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Патент USA US3088829

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United grates ate
Garland B. Funkhouser, Hopewell, Va., assignor to Allied
Chemical Corporation, a corporation of New York
No Drawing. Filed May 20, 1955, Ser- No. 510,046
12 Claims. (Cl. 71-50)
Patented May 7, 1963
10% to 34% by weight of ammonium nitrate and 50%
to 68% by weight water, which is contacted with the
aluminum metal. My invention further comprises the
ammonium phosphate-ammonium nitratea?uoride-water
solutions of the ‘foregoing composition of very low cor-ro
siveness toward aluminum and its alloys.
The invention is of especial importance in its applica
tion to solutions particularly suitable ‘for fertilizer uses,
but the use of the ?uoride to inhibit corrosion of alumi
sion of aluminum metals (aluminum and its alloys) con 10 num is not limited to the solutions of the particular con
centrations used for that purpose. The ?uorides are ef
tacted with aqueous solutions of ammonium nitrate and
fective to inhibit ‘corrosion of aluminum and its alloys by
ammonium phosphate by incorporating in those solutions
aqueous solutions of ammonium phosphates and am
a small amount of an inorganic ?uoride soluble in the
monium nitrates which are non-alkaline, i.e. substantially
solution effective to materially reduce the rate of corro
sion of the metal. The invention further includes those 15 neutral or even having pH values somewhat below 7. It
is apparent, of course, they would not ‘be used in strongly
aqueous solutions of ammonium nitrate and ammonium
acidic solutions under conditions resulting in evolution
phosphate containing in solution therein an inorganic ?uo
hydrogen ?uoride.
ride in amount e?ective to reduce substantially the rate
With respect to the ?uoride which may be added to the
of corrosion of aluminum metals by the solution.
Solutions of ammonium phosphate having the com 20 aqueous ammonium phosphate-ammonium nitrate solu
tion, the preferred, commonly available ?uorides are the
position (NH4)(1_5__1,7)H(1.5_1_3)PO4 and ammonium ni
meta-l, including ammonium ?uoride and bi?uoride,
trate in water have been found particularly suitable for
and the ?uorides and bi?uorides of potassium and sodium.
use ‘as fertilizers either by direct application to the soil or
This invention relates to a process for reducing corro
While the use of a ?uoride of which the cation would
in the preparation of fertilizer compositions. Particu
an insoluble material in the solution is not desirable,
larly those solutions containing (by weight) 11% to 36% 25 form
characteristic is that it imparts soluble ?uo
of the ammonium phosphate, 10% to 34% of the am
monium nitrate and 50% to 68% water have been ‘found
ride to the solution at least in the small amounts needed
for the inhibition of the corrosion of aluminum metals.
to be characterized by low salting out temperatures, below
Accordingly, any ?uoride may be used which is su?i
10° C., and stable with respect to their nitrogen content, 30 ciently soluble in the ammonium phosphate-ammonium
and thus especially ?tted for use as fertilizer solutions.
nitrate solution to impart at least 0.05% dissolved ?uoride
Such solutions are relatively non-corrosive to ordinary
(calculated as F ) to the solution. While the preferred
steel. They may be shipped and handled in steel equip
range of dissolved ?uoride in the solution is that equiva
ment without presenting any real problem of corroding
lent to 0.1% to 0.5% F, this is primarily a matter of cost.
such equipment. However, the fertilizer trade also em 35 Eliective inhibition of the ‘corrosion is obtained using 1%
ploys for similar purposes alkaline, ammoniacal salt solu
F. Substantially more ?uoride than this is not economi
tions, particularly ammonia-ammonium nitrate solutions.
cally justi?ed. Further, it is not desirable to use an
These ammoniacal solutions are corrosive toward steels.
amount of ?uoride exceeding its solubility in the solution
Accordingly, ‘much of the equipment in use for handling
at temperatures above 10° C. because of the practical
fertilizer solutions is constructed of aluminum or alumi 40
desirability that the solutions do not salt out or form a
num alloys, which are adequately resistant to corrosion by
at those temperatures.
these ammoniacal solutions. Since the same equipment
The presence of the ?uoride in the aqueous solutions
is usable 'both for the ammoniacal fertilizer solutions and
of ammonium phosphate and ammonium nitrate serves to
the non-alkaline ammonium phosphate-ammonium nitrate
solutions to which this invention rel-ates, the marketing
and use of these latter solutions has presented the problem
of preventing undue corrosion of aluminum equipment
reduce substantially the rate of corrosion of alloys of alu
minum which are attacked by those solutions in the ab
sence of the ?uoride. Alloys commonly used in equip
ment to be protected by employing this invention range
in ‘which they are handled.
from substantially pure aluminum (over 99%) to alumi
I have discovered that by incorporating in the aqueous
ammonium phosphatedammonium nitrate solutions even 50 num containing up to about 5% of alloying elements,
principally silicon, manganese, magnesium, or chromium,
a very small amount of an inorganic ?uoride soluble
or combinations of these, and the aluminum alloys with
therein, the rate of corrosion of ‘aluminum and of its
a copper content not above about 0.25% .
alloys in contact with these solutions is ‘greatly reduced.
The ‘following example is illustrative of my invention.
It then becomes feasible to vstore, transport and utilize
these solutions in equipment in which they are in contact 55 Amounts expressed as parts are by weight.
with aluminum or an alloy of aluminum.
My invention accordingly comprises incorporating in a
non-alkaline solution of ammonium phosphate and am
monium nitrate in water, 0.05% to 1% by weight of an
Example J.~—A solution was prepared by diluting 657
parts of -a commercial-grade phosphoric acid, analyzing
60.25% P205, with 1447 parts water and partially neu
tralizing the diluted acid with 152 parts of gaseous am
monia. Ammonium nitrate amounting to 743.4 parts
inorganic ?uoride (calculated as F) and contacting the 60 was then added and dissolved in the solution of ammo
resulting solution with an aluminum metal. Preferably,
nium phosphate. The I?nished solution contained 12.82%
these amounts of the ?uoride are incorporated in an aque
N and 13.00% P205 and had a pH of 6.1. The com
ous ammonium phosphate-ammonium nitrate solution
position of the ammonium phosphate present corre
composed of 11% to 36% by weight of an ammonium
sponded to
phosphate having the composition
One portion of the solution was retained as made. To
another portion ammonium ?uoride was added in amount
(NH4) (1.s-1.'1)H(1.5-1.3)PO4
equivalent to 0.1 % F based on the weight ‘of the solution.
Corrosion data for an aluminum alloy of the composition
3.5% magnesium, 0.25% chromium with the balance alu
minum and normal impurities, immersed in these solu
phosphate present in the solution has the composition
(NHU (1.5_1.7)H(1.5_1.a)‘P‘O4
6. The process of claim 5 in which the aqueous am
monium phosphateammonium nitrate solution is com
tions is given in the following table:
posed (by weight) of 11% to 36% of the ammonium
phosphate having the composition
Table I
Test No.
Percent F in solution ____________________________ ._
Penetration (inches/year):
First 7 days _________________________________ ._
Second 7 days _______________________________ H
10% to 34% ammonium nitrate and 50% to 68% water.
0. 0064
in water containing in solution therein 0.05% to 1% by
weight of an inorganic ?uoride (calculated as F).
8. The composition of claim 7 in which the ?uoride is
an alkali metal ?uoride.
The solution containing ?uoride remained nearly clear,
while the one with no ?uoride present became contami
nated with a voluminous white precipitate, presumably
of corrosion products.
To another portion of the ammonium phosphate-am
7. As a new composition of matter of reduced corro
siveness toward aluminum and its alloys, a nonaalkaline
solution of ammonium phosphate and ammonium nitrate
monium nitrate~water solution of the above example,
9. The composition of claim 7 in which the ?uoride
present amounts to 0.05% to 0.1% by weight of the solu
10. The composition of claim 7 in which the ammo
nium phosphate present in the solution has the composi
ammonium ?uoride was ‘added in amount sui?cient to in
tion (NH‘t)(1.5—1.'l)H(1.5-—1.3)PO4
corporate in it 0.5% F (by weight) ‘as dissolved ?uoride.
nium phosphate present in the solution has the composi
In contact with this solution over a period of nine days,
aluminum metal was corroded at a rate of only 0.0036
inch penetration per year.
I claim:
1. The process ‘for reducing corrosion of aluminum and
its alloys in contact with a non-alkaline solution of am- 30
monium phosphate and ammonium nitrate in, water,
which comprises incorporating in said solution 0.05 % to
1% by weight of an inorganic ?uoride (calculated as F)
soluble in the solution.
2. The process of claim 1 in which the fluoride is an 35
alkali metal ?uoride.
3. The process of claim 1 in which 0.05% to 0.1%
of the ?uoride (calculated as F) is incorporated in the
4. The process of claim 1 in which the ammonium 40
phosphate present in the solution has the composition
5. The process of claim 3 in which the ammonium
11. The ‘composition of claim 9 in which the ammo
12. The composition of claim 11 in which the aqueous
ammonium phosphate-ammonium nitrate solution is com
posed (by weight) of 11% to 36% of the ammonium
phosphate having the composition
10% to 34% ammonium nitrate and 50% to 68% water.
References Cited in the ?le of this patent
Tramm et al ___________ __ Apr. 23,
Foss et a1 _____________ __ Nov. 17,
Sutton et a1 ___________ __ Dec. 15,
Sweeney et al _________ __ June 25,
E?eld _______________ __ May 13,
Phillips ______________ __ Apr. 24,
Hesch _________________ __ Oct. 4,
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