In a message dated 98-07-01 12:17:30 EDT, you write:

<< (1) I have some Au foil pieces that were conventionally polished which have
 silicon carbide grit embedded in them that I would like to dissolve away.

Having never actually done this, but sort of familiar with the chemistry
required, I do not envy you your job!   So, saying, it may take successive
treatments in dilute, hot Potassium Hydroxide, and then 50% Nitric Acid, at
room Temperature.  The KOH gets rid of the Silicon, the Nitric takes care of
the carbide.  Rinse between each step, and afterwards, and repeat, as much as
is necessary.  Wow, what a problem.

 (2) These samples were also chemically polished with an etchant composed of
 10% potassium cyanide (KCN) and 10% Ammonium persulfate in water.  I was
 wondering if this solution would leave any residues on the surface....Would
 a 50% hydrochloric acid, 50% Nitric Acid (aquaregia) etch be better?
  >>
As a contributor to Technet who is known for his casualness with chemicals,
all I can say is that I do hope you were not downwind from the KCN/Ammonium
Persulfate treatment, there could be a couple of animals with a permenant
disability, that resembles death...

Neither system should give you residues.  Either system will dissolve gold
from the surface.   Aqua Regia, which formally is 66-75% HCl, with the
remaining being Nitric is the "safer", but still to be treated with a lot of
respect.  The aqua regia is a faster etch.  Either system is overkill.

Consider just a dilute KCN solution, this should likely be enough, unless you
have gotten the surface REAL contaminated.

Rudy Sedlak
RD Chemical Company

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