Atypical pH response of some nonsilicate glasses

Abstract

It is ge nerally believed that a glass, in order to yield electrodes whose voltage characte ristics serve as a satisfactor y indicator of t he hydroge n-ion activity of aqueous solutions in accord with the dictates of the N ernst equation , m ust possess at least a minimum hygroscopic ity and an adequate chemical durability, uniform over an extended pH ran ge. Th ree series of llons ili cate glasses, Na20-MgO-P20 s, Na20-GeO, and BaO-B. 0 3, were investigated for t hese t hree properties. In accord wi th the fact t hat all of t he m embers of t hese series ex hibited very poor chem ical durabi lity and man y of t he m possessed very low h ygroscop icity, none of t he m produced elect rodes t ha t had a satisfa ctory pH response. A. ll of the ser ies co nfirmed t he generally accepted fac t t hat hygroscopicity cannot be d irectly co rrelated with chem ical durab ili ty of glasses. For example, some members of t he BaO-B20 3 se ries possessed h yg roscopic propert ies that co mpared favora bl y with Pyrex 7740, yet had unus uall y poor che mical dura bili ty.