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Патент USA US3096178

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United States Patent 0 ” lCC
Patented July 2, 1963
the above components, i.e. copper, trivalent arsenic, and
carbonate ions, produce in situ a passive ?lm on ferrous
metal that is highly resistant to mechanical damage and
Paul Shapiro, Chicago, Ill., David B. Sheldahl, Gri?ith,
Irld., and Lawrence V. Collings, Park Forest, Ill., as
electrolytic reduction, as well as chemical attack.
The copper compounds in the present invention are the
slgnors, by mesne assignments, to Sinclair Research,
Inc., New York, N.Y., a corporation of Delaware
No Drawing. Filed Feb. 1, 1960, Ser. No. 5,637
16 Claims. (Cl. 71-59)
soluble copper compounds as, for instance, the inorganic
compounds such as cupric carbonates, hydroxides, sul
fates, nitrates, etc. Of the many carbonate ion-produc
ing compounds, the more particularly suitable are the in
organic compounds, for instance, alkali metal and am
The present invention relates to the corrosion of fer
monium carbonates. Preferably, the copper and car
‘ous metals. More ‘speci?cally, the present invention re
bonate components of the present invention are provided
ates to a novel composition having reduced corrosion
by a single compound such as basic copper carbonate.
.endencies toward ferrous metal surfaces.
The quantity of the aforementioned components em
There is a well recognized corrosion problem in in 15 ployed in the present invention can vary considerably but
iustries concerned with the manufacture, storage, trans
are sufficient to give signi?cant protection against corro
)ortation and handling of ammoniacal-ammonium ni
sion. Gene-rally, the concentration of the copper com
rate solutions. In the handling of such solutions it is
ponent is at least about .01 g. per 100 ml. of ammonia
Jften necessary to transport and store them in ferrous
cal solution. The maximum amount of the copper com
:ontainers such as drums, tanks and pipelines. In view 20 pound is limited only by economic feasibility and is gen
)f the corrosive nature of ammoniacal-ammonium nitrate
erally not greater than about 0.2 g. per 100 ml. of am
iolutions against ferrous metals, many manufacturers
moniacal salt solution. The preferred concentration is
10w use storage and transportation facilities constructed
about .05 to .15 g. per 100 ml. of ammoniacal solution.
)f aluminum. Aluminum is used because its oxide ?lm
The amount of carbonate compound employed is usually
'enders the metal inert to attack by the ammoniacal salt 25 that su?icient to provide a carbonate ion concentration
l0llltl0l'1. This remedy, however, is a costly one. Cor
of at least about .005, generally about .02 to .l g. per
osion inhibitors of one type or another also have been
100 ml. of ammoniacal solution. When basic cupric car
:uggested and attempted with varying degrees of limited
bonate is employed, a concentration of about .01 to 0.2
gram/100 ml. of ammoniacal solution, preferably about
One effective method for remedying the problem has
new to deactivate the ferrous metal, for instance, by
‘passivating” the metal surface. “Passivity” is a property
:xhibited by some metals whereby they become inac
.05 to .15, is usually su?icient.
The trivalent arsenic component of the present inven
tion can be provided by a solution of any soluble trivalent
arsenic compound, preferably a soluble inorganic trivalent
ive toward certain chemical reagents. When a piece of
arsenic compound. Inorganic trivalent arsenic compounds
'eactive metal is made passive, its position in the electro 35 that can be employed include, for example, arsenic tri
:hemical series is changed so that it is cathodic to a
>iece of the same metal which is in the active condi
ion. "Passivation” of ferrous metals employed in a
oxide, ‘an arsenite such as sodium, potassium or ammoni
um arsenite and sul?es of trivalent arsenic. Since As2O3
dissolves slowly when added to solutions such as am
xxrrosive environment, is generally accomplished by con
moniacal ammonium nitrate, it is desirable to ?rst dis
acting the metal with an oxidizing agent. The oxidizing 40 solve the compound in alkaline solution such as an aque
lgent reacts with the ferrous metal forming a thin ad
lerent oxide ?lm on its surface. This protective ?lm
:hields the ferrous metal from its environment and virtu
monia, etc. Like the copper compounds, the arsenic
compound may vary in amount, but is su?icient to aiford
tlly no corrosion occurs.
the desired corrosion inhibition. Generally, the concen
ous solution of sodium hydroxide, sodium carbonate, am
Passive ?lms produced by contacting ferrous metal with 45 tration of trivalent arsenic compound is at least about
LQUCOUS solutions of oxidizing agents are found to be
0.01 g./100 ml. of ammoniacal solution, usually less than
rery fragile and easily destroyed by mechanical damage,
about 0.5 g./100 ml. and preferably about .05 to .25
:hemical attack or electrolytic reduction. Hence, the
g./ 100 ml. It is preferred that the composition of the
lddlllOIl of a supplementary inhibitor has been necessary
present invention also contain small effective amounts of
0 provide protection when the passive ?lm is destroyed. 50 alkali metal, eg. sodium, hydroxide which can be con
We have found, however, that some proprietory inhibi
veniently provided in the composition as aforementioned,
ors, i.e. inhibitors containing reduced sulfur, e.g.
by employing an aqueous solution of the sodium hy
~IH4SCN, that are e?ective inhibitors will frequently de
droxide to dissolve the trivalent arsenic component. The
troy the passive ?lm.
amount of alkali metal hydroxide employed will usually
Moreover, most passivation procedures require a two 55 ‘be as stated before for the arsenic compound. In pro
tep process, i.e. the ferrous metal must be ?rst im
viding the ammoniacal ammonium nitrate solutions with
nersed in an aqueous solution of the oxidizing agent be
the components of the present invention, we prefer the
‘ore it can be exposed to the ammoniacal solution. This
absence of signi?cant amounts of halogen ions, e.g. Cl“,
s done for two reasons, (1) corrosion of the ferrous
which are known to be passive ?lm destroyers.
netal in the ammonia-ammonium nitrate solutions is ex 60
remely rapid resulting in the formation of a gelatinous
Ammoniacal ammonium nitrate solutions may vary
considerably in composition. Generally representative
of such solutions encountered in industry and which give
lizing agent to the surface and (2) the oxidizing agent
rise to the corrosion problem discussed hereinbefore, are
nay be destroyed by reaction with ammonia present in
those having approximately about 1 to 80 percent am
he solution forming nitrogen and its oxides.
65 monium nitrate, usually at least about 40 percent, prefer
ably about 60 to 70 percent, about 5 to 35 percent free
It has now been discovered that contacting a ferrous
ammonia, preferably about 10 to 35 percent, and the sub
netal with ammoniacal ammonium nitrate solutions con
aining a soluble copper compound, a soluble trivalent
stantial balance being Water, for instance, about 10 to 65
percent water. These percentages are by weight.
lrsenic compound and carbonate ions produces a “tough”
It has been noted that the corrosion by ammoniacal
vassive ?lm on the ferrous metal that otters improved 70
solutions is intense in the vapor zone, i.e. the portion of
:orro'sion resistance to the metal. It has also been found
the vessel containing the ammoniacal solution which is in
hat ammoniacal ammonium nitrate solutions containing
leposit on the metal’s surface preventing access of the oxi
contact with vapors of the solution.
Although the com
bination of components of the present invention provides
good corrosion protection to the portion of the vessel
characteristics of a ferrous metal such as steel, i.e. makes
the metal more electropositive, the phenomenon can be
effectively studied by observing changes in the single elec
trode potential of the metal. A series of simple electrd
in contact with the ammoniacal solution, adequate pro
tection is not always provided the portion in contact with 5 lytic cells were set up to achieve this end.
vapor. This problem can be easily remedied by the addiA steel rod was ?rst “activated” (i.e. all surface ?lms
tion of vapor phase inhibitors such as urea, NH4NO2,
were removed) by exposure to 15% HCl at 150° F. until
etc. We have also found that the addition of NO{—
hydrogen bubbles were observed. The rod was then
producing compounds such as an alkali metal nitrite to
washed in deionized water and placed in an electrolytic
the ammoniacal solution containing the components of 10 test cell filled with an ammoniacal solution consisting of
the present invention very effectively reduces vapor phase
66.8% NH4NO3, 16.6% NH3 and 16.6% H2O. The elec
corrosion and this may be due to the formation of a
trolytic test cell was a large mouth 8_ounce glass jar hav
CuNH4NO2 complex. The vapor phase inhibitor is gening a salt lbridge comprising a glass tube with agar-agar
erally present in an amount sufficient to provide adequate
solution saturated with KCI connected to a calomel cell
corrosion protection, and conveniently is about 0.05 to 15 immersed in saturated KCi. The calomel electrode probe
0.5 g./1OO ml. of ammoniacal solution.
and the “activated" rod were connected by leads to a
The following examples are included to further illus
trate the invention.
Sheppard potentiometer by which potential measurements
were obtained.
Similar tests were conducted on the am
mania-ammonium nitrate solution containing small con
As aforementioned when a piece of active metal is made 20 Centm_ti?n_s of Various oxidiziflg agents an? combination
passive, its position in the electrochemical series is
of oxldlzlng agents- ‘The mvalent arsefllc compfmnds
changed so that it is more cathodic to a piece of the same
Where employed were 10 each case ?l'st dlssolved Wlth all
metal which is in the active condition. Since the formation of passive ?lms produces a change in the electrical
equal Weight of Sodium hydroxide in dilute aqeuolls 501“
tion. The results are shown in Table I.
Table I
oxidizing agent
21100 in .
Observed single electrode po
tontini of steel (volts to caiomel)
Steel corroded, appearance of a slimy green ppt. on the
steel surface.
Slow corrosion.
Rapid corrosion.
—0.42 to -0.72 (1 hour.) _______ _.
—0.46 to —0.73 (11 minutes)...“
-—0.74 _________________________ __
—0.76 _________________________ __
—0.47 to —0.73 (4 minutes) .... ._
Rapid corrosion, brown ppt. (due to formation of Mn0;)
Rapid corrosion, not too soluble.
Slow corrosion.
Rapid corrosion.
Slow corrosion.
--0.46 to -0.7s (1 minutes)___::: Passive, metal bright and clean.
—0.30 to —0.35 ________________ __
-—(].35 to —0.45
—-0.40 to —0.44 ________________ __
Passive, metal bright and clean, large white ppt. forms,
—0.29 to ——0.20 ________________ __
—0.37 to —0.34 ________________ ..
Passive, metal bright and clean.
Passive, metal bright and clean, large white ppt. forms,
probably insol. AS505.
probably insol. AsiOr.
—0.36 to —0.74 (15 miuutes)...._ Steel corroded.
—0.37 to -0.16
____________ __
~—0.77 _________________________ __
Rapid corrosion.
-0.40 to ~0.35._
Rapid corrosion.
—0.73_ _ .
—0.69 to —-0.74 ________ __
-0.50 to —0.71 (2D mlnutes)____.
-0.76 _________________________ _.
—O.77 _________________________ _.
(IéZ'HQIOOr .............. __
0.1 ________________ __
Table I—Continued
Oxidiziug agent
CuS04 __________________ _.
g./1D0 ml.
Observed single electrode potential of steel (volts to calomel)
0.1 ................ --
—0.39 to —0.28 ________________ __
(N H0300: ______________ ..
AS103 ___________________ ._
Cu(NO=J, _______________ ._
—0.40 to —0.29 ________________ --
_____________ __
-—(]_75 _________________________ .l
Rapid corrosion.
—0.52 to —0.73 (20 minutes)..... Slow corrosion.
—0.76 _________________________ _.
Rapid corrosion.
—0.52 to -0.77 [3 minutes) ____ __
—0.76 _________________________ __
—0.49 to —0.75 (5 minutes) .... -.
Table I above indicates that most oxidizing agents
when added to NH3——NH4NO3 solutions produce un
table if any, passive ?lms on exposed steel surfaces, due
pparently to their reaction with ammonia. Na2Cr2O7,
’2O5, (NH4)2S2O8 and the basic cupric carbonate-tri
alent arsenic combination apparently ‘are not too reactive
Slow corrosion.
tact through the external circuit was maintained with the
steel. If after ?ve minutes the Flade potential was not
exceeded, the copper wire was then brought into physical
contact with the steel. Ordinarily this procedure was
suiiicient to destroy the ?lm. Table II below contains
‘the results of this test.
Table II
Oxidizing agent
Cone. g./100 ml. Time
Time, Physical contact Time,
N1-I3—NH4NO= exposed, Electrical contact min. (wire touches rod) min.
(NliqhSzOs _______ .l
0. 15
—0.21 to —(].78..
0. 5
(NIlImSme ....... -.
—0.30 to -0.77._
0. 75 ________________________ _
________________________ ._
O. 1
26. 5
-0.34 to —0.75__
26. 0
-—0.35 to —0.56_ .
—0.46 to -—0.60__
5. 0
5. 0
________________________ .
—0.56 to —0.75»
—0.(i0 to —0.71__
0. 1
26. 5
-—0.44 to —-0.59__
—0.59 to —0.73_.
23. 5
—0.28 to —D.58l.
-0.2a to —o.59,_ ______ __
0. 1
-—0.581 ________________ _
-.59 to —0.436 I- ______ -
0: 1
1 More than 9 days.
9 More than 6 days.
vith the solution and produce passive ?lms in situ. The
ame is true in tests 33 and 34 where copper, carbonate
nd arsenic were supplied in another manner.
The decay of passivity can be observed by recording
he decrease in potential when a metal cathodic to the
>assive steel is brought into electrical contact with it.
.‘he potential shift in the more active direction (i.e.,
Table II indicates that the basic cupric carbonate
arsenite combination produces a very highly stable and
resistant passive ?lm when introduced to ammonia-am
monium nitrate solutions. The combination is also e?ec
tive in repairing any breaks in the ?lm. A deep scratch
was cut on the face of the coupon.
The coupon was
then reinserted in the ammonia-ammonium nitrate con
taining the basic cupric carbonate-arsenite combination.
nore electronegative) is due to the electrolytic reduction
The coupon was kept in the ammoniacal salt solution for
if the ?lm by the current that is created by the galvanic
ouple. When passive steel is activated there is ?rst a 60 over 2 weeks with no visible signs of corrosion. A good
result was also obtained with another copper, arsenic
teep fall of the potential in the active direction; second,
and carbonate composition in test H.
»y a less step change lasting for a fraction of a min
In summary, the addition of the inhibitor combination
lte to several minutes; and third, by a steep descent
of the present invention to corrosive solutions such as
o the active value (i.e., complete breakdown of the
iassive ?lm; —0.71 to -—0.77 volts‘ to calomel for 65 ammoniacal salt solutions will inhibit the corrosion of
ferrous metal apparatus in which these solutions are
~IH3--NH4NO3). The value of the potential immedi
handled, stored, etc. This will result in greater product
ttely preceding this last descent is called the Fladc
purity and reduce the destruction of shipping and storage
facilities which are used commercially such as in the
To determine the resistance to electrolytic destruction
fertilizer business. This advantage can in turn enable
if the passive ?lms produced by the above reagents, an
lctivated steel rod was ?rst exposed for about a day to
manufacturers of these corrosive solutions to use less
JH3—NH4NO3 solution containing the oxidizing agent
costly equipment for handling these solutions. Further
0 that it might become passivated. Then a two-inch
niece of No. 12 copper wire was placed in ‘the test solu
in many corrosive solutions like ammoniacal salt solu
tions, the cupric components of the present invention
ion with the passive steel. Initially only electrical con 75 produces a clear solution with an intense blue color,
which color can be used to show that a controlled and
of basic copper carbonate is about 0.05 to 0.15 gram/100
ml. of said solution.
9. The composition of claim 7 having added thereto
adequate concentration of inhibitor is present. In addi
tion, copper is one of the trace elements required for
normal growth of many plants. Hence, incorporation
of the cupric compounds of the present invention in
a small, eliective amount of sodium nitrite as a vapor
phase corrosion inhibitor.
10. A composition consisting essentially of an aqueous
ammoniacal ammonium nitrate solution, about 0.01 to
We claim:
less than about 0.5 gram/100 ml. of said solution of
1. A composition consisting essentially of an aqueous
an inorganic tri-valent arsenic compound soluble in said
ammoniacal ammonium nitrate solution, about 0.01
solution, about 0.01 to 0.2 gram/1'00 ml. of said solution
gram to less than about 0.5 g./100 ml. of said solution
of a copper compound soluble in said solution, and about
of a trivalent arsenic compound, soluble in said solution,
.005 to .1 gram/100 ml. of said solution of carbonate
about 0.01 to about 0.2 gram/100 ml. of said solution
ions, the amounts of said compounds and ions being
suf?cient to substantially reduce the rate of corrosion
of a copper compound soluble in said solution, and
about .005 to .1 gram/100 ml. of said solution of car 15 by said solution to ferrous surfaces.
bonate ions, the amounts of said compounds and ions
11. The composition of claim 10 wherein the copper
compound is an inorganic copper compound.
being suf?cient ‘to substantially reduce the rate of cor
rosion by said solution to ferrous surfaces.
12. The composition of claim 11 wherein the am
2. The composition of claim 1 in which there is in
moniacal ammonium nitrate solution is of about 1 to
cluded a small amount of alkali metal hydroxide.
20 80% ammonium nitrate, about 5 to 35% ammonia with
3. The composition of claim 2 in which the hydroxide
the substantial balance being water and the concentration
is sodium hydroxide.
of the trivalent arsenic compound is about 0.01 to 0.5
4. The composition of claim 1 wherein the concentra
gram/100 ml. of said solution, the concentration of ‘the
inorganic copper compound is about 0.01 to 0.2 gram/ 100
tion of the trivalent arsenic compound is about 0.05 to
ml. of said solution and the concentration of the car
0.25 gram/100 ml. of said solution, the concentration
bonate ions is about 0.005 to 0.1 gram/100 ml. of said
of the copper compound is about .05 to .15 gram/100
ml. of said solution and the concentration of the car
13. The composition of claim 12 wherein the copper
bonate ions is about 0.02 to .1 gram/100 ml. of said
and carbonate ions are supplied by the addition of about
5. The composition of claim 1 where the copper and 30 0.01 to 0.2 gram/100 ml. of said solution of basic copper
carbonate ions are supplied by basic copper carbonate.
14. The composition of claim 13 in which the trivalent
6. The composition of claim 3 where the copper and
arsenic compound is arsenic trioxide.
carbonate ions are supplied by basic copper carbonate.
15. The composition of claim 12 in which there is
7. A composition resistant to corrosion of ferrous sur
included about 0.01 to 0.5 gram/said solution of alkali
faces consisting essentially of an aqueous ammoniacal
metal hydroxide.
ammonium nitrate solution of about 40 to 80% am
16. The composition of claim 15 in which the hy
monium nitrate and about 10 to 35% ammonia, having
droxide is sodium hydroxide.
added thereto about 0.05 to 0.25 gram/100 ml. of said
solution of AS303, about 0.01 to 0.2 gram/100 m1. of
References Cited in the ?le of this patent
said solution of basic copper carbonate, and about 0.05 40
to 0.25 gram/100 ml. of said solution of sodium hy
Beekhuis et al. ________ __ Nov. 5, 1940
8. The composition of claim 7 wherein the amount
Hoover _____________ -_ Nov. 17, 1959
ammoniacal fertilizer solutions may enhance their Value
as fertilizers.
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