CA2083264A1

CA2083264A1 - Lubricant composition containing spherical particles

Info

Publication number: CA2083264A1
Application number: CA002083264A
Authority: CA
Inventors: Norman L. Jacobs
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-05-16
Filing date: 1991-05-15
Publication date: 1991-11-17
Also published as: JPH05507304A; WO1991018077A1; BR9106454A; NL9001145A; EP0528909A1; EP0528909A4

Abstract

2083264 9118077 PCTABS00008 A lubricant composition comprises at least 0.1 % by weight of substantially spherical particles of a hard, abrasion-resistant and fracture-resistant, thermally stable and chemically inert material, and up to 99.9 % by weight of a supporting vehicle. The particles are preferably of silica-alumina ceramic material, and preferably have an average diameter of less than 250 µm. Lubricants are suitable for most applications, but are especially useful for conditions of high temperature and pressure.

Description

PCI/~U91 / 0020 Lubricant Co~po~ition~
This invention relates to lubricant compositions such as drilling muds and high pressure lubricants, which can be used with advantage for a variety of applications and especially for applications where extreme pressures and work loads are involved.
Lubricant compositions are materials that can be introduced between opposed solid surfaces, e.g. the surfaces of machine parts, in order to prevent these surfaces from contacting each other and to facilitate any relative motion between them as far as necessary. As a consequence, such lubricant compositions normally need to have hydrodynamic properties, i.e. the capacity of building up an internal pressure which is sufficient to balance the load on the opposed surfaces, and further friction-reducing and wear-reducing properties.
Many lubricant compositions have the form of oils and greases and can be used for a wide variety of applications. Lubricant oils may be based on petroleum derivatives, animal or vegetable oils or on synthetic materials such as polyalkylene glycols, dibasic esters, p~osphaee esters, silicones, silicate esters and the like.
Lubricant greases are combinations of such oils with thickening agents such as e.g. metal soaps, modified clays, fine silicas and the like, and/or fillers such as e.g.

asbestos, graphite, metal carbonates, hydroxides, oxides, phosphates, sul~ides and the like. Moreover, lubricant oils and grease~ may contain special additives, e.g. to resist oxidation and corrosion and to improve such properties as adhesion, ~ilm strength and resistance to water wash out.
EP 3419 discloses a lubricating composition ~or use in the i~otbermal ~orging or sizing o~ metal wor~pieces in a hot die, which comprises a vitreous component which ~uses at a temp-rature above 260C (500F), together with an inorganie abrasive component. It i5 intended that the r eUBST~TUTE S~EE-r ~CI/AU 9 1 / O 0 2 0 RECEIVED ! 7 J U N

vitreous material is a liquid at the forging temperatures used.
Other lubricant compositions have particulate solids as an essential ingredient and can be used in cases where the opposed surfaces are su~jected to extreme pressures and work loads during use. Such particulate solid lubricants may consist of inorganic compounds having laminar crystal lattices such as crystalline graphite, molybdenum disulphide and the like, other soft inorganic compounds such as lead oxide, lime, talc, bentonite and the like, soft organic compounds such as soaps, waxes and fats, soft polymers such as poly(tetrafluoroethylene) or poly(chlorofluoroethylene) and the like, or malleable metals such as aluminium, copper, lead and the like, or fracturable metals such as zinc. All these solid lubricants have in common that they are plastic, elastic, malleable or fracturable and that they are generally soft in the particular sense of having rather low yield limits to their mechanical properties, or in any case, yield limits which are lower than the forces due to pressure or work load exerted upon them during use. The particulate solid lubricants may be used as such or as dispersions in oils, even water-based vehicles.
A drilling fluid containing glass beads is disclosed in GB 1 532 922. The beads have a particle size of fro~ 44 to 88~m and a hardness o~ 5.5 on the Moh's scale. Glass beads are generally unsuitable in the present compositions ~ince they have a low compressive strength aDd tend to break up in use, leaving abrasive particles o~ glass.
Further20re the glass beads used in GB 1 532 922 have a softening point Or about 730C and they are susceptible to attacX by alXali.
The present invention now provides lubricant compositions, which are dispersiOns of solid particles in 3 5 a supporting vehicle. Contrary to the teachings o~ the prior art, ho~ever, the ~olid particles in the invented co~po~itions ar~ substantially spherical part~cles o~ a S~lTUTE S~lEET

RECEIVED l 7 J u N ~

hard, abrasion-resistant and fracture-resistant, t~ermally stable and chemically inert material. Quite surprisingly, compositions having such particles will have excellent lubricating properties under circumstances of high pressure and ~ork loads, as well as other lubricating conditions, just because the yield limits of the mechanical properties of the particles are high enough to resist the forces exerted thereon during use.
An object of the invention is therefore, to provide lo lubricant compositions which will be able to resist high forces due to pressure and work loads during use. Another object is to provide lubricant compositions that can be used in a variety of applications, including bearings and threaded connections irrespective of the existence of high pressures and work loads therein.
Tne solid particles used in the lubricant composition of the invention should be made of a hard, abrasion-resistant and fracture-resistant, thermally stable and chemically inert material, in order to withstand extreme pressure and work loads during use. Suitable particles are made of ceramic materials, although some materials of other nature may also be appropriate.
The particles used in the compositions of the invention are substantially spherical and smooth in order to reduce friction and wear during use or to participate or contribute in other ways towards the lubricating function.
The particles preferably have an average size of less than about 250 microns in diameter for practical purposes, preferably less than about 100 ~icrons and most preferably between about 1 and about 60 microns, although particles outsid- thi~ range may be used for some compositions.
It i~ preferred that the deviation from the average partiele size in a given amount of material should pref~rably be as small as possible so as to provide a unifor~ layer o~ separating and supporting material between opposed parts, irrespective of whether the particl~s occupy ST~UFE St~EET i PCrl,~u~ / 0~20 ~
RECEIVED 17 J U N l9g a s~all or large part (less than or more than 25%) of the volume of a composition.
The particles are hard, abrasion-resistant and fracture-resistant. They are not substantially distorted at high pressures, eg at 10,000 or even 25,000 psi and often over 40,000 eg up to 120,000 psi. The integrity of the particles is maintained in use, and particles effectively do not break up or chip leaving abrasive, broken material. The parti_les preferably have a hardness of at least 5.5, most preferably at least 6.5, on the Mohs scale and typically up to 8, and most suitably about 7.
Particles used in the invention are thermally stable, and will not be substantially distorted at the temperatures achieved in use. Particles which distort with either temperature or pressure are no longer spherical and will not roll and function efficiently as a lubricant.
Suitable particles preferably have a softening point of at least 750C, preferably at least 850C or even at least 1000C, and often up 1500C. Particles are effectively chemically inert, and in practice will only react under extreme conditions with very strong reagents such as concentrated hydrochloric acid.
It is preferred that the particles have an average diameter of from about 1 to 60~m, a specific gravity of from about 2 to 2.5 g/cm3, a specific surface area of from about 1.4 to 1.6 mZ/cm3, and a hardness of from about 6.5 to 8 on the Mohs scale.
Especially suitable particles are those which are manufactured and sold by Zeelan Industries Inc. of St.
Paul, 20 Minnesota, USA, under the tradename Zeeospheres.
These Zeeospheres are thick-walled hollow spheres of silica-alu~ina ceramics having a hardness of 7 on the Mohs scale, a softening point of about 1200C and a specific gravity (ASTM D-153) of between 2.4 and 2.0 g/cm3. Their 3S compressive strength is stated to be greater than 60,000 p5i (i. e. greater t~an 4, 200 kg/cm2) but may in fact be substantially higher. The Zeeospheres are available in e ~_S,,lutE SHEFr PCr/Au 9 i / O 0 2 0 .
RECEIVED i 7 J U N

several types, differing in average particle size; specific gr~vity; and specific surface area. According to manufacturer's published data, some of these types can be specified as follows:
TABLE

Zeeospheres type 200 400 600 800850 X-60 Average particle 5 size, microns4.9 6.9 9.9 27.1 55.9 2.9 Speci~ic gravity (g/cm )(AS~M D-153) 2.3 2.2 2.1 2.02.0 2.3 specifi~ s~Fface area ~m /cm) 1.521.24 1.03 0.620.18 2.31 ~ hile experiments with Zeeospheres of type 200 have given good results, other types may be used with the same or even greater advantage, depending on the lubricant composition in which they are used a~d on the application for which the composition is utilized.
The solid particles as defined above may be used in proportions of at least 0,1% by weight of the total lubri-cant composition. The upper limit will be determined by practical considerations, including the intended application of the composition, and by the nature of the supporting vehicle.
The solid particles are incorporated in a supporting vehicle which may be any petroleum-based, organic-based, silicone-based or even water-based vehicle. Pre~erred vehi-cles are those that have lubricating properties of their own, such as e.g. the well-known lubricant oils and greases.
The lubricant oils to be used as a supporting vehicle ~ay be of any conventional type and may thus be based e.g.
on petroleum derivati~es, animal or vegetable cils, or on synthetic material~, such as polyalkylene glycols, esters Or dibasic organic acids, phosphate esters, silicones, silicate ester~ and the like. The lubricant greases to be used a~ a supporting vehicle will normally be a combination -~ ~ES . 5~- U~E S~i~E .
.~

RECEIVED I 7 J U N ~9 of such oils with thickening agents, such as e g. metal soaps (salts of alkaline or alkaline earth metals with monobasic or polybasic aliphatic acids, such as sodium, lithium, barium stearates, hydroxystearates, oxalates, sebacates and the like), modified clays, fine silicas and the like, and/or fillers or additives such as e.g.
asbestos, graphite, metal carbonates, oxides, hydroxides, phos~hates, sulphates, sulfides, and the like. Such 'hickening agents, fillers and additives are normally used i0 in gelled form or in fine particulate form, as appropriate, and care should be taken that the fillers and additives are non-abrasive and will not by themselves or in combination with other substances, agglomerate to loose their fine particulate form.
1~ In the case of using a lubricant oil or grease as a supporting vehicle, the aforesaid solid particles may preferably be used in a proportion of about 50 to 60~ by weight, based on the total lubricant composition. That is, the composition may preferably comprise about 50 to 60~ by weight of particles of a hard, abrasion-resistant and fracture-resistant, thermally stable and chemically inert material, and about 40 to 50% by weight of a lubricant oil of lubricant grease.
One or more further lubricant materials may be included in the composition of the invention. Examples of suitable further lubricant materials include molybdenum disulphide, other metal sulphides, graphite, talcum, mica, fatty acid esters, halogenated olefin polymers, metal oxides, hydroxides, carbonates, phosphates, sulphates, chlorides, bromides, iodides or combinations thereof, metal stearates, ox~lates, sebacates, metal salts o~ monobasic or polybasic aromatic acids, malleable metals such as aluminium, copper and lead, or any other material compatib~e with and insoluble in the supporting vehicle.
3S Such additional materials, in rine particulate rorm should be essentially nonabrasive and should not by themselves or in combination with water or other substances agglomerate r~ STE ~ ~TE SHEET

PCr/AU 3 1 / 0 0 2 0 RECEIVED , 7 J u N l999 to loose their fine particulate form, or functionality, as appropriate.
If such additional lubricant materials are used, they are preferably present in a proportion of not less than S about 0.1~ by weight of the total composition. A proportion of about 1 to 5~ by weight will be sufficient for many purposes, and therefore is preferred. In that case, the total composition may comprise about 45 ~o 59~ by weight or particles of a hard, abrasion-resistant and fracture-resistant, thermally stable and chemically inert material,about 1 to 5% by weight of particles of another lubricant material, and about 40 toS0% by weight of a supporting vehicle.
Further, conventional additives such as corrosion inhibitors and anti-oxidants, tackifiers and wetting agents, may be incorporated in the composition, normally as a component of tbe supporting vehicle, provided that they do not significantly affect the functionality of the main ingredients in an adverse fashion.
The lubricant compositions of the present invention can be used for a wide variety of applications, and especi-ally for those cases where high pressures and work loads, and high temperatures are involved. The range of possible applications is not restricted to high work loads or high temperatures, however, and utilisation at moderate or even low work loads and moderate or low temperatures may be equally advantageous. Further, utilisation of the lubricant compositions can be made irrespective of any relative motion between the parts to which they are applied and this ~eans that the lubricant compositions of the present invention will ~unction equally well in cases of high relative speed and in cases of low relative speed between the lubricated parts where only a separating function is necessary. In conseguence thereof, the lubricant compo~itions can bo used ~or the lubrication of all machinery, including bearings, construction and mining equipment.

S~iiU~E SHEE~

PCr/AU31/G~2C

In the oil and gas production industry, special types of lubricant compositions are used for application between the male and female parts of threaded tubular connections. This is done to prevent such parts from seizing up or being welded to each other when they are screwed together and also, in many instances, to provide a fluid tight seal between them during use. Such lubricant compositions (often termed "thread compounds") should permit the threaded connections to be made up and broken out several times during the construction of oil and gas wells despite the high work loads exerted on them.
Moreover, after make-up of the threaded connections, the lubricant compositions should be capable of providing a fluid tight seal between the threaded parts, even if an oil or gas, or drilling mud or other fluid material is flowing at high pressure through the tubing or pipe so connected.
It has appeared that the lubricant compositions of the present invention are able to satisfy all these requirements. Further, in the oil and gas production industry, special types of lubricant compositions are nor~ally used for lubrication of threaded connections in a drill string of a rotary drill, connections between drill pipes themselves (rotary shouldered connections or tool joints), connections between the bottom component of a drill pipe and a drill collar, connections between a drill collar and a drill bit, and connections between any other tool or apparatus screwed in place above or below any of these. Such lubricant compositions (e.g. so-called "tool joint compounds" and "drill collar compounds") should permit drill pipes and other apparatus to be screwed together with minimum tendency for continuing make-up while drilling, there~y providin~ for conveyance of energy (torque) from pipe section to pipe section down the length of the drill string and further to the other apparatus, during this operation. ~t has appeared that the lubricant compositions of the present invention are capa~le o~
satisfying such requirements and that they can be used for .~

PCI/AI)-91 / 002 0 8 RECEIVED 1 7 J U N lggl all these different applications, including strings of pipe connected to subsurface motors.
The lubricant compositions of the invention are capable of ~eing used for applications where the term "lubricant" is not nor~ally used ~ut where a certain lubricating function is nevertheless always involved. Such applications are e.g. the use of said compositions as cooling fluids in metal working (such as e.g. cutting, pressing, drawing, honing, grinding and polishing) operations and the use of such compositions as drilling fluids or drilling muds in drilling operations, in which the supporting vehicle may be oil-based, but is preferably water-~ased. In the latter case, it is preferred to use the solid particles in a proportion of at least 5, prefera~ly 5 to 10 parts by weight of the total composition. In other words, the drilling fluid or drilling mud will comprise at least 5, preferably 5 to 10 parts by weight of particles of a hard, abrasion-resistant and fracture-resistant, thermally stable and chemically inert material, and up to 95, preferably 90 to 95 parts by weight of a conventional water-based vehicle for a drilling fluid which may include heavy-weight fillers, thickening agents, wetting agents and the like.
The invention is further illustrated by the following examples.
Example 1 Inaredients: Percentaae bv wei~t:
Zeeospheres, type 200 55 30 Lithium grease (NLGI No. 2) 42 Molybdenum disulphide 3 In this composition, which is suitable for use in bearings, the lithiu~ grease is a dispersion of 7.5 lithium 12-hydroxystearate in petroleum oil.

_.
~'J~S . ~ I iT_ ~E~ ~

PCI/AU ~ 1 / 0 0 2 0 8 RECEIVEI~ ! 7 J U N ?99~

Example 2 Inqredients:Percentaae bv weiaht:
5 Zeeospheres, type 200 s7.0 Crystalline graphite 3.0 Supporting vehicle 40.0 100. 0 Example 3 Inaredients:Percentaqe by weiqht:
Zeeospheres, type 200 57.0 Molybdenum disulphide 3.0 Suppor.ing vehicle 40.0 loo.0 In the compositions of Examples 2 and 3, the supporting vehicle will normally be a grease (e.g. a dispersion of metal soap in oil) which includes a tackifier, a wetting agent, an anti-corrosion agent, and an antioxidant. The compositions are suitable for use in threaded connections.
ExamDle 4 Inaredients:Percentaae bY weiaht:
Zeeospheres, type 20057.0 Molybdenum disulphide3 0 Supporting vehicle 40.0 100.O
In this composition, the supporting vehicle will have the same meaning as in Examples 2 or 3.
Example ~

Lubrication o~ bearinas:
Lubricant compositions comprising lOS, 20~, 30%, 40~, 50%, 55%, 57% and 60S by weight respectively Or sphere~
type 200 in the lithium grease used in Example 1 ~N~GI No.

2) were tested on Timken tapered roller bearings in a Sun S~ JTE SllEel PCT/AU 9 1 / O G 2 0 ~
R~CEIVED I 7 J U N 1g:

Oil company ~earing tester. The bearings were rotated at high speed and at temperatures deliberately intended to cause the decomposition of the petroleum-based supporting grease.
Each test ended when the bearings seized up due to thermal decomposition of the grease. The ti~e period until seizure was measured and showed a gradual increase for the range of compositions, starting with a Zeeospheres content of 10% and ending with a Zeeospheres content of 55%. The time period for compositions having 57% and 60% Zeeospheres content was equal to that of the composition having 55~
Zeeospheres content. Inspection of the bearings afterwards showed in all cases that no wear had taken place in the tests where compositions of 40% and ~ore Zeeospheres content had been used.
Another test was made with a lubricant composition comprising 3S% by weight of Zeeospheres type X-60 and 65%
by weight of lithium grease (NLGI No. 2). The result was about the same as that of the test with a composition having 55~ Zeeospheres type 200 content.
A further test was made with a lubricant composition comprising 30% by weight of Zeeospheres type 200, 3% by weight of molybdenum disulphide and 67% by weight of lithium grease (NLGI No. 2). The result was about the same as that of the test-with a composition comprising 50% by weight of Zeeospheres type 200 and 50% by weight of lithium grease (without molybdenum disulphide).
Additional tests with compositions similar to the last-mentioned composition but wherein the molybdenum di-sulphide had been substituted by an equal amount of zincoxide, zinc orthophosphate, calcium borate, and graphite respectively, gave similar results.

PCrlAIJg1 / 0020 8 RECEIVED t, J U N ~

ExamDle 6 Lubricati~n and sealina of t~readed connections.
A lubricant co~position comprising 57.0~ by weight of Zeeospheres 200, 3.0% by weight of moly~denum disulphide and 40.0% by weight of a supporting vehicle (a lithium grease together with a tackifier and a wetting agent and equivalent to the specifications of an NLGI No. 1 grease) was used to lubricate and seal threaded connections of two test specimens, each consisting of two tubes ("pin by pin pup joints") joined by an Atlas 3radford TC coupling. The coupling was of 2 and 7/8 inch outer diameter and N-80 type steel and further had metal to metal seals. The threaded connections were made up and broken out several times and the maXe-up and break-out torques applied on each occasion were graphically recorded versus time and turns. It appeared from the graphs that the make-up torques for successive make-ups were nearly identical, which indicated that the lubricant composition as used performed effectively and that the process of making up and breaking out did not damage the threads and shoulders and seals.
This was confirmed by visual inspection.
One made-up test specimen was tested ~or sealing properties by illing it with nitrogen gas at high pressure and immersing the article in a water bath. After a test period of 15.5 hours at an internal pressure o~ 12,000 psi ~a40 kg/cm2), the connection was ound to be leak-rree.
~hus, the lubricant co~position as used had no negative e~ect with respect to sealing on the connection with metal to metal seals.
Exa~Dle 7 In another test, a lubricant composition si~ilar to that in Exa~ple 6 was used to lubricate and seal the 3S threaded connect1ons Or a test specimen consisting o~ two tube- o~ 2 and 7/8 inch outer dia~eter and N-80 type steel interconnected at their ends by a coupling. The threads o~

_.~
~U3ST~ c S~cel PcllA-lJ 9 1 / 0 0 2 0 8 - RECEIVED 17 ~UH ~gl the threaded connections were non-sealing and had a leak path between male and female parts when made up. The connections were made up and broken out ten times. Upon inspection, no damage to the threads could be observed.
Sealing properties were found by im~ersing the test specimen in a water bath for 30 seconds at an internal nitrosen gas pressure of lO,000 psi (700 kg/cm2).
ExamDle 8 Lubrication and sealinq of rotarY shouldered connections.
A lubricant composition of the same type as in Example 6 was used to lubricate and seal the threaded connections of a test specimen consisting of two sections of 5.5 inch drill pipe interconnected by a rotary shouldered connection with API threads. The connections were made ùp to a recommended torque and broken out several times without damage to thread, shoulders or others parts.
In another experiment, the same connections were made up several times to an excess of 25% of the recommended torque. Again, no damage was observed.
Exam~le g Utilization in drillina muds.
A conventional drilling mud comprising 88~ by weight of water and 12% by weight of a combination of Wyoming bentonite with thickening agent and wetting agent together with alkali, which is normally satisfactory for drilling oil and gas wells in southern Texas and Louisiana to depths of about 1500 meters, was modified by the addition of Zeeospheres type 200.
In a first experiment, five parts of Zeeospheres were added to lO0 parts of drilling mud and the resulting composition was used in a drilling test on carbonaceous roc~s. A small increase in drilling dept~ was experienced.
3SIn a ~econd exper1ment, ten parts o~ Zeeofipheres were added to lO0 parts of drilling mud and it appeared that~
increa~e in drilling deptb was considerable.

__ __ . __ S~BSTI . VTE S~E~- T

PCI/AU G ~ / iJ U ~ U t RECE1VED 1 7 J U N ~

In both cases, torque on the drill pipe was maintained at substantially the same level and it appeared that the rotational speed was increased. Further, the Zeeospheres were well suspended in the fluid.
ExamDle 10 A composition si~ilar to that illustrated in example 6 was used as a lubricant for a sleeve ~earing required to sustain about 40 tons of work load in certain construction equipment. The lubricant performance was satisfactory. Upon dismantling, no wear was observed in the sleeve.
rxam~le 1 1 A composition comprising 57~ by weight of Zeeospheres type 200, 5~ by weight of zinc phosphate and 38~ of 30 aluminium complex grease (equivalent to an N~GI No. 2 grease) was used as a lubricant for furnace door hinges.
The composition functioned satisfactorily, thus enabling normal operation of the doors after an extended period of time.
COmDaratiVe ExamDle Two sets of microspheres were subjected to a number of assessments to determine their suitability for use in lubricant compositions. Zeeospheres (Zeelan Industries), Type 600 and typical glass beads (3M Co~pany) were compared.
The glass beads used had an average particle diameter of about S0 microns and a fairly narrow size distribution.
Zeeospheres type 600 have an average particle size of about lO~m, but a broader particle size distribution, with some particles up to 44~ in diameter.
The microspheres were subjected to pressure and then exanined under Scanning Electron Microscope (SEM) to obtain a measure of the compressive limits of the microspheres.
Since the particle size distribution of the Zeeospheres is broader, the load exerted on individual particles will be greater.
Typical areas of each type o~ microsphere were prepared by placing a very thin layer o the microspheres s~ 5SiSi'u~F Si~ET

PC~rAU ~ 1 / O 0 2 0 8 RECEIVE~ 1 7 J U ~ lg on a polished 5/16" diameter metal stub. These flat surfaces were machined and polished from standard hardened tool steel drill bit stock. The layers of microspheres were obtained by coating the flat stub with a very thin layer of silver paste obtained by diluting normal silver paste with methylene chloride. The thin layer of silver paste was then pressed into the microspheres to for~ a very thin layer of spheres for testing. The 5/16" diameter stub was placed in a Parr manual press in contact with another identical stub and pressure was applied. The pressure was applied very slowly initially before the final maximum pressure. The force applied to the S/16 "diameter stub was 640~. The outer 1/32 " of the stub was not affected by this force hence the total pressure applied was approximately 13,000 psi. Based on observations from scanning electron microscopic examination of these surfaces after this applied pressure, it appears that the actual contact area is about 1/2 to 1/5 of the total area of the stub. This is, of course, dependent on the surface finish of the metal and the intimate contact of the microspheres.
Based on this, the pressure applied to the microspheres is calculated as between 25,000 psi and 75,000 psi.
Other properties of the microspheres were assessed, including softening point, surface energy, structure and inertness.
Results Glass ~eadsZeeos~heres Co~pressive Strength (p-s-i) 30,000 60,000-100,000 Sortening Point (Degrees C) 589-704 1200 35 Surface Energy low ~igh Structure Amorphous Crystalline Inertness Attacked byInert to acids alkalis and alkalis Hardness 5.5 7 5~ I~S S rTl~TE SHEE~
,..... _ RECEIVEI~ 17 JUH

Glass beads will distort at lower temperatures than Zeeospheres, and will fracture at lower pressures, leaving abrasive particles of glass. The low surface energy of glass beads gives a lower resistance to break, and the amorphous structure of glass also contributes to its lower compressive strength.
Zeeospheres are inert to acids and alkalis, whereas glass beads are attacked and etched by alkalis, leaving rough, abrasive particles.

Claims

1. (amended) A lubricant composition comprising at least 0.1% by weight of substantially spherical particles of a hard, abrasion-resistant and fracture resistant, thermally stable and chemically inert material wherein the particles have a Moh hardness of at least 5.5, a softening point of at least 750°C and a size of 1 to 250µm and are not distorted under a pressure of 700kg/cm2 (10000psi), and at most 99.9% by weight of a supporting lubricant vehicle.

2. (amended) A lubricant composition as claimed in claim 1 wherein the spherical particles have an average diameter of less than 100µm and are not distorted under a pressure of 1750kg/cm2 (2500psi).

3. A lubricant composition as claimed in claims 1 or 2 wherein the particles are of silica-alumina ceramics.

4. A lubricant composition as claimed in claim 1, wherein the particles are thick-walled hollow spheres.

5. A lubricant composition as claimed in claims 1 to 4, wherein the particles have an average particle diameter of from about 1 to 60 microns, a specific gravity of from about 2 to 25 g/cm3, a specific surface area of from about 1.4 to 1.6 m2/cm3, and a Mohs hardness of from about 6.5 to 8.

6. A lubricant composition as claimed in claims 1 to 5, wherein the supporting vehicle is petroleum-based, organic-based or silicon-based vehicle.

7. A lubricant composition as claimed in claim 6, wherein said supporting vehicle is a lubricant oil or lubricant grease.

8. A lubricant composition as claimed in claims 1 to 7, comprising from about 50 to 60% by weight of the spherical particles and from about 40 to 50%

by weight of a lubricant oil or lubricant grease.

9. A lubricant composition as claimed in any preceding claim further comprising at least 0.1% by weight of particles of at least one further lubricant material.

10. A lubricant composition as claimed in claim 9. wherein the further lubricant material is chosen from molybdenum disulphide, graphite, talcum, mica and fatty acid esters.

11. A lubricant composition as claimed in claims 9 or 10 comprising from about 45 to 59% by weight of the spherical particles, from about 1 to 5% by weight of particles of at least one further lubricant material, and from about 40 to 50% by weight of a supporting vehicle.

12. Use of the lubricant composition of any of claims 1 to 11 for lubricating bearings, lubricating and sealing threaded connections and rotary shouldered connections, and lubricating construction and mining equipment.

13. Use of the lubricant composition of claim 1 as lubricants or cooling fluids in metal working operations or as a drilling fluid or mud.

14. A lubricant composition as claimed in claims 1 to 5 wherein the supporting vehicle is a water-based or an oil-based vehicle suitable for a drilling fluid or mud.

15. A lubricant composition as claimed in claim 14 adapted for use as a drilling fluid or drilling mud, and comprising at least 5 parts by weight of thespherical particles and up to 95 parts by weight of a water based supporting vehicle for a drilling fluid or mud.