%0 Journal Article
%T Transformation of meta-stable calcium silicate hydrates to tobermorite: reaction kinetics and molecular structure from XRD and NMR spectroscopy
%A Jacqueline R Houston
%A Robert S Maxwell
%A Susan A Carroll
%J Geochemical Transactions
%D 2009
%I BioMed Central
%R 10.1186/1467-4866-10-1
%X Burning of fossil fuels is believed to be the largest contributor to anthropogenic CO2 emissions and global climate change [1,2]. To reduce emissions and subsequently offset global warming, one solution is to inject CO2 into well-bores of depleted oil and gas reservoirs. Well- bores, however, are lined and plugged with Portland-based cement, which can chemically degrade in the presence of CO2 and water over time [3,4]. This presents a problem for long-term CO2 storage if reservoirs have the potential to leak through abandoned well sites. Deleterious effects can occur from leakage, including contamination of groundwater and subsurface resources and drastic changes to ecosystems [5-8]. In order to predict these processes and subsequently assess the long-term fate and storage of CO2, we need experimental data coupled with accurate simulations to identify reaction rates and pathways for cement dissolution and growth. However, there are few rate data on precipitation reactions and even fewer studies that derive growth mechanisms for cement-based minerals.Calcium silicate hydrates are key components in cement minerals and have been suggested as precursor solids for the growth of stable minerals such as tobermorite and gyrolite [9,10]. Calcium silicate hydrates include many meta-stable and amorphous disordered structures, from which stable and highly crystalline materials such as tobermorite can form when heated. The mineral tobermorite is stable over a temperature range of ~80¡ãC to ~150¡ãC but can be produced at temperatures greater than 200¡ãC as a meta-stable solid [9]. Orthorhombic tobermorite can be found as either a 9 £¿, 11 £¿ or 14 £¿ polytype depending on the number of water molecules present in the structure. The structure of 11 £¿ tobermorite consists of layers of hydrated calcium ions bonded to repeating silicate chains that have bridging and non-bridging Si (Q2) and branching Si (Q3) sites [10-13]. The silicate chains repeat every third tetrahedron, giving rise to t
%U http://www.geochemicaltransactions.com/content/10/1/1