GB1603585A - Lubricants containing certain inorganic sulphides or selenides - Google Patents

Description

(54) LUBRICANTS CONTAINING CERTAIN INORGANIC SULFIDES OR SELENIDES (71) We, EXXON RESEARCH AND ENGINEERING COMPANY, a Corporation duly organised and existing under the laws of the State of Delaware, United States of America, of Linden, New Jersey, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to lubricants containing certain inorganic sulfides or selenides.

S. Soled and A. Wold in "Crystal Growth and Characterization of In2ss PS3", Mat. Res.

Bull. Vol. 11, pg. 657-662, 1976, Pergamon Press, Inc., discuss in their introduction a number of mixed anion rich pnictide compounds of a metal and a chalcogen. They report the work of W. Klingen, Dissertation, Universitat Hohenheim, Germany, 1969, dealing with the crystal growth of the compounds M"PX3 (with M = Fe, Co, Ni, Zn, Mn, Cd, Sn, Hg or Pb; X=S or Se) by means of chemical vapor transport. They go on to indicate that these materials are structurally related to the layer compounds CdI2 and CdCl2 and contain close packed sulfur layers with every other interlayer filled with an ordered arrangement of metal atoms and sigma-bonded phosphorus-phosphorus pairs. The metal atoms are located in octahedral interstices and each phosphorus atom is bonded in a distorted tetrahedron to three sulfur and one phosphorus atom. Because of the large anion-anion interlayers that remain empty (with a typical sulfur-sulfur interplanar distance of 3.4 ), these compounds exhibit easy cleavage parallel to the crystal faces and exhibit lubricity.

In SLE Transactions, 14, 62, (1970) by Jamison and Cosgrove, the lubricating characteristics of a number of layered transition metal disulfides and diselenides were measured. The coefficient of friction was determined using a ball on flat type test apparatus loaded to 250g force. The static wear member was a 3/8 inch steel sphere. The lubricants were hand burnished onto a brass disc which acted as the dynamic wear member.

For the layered transition metal compounds which were studied, three types of lubricating behavior were observed. Some materials did not form adherent films; others did form films but could not support a sliding load; yet others formed films which could support heavy sliding loads. This clearly demonstrates that not all layered materials and more particularly not all layered sulfides are effective under load-bearing conditions.

According to the present invention there is provided a lubricant comprising a lubricating oil or grease and at least one material of the formula MXY3 wherein M is divalent and is selected from Mg, V, Mn, Fe, Co, Ni, Zn, Cd, Sn, Pb and a mixture of two or more thereof, X is phosphorus, arsenic, antimony or mixtures thereof and Y is sulfur, selenium or a mixture thereof.

M is preferably Fe, Zn, or a mixture thereof; Zn being most preferred. X is preferably phosphorus, arsenic, or a mixture thereof; phosphorus being most preferred. Y is preferably sulfur.

The materials may be di- or poly mixed cation or anion solid solutions, that is, the material may include more than one metal and/or more than one chalcogen, for example Znl-4FeqPs3 0 S q S 1 FePSe3~zSz 0 S Z S 3 Zn~qFe,lPSe3~zSz 0 S Z S 3 Such mixed metal and/or mixed chalcogen materials are included within the scope of the invention. In general, preferred materials are ZnPS3, FePS3, and PbPS3.

The said materials MXY3, may be prepared by any number of methods known in the art.

For example, by the direct reaction of the elements in evacuated scalcd silica tube resulting in the formation of polycrystalline materials.

In the embodiment of the invention in which the lubricant includes a lubricating oil then, preferably, the lubricant is a suspension in the lubricating oil of the MXY3 material which has been reduced to a fine particle size by chemical or mechanical means. Briefly, this technique involves dispersing the MXY3 material in a suitable medium such as a small volume of natural or synthetic oil to which has preferably been added a small amount of a surface active dispersing agent. This is then added to the lubricating oil as an additive in suspension.

In the embodiment of the invention in which the lubricant includes a grease, then the finely divided MXY3 material can be directly added and intimately mixed, as by milling.

Normally from 0.1 to 20 wt %, preferably 1 to 5 wt %, of the lubricating component MXY3 will be present in the lubricating oil or lubricating grease.

Included are greases wherein lubricating oil is thickened with salts, soaps, soap-salt or mixed salt complexes, polymeric thickeners (e.g. polymers of Q to C4 monoolefins of 10,000 to 200,000 Staudinger molecular weight such as polyethylene) and inorganic thickeners (e.g. clay, carbon black, silica gel). However, the method of the invention is of particular value in cases where the grease is thickened with a metal soap other than sodium, and particularly where the metal is polyvalent, for example an alkaline earth metal such as calcium, or aluminum.

Generally, the greases will comprise a major amount of either a synthetic or natural lubricating oil, thickened with about 3 to 49 wt. percent, usually 20 to 45 wt. percent, of a thickener. In the case of soap-salt and mixed-salt thickeners, the thickener is usually formed by co-neutralization in oil, by metal base, while heating to dehydrate or remove alcohol (if an alcoholate is used in the metal base) of various mixtures of high molecular weight carboxylic acids, e.g. fatty acids and/or intermediate molecular weight carboxylic acids, e.g.

fatty or aromatic acids, with low molecular weight carboxylic, e.g. fatty acids.

The high molecular weight carboxylic acids useful for forming soap, soap-salt and mixed-salt thickeners include naturally occurring or synthetic substituted and unsubstituted saturated and unsaturated, mixed or unmixed fatty acids having 14 to 30, e.g., 16 to 22, carbon atoms per molecule. Examples of such acids include stearic, hydroxy stearic, such as 12-hydroxy stearic, dihydroxy stearic, polyhydroxy stearic and other saturated hydroxy fatty acids, arachidic, oleic, ricinoleic, hydrogenated fish oil, tallow acids.

Intermediate molecular weight carboxylic fatty acids include those aliphatic, aromatic, alkaryl, etc., saturated, unsubstituted monocarboxylic acids containing 7 to 12 carbon atoms per molecule, e.g., capric, lauric, caprylic, nonanoic, benzoic acid.

Low molecular weight fatty acids include saturated and unsaturated, substituted and unsubstituted, aliphatic carboxylic acids having 1 to 6 carbon atoms. These acids include fatty acids such as formic, acetic, propionic. Acetic acid or its anhydride is preferred.

Metal bases which are frequently used to neutralize the above acids are the hydroxides, oxides, carbonates or alcoholates of alkali metals (e.g. lithium and sodium) or of alkaline earth metals (e.g., calcium, magnesium, strontium and barium) or other polyvalent metals commonly used in grease making, e.g. aluminium. One grease thickener which may be employed is an aluminium complex of C14 to C30 fatty acid and benzoic acid.

Various other additives may also be added to the lubricating composition (e.g. 0.1 to 10.0 wt. percent based on the total weight of the composition) for example, oxidation inhibitors such as phenyl-alpha-naphthylamine; tackiness agents such as polyisobutylene; stabilizers such as aluminium hydroxy stearate.

The lubricating oil employed as such or to produce lubricating grease compositions of this invention may be conventional natural oils as well as synthetic lubricating oils, although the mineral lubricating oils are preferred. The synthetic oils include synthetic lubricating oils having a viscosity of at least 30 SSU at 1000F. such as esters of monobasic acids (e.g. ester of C3 OXO alcohol with C8 Oxo acid, ester of Cí3 Oxo alcohol with octanoic acid esters of dibasic acids (e.g. di-2-ethyl-hexyl sebacate, dinonyl adipate) esters of glycols (e.g. C13 Oxo acid diester of tetraethylene glycol) complex esters (e.g. the complex ester formed by reacting 1 mole of sebacic acid with 2 moles of tetraethylene glycol and 2 moles of 2-ethyl-hexanoic acid, complex ester formed by reacting 1 mole of tetraethylene glycol with 2 moles of sebacic acid and 2 moles of 2-ethylhexanol, complex ester formed by reacting together 1 mole of azelaic acid, 1 mole of tetraethylene glycol, 1 mole of C8 Oxo alcohol, and 1 mole of C8 Oxo acid), esters of phosphoric acid (e.g., the ester formed by contacting 3 moles of the monomethyl ether of ethylene glycol with 1 mole of phosphorus oxychloride), halocarbon oils (e.g. the polymer of chlorotrifluorethylene containing 12 recurring units of chlorotrifluoroethylene , alkylpolysiloxanes (e.g. methyl polysiloxanes, ethyl polysiloxanes methyl phenyl polysiloxanes, ethyl phenyl polysiloxanes), sulfite esters (e.g. ester formed by reacting 1 mole of sulfur oxychloride with 2 moles of the methyl ether ot ethylene glycol), carbonates (e.g. the carbonate formed by reacting C8 Oxo alcohol with ethyl carbonate to form a half ester and reacting this half ester with tetraethylene glycol), mercaptals (e.g. the mercaptal formed by reacting 2-ethyl-hexyl mercaptan with formaldehyde), formals (e.g., the formal formed by C13 Oxo alcohol with formaldehyde), polyglycol type synthetic oils (e.g., the compounds formed by condensing butyl alcohol with 14 units of propylene oxide), or mixtures of any of the above in any proportions. Quite generally the mineral or synthetic oils should have a viscosity within the range of 35 to 200 SSU at 210 F and flash points of 350" to 600" F. Lubricating oils having a viscosity index of 100 or higher may be employed.

According to another aspect, the present invention provides a method of lubricating contacting surfaces which comprises employing a lubricant comprising a lubricating oil or grease and at least one material MXY3 herein defined.

We have found that the said materials MXY3 exhibit remarkable stability over the temperature range 21"C to 450"C (especially from 310 C to 450"C and notably 400-450"C) under a variety of conditions ranging from reducing to inert to oxidizing.

By using such materials, wear can be greatly reduced since they resist breakdown due to atmosphere and temperature conditions particularly oxidation and high temperature decomposition. Consequently, these materials are superior lubricant inorganic components to those known in the art, such as MoS2, which deteriorate in oxidizing atmospheres at relatively low temperatures and ultimately permit high friction and damage to the surfaces they were meant to protect, the damage being recognized as increased wear, galling, abrasion, scoring, corrosion.

In order to illustrate the temperature limit above which thermal decomposition commences, some materials MXY3 were studied under (A) thermal decomposition in inert atmosphere (argon), (B) oxidising conditions and (C) reducing conditions. The temperature at which decomposition or reaction starts is indicated in each case as "T min". The temperature at which decomposition or reaction is complete is shown under the arrow in each case. T min was determined from thermal gravimetric experiments. X-ray analysis was used to identify the end product.

A. Thermal Decomposition

(x + y = 1) Twin. = 450"C

Tmin. = 590"C B. Oxidation

C. Reduction

(x + y = 1) Twin. = 450"C

In addition to the chemical stability of the MPS3 materials at elevated temperatures, their compatibility with other chemicals has also been tested. These materials are stable to, that is do not react with and are not dissolved by, H2O, CS2, and hydrocarbons such as pentane, heptane, cyclohexane, benzene, xylene and toluene. In addition, other organics such as methanol, ethanol, diethyl ether, acetone and trichloromethane neither react with nor dissolve ZnPS3 or FePS3. However, ZnPS3 and FePS3 react with strong acids and bases (for example HCI, HNO3, CH3COOH, KOH, NaOH). The MPS3 materials also react with Lewis bases such as ammonia and pyridine.

The stability of the MPS3 materials in the presence of hydrocarbons is an important feature necessary for the synthesis of lubricating oil and grease dispersions and goes to enhance the desirability of these MXY3 compounds as additives.

Example I 4g of ZnPS3, FePS3 and MoS2 were added respectively to 96g of an aluminium complex soap-salt grease made from the following components: 90 g Animal Fatty Acid 30 g Benzoic Acid 50 g Kolate (aluminium alcoholate, isopropyl) 1742 g Coray* 80/50 (unextracted naphthenic mineral lubricating oil) 6 g UOP* 225 (commercial anti-oxidant) * The words "CORAY" and "UOP" are registered Trade Marks.

The grease was prepared by heating the mixture of acids and alcoholate in the oil, with the removal of alcohol, to form the complex of the aluminium with the fatty acid and benzoic acid, and adding the anti-oxidant. The test materials, i.e. the ZnPS3, FePS3, and MoS2 were mixed respectively into the grease components at room temperature and the resulting formulations were milled so as to mix the solid component uniformly in the grease. In addition, two standard extreme pressure formulations, base grease + 2% Elco (registered Trade Mark) 114 (zinc dialkyl dithiophosphate) and base grease + 3% tricalcium phosphate + 1% sulfurized polybutene were formulated and milled. Each grease formulation was subsequently tested tor extreme pressure properties following the reapproved 1974 ASTM procedure for "Measurement of Extreme-pressure properties of lubricating greases (Four Ball Method)" (Designation D 2596-69). For the base grease and for each formulation the wear scar diameter (mm) was measured as a function of the applied load (Kg). The last non-seizure load and the weld point were recorded and the standard load wear index was calculated. Table II shows the results for these tests.

TABLE II Results of Four Ball Extreme Pressure Tests (ASTM D 2596-69) Load Sample Description ~ Wear Index Base Grease 20 Base Grease + 2% Elco* 114 25 Base Grease + 3% Tricalciumphosphate 33 1% Sulfurized polybutene Base Grease + 4% MoS2 37 Base Grease + 4% FePS3 39 Base Grease + 4% ZnPS3 44 * The word "ELCO" is a registered Trade Mark.

From these data we see that addition of ZnPS3 or FePS3 to an aluminium complex soap grease improves the extreme pressure characteristics relative to the base grease and also with respect to standard extreme pressure formulations. In addition the performance of the grease with 4% ZnPS3 or FePS3 is superior to that found for a grease formulated with an equivalent amount of the well-known solid lubricant MoS2.

Example II ZnPS3 was added, 4%, 2% and 1% by weight, to an aluminium complex soap grease prepared as in Example I. The resulting grease formulations were milled to disperse the solid metal phosphorous trisulfide throughout the grease matrix. Each of these formulations along with the base grease were evaluated using the standard ASTM D 2596-69 and ASTM D 2509-73 test procedures. The load wear index and the Timken (the word "TIMKEN" is a registered Trade Mark) pass designation given in Table III show the effectiveness of ZnPS3 as an extreme pressure additive even when this material is present as only a 1% by weight additive. These greases were not compounded with finely divided particulates and are thus very crude test combinations.

TABLE III Results of Extreme Pressure Test for an Aluminium Complex Soap Grease-ZnPS3 Grease Formulations Load Wear Timken* Sample Designation Index (Pass/Fail) Base Grease 25.6 Not Tested Base Grease + 4% ZnPS3 47.6 Pass Base Grease + 2% ZnPS3 43.8 Pass Base Grease + 1% ZnPS3 34.3 Pass * The word "TIMKEN" is a registered Trade Mark.

WHAT WE CLAIM IS: 1. A lubricant comprising a lubricating oil or grease and at least one material of the formula MXY3 wherein M is divalent and is selected from Mg, V, Mn, Fe, Co, Ni, Zn, Cd, Sn, Pb and a mixture of two or more thereof, X is phosphorus, arsenic, antimony or mixtures thereof and Y is sulfur, selenium or a mixture thereof.

2. A lubricant as claimed in claim 1, wherein M is Fe, Zn, Pb or a mixture of two or all of these.

3. A lubricant as claimed in claim 1 or claim 2, wherein X is phosphorus.

4. A lubricant as claimed in any preceding claim, wherein Y is sulfur.

5. A lubricant as claimed in claim 1, in which the said material is of the formula Znl~qFe PS3, where 06qua1.

6. Lubricant as claimed in any preceding claim, wherein the said material is present in a lubricating oil.

7. A lubricant as claimed in any one of claims 1 to 5, wherein the said material is present in a lubricating grease.

8. A lubricant as claimed in claim 7, wherein the grease thickener is a polyvalent metal salt of one or more carboxylic acids.

9. A lubricant as claimed in claim 8, wherein the grease contains as thickener an aluminium complex of C14 to C30 fatty acid and benzoic acid.

10. A lubricant as claimed in any preceding claim comprising a major proportion by wt.

of the lubricating oil or grease and from 0.1 to 20 wt % of the said lubricating component.

11. A lubricant as claimed in claim 1 and substantially as herein described.

12. A lubricant as claimed in claim 1 and substantially as herein described with reference to Example I or Example II.

13. A method of lubricating contacting surfaces, which comprises employing a lubricant defined in any preceding claim.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE III Results of Extreme Pressure Test for an Aluminium Complex Soap Grease-ZnPS3 Grease Formulations Load Wear Timken* Sample Designation Index (Pass/Fail) Base Grease 25.6 Not Tested Base Grease + 4% ZnPS3 47.6 Pass Base Grease + 2% ZnPS3 43.8 Pass Base Grease + 1% ZnPS3 34.3 Pass * The word "TIMKEN" is a registered Trade Mark. WHAT WE CLAIM IS:

1. A lubricant comprising a lubricating oil or grease and at least one material of the formula MXY3 wherein M is divalent and is selected from Mg, V, Mn, Fe, Co, Ni, Zn, Cd, Sn, Pb and a mixture of two or more thereof, X is phosphorus, arsenic, antimony or mixtures thereof and Y is sulfur, selenium or a mixture thereof.

2. A lubricant as claimed in claim 1, wherein M is Fe, Zn, Pb or a mixture of two or all of these.

3. A lubricant as claimed in claim 1 or claim 2, wherein X is phosphorus.

4. A lubricant as claimed in any preceding claim, wherein Y is sulfur.

5. A lubricant as claimed in claim 1, in which the said material is of the formula Znl~qFe PS3, where 06qua1.

6. Lubricant as claimed in any preceding claim, wherein the said material is present in a lubricating oil.

7. A lubricant as claimed in any one of claims 1 to 5, wherein the said material is present in a lubricating grease.

8. A lubricant as claimed in claim 7, wherein the grease thickener is a polyvalent metal salt of one or more carboxylic acids.

9. A lubricant as claimed in claim 8, wherein the grease contains as thickener an aluminium complex of C14 to C30 fatty acid and benzoic acid.

10. A lubricant as claimed in any preceding claim comprising a major proportion by wt.

of the lubricating oil or grease and from 0.1 to 20 wt % of the said lubricating component.

11. A lubricant as claimed in claim 1 and substantially as herein described.

12. A lubricant as claimed in claim 1 and substantially as herein described with reference to Example I or Example II.

13. A method of lubricating contacting surfaces, which comprises employing a lubricant defined in any preceding claim.