Surface instability and possible polymerization in at high temperatures

Abstract

We have investigated in detail the high-temperature phenomena of by means of optical microscopy, differential scanning calorimetry (DSC), and impedance spectroscopy. The so-called high-temperature transformation temperature is scattered widely over the temperature range of 82-117 , depending strongly upon the experimental conditions such as sample quality and experimental probes. It has been observed by thermomicroscopy that, upon heating above 110 , the cracks appeared at the surface and the crack pattern grew up with increasing temperature above 110 , and on suitable prolonged heat treatment at constant temperature near 110 . The activation energy is estimated from DSC, which revealed the wide scatter of over the range 82-117 . The complex ac impedance spectra near 113 were fitted by superposition of two Cole-Cole types of relaxations. The fast component is interpreted as proton migration in the bulk, while the slow component is accounted for as a cluster formation due to breaking and reforming of the hydrogen bond at the surface.