Note: Descriptions are shown in the official language in which they were submitted.
liC,l;O~ NI) OF Tl-lE 11~ l JON
This ill\ elltion r elates to the inl~ itic)n or co] ro ;ion in ~-atel-
systenls w llich lltilize oxygen-l)earing watel s.
More particularly, this in~elltion r clatcs to the use of compo-
sitions comprising~ low Inolecular weioht l~oly~llers and amiMo tris
10 (methylphosphonic acid) or its water-soluble salts to inhibit the
corrosion oI nletals in water systems which contain oxygen-bearing
wate r s .
. .
Oxygen corrosion is, of cOul se, a serious problem in any
metal-containing water system. The corrosion of iron and steel is
15 of principal concern because of their extensive use in many types oI
water systen~s. Copper and its alloys, aluminum and its alloys, and
galvanized steel are also used in water systems and are subject to
corroslon. We have discovered corrosion inhibitors which will inhibit
oxygen corrosion in water systems containing such metals.
- 20 SUMMARY OF Tl~E INVENTION
We have found that compositions comprising low molecular
weight polymers and amino tris (methylphosphonic acid) or its water-
soluble salts are effective corrosion inhibitors. Suitable polymers
include water-soluble salts of acrylates and methacrylates, un-
25 hydrolyzed or partially hydrolyzed acrylamides, and acrylamido_
methyl propane sulfonates. The polymers may be homo-, co-, or
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ter- polymers of any of the aforementioned polymers and may have
a molecular weight of from about 500 to about 10, 000. The pre-
ferred molecular weight, however, is about 1, 000.
Our corrosion-inhibiting compositions can contain a ratio of
5 polymer to amino tris (methylphosphonic acid) or its water-soluble
salts of from about 10:1 to about 1:5 by weight. The preferred ratio,
however, is from about 5:1 to 1:2 by weight. These compositions
will effectively inhibit corrosion of metals when maintained in a
water system at a concentration of at least about 5 ppm at the above
10 ratios and, preferably, about 30 ppm. Maximum concentrations are
determined by the economic considerations of the particular appli-
cation.
lt may, of course, be desirable to add zinc to the compositions
of this invention for certain applications. The zinc ion may be supplied
15 in many ways. For example, it may be added by utilizing a water-
soluble zinc salt, such as, zinc chloride, zinc acetate, zinc nitrate,
or zinc sulfate or it may be supplied by adding powdered zinc to a
solution of the composition.
Compounds such as benzotriazole or mercaptobenzothiazole
20 may also be added to the final formulation in varying amounts to improve
its usefulness in a wider variety of industrial applications where both
steel and copper are present in the same system.
The following tables show the results of experiments which
demonstrate the effectiveness of the compositions of this invention in
`25 inhibiting metallic corrosion. These tests were run in synthetic
':
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-
104775S
Pittsburgh water. Steel electrodes were used in polarization test
cells with the initial pH at 7. 0. Inhibitor concentrations were calcu-
lated on the basis of 100 percent active material. The amount of
corrosion that had taken place was determined from the current den-
5 sity at the intersection of an extrapolation of the so-called "Tafel"
portion of the anodic polarization curve with the equilibrium or "mixed"
potential value, usually referred to as the corrosion potential, "Ecorr"~
Application of Faraday~s Law allows a computation of a direct mathe-
matical relationship between the current density at ECorr~ expressed
10 in amperes per square centimeter and a more useful corrosion rate
expression such as milligrams of steel consumed per square decimeter ~ -
of surface per day (m. d. d. ) and mils per year (m. p. y. ). This re-
lationship is such that a current dens~ty value of 4. 0 x 10-7 amperes/
. ~
cm2 = 1. 0 mg/dm2/day. Further, the m. p. y. value is calculated from
15 the formula: m. p.y. = m. d. d. x 1. 44 , using a density value of 7. 87 g/ -~
3 density
cm for steel.
` The following table illustrates the synergistic effect of a
composition comprising sodium polyacrylate and amino tris (methyl-
phosphonic acid) or its water-soluble salts as a corrosion inhibitor in
20 tests run at 35C.
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~047755
Table 1
DosageCorrosion Rate
Inhibitor Svstem (mg/l) (mdd)
Control 0 100
Amino tris
(methylphosphonic acid) 15 50
Sodium Polyacrylate
(molecular weight~ 1, 000) 30 78
Amino tris
(methylphosphonic acid)
+
Sodium Polyacrylate15 + 30 12
The following tables illustrate the effectiveness of various
compositions of this invention as corrosion inhibitors in 5-day tests -
run at 140 F., and pH of 6. 0.
Table 2
DosageCorrosion Rate
Inhibitor System (mg/l) (mg/dm2/day)
Contro 1 - - - 2 5 0
Partially Hydrolyzed
Polyacrylamide
(molecular weight ~~7,000) 25 143
Aminomethylene
Pho sphonate (AMP) 1 2 11 5 - -
Partially Hydroly~ed
Polyacrylamide
Am.inomethylene
Phosphonate 25 + 12 42
_ 4 --
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:1047755
Table 3
Do sageCorro sion Rate
Inhibitor System(mg/l)(mg/dm2/day)
Control - _- 2 50
Partially Hydrolyzed
Polyacrylamide 15 200
Amino tris
(methylphosphonic acid) 7. 5 90
Zinc 10 90
10 Partially Hydrolyzed
Polyacrylamide
Amino tris
(methylphosphonic acid) ;-
Zinc 15 + 7. 5 + 10 6
:
