Surface analysis of silicate glass in understanding mechanochemical wear process, corrosion behavior and vibrational properties
Open Access
- Author:
- Liu, Hongshen
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 23, 2021
- Committee Members:
- Phillip Savage, Major Field Member
Seong Kim, Chair & Dissertation Advisor
John Mauro, Outside Unit & Field Member
Christian Pester, Major Field Member
Phillip Savage, Program Head/Chair - Keywords:
- Silicate glass
Mechanochemical wear
Vibrational properties
Corrosion behavior - Abstract:
- Surface properties govern numerous performances of silicate glass, such as mechanical strength, chemical durability and optical properties. Soda lime silicate (SLS) is the key commodity glass material applied for architecture and decoration, automotive windshields, photovoltaic cover panels and so on. In these applications, glass surface defects made by physical contacts of foreign objects seriously compromise the practical strength or durability of glass products. Therefore, it is of significant importance to investigate the surface damage modes to prevent the defects formation and propagation, as well as develop comprehensive understanding of surface properties of silicate glass to optimize its practical performance. Surface damage induced by foreign contact can be generally investigated by two categories, by normal indentation and by tangential shear. Recently, it has been reported a peculiar humidity-dependent surface wear process of SLS glass induced by tangential shear. Specifically, soda lime silicate glass exhibited superior resistance to wear at high humidity in shear-induced tribological test. To enhance mechanical properties, SLS glass panels are often thermally tempered or chemically strengthened. The mechanical properties are improved by compressive stress formation on the glass surface during such processes. However, it was showed that the mechanically strengthened SLS glass demonstrated deteriorated resistance against mechanochemical wear in tribo-test performed at high humidity. To better understand the stress effect on mechanochemical wear behavior without introducing alteration of surface chemistry, stress was created by external force on soda lime silicate glass surface in this dissertation. Flexural bending was applied to generate tensile stress and compressive stress on SLS glass surface to understand their effect on mechanochemical wear behavior and other surface properties. It was found that compressive stress on the surface impaired the wear resistance behavior of SLS glass at high humidity while tensile stress did not alter the superior resistance to wear. In mechanical response, SLS glass formed with compressive stress was more susceptible to plastic deformation upon normal indentation while SLS with tensile stress stayed unaltered compared to stress-free SLS. Such increased tendency towards plastic deformation and mechanochemical wear at high humidity were proposed to be associated with greater Si-O bond strain in the silicate network induced by compressive stress. Moreover, the wear resistance behavior at high humidity of silicate glass is related with compositions of glass network. Previous work showed that such resistance to wear at high humidity was uniquely observed for soda lime silicate glass among many types of silicate glasses tested. In this dissertation, investigation was carried out to understand the composition effect, specifically effect of modifier contents in sodium calcium aluminosilicate (NCAS) glass series, on mechanochemical wear behavior. A series of sodium calcium aluminosilicate glass with various CaO to Na2O ratio were applied for this study. It was observed that the silicate glass comprising both sodium and calcium ions with sufficient content exhibited resistance to mechanochemical wear at high humidity. For silicate glass that has only sodium ion or calcium ion, the resistance to wear at high humidity was not observed. The result indicated that wear resistance behavior at high humidity was affected by mixed modifiers effect (MME) in silicate glass. Further, vibrational properties revealed by IR spectroscopy also demonstrated MME on the aspect of frequency of Si-O-Si stretching vibrational band. Upon aqueous corrosion, it was found that the resistance to aqueous corrosion was improved with increased calcium content in the glass system. The chemical durability of NCAS glass was investigated by both surface structure alteration and leached layer thickness, probed by IR spectroscopy and x-ray photoelectron spectroscopy (XPS), respectively. Intrinsically, mechanochemical wear process induced by tangential shear was related to chemical reaction between Si-O-Si bond in silicate network and hydrous species in ambient environment. It is important to investigate the dynamic interaction between silicate glass and hydrous species to contribute to the understanding of this complicated process. Mixed alkaline earth effect (MAEE) on chemical durability was investigated by a series of borosilicate glass with varied CaO to MgO ratio in the glass system. Borosilicate glasses comprising a variety of modifiers were widely used for pharmaceutical application. The understanding of dependence of chemical durability on mixed modifiers is vital to ensure safety usage in medicine storage and distribution. In this dissertation, a weak MAEE on chemical durability of borosilicate glass was demonstrated in terms of the thickness of the dissolution layer as well as the re-organization of surface structure. Moreover, chemical durability of silicate glass has a particularly crucial application on long-term storage of radioactive waste glass. In this dissertation, the initial surface state effect on aqueous corrosion was investigated by international simple glass (ISG), a boroaluminosilicate glass. The ISG was prepared separately as polished-only and polished-then-annealed before corrosion treatment. Only slight difference in surface elements was found of ISG prepared in two different approaches. However, such small difference led to large impacts on corrosion behavior under the mild corrosion condition, on silicate structure, hydrous species, surface elements and surface roughness. The effect was found less significant under the accelerated harsh corrosion condition. Moreover, the structural properties of silicate glass were commonly acquired by vibrational spectroscopies, such as infrared and Raman spectroscopies. A plethora of papers reporting variations in IR and Raman spectral features of silicate glass upon changes of glass compositions, thermal histories, mechanical stresses, and other surface treatments. However, the interpretations of such spectral features were often not clear and the fundamental physical principles in describing vibrational modes of amorphous glass networks were not well-established. In this dissertation, we demonstrated the investigation of vibrational features in correlation with structural parameters of sodium silicate glass with employing molecular dynamics (MD) simulation. One of the main findings was that the weighted average of position of asymmetric Si-O-Si stretch vibration in IR spectra is better correlated with averaged Si-O bond length in the glass network, rather than the bond angle of Si-O-Si, as sodium content varied in the silicate glass. Our study also raised concerns of previous vibrational assignments in relating the Si-O-Si stretching band with the Qn speciation and relating Si-O-Si bending band with (SiO)n rings of silicate glass in Raman spectra. The limitation of previous vibrational calculation was discussed and the new critical insights from the modern studies were described in correlating vibrational spectral features with structural parameters of silicate glass. Further, a systematic review of vibrational spectroscopies was performed of silica and silicate glass on the aspect of historic origins of currently widely-used spectral interpretation models, insights and limitations of those theoretical calculations and established models, and recent advances with computational approaches in understanding of vibrational spectral features of disordered networks.