Electron Microscope and X-ray Unit (EMX)
High Temperature XRD – In situ analysis
XRD is often used to investigate products after heating, and we speculate at what happened while hot, but it is possible to study some materials at high temperature. This is used to study some reactions in-situ or, in this case, determined the thermal expansion characteristics of the novel MAX phases. The HTK heating stage allows reactants to be laid on a platinum strip and heated in a vacuum (or in air or N2). XRD scans are taken repeatedly throughout the process and you can ‘watch’ what happens. Subtle changes in peak positions indicate the expanding crystal lattice that gives the thermal expansion properties. As the MAX phases are hexagonal there are2 different expansion coefficients both of which could be measured in a single experiment. The decomposition of the original structure above 700°C is also evident. These samples cannot always be made at the high density required for physical measurement of these parameters, and so XRD became the only way to measure these properties.
High-temperature XRD can also unveil reaction kinetics, intermediate phases in a reaction, or high-temperature phases that decompose at lower temperatures, all of which are invisible to someone only taking room temperature scans.
Dr Dylan Cuskelly
School of Engineering
Faculty of Engineering and Built Environment, SE Mech Eng
The University of Newcastle