Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Case No. P-11, 1 20
COP~POSITION FOR PPcOTECTING
~qETAL Sl:1RFACES AGAINST CORROSION
This invention relates to an improved
composition for protecting metal surfaces against
corrosion and, more particularly, relates to an
improved aqueous treating fluid for protecting metal
surfaces against corrosion during contact with aqueous
liquids and/or during the storage of metal components
after they have been treated with aqueous solutions,
and to a concentrate composi~t~on for use in the
preparation of such a~ueous treating fluid.
BACKGROUND OF THE INVENTION
_
In order to pro~ect metallic surfaces
against corrosion when they are in contact with aqueous
liquids or during storage after they have been treated
or contacted with aqueous liquids, it is customary to
add anticorrosion additives to the water or other
aqueous solution which is in contact with the metallic
surfaces. Frequently, the anticorrosion additive
system utilized must provide protection for several
different types of metals. For example, in
recirculating heat exchanger systems or systems
utili~ing aqueous hydraulic fluids, and the like, the
components of which the system is made may be of steel
and/or cast iron, as well as aluminum, copper, brass,
zinc, or other metals or metal alloys, all of which
must be protected against corrosion. In addition to
the need to provide protection to a variety of
different metals, the anticorrosion additives must be
readily soluble and stable in water having various
degress of hardness and must not be adversely effected
....
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by either high or low temperatures. Desirably, such
anticorrosion additives are effective at relatively low
concentrations and must not be toxic or irritate the
skin or have an unpleasant odor. Finally, such
additives should not present any significant waste
disposal problems~
Over the years, numerous aqueous systems
have been developed for the protection of specific,
individual metals against corrosion. In the case of
steel and grey cast iron, for example, alkaline
solutions of nitrites, particularly sodium nitrite,
have been used~ Various organic substances have also
been used to protect these materials, including
benzoatesr borates, soaps an-d salts of amino acids or
of sulfonamidocarboxylic acids, particularly the
alkanolamine salts.
More specifically, European Patent
specification 0,020,042 describes an anticorrosion
agent which contains 5 - 20% by weight of an aliphatic
monobasic acid of 8 - 20 carbon atoms, 0 - 4~ by weight
of a lubricant, 10 - 35% by weight of an aromatic mono-
or polycarboxylic acid and an amine which forms a
water-soluble salt with the aliphatic and aromatic
acids. U.S. Patent 3,573,225 describes an
anticorrosion agent which contains 50 - 100 parts of a
salt of a saturated carboxylic acid of 6 - 18 carbon
atoms with an amine of 6 - 12 carbon atoms, 20 - 200
parts of an alkali metal benzoate and 1 - 50 parts of
an alkanolamide obtained as a reaction product from
ethanolamine and a saturated fatty acid of 6 - 18
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carbon atoms. Finally, German Offenlegungsschrift
2,614,234 discloses an aqueous treatment fluid for
protecting metal surfaces against corrosion which
contains a reaction product of an aliphatic carboxylic
acid of 6 - 10 carbon atoms and a polyoxycarboxylic
acid, such as gluconic acid or tartaric acid, with an
alkanolamine. Although the foregoing, and other,
systems have been found to be capable of reducing the
corrosion of steel and cast iron, they have generally
not been found to provide adequate protection for other
metals.
It has been found, for example, that
virtually the only materials which will provide
corrosion protection for alumlnum are chromates or
silicatesO In aqueous solutions, however, these
materials are stable only at relatively high pH values
and only in soft water. Similarlyt wi~h respect to
zinc, in actual practice only chromates have been found
to be useful for the prevention of corrosion. Although
U.S. Patent 4,093,780 discloses that esters of
thio~lycolic acid are suitable for preventing the
formation of white rust on zinc, the poor
water-solubility and strong, objectionable odor of
these compounds has greatly limited their use.
Moreover, these materials have not been found to
provide any significant corrosion protection for metals
other than zinc.
In the case of copper and brass,
anticorrosion agents based on mercaptobenzothiazole or
benzotriazole have been found to be particularly
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effective and are widely used. These materials, by
tnemselves, have not been found to be effective
anticorrosion agents for steel and, in many instances,
when they are combined with materials which are
effective in protecting steel aqainst corrosion, there
is a substantial decrease in the protection which they
provide for copper and brass.
Actually, very little has been published in
regard to the protection of mutli-metal systems. A
review of this area is given by J. Webber entitled "The
Inhibition of Corrosion in Industrial Cooling Systems",
which appeared in Wirkstoff und Korrosion, Vol. 30
( 1979 ), pages 713 - 722. According to this review,
chromates are the only materials which provide
significant corrosion protection for a number of
different metals, including steel, cast iron, aluminum,
copper, brass and zinc. Chromates, however, cannot be
used in large amounts because of their toxicity and,
recently, their use has been banned completely in many
areas.
In addition to aqueous fluids for protecting
metal surfaces against corrosion, oil emulsions have
also been employed for protecting multi-metal systems.
These, however, have many disadvantages which have
severaly restricted their use. For example, the
emulsions tend to separate in hard water and, as a
concéntrate, they are flammable. Additionally, the
emulsions cannot be disposed of without going through
expensive procedures to separate the oil portion from
the aqueous portion.
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It is, therefore, an object of the present
invention to provide an a~ueous solution for protecting
metal surfaces against corrosion both while the aqueous
solution is in contact with the metal surface and
during the storage of the metal components after they
have been treated with the aqueous solution.
A further object of the present invention is
to provide an improved aqueous solution which will
protect a number of different metals against corrosion.
A still further object of the present
invention is or provide a concentrate composition from
which the improved aqueous anticorrosion solutions may
be prepared.
These and other ob~ects will become apparent
to those of ordinary skill in the art from the
description of the invention which follows.
SUMMARY OF THE INVENTION
Pursuant to the above objects, the present
invention is directed to an aqueous treating solution
for protecting metal substrates against corrosion which
comprises the salt of at least one aliphatic carboxylic
acid containing 6 - 10 carbon atoms (component A), the
salt of at least one polyoxycarboxylic acid having 6 -
8 carbon atoms (component B1, and the salt of at least
one aromatic monocarboxylic acid (component C), wherein
the salt-forming cations of components A, B and C are
predominantly alkali metal ions and wherein the molar
ratio of component A to component B is from about
10 : 1 to 1 : 5, the molar ratio of component A to
component C is from about 5 : 1 to 1 : 5, and the molar
ratio of component B to component C is from about 5 : 1
121g~19
to 1 : 10. ~urprisingly, it has been found that the
foregoing combination of components in the aqueous
treatment solution exhibit a synogistic effect in that
significantly better corrosion protection results are
obtained with this combination that are obtained using
any one of the components along or in combination with
only one further component. Further, it has been found
. that, contrary to conventional practice in which
organic acid corrosion inhibitors are utilized in the
form of the alkanolamine salts of the acid in the
aqueous treating solutions of the present invention,
the alkali metal salts of these organic acids are
significantly more effective.
DETAILED DESCRIPTION OF THE INVENTION
More specifically, in the practice of the
present invention, the improved aqueous treating
solution containing the components A, B and C, as have
been described hereinabove, have a molar ratio of
component A to component B of from about 10 : 1 to
1 : 5 and, preferably, from about 4 : 1 to 1 : 2. The
molar ratio of component A to component C is from about
5 : 1 to 1 : 5 and, preferebly, from about 2 : 1 to
1 : 2. The molar ratio of component B to component C
is from about 5 : 1 to 1 : 10 and, preferably, from
about 2 : 1 to 1 : 4.
The concentrations of the A, B and C
components in the aqueous treating solutions of the
present invention may be varied over a relatively wide
range, depending upon the manner in which the
composition is utilized and the particular metal
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substrates which are to be protected against corrosion.
Typically, the three components Ar B and C are present
in the aqueous treating solution in a total amount of
from about 0.2 to about 4.0% by weight of the aqueous
treating solution. Yreferably, these components are
present in a total amount of about 0.5 to about 2.0% by
weight of the aqueous treating solution. It will be
appreciated~ however, that other amounts of these
components may also be used and still obtain
advantageous corrosion protection results.
As has been set forth hereinabove, component
A is made up of the salt of at least one aliphatic
carboxylic acid having 6 - 10 carbon atoms.
Particularly preferred compounds of this class are the
salts of caprylic acid and/or ethylhexanoic acid.
Component ~ is made up of the salt of at least one
polyoxycarboxylic acid having 6 - 8 carbon atoms.
Particularly preferred compounds of this class are the
salts of gluconic acid and/or heptonic acid. Component
C is made up of the salt of at least one aromatic
monocarboxylic acid. A particularly preferred compound
of this class is the salt of benzoic acid.
The salt-forming cations of these acid
components are predominantly alkali metal ions.
Additionally, however, at least some of such
salt-forming cations may also be ammonium ions. In
this latter instance, however, it has been found that
optimum corrosion protection results are achieved where
the content of ammonium ions in the aqueous treating
solution is not substantially in excess of about 20% of
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the total cation content. Additionally, it is to be
appreciated that although excellent corrosion
protection results are obtained when the components A,
B and C are formed of only one of the acid salts of the
defined classes, in some instances it may be preferable
to form one or more of the components of a combination
of two or more of the acid salts of the class defined.
In addition to the A, B and C components
which have been described hereinabove, the aqueous
treating solutions of the present invention may also
contain one or more non-ionic surfactants, preferably
those having a turbidity point below about 30C. Such
surfactants are water-soluble at low temperatures.
When the turbidity point of ~he surfactants is reached,
the solutions begin to become cloudy and the foaming
action of the surfactant solution is noticeably
reduced. It has been found that by the addition of
these non-ionic surfactants, the wetting of the metal
surfaces is improved so that the treatment solutions
are able to act even on moderately greasy or dirty
metal substrates. Non-ionic surfactants which have
been found to be particularly useful are the polyglycol
ethers of fatty alcohols, fatty amines and polyamines,
and polglycol esters of fatty acids, which have been
reacted with ethyleneoxide and propyleneoxide.
Particularly advantageous surfactants of this type are
the high molecular weight block polymers of
polypropyleneglycol condensed with ethyleneoxide and
the high molecular weight block polymers of
polyethyleneglycol condensed with propyleneoxide.
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Sur~actants of this type are sold under the desiqnation
Pluronic 52 by Wyandotte, U.S.A. Although various
amounts of such surfactant may be used in the aqueous
treating solutions of the present inventions, they are
typically present in amounts from about 0.003 to about
0.5~ by weight of the total solution, with amounts
within the range of about 0.01 to about 0.35~ by weight
being particularly preferred.
The aqueous treating solutions of the
present invention may also contain one or more
additional conventional corrosion inhibitors for
individual metals, provided such additional corrosion
inhibitors are compatible with the other components in
the treating solutions and d-o not have an adverse
effect on the corrosion protection of any of the metal
substrates which are contacted by the solution.
Typical of such other corrosion inhibitors which may be
used are boric acid esters, salts of higher carboxylic
acids, salts of amino acids, salts of
sulfonomidocarboxylic acids and fatty acid
alkanolamides. Where the treating solutions will be in
contact with copper and/or brass components, the
solutions may also advantageously contain
mercaptobenzothiazoles, benzotriazole and their
derivatives. Finally, the aqueous treating solutions
of the present invention may also contain further
additives to prevent or at least minimize attack on the
solution and/or the treated metal substrates by micro-
organisms. Typically, such additives may include
biocides r such as phenol derivatives, formaldehyde or
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compounds which will evolve formaldehyde, triazines,
quarternary ammonium compounds, and the like.
The total aqueous treating solutions will
typically have a pH within the range of about 7 to 10
and, preferably, will have a pH within the range of
about 8 to 9. The salts of the various organic acids
or components A, B and ~ which are used in the present
solutions may be simply prepared by mixing the organic
acid with the appropriate alkali and water at
temperatures of about 40 - 90C.
While the aqueous treating solutions may be
prepared from solid salt mixtures, they are preferably
formulated using a liquid concentrate which can be very
easily diluted with water to~`form the final treating
solution containing the components in the desired
concentrations. Such concentrate componsitions, which
form a part of the present inventionr will typically
contain the components A, B and C in solution in water,
in a total concentration of about 30 - 80% by weight.
Where a surfactant as described above is also included
in the composition, such surfactant may be a part of
the concentrate and is typically present in an amount
within the range of about 0.5 to 10~ by weight of the
concentrate, preferably from about 1 to about 4% by
2S weight.
~ y the use of the a~ueous treating solutions
of the present invention, exceptional anticorrosion
results are obtained on a wide variety of metal
substrates. These solutions are found to provide
corrosion protection for these metal substrates while
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they are in contact with the solution. Additionally,
corrosion protection is provided against residual water
which may remain on the metal surfaces after they have
been removed from the treating solutions.
In order that those skilled in the art may
better understand the present invention and the manner
in which it may be practiced, the following specific
examples are given. In these examples, E~amples 9
through 11 are examples of the compositions of the
present invention. Examples 1 through 8 and 12 are
examples of solutions containing one or more of the
individual components of Examples 9 through 11 but less
than all of these components, or of compositions made
up of sal~s other than the a~ ali metal sal~s.
In testing the various solutions of Examples
1 through 12, test sheets having the dimensions 100 x
20 x 1 millimeters of steel, aluminum, copper, brass
(70/30 copper/zinc)~and zinc were weighed. These test
sheets were then half-submerged in water of 22.4dH
(adjusted by means of clacium chloride additions) both
with an without the addition of various corrosion
inhibitor compositions. The test sheets were
maintained half-submerged in the various solutions in
beakers, covered with a watch glass, for 28 days at a
temperature of 35C. Thereafter, the test sheets were
removed from the solutions, rinsed and dried and again
weighed. The inhibitory value of the various corrosion
inhibitor additives was determined in accordance with
the following formula:
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H - (M1 - M2) 100
Ml
wherein Ml equals the loss in weight in water without
an additive and M2 equals the loss in weight in the
inhibited solution. The various solutions tested and
the inhibitory values obtained are as follows:
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Concen-
Example tration Inhibitory Values
No. Composition g/L Fe Al Zn Cu Brass
1 Water 22.4dH 0 0 0 0 0
2 Na caprylate 15 30 40 10 20 20
3 Na gluconate 15 10 15 10 0 0
4 Na benzoate 15 70 20 10 0 0
6 Block polymer of 15 0 10 20 0 0
polypropylene
glycol with ethy-
lene oxide ~PLUR-
ONIC* 67 from
Wynadotte U.S.A.)
7 Na caprylate 9 30 40 20 20 20
Na gluconate 6
8 Na caprylate 8 80 60 30 20 20
Na benzoate 7
9 Na caprylate 6 90 85 85 40 40
Na gluconate 4
Na benzoate 5
As for Example No. 90 90 90 40 40
9 + PLURO~IC 62 2
11 As for Example No. 90 g0 90 99 99
10 + benzotriazole
12 as for Example No. - 95 70 70 80 80
11, but triethanol-
amine salts
* trade mark
13
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While the above disclosure sets forth and
describes various embodiments of the present invention,
the compositions described are intended to illustrate
but not limit the present invention. It will be
understood that the specific embodiments described
herein are subject to variation and modification by one
skilled in the art having the benefit of the present
. disclosure and .it is, therefore, intended that the
present invention is to be limited solely by the
following claims.
