Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to novel silylalkyl-phosphonates
and their use in the stabilization of aqueous sllicates and as
metal corrosion inhibi-tors. ~ ;
A~ueous silicates as a class of compounds have been known
as metal corrosion inhibitors for aqueous systems. One of the ~ -~
disadvantages of the silicates, however, is the fact that they are ~`
unstable and after use at elevated temperatures tend to gel and
precipitate out of solution. There have been many efforts
therefore to stabilize silicates so that they could be more
persistent in their corrosion inhibiting properties.
Arthur N. Pines et al. in U.S. Patents No. 3,312,622 and
No. 3,198,820 describes combinations of silicone-silicate polymers
as corrosion inhibitors. Although the patent does not
specifically describe the stabilization of silicates, it is
apparent from the specification that the so-called "novel ~;
organosilicon polymer" does in fact contribute to the persistency
of the corrosion inhibition of the silicGne-silicate polymers of
that invention. The novelty, as pointed out therein, is the use
of silyl cationic carboxylates in conjunction with the silicates.
Such materials are discussed as enhancing the corrosion inhibition
of common antifreeze compositions and overcome disadvantages of
other prior art corrosion inhibitors such as handling and
dispensing of the antifreezes; selective corrosion inhibition of ~ ~;
certain metalsr poor shelf life, tendency to attack rubber hoses,
excessive foaming in use and the causing of alcohols to decompose.
In later issued U.S. Patents No. 3,341,469 and No.
3,337,496, Pines et al. describes another system that was found
useful for inhibiting corrosion in aqueous alcohol compositions.
It consisted of a mixture of an alkyl sil~esquioxane, a siloxane
modified with a cyanoalkyl or carbinol group and a silicate.
.~ .
.3~5
These materials are stated as being "remarkably soluble in aqueous
liquids". Further, the compositions are alleged to overcome many ~ -
of the above mentioned disadvantages.
Finally, U.S. Patent No. 3,948,964 issued April 6, 1976
describes the stabili~ation of partially hydrolyzed silicic acid
esters using stabilizers selected from organic compounds such as
cyclic ethers, ether alcohols, carboxylic acid esters and ketones.
Such stabilized materials are described as binders for zinc dust
pigments and the like.
None of the above references, however, describe the
compositions of the instant invention. The advantages of the
prior art methods can be obtained with the instant invention and
additional advantages over the prior art are obtained by this
invention. Most notable are the advantages o low cost, enhanced
effectiveness in stabili2ation of silicates and the persistency of
corrosion inhibition.
This invention consists of several aspects of the same
concept and one aspect is a composition of matter which is an
alkali siliconate silylalkylphosphonate which has the general unit
formula
(I) MoSiRoPoOM
O R'
wherein M is selected from a group consisting of alkaline metal
cations selected from a group consisting of sodium, potassium,
lithium and rubidium and, tetraorgano ammonium cations; R is a
divalent alipha~ic hydrocarbon radical containing 1-3 carbon atoms
,3~ 5
or the benzyl radical; and R' is a hydrocarbon radical containing
from 1-7 carbon atoms.
The phosphonate is derived from silylalkylesters of ~ -
phosphorus by the reaction of an alkali metal hydroxide with the
esters of phosphorus.
The precursor phosphorus compound, that is, the
silylal~ylesters of phosphorus can be prepared by several methods
but it is preferred to prepare them by the method shown in the
U.S. Patent No~ 4,093,641 issued June 6, 1978, to Plueddemann.
Plueddemann's method is easy to carry out and gives high yields
which gives the resulting product a low cost. The precursor
phosphorus compounds are then treated with dilute sodium hydroxide
and refluxed for several hours to saponify the phosphonate
precursor. The resulting product, in the case of the use of
sodium hydroxide, is
O
~aOSiROPOONa
o ~ '
.
i e. the sodium salt of the sodium siliconate silylal~yl-
phosphonate.
M in formula I can be independently an alkaline metal
cation selected from sodium, potassium, lithium and rubidium and
the tetraorgano ~onium cations. Typical tetraorgano ammonium
cations are tetramethyl ammonium and tetraethyl ammonium.
R in the above formula is a divalent aliphatic
hydrocarbon radical containing 1-3 carbon atoms or the benzyl
3~2S
radical. The material should be water soluble so there is a llmit
to the size and type of R. ;
R' is a hydrocarbon radical or a halohydrocarbon radical~
of 1-7 carbon atoms and includes methyl, ethyl, phenyl, halobenzyl :~
or the like.
In actual practice, using a dichlorobenzyldimethyl~
phosphate as an example, the preparation is as follows: ; `
~:: '. :
Cl ~ CH2PO(OCH3)2
Cl
benzyldimethylamine
tCH3O)3SiCH2CH2CH2C1 135-200C./6 hours
Cl ~ CH2POCH2CH2CH2si(OcH3)3 (I)
Cl OCH3 ::
Aqueous
( I ) + NaOH -- - - >
re~lux/several hours
< ~ CH2POCH2CH2CN25iONa
Na
The resulting product is used alone or in conjunction
. ~
with a silicate as will be explained infra.
; ~ .
As mentioned carlier, the products of the invention, the
alkali siliconate silylalkylphosphonates are able to stabilize ;
silicates that are useful as corrosion inhibitors for metals. ` :~
Thus, obvious uses for such materials is in antireeze
compositions where metal corrosion is common due to high ~-:
temperatures which cause decomposition of the alcohols typically
used as freezing point depressants. If the silicates protect the :~
internal metal parts of a cooling system, such as an automobile ~;
. engine, and if the silicates can be induced to have persistency in
the aqueous system, then there is a distinct advantage. :~
This in~ention therefore also contemplates a composition
of matter which is an improved corrosion inhibiting alcohol
composition consisting essentially of an alcohol and, as a
corrosion inhibitor, a corrosion inhibiting amount of a
composition consisting essentially of a combination of (A) an
alkali siliconate silylalkylphosphonate which has the general
formula
(II) MOSiROPOOM ~ :
O R'
wherein M is independently an alkaline metal cation selected from
the group consisting of sodium, potassium, lithium, rubidium and
tetraorgano ammonium cations; R is a divalent aliphatic
hydrocarbon radical containing 1-3 carbon atoms or the benzyl
radical; and R' .is a hydrocarbon radical or a halohydrocarbon : ~-
containing Erom 1-7 carbon atoms, with (B) a soluble silicate
represented by the general unit formula
(III) (MO)asio4-a
wherein M has the meaning above and a has a value of 1~3.
It is contemplated that the alcohol composition can be
anhydrous or contain, in addition to the alcohol and
phosphonate-silicate, relatively small amounts of water and it is
also contemplated that the alcohol composition can contain
relatively large amounts of water, that is, the alcohol
compositions may be "concentrates" or "coolants".
The alcohols that are useful in this invention include
both monomeric alcohols such as methanol, ethanol, propanol and
butanol and polyhydric alcohols such as ethylene glycol,
diethylene glycol, triethylene glycol, propylene glycol, glycerol
and mixtures of the above. What is contemplated are the currently
useful antifreeze alcohols, especially ethylene glycol.
The corrosion inhibitor of the above composition is a
composition of matter which consists essentially o (A) 0.1 to
99.9 parts by weight of an alkali siliconate silylalkylphosphonate
which has the general unit formula
O ~'
MOSiROPOOM
O R'
wherein M is independently an alkaline metal cation selected from
the group consisting o-f sodium, potassium, lithium, rubidium and ~;
tetraorgano ammonium cations; R is a divalent aliphatic
hydrocarbon radical containing 1-3 carbon atoms or the benzyl
radical; and R' ~s a hydrocarbon radical or halohydrocarbon
radical containing from 1~7 carbon atoms, with (B~ 99.9 to 0.1
parts by weight o~ a soluble silicate represented by the general
~ 3
unit formula
(Mo)asio4-a
wherein M has the meaning above and a has a value of 1-3.
As indicated above, essentially all ratios of phosphonate
(A) to silicate (B) are effective to produce a metal corrosion
inhibiting material~ The ratio of ~A) to (B) depends on the
particular system in which it is used. Therefore the ratio of (A)
to ~B~ that is the most useful in this invention is dependent on
the amount of water in the system, the amount and type of alcohol
present, the temperature of the aqueous medium and other additives
or chemicals in the system.
The phosphona-tes have been discussed above and therefore,
turning to component (B) of this invention, it should be noted
that ~he silicates intended herein are t:he water soluble silicates
and are represented by formula III as shown above. M in that
formula has the same meaning as set fort:h ahove for M and is a
cation which would render the silicate water soluble.
Illustrative of these silicates are the alkali metal
orthosilicates, alkali metal metasilicates, the alkali metal
tetrasilicates, the alkali metal disilicates and the ~-
tetraorganoa~nonium silicates.
Specific examples of these silicates are ~otassium
metasilicate, sodium orthosilicate, potassium disilicate, lithium
orthosilicate7 lithium metasilicate, lithium disilicate, rubidium
disilicate, rubidium tetrasilicate, mixed silicates (e.g.
Na20 Li20 2SiO2 and K2o-Li2o~4sio2)~ tetra(methyl) ammonium
silicate, te~ra(ethyl) ammonium silicate, phenyltrimethyl ammonium
silicate, benzyltrimethyl ammonium silicate, ~uanidine silicate
and tetra(hydroxy-ethyl) ammonium silicate. The preferred
silicates are sodium and potassium silicates, especially sodium
disilicate and potassium disilicate.
The silicate used in producing the phosphonate-silicate
inhibitor can be added to the reaction mixture as such or it can
be formed in-situ by adding the appropriate alkali hydroxide and
silica to the reaction mixture.
It is contemplated within the scope of this invention
that the combination of (A) and (B) can be mixtures of (A) and tB)
or partial reaction products of (A) and (B) or mixtures of
mixtures of (A) and (B) and partial reaction products of (A) and
(B).
The phosphonate-silicate combination can be prepared by ~ ~ ;
simply mixing the components (A) and (B), in the proper ratios,
and stirring to homogenize them.
The phosphonate-silicate combination is then added to the
alcohol composition. The order in which the phosphonate, silicate
and alcohol are added is not critical as long as the materials are ~;~
thoroughly mixed.
The alcoholic phosphonate-silicate combinations are found
20 to be useful in other areas besides automotive engine cooling. ~
For example r the materials can be used in refrigeration and air ~ ;
conditioning units, cooling cOilsr heat exchangers and the like.
It was indicated earlier that the phosphonate could be
useful in this invention without actually combining it with a
silicate before use, that is, the phosphonate could be added to
aqueous systems without the silicate. This invention, therefore,
contemplates the use of the phosphonate and the
phosphonate-silicate compositions in aqueous systems other than
anti-free~e systems, that is7 non-alcoholic aqueous systems which
come in contact with metal surfaces, i.e. such uses as controlling
scale in geothermal power plants, scale control in conventional
heat exchange systems and the liXe.
The amount of the combination (A) and (B) required to
protect metals from corrosion depends on the metals to be
protected, the system in which the combination is used, the
temperature of the system and the other components and additives
used in the system. Generally, the combination (A) and (B) is
used in an amount as low as 20 parts per million up to 2 parts per
100 parts based on the weight of the aqueous liquid used.
For automotive engine coolants, it has been found that
200 parts of the phosphonate-silicate, based on a million parts of
the aqueous alcohol coolant is effective to prevent corrosion. In
non-alcoholic aqueous mediums, larger quantities are sometimes
necessary. The preferred range of use for all systems within the
scope of this invention is 200 parts per million parts of aqueous
medium to 2 parts per 100 of aqueous meclium.
It is within the scope of this invention to add various
additives which impart special properties such as anti-foam
agents, both organic and siloxane based, dyes, pH indicators,
other inhibitorsr thickeners and the like.
The following examples are shown to illustrate the
invention and are not intended to define the scope thereof.
~ :
As indicated above, the materials of the art are
subjected to very adverse conditions which affect their
stabilizing properties. The materials of the instant invention
were therefore subjected to adverse conditions in the following
manner: -
~
Nyacol~ 215, a commercial silica sol manufactured by
Nyanza, Inc., Ashland, MA 01721 was used in this example. The
sol, ~hich had a pH of 10.5 and which was Na+ stabilized,
contained approximately 15~ silica which had a particle size of ~
approximately 2 m~m. The pH was reduced using 10% aqueous HCl ~ `
solution as shown in Table I. The freeze-thaw cycle consisted of
placing 1 oz. glass vials of the solutions in a freezer and
freezing for twelve (12) hours. The vials were then removed from
the freezer and allowed to thaw. m e solutions were then checked
for the appearance of precipitate indicating the solution was not
stable.
:
To show the versatility of the materials, a second
colloidal silica was treated and subjected to similar adverse
conditions. See Table II. The silicate was Ludox~ as
manufactured by E. I. DuPont De Nemours and Co., Wilmington,
Delaware. The sol contains 30~ silica and i5 ammonia stabilized.
The pH of the sol was 9. 4 and it had an average particle size of
13-14 m~. The pH was reduced by the addition of 10% aqueous HCl
solution as shown in Table II.
Example 3 ~ - -
This example illustrates the stabilizing effect of the
material in Nalcoag~ 1034A manufactured by the Nalco Chemical Co.,
Chicago, IL 60601. The sol is H+ stabilized and contains 34%
silica. It has an acid pH o~ 3.1 and the average particle size is
16-22 m~m.
The Nalcoag was made less acid by the addition of ammonia-
be ore being tested as shown in Table III.
Example 4
This example illustrates the stahilizing effect of the~
material in Ludox~ SM 30 manufactured by E. I. DuPont De Nemours
and Co., Wilmington, Delaware. The sol is Na+ stabiIized, has a
pH of 9-10 and an average particle size of 7-8 m~m. The solutions~
were tested as shown in Table IV after being reduced in pH by the
addition of 10% aqueous HCl. ;
Example 5
This example illustrates the effect of pH on stability.
Stability of silicate/siliconate mixtures has a minimum generally~
at pH 8.
A 7.5:1 mol ratio of sodium silicate "G" to product was
used. The silicate "G" was a sodium silicate manufactured by
Philadelphia Quartz Co. and has a weiyht ratio of SiO2/Na2O of
3.22 and a pH of 10.8. The product of this invention was a 1 ;~
molal aqueous siliconate, i.e. ~ ~
': ~ . ' .:
O
l, 5sicH2cH2cH2op-oNa ~ "~
CH3 ;
The mixture, after aging 1 day at room temperature, was acidifled
with 10% aqueous HCl to various pH's and observed for gel time.
pH gel tlme
4 > 1 week
6 > 1 week
7 > 1 week
3 1 3/4 hrs.
9 9 hrs.
.
> 1 week
:
;25
m e sample at the pH of 4 showed no gelling at 1 year.
Example 6
This example illustrates the effec-t of aging. A similar
mixture as was prepared in Example 5 above was used for this
example except the one (1) molal solution was 5:1 ratio of the
silicate to the product.
Time Aged Stability at
SampleAt Room Temp. pH 8 _
,
A10 sec. 30 sec. -
B 1 min. 70 sec. ;
C 5 min. 20 min. ~ ;
D15 min. > 1 week
E45 min. > 1 week
Samples D and E were still stable at this writing, some
four weeks (4) from their preparation.
Example 7
This example shows the e~fect with sodium metasilicate, a
low molecular weight silicate. A two molal sodi~m metasilicate
solution was mixed with a two molal product~ i.e.
i.
Ol.5SiCH~CH2CH2OPONa
CH3
in a mol ratio of 7:3. After aging at room temperature for 6
months, the equilibrated mixture was further diluted with sodium
metasilicate as indicated and then the pH was adjusted to 8 with a ~ `
10% aqueous HCl solution and the solutions were then observed for
stability.
mol ratio sodium ;
metasilicate/phosphonate
7:3 4:1 6
Stability at pH 8 ~ 1 week > 1 week 16 min
~ 3~325
Therefore, it can be observed that a mixture of sodium
metasilicate and a phosphonate of this invention, at a ratio of
4:1 provide stable corrosion inhibitors that will not gel when
neutralized. A fresh mixture at a ratio of 4:1 gelled in 6
minutes at pH 8, indicating that a period of equilibration is
beneficial.
Example 8 - Stabilization of a potassium silicate (Kasil 5). :
A one (1) molal potassium silicate solution of weight
ratio of SiO2/K2o of 2.10 (mol ratio 3.3:1) manufactured by
Philadelphia Quartz, was mixed with two ratios of 1 molal
siliconate solutions and after aging 15 minutes the pH was
adjusted to 8 with aqueous 10~ HCl. -
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