Report for the Joint Use/Research of the Institute for Planetary Materials,
Okayama University
2022 fiscal year first term / second term / others
8/May/2023
Category:

International Joint Research/ General Joint Research/ Joint Use of Facility/ Workshop

Name of the research project: Electrical conductivity measurement of partially molten peridotite
under high pressure with implications for the high conductivity anomalies in the deep Earth
Principal applicant: Haibo Liu
Affiliated institution and department: Zhejiang University
Collaborator
Name: Professor Takashi Yoshino
Affiliated institution and department: Institute for Planetary Materials
Research report:1) Please write the research report with free format, but include followings: research purpose, actuallyconducted research, and research outcomes. If necessary, you can add another pages.
2) For the workshop, please write the report for the workshop. Also, attach the program, abstracts, and listof the participants etc.
3) Please add Collaborator's Name, Affiliated institution and department as needed.

Research purpose:
1.

The conductivity of hydrous KLB-1 was measured at 13 and 15 GPa, respectively, to check thedifference in conductivity across the 410 km discontinuity.

2.

Checking the difference in conductivity between dry and hydrous KLB-1 systems.

3.

Confirm the hypothesis that the dehydration melting at the top of 410 km caused the highconductivity anomaly.

Experimental procedures:
1.

Preparation of starting materials
The composition of KLB-1 sample is shown in Table 1, reagent grade oxide and carbonate

powders are weighed and mixed, and ground in an agate mortar with alcohol. The groundfine-grained powder was then placed in a crucible in a muffle furnace with decarburization at800 °C and 12 h. Subsequently, the decarburized powder was pressed into pellets, and the hydrous

and dry KLB-1 were baked in a gas mixing furnace with QFM buffer at 1350 °C for 43 h and 8 h,respectively. The recovered pellets were ground again with alcohol in an agate mortar to obtain dryKLB-1 starting material, and brucite was added to obtain 0.5 wt% hydrous KLB-1 starting material.
Table 1. Composition of KLB-1 sample

2.

KLB-1

weight (g)transform

weight (g)remark

SiO2

44.48

0.4448TiO2

0.16

0.0016

Al2O3

3.59

0.0359FeO

8.10

0.0810Fe2O30.0900

Fe2O3=2FeO+0.5O2

MnO

0.120.0012

MgO

39.22

0.3922MgO

0.3811

Mg(OH)2=MgO+H2O

CaO

3.440.0344

CaCO30.0614

CaCO3=CaO+CO2

Na2O

0.30

0.0030Na2CO30.0051

Na2CO3=Na2O+CO2

K2O

0.02

0.0002

K2CO30.0003

K2CO3=K2O+CO2

Cr2O3

0.31

0.0031

NiO

0.250.0025

Total

99.99

1.0000Synthesis and characterization of dry and hydrous KLB-1 samples
As shown in Table 2, the cell assembly of the nine experiments were similar with minor

differences. We tried Au, Fe, and Mo capsules successively. In general, dry or hydrous KLB-1
powder was loaded into a capsule with 2 mm diameter and 3 mm length, and inserted them into
MgO sleeve with 3 mm diameter, LaCrO3 heater with 4 mm diameter, ZrO2 insulator with 6 mmdiameter and 14 mm octahedron in sequence. W97Re3-W75Re25 thermocouple was set in the middleof the sample capsule to monitor temperature. Before compression, the whole cell assembly waskept in 200 oC vacuum furnace overnight to minimize absorbed water. 32 mm anvils with 8 mm
truncations was later adopted as the second stage in a multi-anvil apparatus. Sintering experiments
were conducted at 7 MN (15 GPa). After reaching the target pressure, increase to the target
temperature at a rate of 50 oC/min. The duration and other detailed experimental conditions aresummarized in Table 2.
The recovered samples after cutting and polishing were used to determine the phase structureusing X-ray diffraction (XRD), and the grain size, composition, and microtexture were determinedusing scanning electron microscopy (SEM) with Electron Backscatter Diffraction (EBSD).
Results
The compositions and typical images of the recovered samples for all experiments are shownin Table 2. We obtained hydrous and dry KLB-1 samples with the ideal composition using Au
capsules, but the samples were almost indistinguishable macroscopically and microscopically.

Wadsleyite has a grain size of 10 μm or more. Sample polishing was always suboptimal due to poor
sintering even with binders. Therefore, we reground the hydrous and dry KLB-1 powder in an agate
mortar with alcohol until the grain size was less than 3 μm.
We resynthesized dry KLB-1 samples using Fe capsule in order to absorb excess water. Afterreaching the target temperature, the temperature drops due to unknown reasons and the temperaturecannot be stabilized. The recovered samples were powdery or brittle due to short duration or low
temperature that did not sinter well. On the other hand, the sample melted or the iron diffused andaggregated to form ringwoodite due to the high temperature. In the last experiment, we changed thelength of the LaCrO3 heater and the temperature seemed to become stable and a well sinteredsample was obtained, and the polishing was also good, but there were still ringwoodite rings near
the Fe capsule due to the high iron content. Therefore, we replaced it with Mo capsules in order tokeep the same redox buffer.
The composition of the recovered samples was as expected using Mo capsules, but the texture
was extremely heterogeneous. Gradient changes in composition and grain size occurred in bothexperiments, and the reason is still unknown.
All recovered samples of conforming composition were used for coring, but they were broken
due to not being well sintered. Therefore, the conductivity measurement experiment was notperformed.

Table 2. Experiment summary
Assembly

1K3567dry
1.24

Au capsule

5K3756hydrous1.28

PressureTemperature⁕

7 MN

1400 ℃
power + 88

7 MN

1200 ℃
power + 15Time

156 min20 minXRD

SEM+EDS⁕⁕

wadsleyite

wad
cpx
gar

wadsleyite

wadcpxgar

Typical image

Fe capsule

5K3765dry
2.14

Fe capsule

1K3573
dry
2.17

7 MN

7 MN

1400-1240-no ℃
linear decrease
TC broke at 20 min
power + 146

30 min1350-1213 ℃
linear decrease
power + 26

24 minolivineolcpx
gar
melt

wadsleyite—ringwoodite
wadsleyite

rwd
wadcpxgar

olivine+pyroxene+garnetFe

MgO sleeve

Fe capsule③5K3772
dry
2.25

7 MN

1350-1271 ℃
sawtooth decrease
power + 30

30 minwadsleyite①②
wadsleyite

ringwoodite

The light patch is ringwoodite

AssemblyPressure

Temperature⁕

7 MN

1350-1210 ℃
decrease
power + 27

7 MN

1350-1130 ℃
P control 40 min
T decrease
T control 28 min(power is stable at527, similarly
power + 122)

7 MN

1350-1225 ℃
T control 45 min
power + 38
P control 10min
T decrease

7 MN

1100-1300 ℃
T control
1100 keep 10 min
1200 keep 30 min
1300 keep 10 min
decrease T keep 30TimeXRD

SEM+EDS⁕⁕

60 minwadsleyite

wadcpxgar

68 minringwoodite
wadsleyite

rwd
wad
gar

55 minwadsleyite

wadcpxgar

80 minringwoodite
wadsleyite

rwd
wadcpxgar

Mo capsule
5K3776dry
3.6

Fe capsule
1K3582dry
3.11

Mo capsule
5K3785dry
3.20

Fe capsule
5K3790dry
3.27⁕ power + refers to the highest power minus the power when the target temperature is initially reached⁕⁕ — refers to no measurement

Typical image