Untitled

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The development of organic coatings for corrosion protection is an elaborate process with a multitude of often interminable investigations and tests of protection properties. Electrochemical methods support the processes of development to a great extent and help to understand mechanisms of action and failure. They are usually carried out on applied coating systems with a completed formulation. An examination possibility is presented in this publication that enables the characterization of water‐based coatings with different formulation variations in the liquid (aqueous) state with the aid of electrochemical noise technique. Thus, selection of binders, pigments, and other additives is supported essentially and made more efficient in a very early phase of formulation development. The paper shows that a unique insight into the dynamic processes of a metal in contact with an aqueous coating dispersion is possible using the example of the development of zinc‐free corrosion‐inhibiting pigments for water‐based coatings. In addition, it is presented in which way the results correlate with the performance of applied coatings.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electrochemical noise of unalloyed steel in mixtures of water‐based binders and pigments

Heyn

Rosemann

Babutzka

et al. 2017

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“…One common method for the quantification of noise data is the calculation of the standard deviation (S) over fixed periods and the further calculation of a noise resistance (R N ¼ SE/Si). Another examination method is the charge (Q), which can be calculated by integration of the rectified current noise over fixed time intervals [11].…”

Section: Electrochemical Noise Measurementsmentioning

confidence: 99%

Corrosion and corrosion testing of magnesium alloys

Bender

Goellner

Heyn

et al. 2007

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The corrosion behaviour of magnesium alloys is not substantially comparable to other metals, such as iron, nickel and copper. It is always accompanied by hydrogen evolution. More hydrogen is evolved at a more positive potential or a higher anodic current density. The 'strange' hydrogen evolution behaviour is a common phenomenon for magnesium alloys and it is called negative difference effect (NDE). The NDE continues to receive considerable discussion.Furthermore, the corrosion behaviour of magnesium alloys depends mainly on the pH value of the surrounding electrolyte. Voluminous reaction products, formed in neutral electrolytes, lead to a diffusion-controlled dissolution on the surface of the underlying magnesium alloy. Therefore, influences from structure and alloying are suppressed very strongly. In alkaline environments, passivation occurs as a result of the formation of a hydroxide layer on the magnesium surface. Therefore, differences in the corrosion behaviour between the alloys are hardly detectable. Measurable effects can only be detected using very 'aggressive' corrosion conditions. Present methods do not adequately take into account the specific character of the corrosion of magnesium alloys. It can be better characterized using a rotating disc electrode for electrochemical measurements, which enables model defined flow conditions on the surface. Furthermore, the application of electrochemical noise offers the possibility of a simple and sensitive assessment of the corrosion susceptibility of magnesium alloys. Due to the high sensitivity of this measurement procedure, it is also possible to carry out examinations under more practical conditions. Unusual features of magnesium corrosionThe corrosion behaviour of magnesium alloys depends on a variety of factors, mainly on the pH values (pH of the surrounding medium and pH near the metal surface) and on the surface film (in dependence of the alloy composition). The type and distribution of the intermetallic phases are also important. The publications of Song and Atrens [1], Kainer [2], Hansen [3], Makar and Kruger [4], Haferkamp et al. [5]and Virtanen et al. [6] describe the essential aspects of the corrosion of magnesium alloys such as the type of corrosion, the corrosion mechanism and influences of the surrounding medium. If the pH is above 12, a stable and self-healing passive layer develops, which is responsible for the high corrosion resistance. The layer varies between a stable and an unstable state for a pH in a range of 10-11. Because of the active dissolution, the hydrogen development increases with decreasing pH values. Relative thick layers of loosely adhering corrosion products are developed, which appear like passivity. The corrosion rate is controlled by diffusion and depends mainly on the layer thickness. During the dissolution and hydrogen development, the pH rises in the area near the surface. The result is a change in the formation of the layer and a higher stability.On magnesium and magnesium alloys, an unusual feature appears which does ...

“…Electrochemical noise measurements (ENM) are well known to be particularly suitable to investigate the early state of pitting corrosion, thus to clarify questions on the mechanism of depassivation due to chlorides [3][4][5][6][7][8][9]. Whereas ENM on different alloys in various solutions are generally accepted, the applicability on steel in concrete is not fully approved yet.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical noise measurements on unalloyed steel in chloride‐containing alkaline environment

Eichler

Bürkert

Beck

2007

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The investigations discussed in this paper aim to clarify whether electrochemical noise measurements (ENM) are capable for application in concrete and mortar, particularly with regard to pitting initiation in such environment. For these purposes, the results of several different test series are compared and discussed. Based on investigations on passivity and pitting corrosion in alkaline solutions with different chloride contents further results in cement paste, mortar and concrete are evaluated.