EIS and SKP study on improvement of the protection performance of an alkyd-varnish coating modified with air-plasma treatment on Q235 steel

Abstract

Electrochemical impedance spectroscopy (EIS) and scanning Kelvin probe (SKP) were used to study the failure of the coating modified with air-plasma treatment in 3.5 % mass fraction of NaCl. The results show that the failure process can be divided into three stages including water penetration, accumulation of corrosion products at the location of a defect, water penetration of the entire coating and coating failure. The EIS results show that the plasma-treated samples exhibit an additional electrical double-layer capacitor that delays the coating failure during the second stage. The potential of the non-plasma-treated samples decrease faster than that of the plasma-treated samples according to the SKP study. As the transition layer, air plasma delays the coating failure due to the chemical bond between the metal substrate and the coating. Keywords: air-plasma treatment, electrochemical impedance spectroscopy, scanning Kelvin probe, coating failure, hydrostatic pressure Elektrokemijsko impedan~no spektroskopijo (angl. EIS) in vrsti~no Kelvinovo sondo (SKP) smo uporabili za preu~evanje po{kodb na prevleki, modificirani s plazmo, v 3,5 mas. % raztopini NaCl. Rezultati ka`ejo, da se nastajanje po{kodb lahko razdeli na tri faze, vklju~no s penetracijo vode: na akumulacijo korozijskih produktov na mestu napake, na prodiranje vode v dele celotne prevleke in na odpoved prevleke. Rezultati EIS ka`ejo, da imajo vzorci, obdelani v plazmi, dodaten elektri~ni dvoslojni kondenzator, ki v drugi fazi upo~asni po{kodbo prevleke (premaza). SKP-analize so pokazale, da se potencial plazemsko neobdelanih vzorcev zmanj{uje hitreje kot tistih vzorcev, ki so bili obdelani s plazmo. Kot prehodna plast, obdelava z zra~no plazmo upo~asni po{kodbo premaza zaradi kemijske vezi med kovinskim substratom in prevleko. Klju~ne besede: obdelava s plazmo, elektrokemijska impedan~na spektroskopija, skeniranje s sondo Kelvin, odpoved prevleke, hidrostati~ni tlak

Effect of molybdate on the stress corrosion cracking of 2205 duplex stainless steel in sulfuric acid solution

“…5 In summary, there are reports on the effects of molybdates on the pitting and SCC behaviour of steels in chloride solutions. [1][2][3][4][5][6][7][8][9][10][11][12] The majority of these reports suggested the use of the inhibiting effects of molybdates on stainless-steel pitting. However, all these studies ignore the effect of molybdates on hydrogen permeation.…”