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"Reliable coating weight procedure for Alodine+SA on Al needed"


We've recently purchased a salt spray chamber to run 168 hr tests for Alodine and 336 hr tests fur sulfuric anodize (aluminum alloys only). I'd like to bring our remaining testing in-house also, this includes the simle coating weight test. The procedure I have for coating weight is to weigh a 3x3 panel, immerse in 50 HNO3 for 1 minute, and re-weigh; Coating (in mg/sq ft) is found by the difference in weight. I know there must be a better procedure because mine is inaccurate, doesn't work on anodize, and is required to be performed 2-3 hours after processing (It's impossible for an outside laboratory to have that kind of turnaround). Does anyone have a better method?

Benjamin J. Curto
Cygnus, Inc. - Ponderay, Idaho, USA


A method of chromate coating weight analysis that has become more popular recently is x-ray fluorescence. It provides quick results that the manufacturers claim are repeatable and accurate. It also doesn't require the use of hazardous chemicals in stripping solutions. It is doubtful that this process could be used for anodized aluminum.

Patrick Patton
Q-Panel Lab Products - Westlake, Ohio


The method you described for Alodine is very reliable. For coating weight of anodize you should use the ASTM B137 [affil. link to spec at Techstreet] 35ml/l H3PO4 20g/l CrO3 100 °C.


Moshe Yaakobv
IAI - Lod, Israel

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