with pressure. 13C MAS NMR spectra for carbon-bearing albite glasses show the presence of dominant fraction of CO2, and minor amounts of CO32-, and CO. At least three distinct carbonate species, such as [4]Si(CO3)[4]Si, [4]Si(CO3)[4]Al, and CO32- were observed. Among those species, the increase in the fraction of [4]Si(CO3)[4]Al species is most prevalent. 13C MAS NMR spectra for NS3 glasses show the presence of carbonate species. The peaks position of the carbonate species shifts to lower frequency upon compression, suggesting the pressure-induced structural distortion of CO32- in the glasses above 6 GPa. Spin-lattice (T1) relaxation time for molecular CO2 in carbon-bearing albite glasses increases with increasing pressure. T1 relaxation time for CO2 species at 6 GPa is 3.5 times longer than that at 1.5 GPa. The corrected solubility of carbon in albite glasses with T1 relaxation increases linearly with increasing pressure. The current experimental results can shed light on experimental opportunity to provide the structural details of carbon in the Earth’s interior.