リン酸-酸化鉄-PVB系さび安定化処理膜のイオン選択透過性と安定さび生成機構 [in Japanese] Ion Selectivity and Mechanism of Stable Rust Formation of Phosphoric Acid-Iron Oxide-PVB Rust Stabilization Surface Treatment Film [in Japanese]
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Despite thier thinness, films applied to weathering steel using a phosphoric acid-iron oxide-PVB rust stabilization surface treatment act to inhibit rust formation and to suppress"rust outflow". The following conclusions were reached in a study of the reasons for the treatment's effectiveness.<br>(1) The treatment film exhibits cation selectivity in a NaCl solution and KCl solution and anion selectivity in a FeCl<sub>2</sub> solution and FeCl<sub>3</sub> solution. Accordingly, by acting to suppress the diffusion of Cl<sup>-</sup>, Fe<sup>2+</sup> and Fe<sup>3+</sup>, the film inhibits corrosion of the iron matrix and the occurrence of"rust out-flow".<br>(2) Examination of artificial rust (amorphous rust) revealed that a compound layer comprised of the treatment film and rust acts as a bipolar film with both cation selectivity and anion selectivity. The compound layer also suppresses the diffusion of Cl<sup>-</sup>, Fe<sup>2+</sup> and Fe<sup>3+</sup>.<br>(3) Because the treatment film has a relatively high permeability for moisture and oxygen, PO<sub>4</sub><sup>3-</sup> and other phosphate ions easily flow out of the film during prolonged atmospheric exposure. It is thought that PO<sub>4</sub><sup>3-</sup>, in addition to imparting ion selectivity to the rust, contributes, together with the alloying elements, to rust stabilization in weathering steel.
- Jitsumu Hyomen Gijutsu
Jitsumu Hyomen Gijutsu 47(4), 366-371, 1996-04
The Surface Finishing Society of Japan