CASS test

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The CASS Test. In the copper-accelerated acetic acid salt spray (CASS) test (42), the positioning of the test surface is restricted to 15 2°, and the salt fog corrosivity is increased by increasing temperature and acidity, pH about 3.2, along with the addition of cupric chloride dihydrate. The CASS test is used extensively by the U.S. automobile industry for decorative nickel—chromium deposits, but is not common for other deposits or industries. Exposure cycle requirements are usually 22 hours, rarely more than 44 hours. Another corrosion test, now decreasing in use, for decorative nickel—chromium finishes is the Corrodkote test (43). This test utilizes a specific corrosive paste combined with a warm humidity cabinet test. Test cycles are usually 20 hours. 

The accelerated corrosion test in most general use is the CASS test in which the articles are sprayed intermittently with a solution made up as follows ... 

The test is much faster than the CASS test (see page 19 49) and is probably more reproducible more important is the fact that it has been correlated with service exposure. 

It has been shown that chromium is virtually unattacked by the CASS test solution Nickel, on the other hand, is corroded at a substantial rate (about 0-072mm/y), the presence of the copper ions tending to maintain the nickel in an active state . Thus, in the CASS test (and in the Corrodkote test as well) accelerated galvanic corrosion of the nickel occurs at any discontinuities in the chromium layer. Good correlation between the results of the CASS test and the performance of plated parts in service has been reported . 

Acetic acid salt spray test (ASS test) Copper-accelerated acetic acid salt spray test (CASS test)... 

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ASTM B368, Std. Methodfor Copper-Accelerated Acetic Acid Salt Spray (Fog) Testing (CASS Test), American Society for Testing and Materials, Philadelphia, Pa., 1990. 

On the other hand, the CASS test utilizes the sodium chloride - copper chloride mixed solution. The addition of copper ion accelerates corrosion much more than the salt spray testing. However, the results might not fit the real phenomenon so precisely in some cases. 

The specimen (after these tests) is evaluated for its extent of corrosion. If it would be genuine research, we could use various electron microscopies such as TEM, SEM, XPS, etc. However, we usually use a rating number method for the evaluation from the practical standpoint. Figure 10 shows schematic figures for the method. We can evaluate the distribution situation by the naked eye, by comparing the tested specimen to the standard samples. There are some other methods similar to the salt spraying test and the CASS test. However, the basic concept for the evaluation method is almost the same. The solution, temperature, and amount of spraying are varied from test to test. 

Copper-Accelerated Acetic Acid Salt Spray Testing (CASS Test)... 

The Copper-Accelerated Salt Spray Test, ASTM B 368, commonly known as the CASS test, is typically used for testing copper-nickel chrome products. It was developed by the American Electroplaters Society as AES Research Project 15 [12], along with the Corrodkote Test (ASTM B 380) and incorporated into ASTM in 1965. 

The CASS test is conducted at an exposure zone temperature of 120°F. The electrolyte solution is a 5 % salt solution, with the addition of copper chloride and glacial acetic acid. The sodium chloride used must be reagent grade in order to produce the mass loss specified on the nickel panels. Similar to B 117, collection rates should be at 1-2 mL/h. 

Nickel panels are used to calibrate and monitor CASS test chamber conditions. The panels must be 7.5 x 10 x 0.09 cm and made from higher grade carbon as described in ASTM B 162. The panels are weighed and placed in each of the four comers of the chamber. After a 22-h exposure period, the panels are removed, cleaned, and reweighed. ASTM B 368 identifies the target weight loss as 0.45-0.85 mg/cm [73]. 

Although a salt spray (fog) chamber and CASS test chamber may be structuraDy identical, users are discouraged from using a chamber that has previously been used for CASS testing as a salt fog chamber. 

The addition of acetic acid to the salt solution used in the salt spray tests was introduced first in 1945 and is currently Annex A1 of ASTM G 85 [Practice for Modified Salt Spray (Fog) Testing]. The acidified test is much more corrosive than the normal salt spray test and is capable of producing a pattern of attack similar to that developed in outdoor service for decorative chromium plate on steel or zinc. It is much slower than the copper-accelerated acetic acid-salt spray (CASS) test in ASTM B 368 [Method for Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test)], [77] which resembles it in effect. 

The CASS test and Corrodkote procedure are employed primarily for testing decorative chromium systems, with the CASS test ako being useful for testing anodized aluminum. These tests were developed to give a more rapid indication of corrosion resistance and a better correlation with service performance. They have come into prominence tis the most widely used modifications of the salt spray test because of their greater speed. Both tests employ cupric ion in the corrodant... 

Testing anodized aluminum specimens. Electrolyte as in salt-spray or CASS test. Specimen is made the cathode to generate high pH at defects. 

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