The Growth of Passive Membranes: Evidence from Ti and Like Metals

TL;DR

This study reveals that Ti passive membranes form through a layered process involving immediate chemisorption and subsequent gradient oxide growth, challenging existing passivation theories and proposing a new incremental oxidation damping model.

Contribution

It introduces a new passivation theory based on incremental oxidation damping, supported by experimental evidence of layered macrostructure formation in Ti membranes.

Findings

Ti forms a stable chemisorbed Ti-O monolayer initially

A gradient oxide layer rapidly develops underneath

Passive membrane growth is governed by incremental oxidation damping

Abstract

Current contradictory understanding of passivation comes from overly-complex passive models, defective characterization and misplaced theoretical approaches. From brand-new experimentation, we find that a Ti passive membrane has spatiotemporally-ordered macrostructure. At the start, a thermodynamically-stable chemisorbed Ti-O monolayer is immediately formed to inactivate the outmost Ti atoms and shield direct reaction of environmental oxygens on metallic matrix, and then an underneath TiOx@Ti ceramet-like non-equilibrium gradient oxide layer rapidly forms. The two layers work synergistically to keep the macro-ordered passive membrane growing slowly via non-linear mechanism of incremental oxidation damping, thus effecting passivation. These findings disprove "the adsorption theory of passivation" and "the theory of passivity film" and inform a new theory we call "passivation theory of incremental oxidation damping".