Relative volatility of borosilicate glasses: a mass spectrometric study

Abstract

A high temperature Knudsen effusion method was used to study the composition of vapour and partial vapour pressures of species in multicomponent borosilicate glasses. Data on the activities of metaborates of alkali metals were obtained. Using an acid-base concept the relative volatility of these glasses was compared and discussed. # 1998 John Wiley & Sons, Ltd. Received 25 March 1998; Revised 1 July 1998; Accepted 2 July 1998 Borosilicate glasses have a wide range of applications in various modern technologies and therefore there is significant interest to study their physico-chemical properties.Vaporization processes play an important role during the preparation, study and applications of multicomponent glasses based on boron oxide and silica at temperatures higher than 1400 K. Information on the composition of vapour and partial vapour pressures as a function of temperature is required when borosilicate glasses are used for the incorporation of nuclear wastes, 1,2 for the production of low volatile glasses, 3 during application of glass solders, 4 during production of ion-selective transistors 5 and details of electronic equipment. 6Recently a series of papers have been published on the vaporization processes of multicomponent borosilicate glasses studied by high temperature mass spectrometry. These have obtained information on the composition of vapour and thermodynamic properties of components in multicomponent systems. In Ref. 7, concerning the vapour over glasses of the Na 2 O-B 2 O 3 -SiO 2 system, the vaporization of sodium metaborate and products of dissociation of sodium oxide were identified. Data on the partial pressures of components as a function of temperature were obtained by the authors 7 in the temperature range 915-1172 K. Later caesium and rubidium borosilicate glasses 8,9 as well as the Na 2 O-B 2 O 3 -SiO 2 -TeO 2 10 system were studied. It should be mentioned that the work in Refs 7-10 was carried out in connection with the disposal and treatment of radioactive wastes. The main trends of the vaporization processes of these glasses has been discussed. For a mixture of alkali oxides compared with B 2 O 3 at similar relative abundances, there are two main vaporization processes, such as vaporization of the individual alkali oxide and alkali metaborate. When the concentration of B 2 O 3 is higher than the alkali oxide mainly alkali metaborate is observed on vaporization. The same vaporization tendency was illustrated earlier in the case of the Na 2 O-B 2 O 3 -GeO 2 system. 11 The following order of the relative volatilities of alkali metaborates was suggested by Asano et al. 9 at constant temperature and constant ratio of oxides in a multicomponent system : p In the present study the results of vaporization of glasses NK1 and NKS are most important for the electronic industry, and for the incorporation of nuclear wastes T2 and T(Cs) the results are considered.