Accelerated testing, surface coatings

Testing of metals for resistance to sulphide stress cracking at ambient temperatures Accelerated test procedures for screening atmospheric surface coating systems for offshore platforms and equipment... 

Weatherfastness tests on coatings have shown that prolonging the dry and wet periods, i.e., extending the usual 17 minute dry cycle to a full 102 minutes and the wet period to 18 minutes, affords results which correlate much better with the Florida outdoor exposure tests. The humidity that penetrates a layer is known to interact with the various components in the coating, adversely affecting the mechanical properties of the material. The above mentioned cycle apparently corresponds much better with the climatic conditions in areas like Florida. If recirculated water is used in accelerated exposure equipment, suspended particles may adhere to the surface of the coating, producing a thin film. This obviously has a detrimental effect on the test results. 

In a search for reliable accelerated test methods for determining coating performance, electrochemical techniques have often been explored. The corrosion resistance of a coated steel panel is a composite of the steel quality, its surface finish and the quality of the coating. For this reason. Bonderite 40 coated steel panels were included in our work. They were employed primarily to aid in the interpretation of the electrical measurements for the nitrile-based photocured samples. 

Accelerated weathering tests are performed in special test chambers all of which are similar in that a coated specimen is exposed in a controlled environment containing a high intensity ultraviolet light source and a facility for spraying water onto the test surfaces. 

Chemical stability predictions are sometimes complicated by the difficulty of determining the pH value of suspensions, which often changes because of surface coating of electrodes and differences between bulk-suspension and supernatant-vehicle readings. Accelerated elevated temperature stability testing often has a pronounced adverse effect on viscosity, particle solubility, and size distribution. 

Various conditions of accelerated corrosion testing are summarized in Table 1.10. According to ISO 14993 [85], water condensation on the test specimens should not occur under wet conditions. The methods of testing organic coatings on metallic materials according to ISO 11997-1 under cyclic corrosion conditions include condensation of water on the test surface during the period of humidity [87]. 

The corrosion protection performance of the sol-gel films was estimated by accelerated test using immersion in a NaCl solution. Fig. 2 demonstrates the coated surface after the immersion tests. The reference sample prepared without titania nanoparticles is strongly attacked after 10 days in 0.05 M NaCl. In contrast, the sample with titania nanoparticles seems almost untouched even after one month in concentrated NaCl solution. 

Very favorable but unsound comparisons can be made for zinc-rich paints as related to metallic zinc coatings by use of accelerated tests because the binder in the paint delays the onset of formation of white corrosion products, whereas in practice, the performance is related to the amount of zinc present and to the general formulation rather than to the initially exposed surface. 

Accelerated tests such as ASTM B 201 are very useful in evaluating the quality of chromate films on zinc or zinc-coated surfaces. The test proceeds until white corrosion products have formed and should not be allowed to continue until red rust forms. Only the time to formation of "white rust is relevant. The effects of impurities on the corrosion rate of zinc can be determined by humidity testing. 

A second key to choosing an accelerated test is a good understanding of the materitil/materials being tested. In the subsection titled Specific Systems, a discussion of the way in which several coated sheet products provide corrosion protection was presented. Selection of a cyclic test that will yield good predictive information must take these factors into account. If the materitJ of interest is known to provide barrier protection due to the formation of a psissive film on the coating surface in the exposure environment of concern. 

Accelerated Test Procedures for Screening Atmospheric Surface Coating S5 tems for Offshore Platforms and Equipment... 

EMMA devices are successfully used by many manufacturers, particularly in the surface-coating industry, who wish to evaluate rapidly the durability of their products outdoors. However, these devices are also used in the study of accelerated weathering of almost all polymeric materials and plastics. One of the largest testing stations in the world is Heraeus DSET Laboratory Inc. (45601N, 47 Ave., Phoenix, AZ 85027-7042, USA) it employs hundreds of EMMA and EMMAQUA devices. 

Recent studies performed with deactivated anodes show [55] that electroless or electrolytic platinum deposition on failed anodes, not only lowered the polarisation behaviour of these anodes (see Fig. 5.20), but also demonstrated an equivalent lifetime as that of a new anode in accelerated life tests in the sulphuric acid solution (see Fig. 5.21). These results unequivocally demonstrate that the deactivation of anodes, for which the Ru loading is still high, is a direct consequence of the depletion of Ru from the outer region of the anode coating. Note that this process of surface enrichment by conducting electroactive species will not lead to reactivating a failed anode, if there is a TiC>2 build-up at the Ti substrate/coating interface. 

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