Hydrolysis and aqueous corrosion of silicate and aluminosilicate glasses via ab initio molecular dynamics simulation

Abstract

Hydrolysis and aqueous corrosion of glass is a complex and puzzling phenomenon. Although many endeavors have been made to investigate corrosion in glass, it is still an open question with many unanswered fundamental issues. To explore the hydrolysis mechanism in glasses and provide new insights into their corrosion, single and mixed alkali ions doped silicate and aluminosilicate bulk glasses are simulated using ab initio molecular dynamics (AIMD). The atomic origin of the hydrolysis reaction is analyzed, and its effects on the structural, electronic, mechanical, and optical properties of the studied glasses are explored. A complete picture of interatomic bonding and charge transfer in the hydrated models is depicted and compared with dry models. A novel quantum mechanical parameter, total bond order (TBO), is introduced to characterize the internal cohesion and strength of the simulated glasses. Water in glass remains as molecular water H2O and dissociated water OH. The ionized water attacks the silicate and aluminosilicate framework and depolymerizes it, producing Si-OH and Al-OH. The small amount of water in silicate glass enhances its mechanical strength while excess water deteriorates it. The aqueous corrosion on a surface is investigated, further simulating the glass-water interface models of aluminosilicate glasses using AIMD. The local short- and intermediate-range order properties embedded in pair distribution function, coordination number, bond-angle, and bond-length distribution are analyzed in detail to delineate subtle variation caused due to hydrolysis. The calculated interatomic bonding and charge transfer are compared and contrasted in the bulk, surface, and interface models. The TBO is used to analyze the effect of hydrolysis on the internal cohesion of studied glasses. Furthermore, the aqueous corrosion effects of Na/K-Cl salts on aluminosilicate glass surfaces are explored. The hydrolysis increases with the increasing concentration of salts, and KCl is more detrimental to the glass network than NaCl. The results presented here provide new insight to understand the aqueous corrosion of glass surfaces and help design mechanically strong and durable glasses.