Transient subsurface hardening of soda-lime-silica glass accompanied by surface network depolymerization caused by superheated steam

Title data

Roy, Barsheek ; Rosin, Andreas ; Gerdes, Thorsten ; Schafföner, Stefan:
Transient subsurface hardening of soda-lime-silica glass accompanied by surface network depolymerization caused by superheated steam.
2022
Event: 26th International Congress on Glass , 3-8 July, 2022 , Berlin, Germany.
(Conference item: Conference , Lecture )

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Abstract in another language

The primary objective of our study is centred on the investigation of alteration of surface nanostructure of soda-lime-silica (SLS) glass by the influence of superheated steam. As a preliminary step, the variation of hardness was studied as a function of depth from the glass surface, with a promising effect with respect to 30%-enhancement—restricted to a depth of 300 nm, for continuous steam-treatment of 30 minutes in the vicinity of the glass transition region (Tg). Presence of hydroxyl groups in the near-surface region was confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy in the form of entrapped water molecules within the silicate rings corresponding to OH stretching vibrations in the mid-IR region [1,2] – which is thought to contribute to subsurface-hardening by filling up the inherent interstitial voids. High-resolution X-ray photoelectron spectroscopic studies of O1s and Si2p orbitals – revealed a relatively depolymerized silicate network with evidence of Q1 saturation up to a depth of about 100 nm, in contrast to Q2 saturation before superheated steam -treatment (Qn: ‘n’ refers to the number of bridging oxygens linked to a silica tetrahedron). Atomic force microscopic investigations corroborated the evidence of surface network depolymerization; in addition to revealing a decrease in void-depth – speculated to be associated with interstitial water molecules in agreement with ATR-IR results.

The subsurface hardening effect was, however, found to be transient in nature with ageing in ambient atmosphere (≈ 25 ℃, 50-60 % relative humidity). Superheated steam proved to be accountable for increasing the vulnerability of the surface network to atmospheric corrosion, which was indeed an interesting discovery. The evidence of entrapped water molecules within the silicate rings observed by a rise in ATR-IR intensity in the mid-IR spectrum corresponding to OH vibrations immediately after steam-treatment, was no longer observed after 1 week of ageing in ambient atmosphere. This was accompanied by a decrease in surface hardness.