NITRIDATION OF SILICATE AND BOROSILICATE GLASSES PREPARED BY SOL-GEL PROCESS

Samples of the systems R2O-SiO2 (R = lithium, sodium, potassium), B2O3 -SiO2 and Na2O-B2O3-SiO2 were prepared by the sol-gel route. After gel ation and drying, heat treatments under ammonia atmosphere were carrie d out up to 1100-degrees-C. The whole nitrogen content (in wt%) of nit rided gels was determined with a Leco equipment. The maximum nitrogen content (in wt%) in lithium silicate gels was 12.6; in binary borosili cate gels 5.0 and in sodium borosilicate gels 7.6. The existence of si licon oxynitride (Si2ON) in some samples treated under ammonia has bee n demonstrated by X-ray diffraction. The nature and amount of the alka line oxides play an important role in nitridation. The nitrogen percen tage content incorporated seems to depend on the whole content of crys talline 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 observ ed. In these samples, devitrification and phase separation, respective ly, also affected nitridation.