A phase transformation–phosphorescence model of europium-doped yttria-stabilized zirconia and its application in two-dimensional thermal history measurement

Abstract

Phosphorescence thermal history sensors are off-line temperature measurement devices with potential applications in harsh environments. However, changes in phosphorescence after heating at various temperatures or for various durations cannot be precisely quantified based on current theory. In this study, europium-doped yttria-stabilized zirconia (YSZ:Eu) was selected as a potential thermal history sensor and its structural and phosphorescence properties were characterized after heating at various temperatures. It was found that the tetragonal-to-cubic phase transformation of zirconia had a major effect on the phosphorescence intensity ratio (PIR) of YSZ:Eu. Accordingly, theoretical and semi-empirical versions of a novel phase transformation–phosphorescence model were developed based on Judd–Ofelt theory and the Avrami equation, and were used to quantify phosphorescence changes induced by heating YSZ:Eu at various temperatures and for various durations. The results of a calibration experiment showed that the PIR increased from 0.5 to 1.0 as the heating temperature and heating duration increased from 900 °C to 1200 °C and from 10 min to 80 min, respectively. The mean relative fitting errors of the theoretical and semi-empirical model were 2.2 % and 5.6 %, respectively. Finally, thermal history measurement was demonstrated in a flame-impingement experiment that was conducted using a phosphor-coated plate subjected to two different heating durations. The phosphorescence signals collected by an industrial camera were processed to yield two-dimensional (2D) surface-temperature distributions of the plate and compared with those obtained using an infrared camera. The average differences between the 2D surface-temperature distributions obtained by the two methods were 5.9 °C and 6.5 °C for 40 min and 80 min heating durations, respectively. These findings enhance theoretical understanding of thermal history sensing and will facilitate advancement from single-point to 2D thermal history measurement.