Russ:

A 10% hydrochloric acid dip test is qualitative but gives good idea of reduced black oxide pink ring protection.  The typical test involves dipping a board section, and a "pass" is given to samples with no visible change to surface appearance after 15 minutes even though most samples will "survive" overnight (In this respect the CCI process is very robust).  

One can observe the rapidity of a failure by checking an unreduced sample.  A coupon that "fails" may show surface variation (black - brown - copper) or total failure and usually does so within the first few minutes.  Note that hydrochloric acid fumes will attack the coupon at the liquid/air surface and are not a sign of failure.

Some use 10% sulfuric, but I have found that the reaction is more observable with 10% hydrochloric.  CCI also has checked deposits with SERA and routine weight gains -- One does not want to hit a vigorous reduction bath with too little thickness -- but the Pink Ring Litmus Test appears to best come from acid dip for now

(Response is given for process using dimethylborane/caustic reduction of conventional black oxide.)

Paul Wilson
Plant Chemist

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----------
> Dear Technetters,
>
> There does not appear to be an industry standard acid resistance test for
> determining the functional quality of a reduced black oxide layer. The acid
> resistance test is a good method for determining the quality with respect to
> pink ring resistance.
>
> Several companies and indeed suppliers have different methods for testing this
> functionality of the Reduced Oxide process.
>
> So I thought it might be worthwhile firing these questions off around the
> world :
> What method is used at your shop to test the acid resistance of your Reduced
> Black Oxide process - in terms of acid type - strength and application method
> and when is it tested?
>
> If you are using an alternative oxide or oxide replacement do you still carry
> out an acid resistance test?
>
> Russ Gregory
> Atotech UK
>
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