Nitridation of silicate and borosilicate glasses prepared by sol-gel process

Abstract

Samples of the systems R2O-SiO2 (R = lithium, sodium, potassium), B2O3-SiO2 and Na2O-B2O3-SiO2 were prepared by the sol-gel route. After gelation and drying, heat treatments under ammonia atmosphere were carried out up to 1100 °C. The whole nitrogen content (in wt%) of nitrided gels was determined with a Leco equipment. The maximum nitrogen content (in wt%) in lithium silicate gels was 12.6; in binary borosilicate gels 5.0 and in sodium borosilicate gels 7.6. The existence of silicon oxynitride (Si2ON) in some samples treated under ammonia has been demonstrated by X-ray diffraction. The nature and amount of the alkaline oxides play an important role in nitridation. The nitrogen percentage content incorporated seems to depend on the whole content of crystalline phases formed during thermal treatment, on the devitrification and on the phase separation of the samples. In borosilicate glasses a higher nitrogen incorporation with increasing B2O3 content was observed. In these samples, devitrification and phase separation, respectively, also affected nitridation.