Note: Descriptions are shown in the official language in which they were submitted.
2139388
PATENT
M 5621 PAM/ALGE
COMPOSITION AND PROCESS FOR DESMU l ll~G AND DEOXIDIZING
WITHOUT SMU l llNG
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to compositions and processes for de~ml-ttin~ metal sur-
faces, particularly the surfaces of ~lllmimlm and m~gn~si~lm and their alloys that contain
5 at least 45 % by weight of ~ mimlm or m~gne~illm, more particularly ~lnmin~lm alloys
co~ sufficient copper to form smut on their surfaces easily when dissolving. The
compositions and processes are also useful for deoxidizing lm~m~ltted surfaces and
achieve deoxidizing without forming smut on the surfaces or otherwise st~ining them.
("Deoxidizing" is to be understood herein as the removal from the surface of metals of
10 oxide films and other adherent inorganic materials that would reduce adhesion to subse-
quently desired protective coatings such as conversion coatings and/or paints and the
like. With most deoxidizing agents, there is a perceptible but controlled dissolution of
the underlying metal while the deoxidizing agent is in contact with it. In contrast, "de-
~mlltting" is to be understood herein as the removal, without significant attack on the un-
15 derlying metal, of powdery and usually darkly colored residues produced on a treatedmetal surface by some prior cleaning, et-.hing, and/or deoxi~ ing trç~tm~nt )
2139388
Statement of Related Art
Since the development of copper co,,l~in~ minllm aerospace alloys several
decades ago, the conventional deoxidizing compositions have normally incl~1ded concen-
trated nitric and/or sulfuric acid and chromates, with fluorides, ferric ions, oxidizers such
s as persulfate and peroxide, and ferricyanide all serving as frequently used optional in-
~ ~dienls. In recent years there has been environmenlally driven incentive to avoid chro-
mates and ferricyanides, but no fully s~ti.~f~ctQry deoxidizer free from these materials is
believed to have been developed.
DESCRIPTION OF THE INVENTION
10 General Principles of Description
Except in the claims and the operating examples, or where otherwise expressly
indicated, all numerical quantities in this description indicating amounts of material or
conditions of reaction and/or use are to be understood as modified by the word "about"
in describing the broadest scope of the invention. Practice within the numerical limits
15 stated is generally pler~ d. Also, unless ~ ,essly stated to the contrary: percent, "parts
of~', and ratio values are by weight; the description of a group or class of materials as
suitable or p,erelled for a given purpose in connection with the invention implies that
mixtures of any two or more of the members of the group or class are equally suitable or
plt;relled; description of constituents in chemical terms refers to the constituents at the
20 time of addition to any combination specified in the description, and does not necessarily
preclude chemical interactions among the con~tit~1çnts of a mixture once mixed; specifi-
cation of materials in ionic form implies the presence of sufficient counterions to produce
electrical neutrality for the composition as a whole, and any counterions thus implicitly
specified should preferably be selected from among other constituents explicitly speci-
25 fied in ionic form, to the extent possible; otherwise such counterions may be freely se-
lected, except for avoiding counterions that act adversely to the objects of the invention;
the term "mole" means "gram mole", and "mole" and its variations may be applied herein
to ionic or any other chemical species with defined numbers and types of atoms, as well
as to chemical substances with well defined conventional molecules.
30 Summary of the Invention
It has been found that molybdate ions and ferric ions have a favorable synergistic
effect in nitric acid based desm-ltting compositions, permitting the çlimin~tion of both
. 213g388
chromates and ferricyanides while producing excellent results in de~mlltting ~lllminllm
and m~n~ei~lm and their alloys, incl~1tling copper co,.~ g alloys. The same composi-
tions can be used if desired as deoxidizers for metal surfaces that have oxide films that
are unwanted, and can accomplish deoxidizing effectively without forming smut on the
5 deoxidized surfaces or otherwise st~ining the surfaces, particularly if not allowed to dry
on the surface before rinsing.
Accordingly, one embodiment of the invention is an aqueous composition that
comprises, preferably consists ess~nti~lly of, or more preferably consists of, water and:
(A) nitric acid;
10 (B) ferric ions;
(C) molybdate and/or con~n~ed molybdate anions; and, optionally, one or more of
the following components:
(D) persulfate (i.e., S208~2, also called "peroxydi~l-lf~te") anions;
(E) fluorine Co~ g anions;
15 (F) sulfuric acid and/or sulfate ions;
(G) surfactant; and,
(H) a dye or other colorant.
Various embodiments of the invention include working compositions for direct
use in treating metals, concentrates and partial concentrates from which such working
20 compositions can be prep~ed by dilution with water and/or mixing with other chemically
distinct concentrates, processes for treating metals with a composition according to the
invention, and extended processes inçlll~ing additional steps that are conventionalper
se, such as rinsing, and, particularly advantageously, subsequent conversion coating
and/or painting or some similar overcoating process that puts into place an organic binder
25 CO~ g protective coating over the metal surface treated according to a narrower em-
bodiment of the invention. Articles of m~nllf~ct~lre incl~1ding surfaces treated according
to a process of the invention are also within the scope of the invention.
At least the most plerelled compositions and processes according to the invention
meet the deoxidizing requirements of U. S. Military Specification MIL-W-6858C, lT 4.2.
30 Description of Pl~relled Embodiments
For a variety of reasons, it is pl erel, ed that compositions according to the inven-
tion as defined above should be substantially free from many ingredients used in com-
2l3g388
positions for similar purposes in the prior art. Specifically, it is increasingly prt;relled
in the order given, independently for each preferably minimi7ed component listed below,
that these compositions, when directly cont~sted with metal in a process according to this
invention, contain no more than 1.0, 0.35,0.10,0.08,0.04,0.02,0.01,0.001, or 0.0002,
percent of each of the following con~tit~lPnts: hexavalent chromium; silica; silicates that
do not contain at least four atoms of fluorine per atom of silicon; ferricyanide; ferrocyan-
ide; thiourea; pyrazole compounds; sugars; gluconic acid and its salts; glycerine; a-glu-
coheptanoic acid and its salts; and myoinositol phosphate esters and salts thereof. It is
also prerelled that the content of ferrous ions be no greater than 5, more preferably not
greater than 3, or still more preferably not greater than 1.1, % of the content of ferric
ons.
Fullllellllol~, in a process accolding to the invention that includes other steps than
the desm-lttin~/deoxi~i7.inE tre~tn ~nt with a composition as described above, when
avoidance of enviroml~ell~al pollution is an important consideration, it is plerelled that
none ofthese other steps include cont~ctinE the surfaces with any composition that con-
tains more than, with inclea~ pl~relence in the order given, 1.0, 0.35,0.10,0.08,0.04,
0.02,0.01,0.003,0.001, or 0.0002 % of hexavalent chromium. On the other hand, the
dç~m~lttin~/deoxi~i7.in~ process taught herein can be advantageously used prior to chro-
mate conversion coating or anodizing in a cl rolllate co"l~inil-E--or, of course, a non
chromate co,,l~inil~E--solution, where one of the latter treatments is needed.
In an acidic aqueous composition to be used according to the invention, either di-
rectly as a working composition or as a source of active ingredients for making up a more
dilute working composition, the concentration of nitric acid preferably is, with increasing
plerel~nce in the order given, at least 0.1, 0.25,0.5,0.9,1.3,1.7,2.0,2.1,2.2,2.3,2.4,
2.5, or 2.6 moles per liter of composition (hereinafter usually abbreviated "Ml'), and, if
the composition is to be used for removing exceptionally heavy scale still more preferab-
ly is, with increasing pl~relence in the order given, at least 2.8,3.0,3.2,3.4,3.6,3.7,
3.8, or 3.9 M. Independently, in a working composition the concentration of nitric acid
pl ~r~l~bly is, with increasing pl erel ence in the order given, not greater than 10, 9, 8,7.4,
6.8,6.4,6.2,6.1,6.0, or 5.9 M, and for economy still more preferably is, with increasing
pl~relence in the order given, not more than 5.7,5.5,5.3,5.1,4.9,4.7,4.5,4.3,4.1, or
4.0M.
2l 39388
For ferric ions, the concentration in either a concentrated or a working composi-
tion preferably is, with increasing plererence in the order given, at least 0.009, 0.02,
0.035, 0.05, 0.06, 0.07, 0.08, or O.O9Mand, if a higher scale removal rate is desired,
more preferably is, with increasing pl~rerence in the order given, at least 0.11, O.13,
O.14, O.15, O.17, O.19, 0.21, or 0.22, M; and independently this concentration in a work-
ing composition preferably is, with increasing pleferel-ce in the order given, not greater
than 1.0, 0.70, 0.62, 0.58, 0.50, 0.45, 0.37, orO.30Morforrnaximum economy still more
preferably is, with increasing prererence in the order given, not more than 0.27, 0.25,
0.24, or 0.23 M. Independently, the ratio of the molar concentration of ferric ions to the
molar concentration of nitric acid in a working composition according to the invention
preferably is, with increasing pr~rerence in the order given, not less than 0.003, 0.005,
0.007, 0.014, 0.018, 0.020, 0.024, 0.028, 0.032, 0.034, or 0.035 and independently prefer-
ably is, with increasing plerelence in the order given, not more than 0.4, 0.3, 0.2, O.1,
0.08, 0.06, 0.055, 0.050, 0.045, 0.041, 0.038, or 0.036.
Because the degree of aggregation of molybdate ions is usually uncertain and is
not believed to affect the favorable action of molybdate ions in compositions according
to this invention, the concellll~lion of these ions is described herein as the stoichiometric
equivalent as molybdenum atoms, even though only those molybdenum atoms that arepresent in some form of molybdate or con~nied molybdate anions are believed to be
effective. In either a concentrated or a working composition according to the invention,
this concentration preferably is, with increasing pr~rerence in the order given, at least
0.006, 0.011, 0.025, 0.031, 0.034, 0.037, 0.039, 0.040, 0.041, or 0.042 M and for maxi-
mum desml-tting activity still more preferably is, with increasing prererence in the order
given, at least 0.046, 0.051, 0.056, 0.060, 0.062, or 0.063 M; and independently this con-
centration in a WOlking composition preferably is not greater than 0.58, 0.41, 0.28, 0.20,
0.16, 0.12, 0.10, or 0.092Mand for economy still more preferably is, with increasing
pl~felence in the order given, not greater than 0.087, 0.081, 0.077, 0.073, 0.070, 0.067,
or 0.065 M. Independently, the ratio of the molar concentration of molybdate ions to the
molar concentration of nitric acid in a working composition according to this invention
preferably is, with increasing prererence in the order given, not less than 0.001, 0.002,
0.004, 0.007, 0.008, 0.009, 0.010, 0.011, 0.013, 0.015, or, 0.016 and independently pref-
erably is, with increasing prefelence in the order given, not more than 0.16, 0.10, 0.07,
~ ~ 2l3g388
-
0.05, 0.03, 0.025, 0.021, 0.018, or 0.017. Also, independently, in either a working or a
con~entrate composition according to this invention, the ratio of the molar concentration
of molybdate ions to the molar concentration of ferric ions preferably is, with increasing
plefelellce in the order given, at least 0.05, 0.088, 0.12, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40,
0.42, 0.44, or 0.45 and independently preferably is, with increasing pl~felellce in the
order given, not more than 4, 3, 2, 1, 0.8, 0.7, 0.6, 0.55, 0.50, 0.49, 0.48, or 0.47.
The presence of persulfate ions, optional component (D) as noted above, is pre-
ferred when very heavy layers of smut are to be removed with the compositions accord-
ing to this invention, and/or when the surfaces to be treated with a composition according
to this invention have been heavily shot peened with iron shot or otherwise caused to in-
clude embedded small particles of iron and then have been etched by a solution, such as
a commonly used solution co.~ g sodium sulfide, triethanol amine, and alkali, that
can convert the iron particles to iron sulfide. For such applications, the oxidizing action
of persulfate provides far more rapid desm~1tting and/or deoxidizing than compositions
according to the invention from which persulfate is omitted. For these speci~li7ed appli-
cations, the concentration of persulfate in either a concentrated or a working composi-
tion, with increasing plt;ference in the order given, preferably is at least 0.020, 0.042,
0.051, or 0.060, M; and, independently, this concentration in a working composition pref-
erablyisnotgreaterthanO.l9, 0.16, 0.10, 0.091, orO.080M. Also, independently, ina
working composition that conl~ls persulfate, the ratio of the molar concentration of per-
sulfate to the molar concentration of molybdate preferably is within the range from 0.4
to 1.5, more preferably from 0.6 to 1.2, or still more preferably from 0.80 to 0.95.
On the other hand, when the surfaces to be treated are covered with only averagethic.l~n~.c~es of smut and/or oxide to be removed, and this smut and/or oxide is substanti-
ally free from iron and/or iron sulfide inclusions, persulfate is preferably omitted from
compositions according to the invention for reasons of economy, because it is consider-
ably more expensive than the other major components of the compositions.
Fluoride co~ )one ll ~) is preferred in most compositions according to the inven-
tion and is preferably supplied by soluble fluoride or bifluoride ions, more preferably the
latter, which are counted as their stoichiometric equivalent as fluoride ions, as are hydro-
fluoric acid and any complex fluorometallic acids or their ions that may be present; the
conce lt ~lion as fluoride in either a working or concentrated composition, with increas-
, 213g388
ing plt;rerence in the order given, preferably is at least 0.01, 0.028, 0.045, 0.055, 0.060,
0.065, 0.070, 0.074, or 0.078 M and for maximum speed of dç~mlltting and/or deoxidiz-
ing action still more preferably is, with increasing plt;rel ence in the order given, at least
0.090, 0.097, 0.105, 0.110, 0.114, or 0.118 M, and independently this concentration in
a working composition preferably is, with increasing pr~rerence in the order given, not
greater than 1.0, 0.7, 0.4, 0.28, 0.24, 0.22, 0.20, or 0.19 M and for economy still more
preferably is not greater than 0.16, 0.14, or 0.12 M. While not being bound by theory,
it is believed that the principal function of the fluoride ion content is to promote slight
etching of the surface treated, so that the use of fluoride is particularly desirable when
treating alloys, such as the 2xxx and 7xxx series of ~ min~1m alloys, that contain rela-
tively high percentages of elements that are electrochemically more noble than alumin-
um. When treating such alloys, an etching rate in the range from 1.3 x 10-4 to 6.4 x 10-4
centimeters of depth per hour from exposed surfaces of the alloys is pr~r~lled during a
dç~ml.tting and/or deoxicli~ing process according to this invention. Such an etching rate
will generally be achieved with the pl~rell~d amounts of fluoride ions noted above, but
if it is not, the fluoride concentration should preferably be adjusted so as to achieve this
desired etch rate. With other alloys that are recognized in the art as more easily desmut-
ted, fluoride ions may be reduced or even omitted altogether, as indicated by their de-
scription as an optional component above.
The presence of sulfate ions, optional component (F), is generally prerel-ed in
compositions according to the invention. The concentration of sulfate ions, including the
stoichiometric equivalent as sulfate ions of any sulfuric acid present, in either a working
or a concel-l-~led composition preferably is, with increasing plerelellce in the order giv-
en, at least 0.03, 0.06, 0.09, 0.20, 0.24, 0.28, 0.30, 0.32, or 0.34Mand for a faster de-
smlltting and/or deoxidizing rate still more preferably is, with increasing prerelence in
the order given, at least 0.38, 0.42, 0.46, 0.49, or 0.51 M, and in a working composition
this concentration independently preferably is, with increasing prerelence in the order
given, not greater than 5, 2.5, 1.9, 1.6, 1.2, 0.91, 0.85, or 0.79Mand for economy still
more preferably is, with increasing plererence in the order given, not more than 0.70,
0.65, 0.62, 0.60, 0.58, 0.56, 0.54, or 0.53 M. Generally, to avoid other materials that
might have unwanted effects on performance, it is plerelled that the sulfate content of
compositions according to this invention be derived from ferric sulfate and sulfuric acid.
21`3g388
Also, independently, the ratio ofthe molar concentration of sulfate ions to the molar con-
centration of nitric acid in a working composition according to the invention preferably
is, with ~CIea~ plerel~nce in the order given, at least 0.01, 0.02,0.04,0.06,0.08,0.10,
0.11,0.12, or 0.13 and independently preferably is, with increasing prererence in the ord-
er given, not more than 1.2,1.0,0.8,0.6,0.4,0.30,0.25,0.21,0.18,0.16, or 0.14.
For component (G), almost any surfactant that is effective to lower the surface
tension and solubilize any organic co~ ",;~ x present on the surface to be treated could
be used in principle, but most kinds of surfactants are unstable in the highly oxidizing
acidic composition. No surfactant with stability for more than a few months at best has
been found; the best known ones are described in the above noted U. S. Application Ser-
ial No. 08/088,998, the pertinent part of which is hereby incorporated herein by refer-
ence, and in the examples below. Particularly if persulfate is not incl~lded in the compo-
sition, no surfactant at all is generally needed.
Collli)onellL (H) is not believed to serve any technical purpose in the composition,
but it is often valued as a safety precaution to workers to indicate the presence of strong
acids by a plolllill~.lL color such as red. An amount of dye or other colorant sufficient to
be readily recognized by workers, without being so large as to impose a significant eco-
nomic cost or adversely impact the intçnded technical functions of the composition, can
be readily chosen by those skilled in the art.
In addition to the other characteristics noted above, a working composition ac-
cording to the invention preferably has, with increasing plererence in the order given, at
least 2,4,6,8,10,12,14, or 15 "points" of total acid, such points being defined for this
purpose as equal to the number of milliliters (hereinafter usually abbreviated "mL") of
1.0 N strong alkali (such as sodium hydroxide) required to titrate a 5.0 mL sample of the
composition, after the sample is diluted with at least about 10 mL of deionized water con-
taining a large excess of potassium fluoride to prevent precipitation of any heavy metal
hydroxides during titration, to an end point with phenolphthalein indicator. For the high-
est de~m-ltting/deoxicli~ing rate, a working composition still more preferably has, with
increasing preference in the order given, at least 18,20,21,22, or 22.5 points of total
acid as thus d~fined Independently, a working composition according to this invention
preferably has, with increasing plererence in the order given, no more than 60,50,45,
35,32, or 31 points of total acid, or for economy still more preferably not more than 29,
.. 213g388
27, 26, 25, or 24 points of total acid. Also and independently, a persulfate cont~ining
working composition according to the invention preferably has an oxidation-reduction
("redox") potential, measured by colllpalillg the potential of a platinum electrode im-
mersed in the composition against a standard saturated calomel electrode immersed in
5 the same composition, within the range of, with increasing pl ~;rerence in the order given,
from 800 to 1100, from 900 to 1050, from 950 to 1035, from 975 to 1029, from 985 to
1020, from 991 to 1011, or from 996 to 1006, millivolts (hereinafter sollle~ les abbrevi-
ated "mv") more oxicii7.ing than the standard electrode.
A working composition according to the invention may be applied to a metal sur-
10 face to be treated by any convenient method, several of which will be readily apparentto those skilled in the art. Immersion is the simplest and is believed most often used.
However, spraying, roll coating, and the like can also be used.
The telll~el~ re during contact and time of contact between the composition ac-
cording to the invention and the metal to be treated thereby may be varied within wide
15 limits to achieve the desired effects, which can often be determined by visual inspection
of the metal surface, after rinsing if necessary. As a general guideline, the temperature
normally preferably is, with increasing prerelellce in the order given, not less than 5, 10,
15, 17, 19, 20, 21, 22, or 23 C and independently preferably is, with increasing
pl~r~lence in the order given, not more than 80, 60, 50, 40, 35, 34, 33, 32, 31, 30, 29, 28,
20 27, or 26, C, and the time of contact normally preferably is, with increasing prererence
in the order given, not less than 0.1, 0.5, 1.0, 1.5, 1.8, or 2.0 minl]tes and independently
pl~rt;l~bly is, with incleasillg plerelence in the order given, not more than 30, 20, 15, 10,
8, 7, 6, 5.5, or5.0minutes.
After treatment according to this invention, the treated surfaces are normally
25 rinsed with water before any subsequent tre~tm.o.nt Particularly if the composition con-
tains persulfate, the rinsing preferably is completed as soon as practical after removing
the treated surfaces from contact with the desml.tting/deoxidizing composition, and if at
all practicable should at least be completed before the desm--tting/deoxidizing composi-
tion has dried into place on any part of the surface--otherwise the surface may become
30 stained. After rinsing the surfaces often are also dried. Rinsing, drying, and any subse-
quent treatments are generally performed in a manner known per se in the art.
The invention is particularly advantageously adapted to the treatment of alumin-
21`39388
um alloys 7150, 7075, 2024, 2324, and 6061; also to any ~ minllm or m~gnesillm alloy
surfaces that have been heavily shot peened or otherwise mechanically worked, and/or
have been chemically milled or heavily chemically etched with alkaline compositions,
before lle~l."~l~l. according to the invention.
If it is desired to supply a concentrate from which the working composition can
be plepared by dilution with water, the primary concentrate preferably does not contain
any persulfate component, which has been observed to be unstable in long term storage
when mixed with the other co~ ol1ellls of a composition according to this invention. Al-
so, the nitric acid and any surfactants desired are preferably supplied separately. A pre-
ferred primary concentrate according to the invention therefore contains only sulfate,
ferric ion, fluoride, and molybdate components, and optionally, dye or colorant, in
addition to water. In one particularly pl~relled concentrate embodiment, the following
colll~)ollellls and concentrations are preferred, each independently except for the addition-
al pl~r~nces for ratios already given above, and with increasing plerelence in the order
given for each series of numbers: at least 2.2, 3.0, 4.4, 5.5, 6.6, 7.7, 8.8, 9.9, 11.0, 11.5,
12.0, 12.5, 13.0, 13.5, 13.8, 14.0, 14.2, or 14.3 % but not more than 45, 35, 25, 18, 17,
16, 15.5, 15.0, 14.8, 14.6, or 14.5 % of sulfuric acid; at least 1.7, 3.5, 4.5, 5.5, 6.5, 7.5,
8.5, 9.0, 9.5, 10.0, 10.2, 10.4, or 10.5 % but not more than 30, 25, 20, 18, 16, 14, 12,
11.5, 11.0, or 10.8 % offerric sulfate (anhydrous equivalent); at least 0.8, 1.6, 2.6, 3.1,
3.6, 4.1, 4.4, 4.6, 4.8, or4.9 % but not more than 15, 12, 10, 8, 7, 6.5, 6.0, 5.7, 5.4, 5.2,
or 5.1 % of ~Illllolfi~lm dimolybdate, i.e., (NH4)2Mo2O7; and at least 0.25, 0.50, 0.75, 1.0,
1.2, 1.3, 1.4, 1.5, or 1.55 % but not more than 4.8, 4.0, 3.5, 3.0, 2.5, 2.0, 1.8, 1.7, or 1.6
% of ammonium acid fluoride. The balance not specified above is water.
During extended use of a composition according to this invention, new constitu-
ents may be introduced into the composition by dissolution of the metal objects treated,
and some of the con~titu~nt~ of the bath may be consumed by reaction. Therefore, as
with other similar treatments, if very long term operation is desired, it is advantageous
to withdraw a portion of the composition continuously for removal of any unwanted
constituents and to replenish depleted desirable constituents. In some cases, only
replenishment may be s~ti~f~ctory, or no treatment of the composition at all may be
required. Normally, however, the ~ccllmlll~tion of ~lllmimlm, copper, and/or zinc cations
in working compositions according to the invention is deleterious to the desired
2l3g388
pelrollllance ofthe compositions.
The practice of this invention may be further appreciated by consideration of the
following, non-limiting, working examples.
EXAMPLES
5 Working Composition Tn~ tlin~ Persulfate
One plerelled working composition contains:
(A) 4.04 MHNO3 (provided by commercial concentrated nitric acid of 42 Baumè);
(B) 0.13 MFe2(SO4)3 (provided by a commercially available 50 % aqueous solution);
(C) 0.059M(NH4)2Mo2O7 (provided from commercial solid salt);
(D) 0.0701 M(NH4)2S208 (provided from co~ lelcial solid salt);
(E) 0.056 MNH4HF2 (provided from commercial solid salt);
(F) 0.354 M H2SO4 (provided from commercial concentrated sulfuric acid);
(G) 0.51 g/L of each of SURFYNOLTM 465 and 440 surf~ct~nt~7 commercially avail-able from Air Products Co and described by the supplier as ethoxylated tetra-
methyl decynediols, the former with an HLB value of 13.0 and the latter with an
HLB value of 8.0; and
(H) 0.18 g/L of NYLOSAN~M RHODAMINETM E-B 90 red dye.
(Note: The total concenll~lion of ferric ions in this composition is 0.26 M, because there
are two ferric ions in each mole of ferric sulfate salt; the total concentration of fluoride
ions is 0.112 M, because there are two fluorine atoms in each mole of ammonium
bifluoride, and the total concentration of sulfate ions is 0.74 M, including 0.39 M
supplied by the ferric sulfate along with the 0.35 M supplied by the sulfuric acid.)
This composition had a redox potential of 1001 mv and 24 free acid points.
Use of a Persulfate Co.~l~in~ Composition According to the Invention
Panels of Type 7150 ~ mimlm, each panel co.,~ g at least one hole in order
to make a more critical evaluation of the staining and/or ~mllttin~ tendency, which is
usually more pronounced in recesses and holes in parts being treated under practical
conditions, were pre-etched to produce a reproducible oxidized and ~m~ltted surface by
immersion for 7 to 10 mimltes ("min") at a temperature within the range from 29.4 to
32.2 C in an alkaline etching solution consisting of water and 120 - 150 g/L of sodium
hydroxide, 11 - 26 g/L of sodium sulfide, 30 - 60 g/L of triethanol amine, and 18 - 50 g/L
2139388
of dissolved ~ minllm
A~er removal from the etching solution, the etched panels were allowed to stand
in ambient air for 2 - 3 min, then successively rinsed twice for 2 - 3 mimltes each time
with deionized water at ambient temperature, then immersed in the above noted desmut-
5 ting composition for 10 min at ambient temperature with air agitation of the composition,allowed to stand in the ambient air for 2 - 3 min, then rinsed twice, the first time for 2 -
3 min and the second time for 1 min, with deionized water. Some of the panels were then
conventionally anodized with s~ti~f~ctory results. Others ofthe panels were allowed to
dry and visually examined. Bright, smooth surfaces without smut were produced.
10 Concentrate Partial Composition for a Working Composition to Contain Persulfate
A plt;rellt;d concel,~ e partial composition consists of 150 parts of sulfuric acid,
50 parts of ammonium dimolybdate, 250 parts of ferric sulfate, 16 parts of ammonium
bifluoride, with the balance to 1000 parts being water. This concentrate can be used, to-
gether with separate sources of nitric acid and persulfate, to make the working composi-
15 tion shown above.Concentrate Partial Composition for a Persulfate Free Working Composition
A prere"ed concentrate of this type consists of 10.7 % of Fe2(SO4)3, 5 % of
~NH4)2Mo207, 14.7 % H2SO4, 1.6 % of NH4F-HF, and the balance water. From 10 to 20
volume % ofthis concentrate, combined with from 20 to 30 volume % of 66 Baumè ni-
20 tric acid in water solution, forms a highly effective general purpose dçsml tter/deoxidizerfor al~ min--m, magnesium, and their alloys. These working compositions can be made
up with hard tap water without loss of performance and can contain up to 1000 ppm of
copper and 1600 ppm of zinc without st~ining the treated surfaces.
