Effect of leaching concentration and time on the morphology of pores in porous glasses

Herein, porous glass was prepared by the acid leaching of phase-separated sodium borosilicate glass. The effects of hydrochloric acid (HCl) leaching concentrations varying from 0.1 to 3 M and of leaching times varying from 2 to 48 h on pore size and shape are reported here. The porous structure evolution was investigated through small angle X-rays scattering measurements and were compared to the classical nitrogen adsorption technique. We argue that the composition of these samples is not significantly modified with the acidic concentrations of the solution or with the leaching times tested. However, as expected a priori, we clearly show strong differences in porous structure. The investigation of different HCl leaching concentrations (from 0.1 to 3 M), with a small variation between each concentration, has enabled the observation of an interesting result. That is, we clearly show a non-linear effect of acidic concentration on the porous structure of these materials. At low acid concentrations, the specific area of these materials is relatively low. Increasing the HCl concentration to approximately 0.7 M leads to a strong increase in a specific BET area and total pore volume. However, further increasing of the acid concentration of the leaching solution leads to a decrease of both the specific surface area and the total pore volume. All of these results due to the presence of colloidal silica inside the pore structure can be explained by the well-known Zhdanov's model. These nanoparticles formed at an intermediate acid concentration seem to cluster when the acidity increases. The effect of the leaching time is less significant than the HCl concentration; however, this same assumption can be explained by the experimental results.