Abstract
Thermally induced coloring and bleaching in reduced phosphate glasses were investigated by means of DTA. As-quenched glasses prepared under reducing conditions are transparent and colorless. On reheating at around the softening temperature of the glasses, they turn red (“striking”). The struck glasses become almost transparent and colorless (“bleaching”) when they are heated above 580°C and quenched subsequently. The resultant glasses (PTC-RP glass) exhibit red-coloring by reheating above 200°C and/or light irradiation. It was explained in terms of transformation of colloidal phosphorus in the PTC-RP glasses that the endotherms at about 60° and 580°C in the DTA curves are due to melting of white and red phosphorus, respectively, and that the exotherm at about 270°C is due to transformation of liquid phosphorus to amorphous red phosphorus, i.e., to ring opening polymerization of P4 molecules.
