Corrosion resistance salt spray tests

Polyester primers are widely used in Western Europe. Although their corrosion resistance (salt spray test) is not as good as that of the other primer types, their mechanical properties are superior. 

Sa.lt Spray Tests. One of the older accelerated corrosion tests is the salt spray test (40). Several modifications of this imperfect test have been proposed, some of which are even specified for particular appHcations. The neutral salt spray test persists, however, especially for coatings that are anodic to the substrate and for coatings that are dissolved or attacked by neutral salt fog. For cathodic coatings, such as nickel on steel, the test becomes a porosity test, because nickel is not attacked by neutral salt fog. Production specifications that call for 1000 hours salt spray resistance are not practical for quahty acceptance tests. In these cases, the neutral salt spray does not qualify as an accelerated test, and faster results from different test methods should be sought. 

As of this writing the 2inc alloys are too new to have actual corrosion resistance data, except for that based on accelerated tests. Zinc—nickel usually shows better results than 2inc-cobalt in salt spray tests. The reverse is tme when the Kesternich test is used. Tin—2inc performs well in both salt spray and Kesternich tests, but appears only to equal 2inc plating and 2inc—nickel in humidity tests. 

Corrosion-resistance test This can be done with the help of a salt spray test. The test piece is suspended in a salt spray chamber (Figure A13.6) for. seven days in 100% relative humidity (IS 101 and IS 11864). After the test, the surface should have no signs of deterioration or corrosion. 

Ductile and easily buffed chromium deposits having satisfactory corrosion resistance have been produced thus 0.005 mm-thick chromium deposits applied to steel by chemical deposition or by eiectrodeposition gave simiiar results when subjected to a salt-spray test . 

Resistance to corrosion Most authors who compare resistance to corrosion of electroless nickel with that of electrodeposited nickel conclude that the electroless deposit is the superior material when assessed by salt spray testing, seaside exposure or subjection to nitric acid. Also, resistance to corrosion of electroless nickel is said to increase with increasing phosphorus level. However, unpublished results from International Nickel s Birmingham research laboratory showed that electroless nickel-phosphorus and electrolytic nickel deposits were not significantly different on roof exposure or when compared by polarisation data. 

Thus it appears that by incorporating parameters such as pore resistance and coating capacitance to the existing theoretical impedance model dealing with metal dissolution one would obtain valuable overall information (14,27). Complemented by results from regular immersion and salt spray tests it should be possible to find satisfactory solutions to corrosion problems of coated metals (9 ). 

The Effect of Adhesive Primers. In practice, adhesive bonds involving metal adherends often use primers as pretreatments of the metal surface prior to bonding. Table IV shows the durability of composite-metal bonds prepared with adhesive C over a series of primers (of varying corrosion resistance) in 240 hour salt spray test. The results indicate that the performance of bonds is directly related to the corrosion resistance of the primer used to prepare the adherend surface. In general, the adhesion of the primer to the steel adherend, rather than the adhesive chemistry. 

Salt Spray Test Panels coated with the standard chromate conversion coating and CMT were compared with each other in their corrosion resistant properties in several ways. The conventional 5% NaCl/S02 fog chamber tests showed excessive corrosion and pitting within one week on chromate conversion coated (COC) 7075-T6 A1 alloy panels. The CMT coated panels were almost uncorroded and without any pits. The plates in Figure 1 show the conditions of the panels after 7 and 14 days exposure in this environment. Even after 14 days exposure the CMT panels were still far better than COC panels. 

Figures 31.20 and 31.21 show the scanned images of SO2 and Prohesion salt spray-tested panels of [2B], respectively. Visual observation of these images reveals that panels that were only acetone wiped and E-coated ([2B](Ace)/E) provided poor corrosion resistance. In contrast, the plasma-modified [2B] panels showed excellent corrosion resistance even after 12 weeks of exposure to Prohesion salt spray,...

Corrosion Resistance. Corrosion resistance has been tested by Cleveland Humidity Chamber and Salt Spray Test on very thin coatings with thickness of 0.2 mils. 

The mass content of such monomers in the UV formulations is similar to that of MAPC1(0H)2 shown in Table 10.4, i.e. less than 3 wt%. For the methacrylate coatings, salt spray tests were eonducted and the resistance to corrosion was assessed over time (Figure 10.5). 

Figure 10.5 Graphical result of the resistance to corrosion after being subject to the salt spray test (0.5 mol NaCl in water at 35 °C).

Figure 10.6 Graphical result of the resistance to corrosion after being subject to the salt spray test (0.5 mol NaCl in water at 35 °C) for PVA, PVBl (48 mol% butyral), PVB2 (73 mol% butyral), PVAP3 (60 mol% butyral and 20 mol% phosphonate), and PVAP4 (50 mol% phosphonate).

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