Led by Dr Valerie Dupont and Dr Tim Comyn from the University of Leeds' Faculty of Engineering, the team carried out a series of experiments on Diamond's High resolution powder diffraction beamline, I11, using intense X-rays to study the carbon capture and hydration process in CaO based materials on the nano-scale. Their observations suggest a mechanism for the interaction between CaO and water during hydration.
"We found that the stresses in the calcium hydroxide phase when bound to CaO were more than 20 times higher than its strength, leading to disintegration and the generation of nano-sized crystallites. Although the generation of a high surface area is a good thing, mechanical friability needs to be kept in check in order to achieve long term reliability for these systems. Our analysis provides an explanation of the enhanced capture/disintegration observed in CaO in the presence of steam. Now we understand this, the next step is to develop methods for improving the materials used, and apply the same techniques to other systems," said Dr Tim Comyn, Faculty of Engineering, University of Leeds.
CaO readily forms a shell of calcium hydroxide when exposed to water in the air (right). Due to differences in atomic congurations (top left) between the oxide and hydroxides, enormous strains develop due to the interface. These strains of 0.78% lead to stresses 20 times higher than the rupture strength of the hydroxide leading to rupture and the generation of nanoparticles.
Deconvolution of the data generated by Diamond (bottom left) allows the Leeds team to determine the size and strain in these layers, from the breadth of the peaks (the peaks from CaOH are far narrower than CaO). Conventional X-ray sources would have considerable peak overlap, making this type of analysis almost impossible.
Roger Molinder, an Engineering and Physical Sciences Research Council (EPSRC) funded PhD student on the project, describes, "Using the
|Contact: Paula Gould|
University of Leeds