Hello Bruce and the responders to this thread. Fluoboric acid could
be an effective pickling agent for the alloys containing silicon
that have been giving problems with soldering. Fluoboric acid
(HBF4) is used in commercial processes for cleaning metal before
electroplating. The acid is effective in removing oxide and
silicate films that may be on the metal surface. The ability of
fluoboric acid to dissolve silicon materials is confirmed in section
K of MSDS 6008 (General Chemical Corporation) where it is noted that
the acid is corrosive to glass, ceramic and metals. Noble metals
are not attacked by the acid to any appreciable extent. Fluoboric
acid/hydrogen peroxide mixtures have been recommended for removal of
soft solder in at least two publications (B. Knuth, Jeweler’s
Resource, First Ed., Jewelers Press, p. 46 and Oppi Untracht, Metal
Techniques For Craftsmen, 1968, p. 182) Please note that Bruce Kunth
confirmed a typographical error for the name of the acid. That
error has been corrected in the 2000 edition. He has used the
fluoboric acid/hydrogen peroxide system for soft solder removal from
gold jewelry and found it satisfactory.
Fluoboric acid is provided as a 48% solution in water. It is stable
but should not be boiled. If silicon forms a layer on heating as
suggested by James Binnion, it might be necessary before soldering
to heat the work to near soldering temperatures, cooling in standard
pickle and then dipping in the fluoboric acid. The acid does not
appear to be any more hazardous or difficult to work with than the
other strong and corrosive acids frequently used, based on the
in the MSDS. It surely is not in the same class as
hydrofluoric acid. One source for the acid is Chemical Associates
in Pennsylvania. They quote a price of $26.03 for a liter of the
48% solution.
This is just a suggestion. I have not tried it. The information
available suggests it should work if silicates are the cause of the
problems cited. However, there sometimes is a “slip twix the cup
and the lip” so a trial should proceed with caution I have not had
the problem so far even although 90% of the repair work I see is
10K.
Captain Blood
"Marlinespike Seamanship in Precious Metals"
@Alden_Glenda_Blood