Organic coatings evaluation methods

Electrochemical Noise Methods for Organic Coating Evaluation... 

One costly form of degradation is corrosion of metallic objects and structures. Organic coatings are widely used to protect these objects from corrosion. No completely acceptable and predictive methods exist for the evaluation of corrosion protection. Since corrosion is an electrochemical phenomenon, electrochemical testing may provide the evaluation tools which are wanting. 

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

This method falls short only when the capacitance values of the metal-solution interphase are so small [70] (of the order of some picofarads) that the limit of the impedance modulus as l/u> —y 0 does not provide a reliable evaluation when the maximum frequency value is about 60 kHz. This situation can be observed especially in the case of organic coatings where, for practical purposes, the presence of microscopic defects is negligible. 

Liu, T., Is the Salt Fog Test an Effective Method to Evaluate Corrosion Resistant Coatings Corrosion Control by Organic Coatings, H. Leidheiser, Jr., Ed., National Association of Corrosion Engineers, Houston, TX, 1981, pp. 247-254. 

Morales A., Ajona J.I. Durability, performance and scalability of sol-gel front surface mirrors and selective absorbers. J. Phys. IV France 1999, 9 513-518 Murray J.M. Electrochemical test methods for evaluating organic coatings on metals an update. 

Electrochemical impedance spectroscopy (EIS) offers an advanced method of evaluating the performance of metallic coatings (passive film forming or otherwise) and organic barrier coatings. The method does not accelerate the corrosion reaction and is nondestructive. The technique is... 

The wide variability of absorption and diffusional properties of chemical species in organic polymer films makes them useful as selective or complete permeation barriers (e.g., gas separation membranes and passivating layers [1,5,82]) and selective chemical sensor coatings [83]. For these applications, a method for rapidly and directly evaluating the solubility and diffusional properties in thin films is useful. Diffusional properties can be evaluated by monitoring the transient up-... 

The growth influence of organ-specific biomatrices can also be evaluated. A BM coating can be left on a dish after removal of the cells by nonenzymatic methods, as described for the preparation of the subendothelial matrix (see Chapter 2, Section 2.3.4.1). Alternatively, a whole organ-specific biomatrix can be prepared from organ homogenates, as detailed in Chapter 2, Section 2.3.3.4. Tumor cells are then plated, usually at clonal density, on the matrix, and growth of colonies is detected after a week or two (Doerr et al., 1989). 

The US National Association of Corrosion Engineers (NACE) has published a test method for evaluating coatings. TMOl 105-2005 Test Procedures for Organic-Based Conductive Coating Anodes for Use on Concrete Structures . 

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