Protection of Pure Iron

SAIE by low-pressure plasma polymerization of TMS was extended to pure iron [8]. Polished pure iron samples (3x3 cm) were plasma pretreated before deposition of TMS plasma polymer. Two to six samples of pure iron were placed on a CRS plate (15 X 10 cm) maintaining the electrical contact so that each pure iron sample acts as the cathode of DC discharge. A few small pieces of silicon water were also placed on the CRS plate to maintain the electrical contact and were used for the estimation of the thickness of TMS plasma polymer by ellipsometry. 

Sample Pretreatment TMS treatment time (s) Coating thickness (nm) 

The electrochemical tests were carried out in a quiescent aerated borate-sulfate buffer solution (0.025 Na2B4Ovl0 H2O + O.5M Na2S04) prepared from distilled water 

The Kelvin probe was used to study the oxidation state at the interface to the metal surface. Grundmeier and Stratmann have shown that the potential measured by the SKP depends on the oxidation state of iron oxide films according to the following equation [9]  

It is clear from the study on pure iron that oxides participate in LCVD of TMS, and characteristics of plasma polymer films differ depending on the extent of oxides present on the surface when LCVD is applied. Oxides on the surface of pure iron are more stable than those on steel and hence more difficult to remove, but this can be effected by plasma pretreatment with (Ar + H2) mixture. SAIL by LCVD involving removal of oxides provides excellent corrosion protection of pure iron. The key factor of SAIL by LCVD for corrosion protection of metals in general is the handling of oxides, which depends on the characteristic nature of the metal oxide to be handled. Once strong chemical bonds were formed between nanofilm of plasma polymer, either through oxides or direct bonding to the substrate metal, the LCVD film acts as the barrier to corrosive species. 

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