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Geophysical Monograph Series
Vol. 67
CHARACTERIZATION
OF SAMPLE
ENVIRONMENT
IN A UNIAXIAL
SPLIT-SPHERE
APPARATUS
Robert C. LIEBERMANN and Yanbin WANG
Centerfor High PressureResearch* and Departmentof Earth and SpaceSciences,
State Universityof New York, StonyBrook, N. K 11794-2100, USA
Abstract. The distributionsof stressandtemperaturein solid-mediatype,
high-pressureapparatusare importantparametersin characterizingthe
sampleenvironmentandin the designof experimentsat highpressuresand
temperatures.In a 2000-ton uniaxial split-sphereapparatus(USSA-2000),
we have developed techniquesto control and monitor the pressureand
temperaturedistribution,the deviatoricstressand strain,and the oxygen
fugacity. Pressurecalibrationat room temperatureis a function of anvil
dimensions,grade of tungstencarbide and gasket design;the pressure
gradientdeterminedusingthe Bi and CaGeO3 transitionsandthe densification of amorphoussilica varies from 50 to 500 MPa/mm. At high
temperature,the cell pressurecan be enhancedor diminishedrelative to
room temperature;in pyrophyllite cell assemblies,relaxationprocesses
causethe pressureto decreasewith run duration.Temperaturegradients
are measuredby monitoringmultiple thermocouplesor applicationof
pyroxene geothermometryin examinationof the run products;these
gradientsare sensitiveto the capsuleandmediasurroundingthe sample
andvary from 15 to 150øC/mm.The deviatoricstressat hightemperature
is estimatedwith the use of syntheticMgO and natural olivine single
crystalsas in situ piezometers;it is governedby the propertiesof the
confiningmediasurrounding
thesampleandcanbeadjustedandcontrolled
from lessthan 10 MPa in NaC1 to more than 500 MPa in BN or MgO cell
assemblies.Strain marker experimentsat room and high temperature
demonstratethat the deformationis relatively uniform throughoutthe
specimen.Soft Fe capsuleshavebeenemployedto containolivine single
adapting technologiesfor the USSA-2000 is to create a
"sample friendly" apparatus for physical, chemical and
mechanicalexperimentsof importanceto geophysicsand
geochemistry.
The purposeof this paper is to describethe techniques
which havebeendevelopedin our laboratoryto controland
characterizethe sample environment,including pressure,
temperature,
deviatoricstressandstrain,andoxygenfugacity,
as well as the computer-controlledsystem to adjust and
monitor the heating,cooling and decompressioncycles.
High PressureApparatus
The USSA-2000 was designedafter a similar 5000-ton
devicedevelopedby E. Ito at theInstitutefor the Studyofthe
crystals
andtobufferthepo2fordiffusion
experiments.
Thesecontrollable
environmentalparametershave been utilized to design and execute a
variety of high-pressure,high-temperatureexperimentsto studykinetics
and mechanisms, deformation, diffusion, crystal growth, hot-pressing
andphaseequilibriafor materialsof geophysicalandpetrologicalinterest.
Introduction
The continueddevelopmentof large-volumehigh-pressure
apparatusover the past twenty-five years, most notably in
Japanbutmorerecentlyalsoin othercountries,hasprovided
many exciting opportunitiesand challengesfor researchin
thephysicsandchemistryof Earthmaterials.Justprior to the
3rd U.S.-JapanHigh PressureSeminarin January1986, we
installeda 2000-ton uniaxial split-sphereapparatus(USSA2000) in ourlaboratoryat StonyBrook(seephotoin Fig. 1).
In additionto thelargesamplevolume,(50 mm3at 10GPa
and3 mm3at 25 GPa),a key featureof suchapparatus
is the
ability to adjust,control,and characterizethe sampleenvironmentandtherebytakeadvantageof thetechniquesdeveloped at lower pressures.Our objectivein developingand
*A NSF Scienceand TechnologyCenter.
Figure 1. PhotoofTibor Gasparikinsertingthe MA-8 second-stage
anvilsin
the 2000-tonuniaxial split-sphereapparatus(USSA-2000).
19
High-PressureResearch:Application to Earth and Planetary Sciences,editedby Y. Syonoand M. H. Manghnani,pp. 19 - 31.
¸ by Terra ScientificPublishingCompany(TERRAPUB), Tokyo / AmericanGeophysicalUnion, Washington,D.C., 1992.
Geophysical Monograph Series
Vol. 67
UPPER
GU I DEBLOCK
UNIAXIAL
PRESS
GUIDEBLOCKS
NO. 6
ANVIL
NO. 4
070
SPLIT-SPHERE
CUBE
ILS
2000TON
ClACK
I [
LOWER
GUIDEBLOCK
Figure 2. Schematicdiagramof USSA-2000 and detailsof first-stage
sphericalanvilsin guideblocks.
Earth's Interior of Okayama University (Ito and Yamada,
1982; Ito et al., 1984; seealso Liebermannet al., 1985). As
shownin Fig. 2, it consistsof a 2000-tonuniaxialpresswith
a two-stageanvil systemcapableof generatingpressures
above 20 GPa and temperaturesin excessof 2000øC. The
first stageis a tool steel spheresplit into six parts, glued
permanentlyinto upperand lower guideblocks,andenclosing a cubic cavity (60 mm on edge) which containsthe
secondstageanvil assembly.The lower guideblockcan be
removedfrom the presson a carriageto facilitate accessto
the secondstageandcell assemblyduringthepreparationof
an experiment.The pressis driven by a hydraulicsystemof
domesticdesign;a hydraulicpressureof 180 MPa appliedto
thejack (diameter= 370 mm) correspondsto an axial force
of 2000 tons and generatesa pressureof 3.1 GPa on the
interfacebetweenthe first and secondstageanvils (Fig. 3).
I
HYDRAULIC
PRESSURE
[KGF/CM*CH)
HYDRAULI
ANVIL
TRUNCATED
SURFACE
PRESSURE
AND
C
VS
PRESSURE
PRESS
TONNAGE
1
MAX.
1860
, P
q30
ANVIL
TRUNCATED
SURFACE
PRESSURE
6020
I MAX.
$2040
P; (KGF/CM*CM)
t ooo
MAX.2000
PRESS
TONNAGE
(TONF)
Figure3. Presstonnageandpressure
at surfaceof thefirst-stage
anvilforUSSA-2000asa functionof hydraulicpressure
appliedtojack
(370 mm diameter).
20
LIEBERMANN
ET AL.
Geophysical Monograph Series
Vol. 67
blies(Fig. 5) usingthephasetransitionsin Bi I-II (2.55 GPa),
Ba I-II (5.5 GPa), Bi III-V (7.7 GPa; all from Lloyd, 1971),
ZnS (15.5 GPa; Block, 1978), GaAs (18.3 GPa; Suzukiet al.,
1981) and GaP (22.5 GPa; Dunn and Bundy, 1977). The
calibrationsfor the 18/12, 14/7.5 and 10/5 cells were performed using Kennametal grade KZ 313 tungstencarbide
cubes, while the 10/4 and 7/2 calibrations are for Toshiba
W C ANVI
Cl
PRESSURE MEDIUM
Tungaloy grade F material. The strengthof these secondstageWC anvilsplays a critical role in generatingpressures
above15 GPa. We havetestedthesetwo gradesplusHertel
gradeKF1 HIP (providedby the BayerischesGeoinstitutin
Bayreuth,Germany): all of the anvils exhibitedsignificant
plasticdeformationnearthe triangularfaceat cell pressures
above 16 GPa (Fig. 6). At the GaAs transition,this deformation was mostpronouncedfor the Kennametaland least for
/ ' SPACER
PREFORMED••
the Toshiba
cubes.
The pressureefficiency(ratio of cell pressureto hydraulic
oil pressureon the ram) hasbeenfoundto be very sensitive
to the detailsof the designof the preformedgaskets(Fig. 4).
For the 7/2 cell assembly,the calibrationcurvein Fig. 5 is for
pyrophyllitegasketsof squarecross-section
(Type A in Fig.
7). If either the cross-sectional
area of the pyrophylliteis
increased(Type B) or teflon back-up gasketsare addedto
reduce
flow of the pyrophyllite (Type C), the pressure
•---3
2mm----•
efficiency is dramatically diminished.Consequently,the
Figure4. Secondstageof theUSSA-2000 with theassemblyof eighttungsten Type A gasketandthe Toshibacubeshavebeenadoptedfor
experimentsof MgSiO3-perovskite(seeWang
carbidecubicanvilsof truncationedgelength(a) whichcompress
an octahe- the synthesis
dral pressuremedium(modifiedafter Sawamoto,1986).
et al., 1990).
We havetwo experimentswhich bearon the questionsof
The second stage is assembledoutside the press and the pressuredistributionwithin the cell assemblyat room
consistsof eight tungstencarbidecubesseparatedby pre- temperature.As part of a neutrondiffraction study in irreformed gaskets and spacers.Each cube has one comer versiblydensiftedfusedsilica (Susmanet al., 1990), we intruncatedinto a triangularface; the eight truncationscreate serteda specimenrod directlyintothe 10/5 cell assemblyand
an octahedralcavity in which the pressuremediumis com- compressedit to a hydraulicpressureof 500 barsat 25øC for
pressed(Fig. 4). The cell assemblyis an octahedronmadeof a periodof 2 hr; this shouldcorrespondto a cell pressureof
pyrophyllite or semi-sinteredMgO. The secondstage is 18 GPa accordingto Fig. 5. Upon recovery from the high
electricallyinsulatedfrom the first stageby phenolicsheets. pressureapparatus,
thefusedsilicaspecimens
(nowassuming
Electricalinsulationbetweenthe adjacentcubesis provided an hour-glassshapedue to extrusionof the octahedralcell)
by teflon tape.
werefoundto becrackedby microfracturebutstill intact(Fig.
Cell assembliesusedin the USSA-2000 are identifiedby 8). A sectionthroughthe specimenwasprobedwith a laser
a pair of numbersseparatedby a slashwherethe firstnumber beam, and the pressureprofile was estimated from the
representsthe edgelengthof the ceramicoctahedronandthe Brillouin frequencyshiftsby M. Grimsditch(see Susmanet
secondnumberis the truncationedge length (TEL) on the al., 1990). Figure 8 demonstratesthe "negativeanvil" effect
comerofthe tungstencarbidecubes.For example,an assem- in that the pressureat the anvil face is 2 GPa higherthan at
bly whichutilizes an octahedronof edgelength 18 mm with the center of the cell. There is little or no radial pressure
cubestruncatedto 12 mm is designatedas the 18/12 cell gradient,however. These observationsand the fact that the
assembly,18/12, 14/7.5, 10/5, 10/4, 7/2 are different types densificationprocesswas time-dependent,are most likely
currentlyin use in our laboratory.
the result of relaxationprocessesin the compressedsilica
specimenas reportedearlier by Meade and Jeanloz(1987,
Pressure Calibration
and Distribution
1988). Of more direct relevanceto the actual conditionsin
most of our USSA-2000 experiments,the pressuregradient
The cell pressureversusram load relationshiphas been at roomtemperaturealongthe lengthof the samplefrom the
calibratedat room temperaturefor eachof thesecell assem- midpoint of the furnaceto the cold end hasbeen determined
LIEBERMANN
ET AL.
21
Geophysical Monograph Series
Vol. 67
FORCE (tons)
25
I00
200
I
I
300
400
I
500
I
600
I
700
I
I
GaP
2O
_
GaAs
ZnS
•
7/2
•'""'••• X •
USSA-2000
STONY BROOK
-x--•-
••' .....
10/5
14/7.5
© MgO
Bi•_½
o Pyrophyllite
Ba
i
I00
200
300
400
500
600
700
800
GAUGE PRESSURE (bar)
Figure5. Cell pressure
vs.hydraulicoil pressure
for variouscell assemblies
at roomtemperature.
Data for the7/2 and 10/4assemblies
arefor ToshibagradeF carbidecubeswhilethosefor the 10/5, 14/7.5and18/12assemblies
arefor Kennametal
gradeKZ 313 cubes.
the cell pressureto be eitherincreasedor decreasedfrom the
value based on the room temperaturecalibration.Phase
transformations
to a more densephaseor dehydrationin the
_•,
0
solidmedia in the hot zone of the samplechambercausea
TungstenCc•rbid½
generaldecreaseof the pressure.The cell pressurewill also
decreasedue to compactionand sinteringof the pressure
mediumandcell partsduringcompression
at hightemperature.Anotherfactorwhichtendsto decrease
thecellpressure
is the decreasein the shearstrengthof
Figure6. Typicalplasticdeformationobservedin thetungstencarbidecubes. at high temperatures
the pressuretransmittingmedium. The heatingof the cell
For the 7/2 assemblyand Type C gaskets(Fig. 7, the amplitudes of the deformationafter achievingthe GaAs transitionhas been measuredfor the
tends to act in the oppositedirection by increasingthe
KennametalKZ 313 (150 micron),HertelKF 1HIP (100 micron)andToshiba
volumeofthehighpressure
chamberduetothermalexpansion
F (75 micron)grades.
andcompensates
(partiallyor completely)the effectscausing a decreasein the cell pressure.
to be 0.04 GPa/mmin experiments
usingthetransitionsin Bi
The actualcell pressuresgeneratedat high temperature
in a 18/12pyrophyllitecellassembly(Remsbergetal., 1988). will be the resultantof thesecompetingfactorsunder the
Pressuregradientsat hightemperaturearelikely to be lower prevailingconditionsof temperatureand pressureand are
andarecertainlylessthan0.1 GPa/mmin the 18/12assembly dependent
upontheinherentphysical,chemical,thermaland
based on reversalsof the garnet-perovskitetransitionin mechanicalpropertiesof the materialof the cell assembly.
CaGeO3(Susakiet al., 1985) by Wang (1991).
Consequently,
it is difficultto predictin advancewhetherthe
Variouscompetingfactorsat hightemperatures
will cause pressuresat high temperaturewill be higher or lower than
• Anv•
0i•nn•r
22
LIEBERMANN
ET AL.
Geophysical Monograph Series
0
•
.........
7-2
Vol. 67
• ......... t ......... • .........
Assembly, Rm T
Toshiba F-grade
25
! .........
I .........
80
•
70
Carbides
x
CaGe03
½ 6o
GaP
l/2hour •"'"•
. .]'• 2hou•
TTT-'•
• 5o
•;20
• 4o
J
•15
J
50
o 20
0
MgO
/
•
I00
2(•0
500
400
LOAD
...................
0
,
100
...................
200
, .........
300
400
Oil Pressure,
, .........
500
5O0
x
600
700
Uons)
,
600
"700
bar
Figure 7. Roomtemperaturepressurecalibrationfor the 7/2 systemusing
ToshibaF-gradecubes.Threedifferentgasketsystems(A, B, andC) were
testedwith the followingcross-sectional
dimensions:
Type A 2.4 x 2.4 mm pyrophyllite
Type B 2.5 x 3.2 mm pyrophyllite
Type C 2.4 x 3.2 mm pyrophyllite
and 2.4 x 3.2 mm teflon back-ups.
Figure9. Pressure
calibrationof 18/12cellassembly
atroomtemperature
and
hightemperature.
Datafor pyrophyllitecellssuggests
thatcellpressure
drops
as a function of time due to flow and relaxation of materials within the cell.
No suchtime-dependent
behavioris observedfor theMgO cells(seealsoLu,
1990).
pyrophylliteoctahedronis replacedby semi-sintered
MgO,
thepressureefficiencydecreases
butthecell pressureathigh
temperatureis no longera functionof run duration(Fig. 9).
TemperatureCalibrationandDistribution
Temperatures
in the sampleare generatedvia cylindrical
furnacesof graphite,lanthanumchromite,or metalsinserted
in the octahedralcell (e.g. Fig. 10) and measuredwith
W3%Re/W25%Re thermocouples
andcontrolledautomatically. No correctionfor the effectof pressureon the thermocouple
emfisapplied;althoughsuchW-Re thermocouples
are less ductile than those fabricated from Pt-Rh and thus
4mm
I
Figure8. Schematic
cross-section
of recoveredsilicasamplecompressed
to
500 barsoil pressureat 25øC in a 10 mm MgO sampleassembly.Brillouin
frequencyshiftsat pointsmarked 1 to 7 are usedto estimatethe pressure
distributionin the sample.Points1-4 are at 14 GPa, while points5-7 are at
16 GPa (datacourtesyof M. Grimsditch;seealsoSusmanet al., 1990).
moreproneto breaking,theeffectof pressure
ontheiremfis
generallythoughtto be lesspronounced(e.g. Gettingand
Kennedy, 1970; Ohtani et al., 1982).
The temperaturedistributionin the samplemay be adjustedby modifyingthe cell designaccordingto the objectives of the experiments:for example, to producehigh
temperaturegradientsfor crystal growth or to capture a
univariantphaseboundaryor low temperaturegradientsto
synthesizelarge specimensof singlephaseand homogeneous
texture.
For the 10/5 cell assembly(Fig. 10), Gasparik(1989) has
estimatedthe temperaturedistributionin the encapsulated
thoseat room temperature.In the 10/4 assembly,Gasparik sampleusingthemethodof Takahashiet al. (1982) basedon
(1989) observedthat the cell pressureswere 2 GPa lower at thesolubilityofenstatitein thediopsidicpyroxenecoexisting
1400øC than at 25øC. By contrast, Gwanmesia and with the enstatiticpyroxene.Figure 11 is a plot of the
Liebermann(this volume) have found a 2.5 GPa pressure isothermsinferred from the enstatite-diopsideexperiment
enhancement
at 1000øCin the 14/7.5 assemblycomparedto andshowsthatthe axial gradientis ~ 150øC/mm.By replacthe room temperaturevalue. In the 18/12 pyrophyllitecell ing the molybdenumcapsulewith rhenium,Presnalland
assembly,thereis an enhancement
of 1 GPa for runsof 0.5 Gasparik(1990) have been able to performruns of 2 hr
up to 2400øCfor pressures
of 16.5
hr duration,butonly0.5 GPafor runswhichlast2 hr or longer durationat temperatures
(seeFig. 9 from Lu, 1990;RemsbergandLiebermann,1991) GPawith no observedcontaminationof the sampleandwith
dueto flow andrelaxationin thepressuremedium.When the stabletemperaturecontrol.
LIEBERMANN
ET AL.
23
Geophysical Monograph Series
CELL-ASSEMBLY
Vol. 67
FOR 1OMM OCTAHEDRON
:,','":•
Magnesium
Oxide
I
LanthanumChromite
•
Zirconia
:• Molybdenum
"•
ß Sample
•
•-• AluminaCeramic
Thermocouple
Wire
Figure10. Cellassembly
fordetermining
thetemperature
distribution
using
theenstatite
content
ofdiopsidic
pyroxene
coexisting
withenstatitic
pyroxene
(fromGasparik,
1989;--rhenium
replaces
molybdenum
asthecapsule
inthe
highertemperature
experiments
of Presnall
andGasparik,
1990).
lOOKBARTHERMOCOUPLE
Tc
0 øC
HOT SPOT
<ASSEMBLY
Pyrophyllite
CrushableAlumina
Graphite
PlatinumCapsule
MagnesiumOxide
Sample
Alumina Ceramic
Zirconia
Steel
Thermocouple
Wire
Figure12. 18/12mmpyrophyllite
cellassemblies
withradial(a)andaxial(b)
thermocouple
configurations
(seealsoRemsberg
andLiebermann,
1991).
CENTER
-30oC
<SAMPLE
-50øC
...- •
CENTER
_70oC
Tc
-ioooc
-15ooc
-2oooc
14OOøC
16OOøC
17OOøC
1MM
Figure11. Cross-section
of an experimental
chargein a 10mmMgO cell
assemblyshowingthe isotherms
inferredfrom the enstatite-diopside
data
whicharein Fig. 3 of Gasparik(1989).
24
LIEBERMANN
ET AL.
Recently,KawashimaandYagi (1988;seealsoKawashima
etal., 1990)havedemonstrated
thathomogeneous
temperaturedistributions
canbeachieved
withincylindricalfurnaces
by selectingproperresistivitiesfor the furnacetubeandend
caps.Gwanmesiaand Liebermann(this volume)have employedthisconceptin their 14/7.5cellassembly
by usinga
telescopic
graphitefurnaceandtantalumendcaps.Measurementsof thetemperatures
atthecenterandendof thesample
withtwo axialthermacouples
indicatethatthetemperature
gradientis lessthan 15øC/mmoverthe 3 mm lengthof the
sample.For the 18/12 cell assembly,we have usedboth
radialandaxialthermocouple
configurations
(Fig. 12). Althoughthe radial thermocoupleis easierto fabricate,it has
severaldisadvantages
(seealsodiscussion
in Herzbergetal.,
1990): (1) a hole mustbe drilled in the heaterwhich creates
localirregularities
in resitivityandtemperature;
(2) chemical
Geophysical Monograph Series
Vol. 67
reactionor contactof thethermocouplewireswith the heater
leads to ambiguitiesin the actual location of the nominal
temperaturemeasurement;and (3) the thermocouplereferencejunction is at the triangularface of the carbideanvils,
thusnecessitatinga secondmeasurementof anvil temperaturefor correction.For thosereasons,theaxial thermocouple
configurationhasbecomethe designof choicein our laboratory.
Deviatoric
Stress and Strain
All large-volume,high-pressureapparatustransmitpressure to the specimenvia solid media (e.g., boron nitride,
pyrophyllite,magnesiumoxide,alkalihalides)whichexhibit
a finite shearstrengthandthusimposea non-hydrostaticor
deviatoric stresson the confined specimen.Although this
topic has been the subjectof considerableinterestin the
petrologyandmineralphysicscommunities,we haveonly a
qualitativeunderstanding
of thisdeviatoricstress:e.g.,pyrophyllite is lesshydrostaticthan sodiumchloride;opposed
anvil devices are less hydrostaticthan piston-cylinderor
multi-anvil devices(seealsoKaratoand Ogawa, 1982).
Triaxial deformationexperimentsin other laboratories
•mm
::::•
'•' Pyrophyl
lite
1
Graphite
[•'• MgO
•
Sample• Capsule
Figure14. 18/12cellassemblyfor deformationexperiments
usingtheUSSA2000.
have shownthat the densityof free dislocationsinducedin
olivine during steady-statecreep at high temperatureis
proportionalto thesquareof theapplieddeviatoricstress(
or3)as shownin Fig. 13 (seeKohlstedtand Weathers,1980
for a review). This relationshipprovidesa directway to infer
IO0
_
_
OLIVINE
(after
Kohlstedt
etal.,
1976
a)
cz=
3/,/
_ q-(r•:
cz/Jbp
'/e
-
•• •
•"'""•'•1
Pyrophyllite+MgO-
- ""i"i'iOOl]
B
Nc
I
_1
•'
• USSA-2000(18mm)
T
106
_
m:l
Girdle-Anvil
Apparatus
INaCI/ff_--•.....
0.1
_
107
10
8
10
9
DISLOCATION DENSITY (p),cm
I0I0
I0
_2
Figure13. Deviatoricstress
(rrl-rr3)asa functionof densityof freedislocations
for olivinesinglecrystals.
Thesolidlinerepresents
the
fitof(Crl-Cr3)
= apbp
1/2,(where
a isanempirical
constant,
pthemean
shear
modulus,
andbisthemagnitude
oftheBurgers
vector
of
themobiledislocations
tothedatain solidandopencircles,Kohlstedtetal., 1976).Thedottedarearepresents
therangeof thedeviatoric
stress
inferredfromtheobserved
dislocation
densities
frompiezometer
runs([ 101]C orientation
in pyrophyllite
+ MgO cell)in USSA2000. The shadedareasrepresent
rangesof the deviatoricstresses
([ 101]C orientation
in NaC1andBN cellsandalsofor the [001]
orientationin theBN cell in the girdle-anvilapparatus
fromWang et al. (1988).
LIEBERMANN
ET AL.
25
Geophysical Monograph Series
Vol. 67
OOl
o oo
-o
Ol
• -o02
•
-oo3
• -o04
-0
05
-0.06
-0.5
Figure15. Photomicrographs
showingcontrastof dislocationdensityin the
olivine piezometerbefore (A) and after (B) deformationin 18/12 cell
assembly(Fig. 15).
0.0
0.5
1.0
1.5
2.0
2.5
Figure18. Verticaldisplacement
of theMgO grains(DeltaY) versusvertical
positions
Y in thetwo-phasespecimen
afterdeformedat 8.5 GPaand1000øC,
for 1 hr. The linearfit givesan averageverticalstrain(the slopeof the fit) of
2%, with R = 0.94.
({x•-{x3)in large-volume,high-pressureapparatus.
Ingrin and Liebermann(1989) have demonstratedthe
feasibility of this approachin a pilot study using single
crystalsof SanCarlosolivine and syntheticMgO as in situ
piezometers
to monitorthedeviatoricstressin a girdle-anvil
typeapparatus.
By adjusting
thedesignof thecellassemblies
surroundingthe specimenat high temperature,(rr•-rr3)was
varied from 1 to 10 percentof the confiningpressureof 4
GPa.
Figure 16. Deformationpatternin the 18/12 cell assembly(Fig. 15) at room
temperature(A) before,(B) after deformationat 8 GPa.
Wang et al. (1988) conducteda more extensiveseriesof
experimentsusingnatural olivine singlecrystalsas in situ
piezometersandwereableto showconclusivelythatmostof
the dislocationsare producedat peak temperatureandpressureandthatthe dislocationdensityis relatively independent
of P-T paths.Experimentsat maximumpressureP- 4 GPa
and temperatureT = 1050øC for t = 1 hr in NaC1 cell
assembliesand various P-T paths yield specimenswhose
dislocationdensitiesareunchangedfrom the initial value of
2 x 106cm-2, implyingthatthedeviatoricstress
waslessthan
14MPa (seeFig. 13).In BN cell•ssemblies,
therecovered
specimenfrom high P-T experimentsexhibitmuchhigher
densitiesof dislocations
(•109 cm-2) whichhavebeenproducedby steady-state
plastic deformationof the olivine
crystalsundera deviatoricstressof•300 MPa. Thisvalueof
Figure 17. Back-scattered
SEM micrographof deformationpatternin a
polycrystallinespecimenat high temperature.SpecimencontainsCaGeO3
perovskite(gray background)andMgO (dark grains).(A) before,(B) after
deformation
26
at 8.5 GPa and 1000øC for 1 hr.
LIEBERMANN
ET AL.
deviatoricstressin BN has been corroboratedby observations of the subgrainsize and recrystallizedgrain size in
specimens
of longerrun duration(3 hr).
Thistechnique
hasbeenextended
tohigherpressures
in the
USSA-2000 using a 18/12 cell assemblycontainingtwo
samplechambers
(Fig. 14), onefor a specimenandonefor
the in situ olivinepiezometer.For the cell assemblyin Fig.
14 in which singlecrystalMgO is the specimenin the lower
chamber,dislocationdensitiesof 2-4 x 109/cm
2 havebeen
observedwhich implies that the deviatoricstressis about
400-500 MPa (Fig. 13). The opticalphotomicrographs
in
Geophysical Monograph Series
Fig. 15 show the dislocationdensityin olivine recovered
afterloadingto 8.5 GPawithoutheating(A) andafterheating
and deforming for 1 hr at 1000øC and 8.5 GPa (B) with
polycrystallineCaGeO3-perovskite
in the lower chamber.
The microstructureof the samplerecoveredfrom the zerohour run representsthe effectsof loadingandunloadingat
roomtemperature.The characteristic
featureof this sample
is the microcracks normal to the vertical direction which are
undoubtedlydueto unloadingunderthestressconditionwith
1 beingvertical.Freedislocation
densityis about2 x 107
cm-2, a typicalvalueforthestartingmaterial.Forthesample
deformedat 1000øCfor 1 hr, however,dislocationdensityis
at leastoneorderof magnitudehigher,andthe distributionof
the dislocationsis ratherhomogeneous.
TEM studysupports
this observation,and gives a dislocationdensity3 (+0.5) x
108 cm -2.
Two typesof experimentsusingstrainmarkertechniques
havebeenperformedin orderto understand
the deformation
processin the cell assembly(see alsoWang, 1991). In the
first, a singlecrystalof MgO ([ 100] vertical orientation)is
placedin thelowerhalfofthe assembly.The entireassembly
was cut alongthe samecross-section
shownin Fig. 15, and
22 TEM coppergridsweremountedonthe surface(Fig. 16).
The oppositesurfacewascoveredby teflontape,andthetwo
halves of the assemblywere then brought togetherand
compressed
to 8 GPa at room temperaturefor 30 min and
decompressed.
By comparinginitialandfinal configurations,
a flow patternin the cell assemblycanbe obtained.Thereis
a discontinuityacrosstheinterfacebetweenthepyrophyllite
pressuremediumandthe MgO sleeve,within which deformation is relatively uniform. The MgO single crystalhas
experiencedconsiderable,but rather uniform, axial compressionand radial expansion,whereasthe strain in San
Carlos olivine specimenis negligible. The flow pattern
revealedby Fig. 16 illustratesthe mechanismof generating
deviatoricstressin the cell assembly.The strengthsof the
specimenand piezometerare muchhigherthan that of the
surrounding
pyrophyllite.During compression,
pyrophyllite
Vol. 67
in Fig. 17a. The two half cylinderswere then put together
with a 24-[tm-thick Pt foil in betweenand deformedat 8.5
GPa and 1000øCfor 1.5 hr. On recovery,a 2.6% shortening
was obtainedby lengthmeasurement.The samesurfacewas
examinedagainusing SEM (Fig. 17b). Horizontal and vertical positions(x' andy') of the centerof each MgO grain
were obtainedusingthe samecoordinatesystem,and horizontalandverticaldisplacements
(dx-- x-x ' anddy =y-y ')
were obtained.Figure 18 showsthe vertical displacement
(dy) vs verticalposition(y) for morethan60 MgO grains.A
least squaresfit gives a slope of 2%, which is the axial
compressional
strainof the specimen.This value is in good
agreementwith the length changemeasurement.A similar
plotwasobtainedfor dxvsx and,althoughthe scatteringwas
greater,a-0.6% (tensile) strainwas obtained.Thus, deformation is relatively uniform throughoutthe specimen,and
themaximumcompressional
principalstrainisapproximately
vertical. The distributionof the datapointsin Fig. 18 shows
that althougha temperaturegradientexistsin the cell assembly, its effect on macroscopicstrain distributionis negligible.
The developmentof the in situ stresstechniquealongwith
various methodsof measuringthe strain undergoneby a
sampleunder high pressureand temperature(see Wang,
1991) offers the opportunityfor performingqualitativedeformationexperimentsthroughoutthe entire range of P-T
conditionsfor the uppermantle.
OxygenFugacity
As part of an interlaboratoryproject to measureFe-Mg
interdiffusionin natural single crystalsof olivine at high
pressuresand temperatures,we have developedtechniques
to control the chemical
and mechanical
environment
of the
sample.This work was conductedin collaborationwith the
laboratory of Olivier Jaoul in Orsay, France; additional
detailsmay be found in Bertran-Alvarezet al. (1991).
Singlecrystalsof natural San Carlosolivine were cut into
extrudes, and the total volume of the cell is reduced. The
2 mm thick sliceswith the [010] crystallographicaxisnormal
corresponding
decreasein linear dimensionin the vertical to the cuttingplane.Severalcylindersof 2.2 mm in diameter
direction is partly accomplishedby length changein the were cored from each slice (Fig. 19a), after which their
specimenandthe piezometer.Deformationin the specimen lengthis shortenedto 1.5 mm to eliminatechippedfacesand
is characterizedby a verticalcompression
and a horizontal providethebestresistanceagainstfracturing.One endisthen
expansion,whicharepresumablycausedby a nearlyvertical polished with 0.3 btm alumina powder. The cold-worked
maximum compressional
principalstress.
layer resulting from the polishing is finally etchedfor 15
The secondtypeof strainmarkerexperimentwasdesigned secondswith dilutehydrofluoricacidandcarefullycleaned.
for hightemperatures.
A hot-pressed
specimencontainingan A thin layer (450 A) of fayalite (Fe2SiO4)was depositedon
equi-molarmixture of CaGeO3perovskiteand MgO (the the polishedendby RF sputtering.With this configuration,
thermodynamically
stablephaseassemblage
above8 GPa) a Fe-Mg interdiffusioncoupleisformedwith thethinfayalite
wascutalongitscylindricalaxis,andoneof thesurfaces
was layer as the iron reservoir,and the olivine a quasi-infinite,
examinedusingscanningelectronmicroscopy(SEM). HoriMg-rich medium(comparedto the fayalitelayer).
zontal and vertical positions(x andy) of the centerof each
For the diffusion experiments,two cylindrical crystals
MgO grainwere determinedin the coordinatesystemshown prepared in the above fashion are placed together as a
LIEBERMANN
ET AL.
27
Geophysical Monograph Series
Vol. 67
andcompressibilitiesareanisotropicandthisdiffer from one
crystalto the other,sothattherisk of theirweldingduringthe
experimentis reduced.
This couple is fitted into a soft iron capsule(Fig. 19c)
which sealsduring pressureand temperatureincrease.The
capsuleis insertedin a graphitefurnace surroundedby a
semi-sinteredMgO sleeve(30% porosity)which minimized
deviatoricstressandisolatedthe specimenchemicallyfrom
the furnace.That entirecylindricalassemblyis insertedinto
an 18 mm octahedralpyrophyllitecell assembly(Fig. 19d).
The iron capsuleis placedin the centerof the cell assembly
a)
•
so that the zone in which
fayahte
layer
diffusion
occurs is situated in a
minimal thermal gradient.
The use of Fe capsuleshasbeen a major improvementin
the quality of theseexperiments.The iron capsuleexhibits
threevaluablecharacteristics.
Firstly,it sealsin thebeginning
of the experiment and therefore chemically isolatesthe
diffusion couple from other parts of the cell assembly.
Secondly,the ductile behaviorof Fe helps to preservethe
mechanicalintegrity of the single crystalsduring the experiment;this capsuleis very efficient in protectingolivine
fromtherelativelylargedeviatoricstressin thiscell assembly.
1 mm
Thirdly,theassociation
of olivineandironmaintains
thepo2
•iron
I graphite
•] olivine
1 mm
(d)
thermocouple
at a knownvaluewhich dependson •, a parameterdescribing
the cationicdeparturefrom stoichiometryin olivine. In that
case,Po2is fixedby 3 independent
parameters:
theactivities
of the two solid phases,namely iron and olivine, and the
additionalparameter• (Nakamura and Schmalzreid,1983;
Jaoulet al., 1987). For our experimentsat 7 GPa and900øC,
thisresults
inafixedpo
2at10-14'0+0'2
bar(Bertran-Alvarez
et
al., 1991).
The experimentsto datehavebeenperformedat temperaturesof 900øC,anda pressureof 7 GPa. In theseruns,theP-
Tpathshavebeenidenticalto ensurea goodreproducibility
Figure 19. Specimenconfigurationfor high-pressure,
high-temperature
(a) P is increasedat an average
diffusionexperiments:(a) olivine singlecrystalwith thin film of fayalite of the diffusionexperiments:
rate of 0.1 GPa/min to the maximumP at room T; (b) T is
sputtered
ononeend;(b) specimensandwichof two olivinecrystalswith their
[a] axescrossedwith an angleof•90 øandtheirfayalitelayersin themiddle increasedat 15øC/minto 900øC; (c) P and T are maintained
of thesandwich;(c) thespecimensandwichinsertedintoanironcapsulewith
constantfor 6 hours; (d) T is decreasedslowly to room
capsat eachend;(d) cross-sectionof theoctahedral18 mm cell assemblyfor
temperatureover 4 hours;and (e) P is releasedvery slowly
theUSSA-2000 apparatus.
Thejunctionof thethermocouple
wires(W3%Re
to atmosphericpressureovera periodof 10 to 15 hours.The
andW25%Re) is situatedalongthecircumference
of theironcapsulenearits
heating, cooling, heating and decompressionrates were
midpoint.
monitoredby a computer-controlledsystemdescribedbelow. Suchprolongedcoolingand decompression
pathsare
essentialto protect the crystalsfrom thermal shock and
sandwichwith the iron silicate layer between two semi- stresseswhich might generatecracks,and thus hamperthe
infinite media of olivine (Fig. 19b). The sandwicharrange- diffusionprofile analysis.
A specialprocedurewas developedto retrieve the speciment helps to prevent iron loss from the fayalite layer; in
otherwordsFe is only ableto move from fayalite to olivine, mens after the high P-T experimentsand to preservethe
thusestablishinggoodboundaryconditionsfor the interdif- interface between the crystals (Fig. 20). When the cell
fusion problem. When put together, the two crystals are assemblyis recoveredfrom the apparatus,the innermost
orientedwith their [a] axescrossedat an angleof-• 90ø.Such MgO sleeveis firmly bondedto the Fe capsule.To openthe
a dispositionfacilitatesthepreservationandrecoveryof the capsule,a groove is cut aroundthe circumferenceof this
diffusion interfacebecausethe linear thermal expansivities sleeveat the midpointof the capsule.The capsuleandsleeve
28
LIEBERMANN
ET AL.
Geophysical Monograph Series
Vol. 67
ussA2000
•.
,
•}
!
0
2
4
6
8
10
12
14
Figure20. Retrievalof samples(a) aftercuttinga groovein theMgO sleeve
(b) theironcapsuleis chemicallydissolved(c) to enablethecrystalspecimen
to be easilyseparated
(d) seetext for details.
Figure22. Hydraulicpressure
onjack for USSA-2000asfunctionoftime for
the decompression
cycle after a high-pressureexperiment;compareautomaticcontrolvia computerwith manualoperationof pressurereleasevalve.
tered,exceptfor somechippingof the specimenat the edges.
Further examinationof the recoveredspecimensby transmission electron microscopy verified that there was no
chemical
reaction at the contact between the olivine
and the
Fe capsule,and revealedno substantialincreaseof dislocationdensitynearbythediffusioninterface(whichis supporting
evidence for the relatively low deviatoric stressin these
experiments).
The ability to controltheP and Tcycles in the USSA-2000
is critical to the successof these diffusion experimentsin
single crystalsas well as in the fabrication of fully-dense
Figure 21. Optical photomicrograph
of recoveredsampleshowingthe
polycrystals
for acousticstudies(asdescribedby Gwanmesia
excellentmechanicalandchemicalconditionof thespecimen
with onlya few
and
Liebermann,
this volume). Computer control of the
cracksparalleltothediffusioninterface(toppicture).Thenumberof fractures
heating and cooling path is common now in many highoccurring
perpendicular
to theinterfaceis in generalmuchtoolow to allow
fasterdiffusionprocesses
thanlatticediffusion.The remainingpartof theFe
pressurelaboratories,but this is less true for the pressure
capsuleis seenon therightsideof thecrystal(in black).
path. By combininga needle-typebleed valve with a servocontrolled direct current motor, our electronicsengineer
BenedictVitale has designedand constructeda computerare then placed in a nitric-sulfuric acid solution which basedsystemtomonitorandcontroltherateof decompression.
smoothly
dissolvesthe Fe capsuleat the groove and allows us to With thissystem,it is nowpossibleto depressurize
separate
thetwo partsof thespecimenexactlyatthediffusion overextendedperiodsof time (up to 50 hr) andtherebyavoid
interfaceswhich are then availablefor the RBS analysis.
the irregular,and sometimestoo rapid, decreaseof pressure
The carefulexperimentalproceduresdescribedaboveen- observedwhen the hydraulicsystemis controlledmanually
abledus to retrieve sampleswhich are almostunfractured (Fig. 22). Not only hasthisenabledusto recoverintactsingle
(Fig. 21). There are, however, somecracksparallel to the crystalandpolycrystallinespecimens,but it hassignificantly
diffusioninterface(top of the picture),originatingfrom the reducedthelikelihoodofblowoutsofthegasketsandextended
decompression
cycle;sincethe cracksareproducedafterthe thelifetimesof thetungstencarbidecubesin thesecondstage
of the USSA-2000.
annealingperiod,they do not affectthe diffusionprocess.A
careful examinationof the physical stateof the specimen
surfaceusing an optical microscopeat variousmagnifica- Acknowledgments.The StonyBrook High PressureLaborationsrevealedthat the surfacewas almostcompletelyunal- tory was establishedin 1984 by R. C. Liebermann,C. T.
LIEBERMANN
ET AL.
29
Geophysical Monograph Series
Vol. 67
Prewitt and D. J. Weidner with the joint supportof the
National
Science Foundation
Division
of Earth Sciences and
Akimoto and M. H. Manghnani,pp 405-419, AcademicPublications,
Tokyo, 1982.
Ito, E., E. Takahashi,andY. Matsui, The mineralogyandchemistryof the
lower mantle:An implicationof ultrahigh-pressure
phaserelationsin
thesystemMgO-FeO-SiO2,EarthPlanet.Sci.Lett., 67,238-248,1984.
Jaoul,O., B. Houlier,M. Cheraghmakani,R. Pichon,andR. C. Liebermann,
Surfacedestabilizationand laboratoryinducednon-stoichiometry
in
San Carlos olivine, Phys. Chem.Minerals, 15, 41-43, 1987.
Karato,S. andM. Ogawa,High-pressurerecoverof olivine:Implications
for creepmechanisms
andcreepactivationvolume,Phys.Earth Planet.
the State University of New York at Stony Brook. In this
endeavor,we benefittedgreatly from the advice,help and
encouragement
of manyof ourJapanese
colleagues,
including
S. Akimoto, O. Fukunaga,E. Ito, H. Kanda, M. Kato, M.
Kumazawa, E. Ohtani, H. Sawamoto, E. Takahashi, M.
Wakatsuki,H. Watanabeand T. Yagi.
We are particularly grateful to Tibor Gasparik for his
Inter., 28, 102-117, 1982.
leadingrole in developingtechniquesfor experimentsusing Kawashima,Y. and Y. Yagi, Temperaturedistributionin a cylindrical
furnacefor high-pressure
use,Rev. Sci. Instrum., 59, (7), 1186-1188,
the USSA-2000. We thank him and our other colleagues
1988.
Yves Bertran-Alvarez,FrancoisGuyot,GabrielGwanmesia,
Kawashima,Y., T. Tsuchida,W. Utsumi, and T. Yagi, A cylindrical
MasamiKanzaki,JaidongKo, RenLu, RosemaryPacaloand
furnacewith homogeneous
temperaturedistributionfor use in a cubic
Anne Remsberg for many discussionsand permissionto
high-pressurepress,Rev. Sci. Instrum., 61,830-833, 1990.
refer to their work. We have also profited from the contri- Kohlstedt,D. L. andM. S. Weathers,Deformation inducedmicrostructures,
paleopiezometers,
anddifferentialstressesin deeplyerodedfaultzones,
butions of visiting scientistsC. T. Herzberg and D.C.
J. Geophys.Res., 85, 6269-6285, 1980.
Presnall to our laboratory.We thank Tibor Gasparikand
Kohlstedt,D. L., C. Goetze,andW. B. Durham,Experimentaldeformation
reviewer A. Navrotsky for constructivecommentson this
of singlecrystalolivine with applicationof flow in the mantle, in The
paper.The designandconstruction
of the hydraulicsystem
Physicsand Chemistryof Minerals andRocks,editedby R. G. J. Strens,
anditslaterautomationwouldnothavebeenpossiblewithout
pp. 35-49, JohnWiley, New York, 1976.
the skill and dedication
of A. Catalano
and B. Vitale.
The High PressureLaboratoryis currentlysupportedby
NSF grant89-17563 from the Instrumentation
andFacilities
Program.This laboratoryis now part of thenewNSF Center
for High PressureResearch(EAR 89-20239) establishedat
StonyBrook in conjunctionwith PrincetonUniversity and
the GeophysicalLaboratoryof the CarnegieInstitutionof
Washington.The researchreported in this paper is also
supportedby an NSF grant EAR 89-17097.
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