IAV tribology

7/17/2019 IAV tribology

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Dry friction and wear rates as under liquid lubrication of

Ceramic/ Carbon couples up to 450°C

Jens Kleemann

Rolls-Royce Deutschland Ltd. & Co. KG, D-15827 Dahlewitz/Berlin

Mathias Woydt

Federal Institute of Material Testing and Research, D-12200 Berlin

SummaryIn a high temperature tribometer, stationary carbon have been tested against different rotating Ceramics (SiC,

Si3 N4, Al2O3, WC-6Ni, MgO-ZrO2, (Ti, Mo)(C, N) and stainless steel 1.4876) and the friction and wear behav-

iour have been characterized. The test conditions were chosen as follows:

Normal force Fn = 10 N, sliding velocity v=1-5 m/s, temperature T= 25-500 °C, sliding distance s= 20 km, with

H2O-steam, without intermediate medium and under vacuum. The rotating disks were sharpened, polished and

lapped.

For the most raw material combinations the wear picture is known from the literature. A transfer film with typi-cal wear pattern was found on the rotating disk. With the transfer film lubrication, lowest coefficient of friction

has been found around µ 0,07 in combination with a minimum wear rate of K v 5,010-7

mm³/Nm at 400°C,

v=3 m/s under steam and lapped surface. The combination of antimony graphite EK3245 against MgO-ZrO 2 did

not form carbonaceous transfer layer. Through advanced variation of the roughness up to R PK = 0,011 µm the

wear rate has been reduced up to K v 3.510-8

mm³/Nm at a stable coefficient of friction in a „millirange“ of µ~

0,008 for a sliding distance of 20,000 km. The wear coefficient of EK3245 remains at 4 m/s and temperature of

400°C. As well for the ceramic Al2O3 the coefficient of friction was established in a „millirange“.

With the help of AFM microscope a tribochemical reaction layer has been detected on the used MgO-ZrO 2 ce-

ramic. The identified layer has had a thickness of approximate 50 nm. The chemical elements Zr(OH)4, Sb,

Sb2O3 and Sb2O4 were detected by using Laser Raman and Small Spot ESCA XPS analysis. A carbonaceous

layer could not be confirmed by using these methods of analysis.

A theoretical life time prediction was carried out for the tribological system piston ring/ cylinder in accordance

to the operating conditions of a specific steam engine. The life-time was predicted by means of calculation the

specific (Typical) engine loads and in comparison to the maximum allowable frictional power loss based on the

previously measured wear rates in the low-wear regime. The limits for low-wear/high-wear transitions of the

selected couples were not reached.

1 Introduction

Even under using of latest knowledge from the

research, there is no dry friction mechanism to

substitute the liquid lubrication [1, 2, 3]. Due to

physical characteristics there are boundaries for oils

and greases with regard to high temperature stabil-

ity and –rheology. Above these limits (T>350°C),

where liquid lubricants will be thermal unstably,

dry lubricants can take over the tasks of lubrication

if they have similarly low friction and wear rates.

The use of dry lubricants under boundary condi-

tions has been established for some decades. Inaccording to different applications dry lubricants

exists as pure solid lubricant, gliding varnishes,

coating, as additives inserted in high temperature

materials or as composite up to 1000 °C. Ceramic

engineering materials enforced thereby more and

more.

According to common approach, the tribological

behaviour depends on the formation of a transfer

film on polymer materials [4,5,6,7,8], on extrinsic

or intrinsic solid lubricants [9,10,11], as well as soft

metals [9] (In, Pb, Au) under solid friction [12,].

This well-known wear mechanism is also valid for

Molybdändisulfid [13].

Usually graphite forms also a various pallet of car-

bonaceous reaction products at the transfer layer

[14].

Load, sliding speed, environment, contact geome-

try, roughness adhesion tendency etc. influence the

formation of the layer [15,16].

- 1 -



-well-defined and constant environment conditions,

like vacuum, hydrogen or nitrogen

The characteristics to form a tribological layer

determins the friction and wear behaviour of poly-

mers and solid lubricants. The surface roughness of

the disk determines the thickness of the transfer

film. For each combination solid lubricant /disk or

Polymer/disk“ an optimal thickness of the layer iswell known. A thickness optimum caused by low

friction and low wear rates. After the run in and

formation of the transfer layer the solid lubricant

runs against itself with more or less no contact to

the counter body. Until the run in is not finished,

the wear rate will be high, because of required ma-

terials transfer.

-environment temperature less than 300°C

-less interactions

-parallel oriented shear layer

Nowadays, such requirements and operating condi-

tions are only relevant in the field of micro

mechanics und astronautics however not in me-

chanical engineering or in the automotive industry.

Tribological reactions [23] represents a further

strategy for reduction of friction and wear. Follow-

ing reactions offer a high potential for reducing

friction and wear:The aim to present sliding couples under solid con-

ditions that are comparable to liquid lubricants can

be fulfilled only by the way of avoidance the trans-

fer film.

a. Adsorption of Water [24,25],

b. Formation of hydroxide [26,27],c. Formation of oxides [28,29] und

d. Vapor phase lubrication [30,31] .2 State of Technology

In this work, the tribological relevance of hydrox-

ides will be outlined. The tribological effects that

were obtained so far through the tribochemical

formation of oxides on non-oxide ceramics is in

detail summarized at [28, 29].

Investigations in the last years at different construc-

tion ceramics under dry frictional conditions up to

high temperatures have shown that coefficients of

friction less than µ 0,1 are not even possible. [17,

18]. At these investigations the wear rates are also

not higher than K v>510-7

mm³/Nm. An overview of

dry friction and wear of ceramics has been given by[19, 20]. Mainly, investigations have been done

under atmospheric standard conditions at sliding

speed around 1 m/s and load of 10 N. The wear

coefficients of k v 110-7

mm3/Nm that were partly

reached caused always friction coefficients of µ

0,3.

Under atmosphere conditions, the reaction between

the ceramic surface and steam will be a natural and

odds-on form of lubrication. In the following this

report work up this subject.

By adding up to 6 % by volume of powdered boron

carbide (B4C) with a grit size between about 100

and about 1500 grit in carbon fiber reinforced car-

bon matrix [32], the coefficient of friction lie in a

range of 0,022 to 0,061 at temperatures up to 600

°C, when sliding against magnesium-aluminium-

silicate disks (P~ 0,137 MPa, v ~ 0,54 m/s). The

composite matrix consists of carbon black filler,

resin char and pyrolitic carbon.

Typical lubricated tribological systems achieve

coefficients of friction between 0,15 till 0,05 under

mixed or boundary conditions. Furthermore the

coefficient of friction will decrease up to 10-3

under

hydrodynamic conditions. Dry running tribologicalsystems should have to show friction coefficients

between 0,001 and 0,015 in order to be competitive

against lubricated systems. 3 Experimental InvestigationFirst in the last years, investigations showed up at

special coatings that friction coefficients are reach-

able under dry conditions up to 10-3

[21, 22]. The

effect of the „gliding without friction“ is tied to the

following conditions:

In these investigation the tribological behaviour of

high temperature ceramics have been characterized

under dry conditions up to 5 m/s sliding speed in

deionizied steam with temperatures up to 500 °C.

Along with the normal force of 10 N, the corre-

sponded initial herzian pressure was p~ 135 N/mm².

The experimental setup was equivalent to tribologi-cal system „Piston ring/ Cylinder“ in accordance to

the steam engine [33]. The stationary probe always

-atomistically smooth surface (roughness 2 nm)

-friction capacity less than 1 mW/mm²

-frequency free elastic micro contact

-no reaction layers on the surface

- 2 -



consisted from graphite. Characteristic is the self-

lubricated property of graphite as known from dif-

ferent intrinsic or extrinsic solid lubricants.

Various combinations of materials have been tested

in a large use field at a high temperature tribometer

(HTT). All materials were steam degradation resis-tant. The schematic construction of the HTT is

described in [34] and recognizable in Picture 8-1 as

IR-Thermography.

For this purpose, the parameters sliding speed,

temperature, environment, processing and rough-

ness have been varied. A summary of all examined

materials and parameter combinations gives

. In this publication only the combinations graphite

against Al2O3 and against MgO-ZrO2 have been

considered. By means of different analytics, the

presence of tribochemical reaction layer were de-tected and characterized.

4 Experimental Results

On the ceramic disks Si3 N4, SiC, WC-6Ni,

(Ti,Mo)(C,N) and the stainless steel 1.4876 the

presence of carbon could be detected on the wear

track. [Picture 8-3]. In this case, the well known

wear mechanism „graphite gliding took effect. The

minimal achieved wear coefficient was Kv 5,010-

7 mm³/Nm in conjunction with a coefficient of

friction about µ 0,07. This results were found on

lapped SiC- and TM10-probes with a roughness of

R pk = 0,2µm at 400°C in H2O-steam. All other pa-

rameter and topographies resulted in larger friction

coefficients. These results represent only knowl-

edge that is well known from the literature.

The sliding couple Al2O3/ EK3245 and MgO-

ZrO2/EK3245 depart from the rule of formation of

graphite layer. Both oxide ceramics reached dryfriction coefficients about „millirange“, which were

stable over the complete sliding distance (Diagram

8-1).

The light microscopy (Picture 8-2) shows, that

carbon on the Al2O3 ceramic is only detectable in

less concentrations. On the MgO-ZrO2 ceramic the

presence of carbon is only visible in the pores and

not on the surface plateaus (Picture 8-4).

Picture 8-5 make the influence of antimony clear.

This unexpected result has been established in addi-

tional tests. By means of polishing the roughness of

the MgO-ZrO2 ceramic has been reduced up to R pk =

0,011µm. The consequence of smoother surface

was an additional reducing of the coefficient of

friction up to K v 3.510-8

mm³/Nm.

Detected friction coefficients were about µ 0,008.

Corresponding results are representing in Diagram

8-3 and Table 8-2.

Diagram 8-2 shows the coefficient of friction ofgraphite EK3245 as function of the sliding speed.

The coefficient of friction in the range of 10-8

mm³/Nm was found up to 4 m/s between 250 °C

and 450 °C.

Several times repetition has produced identical

results of this ultra low friction and wear.

For comparison reasons, a second antimony im-

pregnated graphite (FH82A) has been tested against

MgO-ZrO2 (R pk = 0,011µm). With a sliding speed of

3 m/s at 400°C the friction coefficient could not

keep down. as previous sliding couple. The friction

coefficient was between 0,02 and 0,025.with a

respective coefficient of wear about K v= 4,010-7

mm³/Nm.

5 Analytical Investigation

By means of surface analytic AFM Microscope,

Laser Raman and Small Spot ESCA, the surface

change of the ceramic MgO-ZrO2-has been ana-lyzed before and after tribological testing. The

focuses of investigations were the formation and

presence of tribochemical layers in the wear track

caused by Graphite, Antimony, Zirconium Oxide

and Steam.

5.1 AFM Microscopy

The in Picture 8-6 presented surface topography

shows the formatted reaction layers in the wear

track on MgO-ZrO2. In the lower unused area of the

100 x 100 µm photo, grain boundaries of each sin-

gle crystal are recognizable. The upper picture area

presents the transition region to the used zone. The

formation of a tribochemical reaction layer has been

detected with the shape of agglomerates. The pro-

file (Picture 8-7) shows the raised layer with a

thickness about 50 nm

5.2 Laser Raman

Laser-Raman is well suitable for structural analysis

of nanocrystalline phases. For the investigation ofthe graphite transfer layer on MgO-ZrO2, the disk

has been scanned with the 488nm Raman-

- 3 -



Spectrum. Scans has been made into the pores and

on the wear track (Diagram 8-4). The spectrum of

the measurement on the wear track owns in the area

of 1300 cm-1

till 1500 cm-1

only the known fluores-

cence bands of MgO-ZrO2. No typical carbona-

ceous peaks could be found.The measuring in the pore yielded a Raman peak at

1576 cm-1

at 1619 cm-1

. This peak was identified as

carbon [35].

Even though carbon hasn’t been found, Diagram

8-5 shows different results of the intensity under

equal measuring conditions (10 mW Laser power,

90 sec. Count time). In the area of the track, im-

pulses were between 14500 – 22000. Outside the

track impulse about 24000 were detected. The track

seems to be covered with a thin layer, which weak-

ens the laser light as well as the reflected back scat-tered light By means of Small Spot ESCA and XPS

additional investigations has been made.

5.3 Small Spot ESCA XPS

On the unused MgO-ZrO2-ceramic, binding ener-

gies of zirconium Zr 3d5 with 181,5 eV, binding

energies of magnesium Mg2s with 88,1 eV and the

belonging binding energies to oxygen O1s with

529,9 eV have been detected. These binding ener-

gies were allocated to ZrO2 and MgO. Because of

the oxygen peak O2s with 525,8 eV absorbed H2O-

steam was existing on the surface.

Under dry test conditions, the detected Zr- binding

energy showed not difference in according to the

unused MgO-ZrO2-ceramic. The detected peaks

could also assign to ZrO2 and MgO ceramics. Addi-

tional analysis on the wear track produced binding

energy- peaks of antimony Sb4d4. the binding en-

ergy of Sb4d with 33,86 eV could classify to the

metallic antimony. In accordance with the literature

the peak Sb4d with 35,14 eV is Sb2O4. The detected binding energy of O2s with 29,95 eV could assign

to adsorbed H2O.

With the help of Small- Spot- ESCA analysis, on

the wear track of MgO-ZrO2 ceramic zirconium

dioxide peaks Zr3d5 with 181,74 eV and Zr3d3

with 184,21 eV, as well as an unknown zirconium

peak have been detected under H2O steam at 400°C

(Diagram 8-6). The supposition that, it could be a

kind of hydrate or hydroxide has been confirmed by

means of Zr(OH)4-reference powder (Diagram 8-7).The binding energy of Zr3d5 with 183,36 eV and

Zr3d3 with 185,83 eV have been clearly identified

as zirconium hydroxide Zr(OH)4 (CAS: 14475-63-

9, density= 3,25 g/cm³). The binding energies for

zirconium of 183,6 eV for zirconium hydroxyde

were additionally confirmed by [36].

At the consideration of the antimony elements, a

third has been detected compared with metallic andoxide antimony.

Because of missing reference, the third antimony

element could not specified in detail. It could be an

Oxide of antimony with a higher oxidation rate

(Sb2O4+n). (Diagram 8-8).

6 Discussion

During the tests there has been analysed the forma-

tion of a tribochemical reaction layer by using

graphite against MgO-ZrO2 ceramic disks by tem-

perature at 400°C and H2O steam. The formation of

antimony oxide of different oxidation grades could

be evidenced. Due to quantitative analysis a reac-

tion layer of hexagonal agglomerates were found.

The identified layer at the counter disk had a thick-

ness of approx. 40 nm.

There was none indication of clear changes in the

structure of the zirconium oxide ceramic which

improved the behaviour. For the first time graphite

debris which are in condition of formation of trans-

fer layer on ceramics has surprisingly not been

identified. These extremely low friction and wear

rates are subject to a positive combination of vari-

ous parameters.

The major impact is attributed to the zirconium

hydroxide [37] that is thermal stable up to 650°C.

Especially the XPS-data in Figures 8-6 and 8-7

suggests, that hydrous zirconia ZrO2nH2O was not

formed [36].

Referring to various papers, reduction effects on

wear and friction were stated in the formation ofHydroxides and „Pseudo-Hydroxides“ [38] formed

on TiO2-, ZrO2- and Al2O3-surfaces.

Gates [39,40] gave evidence on decreased wear and

friction rates in H2O caused by the formation of a

transfer layer as Al(OH)3 [Gibbsite] or -Al(OH)3

[Bayerite] and Boehmite [-AlO(OH), HV~8.000

MPa] on Al2O3. Relatively weak bonds reflect the

structure of both hydroxides and hydrates. The

difference is only the kind of layer stacking (Picture

8-8).). Boehmite will be formed above 194°C and

Gibbsite above 100°C.

- 4 -



Gardos [41] investigates the characteristic of oxida-

tion of MoS2 under friction and wear contact. In

this connection he characterised also the influence

of Hydroxides of friction and wear. He describes

the formation of an outer oxidation layer. The layer

consists of MoO3 which has low shear stress.On the boundary layer of MoO3, H2O molecules are

available which are bonded by hydrogen. For this

reason, hydroxides are not impossible. Particularly

the low friction and wear rate of Molybdänhydrox-

ide-Hydrate (Ilsemannite, JCPDS.-Nr. 210574) has

been confirmed [42] in corresponding investiga-

tions. Picture 6-1 shows the coordination of H2O-

molecule between Molybdenum [43]. In this case

[MoO5(OH2)]n is present in an octahedron shape.

Hydrogen bonding connects the different Above

450°C the dehydratation to MoO2,8 is closed.

Picture 6-1 Projection of MoO3x1H2O-Structure

into [001]-direction

The Cobalt hydroxide (Co(OH)2) that was used as

an additive has shown a wear reduction in corre-

sponding investigations [44]. Zirconium hydroxide

has also a layer structure [45] which preferred a

favourable friction and wear characteristic [46].

Picture 6-2 atom model of Sb2O3 Valentinit

The tested graphite EK3245 (with approx. 10%

antimony) had the largest share in antimony of

everybody. The physical properties are similar to

the metallic lead or tin. Because of low shear

strengths these metals are preferred to using into

bearings. At the analytical investigations Sb, Sb2O3

as well as Sb2O4 have been detected.

Sb2O3 [Valentinite, CAS: 1317-98-2, HV~780 MPa,=5,76 g/cm³] is thermodynamic stable in the range

from room temperature up to 370°C. Valentinite

has very long double- bonds, which keep together

with less Sb-O bonds [47].

For this reason Sb2O3 is a preferred additive for

gliding varnishes, for oils or for powders [48].

From 370 °C Sb2O3 reacts very slow exotherm to

Sb2O4 (Cervantit, HV~2,600 MPa). Due to hot envi-

ronment up to 400°C, presence of steam and addi-

tional increase of temperature because of friction

power (hot spots) other oxides of antimony are possible.

As a further influence parameter, the catalytic effect

of graphite, steam and zirconium has to be men-

tioned.

On the one hand, the intercalation of steam into

graphite caused a decrease of shear strength and

reduction of the coefficient of friction.

On the other hand, the steam is reacting with graph-

ite around 400°C. Following reactions are possible

[49]:

C + H2O CO + H2

CO + H2O CO2 + H2

These reactions are supported by the hot spot tem-

perature increase in the micro contact due to exo-

thermal reaction from Sb2O3 to Sb2O4.

Picture 6-3 atom model of Sb2O4 Cervantit

The extreme low friction and wear coefficient that

were achieved are based on a favourable combina-

tion of each single analysed reaction.

- 5 -



7 Wear Life Prediction

The previous elaborated tribological data represent

the base in order to answer the question, if a dry

running steam engine is possible from the tribologi-

cal point of view. The theoretical life time predic-tion was carried out for the tribological system

piston ring/ cylinder [Picture 8-9] in accordance to

a state of the art steam engine [50,53]. The life-time

was predicted using the specific (Typical) engine

loads and in comparison to the maximum allowable

frictional power loss based on the previously meas-

ured wear rates in the low-wear regime. The basic

methodology is published in [51].

7.1 Determination of the Material SpecificFrictional Power Loss

The characteristic of the applied test geometry is,

that due to the point contact, the wear starts at

“high” contact pressures (PH < 135 MPa), which

decreases with increasing wear scar diameter. Since

the test equipment measures the total wear length of

both samples, the wear rate can be correlated to the

contact pressure at any test time. Diagram 8-9

shows the transition from severe to mild wear and

the resulting critical geometric contact pressure for

this set of test parameters. Based on this diagram

the allowable frictional power loss [PxVxµ; P=geometric contact pressure, V= sliding velocity and

µ = coefficient of friction] were calculated on Table

8-3.

7.2 Specific Engine Loads

For practical application, the critical contact pres-

sure and resulting frictional power loss of the mate-

rial couple have to be below the current engine

loads to ensure always low wear rates. Exemplary

engine loads were calculated with following as-

sumptions:

Temperature of 400°C, injection pressure of the

steam of 5,0 MPa with an expansion to e.g. 1,2

MPa. sliding speed of 3 m/s and minimum life time

of 10,000 h.

The upper first piston ring was considered as the

highly loaded component, but also including the

second piston ring and the carbon piston itself in

the predictions.

On the basis of a typical carbon piston ring dimen-

sions [height=5 mm; thickness= 8 mm; =160

mm] with an allowable loss of radial thickness t=3

mm the wear coefficient has to be in the range of

110-8

mm³/Nm to achieve a life time of approx.

10,000h.

The frictional power loss (Diagram 8-9) can be

calculated using the steam pressure versus crank

angle resulting with the geometric data in a function

of normal force for each tribosystem versus crankangle and the sliding speed versus crank angle.

The ultra low wear coefficient (for dry running!)

coming out from the tribological analysis could

only me matched in the tribometer investigation

from the couple MgO-ZrO2/ EK3245 and nearly

with Al2O3/ EK3245 after running-in (in the low-

wear regime!) as shown in Diagram 8-9.

The outcome of the values in table 8-3 is that the

frictional load in the engine has to be below 0,8

W/mm² for MgO-ZrO2/ EK3245 and below 0,25 for

Al2O3/ EK3245. Diagram 8-10 is showing the re-quired maximum frictional load under above men-

tioned conditions.

Comparing to Table 8-3 these material couples are

able to meet the criteria for a low wear rate in the

mentioned steam engine applications.

Leaving out the running-in wear from the wear

rates given in chapter 4 lead to differential wear

rates of 1,1210-8

mm³/Nm for MgO-ZrO2/ EK3245

and 3,4510-8

mm³/Nm for Al2O3/ EK3245.

This notable comparison does not substitute engine

tests, but predicts a high potential for a reasonable

integration of these material couples in the steam

engines without a liquid or gas phase lubrication

[52].

8 Acknowledgements

The authors would like to take this opportunity to

thanks Mr. J. Schwenzien for the profile and sur-face measurement, Mrs. S. Binkowski and Mrs. R.

Pahl for the microscopy and test body preparation.

Furthermore the authors would like to say thank

you to Dr. K. Witke for Laser Raman investigation.

Thanks are also addressed to Mr. D. Treu for the

Small-Spot-ESCA-Measurements and to Dr. T.

Schneider for the AFM-profilometry.

The experimental works was in part financially sup-

ported by Ingenieurgesellschaft Auto und Verkehr

(IAV GmbH, D-10587 Berlin) in the frame of the

“Zero Emission Engine” [53]. The application of

this work is in part now continued by Enginion AG,

D-13355 Berlin.

- 6 -



Parameter Couples and Test Conditions

DiskAl2O3

[A19999.7]MgO-ZrO2

[ZN 40]SSi3 N4

[ND 200]SSiC

[EkaSiC D]WC-6Ni

[C7P](Ti,Mo)(C,N)

[TM 10]]Stahl 1.4876

PinEK 32451

antimonyimpregnated

EK 32051

antimonyimpregnated

R 77101

Kunstharzimpregnated

FH 82A2

antimonyimpregnated

FU 24512

Mesophase

ISO 883

Mesophase

ZXF-5Q4

Mesophase

roughness [µm] rotating

disk0,01 0,06 0,15 0,2 0,35 0,5 -

manufacturing polished lappedgrinded

[radial]

grinded

[axial]Pen shoot lapped - lapped -

Sliding speed [m/s] 1 2 3 4 5 - -

temperature [°C] 20 100 200 300 400 450 500

ambiente H2O- liquidH2O steam

100% rel. H.

air

50% rel. H.

UHV

210-3Pa- - -

Table 8-1 test parameter at 20,000m sliding distance and 10 N normal force1 Fa. SGL Carbon,

2 Fa. Schunk,

3 Fa. MGG/ Toyo Tanso,

4 Fa. Poco

Picture 8-1 Thermography of the couple EK3245 /MgO-ZrO2 under dry conditions at 22 °C, v= 3 m/s,

Fn= 10 N and s= 17.000 m

Picture 8-2 Morphology of the wear track EK3245 / Al2O3, 400°C, H2O steam, v=3m/s, Fn= 10 N

and s= 20.000 m

- 7 -



Picture 8-3 Morphology of the wear track ISO 88 /SSiC, 400°C, H2O steam, v=3m/s, Fn= 10 N

and s= 20.000 m

0

0,01

0,02

0,03

0,04

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

sliding distance s [m]

C o e f f i c i e n t o f f r i c t i o n µ

F N =10 N

v =3 m/s

t = 400°C

s = 20000 m

steam

Disk:MgO-ZrO2 / Al2O3

Ball: EK3245

EK3245 / MgO-ZrO2

EK3245 / Al2O3

Diagram 8-1 solid-state coefficient of friction as function of sliding distance of antimony impregnated

graphite against Oxide ceramic at 400°C

Picture 8-4 Morphology of the wear track EK3245 / MgO-ZrO2 400°C, H2O steam, v=3m/s, Fn= 10 N

and s= 20.000 m

- 8 -



Picture 8-5 Morphology of the wear track on MgO-ZrO2 ceramic with the graphite:

left , a) ISO 88 right, b) EK 3245

Number. 1 2 3 4 5 6 7 8 9

manufacturing /

grain size

polished

1µm

polished

3µm

polished

6µm

polished

9µm

polished

15µm

polished

15µm

lapped

20 µm

lapped 50

µm

lapped

80 µm

Roughness R pk [µm] 0,007 0,010 0,011 0,021 0,033 0,035 0,029 0,046 0,183

Coefficient of wear

K v [mm³/Nm]1,34 10-7 6,01 10-8 3,27 10-8 8,01 10-8 1,01 10-7 1,52 10-7 1,29 10-7 1,44 10-7 5,08 10-7

Friction coefficient µ 0,02 0,01 0,008 0,03 0,02 0,04 0,03 0,02 0,01

Table 8-2 Friction coefficient and coefficient of wear of EK3245 as a function of the roughness andmanufacturing of MgO-ZrO2 at 400°C H2O-steam

0

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0,08

1 2 3 4 5

sliding velocity s [m/s]

C o e f f i c i e n

t o f f r i c t i o n µ

F N =10 N

t = 400 °C

s = 20000 m

steam

Disk: MgO-ZrO2

Ball: Carbon EK 3245

Diagram 8-2 Coefficient of friction of MgO-ZrO2/EK3245 as a function of the sliding speed at aroughness of R pk 0,01 µm

- 9 -



1,00E-08

2,10E-07

4,10E-07

6,10E-07

8,10E-07

1,01E-06

1,21E-06

1,41E-06

1,61E-06

W e a r C o e f f i c i e n t B a l l [ m m ³ / N

m ]

100 200 300 400 450 500

Temperature T [°C]

dry air

steam

F N =10 N

v =3 m/s

s = 20000 m

Disk: MgO-ZrO2

Ball: Carbon EK3245

Diagram 8-3 wear coefficient of MgO-ZrO2 as a function of the environment under dry friction with and

without steam

0

5000

10000

15000

20000

25000

30000

1100 1200 1300 1400 1500 1600 1700 1800

wave lenght cm-1

I n t e n s i y

0

500

1000

1500

2000

2500

3000

3500

wear track

pore

Diagram 8-4: Laser- Raman peaks on MgO-ZrO2 into the wear track and pore

- 10 -



0

5000

10000

15000

20000

25000

30000

1100 1200 1300 1400 1500 1600 1700 1800

wave lenght cm-1

I n t e n s i t y

wear track

pore

Diagram 8-5: Laser Raman peaks on MgO-ZrO2 wear track and into pore

Picture 8-6: Topography of the wear track MgO-ZrO2/EK3245 at T= 400 °C H2O-steam

Picture 8-7: Profile measurement on the wear track of MgO-ZrO2/EK3245 at T= 400 °C H2O-steam

- 11 -



Diagram 8-6 Binding energy of Zr after testing

Used at 400 °C, steamed, offset +2,22

Diagram 8-7 Binding energy of Zr(OH)4

Reference powder, offset +0,00

Diagram 8-8 Binding energy of Sb after testing at 400 °C, steamed, offset +2,22

- 12 -



Picture 8-8 Structure of Bayerit and Gibbsit as Hydroxide or Hydrate of Aluminum oxide

Picture 8-9 typical piston/ cylinder arrangement of steam engines

- 13 -



0

0,005

0,01

0,015

0,02

0,025

0,03

0,035

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

sliding distance s [m]

l i n e a r W e a r R a t e W l [ m m ]

FN =10 N

v =3 m/s

t = 400°C

s = 20000 m

H2O steam

Disk: MgO-ZrO2 / Al2O3

Pin: EK3245 Al2O3

MgO-ZrO2

Pcritical=8,32 N/mm²

Pcritical=28,29

Diagram 8-9 linear wear as a function of sliding distance of MgO-ZrO2 and Al2O3 mated with EK3245

Materi al cou-pl es

Pcr [N/ mm²]

v[m/ s]

µ P v µ[W/ mm²]

Al 2O3/ EK3245 8, 32 3 0, 01 0, 25MgO- ZrO

2/ EK3245 28, 29 3 0, 01 0, 8

Table 8-3 calculated frictional power loss with a friction coefficient of µ=0,01

Friction power loss for µ= 0,01

0,00

0,05

0,10

0,15

0,20

0,25

0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360

Crankshaft Angle

p x v x µ [ W / m m ² ]

Piston

1. Pistonring

2. Pistonring

Diagram 8-10 Frictional power load/loss as a function of crankshaft angle

- 14 -



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