Surface energy distributions on silicoborate glasses

Abstract

The energy distribution functions, X( E), corresponding to the adsorption of several molecular probes on four sodium silicoborates have been obtained from their adsorption isotherms. These isotherms have been obtained using frontal analysis by the characteristic points method. X( E) has been determined by the Hobson method using the Langmuir model for the local adsorption isotherm. The adsorbents were three glasses prepared in the laboratory with different B 2O 3 concentrations; commercial E-glass has been studied too. The molecular probes were chosen in order to obtain different interactions with the glass surfaces studied. These probes were n-hexane, benzene, methanol and n-butylamine. Their X( E) exhibit different peaks which correspond to different kinds of gas–surface interactions. For n-hexane and methanol these interactions are mainly due to hydroxyl groups existing on the glass surface. For benzene and n-butylamine the interaction with boron atoms on the glass surface must be taken into account. The four sodium silicoborate glasses showed similar energy distribution functions, with peaks changing with B 2O 3 concentration in the glass. Therefore, the B 2O 3 oxide increases the surface heterogeneity of the studied glasses. In all cases the laboratory prepared sodium silicoborate glasses showed the same behaviour, and in most cases the commercial E-glass did not fit the results. This led us to the conclusion that the constituents of the E-glass other than SiO 2 or B 2O 3 (such as CaO, Al 2O 3) create another kind of heterogeneity on the glass surface. Further experiments are needed in order to determine such effects on the X( E). This work demonstrates that the methodology used provides information on the surface properties of sodium silicoborate glasses.