Note: Descriptions are shown in the official language in which they were submitted.
1(~4~39~7
,
BACKGROUND OF THE INVENTION
It is known in the art to which this invention pertains
that nickel and related metallic coatings on the contact tips of
the plating racks of electroplating apparatus can be removed by
either mechanical means or chemical techniques. In themechanical
approach it has been conventional to use a hammer or like tool
means to shatter the unwanted nickel deposit on the contact tips,
and while this treatment is generally effective, it suffers from
the disadvantages of being time-consuming and may ultimately
result in damage to the metal base. Thèn too, some plating racks
contain several hundred individual tips, so that mechanical
removal of the unwanted coatings thereon leads to substantial
labor costs.
Chemical methods for dissolution of the nickel deposits
on stainless steel racks have generally employed nitric acid,
and while this approach represents an improvement over the
hammer method, the use of nitric acid by itself is tedious since - ;
nickel is only slowly attacked by this acid. It has accordingly - -
been customary to add a catalyst such as a chloride ion, but this
substance in the presence of strong nitric acid forms nitrosyl
chloride which is a gas at tèmperatures above about-5.5C., and
accordingly, its benefit to the stripping solution is soon lost
by volatilization. The addition of other ions to the solution
has also been proposed, as the iodate ion disclosed in Patent No. ! '
3,399,143: however, following these teachings does not obviate - -
the objection of relatively slow stripping speeds, and may under
particular conditions cause damage to the stainless steel contact
tips.
,,, . ,,, ,, , ; ,,, . :; ,, ;, ,., .. ;. ,, ., ,,", ; .,~,. ,, .. ,.,, , , ., ........ , .':
1()4~87
SUMMARY OF THE INVENTION
The invention is directed to a composition for strip-
ping accumulated nickel deposits from plating apparatus and
the like, which comprises nitric acid and sources of chloride,
copper and tellurium or selenium ions, said chloride ion being
present in concentrations of about 0.01 to 0.5 M and said
tellurium or selenium ions being present in small but effective
amounts sufficient to accelerate the stripping rate without
noticeable deleterious effects upon the plating apparatus.
The invention also relates to a method of stripping
nickel deposits from articles by immersing them in a concentra-
ted nitric acid solution containing a chloride catalyst, which
comprises adding to said solution a small but effective amount
of a selenite or tellurite compound capable of providing sele-
nium or tellurium ions in the solution.
The instant invention is particularly directed to a
novel composition for removing nickel and generally similar
unwanted deposits from plating racks and like articles and to a --
process for utilizing said composition, the formulation conceived
by applicant comprising about 4.5 to 14.5 moles/liter of 42
Be. nitric acid, a chloride ion in the amount of 0.01 to 0.5
moles/liter, a copper ion in the amount of about 0.01 to 0.5
preferably 0.01 to 0.1 moles/liter,and a source of tellurium or
selenium ions in the amount of approximately 0.005 to 0.2 moles/
liter. Preferably,the molar ratio of tellurium or selenium ions to
chloride ions is in the general range of about one to three.
While applicant does not wish to be bound by a partic-
ular theory, it would appear from work performed to date that
tellurium or selenium when admixed with the other constituents
of the solution herein disclosed in the general molar ratios
above set forth possesses film-forming capabilities. This is
-2-
: ,:
. , . ., . " ~, . . .
10~987
perceptible to the naked eye when an examination is made of a
stainless steel substrate, and is the apparent reason why there
is no noticeable attack upon the surface being stripped and also
why unwanted nickel deposits can be removed at speeds approximate-
ly 30% faster than commercially available plating solutions.
The invention also relates to an aqueous solution
for stripping accumulated nickel deposits from plating apparatus,
which contains therein about 2 to 10 grams per liter of tellurium
or selenium dioxide, 600 to 850 grams per liter of nitric acid,
2 to 20 grams per liter of CuSO4.5H2O, and 3.5 to 35.5 grams per
liter of a source of chloride ions.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The stripping solution employed in the practice of
this invention may be prepared by either one of two procedures.
First, there can be initially formed a sodium or potassium salt
of tellurium dioxide (tellurous acid anhydride) or selenium
dioxide (selenous acid anhydride) by mixing approximately 15 grams
of Te 2 or Se 2 with about 10 to 12 ml. of NaOH or KOH, ~ -
diluting the solution obtained to about 150 ml, and thereafter -
filtering ~ -
";'-
`''' '''.'
- 2a - -
.
9~37
out the precipitate. A preferred concentration for the hydro-
xide used is about 50%. The sodium or potassium tellurite or
selenite obtained is then combined with measured quantities of
nitric acid, cupric sulfate and sodium chloride to provide the
novel stripping solution of this invention.
A second procedure for formulating the stripping solu-
tion is to directly admix predetermined amounts of Te 2 or SeO2
HN03. CuS04 . SH20, and NaCl. This procedure is somewhat less
expensive than going through the first approach, however, at
times it may be found that combining the TeO2 or SeO2 directly
with HN03 produces a somewhat violent reaction. The first
mentioned procedure is accordingly preferred at the present time.
The invention will now be more fully described wlth
reference to the following examples, which were run at a solution
temperature of approximately 40C.
E~AMPLE I
A solution was made up of 500 mil. HN0 , 5.7 g. CuS0 .
SH2o, 3.3 g. NaCl and 3.0 g. FeC13 , which were diluted to 1
liter. A stainless steel part having a nickel deposit thereon
of about one mil in thickness was immersed therein, and it took
about 87 seconds before the deposit was removed.
EX~Ml?LE I I
There was formulated a solution containing 500 ml. ~ -
HN03 , 5.7 g. CuS04. SH20, 3.3 g. NaCl, 2.0 g. of a commercially
available strip aid (composition unknown), and this mixture -
diluted to 1 liter. It took about 141 seconds to remove a one
mil thick nickel deposit from a stainless steel part. -
EXAMPLE I I I : .
A solution was made up of 500 ml. HN03, 5.7 g. CuS04,
5H2O, 3.3 g. NaCl and 1.5 g. Na2TeO3, which were diluted to 1
liter. It only took 33 seconds to strip a one mil nickel
deposit from a stainless steel part.
9~7
T~ M P T . F~ T t7
The procedure of Example III was followed except that
Na2SeO3 was substituted for the Na2TeO3. The same thickness
deposit was removed in 35 seconds.
`' EXAMPLE V
The procedure of Example III was again followed, except
that 1.5 g. NaF was used in place of the Na2TeO3. A nickel de~osi~
o the same thickness took 110 seconds to be removed from a stain-
l~ss steel part. -
EXAMPLE VI
.
Therè was formulated a stripping solution containlng
500 ml. HNO3, 5.7 g. CuSO4-5H2O, 3.3 g. NaCl, 1 g.KBrO3 and 0.3
~. KIO3 which was diluted to 1 liter. A one mil nickel deposit
was removed from a stainless steel part in 100 seconds. - -
EXAMPLE VII
A solution was made up of 500 ml. HNO3, 5.7 g. CuSO4 5~120,
3.3 g. NaCl and 1 ml. bromine, the mixture being diluted to 1 liter.
A one mil nickel deposit was stripped from a stainless steei part
in 94 seconds.
EXAMPLE VIII
There was formulated a stripping solution containing
500 ml. HNO3, 5.7 g. CuSO4 5H2O, 3.3 g. NaCl, and 10 ml. Na2TeO3 -~
solution prepared as earlier described, and this mixture was
diluted to 1 liter. A nickel deposit of a thickness of one mil
w2S stripped in only 58 seconds. ~ :
EXAMPLE IX ~
~ solution was prepared as in Example VIII, but the ~ ~;
amount of Na2TeO3 solution was increased to 20 ml. A deposi~ ,
of the same thickness was removed in only 33 seconds.
~', -' , ' ,
-4-
'.' ' '
104~3987
EX~PLE X
There was formulated a stripping ~olution containing
2 g/l TeO2 , 600 g/l HNO3 , 5.? g/l CuSO4.5lJ2O and 3.3 g/l
NaCl. An unwanted nickel deposit one mil thick was stripped
S from a stainless steel part in 2? seconds, which is about 30%
faster than commerically available strippers.
In the exemplary formulations set forth above, potassium
hydroxide can readily be subst.itu'ed for sodium hydroxide;
potassium, manganese or cupric chloride can be used in place of
sodium chloride; and cupric nitrate or chloride axe substituents
for cupric sulfate. Further, if desired, a portion of the nitric
acid may be replaced by an equivalent (i.e., acid equivalent)
amount of sulfurric acid, thereb~ satisfying the hydrogen ion
requirement by a less expensive acid~
Various modifications i,~ the compositions of this
invention have been pointed out herein, and these and other
changes can of course be effected without departing from the
spirit of the invention of the scope of the subjoined claims.
. "" . ' .
.~' ' ,' '.; .
.-. .
.~;
. ~ -
.. . . . . . . . . . ... . . . . .. . ... .. . . .
