An energy-dispersive diffraction system has been developed to study a variety of chemical reactions involved during the synthesis and in-service performance of industrial materials. Three basic cell systems have been designed, the choice for use depending on the characteristics of the specimen and on the nature of the conditions to be imposed (heating, gas-environment, etc.). These cells and their application are described by reference to three examples taken from recent studies: the hydration of cements, the synthesis of ceramics, and the crystallisation of amorphous (magnetic) metal alloys. It is found that, with the superior time resolution available with energy-dispersive diffraction, the reaction kinetics can be determined and new aspects of synthesis/performance can now be realised.