At the ANKA facility in Karlsruhe, we have been developing mineralogical applications based on FT-IR micro- spectroscopy. Our aim is to address the need for more sophisticated investigations by using the advantages of the synchrotron edge radiation (SER) in the infrared spectral range compared to conventional laboratory sources: higher flux in the far IR and higher spatial resolution because of the higher brilliance in the complete IR domain.
One of our research directions is the study of new and not fully understood mineral crystal structures, transitions from semi-amorphous into crystalline state, mechanisms of incorporation of toxic ions into the mineral crystal structures. This will complement our results obtained by XRD, SEM methods, etc.
Another important need in many mineralogical applications is the identification of individual minerals as a function of spatial distribution. Images of the highest spatial resolution have been obtained using an atomic force microscopy. Unfortunately, there is no ability to differentiate crystallochemical differences with this technique. On the other hand, techniques such as (E)SEM provide some chemical information albeit at modest spatial fidelity. This trade-off between crystallochemical specifity and spatial fidelity means that we must often combine techniques in order to address analytical needs.
Infrared microscopy combines the rich crystallochemical specifity for samples even in amorphous state associated with vibrational spectroscopy. By using synchrotron-based infrared microspectroscopy we can investigate samples down to the diffraction limit. This extends a mainstream characterization tool into a new region of use.
The use of this technique can provide much new insight into the nature of mineral systems and mineral surface reactions. Examples with application to cement mineralogy that demonstrate the power of this technique will be discussed.
In this presentation we will focus on C-S-H phases, the main products of hydration of cement materials. These are amorphous calcium silicate hydrates (C-S-H), which are mostly characterized by their Ca/Si (C/S) ratio. The composition of the phases within the CaO-SiO2-H2O system varies over a large C/S range (0.6 to 2). Their properties determine to a large extend the physical properties of the whole system. Some critical points related to C-S-H that we would like to address using SER-FTIR will be presented: - carbonation of fresh and hardened cement pastes, - structure and incorporation of heavy metals in C-S-H phases, etc.
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