Hands-on courses - hpcat

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Nov 15, 2013 (3 years and 11 months ago)

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Paris
-
Edinburgh Cell Workshop
2013


May 23
-
24, 2013, Advanced Photon Source, Argonne National Laboratory






Hands
-
on Trainings


Table of Contents


Course
1:


PE cell assembly preparation

-

Tony Yu



C
ourse
2:

PE cell high
-
pressure experiment

-

Curtis Kenney
-
Benson


Course 3:

Ultrasonic measurement in PE cell

-

Yoshio Kono




Course 4:

Liquid/amorphous EDXD Data Analysis and Falling Sphere
Viscometry Demonstration
-
Changyong Park




Training
C
ourse 1:

PE cell assembly preparation

Tony Yu


This training course provides an opportunity to practice using PE cell parts for use in a high
-
pressure
experiment. Trainees will get a feel for the ceramic parts and assemble them for an actual experiment
i
n the high
-
pressure PE press (Training Course 2).


Training procedures

1. Understand a standard PE cell design and parts.

2. Assemble PE cell parts for high
-
pressure experiment in training course 2.



A standard PE cell assembly design in HPCAT

A standard PE cell assembly has been designed for stable high
-
pressure and high
-
temperature
experiments up to around 7 GPa and 2000 °C. Cup
-
shaped WC anvils with the cup diameter of 12 mm
and the bottom diameter of 3 mm are used to generate high pressures

(e.g. Yamada et al., 2011). The
cell assembly mainly consists of a boron
-
epoxy (BE) gasket, an MgO ring, ZrO
2

caps, a graphite heater
and a BN sample capsule. Large volume samples of up to 2 mm in both diameter and length are
accommodated by this cell a
ssembly. A ring
-
shaped BE is used as gasket with a supporting outer Lexan
ring. The BE gasket and ZrO
2

caps in the assembly provide good thermal insulation for high temperature
experiments. An MgO ring is placed between BE gasket and graphite heater to i
ncrease stability of the
cell assembly and maintain anvil gap. High temperature is generated by the graphite heater. The
sample for this training is a mixture of GeO
2

and B
2
O
3

powder, and trainees will melt the sample in
training course 2.








Procedures to assemble standard PE cell


(1) Assemble Lexan ring, Boron
-
epoxy gasket, and MgO ring.


(2) Put graphite heater in the Assembly (1), and attach ZrO
2

middle cap at the both ends of graphite
heater.


(3) Put glue on ZrO
2

cap (Do not glue on gra
phite heater) and attach molybdenum foil over the graphite
heater. Put ZrO
2

top cap on it and glue at the slope of the ZrO
2

caps. Then, put silver
-
paste glue on the
side of tantalum rod and insert the tantalum rod into the top ZrO
2

cap.


(4) Flip the a
ssembly (3). Pack sample powder in BN capsule. Put BN capsule with sample powder in the
assembly (3), and close with BN cap.


(5) Similarly to process (3), attach molybdenum foil, ZrO
2

top cap and tantalum rod.







Reference

Yamada, A., Y. Wang,
T. Inoue, W. Yang, C. Park, T. Yu and G. Shen, Review of Scientific Instruments 82,
015103
-
015107 (2011).
















Training C
ourse 2:

PE cell high
-
pressure experiment

Curtis Kenney
-
Benson



This training course provides an opportunity to conduct a
high
-
pressure and high
-
temperature
experiment using a VX5 type Paris
-
Edinburgh (PE) press. Trainees will operate the hydraulic pump
system to increase pressure and resistive heating to melt the GeO
2
-
B
2
O
3

sample.


Training procedures

1. Understand PE pre
ss components.

2. Setup a PE cell in the press.

3. Increase pressure.

4. Heating.

5. Quench the molten sample and decompress.

6. Check the sample by opening cell assembly.


High
-
pressure and high
-
temperature experiment using standard PE cell

The standard PE cell is capable of high
-
pressure and high
-
temperature experiment up to around
7 GPa and 2000 °C. Figure 1 shows an example of pressure generation curve and temperature
calibration curves. The standard cell asse
mbly uses 12 mm cup anvils to generate pressures to around 7
GPa at room temperature. The use of smaller anvil sizes increases pressure efficiency, and we are
developing cell/anvil combinations to generate higher pressures. Temperature calibration has be
en
carried out up to 2000 °C and up to 97 tons, which corresponds to ~6 GPa. We fit these data to a two
dimensional (power and load) polynomial equation and use th
ese

temperature calibration curves to
estimate temperature in liquid structure measurement.


Reference

Kono, Y., C. Park, C. Kenney
-
Benson, G. Shen, and Y. Wang, Physics of the Earth and Planetary Interiors,
under review.



Figure 1
(Kono et al., under review)

Training procedures


Paris Edinburg Press Components



The PE press used at HPCAT has two primary systems for sample environment control: a
pressure building system and a high temperature heating system. Cell pressure is increased by a two
stage hydraulic system located at the bottom of the portable PEC contr
ol rack. The schematic for the
hydraulic system is shown in Figure 2. The initial compression (up to ~3000 psi) is accomplished through
the use of the low pressure pump. In order to reach higher pressures (up to 20,000 psi) the high
pressure portion of the

system is isolated by closing valve 1, and pressure is increased by engaging the
High Pressure Generator. The sample heater power supply is located just above the hydraulic system in
the PEC control rack. The sample temperature can be controlled by changi
ng the power delivered to the
cell as illustrated in Fig. 1. The PC at the top of the rack is used to control the power delivered to the cell,
as well as monitoring the pressure in the hydraulic system.


Loading a cell in the press


The assembled PE Cell

from training #1 should be placed onto the lower anvil before manually lowering
the upper anvil down to touch the top of the cell. Stop as soon as contact with the cell is made. During
this process, care should be taken that the tantalum wire electrodes d
o not fall from the cell, and that
the orientation of the cell is upright. Carefully place the shield over the press, aligning the notch on the
shield to avoid hitting the lower anvil electrode/cooling block.


Increase pressure


To compress the PE cell fol
low these steps. Safety goggles must be worn throughout the procedure.



Open valves 1, 2 and 3, and close the vent cap on the low pressure pump.



Close the check valve on the low pressure pump.



Use the low pressure pump to increase oil pressure, to about
400 PSI.



Make all water and electrical connections on the press (see Heating below).



Use the low pressure pump to increase oil pressure, to about 3000 PSI.



Close the low pressure pump isolation valve (Valve 1).



Turn the handle on the high pressure genera
tor clockwise to increase pressure to 5,000 PSI.


Heating


The heater current follows a path from the lower anvil, through the tantalum wires, to the heater and
then out the upper anvil/press body. The lower anvil is electrically isolated from the rest of
the press by
a Kapton sheet below the anvil, and a PEEK plastic ring around the anvil. When current is applied to the
heater, these plastic parts are at risk, so cooling blocks are attached to each anvil to carry away excess
heat. Once the sample is compr
essed to 400 psi, follow these steps:




Attach the cooling water lines to each anvil.



Turn the cooling water valves on.



Set the position of the manual output switch mounted just below the Hewlett
-

Packard power
supply in the rack to “OUTPUT DISABLED”. It i
s now safe to handle the high current cables.



Attach the cable with the red band to the lower anvil cooling block.



Attach the cable with the black band to the top of the press body.



Complete the compression to the target pressure.



Set the output switc
h to “OUTPUT ENABLED”.



Open the user interface on the control computer if not already running.



Push the red “Clear Faults” button at the lower right of the user interface.



Set the incremental adjustment on the power level to 1 watt.



Set the target power to

zero.



Turn the Power Output on.



Set current limit to 200.



Turn the PID control on.



Slowly increase the power level to raise the temperature (~1 W/sec.).



When the power level reaches 340 watts, let the power remain constant for 5 min.


Quench the molten
sample and decompress


After the 5 minute heating period, quench the sample by turning the PID control off, then push the
“Output Off” button on the user interface and set both the target power and voltage to zero. Switch the
manual output switch to “OUTPUT DISABLED” and
wait un
til

the temperature of the press
surface is
lowered enough to touch
safely. Remove the heater cables from the press. Allow the cooling water to
run for 5
-
10 min. to assure that the anvils have cooled. Turn off the cooling water flow and disconnect
the w
ater lines. Decompress by rotating the high pressure generator counterclockwise until the
pressure is approximately 3000psi. Slowly open Valve 1 to equalize pressure between the two stages of
the hydraulic system. Open the vent cap on top of the low pres
sure pump, then slowly open the check
valve. Once the pressure reads zero, manually retract the upper anvil and remove the cell from the
press with a pair of tweezers.


Check the sample by opening cell assembly


Return to the sample lab and cut the cell o
pen. The cells have a tendency to shatter when cut, so be
careful to contain the cell fragments. Find the central graphite/BN core and shave it open with a razor
blade to reveal the sample material.





Figure 2

Figure 1

Training
C
ourse
3
:

Ultrasonic measurement in PE cel
l

Yoshio Kono


This training course provides an opportunity to use ultrasonic measurement in the PE cell for measuring
elastic wave velocities at high pressure and high temperature conditions. Trainees will operate
ultrasonic measurement equipment to collect ultrasonic
signal data and will conduct data processing to
determine elastic wave travel time by using a locally developed macro program on Igor Pro.


Training procedures

1. Understand ultrasonic measurement setup.

2. Operate ultrasonic measurement equipment and co
llect ultrasonic signal data.

3. Analyze elastic wave travel time using a locally developed macro program on Igor Pro.


Experimental setup


We will conduct an ultrasonic measurement of SiO
2

glass simplified from the study of Kono

et al. (2012). In order to
generate and receive ultrasonic signals in PE cell, a 10°Y
-
cut
LiNbO
3

transducer is attached to
the
back
side

of the top WC
anvil. The 10°Y
-
cut LiNbO
3

transducer has the capability to
generate and receive both compressional and shear waves
simultaneously. The transducer is connected to a co
-
axial
cable, which goes through a hole at the top of the PE press.
This co
-
axial cable connects to the ultrasoni
c equipment (pulse
generator, oscilloscope, and amplifier), which are located
outside the 16
-
BM
-
B hutch. A pulse generator (Tektronix
AFG3251) generates 20 MHz (for shear wave) and 30 MHz (for
compressional wave) electrical sine waves, and the electrical
signal is divided into two directions by a directional bridge
(Agilent RF Bridge 86205A) (Fig. 1). One signal is directed to
the oscilloscope through a
-
40 dB attenuation path and the
other signal goes to the LiNbO
3

transducer through the
directional brid
ge.


Elastic waves generated by the LiNbO
3

transducer pass
through the WC anvil and propagate into the Al
2
O
3

buffer rod
and the SiO
2

glass sample (Fig. 2). A series of reflected elastic
wave signals came from the interfaces of anvil/buffer rod (R0),
buf
fer rod/sample (R1), and sample/backing reflector (R2).
This series of reflected signals and the attenuated input signal
are amplified by a 40 dB amplifier with a bandwidth of 0.2
-
40
MHz (Olympus Model 5678 Ultrasonic Preamplifier) (Fig. 1).


Figure 3a shows an example of waveform obtained for
the SiO
2

glass sample. The data show clear reflected signals of
R0, R1, and R2 for both compressional and shear wave. The
elastic wave travel time was determined by the pulse echo
overlap method using

the reflected signals from the buffer
rod/sample (R1) and sample/backing reflector (R2) interfaces
(Fig. 3b).



Figure 2

Figure 3

Data acquisition


The pulse generator can be controlled by the ArbExpress software installed on the oscilloscope PC. In
ArbExpress, you only

need to change the parameter ‘Output Frequency’. The ‘Output Frequency’ in
ArbExpress is frequency for 3
-
cycle sine wave, the input of ‘Output Frequency’ is the value of the target
wave frequency divided by 3.


1. Input 6.67M (for 20 MHz shear wave) or 10M (for 30
MHz compressional wave) in ‘Output Frequency’ window
in ArbExpress, and then press ‘Apply’ button. Please
confirm capital M (indicates Mega Hz).

2. Go to oscilloscope application ‘TekScope’.

3. Press
‘Run/Stop’ button, and refresh ‘CH1’ by turning
OFF and ON.

4. Wait until acquisition (averaging) become >1000.

5. Press ‘Run/Stop’ button to stop acquisition, and press
‘Save as’.

6. Save file as ‘.csv’.


Data analysis


Data analysis can be done semi
-
automatically by using a
locally developed macro program on Igor Pro (cf. manual
of elastic wave travel time analysis program). Regarding
the data analysis, we need to consider acoustic impedance
relation of this experiment. Since the acoustic impedance
of the Copper backing reflector (Z
Cu
=~45) is larger than
that of the SiO
2

glass sample (Z
S
=~12), the sample/backing
reflector (R2) interfaces yielded a negative reflection
coefficient (=(Z
S
-
Z
Cu
)/(Z
S
+Z
Cu
)). Therefore, the R2 signal
needs to be inverted to
overlap with the R1 signal in
phase. The macro ‘usfn()’ calculates elastic wave travel
time after inverting the R2 signal before overlapping.
There is another macro for conducting elastic wave travel
time analysis without inverting the R2 signal.


Refere
nce

Kono, Y., C. Park, T. Sakamaki, C. Kenney
-
Benson, G. Shen and Y. Wang, Review of Scientific Instruments
83, 033905
-
033908 (2012).











Training
C
ourse
4
:

Liquid/amorphous EDXD Data Analysis and

Falling Sphere Viscometry Demo
nstration

Changyong

Park


The data
process

of

measured liquid/amorphous EDXD spectra consists of
a few

critical proce
dure
s
including the primary beam estimation
,
the Compton background

subtraction
, and the structure factor
normalization.
The procedures are quite different from typical angle
-
dispersive diffraction data process,
and there are several practical aspects by which the success of data analysis is affected. In this course, a
set of amorphous EDXD data analysis and the pair distrib
ution
function

analysis are
exercised

to
understand those practical factors. P
re
-
measured EDXD data from SiO
2

glass and
Python
-
based
a
ll
-
in
-
one type data analysis

software is provided to practice the analysis.



In the second part of training, Falling Sph
ere Viscometry is demonstrated with a captured video and
ImageJ object tracker plugin application. With an example of FeS melt viscosity measurement, the
practical factors involved in the experimental design are discussed.



Training
goal
s


1.
Understand critical data reduction processes for liquid/amorphous EDXD data analysis and gain
experience
s

with the issues involved in these analysis.

2. Explore the factors affecting liquid viscosity measurement with the Falling Sphere method.


Liquid/am
orphous EDXD data reduction


The observed energy dispersive x
-
ray diffraction spectrum at a given 2
θ

angle can be described:

























































(1)


where,
s
(2
θ
) is a scale factor,
P
(2
θ
) ≈ cos
2
(2
θ
) the polarization factor for linearly polarized synchrotron
beam in the horizontal plane,
A
(2
θ
,
E
) the x
-
ray attenuation,
C
(
E
)
an
energy dependent term (e.g.,
detector efficiency),
I
P
(
E
) the primary white beam profile,
I
coh
(2
θ
,
E
) and
I
inc
(2
θ
,
E
) are the coherent and
incoherent scattering from the sample, respectively. Practically, the polarization factor is a constant for
the fixed angle and the angle dependence of x
-
ray attenuation
is
negligible for a cylindrical sample (i.e.,
A
(2
θ
,E
)


A
(
E
)).

Thus, equation (1) can be effectively rewritten as:













































(2)


The scaled primary beam,
s’
(2
θ
)
I
P,eff
(
E
), can be approximated by a non
-
linear least square fitting with Eq. (2) with
respect to the highest 2
θ

angle

data. Here, the unknown
I
coh
(2
θ
,
E
) is replaced with calculated <
f
2
(2
θ
,
E
) >
for the best approximation of the primary beam, and































(3)




























(4)
















(5)


where,

c
i

is the atomic fraction and
f
i
(
q
) the atomic scattering factor of
i
-
th
element, respectively. The parameters to calculate
f
(
q
) and
I
Compton
(
q
) are
from International Tables for X
-
ray Crystallography [Ed. Ibers and Hamilton]
and refs. [Cromer and Mann, 1967; Cromer, 1969], respectively.


The structure factor for liquid is defined

as
:































(6)


where,
















. For each measured spectrum at different
2
θ

angles, a fragmented structure factor
S
(
q
) =
S
(2
θ
,
E
) can be obtained
using the estimated
I
P,eff
(
E
) as follows:





































[



















]


























(7)


These fragmented structure factors are to be rescaled in reverse sequential order with respect to the
one obtained at the highest
-
2
θ
, which oscillates around one by definition. An evenly spaced
S
(
q
) in
q
-
space
is

obtained
by
error weighted spline
-
smoothening
of
the merged structure factor
.


The error
-
bars are rigorously propagated from the counting statistics of raw data, assuming the counting
probability follows the Poisson distribution (i.e., σ
I
=√I), and are convoluted with
the uncertainty involved
in the primary beam estimation. The increasing errors with increasing
q

arise

from the effect of the
atomic scattering factor for x
-
rays decaying with
q

and being further weighted with the shape of the
primary beam profile. The req
uired counting statistics to compensate this effect should be proportional
to 1/ <
f
2
(
q
) >, which is
im
practical, therefore the practical limit of the
S
(
q
max
) is often chosen smaller
than the instrumental limit (e.g.,
q
max

= ~19 Å
-
1

at 2
θ

max

= 34.9 ° and
E
max

= 65 keV for the primary beam
estimation in this example). The maximum
q
max

defines the spatial resolution in real space, Δ
r

= π/
q
max
,
thus the limited
q
max

also limits the finest features that can be observed in the real space distribut
ion of
pair distribution function.


From an evenly spaced
S
(
q
),
the reduced

pair distribution function
G
(
r
) is obtained as:

























[










]






(8)


where,

[










]

is the Lorch modification function to implement
the resolution broadening in real space. Th
is

modification
function effectively removes the data truncation error in the
Fourier transform.






References

Waseda, Y., The Structure of Non
-
Crystalline Mater
ials, McGraw
-
Hill, New York, 1980

Egami, T., 1978. Structural relaxation in amorphous Fe40Ni40P14 B6 studied by energy dispersive X
-
ray
diffraction. Journal of Materials Science 13, 2587
-
2599.

International Tables for X
-
ray Crystallography, Ed. Ibers

and Hamilton

Cromer, D.T., 1969. Compton Scattering Factors for Aspherical Free Atoms. The Journal of Chemical
Physics 50, 4857
-
4859.

Cromer, D.T., Mann, J.B., 1967. Compton Scattering Factors for Spherically Symmetric Free Atoms.

The
Journal of Chemical Physics 47, 1892
-
1893.




Falling sphere viscometry



Viscosity (

) of fluid can be calculated with the Stokes’ equation by using the terminal velocity of falling
sphere (

) with correction
factors
for wall effect (F) [Faxén, 1922]

and end effect (E) [Maude, 1961]:




E
F
gd
l
s
s




18
2



(1)

5
3
95
.
0
09
.
2
104
.
2
1




























l
s
l
s
l
s
d
d
d
d
d
d
F

(2)

2
2
8
9
2
8
9
1









Z
d
Z
d
E
s
s

(3)


where


and
d

are density and diameter, respectively, with subscripts
s

and
l

denoting the probing
spheres and liquid, respectively. Z is the sample height.


In order to determine the viscosity precisely, measurements of diameter of the probing sphere (d
s
),
density difference between the probing sphere and the liquid sample (

s
-

l
), and the falling
-
sphere
terminal velocity (

) are important. The size of ball can be precisely measured by various means. The
d
ensity of the sphere ball as a function of pressure can also be calculated by using a known equation of
state

(e.g., platinum, rhenium, and so on). However, it is difficult to measure liquid density
in situ

combined with the viscosity measurement. Fortunately, in reality, the uncertainty of liquid density can
be minimized by adopting a sphere material having a si
gnificantly higher or lower density than the liquid
density. For example, in the case of Pt sphere (21.45 g/cm
3

at ambient condition) in liquid NaCl sample
(1.547 g/cm
3
at ambient condition) [Kono et al., 2013], a 10% uncertainty in liquid density estimat
ion will
influence the viscosity estimation only by 0.8%.


The uncertainties in terminal velocity play a dominant role in the precision of the viscosity
determination [
Brizard

et al., 2005]. Precision of terminal velocity measurement depends primarily on
frame rate of the cam
era. Previous high
-
pressure viscosity measurements were conducted using limited
imaging rates (typically from ~30
-
60 to 125 frames/second, or fps), which are suitable only for highly
viscous materials such as silicate or oxide melts. Some studies report
viscosities in the 4
-
20 mPa s range
for iron alloy melts using falling sphere velocities determined based on only 2


4 images. This limited
imaging rate makes it difficult to ensure that the falling sphere has reached terminal velocity and results
in lar
ge uncertainties in the calculated viscosity. The high
-
speed camera (Photron FASTCAM SA3)
that
we are using these days can

collect images at a rate of more than 1000 fps and is ideal for precise
viscosity measurements on low viscosity materials [Kono et a
l., 2013].




Figure 1

The high
-
speed camera has a maximum image size of 1024 pixels in both horizontal and vertical and is
located approximately 1.2 m downstream from the PE cell.


Variable pixel resolutions of 2.8
-
5.9 µm/pixel are available by using 5 or 10 times infinity
-
corrected
objective lenses combined with lens tube lengths of 25
-
76 mm.


Figure 1 shows an example of falling W95Re5 sphere (126
µ
m
in diameter) in liquid FeS recorded at 500 fps with an exposure
time of 2 ms per frame.


The position of the W95Re5 sphere in each frame was
analyzed by using the Tracker
plugin in
ImageJ

software
. The
excellent linearity in the sphere travel distance

and constant
falling velocity with time indicates that terminal velocity was
achieved (Fig. 2). Then, viscosity can be calculated with the
Stokes’ equation (Eq. (1)).



It is important to monitor the motion of falling sphere with
substantial oversampli
ng in order to determine terminal
velocity precisely. The high
-
speed camera plays an important
role here. Low sampling rates of the falling sphere position
may cause misinterpretation of terminal velocity, thus causing
large uncertainties in the viscosity
estimation.



References

Faxén, H., 1922. Annalen der Physik 373, 89
-
119.

Maude, A.D., 1961. British Journal of Applied Physics 12, 293.

Brizard, M., Megharfi, M., Verdier, C., 2005. Metrologia 42, 298
-
303.

Kono, Y.,
Kenney
-
Benson, C.,
Park,

C.,

and

Shen
, G.
,
Phys. Rev. B 87, 024302 (2013)

















Figure 2