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Tribochemistry of phosphoric acid sheared between quartz surfaces: A reactive molecular dynamics study

Evidence and attribution

Authority of statements

Prose below summarizes the publication identified by doi, title, and pdf_path. The corpus filename references Tianbao and proof/galley; the first author on the article is Yue.

Summary

ReaxFF sliding simulations of phosphoric acid confined between quartz surfaces probe tribochemical mechanisms behind low friction in this system. The friction coefficient correlates positively with the number of interfacial hydrogen bonds—weaker H-bond networks favor lower friction. Two regimes appear: for 300–600 K, no chemistry is required; friction drops as molecular motion accelerates and H-bonds weaken. For 800–1400 K, reactions polymerize phosphoric species and release interfacial water that lubricates, reaching \(\mu \approx 0.02\) in the reported conditions.

Methods

Force field: ReaxFF with Si/O/H/P parameters merged from bulk silica and phosphoric acid training sets and refined against DFT for interfacial interactions (as described in the article).

Model: Hydroxyl-terminated α-quartz (101̄0) slabs (~29.46 Å × 21.608 Å × 8.504 Å each); 44 orthophosphoric acid molecules fill the gap; the interface is pre-relaxed at 300 K to remove bad contacts before sliding.

MD protocol (LAMMPS): Velocity-Verlet integration with \(\Delta t = 0.25\) fs; normal pressure 600 MPa on the upper slab (−z); the top rigid layer slides at 100 m/s (1 Å/ps) along +x while the bottom rigid layer stays frozen; Langevin thermostats (damping 100 fs) act on the two layers adjacent to the rigid plates; PBC in plane.

Temperature schedule: Eight runs ramp from 300 K to target temperatures 300, 400, 500, 600, 800, 1000, 1200, and 1400 K to span thermally activated friction versus tribochemical regimes. The peer-reviewed PDF for the same article is on 2013yue-venue-jp406360u (papers/Yue_Ma_Yeon_JPCC_tribochemistry_2013.pdf). Corpus proof/galley PDF: papers/Tianbao_JPCA_phosphate_treibology_proof.galley.pdf (first author on the article is Yue).

Barostat / pressure control: the protocol applies a target normal stress (600 MPa along −z) via the rigid-plate setup described above rather than a textbook isotropic NPT barostat on the full supercell (Methods narrative as curated from the article text on 2013yue-venue-jp406360u). Electric field: N/A — not used. Replica / enhanced sampling: N/A — not used. Total trajectory length per condition: N/A — confirm in the J. Phys. Chem. C PDF if operators need exact ps/ns production times beyond this galley-oriented wiki layer.

Findings

The cumulative friction coefficient \(\mu\) correlates positively with the number of interfacial hydrogen bonds; weaker H-bond networks align with lower \(\mu\). For 300 K ≤ T ≤ 600 K, no tribochemical reaction is reported; friction falls mainly because molecular motion accelerates and the H-bond network weakens thermally. For 800 K ≤ T ≤ 1400 K, tribochemistry polymerizes/clusterizes phosphoric species and generates interfacial water, enabling an ultralow-friction branch with \(\mu \approx 0.02\) in the authors’ high-temperature trajectories.

Comparisons & sensitivity. Trends are organized primarily vs temperature across the eight target states and vs interfacial H-bond statistics as summarized above; comparisons to experiment or broader tribology literature, if any, belong to the Discussion in the VOR PDF.

Limitations & outlook. Idealized flat quartz–acid contact and high-T chemistry limits are noted under ## Limitations; galley/proof PDFs may differ slightly from final pagination.

Corpus honesty. This slug uses a proof/galley filename; use paper:2013yue-venue-jp406360u for the version-of-record PDF path when citing canonical layout.

Limitations

Ideal crystalline quartz vs amorphous silica in experiments; proof PDF may differ from final layout.

Relevance to group

Demonstrates ReaxFF tribochemistry on oxide–acid interfaces with van Duin parametrization support.

Citations and evidence anchors

  • DOI: 10.1021/jp406360u
  • Extract: normalized/extracts/2013tianbao-venue-research_p1-2.txt