Influence of acid leaching surface treatment on indentation cracking of soda lime silicate glass

Summary¶

Acid leaching of soda lime silicate (SLS) increases apparent crack resistance at the treated surface during Vickers indentation relative to a polished baseline; combined dry vs humid N₂ tests and ReaxFF reactive molecular dynamics in ADF link humidity-dependent radial cracking to water transport through the leached layer and to pressure-driven restructuring of the near-surface silica network. Past work showed that water or acid soaking can raise the mechanical strength of SLS glasses. This study extends that story with controlled environments and atomistic load mimics (see ## Methods). Vickers tests in controlled environments show humidity-dependent radial cracking, implicating water transport through the leached layer in crack propagation to the surface. Reactive MD with ReaxFF indicates that the leached layer can undergo mechanochemical reactions under indentation load, increasing bridging-oxygen connectivity in the silica network and hindering transport of environmental water toward subsurface crack tips. The authors propose that load-driven restructuring in the leached layer lowers the kinetics of water delivery to critical flaws, producing the observed enhancement in apparent crack resistance.

Methods¶

Experiments: Vickers indentation on acid-leached soda lime silicate (SLS) glass in a chamber with dry or humid nitrogen (abstract cites ~90% RH for the humid case). A 1.96 N load is used in the discussion tying indent depth to the modeled stress state (see article for full indentation and imaging protocol).
Reactive MD (PDF): Na/Si/O/H ReaxFF as implemented in the Amsterdam Density Functional (ADF) package; integration with Verlet, time step 0.25 fs, Berendsen thermostat (100 fs damping) and barostat (5 ps damping) where NPT is used.
Model system: Acid-leached region built from a 70:30 mol% SiO2:Na2O glass in a ~4.30 x 4.37 x 12.05 nm periodic cell (758 of 1200 Na+ in top/bottom thirds exchanged for H+ to mimic leaching). Initial NVT equilibration at 300 K (0.25 ns) yields a silanol-enriched surface.
Indentation mimic: NPT at 300 K with hydrostatic pressures 0.1, 0.5, 1, 5, and 10 GPa for 100 ps; condensed water from reactions removed, then 1 atm, 300 K NPT 25 ps before analysis of network/water transport.

MD details (leached-glass + pressure ramp). PBC ~4.3 × 4.4 × 12.05 nm cell; Na⁺ → H⁺ exchange in top/bottom thirds (758/1200). NVT 0.25 ns at 300 K; then NPT sweeps with Berendsen thermostat (100 fs damping) and barostat (5 ps damping) at 0.1–10 GPa per 100 ps; final 1 atm NPT 25 ps before bridging-oxygen / water transport analysis. Electric field: N/A —. Umbrella / replica: N/A —.

Findings¶

Acid leaching increases apparent crack resistance of the treated SLS surface during indentation relative to the untreated case under the reported conditions.
Radial cracking under Vickers indentation shows a humidity dependence, supporting a role for water transport through the leached layer in crack growth paths to the surface.
Reactive MD indicates pressure-induced mechanochemical reactions in the leached layer during loading that increase bridging-oxygen connectivity in the near-surface silica network.
Those structural changes are argued to impede molecular water transport from the environment toward the subsurface crack tip, motivating a hypothesis that reduced water transport kinetics to flaws explains the enhanced apparent crack resistance of the acid-leached surface.

Limitations¶

Local PDF extraction in the corpus is pages 1–2–oriented; full numerical indentation loads, simulation cell sizes, thermostat/ensemble choices, and run lengths should be taken from the version-of-record PDF and any supporting information when extending this note.

Relevance to group¶

Adri C. T. van Duin is a co-author; the work couples glass surface chemistry, mechanics, and ReaxFF-based reactive simulation for an engineering glass system.

Citations and evidence anchors¶

DOI: 10.1016/j.jnoncrysol.2020.120144