Solid-State 29Si{27Al} TRAPDOR-MAS and CP-MAS 29Si NMR Experiments on the Atomic Structural Environments of Aluminum and Silicon in Siliceous Sinters
EMSL Project ID
34312
Abstract
This study proposes to accumulate preliminary data documenting the atomic environment of silicon in thermal spring deposits. These 'siliceous sinters' form at low temperatures (30 to 105 C), under different pH (generally 6 to 9) and water chemistry conditions. Since siliceous sinters are an important site for the preservation of microfossils of ancient microbial lineages, understanding how and when microfossils are preserved in the geological record is critical to unraveling the authenticity of purported fossil organisms. Solid-state silicon, aluminum, and boron NMR spectra are distinct for siliceous sinters formed in different locations and under different thermal and chemical environments. This is known from studies conducted in summers 2002 and 2003. Most recently, cross-polarization experiments with silicon showed two dominant types of silicon environments, Q3 and Q4. Q3 sites have significant amounts of silanol groups in network modifying sites but it is not know whether other ions populate neighboring cation sites. Other cations could modify the silica network either by terminating silicate chains or by substituting for silicon in the structure. Hypothetically, if consistent differences are noted in the number and type of neighboring cations, then subsequent silica phase transition rates would be affected. This is important in the potential preservation of microfossils from thermal spring environments. I propose to use TRAPDOR experiments to determine whether Al, in addition to protons, occupy nearest neighbor sites in the silicate matrix. Al would be a network former.
To this end, I propose a limited series of experiments using a small set (4 to 6) samples. TRAPDOR experiments would be conducted by monitoring Si-29 NMR while simultaneously irradiating the sample with the Al resonance frequency. Potential problems arise because of the proximity of Si-29 and the Al resonance frequency.
Project Details
Project type
Limited Scope
Start Date
2009-04-22
End Date
2009-06-22
Status
Closed
Released Data Link
Team
Principal Investigator