CHEMICAL-RESISTANCE TO WATER OF FLUOROZIRCONATE GLASSES MODIFIED WITHNITROGEN

Chemical resistance of fluorozirconate glasses of the following compos itions (mol%): 58 ZrF4, 36 BaF2, 6 LaF3, 10 AlF3 and 58 ZrF4, 36 BaF2, 6 LaF3, 10 AlN, to water and humid air of 100% relative humidity were investigated. Hydrolytic susceptibility of the glasses was examined b y chemical methods analysing the compositions of water solutions in co ntact with glass samples of standard dimensions. The normalized etchin g rates for the particular components diminish in the following order: F-, Zr4+, Ba2+, La3+, Al3+. Based on the transmittance curve of the e xamined glasses it has been found that on the surface of the glasses t he following groups occur: OH-, H2O, Zr(OH)(4). Changes on the surface of the glasses were observed in a scanning microscope. Layers of the hydrolysis products on the surface of a glass not subjected to nitroge n hardening are loose and porous, while on the surface of a glass cont aining nitrogen they are more dense and contain less water. The result s of the chemical, optical and physical investigations of glasses expo sed to water in the temperature range 20-80 degrees C allow the conclu sion that additions of nitrogen, even as small as some hundredths of 1 wt.%, can influence the increase of the glass resistance to water and to atmosphere of 100% relative humidity.