Simultaneous neutron diffraction and microwave dielectric characterisation of ammine materials – a non-destructive, non-contact characterisation tool for determining ammonia content in solids

Abstract

We have investigated ammonia adsorption in group two halides (MgI₂ and CaBr₂) using custom-built apparatus that permits simultaneous neutron diffraction, microwave dielectric characterisation and out-gas mass spectroscopy of solid state materials during ammonia adsorption. Deuterated ammonia was flowed over the sample and the uptake – as measured by mass flow meters, mass spectroscopy and structure – compared with the change in dielectric constant. An excellent correlation between ammonia content and dielectric property was observed and, when linked to diffraction, mass flow and mass spectroscopy data, could be used to determine the amount of ammonia present within the solid. The combination of these techniques could also be used to differentiate physisorbed and metal-coordinated ammonia and explain subtleties in the observed structural transformations.