HCl Leaching Rate and Microstructure of Phase‐Separated Borosilicate Glasses

The leaching rate in HCl solution and the glass transition temperature (Tg) of a borosilicate glass (SiO2 70, B2O3 23, and Na2O 7 wt%) were measured as a function of heat treatment for glass‐in‐glass phase separation. The leaching rate varied together with Ty, approaching an equilibrium value unique to the heat‐treatment temperature. As the heat‐treatment temperature decreased, the equilibrium leaching rate increased. These results plus electron microscopy of sample structure established that the leaching rate is primarily controlled by the composition of the chemically less durable phase, and the effect, if any, of microstructure size is small. In contrast to previous reports, extremely long heat‐treatment times were required to attain the equilibrium composition. Copyright © 1978, Wiley Blackwell. All rights reserved