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Revealing Grain Boundaries
Name: Anthony
Status: student
Grade: other
Location: OH
Country: USA
Date: March 2009
Question:
I am trying to understand the chemistry
behind nickel etching. I have a solution of ferric
chloride, hydrochloric acid, and nitric acid and I
am putting nickel pieces into the solution. How
does each chemical contribute to revealing the
grain boundary?
Replies:
Hi Anthony,
That is quite a concoction you are using! Etching of nickel is commonly
done in some of the reagents you mention, but not all of them mixed
together.
Etching nickel simply requires an acid and an oxidizing agent. A 30%
to 50% dilution of nitric acid in water is commonly used (may need to
be heated to 40° or 50°C). Nitric acid is also an oxidizing agent.
This is a dangerous chemical! Proper safety equipment is required
Another possibility is either hydrochloric or sulfuric acids (which
are not oxidizing agents), diluted to 30% or more in water, with part
of the water replaced with Hydrogen peroxide (an oxidizing agent).
This may not be so easy to do because hydrogen peroxide is not
commonly available except in high dilution (more than 6% or so).
Ferric chloride, acidified by mixing with hydrochloric acid, can also
be used, and is favored because it generates no violent gassing.
Similarly, ammonium persulfate solution can be used for the same
reason, and also because it is not acidic. In fact, both of these
reagents were very common copper etchants used at one time in printed
circuit board manufacture, before better copper-specific etchants
supplanted them.
Whenever using these chemical, be sure that you are following all safety procedures
and are wearing proper protective equipment.
Regards,
Bob Wilson
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Update: June 2012
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