New microbalance measurement of ceramic reactivity: a scoping study.

The basis for the scoping study proposed here is a new law, discovered by the applicants, which shows that the mass gain and associated expansive strain caused by the chemisorption of atmospheric moisture by fired clay ceramics are both proportional to (time)1/4. This fractional power law dependence means that equal amounts of mass will be gained after 1, 16, 81, 256 etc seconds/ days/ years (corresponding to t = 14, 24, 34, 44 seconds/ days/ years). This progressive chemically driven process indicates a very remarkable rehydroxylation of the fired clay which is so slow that it continues certainly over all practical historical timescales. Indeed we have found residual reactivity in 2000 year old ceramic. The extremely slow progress of the reaction appears to be fundamental to these materials and must be scientifically significant. The underlying mechanisms of this reaction are as yet far from understood. However, mass gain must be the more fundamental measure of the underlying chemisorptive process, with expansive strain being a consequence of this. In support of this approach, we have recently been successful in obtaining funding from EPSRC for an ultra-high accuracy recording microbalance (CiSorp Water Sorption Analyser). This new equipment provides an entirely new level of precision in mass measurement and environmental control. We have already obtained some spectacular results using this equipment which have enabled us to examine the mass gain process with an unprecedented level of precision and which give full confidence in the use of the mass gain approach to study the kinetics of the chemisorption/rehydroxylation process. In this scoping study we aim to shift the emphasis from strain measurement (which, with one exception, has been the only investigative tool employed since studies of moisture expansion began in the 1920s) to mass measurement as the better methodology for studying the fundamentals of the reaction process. It is urgent to establish comprehensively that this new equipment will so greatly revolutionise the study of chemisorption in fired clay ceramics that the focus of future work should be transferred to mass measurement. The proposed work, which is entirely based on a number of new discoveries made by the applicants, is a contained and focussed study to assess the magnitude of the mass gain effect in a wide range of ceramic types that have not yet been examined using this technique. This will give new insights into a number of phenomenological features of fired clay ceramic behaviour which have yet to be explored and will form an essential basis for any further scientific examination of these materials. The main objectives of the project are to carry out the first microbalance measurements of mass gain in freshly fired ceramic and to establish the significance of the quartz transition temperature (575 deg C) on mass gain in the same materials that have been reheated to both the original firing temperature and 500 deg C. This will allow us to establish whether reheating can indeed return the ceramic to its as fired state as has been claimed, but never proven, in previous work based on strain measurement. We will also assess the use of powdered samples (compared to small bulk samples) as a means of measuring mass gain in potentially much less reactive materials such as porcelain and other refined ceramics. Finally, from careful measurements of mass gain at different temperatures, to calculate the activation energies of the Stage I and Stage II reactions.