Moisture expansion and mass gain in fired clay ceramics

We report the first measurements of mass gain and expansive strain in clay ceramics immediately following firing. The results show that both mass gain and expansive strain follow a well defined two-stage process, each stage of which is linear with (time)1/4, with a transition from the first to the second stage commencing at t ∼ 1.5 h. The first stage mass gain and strain rates are ∼3.5 times greater than the second stage rates. The strain is found to show the same linear relationship with mass throughout both stages providing evidence that the underlying physical process is the same in each stage. The early time measurements are unique in providing experimental evidence for t1/4 kinetics for both strain and mass gain over times ranging from minutes to days and are consistent with earlier strain data showing t1/4 kinetics over times ranging from days to centuries.