Hydrothermal synthesis of cement phases: An in situ synchrotron, energy dispersive diffraction study of reaction kinetics and mechanisms

Abstract

The equipment and methodology for in situ study of hydrothermal reactions using synchrotron radiation are described. This equipment is currently used at the Synchrotron Radiation Source, Daresbury Laboratory, UK, at temperatures up to about 230°C. To demonstrate the utility of this approach three experiments are described: crystallization of Fe- and Cr- doped tobermorite starting compositions to produce mixed tobermorite/xonotlite end products; crystallization of gyrolite and pectolite from a starting gel of gyrolite composition reacted with NaOH solution; and formation of the hydrogarnet, katoite, from a mixture of portlandite, amorphous alumina and amorphous silica. Kinetic analyses using the Ammi equation are reported for each system and used to calculate rate constants and deduce reaction mechanisms. Higher synchrotron X-ray energies (up to 200 keV) would allow thicker walled pressure vessels to be used, with a consequent increase in temperature to supercritical conditions, perhaps to above 400° C.

Key Words:

• Cement minerals
• Gyrolite
• Tobermorite
• Hydrogamet
• Pectolite
• In situ difhction
• Reaction kinetics