US3532623A - Oleophilic metals - Google Patents

Description

3,532,623 OLEOPHILIC METALS Aleksander Jerzy Groszek, London, England, assignor to The British Petroleum Company Limited, London, England No Drawing. Filed Mar. 5, 1969, Ser. No. 804,667 Claims priority, application Great Britain, Mar. 7, 1968, 11,109/ 68 Int. Cl. C10m /02 US. Cl. 25226 3 Claims ABSTRACT OF THE DISCLOSURE Metal flakes having a high surface area of at least 1 square metre per gram produced by grinding metals in an organic liquid can thicken lubricating oils to greases.

This invention relates to compositions containing metal flakes more particularly it relates to liquids having metal flakes dispersed therein.

1 have now found that compositions incorporating metal flakes, and which have a high surface energy, high surface area and low bulk density, have many useful properties.

The present invention provides a composition comprising a liquid dispersion medium having dispersed therein metal flakes having a surface energy of at least 0.01 calorie per gram, a surface area of at least 1 square metre per gram and a bulk density of less than 1 gram per cc.

The metal flakes which are useful in the present invention can be prepared by grinding a metal in an organic liquid (hereinafter referred to as the organic grinding liquid) in the presence of a grinding aid such as a loadcarrying additive for lubricants. Preferably a high energy mill such as a vibration ball mill of vibrational amplitude of at least 2 mm. and a vibration frequency of at least 500 cycles a minute is used.

The organic liquids used as the grinding medium include hydrocarbons especially n-heptane, iso-octane, cyclohexane, toluene, hexadecane or a hydrocarbon fraction obtained by the distillation of petroleum. Other liquids which can be used include most volatile oxygen-, halogen-, nitrogen-, and sulphur-containing liquids. Preferably the grinding liquids have a surface tension less than 72 dynes/ cm. more preferably less than 45 dynes/cm. at 25 C. The viscosity of the liquid at the grinding temperature must be sufliciently low to enable the grinding action to be sufficiently energetic to produce a metal powder having the desired surface energy, surface area and bulk density, for this reason liquids with a viscosity of less than 30 centistokes, more preferably less than 3 centistokes and most preferably less than 1 centistoke at 100 F. are preferred.

By grinding aid is meant a compound which facilitates grinding and is selected from load-carrying additives for lubricants, fatty acids, fatty acid esters and fatty alcohols.

The grinding liquid can contain any conventional loadcarrying additive for lubricants. Lubricant load-carrying additives are usually compounds containing one or more elements of Groups 5, 6 or 7 of the Periodic Table especially nitrogen, phosphorus, sulphur and chlorine. The grinding liquids may also contain, as a grinding aid, a fatty alcohol, fatty acid or ester thereof either in addition to the load-carrying additive or in its place. In general the better the lubricating activity of the additive or acid on the unground metal the more effective it will be in the grinding process. The preferred load-carrying additive is carbon tetra-chloride and the preferred fatty acids are stearic acid, palmitic acid or their vinyl esters. Cetyl alcohol may also be used.

Suitable metals which can be used in the present invensates mm tion include the transition metals, especially iron, aluminium, copper, zinc, tin and lead. Alloys such as cast iron, steel and brass may also be used.

The grinding preferably takes place in the substantial absence of air and more preferably the metal is below the surface of the grinding liquid for the duration of the grinding.

Preferably the metal flakes used in the present invention have a surface energy of at least 0.05 calorie per gram, a surface area of at least 2 square metres per gram and a bulk density of less than 0.5 gram per cc. In some cases surface energies of more than 10 calories per gram and as high as calories per gram can be obtained.

The surface energy of the metal flakes can be determined using the flow micro-calorimeter as described in Chemistry and Industry March 20, 1965, pp. 482-489, using n-butanol adsorbed from n-heptane.

The high surface energy of the metal flakes used in the present invention enables stable dispersions in liquids to be formed, these dispersions have a long life with little settling out.

The dispersion medium is hydrocarbon, mineral or synthetic base oil, silicone fluid or any other liquid which does not react with the metal flakes.

The amount of metal dispersed in the liquid depends on the use to which the dispersion is to be put, but is preferably 130% by wt. However if the liquid is a lubricating oil, a grease composition is formed if a sufiicient quantity of the metal flakes are dispersed in the oil. For forming a grease composition from 10% wt. to 25% of the high energy, metal flakes are usually dispersed in a mineral or synthetic base oil.

The lubricating base oil, may be a mineral or synthetic oil. Suitable mineral oils are refined mineral oils obtained from petroleum, for example, those having a viscosity at 210 F. within the range from 2 to 50 centistokes, preferably 4 to 40 centistokes.

Synthetic lubricating oils include organic esters, polyglycol ethers, polyphenyl ethers, fluorinated hydrocarbons, silicate esters, silicone oils and mixtures thereof.

The most important class of synthetic oils are the organic liquid polyesters, particularly the neutral polyesters, having a viscosity at 210 F. within the range from 1 to 30 centistokes. The expression polyester is used to mean esters having at least tWo ester linkages per molecule. The expression neutral is used to mean a fully esterified product. Examples of suitable polyesters include liquid diesters of aliphatic dicarboxylic acids and monohydric alcohols, such as, for example, dioctyl sebacate, dinonyl sebacate, octyl nonyl sebacate, and the corresponding azelates and adipates; liquid diesters of aliphatic dicarboxylic acids and phenols and more complex polyesters.

The finely divided metal powder can be incorporated into a grease by a number of methods. It is preferred to incorporate the finely divided metal powder into a grease, immediately after grinding. However, if the finely divided metal powder is prepared some time before incorporation into the grease, it is preferred to store the finely divided metal powder in an air-tight container to prevent deterioration.

The slurry of metal flakes produced in the grinding process can be converted into a grease by, for example:

(a) The grinding liquid is filtered off. The resulting filter cake is ground by, for example, feeding the cake through a colloid mill and stirring the resulting powder into the oil. The resulting grease is finished by colloid milling.

(b) The grinding liquid is boiled off rapidly to avoid the formation of a metal powder cake and the resulting 3 powder is stirred into the oil and the grease finished by colloid milling.

(c) Oil is added to the slurry of finely divided metal powder and the grinding liquid distilled off.

((1) Oil is added to the slurry of finely divided metal powder and the mixture circulated through a homogeniser (for example, of the Manton-Gaulic type) so that temperatures up to or exceeding 140 C. are produced. The temperature must be high enough to drive off the grinding liquid.

(e) The metal might also be ground directly in the base oil for the grease. For example, a low boiling point, low viscosity, low surface tension mineral lubricating oil with a viscosity up to 600 centistokes at 100 F. (38 C.) can be used. Elevated temperatures up to 400 C. can be used during the grinding.

Methods (d) and (e) are particularly preferred. In general, the finely divided metal powders can be incorporated into the base oil either at ambient temperatures or, if desired, at elevated temperatures, for example, up to 400 C.

are nearly filled with inch diameter hardened steel balls. The mill is fitted with a Mr horsepower electric motor and the oscillation can be adjusted from 1 to 4 mm. In operation, each cylinder was filled completely with n-heptane containing dissolved therein the lubricating additive and steel balls and from 10 to 50 grams of metal powder of from 50 to 400 British Standard mesh were added. The ends were then sealed with metal caps fitted with rubber washers and grinding carried out at an oscillation of 4 mm. and a frequency 10f 3000 vibrations per minute. After grinding the balls were sieved from the slurry of metal powder and nheptane and lubricating additive and the treated metal powder recovered by filtration, washing and drying.

Th metal powders were stirred into a 160/95 mineral base oil to form a grease which contained by weight of the metal.

The base oil used had a viscosity of 160 Redwood No. 1 secs. at 140 F. and a viscosity index of 95.

The properties of these greases are shown in the following table.

Wt. 01 Surface Surface grinding energy 1 area, Worked I additive, cals. metres Bulk penetration Unworkcd Metal Grinding additive percent wt. per gram gram density 60 strokes penetration Steel Stearie acid. 5 106 18 0. 19 223 200 Aluminum Palmitie acid 5 0. 12 1 0. 19 324 298 1 Heat of inter action of n-butanol, measured without removing any absorbed grinding fluid.

The greases according to the invention have remarkably high Drop Points. When their drop points are measured according to the IP or ASTM standard methods, they are found to be above 400 C.; such greases are described as infusible and are difficult to produce by conventional methods. By using carefully selected base oils, for example, synthetic oils with high oxidation and thermal stability, greases having a unique combination of properties can be produced.

In certain circumstances it may be advantageous to add dispersants to the metal either before grinding or after grinding. In this way the dispersion of the finely divided metal powders may be aided. Viscosity index improvers, metal deactivators, anti-corrosion agents, anti-oxidants, etc., can also be added to the greases of the invention.

It has been found that the dispersions of the present invention possess load-carrying properties, and that dispersion of metal flakes in lubricating oils improve the load-carrying behaviour of the oils.

Liquids containing ferromagnetic flakes have properties which differ in some respects from liquids containing non-ferromagnetic flakes. Dispersions of iron flakes in a liquid render the whole liquid susceptable to magnetic fields. Thus it is possible to move the bulk of the liquid by magnetic forces. This is also true of greases thickened by iron flakes. Grease thickened by iron flakes are also electrically conductive. These properties of dispersions of iron flakes are very useful in electric power systems, transmission devices, pumps and non-mechanical valves.

Greases thickened by iron flakes also harden upon working in contrast to ordinary greases. Thus the values for penetration of the grease decrease upon working.

The dispersions of other metals in organic liquids are useful in electrostatic applications such as in control mechanisms, such as valves.

EXAMPLE Various metals were ground in n-heptane containing various lubricating additives using a Megapact mill manufactured by Pilamec Limited.

In this mill the grinding chambers are steel cylinders of 1% inches internal diameter by 15 inches long and The grease formed by the steel flakes had a specific resistance of 45 ohms/cm.

When this grease was placed in a magnetic field the grease hardened and stiffened.

Dispersions were obtained by dispersing the metal flakes in n-heptane and leaving them undisturbed for 24 hours. The suspensions were black in colour and contained 5% by weight of the flakes. No settling out was observed after this time.

When a magnetic field was applied to the suspension containing iron flakes the whole bulk of the liquid was affected and its shape was altered in response to the magnetic field. There was no separation of the iron flakes under the influence of the magnetic field.

It is very surprising that the metal flakes thicken the oils to greases, and that the liquids containing iron flakes should be rendered susceptible to magnetic fields throughout their bulk.

What I claim is:

1. A lubricating composition consisting of a lubricating oil containing an effective amount of oleophilic metal flakes selected from metals and alloys prepared by grinding a metal selected from metals and alloys in an organic liquid distilling below 500 C., having a viscosity below 600 centistokes at 38 C., and having a surface tension below 72 dynes/cm. at 25 C., until said metal becomes oleophilic and has a surface area of at least 1 square meter per gram.

2. The lubricating composition of claim 1 in the form of a grease.

3. The lubricating composition of claim 1 in the form of a dispersion.

References Cited UNITED STATES PATENTS 2,742,427 4/ 1956 Reiff 25226 3,180,835 4/1965 Peri 252-26 3,267,032 8/1966 Ravener 25226 3,409,549 11/1968 Freeman 25226 DANIEL E. WYMAN, Primary Exaimner I. VAUGHN, Assistant Examiner