BaO, ZnO, B2O3, PbO, and SiC effects on phosphorescent afterglow damping and thermal stability of SrAl2O4 base pigments at industrial glazes

Phosphorescent glazes are usually used in direction signs of emergency routes. That is why afterglow damping and thermal stability of phosphorescent pigments are the most decisive factors of phosphorescent glazes. This study aims to choose a suitable glaze to enhance the time and intensity of the afterglow. For this reason, the effects of BaO, ZnO, B2O3, and PbO additives on the afterglow intensity and lifetime of reference industrial glaze containing SrAl2O4 phosphorescent material were investigated. 5, 7, 10, 15, and 20 %wt SrAl2O4 phosphorescence powder was mixed with base industrial glaze to recognize the optimum component. Samples were fired at 1040 °C for 40 min in the same conditions and then were analyzed by photoluminescence spectroscopy. Results showed that increasing the SrAl2O4 proportion increased samples afterglow damping time, and 10 %wt SrAl2O4 was chosen as the optimum amount. Also, BaO is more efficient for increasing the intensity and afterglow lifetime. Moreover, 0.02, 0.03, 0.05, and 0.1 %wt SiC were added to the reference industrial glaze containing 10 %wt SrAl2O4 to investigate the reduction firing conditions on the glaze afterglow. Increasing the SiC ratio up to 0.02 %wt increased the afterglow lifetime from 5 ± 0.4 to 27 ± 1.7 min, but the afterglow intensity was decreased. Despite this, adding 0.03, 0.05, and 0.1 %wt SiC darkened the glaze and reduced the intensity and afterglow lifetime. The sample containing 0.1 %wt SiC did not melt properly, and this sample did not have any afterglow. Furthermore, the temperature required for firing affects the afterglow of the samples. On the other hand, to investigate the effect of temperature, the base industrial glaze containing 10 %wt SrAl2O4 was fired at 1040, 1120, and 1140 °C to determine thermal stability. The sample fired at 1140 °C had almost no phosphorescent afterglow. Also, dilatometry tests at the temperature of 600 °C and hot-stage microscope analysis were performed to determine the linear coefficient of thermal expansion and the melting point of the samples, respectively. The results showed the linear coefficient of thermal expansion of the industrial glaze with 10 %wt SrAl2O4 was 73.3 × 10−7 1/°C, and it could be changed between 58.5 × 10−7 1/°C by adding 10 %wt B2O3 to 73.5 × 10−7 1/°C by adding 10 %wt BaO. The melting point of the pure industrial glaze was 1130 °C, and adding 10 %wt, SrAl2O4 decreased it to 1076 °C. Also, by adding 10 %wt BaO, ZnO, B2O3, and PbO to phosphorescent glaze, melting point was obtained 1128 °C, 1020 °C, 1030 °C, and 974 °C respectively. The same sample with 0.02 %wt SiC melted at 1154 °C.