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NBS

PUBLICATIONS

NBSIR 82-2545 (ONR)

Investigation of the Lubrication

Mechanisms of the Complex

Metal Sulfide, SbSbS 4

I

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Center for Materials Science

Metallurgy Division

Washington, DC 20234

October 1, 1980 - September 30, 1 98|

Annual Report

N0001 4-80- F -0031

Issued July 1 982

-QC—

100

. U5b

02-2545

1982

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Prepared for: Office of Naval Research

Department of the Navy

Arlington, VA 22217

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NBSIR 82-2545 (ONR)

INVESTIGATION OF THE LUBRICATION

MECHANISMS OF THE COMPLEX

METAL SULFIDE, SbSbS 4

L. K. Ives M. B. Peterson

J. S. Harris

P. A. Boyer

A. W. Ruff

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Measurement Laboratory

Center for Materials Science

Metallurgy Division

Washington, DC 20234

October 1, 1980 - September 30, 1981

Annual Report

N0001 4-80F-0031

Issued July 1 982

Prepared for: Office of Naval Research

Department of the Navy

Arlington, VA 22217

2 1982

U S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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TABLE OF CONTENTS

I. Introduction

II. Background

III. Test Methods and Materials

A. Pin and V-block Tests

B. Block and Ring Tests

C. Four-ball Tests

D. Ring Compression Tests

E. Three-pin on Disk Tests

F. Reciprocating Linear Sliding Tests

G. Lubricant Materials

IV. Results and Discussion

A. SbSbS4 as a Solid Lubricant

B. Confirming Four-ball Tests and Pin and V-block Load

Capacity Tests

C. Comparison of SbSbS4 with other S-containing and

Solid Lubricant Additives

D. Anti-wear Behavior of SbSbS4 as an Additive

E. Analysis of Debris and Surface Films

V. Conclusions

Acknowledgements

References

ABSTRACT

Studies have been carried out to determine certain basic properties

of the complex metal sulfide, SbSbS4, that pertain to its use as a solid

lubricant and lubricant additive material. Past research had demonstrated

that this material exhibited superior extreme pressure (EP) performance,

antiwear properties, and high temperature stability. The present research

has verified the performance under EP conditions as an additive to a

base grease. However the performance of SbSbS4 as a solid lubricant (in

the form of a powder) was not found to be effective at temperatures below

about 225 °C. It was noted though that, when used as a dry powder lubricant,

the compound did produce a thick adherent film on steel surfaces in sliding

contact. Six different types of wear and friction tests were carried out

under various conditions of load, sliding speed, contact geometry,

temperature, and time, in order to fully explore the potential of SbSbS4

as a lubricant on several different metals. In a number of cases, its

performance was compared with M0S2 and with other sulfur containing

additives in lubricants. Electron microscopy studies on film material

removed from the sliding contact surfaces have shown that the interaction

of sulfur released from SbSbS4 with the steel surface, presumably at

locally elevated temperatures, is a principal mechanism. However, the

physical characteri sti cs of the SbSbS4 film in the contact zone probably

also have a significant role in its overall performance.

I. Introduction

This report will describe results obtained in a project concerned with

evaluation and characterization of the wear properties of metal surfaces

lubricated with certain inorganic solid sulfur compounds.* Several of those

materials, such as SbSbS^, have been shown to exhibit superior extreme

pressure (EP) performance, antiwear properties, and high temperature stablility,

under laboratory test conditions (1-4). It was important in the present

work to determine more fully the conditions under which these compounds

were effective, to compare their performance with other known lubricants,

and to improve the understanding of the mechanisms by which they function.

The study thus far has concentrated on one compound, SbSbS^, antimony

thioantimonate. That material had been studied before (1-4) and was found

to possess very good EP lubricating characteristics. It was thought that

this compound could serve as a high quality solid lubricant material, and

that it might offer improved performance in bearing applications involving

metals such as stainless steels and titanium alloys. Navy requirements

for lubricants, both as additives to oils and greases, and in dry -Mlm

applications, are varied and involve a wide range of contact loads, speeds,

and environments. The development of new lubricant materials with improved

EP and other characteri sties would be of significant value in many Navy

applications, particularly if bearing maintenance intervals could be

lengthened as a result, or if more corrosion resistant metals could be

employed in bearings without compromising the wear performance. The

availability of proven, tested alternatives to presently used materials,

such as graphite and molybdenum disulfide, would also contribute to Navy

program needs

.

Commercial products are identified in this report in order to fully describe

the materials used and the testing conditions involved. Endorsement of such

materials by NBS is not implied.
The present study has examined the performance of SbSbS^ under dry

sliding conditions and as an additive to oils and to grease. Six different

tests have been carried out at temperatures from 20°C to 500°C. Several

different metallurgical combinations have been studied with wear and

friction data obtained. An important aspect of this work has been the

attempt to identify the mechanisms by which the SbSbS^ compound functions.

1 1 . Background

In 1 968 a paper by Devine (1) et al . reported on "New Sulfide Addition

Agents for Lubricant Materials." Arsenic and antimony sulfides were

added (5% by weight) to a base grease, and evaluated using the four-ball

EP test. The compounds studied significantly increased the

seizure load* and the weld load** over that measured for the base grease.

Certain sulfides (AsSbS^, AsAsS^, Sb^, and Sb^S^) increased the

weld load to greater than ^00 kg compared with 80 kg ^or the base grease

and 200 kg for a 5 % MoS^ addition. Based upon these promising results

further studies of the mixed metal sulfides were conducted by the Naval

Air Development Center (2-4). A variety of these sulfides including SbSbS^

were evaluated as grease additives using the four-ball EP test. They gave

approximately the same seizure load as obtained with MoS 9 -containi ng greases

but gave much higher weld loads. However, most of these compounds did not

*Seizure load: load in the four-ball EP test at which a rapid increase in

wear scar diameter is noted.

**Weld load: load in the four-ball EP test at which welding occurs between

the balls.

9
pass the ASTM copper corrosion test, except for the SbSbS^ compound.

That compound was also effective as a lubricant additive with stainless

steel whereas MoS^ as an additive was not. Good endurance lives were

also obtained when these compounds were used as dry film lubricants in

a phenolic binder. However, when used as dry solid lubricants they

were not as effective as MoS 9 in the press fit test where a cylindrical

pin is pressed into a bushing. Further investigations of SbSbS^ as a

grease additive were conducted by King and Asmerom (5). Using the ASTM

standard four-ball test (D2596) they showed dramatic increases in the

weld load and seizure load (Table 1) over that for the lithium base

grease (RM81) and the MoS^ additive in grease.

Other greases were studied with the same additives and showed

essentially the same effect. It was also found that only small

concentrations of SbSbS^ in the grease were needed to significantly

increase weld load capacity and that there was a strong concentration

effect (Fig. 1). These results generated considerable interest in

SbSbS^ and raised the question as to the mechanism responsible for the

enhanced performance imparted by SbSbS^.

Although a great deal of work has been reported on the behavior

of soluble additives such as sulphur, phosphorous, and chlorinecontaining molecules, there has been relatively little work reported

on solid additives other than MoS^. Gansheimer (6) investigated

solids such as inorganic phosphates, oxides, hydroxides, and sulfides.

He reported four-ball o.K. loads* on the materials shown in Table 2.

*Gansheimer (6) does not define O.K. load. However, it usually refers

to a load which is a small constant increment (e.g. 10 kg) below the

weld load.

3
Additional studies were conducted (7,8) afterward to determine the

mechanism of lubrication by such solids when added to oils and greases.

It was shown that below the seizure load, MoS^ formed a film on the

contact surfaces even though the surfaces were effectively lubricated in

boundary conditions by the oil. Above the seizure load reaction

occurred betweenthe MoS^ and the metal surface to form iron sulfide. It

was also discovered that molybdenum diffuses into the steel and hardens

the surface. The formation of Mo^C was suggested. In the case of

Zn

2

P

2 04

^ was shown that the process did not involve film formation but

rather a reaction to form FeP in the contact region. The reactions

involved can be quite complex. When Ca(0H)

2 was added to fluorosilicone

oil a reaction occurred at the metal surface to form CaF^ which was stated

to be responsible for improved lubricating properties.

Another investigator (9) added a number of different solid oxides

to mineral oil and found large increases in both the load wear index and

the weld load (Table 3). The increase in the weld load could be directly

correlated with oxide hardness: softer oxides gave higher weld loads. It

should also be noted that extremely high weld loads were obtained with

B

2 03

and Sb^, both of which are low melting (577°C and 656°C respectively)

glassy oxides. Unfortunately the authors did not define the conditions

under which the weld load was obtained so that direct comparisons with

SbSbS^ are not possible.

Thus it can be seen that when a solid is used in conjunction with a

fluid lubricant it may improve the wear behavior by two different

mechani sms

:

4
1. The solid may form a film on the surface, such as was found with

MoS ? and the oxides. This takes place primarily in the low load

region. This film reduces wear only slightly with an effective

lubricant but has a major effect on the seizure load. The softer

the film the greater the increase in seizure load that occurs.

2. The solid may participate in a reaction with the surface to form

another film. This effect is most noticable in region II at higher

loads (Fig. 2) where it significantly reduces wear and significantly

increases the weld load.

The mechanism of action of solid additives seems clear. In region II (Fig. 2)

the film that is formed prevents metal welding. The weld load is effectively

increased by replacing metal welding by film failure.

The mechanism by which a solid film increases the seizure load is

somewhat more complicated. However some guidance is available from the work

reported in reference 10 concerning the mechanism of boundary lubrication

with oil. ^rom a detailed study of the seizure process it was concluded that

failure was dependent upon the temperature reached during run-in. If the

temperature did not reach the "lubricant desorption temperature T*", low wear

would result with surface polishing. For temperatures greater than T*, local

seizure will result producing a high wear rate. Thus the seizure load is

determined by the condition T = T* where T is the actual surface temperature.

Higher seizure load will result from lower surface temperatures. The principal

means of accomplishing lower surface temperatures is to lower the friction

coefficient at the contact. In cases where friction coefficients were measured

5
(11), the highest seizure loads were found with the lowest friction additives.

Thus it can be postulated that the solid films laid down in region I

(low loads - Fig. 2) increase the seizure load by lowering friction. Almost

any soft solid could perform in this way if it remained firmly attached to

the surface. However good adhesion is difficult in the presence of surface

active lubricating molecules.

In dry contacts a large number of compounds have been found which lower

friction and prevent wear and surface damage at a rubbing contact. The general

types of solid lubricants along with examples are listed in Table 4. One

common property of all these materials is that they are relatively soft.

Many compounds which do not lubricate at room temperatures become more

effective at higher temperatures. This is illustrated in Fig. 3 from (12)

where friction coefficients for a variety of materials are plotted against

temperature. The reduction in friction is due to the lower shear strength in

the solid film at higher temperatures. The conclusion drawn from such studies

is that almost any compound will behave as a solid lubricant as the operating

temperature approaches the melting point of the compound. However to be

effective it has been shown that a layer of the solid must be -'"irmly attached

to the metal surface. Soft solids which did not adhere do not perform

well as solid lubricants.

Available data on sulfides used as solid lubricants are limited other

than for MoS ? and WS^. Some values for coefficient of friction are given in

Table 5. It can be seen that many sulfides are at least partially

6
effective as solid lubricants within a specified temperature range. An

interesting result with solid sulfide additions has been reported by

Haltner and Oliver (13). In that work 10% of a variety of metal sulfides

were added to MoS ? and films of the mixtures were then formed on steel

surfaces. The load capacity of the film was then measured. Increases

in load capacity by a factor of 20 over MoS^ alone was found for Sb^S,-.

It was suggested that the most effective additives are those which have

the lowest thermal stability. That is, a chemical interaction of the sulfide and

the metal surface was suggested. It was also stated that sulfides, especially

stannic sulfide, form stable, adherent films.

SbSbS^ is a newly developed material and many of its properties are

unknown. It can be characterized as a soft amorphous or glassy solid.

Thus it would be expected to have potential as a solid lubricant.

Glasses are particularly effective at high temperatures where they are

used as metal working lubricants (see also in Fig. 3). The temperature

range of effectiveness of SbSbS^ has not been determined yet.

One important question to be asked concerns the mechanism (deposited

film or reactive film) that applies to SbSbS^. There can be no firm

answer based upon the published literature. However it should be noted that

the primary effect of SbSbS^ according to published data is in region II

where much lower wear rates and higher weld loads are reported. Furthermore, this compound contains large quantities of sulfur which is

well known for showing strong EP effects. Thus one might suspect a

reactivity effect involving sulfur.

7
The effect of sulfur on wearing contacts has been the subject of a

large number of studies (references 14 to 20). In the work of Davey

(14-18) and the later work of Forbes (19) using soluble organic additives

the following mechanisms were proposed. At low loads (region I - Fig. 2)

the sulfur molecule is either physically or chemically adsorbed on the

steel surface of interest. The sulfur atom is attached with the chain

oriented perpendicul ar to the surface. At higher loads (region II),

cleavage of the sulfur-sulfur bonds occurs and a sulfur-metal reaction

can occur. The actual effectiveness of an organo-sul fur compound is

related to the ease of splitting the S-S bond necessary for adsorption

and the sulfur-iron interaction. Obviously the first step for reaction

to take place involves adsorption at the surface. In region II the

actual film does not appear to be pure sulfide (21) but some mixture of

metal oxide and sulfide. As the weld load is approached, a higher

percentage of oxide is found. This is understandable since Buckley (22)

has shown oxygen replaces sulfur in a metal sulfide compound. In later

work Sakurai (23) confirmed the sul fur reactivi ty role and found that an

optimum sulfur concentration existed. This optimum concentration is

that needed to give a critical film thickness for minimum wear. A

direct correlation (15) is found between wear and reactivity in region

II as shown in Fig. 4. It should be noted that the maximum load carrying

capacity is obtained with sulfur additions.

In summary a number of explanations can be proposed to account for

the effective lubrication characteristics found for SbSbS^:

8
(1) It can form an effective solid film lubricant, both dry and when

contained in a fluid lubricant.

(2) It can serve as a source of sulfur which improves both dry and

fluid lubrication especially in the high load region.

(3) Upon decomposition under EP conditions, antimony is liberated

which can act as a lubricant or which can contribute to the formation

of a lubricating film.

(4) Lubrication reactions can be more complicated; the SbSbS^ may be

involved in reactions with the lubricant itself or with oxygen

present at the contact.

In the present study a series of experiments were carried out to consider

the feasibility of these different explanations.

Ill . Test Methods and Materials

Testing procedures involving six di fferent machines were used to

evaluate the friction and wear characteristics of SbSbS^ both in the dry powder

form and when blended as an additive with base lubricating fluids. The same

procedures were also applied to other lubricating materials for comparison

purposes. Three of the test machines, the four-ball EP machine, the pin and Vblock (Falex) machine, and the block and ring (LFW-1 ) machine are widely used

for lubricant testing. Two other wear test machines, the 3-pin on disk machine,

and the reci procating linear sliding high temperature machine were special

laboratory designs. The sixth machine, a ring compression apparatus was,

strictly speaking, not a wear test machine but an application of

a commercial compression-tension testing machine operating in the compression

mode. All tests were conducted in laboratory ai r (21 -23°C) . The relative humidity

9
was monitored but not controlled; it was found to vary between 40 and 60%.

In the remainder of this section a brief description of each of the test

systems will be presented together with a summary of the test procedures

that were applied.

A. Pin and V-block Tests

A detailed description of the pin and V-block machine (also known

as the Falex machine) can be found in a paper by Faville and Faville (24)

as well as in three ASTM standard test methods (D2627, D3233, D2625) which

are based on this machine. The test specimens consist of two blocks with

96° V-grooves and a cylindrical 6.35 mm diameter pin. The V-blocks are

held in a lever arm mechanism and squeezed against the rotating pin.

The load can be adjusted manually or increased automatically. The

magnitude of the load is usually indicated by a dial gauge; however,

the present machine was modified to include a strain gauge type load

cell which allowed the load to be indicated electronically. The torque

imparted to the V-blocks as a result of the friction force was also

measured by a strain gauge type load cell. Load and friction force together

with specimen temperature, which was measured by means of a thermocouple spot

welded to one V-block, were continuously recorded during each test. The test

specimens specified in the ASTM standards, V-blocks of 1137 steel and pins

of 1335 steel, were used in many tests. To evaluate the behavior of SbSbS*

4

with other metals, specimens of 440 stainless steel, 52100 steel, 4340 steel,

and Ti-6A1-4V were also employed.

10
Tests were carried out with two different procedures. One was a

modification of ASTM D3233, method A, which is designed to determine the

load carrying capacity of fluid lubricants. In that procedure after a

5 min. run-in at 1330 N (300 lb) the load is advanced automatically until

failure occurs either by fracture of the specimen locking pin, of the

specimen pin itself, or by extrusion of the specimen pin. The failure event

is accompanied by a marked rise in friction force when seizure and

fracture occur, or by a drop in the load advance rate when pin extrusion results.

The load at which the failure event occurs is designated the load

carrying capacity of the lubricant according to this test. The ASTM

method specifies that the specimens be immersed in a fixed volume of

lubricant. A different procedure was adopted when the test was applied to

greases. The V-grooves of the V-blocks were filled with grease and then

squeezed against the pin. No additional grease was applied during the

test.

A second test procedure was used to measure wear as well as load carrying

capacity. This procedure consisted of a series of 30 min. tests

starting at a gauge load of 445 N (100 lb) with each succeeding test being

run at a load of 445 N (100 lb) higher than the former. The series was

terminated when failure occurred before the 30 min. test period was completed.

The maximum load at which the lubricant was able to survive the 30 min.

test period was considered to be the load carrying capacity of that

lubricant. A major difference between this procedure and the first procedure

described involves the relationship between temperature and load. In the

11
first procedure load is rapidly advanced and there is no opportunity for

the achievement of steady state thermal conditions. A steep temperature

gradient exists at the contact surface. In the 30 min. constant load test,

the specimen temperature is allowed to rise to a steady state value;

consequently, for a given load the surface temperature of the specimen may

be considerably higher than in the first procedure.

Wear was determined by measuring widths (lengths were approximately constant)

of the four wear scars on the two V-blocks and calculating the average wear

volume. These measurements were found to be most useful when various

lubricants gave large differences in wear rates. Small differences could

not be resolved because of scatter in the data.

B. Block and Ring Tests

The block and ring tests were conducted with a commercial LFW-1

machine equipped with a 30:1 lever arm and a strain gauge type load cell

for the measurement of friction. Grease was supplied to the rotating

ring by means of a commercial grease feeder adjusted to deliver a volume of

3

0.5 cm at 20 min. intervals. The grease was supplied directly to the rotating ring

from a nozzle with a rectangular opening approximately equal to the width

of the ring. During the course of a test the grease was allowed to

accummulate in the vicinity of the nozzle and the entrant side of the block.

One test was conducted with dry SbSbS^ powder as a lubricant. In that

case the powder was applied repeatedly to the ring with a small artist's

brush during the test.

The test procedure employed was designed primarily to determine

the wear rate under conditions of low sliding speed and high load

12
(below seizure). Most of the tests were conducted at a load of 267 N

(60 lb) and a sliding speed of 5.5 cm/s. Wear is reported here as the volume

of material lost from the block. The volume was calculated from the

measured width and length of the cylindrical wear scar. Surface profile

traces across selected scars indicated that the scar shape conformed

closely to the ring geometry. Both ring and block were of 52100 steel.

The ring hardness was 62 HRC and the surface roughness across the

circumference of the ring, perpendicular to the grinding direction was

0.17 ym R Similarly, the block hardness and surface

a finish were 62 HRC and 0.25 ym R , respectively . Details

a on conducting wear tests with the LFW-1 machine are discussed in ASTM D2714.

C. Four-Ball Tests

The four-ball test was employed mainly to confirm the results of King

and Asmerom (5) who first evaluated the load capacity of SbSbS^ in this

way. A description of the four-ball EP test machine and the test procedure

employed is described in ASTM method D2596. Briefly, the test

specimen configuration consists of one steel ball that is rotated

in the apex of three stationary steel balls. Ten second runs are made

at increasing loads until failure occurs. A new set of specimens are used

at each load. The rotating speed is 1770 RPM; the ball material is

SAE 52100 steel. The weld point is defined as the load at which the balls

weld together or a wear scar diameter of greater than 4 mm is obtained.

D. Ring Compression Tests

A ring compression test has been developed (25) (26) previously

to measure friction under typical metal working conditions. The test

involves compression of a metal ring between two flat metal platens.

Changes in the ring diameter at a given amount of deformation (reduction

13
in ring thickness) can be directly correlated with friction coefficient

at the ring-platen surfaces. This technique can be used to evaluate the

effectiveness of solids as lubricants at high normal pressures while minimizing

the temperature rise during the test. In these tests, rings of 1018 steel

(1.9 cm 0D x 9.5 mm ID x 6.35 mm thickness) were compressed 50% between

flat plates of 0-2 tool steel finished to 4-8 ym R . The solid or

a fluid lubricants were applied uniformly to the ring surfaces at the start

of the test. The coefficient of friction was determined by the change in

the internal ring diameter using the calibration data given in Table 6 from

reference 25.

E. Three-pin on Disk Tests

For certain tests a pin-on-disk apparatus was used (Fig. 5). The specimen

configuration consists of 3 hemispherical or flat ended pins sliding against a flat

plate and forming a single wear track. The pins were held in a round disk

which was mounted in a drill press chuck. The drill press had been

modified with a variable speed motor and gear drive to operate up to

a speed of 350 RPM. Alignment of the contact was achieved by means

of a ball mounted between the pin holder and the chuck. The flat

disk specimen was mounted on a small table below the pin holder and was

supported by a ball bearing. In operation the table was restrained by a

fixture to which a load cell was attached; this allowed continuous recording

of the friction force during the wear test. The table also contained a

cavity in which resistance heaters were inserted for high temperature

wear test operation. Water cooling was provided to protect the ball

bearing during heating. The load was applied through the drill press

spindle. The spindle was modified to reduce vertical friction forces

14
which might interfere with the transmission of the applied load to the

specimens. Small guide vanes were attached to the upper pin holder so

that the lubricants in the powder form were continuously returned to the

sliding track in front of the pins during the test. The solid powders

were spread on the disk with a thickness of approximately 3 mm. Hardened

SAE 52100 steel balls and 0-2 tool steel disks were used for most of the

experiments. Tests were run at a load of 237 N (53.3 lb), a speed of

10 cm/s, and temperatures from 20°C to 250°C.

F. Reciprocating Linear Sliding Tests

For high temperature tests a reci procati ng sliding rig was used

(Fig. 6). It consisted of a flat ended pin (6.35 x 6.35 mm) sliding back

and forth against a flat plate; the track length was 25 mm. The pin

was held in an arm which was moved back and forth by an air motor. One

end of the moving arm was supported by a universal joint so that it could

move in both the linear horizontal and vertical directions. Load was applied

by an air cylinder which was mounted directly above the specimen pin. Motion

was imparted to the moving arm through strain gauges so that the friction

force could be measured. The flat plate specimen was fastened to a block

mounted directly under the pin. The test specimens were surrounded by

a furnace. Heat was supplied to the upper and lower specimens by cartridge

heaters mounted in the specimen holder blocks.

In operation, the specimens were placed in the test rig and

15
brought to the desired operating temperature. The lubricant was applied

as a powder (3 mm depth) on the flat plate and the test begun. M2

tool steel specimens (60 HRC) having a sand blasted surface finish

were employed. A load of 142 N (32 lb) and a velocity of 25 mm/sec

was used. Ten minute test runs were made at increasing

temperature levels from room temperature to 580°C. Friction was plotted

as a function of temperature.

G. Lubricant Materials

A list of the lubricants studied in this program is given in Table 7.

Tests were conducted on dry powder materials and on many of the same

materials blended with two different base fluids, a lithium 12 -hydroxy stearate grease

designated RM81 by its manufacturer and a laboratory grade of white paraffinic

mineral oil. Several of the solid materials, most notably MoS^, were

selected because of their known good qualities as solid lubricants. These

served to provide reference data to which results obtained with other

materials, in particular SbSbS^ could be compared.

IV . Results and Discussion

Test results and analysis of these results are presented in the following

sections

.

A. SbSbS^ as a Solid Lubricant

SbSbS^ has been referred to be a solid lubricant. According to the general

usage of this term, SbSbS^ in the solid form and not in combination with a

fluid or other solid material would be expected to reduce substantially friction

16
and wear. To achieve this function a layer of the solid lubricant must

exist at the contact surface between sliding members and a significant

proportion of the sliding and shear must take place on or within this layer.

The mechanical properties of the solid lubricant layer are such that

traction forces are lower than would otherwise exist. As discussed

previously, the solid lubricant function may depend on temperature and

pressure. (The gaseous environment may also be important, but in the present

investigation, it was confined to room air.) To explore the solid lubricant

behavior of SbSbS^, tests were conducted at various temperatures and loads.

An example of the variation of friction coefficient with sliding distance at room

temperature obtained with the 3-pin on disk machine is shown in Fig. 7.

In these tests dry powder was spread on the disk surface and the test commenced.

As noted earlier, vanes located on the pin holding member continually returned

powder to the wear track on the disk after it was pushed away by the pins.

The friction coefficient trace in Fig. 7 rises rapidly with large

fluctuations to a value of about 0.7. Examination of the

pin and disk sliding contact surfaces revealed the presence of a

relatively thick compacted film of SbSbS^. Optical micrographs of disk

and pin contact surfaces are shown in Fig. 8(a) and 8(b). Close

examination of the disk surface revealed some small areas of bare metal

in the wear track. It appears that during sliding the film was sometimes

attached to the pin and sometimes to the disk. The frictional behavior was

controlled by shear between the thick film and the metal surfaces and to

some extent by shear within this film. The shear stresses involved are

much larger than with MoS

2 which under comparable conditions gave a

friction coefficient of 0.05.
Additional tests on dry SbSbS^ were conducted at higher temperatures.

Figure 9 shows the variation of friction coefficient with temperature.

In this experiment the heater was switched on and the temperature allowed

to rise while sliding took place. The friction coefficient remained at

a value of approximately 0.8 until a temperature of about 225°C was

reached. The friction coefficient then decreased with increasing temperature

to a value of about 0.4. The maximum temperature attainable (limited by

heater power capacity) was about 250°C. On turning the heater off the

coefficient of friction recovered to its original value when a temperature

of about 175°C was reached. Sliding was terminated in one test at 250°C.

After cooling to room temperature, examination of the specimen surfaces

showed that again there were thick patches of solid film in the wear track

(Fig. 10). Flakes of the film were stripped from the surface using an

extraction replica and examined in the transmission electron microscope.

They were determined to be the crystalline phase Sb^S^ by means of electron

diffraction. Thus the original amorphous compound SbSbS^ underwent a

transformation involving the loss of an S atom. During the elevated temperature

tests which were carried out in air, oxidation of the steel surface occurred,

turning it first to a straw color and then blue when 250°C was reached.

A test was run without SbSbS^ lubrication to investigate the effects

of specimen oxidation. The friction coefficient vs temperature results

are shown in Fig. 11. The behavior is somewhat similar to that obtained with

18
SbSbS4 - Comparing Fig. 9 and 11 it can be seen that despite the larger

fluctuations, the friction coefficient in unlubricated sliding is close

to 0.8 until a temperature of about 190°C is reached. The friction coefficient then drops to about 0.6. On turning off the heat at 250°C,

the friction coefficient increased slowly with decreasing temperature

reaching its initial value of 0.8 at about 60°C. Although oxidation of

the steel specimen surfaces may contribute to the results obtained with

SbSbS4 , it cannot account for a large part of the observed effect.

The test procedures used above (rising and falling temperatures)

do not necessarily establish the critical temperatures at which changes

in friction coefficient occur. However, the results do indicate that

variations in friction coefficient may be dependent on factors other than

a change in the lubricating qualities of SbSbS4. Additional experiments,

perhaps in an inert atmosphere would be required to separate the effects

of oxidation from those due to SbSbS4 . With respect to the solid lubricating

characteristics of SbSbS 4 two observations are important: (1) over the

temperature range from 22°C to 225°C the compound exhibits a friction

coefficient on steel much higher than with good solid lubricants, (2) SbSbS 4

forms a rather strongly adherent film on the surface. The latter property

of SbSbS4 may contribute to its good performance as an additive as discussed

later in this report.

A different test device (reciprocating linear slider) was used to

reach a temperature of 650°C. The friction coefficient vs temperature data

19
for SbSbS4 determined using this tester are shown in Fig. 12. Friction

is constant at about 0.24 up to 250°C, then it decreases gradually to

0.14 at a temperature of 450°C. Again it is clear that SbSbS 4 becomes

a much more effective solid lubricant at high temperatures and may

compare favorably in friction coefficient with inorganic lubricant

compounds (Fig. 3). This could account for the increased load capacity

of greases containing SbSbS 4 . It should be noted, however, with this

test the coefficient of friction values were much lower than were found

for the pin-on-disk test. The reason for this difference is not clear

at the present time.

In order to evaluate the high pressure lubrication properties of

SbSbS 4 under conditions that minimize frictional heating effects, the

ring compression test was used. Since pressures are at or above the yield

strength of steel, this is a very severe lubricant test. However good

solid lubricants perform well under such conditions. Data on several

lubricants obtained with 1018 steel rings are listed in Table 8.

Basically these results show that SbSbS4 did not provide the same

measure of solid lubrication as M0S 2 under these conditions. M 0 S 2 reduced friction from a value of 0.24 obtained without lubricant to

0.035. When RM81 grease was employed, a value of 0.05 was obtained.

Blending 5 w/o M 0 S 2 with the grease gave 0.04. SbSbS 4 gave a friction

value of 0.19 alone and 0.06 when used with the RM81 grease. These

results indicate that SbSbS 4 is not a solid lubricant at room temperature

in the conventional sense at higher contact pressures. It may be concluded

that SbSbS 4 (or its reaction products) is an effective lubricant at

20
temperatures from 225°C to 650°C. In this regard it is much better than

M0S 2 which oxidizes at 350°C in air and is then no longer effective.

B. Confirming Four-Ball Tests and Pin and V-Block Load Capacity Tests

Four-ball EP tests were conducted on RM81 base grease, RM81+5 w/o

SbSbS4 and RM81+5 w/o M 0 S 2 . The data are plotted in Fig. 13 together

with the results of King and Asmerom (5). The agreement is very good, thus

confirming the outstanding EP behavior of SbSbS 4 as an additive in this

test.

Pin and V-block EP tests conducted using ASTM method D3233 demonstrated

the significant superiority of RM81+5 w/o SbSbS4 over the base grease

alone. However, the difference here between RM81+5 w/o SbSbS4 and

RM81+5 w/o M 0S 2 was not nearly as great. In addition to the relatively

soft 1137 steel block (20 HRC) and 3135 steel pin (90 HRB), the standard

specimen materials specified in Method D3233, three hardened steel

specimen materials and a non-steel, Ti-6A1-4V, were examined. These

results are shown in Table 9. When the hardened steel specimens were

used, the failure load was nearly doubled for the RM81 base grease,

compared to the standard specimens. With RM81+5 w/o M 0 S 2 , a moderate

increase was obtained with 4130 steel and 440C steel compared to the

standard specimens but there was almost no change for 52100 steel. When

RM81+5 w/o SbSbS 4 was used, the failure load was about the same for all

steel specimens.

21
It may also be noticed that there was essentially no difference

in failure load for RM 81+5 w/o MoS.^ and RM 81+5 w/o SbSbS^ when

4130 steel and 440C steel specimens were used. Large differences were

primarily the result of using SAE 52100 steel as found in the four-ball

test results.

To understand these results it is necessary to consider in more detail

the pin and V-block test itself. The failure load, as described earlier, is

determined by specimen pin fracture, fracture of the locking pin, or by

extreme wear. Mechanical properties of the specimens and other metallurgical

factors as well as lubricant properties will almost certainly play a role

in determining failure load. A good example of the importance of "other"

metallurgical factors is demonstrated by the almost complete ineffectiveness

of the lubricants in question with T i -6A1 -4V . With specimens of the latter

material, failure occurred during run-in at 1330 N (300 lb). The higher

failure loads of RM 81 base grease when tested with 52100, 4130 and 440C steel

compared to the 1137/3135 steel combination appear to be a result of the

higher strength of the former steels. The friction coefficient and load

traces for tests employing the 1137/3135 specimen combination lubricated

with RM 81 are shown in Fig. 14a. Run-in is not shown; only the portion

where the load was automatically advanced to failure is shown. The friction

coefficient remains constant with increasing load until it rises

abruptly at a load of ^2700 N (600 lb) and the test is terminated, in this

case, by fracture of the specimen pin. Figures 14b, c and d show correspondi ng

friction coefficient, temperature, and load traces for specimens of

52100, 440C, and 4130 steels, respectively . Only the run-in portion of

the test during which failure occurred is shown for Ti-6A1-4V in Fig. 14e. A

marked rise in the friction coefficient occurs at 2700-3100 N (600-700 lb)

for the steels, 52100, 4130 and 440C but actual failure of the specimen

22
pin (or locking pin) did not take place until a much higher load was

attained. In fact, the friction coefficient is seen to recover to

a lower value, after its initial rise, before increasing to failure.

Although direct analytical information was not obtained to explain this

behavior, it is hypothesized that chemical reactions with the lubricant

or perhaps oxidation led to the intermediate reduction of friction force.

Chemical reaction is certainly favored by the rising temperature which

accompanies frictional heating. Variations in friction such as those

shown in Fig. 14b-d are well known to occur with steel under non-lubricant

sliding conditions in air (27).

Load, temperature, and friction coefficient traces similar to those

for RM 81 are shown for RM 81+5 w/o MoS^ and RM 81+5 w/o SbSbS^ in

Figures 15 and 16, respectively. These examples are representative;

other tests did not necessarily repeat in detail the small variations

shown but the general behavior was quite similar. In common with RM 81,

the mixture RM 81+5 w/o MoS^ shows a rise in the coefficient of

friction at 2700-3100 N (600-700 lb). That rise did not, however,

lead to the failure of the pin for the standard 1137/3135 steels,

as occurred with the base grease alone. In fact, recovery occurred and the

ultimate failure load for 1137/3135 steel was about the same as for 52100 steel.

With RM 81+5 w/o SbSbS^ (Fig. 16) an initial decrease in coefficient of friction occurred and a rise was not observed until a load in the range

5800-6700 N (1300-1500 lb) was reached. In summary, these results

indicate that with steel specimen materials, there is an increase in

friction coefficient at 2700-3100 N (600-700 lb) for the RM 81 base

grease. Addition of 5 w/o MoS^ reduces the size of this increase while

5 w/o SbSbS^ eliminates or perhaps delays it until a load in

the range 5800 -6700 N (1300 -1500 lb) is reached.

23
A common feature of both MoS^ and SbSbS^ is the presence of sulfur.

Because of the well known effectiveness of sulfur as an EP agent, 0.43w/o

elemental sulfur powder was blended with RM 81 base grease and subjected

to the pin and V-block test. The load and friction force traces for

one test are shown in Fig. 17. The behavior is similar to that of

RM 81+5 w/o SbSbS

4

.

C. Comparison of SbSbS^ with Other S-containing and Solid Lubricant Additives

Additional pin and V-block tests were conducted on the RM 81 base

grease with several solid lubricant additives and three proprietary

soluable sulfur-containing organic additives. These were compared with elemental

sulfur. The solid lubricants (PbO, HB0

3

and PbO plus graphite) were chosen because

they are excellent high temperature solid lubricants. It was hypothesized that

the SbSbS^ might behave in a similar manner. The organic sulfur and elemental

sulfur additives were included to evaluate the role of sulfur reactivity.

The additives examined together with their measured maximum pass loads

in the pin and V-block test are listed in Table 10. Separate tests were

carried out at 445 N (100 lb) load increments starting with 445 N (100 lb)

until a load was reached at which failure occurred before an arbitrarily

chosen period of 30 minutes was attained. The maximum load at which the

30 min. test could be completed was designated the maximum pass load for the

lubricant. None of the solid additives listed in Table 10 except SbSbS^

sustained a load of 1780 N (400 lb) without failure. With a soluble sulfur

containing additive, Anglomal, and when 1% elemental sulfur was dissolved

in RM 81 , a maximum pass load of 1780 N (400 lb) was obtained. Also,

24
0.2% dissolved sulfur in RM 81+5 w/o MoS^ raised-the maximum pass load

from 1330 N (300 lb) to 1780 N (400 lb).

These results strongly suggest that the sulfur effect is more

significant than the possible high temperature solid lubricant effect.

To investigate further the significance of sulfur on the behavior of

SbSbS^, pin and V-block 30 minute wear tests were carried out on white

paraffinic mineral oil containing S and SbSbS^. The white mineral oil

was used to avoid the possible effects of soaps or impurities

in the grease. The lubricants studied are listed in Table 7. Two of

the lubricants were prepared by first mixing 5 w/o SbSbS^ dry powder

in mineral oil and then filtering out the solid residue. In one case

the mixture was heated to 120°C for 30 min. before cooling to room

temperature and filterings and in the other case the mixture was stirred

at room temperature for 16 hrs. before filtering. The filtering process

itself required several hours. X-ray fluorescence analysis of the

filtrates indicated the presence of 0.16 w/o S in the heated and 0.08 w/o S

in the unheated filtrate but only a trace concentration ( < 0 . 001 % ) of

antimony was detected in both cases. The.SbSbS^ powder itself was reported (28)

to contain less than 0.1 w/o uncombined sulfur. These results indicate

that some sulfur is given up to mineral oil by the SbSbS^ compound.

The pin and V-block test results given in Fig. 18 show that the filtered

blends exhibit a wear behavior that is similar to mineral oil having the

same concentration, of elemental sulfur.

These results clearly demonstrate that sulfur interaction with

the steel surface plays an extremely important role in the EP and antiwear behavior of SbSbS^.

25
D. Anti -wear Behavior of SbSbS^ As An Additive

The superior EP performance of ShSbS^, as an additive to RM 81 base

grease has already been described. King and Asmerom (5) have employed

four-ball wear tests (ASTM D2266 and D2596) to demonstrate that the wear

rate characteristic of RM 81+5 w/o SbSbS^ is equal to or better than either

RM 81+5 w/o MoS^ or RM 81 alone. The test conditions specified by ASTM D2266

and D2596 are relatively severe with respect to load and speed, and

consequently, also as regards temperature. The question arises as to

what the behavior of SbSbS.^-contai ni ng greases would be under less severe

conditions, particularly where the temperature might not much exceed room

temperature (22°C) and the physical rather than chemical -reactive

properties might be stressed. To answer this question a series of block

on ring tests was conducted at a load of 267 N (60 lb) and sliding

speed of 5. 5. cm/s. The results of tests on three different lubricants,

RM 81 base grease, RM 81+5 w/o SbSbS^ and RM 81+0.43 w/o S, are shown in

Fig. 19. The concentration of elemental sulfur listed was

chosen to equal the quantity of sulfur that would be available from 5w/o

SbSbS^ if the latter compound was converted to Sb^S^. The steady state

-9

wear rate obtained with RM 81 was 7X10' mm

3 /mm and is substantially higher

than the value 1.8 x 10

^ mm

3 /mm obtained with RM 81+5 w/o SbSbSA

. It may be

noted that a relatively high run-in wear rate was obtained with RM 81+5 w/o SbSbS A

and that a sliding distance in excess of 1000 m was required to enter the

steady state regime. The calculated steady state wear coefficient* for

RM 81+5 w/o SBSbS^ is K = 5 x 10~ 9

. This value is indicative of mild wear and

demonstrates the good anti-wear characteri Stic of SbSbS^ under these conditions.

volume loss • hardness

load • sliding distance

26
Similar tests conducted on RM 81+0.43 w/o S gave essentially the same wear

rate as those for RM 81+5 w/o SbSbS^. This result seems to further

substantiate the sulfur contribution in the case of SbSbS^. Additional

tests will be required to better establish the comparative behavior of

elemental sulfur and SbSbS^.

E. Analysis of Debris and Surface Films

The observation of thick films on surfaces lubricated with dry

SbSbS^ powder has already been discussed. These films were easily

revealed by optical microscopy. Specimens lubricated with mineral oil

and grease, both with and without additives, were not covered with such

thick films. Depending on test conditions and the lubricant used, solid

films could sometimes be seen with the optical microscope. In some cases

the entire wear surface appeared to be covered by a film, while in other

cases only part or none of the surface was covered by a visible film. It

is thought that the explanation for these apparently disparate observations

lies in the fact that all surfaces were covered by films but that the

thickness varied. Only when the films were sufficiently thick were they

observed. Since the exi stance of a solid film and the nature of that film

are probably the most important factors determining boundary lubrication

characteristics, a study was initiated to characterize films that were

present under test conditions employed in this investigation.

27
Two approaches were taken to study the films. Both employed

transmission electron microscopy. In one method wear debris particles

from used lubricants were examined. It was assumed that either some portion

of the original film resided on those particles or that the entire particle

was in fact film that had been rubbed off the surface. In the second method,

fragments of the film were stripped off the surface by means of a replica

technique. The debris particles and film fragments were examined in an

analytical electron microscope (AEM). Crystal structure information was

obtained by means of electron diffraction and information on composition

for elements with atomic numbers equal to or greater than 11 (Na) was

obtained by means of an x-ray energy dispersive spectrometer system (EDS).

Debris particles from two pin and V-block tests have been examined.

In the first case, RM 81+0.2 w/o S was used as a lubricant and the test was

conducted at a load of 1330 N (300 lb) for a period of 30 min. A considerable

quantity of debris was accumulated in the grease that remained on the

specimens at the end of the test. Relatively large metal particles were

visible optically. An abundance of very small particles

was also present. A number of these small particles, often in clusters,

were examined on carbon support films in the TEM. Electron diffraction

indicated that the particles had a crystal structure appropriate to the

spinel form of iron oxide, Fe^O^. Energy dispersive x-ray analysis

indicated the presence of Fe; a sulfur peak also was observed. There

were no diffraction lines to indicate that sulfur was combined with iron

28
to form a sulfide. It is not known to what extent sulfur may be

incorporated in the Fe^ structure.

In the second case, debris particles were studied that had been

generated in a test employing mineral oil to which SbSbS^ powder had

been added and subsequently filtered. A 30 minute wear test was conducted at

a load of 2220 N (500 lb) with this lubricant. Debris particles from the used

oil were similar to those from the test employing RM 81+0.2 w/o S to the extent

that some large metal particles were present together with a large quantity

of very small particles. Electron diffraction analysis of the small

particles, however, indicated that they were very nearly identical in

structure to a variety of pyrrhotite, Fe-|_ x (5C) and not Fe^. Pyrrhotites

are iron-deficient iron sulfides exhibiting a variety of different superstructures based on the hexagonal NiAs subcell.

Film fragments removed from two block wear scars after conducting

ring and block tests were examined. Both blocks were tested under

approximately the same conditions, 267 N (60 lb) load and sliding distance of

^5000m. In one test RM 81+5 w/o SbSbS^ was used as a lubricant and in the

other test RM 81+0.43 w/o S was employed. It may be recalled that 0.43 w/o S

corresponds to the amount of sulfur that would be available if 5 w/o SbSbS^

was converted entirely to Sb^S^. Film fragments from the test employing

RM 81+5w/o SbSbS^ were of two types. One type of fragment was essentially

structureless in appearance. Fig. 20(a). According to electron diffraction

it was amorphous. EDS analysis indicated that it was composed of Sb and

S. Thus, it is hypothesized that the film was derived directly from the

amorphous SbSbS^ powder as a result of the powder particles being rubbed

29
over the surface during sliding. The second type of film also shown in

Fig. 20(a) appeared to be composed of very small crystallites about 10 nm

in size. Bright field and dark field micrographs of a different polycrystalline fragment are shown in Fig. 20(b) and (c). The crystal structure

was determined by electron diffraction to be consistent with pyrrhotite

Fe-j _^S (5c). As further support of this identification, EDS indicated the

presence of both Fe and S at about the same concentration. A similar

analysis of film fragments from the block lubricated with RM81+0.43 w/o S,

(Fig. 21) revealed only polycrystalline films which were very similar in

appearance to polycrystall ine films found with RM81+5 w/o SbSbS^. Electron

diffraction, however, indicated a crystal structure consistent with pyrite,

FeS^. By means of EDS it was determined that the concentration of S was

considerably higher than Fe.

The results described above concerning the nature of debris particles

and surface films are preliminary. Additional specimens need to be

examined both from duplicate tests and conducted under different

conditions to confirm the present observations and establish more fully

the relationship between lubricant composition, test conditions, and

film characteristics. However, analysis of the present results suggests

the following. Iron oxide may form when a sulfur containing lubricant

is employed under conditions when oxygen has ready access to the contact

surface and frictional heating results in an elevated temperature. Under

conditions where oxygen was not so readily available or lower loads and

temperatures existed, sulfides are present when sulfur bearing additives are

used. Perhaps the most significant result, however, is that with SbSbS^

the iron sulfide, pyrrhotite, was identified as the principle constituent

of the surface film.

30
V. Conclusions

1) When used as a dry powder SbSbS 4 yields a coefficient of friction of

0.5-0. 8 at temperatures below about 225°C in air.

2) At temperatures above approximately 225°C, SbSbS 4 exhibits a friction

coefficient in the range 0. 2-0.4, and therefore has characteristics

of a high temperature solid lubricant.

3) When rubbed dry, SbSbS 4 forms a thick adherent and durable film on

contacting steel surfaces at temperatures from 20°C to 250°C.

4) When employed as an additive in a lithium soap based grease, SbSbS 4

was found to exhibit outstanding extreme pressure performance with

steel specimens according to pin and V-block and 4-ball tests. These

results confirm those of other investigators.

5) SbSbS 4 as an additive in lithium soap grease was not an effective

EP lubricant against Ti-6A1-4V.

6) The extreme pressure behavior of SbSbS^ was similar to other known

sulfur releasing additives.

7) The boundary friction and wear characteri sties of SbSbS4 when employed

as an additive in mineral oil and grease (lithium soap) appear to be

associated with the release of sulfur. Iron sulfide films were

identified on steel surfaces. A solid film of amorphous SbSbS 4 was

also formed on the surface.

31
Acknowl edgements

Support from the Office of Naval Research and the continuing

encouragement of Harold Martin, ONR, during this study are gratefully

recognized. Many useful suggestions and comments were received from

James King and Piero Nanelli, Pennwalt Corp. The authors also wish to

thank the following: Lubrizol Corporation for supplying organic sulfur

additives, H. Spitzer and M. Everett (U. S. Army, Fort Belvoir) for

making available for our use an EP four-ball test machine, and expecially

Peter Pella (NBS) for conducting x-ray fluorescence analyses on several

oil samples.

32
References

1. M. J. Devine, J. P. Cerini, W. H. Chappell, and J. R. Soulen,

"New Sulfide Addition Agents for Lubricant Materials," ASLE

Trans. Tl_, 283-289 (1968).

2. M. K. Leish and J. L. Hammond, "Complex Chalcogenides as Anti-Wear

and Extreme Pressure Addition Agents for Lubricating Greases,"

U. S. Department of the Navy, Naval Air Development Center, 1971,

Report No. NADC-MA-7159.

3. M. K. Leish, "Complex Chalcogenides as Solid Film Lubricant

Additives," U. S. Dept, of the Navy, Naval Air Development Center,

1972, Report No. NADC-7201 1 -VT.

4. M. K. Gabel, "Complex Chalcogenides as Antiseize Additives,"

U. S. Dept, of the Navy, Naval Air Development Center, 1973,

Report No. NADC-73196-30.

5. J. P. King and Y. Asmerom, "Antiwear Properties of Antimony

Thioantimonate," Progress Report #4, Dec. 13, 1979, to Office

of Naval Research.

6. J. Gansheimer, "On the Lubricating Properties of Mixtures of

Mineral Oil with Certain Inorganic Phosphates, Hydroxides, and

Sulfides," ASLE Trans., 15, 201-206 (1971).

7. J. Gansheimer, R. Hoi inski, "Molybdenum Disulfide in Oils and

Greases Under Boundary Conditions," ASME Trans., JOLT, April,

242-248 (1973).

8. R. Holinski, "Lubrication Mechanism of Solid Lubricants in Oils,"

ASLE Trans. 18_, 263-269 (1975).

33
9 . J. M. Palacios, A. Rincon and L. Arizmendi," Extreme Pressure

Lubricating Properties of Inorganic Oxides," Wear, GO, 393-399

(1980).

10. A. Begelinger and A. W. J. BeGee, "Boundary Lubrication of Sliding

Concentrated Steel Contacts," Wear 22, 337-357 (1972).

11. C. V. Agarwal , V. K. Verma and R. S. Singh, "The Assessment of

Dithiocarbamates as Extreme Pressure Lubricant Additives," Wear,

64, 33-38 (1980).

12. M. B. Peterson and S. F. Murray, "Materials for Sliding and Rolling

Contacts," Chapter 9, Boundary Lubrication - A Critical Survey,

ASME (1969).

13. A. J. Haltner and C. S. Oliver, "Frictional Properties of Molybdenum

Disulfide Films Containing Inorganic Sulphide Additives," Nature,

pp. 308-309 (Oct. 1960).

14. W. Davey, "Some Observations on the Mechanism of the Development

of Extreme Pressure Lubricating Properties by Reactive Sulphur in

Mineral Oils," J. Inst. Petroleum, 3]_, 154 (1945).

15. W. Davey and E. D. Edwards, "The Extreme Pressure Lubricating

Properties of Some Sulphides and Disulphides, in Mineral Oil,

as Assessed by the Four-Ball Machine," Wear, ]_» 291-304, (1957/58).

16. W. Davey, "Some New Extreme Pressure (E.P.) Lubricating Oil Additives

Containing Chlorine and Sulphur," J. Inst, of Petroleum, Vol . 33,

No. 285, 527-530 (1947).

17. W. Davey, "Some Observations on the Development of Extreme Pressure

(E.P.) Properties by Chlorine and Sulphur Additives in Mineral Oil,

as Assessed by the Four-Ball Machine," J. Inst, of Petroleum,

Vol. 32, 575-581 (1946).

34
18. W. Davey, "The Extreme Pressure Lubricating Properties of Some

Chlorinated Compounds as Assessed by the Four-Ball Machine,"

J. Institute of Petroleum, Vol . 31, No. 255, 73-88 (1945).

19. S. Forbes, "The Load-Carrying Action of Organo-Sulphur Compounds -

A Review," Wear, 1_5, 87-96 (1970).

20. K. G. Allum and S. Forbes, "The Load-Carrying Mechanism of Organic

Sulpur Compounds-Appl ication of Electron Probe Microanalysis,"

ASLE Trans. H, 1962-175 (1968).

21. D. Godfrey, "Chemical Changes in Steel Surfaces During Extreme

Pressure Lubrication," ASLE Trans. J5, 57-66 (1962).

22. D. H. Buckley, "Oxygen and Sulfur Interactions with a Clean

Iron Surface and the Effect of Rubbing Contact on These Interactions,

ASLE Trans. Vol. 17, 206-212 (1973).

23. K. Nakayama and T. Sakurai , "A Contribution to the Mechanism of

Chemical Wear Under Boundary Lubrication," Bulletin Japan Pet. Inst.

15, 107-114 (1973).

24. F. A. Faville and W. A. Faville, "Falex Procedure for Evaluation

Lubricants," 23rd ASLE Annual Meeting, Cleveland, OH (May 1968).

25. A. T. Male and M. G. Cockcroft, "A Method for the Determination of

the Coefficient of Friction of Metals Under Conditions of Bulk

Plastic Deformation," Journal of the Institute of Metals, _93,

38-46 (1964-65).

26. A. T. Male, "The Effect of Temperature on the Frictional Behaviour

of Various Metals during Mechanical Working," J. Inst, of Metals,

93, 489-494 (1964-65).

27. T. F. J. Quinn, "Role of Oxidation in the Mild Wear of Steel,"

Brit. J. App. Phy., Vol. 13, 33-37 (1962).

28. Private communication, J. P. King, Pennwalt Corp.

35
29. M. B. Peterson and S. Ramalingam, "Coatings for Tribological

Applications," in Fun damentals of Friction and Wear of Materials ,

ASM, pp. 331-372, 1981

.

36
FIGURE CAPTIONS

1. Concentration effect on weld point for SbSbS 4 and M0S 2 in lithium grease.

Data from King and Asmerom (5).

2. Schematic representation of four-ball extreme pressure test behavior.

3. Friction coefficients for a variety of solid materials vs temperature (13).

4. Load carrying capacity vs chemical reactivity for EP agents (15).

5. Schematic drawing of three-pin on disk wear test machine.

6. Photograph of reci procating high temperature friction and wear test machine.

7. Friction coefficient vs sliding distance for dry SbSbS 4 powder using three

pin on disk tests (242 N load, 10 cm/s sliding speed, 52100 steel pins,

0-2 tool steel disk),

8. Optical photograph of film generated on disk (0-2 tool steel) and on pin

(52100 steel ball) (b) surfaces after sliding with SbSbS 4 powder at room temperature.

9. Friction coefficient variation with temperature for dry SBSbS4 powder

using three-pin on disk test (52100 steel pins, 0-2 too steel disk).

10. Optical micrograph of wear track on disk surface showing adherent film

after sliding at 250°C (52100 steel pins, 0-2 tool steel disk).

11. Coefficient of friction variation with temperature for unlubricated sliding

using three-pin on disk test (52100 steel pins, 0-2 tool steel disk).

12. Coefficient of friction vs temperature using reciprocating sliding test

rig (M-l tool steel specimens).

13. Four ball EP test data compared to results from King and Asmerom (5)

(52100 steel balls).

14. Pin and V-block EP test results on RM81 base grease using different

specimen materials. Test procedure was similar to that described in

ASTM D3233 Method A. Simultaneous record of load, coefficient of

friction and block temperature shown, (a) 1137 steel V-blocks and

3135 steel pin, (b) 52100 steel, (c) 440C stainless steel, (d) 4130

steel, (e) Ti-6A1-4V.

15. Same conditions as Fig. 14(a) with RM81+5 w/o M 0 S 2 .

16. Same conditions as Fig. 14(a) with RM81+5 w/o SbSbS 4 .

37
17. Same conditions as Fig. 14(a) with RM81+0.43 w/o S.

18. Pin and V-block 30 min. wear test results on mineral oil blends

(1137 steel V-blocks and 3135 steel pin).

19. Block and Ring wear test results on RM81 , RM81+5 w/o SbSbS4 and

RM81+0.43 w/o S (52100 steel specimens).

20. Transmission electron micrograph of film fragments stripped from

block wear scar after block and ring tests (52100 steel specimens).

Test lubricant was RM81+5 w/o SbSbS4 . (a) Amorphous SbSbS4 film and

crystalline pyrrhotite film fragments are present, (b) crystalline

pyrrhotite film at higher magnification, (c) dark field image of (b)

to indicate size of individual grains.

21. Transmission electron micrograph of film fragment stripped from

block (52100 steel) wear scar lubricated with RM81+0.43 w/o S.

Polycrystal 1 i ne film was determined to be FeS2»

38
TABLE 1

Seizure and Weld Load Results for Base Grease and Additives (5)

Lithium Grease

(RM 81

)

RM 81 +

5 % MoS

2

RM 81 + l%SbSbS

4

RM81 + 5%SbSbS

4

Seizure Load (kg) 40 50 50 100

Weld load (kg) 160 250 400 750

39
TABLE 2

Gansheimer's Results on Solid Additives in Oil (6)

Material O.K. Load (kq)

Zn

2

P 2°7 260

Ca(0H)

2

200-220

MoS

2

200-220

Graphite 200-220

ZnS 160

Base Oil 100

40
TABLE 3

Load Wear Index & Weld Loads for Oxides as Addi

Load Wear Index Weld Lc

Oxides* (kg). (kg)

B2°3 74 > 800

CaO 72 500

Bl 2°3 59 500

Sb 2°3 58 > 800

CdO 54 630

BaO 53 315

PbO 51 200

CuO 45 252

ZnO 42 200

Sn0

2

35 200

NiO 34 252

Fe 2°3 29 200

MgO 19 160

Si0

2 15 160

Al 9O

q 14 160

*In all cases the oxide concentration was

15 wt.%.

41
TABLE 4

Solid Lubricant Types

Organic Soaps, Fats, Waxes

Polymers Teflon, Polyethylene, Methacrylates

Metals Indium, Tin, Lead, Silver

Inorganics AX, AX^, Oxides, Sulfides, Chlorides

Glasses B2O3, Pb0-Si02, PO4

42
TABLE 5

Friction Coefficients of Some Sulfides (29)

Solid

Material

Friction

Coeffi cient

MoS2 0.047

WS 2 0.08

Ti S 2 0.20

CuS 2 0.21

PbS 2 0.15

43
TABLE 6

Calibration Data for Ring Compression Tests (25)

Measured

Decrease of Friction

Internal Diameter Coefficient

T*5

+60 0.57

50 0.40

40 0.28

30 0.18

20 0.12

10 0.08

+ 5 0.06

0 0.055

- 5 0.040

-10 0.042

-20 0.025

-30 0.02

-40 0

44
TABLE 7

List of Lubricants Employed in Study

Dry Powders

SbSbS4

MoS 2

Grease Blends

RM 81

RM 81+5 w/o SbSbS4

RM 81+5 w/o MoS2

RM 81+0.2 w/o S

RM 81+0.43 w/o S

RM 81+1.0 w/o S

RM 81+5 w/o S

RM 81+5 w/o PbO

RM 81+5 w/o HBO 3

RM 81+5 w/o SbSbS4

RM 81+5 w/o Anglamol*

RM 81+5 w/o A60048*

RM 81+5 w/o 60294*

RM 81+PbO + Graphite

RM 81+0.2 w/o S + 5 w/o MoS2

RM 81+0.2 w/o S + 5 w/o Sb2S 3

Paraffinic Mineral Oil Blends

Min Oil

Min Oil +5 w/o SbSbS 4 16 hr. filtered 0.08 w/o S, trace Sb (< 0.001 w/o)

Min Oil +5 w/o SbSbS^ -30 min at 120°C filtered •> 0.16 w/o S, trace

Sb (< 0.001 w/o)

Min Oil +0.1 w/o S

Min Oil +0.2 w/o S

Additives provided by Lubrizol Corp. See footnote, p. 1.

45
TABLE 8

Friction Coefficients of Various Lubricants

Determined by Ring Compression Test

Lubricant Friction Coefficient Surface Damaqe

None 0.24 Some welds at outer

edge. Polished inner

radius

RM 81 Grease 0.050 Original grinding marks on inner radius. Polished on outer radius

HoS^ powder 0.035 Highly polished surface,

film of Mc-S^

SbSbS^ powder 0.19 Roughened surface, no evidence of film

RM 81 grease + MoSg (5%) 0.040 Original grinding marks,

polished at outer edge

RM 81 grease + SbSbS

4 (5%) 0.060 Rough surface

46
TABLE 9

Pin and V-Block E.P. Test Results

According to ASTM D3233 Method A

Test

Specimens RM 81

RM 81 + 5% MoS?RM 81 + 5%SbSbS4

RM 81 + 0.43% S

52100 5500 N 1250 lb7000 N 1575 lb8000 N 1800 lb

-

4130 5300 N 1200 lb

9000 N 2025 lb

8700 N 1950 lb

-

440C 6100 N 1375 lb

2900 N 2000 lb9100 N 2050 lb

-

Ti -6A1 -4V * * * -

3135 PM/

1137 V-blocks

2300 N 525 lb

6900 N 1550 lb8700 N 1950 lb8000 N 1800 lb

Seized during run-in at 1300 N (300 lb)

47
TABLE 10

Pin and V-Block 30 Min. Constant Load E.P. Test Results

on Various Additive Compounds

Lubricant Max Pass Load

RM 81 890 N (200 lb)

RM 81+5 w/o M 0 S 2 1330 N (300 lb)

RM 81+5 w/o SbSbS4 1780 N (400 lb)

RM 81+5 w/o PbO 890 N (200 lb)

RM 81+5 w/o HBO 3 1330 N (300 lb)

RM 81+5 w/o Sb?S 3

< 1330 N (300 1 b)

RM 81 +PbO+Graphite+

< 1330 N (300 1 b)

RM 81+5% Anglamol 33* 1 780 N (400 lb)

RM 81+5 w/o Anglamol 6004A +

< 1780 N (400 1 b)

RM 81+5 w/o 0S#60294*+

< 1780 N (400 1 b)

RM 81+0., 2% S 1330 N (300 lb)

RM 81+0. 2%S+5 w/o M 0 S 2 1780 N (400 lb)

RM 81+0.,2%S+5 w/o Sb 2

S 3 1330 N (300 lb)

RM 81+1. 0%S 1 780 N (400 lb)

*Provided by Lubrizol Corp. Angamol 33 and 0S#60294 are sulfur-containing

additives. Anglamol 6004A is a sulfur-phosphorous additive. See footnote, p. 1.

+Failure occurred at the indicated load; tests not carried out at smaller loads.

48
Fig. 1 Concentration effect on weld point for SbSbS^ and

M0 S

2 in lithium grease. Data from King and Asmerom (5).

49
WEAR

SCAR

DIAMETER

Fig. 2 Schematic representation of four-ball extreme

pressure test behavior.
JOOI o

LlJ qc35

(T

LU

CL

51

Friction

coefficients

fora

variety

of

solid

materials

vs

temperature

(12).
O ~ o o o o' g

CL, T3a

aS

a

<D a,

T3a

aS

cj

<D «

*oa

05

<U •> C

g c g E

2 5 _o « llil

SSt;? _o o § 3

a g

*oo'

<D <C

- j: r

o- 3 £-E

S?o -2

W

<D O ~0 5 S

3 §

2 3

g2 >> -C

3 O

T3 3 £ TO 3

o I. Li « ^

« ^ -e o > G Qj f— 2 7 g H o _c _0 "3 3. WQ-Q

cj -a S Q

*oo

3

CO&ej

-*-> a

»oo

3

CObcS a

<u

bis^ -

^ - s - s OM £ o ^ _a* _

P w o w ^ *3° C C «*- P o w o ^

£

o

>>G

<V -C

' _&

“5o

^ £

G 5 <1) ^ g 59 -G w

£> O >1

*0 --T w >

"3 _- o -*> o III ogs

S f 3 -g (5 f

*—i co rt* »o co cc o o <M co

i.o<4-

+->

+-> o

fO

0)

S-

(X3 0

1

a> -Co

00>

£*

u

03Q.

n3o

CD in C i—

i- 00

s- +-> 03 C

o <ucd

”0 03

1X3 o a.

CD

52
53

Fig.

5

Schematic

drawing

of

three-pin

on

disk

wear

test

machine.
Fig. 6 Photograph of reciprocating high temperature friction

and wear test machine.

54
N0I10IJJ JO 1N3I3I3330D

O

o

o

<T>

O

00

o

r^-

o

CD

O

lO

o

o

rO

Oc\)

O

O

G

LJO

£

CO

Q

55

Fig.

7

Friction

coefficient

vs

sliding

distance

for

dry

SbSbS^

powder

using

three-pin

on

disk

tests.

(242 N

load,

10

cm/s

sliding

speed,

52100

steel

pins,

0-2

tool

steel

disk).
Fig. 8 Optical photograph of film generated on disk (0-2

tool steel) and on pin (52100 steel ball) (b) surfaces

after sliding with SbSbS^ powder at room temperature.

56
250

NOIlDIdJ JO 1N3I0IJJ3O0

g

'E

cr>

cn

(CL) 3dfUVd3dlAI31

57

Friction

coefficient

variation

with

temperature

for

dry

SbSbS.

powder

using

three-pin

on

disk

test

(52100

steel

pins,

0-2

tool

steel

disk).
Fig. 10 Optical micrograph of wear track on disk surface

showing adherent film after sliding at 250°C (52100

steel pins, 0-2 tool steel disk).

58
250

NOIIOIHJ JO 1N3I0IJJ300

o m o m

cj — —

(0o ) 3dniVd3dlAI31

59

Fig.

11

Coefficient

of

friction

variation

with

temperature

for

unlubricated

sliding

using

three-pin

on

disk

test

(52100

steel

pins,

0-2

tool

steel

disk).
r oo

COO

MUJ

<r

Z>£

cr oO CL

»*> ^

LjlJ hO

CMOoo

60

Fig.

12

Coefficient

of

friction

vs

temperature

using

reciprocating

sliding

test

rig.

(M-l

tool

steel

specimens).
SCAR

DIAMETER

(mm)

LOAD (kg)

Fig. 13 Four ball EP test data compared to results from King

and Asmerom (5). (52100 steel balls).

%•-

61
(•) d

e

Fig. 14 Pin and V-block EP test results on RM81 base grease

using different specimen materials. Test procedure

was similar to that described in ASTM D3233 Method A.

Simultaneous record of load, coefficient of friction

and block temperature shown, (a) 1137 steel V-blocks

and 3135 steel pin, (b) 52100 steel, (3) 440C stainless

steel, (d) 4130 steel, (e) Ti-6A1-4V.

62
0o ami

o o o

lO o IT) N lO CM

i

1 1 1 r

NOIlDIUd dO !N3IDIdd300

63

Fig.

15

Same

conditions

as

Fig.

14(a)

with

RM81+5

w/o

MoS
Do aiAGi

o o o

in o in

m CVJ t 1 i— s——i \—~t r

NOIlOldJ JO 1N3IDIJJ30D CDcoKcDin^rocvj

£

oi x (n) avon

64

Fig.

16

Same

conditions

as

Fig.

14(a)

with

RM81+5

w/o

SbSbS
D0 dl/\!3JL

o o o

If) o in

C\J

i i

1 1 1 1 1 r

NOIlOIdd JO 1N3IDIJJ30D

65

Fig.

17

Same

conditions

as

Fig.

14(a)

with

RM81+0.43

w/o
PIN

AND

V-BLOCK

WEAR

TEST

RESULTS

2200 N

(500

LB.)

LOAD

O

MINERAL

OIL

AND S

BLENDS

66

Fig.

18

Pin

and

V-block

30

min.

wear

test

results

on

mineral

oil

blends

(1137

steel

V-blocks

and

3135

steel

pin).
o

C\l

CO

CO

<3

-

CO

o

CO

CO

^3

-

C\J

o

ro

£_0I X ( £

UULU) 9LUn|0/\ JD 0M

67

Sliding

Distance

(m)xlO
Fig. 20 Transmission electron micrograph of film fragments

stripped from block wear scar after blo.ck and ring

tests (52100 steel specimens). Test lubricant was RM81+5 w/o SbSbS.. (a) Amorphous SbSbS. film and

crystalline pyrrnotite film fragments are present,

(b) Crystalline pyrrhotite film at high magnification. (c) Dark field image of (b) to indicate

size of individual grains.

t

68
Fig. 21 Transmission electron micrograph of film fragment

stripped from block (52100 steel) wear scar lubricated with RM81+0.43 w/o S. Polycrystal 1 i ne film

was determined to be FeS^.

69

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SECURITY CLASSIFICATION OF THIS PAGE (When Date Entered) REPORT DOCUMENTATION PAGE READ INSTRUCTIONS

BEFORE COMPLETING FORM

1. REPORT NUMBER

NBSIR 82-2545

2. GOVT ACCESSION NO. 3. RECIPIENT’S CATALOG NUMBER

4. TITLE (and Subtitle) INVESTIGATION OF THE LUBRICATION MECHANISMS

OF THE COMPLEX METAL SULFIDE, SbSbS

4

5. TYPE OF REPORT 6 PERIOD COVERED

Annual Report

Oct. 1, 1980 - Sept. 30, 198

6. PERFORMING ORG. REPORT NUMBER

NBSIR 82-2545

7. authorc*; L. K. Ives, M. B. Peterson, J. S. Harris,

P. A. Boyer, A. W. Ruff

8. CONTRACT OR GRANT NUMBERf*,)

N0001 4-80-F-0031

9. PERFORMING ORGANIZATION NAME AND ADDRESS

National Bureau of Standards

Department of Commerce

Washington, DC 20234

10. PROGRAM ELEMENT. PROJECT, TASK

AREA 4 WORK UNIT NUMBERS

11. CONTROLLING OFFICE NAME AND ADDRESS

Office of Naval Research

Department of the Navy

Arlinaton. VA 22217

12. REPORT DATE

July 1982

13. NUMBER OF PAGES

69

14 MONITORING AGENCY NAME 4 ADDRESSfff different from Controlling Office) IS. SECURITY CLASS, (of this report)

15«. DECLASSIFICATION/DOWNGRADING

SCHEDULE

16 DISTRIBUTION STATEMENT (of this Report)

17. DISTRIBUTION STATEMENT (of the abstract entered In Block 30, II different from Report)

18 SUPPLEMENTARY NOTES

19. KEY WORDS (Continue on reverse side If neceesary end Identify by block number)

Friction, wear, lubrication, metals, complex metal sulfide, surfaces.

20. ABSTRACT (Continue on reverse aide If necessary and Identity by block number)

Studies have been carried out to determine certain basic properties

of the complex metal sulfide, SbSbS., that pertain to its use as a solid

lubricant and lubricant additive material. Past research had demonstrated

that this material exhibited superior extreme pressure (EP) performance,

antiwear properties, and high temperature stability. The present research

has verified the performance under EP conditions as an additive to a base grease. However the performance of SbSbS

4 as a solid lubricant (in

1473 EDITION OF 1 NOV 65 IS OBSOLETE

S/N 01 02-L F-01 4-6601 DD FORM

L' U 1 JAN 73 SECURITY CLASSIFICATION OF THIS PAGE <’IW»#n Data Entered)
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the form of a powder) was not found to be effective at temperatures below

about 225°C. It was noted though that, when used as a dry powder lubricant,

the compound did produce a thick adherent film on steel surfaces in sliding

contact. Six different types of wear and friction tests were carried out

under various conditions of load, sliding speed, contact geometry,

temperature, and time, in order to fully explore the potential of SbSbS^

as a lubricant on several different metals. In a number of cases, its

performance was compared with MoS

? and with other sulfur containing

additives in lubricants. Electron microscopy studies on film material

removed from the sliding contact surfaces have shown that the interaction

of sulfur released from SbSbS^ with the steel surface, presumably at

locally elevated temperatures , is a principal mechanism. However, the

physical characteristics of the SbSbS. film in the contact zone probably

also have a significant role in its overall performance.

USCOMM-NBS-DC

SECURITY CLASSIFICATION OF THIS P AGEfWien Date Entered)
U.s. Dfc PT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (Sec instructions)

4. TITLE AND SUBTITLE

Investigation of the Lubrication Mechanisms of the Complex Metal Sulfide, .SbSbS^

5. AUTHOR(S)

L. K. Ives, M. B. Peterson, J. S. Harris, P. A. Boyer, A. W. Ruff

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struct/on s)

national bureau of standards

DEFARTf'ENT OF COMMERCE

WASHINGTON, D.C. 20 234

7. Con traci/Grant No.

8. Type of Report £< Period C c \ _ r e

d

9.

SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, Stote, ZIP)

10.

SUPPLEMENTARY NOTES

j Document describes a computer program; SF-185, FlPS Software Summary, is attached.

li. ASS i RACT (A 2C0---,ord or less factual su~mory of most significant information. bibl'Og'cphy or literature survey, mention it here)

If document includes a si gn i fi coni

arried out to determine certain basic properties of the

complex metal sulfide, SbSbS., bbbbb , that pertain pertain to its use as a solid lubricant and

lubricant additive material. Past research had demonstrated that this material

exhibited superior extreme pressure (EP) performance, antiwear properties, and

high temperature stability. The present research has verified the performance

under EP conditions as an additive to a base grease. However the performance

of SbSbS^ as a solid lubricant (in the form of a powder) was not found to be

effective at temperatures below about 225° C. It was noted though that when

used as a dry powder lubricant, the compound did produce a thick adherent film

on steel surfaces in sliding contact. Six different types of wear and friction

tests were carried out under various conditions of load, sliding speed, contact

geometry, temperature , and time, in order to fully explore the' potenti al of

several different metals. In a number of cases, its

with MoS 9 and with other sulfur containing additives

studies on film material removed from the

that the interaction of sulfur released from

surface, presumably at locally elevated temperatures , is a However, the physical characteristics of the SbSbS film

SbSbS^ as a lubricant on performance was compared

in lubricants. Electron microscopy

sliding contact surfaces have shown

SbSbS^ with the steel

principal mechanism,

in the contact zone probably also have a significant role in its overall performance

12.

KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Antimony thioantimonate; electron microscopy; lubricant additive; solid lubricant;

wear; wear debris.

13.

AVAILABILITY

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