An Investigation of Selenium Decolorising

JSGT_1935_V19_T043_T103

Following a critical survey of the literature on selenium decolorising, an investigation of the decolorising of a soda–lime–silica glass by selenium has been made. The colours have been expressed quantitatively on the Lovibond scale. Standardised melting and cooling conditions were worked out and a series of melts were obtained from which the effects of the addition of minor constituents on selenium colours were recorded. A number of the glasses were subjected to reheating and sunlight treatment. As a result of these experiments a theory of the reactions occurring is proposed. The theory is as follows: the iron in glass is present as ferric oxide which decomposes with increasing temperature to ferrosoferric oxide with the loss of oxygen. The reaction is irreversible unless oxidising agents remain in the glass. Selenium reacts with the ferrosoferric oxide forming a ferrous selenide. Arsenic combines with ferrosoferric oxide forming ferrous arsenate, which is ionised by the action of sunlight. Sunlight has no effect on selenium or selenium compounds in glass. At high temperatures arsenic also probably combines with selenium to form a complex which decomposes at about 700°.

E. J. Gooding & J. B. Murgatroyd