Note: Descriptions are shown in the official language in which they were submitted.
~;~32863 -
2410
ANTIFREEZE CONCENTRATES AND COOLANTS
CONTAINING HETEROPOLYMOLYBDATE COMPOUNDS
Background of the Invention
1. Field of the Invention
This invention relates to polyhydroxy alcohol-
based antifreeze concentrates and coolants. Conventional
components are used except for certain heteropolymolybdate
compounds .
2. Description of the Prior Art
Moly~dates, phosphates, and silicates are well
known components of antifreeze to inhibit various types of
corrosion. These inhibitors can be used individually or as
mixtures, but thece is no apparent synergism which results
from using mixtures.
Heteropolymolybdates are known compounds and have
been used to lnhibit the corrosion of carbon steel in
WatQr. See Xu et al, "Study of Heteropolymolybdates as
Water Corrosion Inhibitors," Chemical A~stracts, Vol. 96,
129508h (1981).
Summary of the Invention
The subject invention relates to polyhydroxy
alcohol-based antifreeze concentrates for engines containing
aluminum parts comprising:
(a) an effective corrosion inhibiting amount of a
heteropolymolybdate compound having the
following structural formula:
3~
lZ9;2~63
[ X Mo 1240 ]
where xn+ = P+S or Si+4,
tb) a buffer compound in an amount such that the
RA of the antifreeze concentrate i~ at least
10,
(c) from 0.1 to 1.0 weight percent of a nitrate,
said weight percent based upon the total
weight of the concentrate
(d) water, and
(e) one or more polyhydroxyl alcohols ~uch that
the weight ratio o water to polyhydroxyl
alcohol is from 0.1:100 to 10:100.
The heteropolymolybdates are effective inhibitors
again~t solder corrosion and aluminum corrosion. Data
sugge~ts they provide more effective corrosion protection
than could have been predicted when considering the amount
of active metal bonded in the heteropolymolybdate structure.
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Descri tion of the Preferred Embodiments
p
The heteropolymolybdate compounds are known
compound~' and are commercially available. Two of the best
known, and, therefore, used on a preferred basis are 12-
molybdophosphate and 12-molybdosilicate. Both of these
compounds are available from AMAX Corporation. These
compounds are used in an amount effective to inhibit the
corrosion of aluminum metal parts. Generally, they are used
in an amount of 0.1 weight percent to 1.0 weight percent,
1~ said weight percent based upon the total weight of the
concentrate.
The buffer compound used may be a phosphate,
borate, or carbonate in any o their avallable forms. The
amount of buffer used ~s ~uch that the pH of the resulting
coolant will havQ a reservQ alkalinity (RA) of at least 5
or a coolant and at lea~t 10 for a concentrate. RA i8 a
measure of buffer capacity and 19 determined by titrating a
10 ml neat coolant sample (which is preferably diluted to
100 ml) with 0.1 N hydrochloric acid to a pH of 5.5. The
milliliters of acid used is equal to the RA of the coolant.
A water-soluble nitrate, which i9 preferably used
in a corrosion inhibiting amount to provide specific
-
'See Advanced Inorqanic Chemistr~, F.A. Cotton and
G. Wilkinson, pp 949-957, Interscience Publishers, N.Y. (3rd
edition, 1973).
12~2863
corrosion protection of aluminum, can be derived from any
inorganic nitrate compound which i8 capable of ionization to
provide nitrate ions in sufficient concentration to pass-
ivate an aluminum or aluminum alloy surface. The water-
soluble nitrate can be derived from nitric acid or an alkali
metal or alkaline earth metal nitrate. Preferably, the
water-soluble nitrate is an alkali metal nitrate. lt is
possible to add nitric acid to the aqueous liquid and
subsequently add an alkali or alkaline earth metal hydroxide
to neutralize the nitric acid and obtain an aqueous solution
having a pH in the desired pH range. Useful water-soluble
nitrate salts are sodium nitrate, potassium nitrate, lithium
nitrate, cesium nitrate, rubidium nitrate, calcium nitrate,
strontium nitrate, and magnesium nltrate. Preferably sodium
or potassium nitrate is utlllzed. q'he proportion of nitrate
ion utillzed, calculated as sodium nitrate, is generally
about 0.1 weight percent to about 1.0, preferably 0.1 weight
percent to 0.5 weight percent based upon the weight of the
antifreeze concentrate.
A water-soluble nitrite can be included optionally
in the coolant compositions, antifreeze concentrates and
metal corrosion inhibiting compositions of the invention as
a specific corrosion inhibitor for cast iron and mild steel
in contact with an aqueous liquid. Preferably, the water-
soluble nitrites are alkali metal nitrites such as potassium
129Z863
and sodium nitrites. These corrosion inhibitors can be
utilized generally in the antifreeze concentrates and
coolant compositions of the invention in a proportion of
about 0.05 weight percent to about 0.5 weight percent based
upon the weight of the antifreeze concentrate.
The antifreeze concentrate preferably contains a
water-soluble inorganic silicate represented by the average
formula:
(M20) (SiO2)n
wherein n has a value from 0.5 to 4, or preferably from 1.0
to 2.5 and wherein M is a cation that forms a water-soluble
silicate and a is the valQnce of the catlon represented by M
and has a value of at least 1. Illustrative of these
silicates are the alkali mQtal orthosllicates wherein M is
an alkali metal and n is 1, the alkali metal metasilicates,
the alkali metal tetrasilicates, the alkali metal disili-
cates, and the tetra(organo) ammonium silicates. Specific
examples of these silicates are potassium metasilicate,
sodium orthosilicate, potassium disilicate, lithium ortho-
silicate, lithium metasilicate, lithium disilicate, rubidium
disilicate, rubidium tetrasilicate. tetra(methyl)ammonium
silicate, tetra(ethyl)ammonium silicate, phenyltrimethyl
ammonium silicate, benzyltrimethyl ammonium silicate,
~29Z~3~i3
guanidine silicate, and tetra(hydroxyethyl)ammonium
silicate. The preferred silicates are sodium and potassium
silicates, especially sodium metasilicate and pota~sium
metasilicate. Particularly desirable are the commercially
available sodium silicate aqueous solutions containing a
weight ratio of ~ilicon dioxide to sodium oxide of 1.8:1,
2.5:1, and 3.22:1.
The amount of silicate used in the antifreeze
composition is generally from 0.1 to 1.0 weight percent,
said weight percent being based upon the total weight of the
antifreeze concentrate.
In addition to the water-soluble silicate, the
coolant preferably contains a siloxane which acts as a
silicate stabilizer. Representative examples of siloxanes
which can be used in conjunction with the silicate are found
in U.S. Patents 4,362,644: 4,434,065: 2,968,643; 3,215,643:
3,341,469; 3,337,496: 3,312,622: 3,198,820: 3,203,969;
3,248,329: and 3,507,897. Ihe slLoxanes are used in amourlts
such that the wei~llt ratio oE total silicate to siloxane in
the antiFree~e conlpositlon i~ froln 2 to lO, preferably
from 4 to 8.
Th~ antlfree~e concentrates utilize at least one
water-soluble alcohol which i9 defined to include both
monohydric alcohols (such as methanol, ethanol, and pro-
~29ZE3~i3
panol) and polyhydric alcohol~ (such as ethylene glycol,
dipropylene glycol, propylene glycol, diethylene glycol,
triethylene glycol, and glycerol). The alcohol can also
include hydrocarbon alcohols and alcohols containing ether
linkages. Mixtures of alcohols are also useful in the
compo~itions of this invention. In view of it~ desirable
physical properties such as its low molecular weight and its
low volatility, ethylene glycol is an especially useful
alcohol in these compositions and mixtures of ethylene
lU glycol and diethylene glycol are preferred. Especially
preferred are mixtures of about 80 percent to about 98
percent ethylene glycol and 2 percent to about 20 percent of
diethylene glycol all by weight and based upon the total
weight of the antifreeze concentrate.
The antifree2e concentrates are adapted or
economical sh1pment and storagQ and can be diluted with
watQr to orm coolants for use in the cooling systQms of
water-cooled internal combustion engines. The antifree~e
concentrate ha~ a weight ratio of water to polyhydroxy
alcohol of 0.1:100 to 1:20, preferably from 1:50 to 1:20.
The antifree~e coolant has a weight ratio of water to
polyhydroxy alcohol of from 1:2 to 4:1, preferably from 1:1
to 3:1.
To provide for the corrosion protection of copper,
bra~s and solder, the coolants preferably contain in a
129Z8~3
corrosion inhibiting amount at least one water-soluble ~alt
of a triazole or thiazole compound. Representative useful
thiazoles include the alkali metal salts such as the sodium,
potassium, lithium, rubidium, and cesium salts of thiazoles
such as mercaptobenzothiazole, 4-phenyl-2-mercaptobenzothia-
zole, 4-methyl-2-mercaptobenzothiazole, and 5-methyl-2-
mercaptobenzothiazole. Representative useful triazoles
include the alkali metal salt~ of benzotriazole, tolyl-
triazole, benzotriazole carboxylic acid, alkyl esters of
benzotriazole carboxylic acid having 1 to 8 carbon atoms in
the alkyl group such as the methyl and butyl esters thereof,
and ~enzotriazole derivatives having various substituents on
the aromatic ring, i.e., N02, Cl, and NH2.
At least one thiazole or triazole compound can be
lncorporated into the aqueou~ coolant or antlfreeze concen~
trate composition or into the corrosion inhiblting composi-
tion intended or sub~equent addition to the cooling system
of an internal combustion sy4tem in the acid form of the
thiazole or triazole. In the resulting alkaline solution of
the coolant or antifreeze concentrate or corrosion inhib-
iting composition, the acid form is converted to the salt
which is water soluble. The thiazole or triazole, calcu-
lated as the sodium salt, i3 incorporated into the coolant
solution and the antifreeze concentrate generally in the
proportion of about 0.1 percent by weight to about 0.5
129Z~63
percent by weight based upon the weight of the concen-
trate. Preferably, the proporation of thiazole or triazole
is about 0.05 weight percent to about 0.5 weight percent and
most preferably about 0.1 weight percent to about 0.25
weight percent, all based upon the weight of the antifreeze
concentrate. The weight percent of the thiazole or triazole
is calculated 90 as to provide an equivalent ion concentra-
tion as would be provided by sodium mercaptobenzothiazole
with respect to the thiazole compounds and sodium tolyltri-
azole with respect to the triazole compounds.
Other conventional metal corrosion inhibitors,
such as water-soluble molybdates and benzoates, particularly
the alkali metal salts thereof can be used for thelr known
metal corrosion inhibiting effects. Other special additives
such as antifoam agents, identlying dyes, pH indicators,
sealants which prevent leakage o the coolant from the
coollng system, anticreep agents which prevent seepage of
the coolant lnto the crankcase of the internal combustion
engine, and the like, can be added to the heat-transfer
compositions of the invention.
The corrosion inhibited heat transfer compositions
of this invention can be prepared in any convenient manner
by adding at ambient temperature and pressure the required
metal corrosion inhibitors to water optionally containing a
water-soluble alcohol and various conventional additives for
~Z9Z~63
imparting special properties to the heat-transfer medium.
The mixed liquid or solid metal corrosion inhibitor composi-
tions can be prepared simply by combining dry or liquid
forms of the components and mixing at ambient temperature
and pressure until a uniform dry mixture or aqueou~ solution
or di~persion of the components is obtained. Silicates in
the absence of ~iloxanes, however, should not be exposed to
a pH of <9.
Many metal corrosion-inhibiting compositions can
be prepared in accordance with the teachings of the inven-
tion. The following compo~itions are, therefore, merely
representative. Where not otherwise specified throughout
this specification and claims, temperatures are given in
degreQs centigrade and parts, percentages, and proportions
are by weight.
-- 10 --
lZg2~3
Examples
In the Examples which follow a base antifreeze was
prepared having the following composition and an RA value of
7.7.
Amount
Component (weight percent)
Ethylene Glycol 93.5
Diethylene Glycol 5.0
NaN03
Borax 5 H2O l.O
Test antifreezes were prepared by adding various
inhibitors to the ba~e antifreeze. These formulations are
de~cribed ln Table I.
TABLE I
Amount of
Inhibitor
Example Inhibitor (weight percent)
1 12-molybdophosphatel.O
2 12-molybdosilicate 1.0
C-l 2 4 2 1.0
C-2 Na2HPO4 1.0
C-3 Na2SiO3 0 5
A screening te~t was then conducted on the
foregoing antifreezes according to glavanostaircase polari-
lZ~Z~363
zation method (GSCP) as described by S.T. Hirozawa in the
article entitled "Galvano~taircase Polarization" in the
Journal of the Electrochemical Society, Vol 130, No. 8,
tAugust 1983), and in the paper delivered at the
Corrosion 85 Symposium entitled "Corrosion Monitoring by
Galvanostaircase Polarization" by S.T. Hirozawa, Paper
No. 85.
Es3entially the test method lnvolves passing
incrementally a current through a solder which is immersed
in the test antifreeze to determine its breakdown poten-
tial (~Eb) which is related to the general corrosion rate of
the solder. The higher ~Eb, the greater the inhibition
agalnst general corrosion. This test wa3 conducted with
three different types of solder whose various concentratlons
of metal~ is shown below:
Pb Sn Ag
Solder A 96.5 3.0 0.5
Solder B 93.5 6.0 O.S
Solder C 70.0 30 0
~EEb in ~able II which follows is expressed in millivolts.
The number in parenthese3 is the calculated ~Eb which would
have been expected based upon the amount of molybdate,
phosphate, and silicate in the heteropolymolybdate compound
used and the ~Eb for an equivalent weight of these compounds
- 12 -
~ZS~2~f~i3
determined separately, i.e., as in Examples C-l, C-2, and
C-3.
TABLE II
Solder A Solder B Solder C
Antifreeze (~Eb) (QEb) (~Eb)
1 710 tl40) 430 (71) 260 (98)
2 170 (136) 300 370
C-l 140 65 80
C-2 140 200 465
C-3 50
The test result~ show that in all cases the experimental
value of ~Eb for the heteropolymolybdate was higher than the
expected calculated value.
The test antireeze was then tested for sand
abrasion as follows. Two preweighed 1" ~ections of aluminum
radlator tube stock WerQ mounted on a specimen holder. They
were vacuum-brazed by the usual heat cycle used in the
fabrication of aluminum radiators. The specimen holders
were then filled with about 900 milliliters of a solution
made up from 1 part antifreeze in 5 parts 100-100-100 ASTM
corrosion test water and 5 grams of casting sand were
added. Solutions were heated and maintained at 190F and
pumped at a nozzle velocity of 443 centimeters/second for 24
lZ928~3
hours. The aluminum specimens were then removed from the
holder and cleaned with chromic acid and reweighed. The
weight loss is measured in milligrams. The numbers in
parentheses are the calculated weight losses expected based
upon the amounts of moly~date, phosphate, and silicate in
the heteropolymolybdate and the weight 109s results from
these compound~ when used separately. The test results are
summarized in Ta~le III.
TABLE III
AntifreezeWeight Loss (mg)
1 20 (112)
2 38 (112)
C-l 114
C-2 38
C-3 38
To test the stabillty o the heteropoly structure
at a pH ~4.5, the following experiment was conducted. A
test solution was prepared having a pH of 8.5 containing 12-
molydophosphate. The test solution was heat cycled four
weeks (4 hours at 190F and 8 hours off). The sand abrasion
test was then carried out at time 0, one week, two weeks,
and four weeks on four different sample specimens. The
results are given in Table IV.
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TABLE IV
Period of Heat Cyclin~ Weight Loss, mq
0 36
1 week 36
2 weeks 28
4 weeks 28
The results indicate that the 12-molydophosphate i9 effec-
tive at a high pH, and must, therefore, be ~table contrary
to expert opinion.
