First-Principles Study of the Adsorption and Depolymerization Mechanisms of Sodium Silicate on Iron Surfaces at High Temperature

Abstract

Silicate glasses are potential materials for lubrication at elevated temperature because of their exceptional thermal stability, low cost, and environmentally friendly properties. Although the frictional behaviors and characterizations of silicate glass tribofilms have been studied by a number of experiments, the formation mechanisms as well as the chemical insight into the iron–silicate tribofilm still remain unclear. In the present study, the adsorption and depolymerization of the sodium sorosilicate cluster Na6Si2O7 on a Fe(110) surface have been studied using both first-principles molecular dynamics and density functional theory. Comparisons of adsorption processes and electronic structure of some typical configurations at different temperatures have been carried out. The results strongly suggest that the silicate cluster chemically adsorbs on the Fe(110) surface by forming multiple Fe–nonbridging oxygen (NBO) bonds. The iron surface plays an important role in the dissociation of the NBO by significantly reducing the strength of Si–NBO bonds. Electronic structure calculation reveals that the charge transfer between the lubricant and the iron surface during the adsorption may lead to a flow of alkali ions and a layering process in the tribofilm. Depolymerization is observed at higher temperature and has larger activation energy compared to Si–NBO dissociations, indicating that the process is more difficult. Temperature is also an important factor that contributes to the dissociation of NBOs as well as the depolymerization of the lubricant, both of which can have several impacts on the lubricity of the tribofilm. This study provides a detailed understanding of the chemical reaction of sodium polysilicate on the iron surface at high temperature.

Tribochemistry and Lubrication of Alkaline Glass Lubricants in Hot Steel Manufacturing

“…With a sodium silicate lubricant, the silicate cluster chemically adsorbs onto the iron surface by forming multiple Fe-Onb bonds, which have a strong covalent characteristic compared to the Si-O bonds [38]. This strong covalent bond confirms the adhesion capability of the sodium silicate to the metal surface.…”

“…It is important to investigate the chemical mechanism of how a glassy lubricant works when it is applied in practice at high temperature and pressure in metal forming. We have carried out some theoretical investigations of the adsorption and thin film lubrication of Na [25,35,36], as well as sodium silicate, Na 6 Si 2 O 7 , on iron and iron oxide surfaces [37,38]. These studies have overcome the drawbacks of previous experiments and provided a deep insight into the chemical reactions in the tribofilm.…”

Synergistic adsorptions of Na2CO3and Na2SiO3on calcium minerals revealed by spectroscopic andab initiomolecular dynamics studies

“…14,15,28,31 In other words, the prior addition of Na 2 CO 3 induces a higher efficiency of Na 2 SiO 3 in terms of gangue mineral depression, which allows a better otation selectivity and, hence, higher metal grades in the otation concentrates. At the moment, although the adsorption of Na 2 SiO 3 species has been considerably investigated, 29,[32][33][34][35] very few studies have been conducted on the Na 2 CO 3 /Na 2 SiO 3 system in otation 17,28,31,36 and the synergistic effects exhibited by this reagent combination are still poorly understood. Some authors have successfully investigated surface reactivity and synergistic adsorptions/ reactions by Fourier transform infrared spectroscopy (FTIR), [37][38][39][40] by X-ray photoelectron spectroscopy (XPS), [41][42][43] and by ab initio molecular dynamics (AIMD) 37,[44][45][46] with couplings between the above-mentioned techniques.…”

Nanoscale iron (oxyhydr)oxide-modified carbon nanotube filter for rapid and effective Sb(iii) removal

“…32 Similarly with Sb, silicate is also inclined to react with metal oxides to form an innersphere complex. 33 This similar chemisorption mechanism of silicate and Sb(III) could explain the pronounced suppression of Sb(III) sequestration when compared with other coexisting anions. It is worth noting that the concentration of competing anions is much higher than the actual aquatic conditions, such that the inhibitory effect could be limited in practical applications.…”