US3371046A

US3371046A - Inhibition of corrosion of hydraulic fluids

Info

Publication number: US3371046A
Application number: US334615A
Authority: US
Inventors: Robert S Mccord
Original assignee: Douglas Aircraft Co Inc
Current assignee: Douglas Aircraft Co Inc
Priority date: 1963-12-30
Filing date: 1963-12-30
Publication date: 1968-02-27
Anticipated expiration: 1985-02-27

Description

United States Patent thee 3,371,04fi Patented Feb. 27, 1968 3,371,046 INHIBHTION OF CGRROSION (3F HYDRAULIC FLUilLIaS Robert S. McCord, Pacific Palisades, Califi, assignor to Douglas Aircraft Company, Inc., Santa Monica, Calif., a corporation of Delaware No Drawing. Filed Dec. 30, 1963, Ser. No. 334,615

17 Claims. (Cl. 25275) This invention relates to compositions and to hydraulic fluids containing phosphinates, and is particularly concerned with improved phosphinate-containing compositions and hydraulic fluids which are inhibited against corrosion of metals, particularly iron.

In my copending application, Ser. No. 334,588, filed Dec. 30, 1963, is disclosed novel hydraulic fluids containing a phosphinate as a major component, and designed for operation at high temperatures in the hydraulic systems of modern aircraft, particularly supersonic aircraft. Such hydraulic fluids have many advantages over prior art hydraulic fluids employed in hydraulic systems of aircraft, particularly high stability and high fire resistance. Although the phosphinate component, specifically the aryl dialkyl phosphinate, of the hydraulic fluids described in my above copending application, or mixtures of such phosphinate with thickeners, such as described in my above application, and forming the improved hydraulic fluids thereof, are suitable for use with and are substantialy non-corrosive to many metals and alloys such as aluminum, titanium, silver and certain types of steels, e.g., 18-8 stainless steels, such phosphinates or mixtures thereof with thickeners corrode certain metals such as low carbon steels. Such low carbon steels are exemplary of the types of steel often used for construction of pumps employed in hydraulic systems of aircraft.

It is accordingly an object of the invention to inhibit corrosion of metals such as iron by compositions containing organic phosphinates.

Another object is to provide hydraulic fluids containing organic phosphinates as a major component, and which have substantially reduced corrosiveness on metals such as iron, especially low carbon steels, and particularly at high temperatures, e.g., of the order of about 400 F.

Another object of the invention is the provision of improved hydraulic fluids containing an aryl dialkyl phosphinate as a major component, and a suitable thickener, and inhibited against attack of metals such as iron, particularly low carbon steels, by incorporation of an effective inhibitor.

A still further object of the invention is to provide novel hydraulic fluids containing an aryl dialkyl phosphinate, preferably phenyl di n-butyl phosphinate, as a major component, and a suitable thickener, e.g., a polyalkyl methacrylate, effective to increase substantially the viscosity index of said phosphinate, and providing a thermally stable and fire-resistant hydraulic fluid operable at high temperatures in the range of about 400 to about 350 F., said hydraulic fluids having an additive incorporated therein inhibiting or substantially reducing attack of such hydraulic fluids on iron, particularly low carbon steels, particularly at high temperatures of the order of about 400 F., preferably Without adversely affecting the properties of such hydraulic fluids.

Other objects and advantages will be in part apparent and in part obvious from the following description of the invention.

The term iron employed in the specification and claims, unless otherwise indicated, is intended to denote and include iron and steels, particularly low carbon steels.

I have found that by addition of a small or minor amount of a class of certain organometallic compounds, namely, polyphenyl metal compounds wherein the metal is selected from the class consisting of bismuth, antimony and tin, e.g., triphenyl bismuth, to an organic phosphinate, particularly an aryl dialkyl phosphinate, or to a composition containing such phosphinate in admixture with other materials, the resulting phosphinate material or composition containing such additive unexpectedly exhibits substantially reduced corrosion on iron, particularly low carbon steels, as compared to the phosphinate or phosphinate-containing composition in the absence of such additive. The invention principles are particularly ap plicable to the phosphinate-containing mixtures forming the hydraulic fluids described in my above copending application, preferably employing an aryl dialkyl phosphinate as a major component and including a minor proportion of a suitable thickener. Of particular significance, such corrosion inhibition is attained substantially without adversely affecting the properties of the phosphinate-containing material and particularly the important properties of the above-noted hydraulic fluids, in the absence of such polyphenyl organometallic additive.

The hydraulic fluids described and claimed in my above copending application contain monoaryl dialkyl phosphinates having the general formula where R is aryl, e.g., phenyl or naphthyl, and R is an alkyl group of from 4 to 8 carbon atoms, preferably an alkyl group of from 4 to 6 carbon atoms. Thus, the alkyl groups can be butyl, pentyl, hexyl, heptyl and octyl. Also, branched chain alkyl groups can be employed. In this respect, aryl dialkyl phosphinates can be employed Wherein the alkyl groups are secondary and tertiary butyl, neopentyl, branched chain hexyls and heptyls, and also branched chain octyl groups, such as isooctyl. Preferably, aryl dialkyl phosphinates are employed wherein the alkyl groups are straight-chain alkyls. The two alkyl groups in the phosphinates may be the same or different.

In the process of manufacture of the above monoaryl dialkyl phosphinates, the final reaction product contains, in addition to the desired 'aryl dialkyl phosphinate, small amounts of other side reaction products, including phos phinates and phosphine oxides. Thus, for example, in the preparation of phenyl rli n butyl phosphinate for use in hydraulic fluids, according to the invention, by practice of the above process a mixture of products is formed composed of about 70% to of the phenyl di n-butyl phosphinate, about 10% to about 15% of diphenyl n-butane phosphinate, and about 10% to about 15% of tri n-butyl phosphine oxide. This impure material itself is substantially as suitable as the purified aryl dialkyl phosphinate. To obtain a purer material, the above mixture may be distilled to increase the amount of phosphinate and reduce the amounts of the above-noted side-reaction products. Thus, the above-described mixture may be distilled to obtain a composition composed of about 87% of the phenyl di n-butyl phosphinate, about 7% diphenyl n-butane phosphonate, and about 6% tri-n-butyl phosphine oxide. Hence, the term aryl dialkyl phosphinate employed herein and in the claims is intended to denote either the pure compound or an impure mixture containing a major proportion of aryl dialkyl phosphinate.

If desired, a single one of the above-defined phosphinates can be employed in the hydraulic fluid or a mixture of such phosphinates can be employed. The preferred aryl dialkyl phosphinate is phenyl di n-butyl phosphinate.

According to the above application, a minor amount of a compatible thickener or thickening agent is employed in conjunction 'with the aryl dialkyl phosphinates in order to provide a hydraulic fluid having proper viscosity characteristics at hydraulic fluid operating temperatures of the order of 400 to 550 F., a minimum increase in-viscosity at low temperatures and a high viscosity index. Thus, such thickener should be effective to increase the viscosity index of the phosphinate-containing hydraulic fluid to at least 75, e.g., in the range of about 75 to about 150, with the resulting fluid containing the thickener having a viscosity at low temperatures down to about 40 P. not in excess of about 14,000 centistokes. The thickener should also have high thermal stability at temperature of at least 400 F., and provide a hydraulic fluid having high fire resistance. Examples of suitable thickeners for this purpose include the polyalkyl methacrylates, the polyalkylene glycols, the polyurethanes and the methyl phenyl silicone polymers, in the order of preference named.

The polyalkyl methacrylates employed are generally those resulting from the polymerization of alkyl methacrylates in which the alkyl groups can have an average of from about 3 to carbon atoms. Preferably, the alkyl groups of the methacrylate can vary from about 4 to about 8 carbon atoms. The poly n-butyl methacrylate is preferred for use with the preferred phosphinate material, i.e., phenyl dibutyl phosphinate. The average molecular weight of the polyalkyl methacrylate can range from about 7,000 to about 12,000. Another suitable thickener are the high molecular weight polyalkylene glycols. Suitable materials of this type are those in which the alkylene groups contain from 2 to 3 carbon atoms. Thus, specific examples of such polyalkylene glycols are the high molecular weight polypropylene glycols, polyisopropylene glycols, and copolymers such as the ethylene glycol, isopropylene glycol copolymer. Such high molecular weight polyalkylene glycols are characterized by having a range of viscosity of about 1,400 to about 23,000 centistokes at 100 F, Also suitable as thickeners are the urethane polymer liquids. These may be urethane polyether or urethane polyester materials. Another thickener which can be added to the above aryl dialkyl phosphinate arethe liquid methyl phenyl silicone polymers, preferably of high molecular weight and characterized by having a viscosity e.-g., in the range of about 450 to about 575 centistokes at 100 F. The polymers of this type most useful in the hydraulic fluids of the above application are those having a high phenyl to methyl ratio, e.-g., of at least about 1:1 and which may be about 2:1, or higher.

Usually a minor proportion, and generally from about 0.5% to about 10% by weight of the thickener, based. on the weight of the total composition, produces the desired effectiveness in the aryl dialkyl phosphinate base stock. In preferred practice, a proportion of about 1% to about 5% by weight of thickener is employed.

The entire description of the phosphinates and the hydraulic fluids containing such phosphinates in my abovenoted copending application is incorporated herein by reference.

The polyphenyl bismuth, antimony and tin compounds which I have found to be effective for inhibiting or substantially reducing corrosion oftheabove phosphinatecontaining compositions or hydraulic fluids on iron, particularly low carbon steels, according to the invention, contain at least two phenyl groups. Although it is desirable that the phenyl content of such inhibitors be as high as possible for greatest effectiveness, in some instances these compounds can also be alkylated in order to increase their solubility in the phosphinate-containing composition or hydraulic fluid.

Specific examples of suitable additives for purposes of the invention include triphenyl bismuth, triphenylantimony, hexaphenyl di tin, tetraphenyl tin, and diphenyl dibutyl tin. These compounds have the following respective formulae.

s s) s (CGHS) 3 s 5)s ]2 s s 4 s 5)2 4 9) 2 It has been found that the addition of a small amount of one of the above organometallic additives, or a mixture thereof, to the above-described phosphinates, or to the above-described hydraulic fluids containing such phosphinates, reduces the attack of such materials on low carbon steels to a small fraction, e.g., about one-tenth, of the corrosion in the absence of such additive.

The development of suitable inhibitors against attack of the above-described phosphinates on iron, andwhich are compatible and suitable for use with such phosphinates, and particularly for incorporation in the above-described hydraulic fluids containing such phosphinates as an essential component, without adversely affecting the properties of such materials, has been complex. The difficulties in developing suitable additives for this purpose, and particularly for use with such hydraulic fluids, are the requirements that such additives must be compatible with or soluble in such phosphinate-containing compositions or hydraulic fluids over abroad temperature range, the additives shouldnotcause undesirable gelation of these compositions tending, for example, to transform such compositions or fluids into a thixotropic material, and should not have any adverse side effects or side reactions on the components of these compositions, particularly the organic phosphinates, specifically the aryl dialkyl phosphinate component thereof. Also, it is important that the inhibitor not operate to increase corrosion on other metals which are not normally affected by the phosphinate-containing material, and also the volatility of the additive should be low enough so that the inhibitor is not volatilized at the higher temperatures ofoperation. Further, for preferred use in the above-described hydraulic fluids which are intended'for operation at high temperatures in the rangeof 400 to 550 F., it is necessary that such additives have good thermal stability at temperatures of at least about 400 F., preferably in the range of about 400 to about 550 F., and fire resistance.-

The above described polyphenyl metal compounds, in addition to possessing high inhibiting effectiveness against the attack of the above organic phosphinates on iron, also possess substantially all of the abovecharacteristics. However, the tetraphenyl tin additive has very limitedsolubility at room temperature in the above-described phosphinatesor phosphinate-containing hydraulic fluids, and requires other means, such as, for example, the use of a mutual solvent for the dialkyl aryl phosphinate and the tetraphenyl tin, suchsolvent preferably having good stability at high temperatures, for proper incorporation and solubilization of the tetraphenyl tin in the phosphinate or hydraulic fluid. Hence, it is not preferred to use tetraphenyl tin as an inhibitor. The preferred additives for use in such hydraulic fluids according to the invention are triphenyl bismuth, triphenyl antimony and hexaphenyl di tin. The-triphenyl antimony has less fire resistance than triphenyl bismuth, and hexaphenyl di tin has lower solubility in such hydraulic fluids than triphenyl bismuth. Thus, a particularly desirable additive for cor.- rosion inhibition according to the invention is triphenyl bismuth.

The amount of polyphenyl metal additive incorporated into the organic phosphinate-containing;material, preferably the above-described hydraulic fluids, to achieve the above-described inhibiting effectiveness, can range from about 0.01% to about 3%, preferably from about 0.01% to about 1%, by weight of the composition. The use of about 0.5% by weight of such additive has been found particularly satisfactory. Where the above tin compounds are employed as inhibitors according to the invention, e.g., hexaphenyl di tin, due to the lower solubility of such additives in the phosphinate-containing compositions or such hydraulic fluids, amounts of such additives in the lower portions of the above ranges are preferably employed. With respect to the tetraphenyl tin additive, although this compound is soluble in the phosphinate-containing composition or hydraulic fluid when employed in effective amounts at hi her temperatures, e.g., above 160 F., as previously noted, it is usually also necessary to employ other means, such as a mutual solvent, to maintain such tin compound in solution in the phosphinatecontaining material or hydraulic fluid at lower temperatures, and to maintain such material or hydraulic fluid in a single phase throughout a broad temperature range. Although an amount of additive greater than 3% can be employed where such amount of additive is soluble in the base phosphinate material, such larger amounts usually do not materially enhance the effectiveness of the additive. Amounts of additive smaller than 0.01% by weight generally are of reduced effectiveness in producing the desired inhibition of corrosion according to the invention.

The following are examples of practice according to the invention:

EXAMPLE 1 The following compositions were prepared by dissolving in each case the indicated amount of inhibitor in the indicated amount of phosphinate.

Composition A Percent by weight Phenyl di n-butyl phosphinate 99.5 Triphenyl bismuth 0.5

Composition B Phenyl di n-butyl phosphinate 99.5 Triphenyl antimony 0.5

100.0 Composition C Phenyl di n-butyl phosphinate 99.5

Composition E Phenyl di n-butyl phosphinate 99.5 Diphenyl di n-butyl tin 0.5

Each of Compositions A to E, and a control consisting of phenyl di n-butyl phosphinate alone in the absence of any inhibitor, was tested for corrosion on iron in the form of a low carbon steel, specifically, a mild carbon steel meeting the requirements of Federal Specification QQ-S-636, copper, aluminum, titanium and silver, metals often used in construction of a hydraulic system for modern aircraft, as follows: 1" X 1" x .032" thick samples of each of these metals were arranged in layers strung on a fine iron wire and separated by stainless steel washers, the washers separating the specimens sufficiently for the fluid being tested to reach their surfaces while the iron wire holds the bundle together in electrical contact as occurs in use. A separate bundle of such specimens was immersed in each of the fluid Compositions A to E and the control, and such fluids heated to 400 F. for 24 hours. The bundles of specimens were 6. then removed from the fluids and cooled, and the change in appearance of the fluid and the respective metal samples, and the weight loss of each metal sample determined.

The results of these tests showed that substantial corrosion of the iron sample occurred in the control fluid not containing the invention inhibitor, and the appearance of the surface of the iron sample was rough and discolored. Thus, the iron sample immersed in the control fluid had a weight loss of 7.0 mg./cm. The control fluid had changed in appearance to an opaque black sedimentcontaining fluid due to such corrosion. A minor amount of corrosion of the copper sample occurred in the control fluid. However, the aluminum, titanium and silver samples contacted with the control fluid remained substantially uncorroded.

On the other hand, the tests showed that the iron sam ples contacted with fluid Compositions A to E containing the invention inhibitors had minimum or substantially little corrosion following the above treatment of such samples in these fluids. Thus, weight loss tests of the iron samples contacted with Compositions A to E showed reduction of corrosion of the iron samples to about the order of one-tenth of the corrosion of the iron sample contacted with the control fluid as described above. However, Composition E was not quite as effective against corrosion of the iron as compared to Compositions A to D. It was further observed that there was reduced corrosion of the copper samples contacted with Compositions A and B containing triphenyl bismuth and triphenyl antimony, respectively, as compared to the control containing no inhibitor. The aluminum, titanium and silver samples contacted with Compositions A to E fluids remained uncorroded, showing that the invention inhibitors have no adverse effect with respect to the corrosion of such metals. Fluid Compositions A to E following treatment, although darkened to some extent, were essentially clear in appearance, with substantially no sludge formation visible.

EXAMPLE 2 The following Compositions G, H, J and K are prepared by dissolving in each case the indicated amount of inhibitor in the indicated amount of phosphinate and polyalkyl methacrylate or polyalkylene glycol thickener forming a hydraulic fluid, Composition F being the control.

Composition F Percent by weight Phenyl di n-butyl phosphinate 94 A mixture of 30% by weight of a poly n-butyl methacrylate having an average molecular weight of 7,900, and by weight of an organic phosphate ester as a carrier and solvent, marketed as Acryloid R-3876X by Rohrn & Haas Co. 6

100 Composition G Phenyl di n-butyl phosphinate 93.5 Acryloid R-3876X 6.0 Triphenyl bismuth 0.5

100.0 Composition H Phenyl di n-butyl phosphinate 97.5 High molecular weight polyalkylene glycol, believed to be an ethylene glycol, isopropylene glycol copolymer having a viscosity of 2,620 centistokes at 210 F. and 19,500 centistokes at 100 F., marketed as Union Carbide Chemical Companys #H-90,000 2.0 Triphenyl antimony 0.5

Composition J Phenyl di n-butyl phosphinate 93.5 Acryloid R3876X 6.0 Hexaphenyl di tin 0.5

Composition K Phenyl di n-butyl phosphinate 93.5 Acryloid R-3876X 6.0 Tetraphenyl tin 0.5

Composition L Phenyl di n-butyl phosphinate 93.5 Acryloid R-3876X 6.0 Diphenyl di n-butyl tin 0.5

Each of the hydraulic fluid CompositionsF to L is tested for corrosion on iron, copper, aluminum, titanium and silver, in the same manner and by the same procedure as set forth in Example 1 above.

The results obtained are generally similar to those obtained in Example 1. Thus, Composition F, the control, containing no inhibitor according to the invention, causes substantial corrosion of the iron sample practically to the same extent as did the control in Example 1, whereas Compositions G to L, hydraulic fluids containing phosphinate, thickener and invention inhibitor, substantially reduce corrosion on the iron samples essentially to the same extent as did Compositions A to D of Example 1. Similarly, as in the case of Example 1, Composition F, the control, and also the inhibited hydraulic fluids, Compositions G to L, cause essentially no corrosion of the aluminum, titanium and silver specimens.

Hence, it is apparent that the presence of the thickener in the phosphinate-containing hydraulic fluids of Compositions G to L essentially has no effect on the function of the invention inhibitors in the inhibited hydraulic fluids of the invention for reducing corrosion on iron.

EXAMPLE 3 The procedures of Examples 1 and 2 are repeated, but employing in each of Compositions A to E, and G to L, 1% of the inhibitor instead of 0.5%, and decreasing the amount of the phosphinate in each case by 0.5%.

Although results are obtained similar to those of Examples 1 and 2, the use of 0.5% of the inhibitor as in Examples 1 and 2. appears to produce somewhat-better inhibition results over the use of 1% of the inhibitor.

EXAMPLE 4 The following formulations were prepared.

Composition M Percent by Weight Corrosion tests were run using Compositions M and N above, and employing the same procedure and metal samples as in Example 1.

Inhibition of corrosion on the iron and copper samples was obtained, but in the particular case of Composition N, containing the large 5% of triphenyl antimony inhibitor,

it was found that this large amount of such inhibitor rendered the hydraulic fluid less fire resistant.

EXAMPLE 5 The following are additional examples of inhibited phosphinate-containing compositions according to the invention.

Composition 0 Percent'by weight Phenyl di n-pentyl phosphinate 96.8 A poly n-hexyl methacrylate having an average molecular weight of about 8,000 to about 10,000 3.0 Triphenyl bismuth 0.2

100.0 Composition P Phenyl di n-hexyl phosphinate 93.5 A polypropylene glycol 6.0 Hexaphenyl di tin 0.5

100.0 Composition Q Phenyl di neopentyl phosphinate 99 Triphenyl antimony 1 100 Composition R Phenyl di isooctyl phosphinate 94.4 A urethane polymer liquid 5.0 Triphenyl bismuth 0.6

100.0 Composition S Naphthyl di n-butyl phosphinate 96.5 A poly n-butyl methacrylate having an average molecular weight of about 8,000 3.0 Hexaphenyl di tin 0.5

100.0 Composition T Phenyl di n-butyl phosphinate 94.5- Methyl phenyl silicone polymer marketed as DC710 by Dow Corning Co. and believed to be a high molecular weight polymer having a high phenyl to methyl ratio 5.0 Triphenyl bismuth 0.5

100.0 Composition U Phenyl di n-butyl phosphinate 94.5 A poly n-butyl methacrylate of molecular weight about 8,000 0.5 Tetraphenyl tin 0.5

100.0 Composition V Phenyl di neopentyl phosphinate 94.3 Acryloid R-3876X 5.0 Diphenyl di nbutyl tin 0.7

Composition W Naphthyl di neopentyl phosphinate 93.6 A poly n-butyl methacrylate having an average molecular weight of about 8,000 6.0 Triphenyl bismuth 0.4

From the ioregoing, it is seen that the invention provides phosphinate-containing compositions and'valuable phosphinate-containing hydraulic fluids which are inhibited against attack of iron, particularly low carbon steels, important metals of construction of components of aircraft hydraulic systems, and which metals are subject to substantial corrosion in the presence of such uninhibited phosphinate-containing compositions and hydraulic fluids.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention, as set forth in the appended claims.

I claim:

1. A composition consisting essentially of an aryl dialkyl phosphinate having the formula where R is an aryl group selected from the class consisting of phenyl and naphthyl, and R is an alkyl group containing from 4 to 8 carbon atoms, and about 0.01% to about 3% by weight of said composition of a compound selected from the group consisting of triphenyl bismuth, triphenyl antimony, hexaphenyl di tin, tetraphenyl tin, and diphenyl di n-butyl tin.

2. A composition as defined in claim 1, wherein said phosphinate is phenyl di n-butyl phosphinate.

3. A composition as defined in claim 1, wherein said compound is triphenyl bismuth.

4. A composition as defined in claim 1, wherein said compound is triphenyl antimony.

5. A composition as defined in claim 1, wherein said compound is hexaphenyl di tin.

6. A composition as defined in claim 1, wherein said compound is triphenyl antimony and said phosphinate is phenyl di n butyl phosphinate.

7. A composition consisting essentially of an aryl dialkyl phosphinate having the formula where R is an aryl group selected from the class consisting of phenyl and naphthyl, and R' is an alkyl group containing from 4 to 8. carbon atoms, and from about 0.5% to about 10% by weight of a material selected from the group consisting of polyalkyl methacrylates wherein the alkyl groups contain an average of from about 3 to 10 carbon atoms, and having an average molecular weight in the range of from about 7,000 to about 12,000, polyalkylene glycols, wherein the alkylene groups contain from 2 to 3 carbon atoms, and having a range of viscosity of about 1,400 to about 23,000 centistokes at 100 F., urethane polymer liquids, and liquid :methyl phenyl silicone polymers having a viscosity in the range of about 450 to about 575 centistokes at 100 F., said material being compatible with said phosphinate and effective to increase the viscosity index to at least 75, and about 0.01% to about 3% by weight of said composition of a 10 compound selected from the group consisting of triphenyl bismuth, triphenyl antimony, hexaphenyl di tin, and tetraphenyl tin, and diphenyl di n-butyl tin.

8. A composition as defined in claim '7, compound is triphenyl bismuth.

9. A composition as defined in claim 7, compound is triphenyl antimony.

10. A composition as defined in claim 7, compound is hexaphenyl di tin.

11. A composition as defined in claim 7, wherein said compound is triphenyl bismuth and said phosphinate is phenyl di n-butyl phosphinate.

12. A composition as defined in claim 7, wherein said material is said polyalkyl methacrylate.

13. A fire-resistant hydraulic fluid consisting essentially of phenyl di n-butyl phosphinate, about 0.5% to about 10% by weight of polybutyl methacrylate and having an average molecular weight in the range from about 7,000 to about 12,000, and about 0.01% to about 1% by weight of triphenyl bismuth.

14. A fire-resistant hydraulic fluid consisting essentially of phenyl di n-butyl phosphinate, about 0.5% to about 10% by weight of polybutyl methacrylate and having an average molecular weight in the range from about 7,000 to about 12,000, and about 0.01% to about 1% by weight of triphenyl antimony.

15. A fire-resistant hydraulic fluid consisting essentially of phenyl di n butyl phosphinate, about 0.5 to about 10% by Weight of polybutyl methacrylate and having an average molecular weight in the range from about 7,000 to about 12,000, and about 0.01% to about 1% by weight of hexaphenyl di tin.

16. A fire-resistant hydraulic fluid consisting essentially of phenyl di n-butyl phosphinate, about 0.5% to about 10% by weight of a polyalkylene glycol wherein the alkylene groups contain from 2 to 3 carbon atoms, and having a range of viscosity of about 1,400 to about 23,000 centistokes at 100 F., and about 0.01% to about 1% by weight of triphenyl antimony.

17. A composition consisting essentially of di n-butyl phosphinate and about 0.01% to about 3% by weight of said composition of triphenyl bismuth.

wherein said wherein said wherein said References Cited UNITED STATES PATENTS 2,174,019 9/1939 Sullivan 252-78 X 2,177,561 10/1939 Cook 252-389 X 2,578,359 12/1951 Jenkins 252- X 2,636,862 4/1953 Watson 252-78 2,947,699 8/1960 Wasson et al 252-76 3,245,907 4/1966 Stark et al 252-75 X OTHER REFERENCES Coates: Organo-Metallic Compounds, second edition, 1960, John Wiley and Sons, Inc., New York, p. 228.

LEON D. ROSDOL, Primary Examiner.

S. D. SCHWARTZ, R. D. LOVERING,

Assistant Examiners.

Claims

1. A COMPOSITION CONSISTING ESSENTIALLY OF AN ARYL DIALKYL PHOSPHINATE HAVING THE FORMULA

7. A COMPOSITION CONSISTING ESSENTIALLY OF AN ARYL DIALKYL PHOSPHINATE HAVING THE FORMULA