Lubricating Compositions and Process Using Complex Metal Chalcogenides

This invention relates generally to high temperature lubrication and more specifically to lubricant compositions and their use. The compositions contain complex metal chalcogenides which are compatible with various steels and alloys and which provide antiwear and extreme pressure properties.

Commonly used solid lubricants or solid lubricant additives are graphite, molybdenum disulfide, polytetrafluoroethane, lead oxide, boron nitride, alkaline metal borates, arsenic thioantimonate, and so forth. These solid lubricants have certain disadvantages, such as limited high temperature stability, hydrolytic instability, potential toxicity, inferior performance under high vacuum or high temperature, or undesirable by-products after exposure to high temperature. Antimony thioantimonate (SbSbS.sub.4) has excellent extreme pressure and antiwear properties when used as a lubricant additive as described, for example, in U.S. Pat. No. 3,965,016. In modern high temperature lubricating applications using various steels and alloys, lubricants having even better antiwear properties are desirable.

In accordance with this invention, there are provided lubricating compositions comprising a lubricant and at least one complex metal chalcogenide selected from the group having the formula

Where M is a metal selected from the group consisting of: Na, K, Cs, Mg, V, Mn, Fe, Co, Al, Cu, Ga, In, Bi, As, Ni, Zn, Cd, Sb, Sn and Ce;

where M' is a metal selected from the group consisting of Mo and W;

where A is S or Se;

where x ranges from 1 to 3;

where p is 1 or 2 depending on the oxidation state of M;

where m ranges from 1 to 5 depending on the oxidation state of M;

and n ranges from 0 to 6.

Also provided is a method of lubrication comprising contacting the surface to be lubricated with a lubricating composition comprising at least one complex metal chalcogenide selected from the group having the formula defined above. The chalcogenides can be used either as solid, primary lubricants or as additives to lubricating compositions such as greases, mineral oils, synthetic fluids and aqueous media to improve the extreme pressure and antiwear properties of the lubricating compositions.

The complex metal chalcogenides which are useful in the lubricating compositions and process of the invention have the general formula:

Where M is a metal selected from the group consisting of: Na, K, Cs, Mg, V, Mn, Fe, Co, Al, Cu, Ga, In, Bi, As, Ni, Zn, Cd, Sb, Sn and Ce;

where M' is a metal selected from the group consisting of Mo and W;

where A is S or Se;

where x ranges from 1 to 3;

where p is 1 or 2 depending on the oxidation state of M;

where m ranges from 1 to 5 depending on the oxidation state of M;

and n ranges from 0 to 6.

The complex metal chalcogenides can be used as lubricant compositions per se by applying them to the surface requiring lubrication either alone or in combination with other solid lubricants. Such use is especially applicable where very high operating temperatures are involved so that base greases or oils would decompose at the operating temperatures. The chalcogenides are also advantageously used as lubricant additives to greases, mineral oils, synthetic fluids, or aqueous media to provide lubricant compositions having superior extreme pressure and antiwear properties.

The complex metal chalcogenides generally are incorporated in lubricant compositions in a particulate form, i.e., as a finely-divided powder having a particle size, in general, within the range of about 0.01 micron to about 100 microns, and preferably within the range of about 0.01 to 10 microns. The compositions embodied herein are useful for lubricating the contacting surfaces of a wide variety of materials, for example, metals such as steel, molybdenum, copper, zinc, bronze, brass, Monel and other metals and metal alloys, plastics, ceramics, graphite, and other materials, wherein the contacting surfaces may be of the same or different materials. The grease can be a natural petroleum grease, which may contain small amounts of antioxidants, anti-corrosives, or other additives; or a synthetic grease comprised of a synthetic ester such as dioctyl sebacate, dioctyl adipate, tributyl phosphate, di-2-ethyl hexyl sebacate, and the like, containing from about 5% to 45% of a thickener such as lithium stearate, aluminum stearate, lithium hydroxy-stearate, calcium stearate, silica, clay, and the like; and small amounts of other additives, such as antioxidants and anti-corrosion agents. Other greases which are improved by the complex metal chalcogenides include silicone greases comprised of a a silicone oil contianing a thickening agent such as tetrafluoroethylene polymers and copolymers and other fluoropolymers. The complex metal chalcogenides also find utility as a component of a lubricating dispersion comprising a liquid oil carrier such as a hydrocarbon oil, synthetic ester oil, or silicone oil.

The effective amounts of complex metal chalcogenide used in the lubricant compositions and process will vary depending upon the particular application. Generally, amounts of from about 0.1 to 60% by weight based on the total weight of the lubricant composition, preferably about 0.5 to 20% by weight, are useful where the chalcogenide is used as a lubricant additive and up to 100% where the complex metal chalcogenide is used as a primary lubricant. Other lubricant additives can also be employed in the compositions of the invention such molybdenum disulfide or antimony thioantimonate.

The invention is further illustrated by, but is not intended to be limited to, the following examples in which complex metal chalcogenides of zinc, cerium and antimony were prepared and tested as lubricant additives in greases.

Ammonium oxythiomolybdate, (NH.sub.4).sub.2 MoO.sub.2 S.sub.2, was prepared according to a published procedure (G. Kruss, Ann. Chem., 225 (1884), F. W. Moore and M. L. Larson, Inorg. Chem., 6 (5) 998-1003 [1967]) by treating an ammonium paramolybdate solution [10.0 grams of (NH.sub.4).sub.2 Mo.sub.7 O.sub.24.4H.sub.2 O dissolved in 600 ml of 3.3 normal ammonium hydroxide solution] with H.sub.2 S at 4-7.degree. C. The resulting yellow solid was isolated by filtration under a nitrogen atmosphere and washed once with ice water and twice with 95% ethanol. After drying under a nitrogen stream, 17 grams of ammonium oxythiomolybdate, (NH.sub.4).sub.2 MoO.sub.2 S.sub.2, was obtained.

Cesium oxythiomolybdate, Cs.sub.2 MoOS.sub.3, was prepared according to a published procedure (V. A. Muller, et al. Z. Anorg. Und. Allgem Chem., 371, 136-148 [1969]). A mixture of 5.0 grams of sodium molybdate, Na.sub.2 MoO.sub.4.2H.sub.2 O, 9.1 grams of cesium acetate (15% excess) and 15 ml of 30% by weight ammonium hydroxide solution produced a solution having a pH of 12.8. The solution was acidified with 4.6 grams glacial acetic acid to lower the pH to 10 and then H.sub.2 S was bubbled through the solution. An orange, crystalline solid formed which was isolated by filtration, washed with ethanol, and dried at 110.degree. C. for five hours. The product weighed 9.0 grams (yield 92%).

Calculated for Cs.sub.2 MoOS.sub.3 : Cs, 56.4; Mo, 20.3; S, 20.3. Found: Cs, 54.2; Mo, 21.1; S, 21.9.

An aqueous solution of ZnCl.sub.2 (5.4 grams in 50 ml of distilled water) was slowly added to a solution of (NH.sub.4).sub.2 MoO.sub.2 S.sub.2 (9.0 grams in 100 ml of distilled water), which compound was prepared accordingly to procedure A. The reaction mixture was agitated for one hour at room temperature after complete addition of the ZnCl.sub.2 solution. A black solid was collected on a filter, washed twice with distilled water and dried at 110.degree. C. for three hours (6.6 grams 66% yield). X-ray diffraction study indicated that this material was amorphous.

Calculated for ZnMoO.sub.2 S.sub.2.3H.sub.2 O: Mo, 30.8; S, 20.6; Zn, 21.0. Found: Mo, 29.8; S, 23.4; Zn, 23.9.

An aqueous solution of 4.4 grams of ZnCl.sub.2 in 30 ml of distilled water was slowly added to a solution of 15.4 grams of Cs.sub.2 (MoOS.sub.3), which was prepared according to procedure B, in 100 ml of distilled water at room temperature resulting in precipitation of a brown solid. The reaction mixture was refluxed for 1.5 hours and filtered. The solid product was washed several times with distilled water and dried at 105.degree. C. for three hours. The gray, solid product (10.2 grams) was amorphous as determined by X-ray diffraction.

Calculated for ZnMoOS.sub.3.3H.sub.2 O: Mo, 29.3; S, 29.3; Zn, 19.9. Found: Mo, 30.9; S, 29.9; Zn, 23.4.

A solution of 19.8 grams of CeCl.sub.3.7H.sub.2 O in 82 ml of distilled water and a solution of 20.7 grams of (NH.sub.4)MoS.sub.4 in 152 ml of distilled water were added simultaneously to a flask under a nitrogen atmosphere. The resulting reaction mixture was refluxed for 4.5 hours with agitation and was then allowed to cool to room temperature. A brown solid was isolated by filtration and washed with distilled water, acetone and CCl.sub.4, respectively. The solid product was dried at 95.degree. C. for 12 hours following which it was found to weight 25 grams. The product was found to be amorphous by X-ray diffraction. A sample of the hydrated product was heated at 110.degree. C. for 20 hours and then at 144.degree. C. for 30 minutes, resulting in 2.4% and zero percent weight reduction, respectively. This would indicate that complete dehydration below 144.degree. C. is difficult.

Calculated for Ce.sub.2 (MoO.sub.1.2 S.sub.2.8).sub.3.6H.sub.2 O: Ce, 28.2; Mo, 28.0; S, 27.1 (10.9% H.sub.2 O). Found: Ce, 30.3; Mo, 28.3; S, 26.3.

A solution of 9.3 grams of CeCl.sub.3.7H.sub.2 O in 36 ml of distilled water was added dropwise to a hot solution of Cs.sub.2 MoOS.sub.3, which was prepared according to procedure B, (17.7 grams in 150 ml of distilled water). The reaction mixture was refluxed for 1.5 hours after complete addition of the cerium chloride solution. The dark brown solid which deposited was isolated by filtration and washed with distilled water and acetone, respectively. The solid product was dried at 100.degree. C. for six hours (dry weight=10.1 grams).

Calculated for Ce.sub.2 (MoOS.sub.3).sub.3 : Ce, 31.0; Mo, 31.8. Found: Ce, 31.7; Mo, 28.0.

A solution of (NH.sub.4).sub.2 MoS.sub.4 (10.3 grams dissolved in 100 ml distilled water) was combined with a solution containing 3.85 grams Sb.sub.2 O.sub.3 and 46.5 grams 45% by weight KOH. The resulting solution was chilled below 5.degree. C. and was added dropwise with hydrochloric acid solution (82 grams 37% by weight HCl diluted with 70 ml distilled water) under a nitrogen atmosphere at a temperature between 5.degree. and 13.degree. C. with agitation. A dark solid was deposited at the end of the addition of hydrochloric acid (pH 1-2). The solid was isolated by filtration and washed with distilled water, 95% EtOH and CCl.sub.4, respectively. After drying under vacuum, a dark gray solid (13.2 grams) was obtained.

Calculated for Sb.sub.2 (MoOS.sub.3).sub.3 : S, 33.2; Mo, 33.1; Sb, 28.0. Found: S, 35.3; Mo, 29.3; Sb, 27.9.

Lubricant compositions were prepared by mixing 5% by weight of the zinc complexes prepared by procedures C and D with lithium grease. Compositions containing the zinc complexes which were partially dehydrated were also prepared. The compositions were tested in comparison to both a lithium grease control and a lithium grease which contained 5% by weight of molybdenum disulfide as set out in Table I.

Lubricant compositions were prepared by mixing 5% by weight of the cerium complex prepared by procedure E with both lithium and Al complex greases and by mixing 5% by weight of the antimony complex prepared by procedure F with lithium. These compositions were tested in comparison to both grease controls without additives and those containing 5% by weight of molybdenum disulfide as set out in Table II.

Tables I and II list the weld points, load wear indices, and wear scar diameters of the cesium and zinc oxythiomolybdate containing lubricants. As shown in Tables I and II, the superior lubricating properties, including extreme pressure and antiwear characteristics of these complex metal chalcogenides in greases, when compared to molybdenum disulfide, was demonstrated in the Shell Four Ball EP and wear testers using two different steels, 52100 tool steel and stainless steel 440. The results also show that the outstanding antiwear characteristics of the hydrated zinc samples were not adversely affected by partial dehydration at 350.degree. C.

In order to illustrate the effect of using different amounts of additive on the lubricating properties, lithium grease lubricant compositions were prepared and tested which contained, by weight, 0.1, 0.5, 1 and 3% of the cerium complex used in Example 3. The test results obtained using the compositions are shown in Table III.

Heretofore, there have been severe limitations placed on the use of corrosion-resistant alloys, such as stainless steels, because of their inferior antiwear properties. This is because very few lubricant additives exhibit good compatibility with these alloys. One of the outstanding features of the composition and process of this invention is the superior antiwear properties for various steels and alloys, particularly corrosion-resistant alloys like stainless steel 440.