Supplementary material
Control and monitoring of oxygen fugacity in piston cylinder experiments
Vladimir Matjuschkin1*, Richard A. Brooker1, Brian Tattitch1, Jon D. Blundy1 and
Charlotte C. Stamper1
1
School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's
Road, Bristol BS8 1RJ, United Kingdom
* vladimir.matjuschkin@bristol.ac.uk
Details of the various series of preliminary experiments to evaluate different
components of piston cylinder cell assemblies are provided here. Information on the
piston cylinder apparatus (with the exception of “JG” experiments) and analytical
methods are those given in the paper itself.
“CNP” experiments
The “CNP” experiments (abbreviation for “Co-Ni-Pd”) were conducted in order to
examine the ability of packing/spacer materials (Pyrex and MgO) to retain constant
hydrogen fugacity (ƒH2) in experimental capsule assemblies. The test assembly
consisted of a single Au80Pd20 capsule in which 3 different solid oxygen fugacity
sensors were placed and separated by Al2O3 powder. Water (8µl) was added to the
outer capsule in order to activate the ƒO2 sensors. The experimental hypothesis was
that consistency of ƒO2 values obtained from sensors will indicate constant hydrogen
pressure in the Au80Pd20 capsule, whereas discordant values will point out hydrogen
mobility or ƒH2 disequilibrium.
Experimental procedure
Single Au80Pd20 alloy capsules of ø=3mm were filled with three different ƒO2 sensors,
separated by crushable Al2O3 powder. i) Ni64Pd36 sensor was prepared by mixing Ni
and Pd metals powders, in a proportion corresponding to logƒO2=NNO+0.36 log
units. ii) The second oxygen sensor was mixed in the same proportion, however,
Ni(OH)2 was used instead of Ni metal; at high temperatures conditions Ni(OH)2
decomposes to NiO and H2O. iii) The Co28Pd72 sensor was mixed from Co- and Pdmetal powders in a proportion corresponding to NNO+0.04. 10±2µg of each sensor
and 8µl water were placed in each capsule, welded shut, pressed and weighed. After
storage at 200°C for at least 5 hours, capsules were reweighed to ensure that no water
loss had taken place. Experiments were carried out at 1GPa and 1000°C using the
usual procedure described in the main document. Run durations varied from 12 to 33
hours (see table S1).
Experimental results
The compositions of sensors from runs and evaluated values of ƒO2 are presented in
the table S1 and Fig. 1 in the main text. The MgO-lined experiments demonstrate
discordant ƒO2 values in 13, 15 and 24 hours runs, which we attribute to progressive
hydrogen loss. Large ƒO2 variations between sensors correspond to disequilibrium
and delayed reaction of the sensor. Only the 33-hour run “CNP-MgO-33” produced
consistent ƒO2 values across all sensors signifying full equilibration. In contrast, the
agreement of ƒO2 values between all sensors when using Pyrex confirms the
maintenance of constant ƒH2.
Knowing the exact amount of added starting materials it was possible to make an
estimate of ƒO2-equilibrium in the Pyrex experiments, assuming that no hydrogen loss
took place. The carefully weighed amount of Ni(OH)2 is the only available source of
oxygen in the 3 sensors and this is released by the reactions:
Ni(OH)2=NiO+H2O
NiO+Pd=NiPd+O
The other 2 sensors can only decrease their Ni or Co by access to this oxygen which
increases the activity of Pd. Measuring the Ni:Pd ratio in the Ni(OH)2 sensor as it
breaks down gives a constrain on the O available for redistribution. In a closed system
with O mass is fixed there can be only one unique answer for the Ni in the two NiPd
sensors and the Co in CoPd sensor at equilibrium which can be calculated by simple
mass balance. If hydrogen is lost from the system, more H2O is converted to O2 and
the new oxygen allows more Ni or Co into the sensors equivalent to increasing the O2
mass budget. It is clear from measuring the Ni and Co content of the alloys (see table
S1) if this mass balanced situation has been preserved or not, even before any
equilibrium has been reached. However, these change in Ni or Co will reach
equilibrium at different rates depending on how far they have to move (i.e. how much
Ni or Co they need to loose), so some time is required before all the sensors give the
same ƒO2. In the Fig. 1b where MgO allows considerable hydrogen loss the NiPd
represents the sensor with the highest Ni content and as a result has to change the
least in response to the oxidation caused by hydrogen loss. In contrast, the other two
sensors take some time to react. Hence, they show very different behaviors in Fig. 1b.
The calculated value of +0.55±0.45 log ƒO2 units relative to NNO buffer was
achieved by a mass-balance calculation taking into account a maximum weighing
error of 2µg. Thus, the elevated ƒO2 values for Pyrex in the longer duration
experiment (26 hrs) demonstrate that slow on-going hydrogen loss resulted in
oxidation of about +0.25 logƒO2 units above the nominal value. In comparison, MgO
experiments were more oxidized, reaching +0.5 logƒO2 relative to the upper limit of
the no hydrogen loss field (Fig. 1a,b).
Table S1: Composition of oxygen sensors in run products and their corresponding
ƒO2 calculated relative to Ni-NiO oxygen buffer (NNO). The values represent mean
values of 20-50 point measurements, and the numbers in brackets refer to 2
reproducibility in the last decimal place.
Sample
Pressure
medium
material
MgO
Sensor
Run product Resultant
Duration
[hours]
NiPd
CoPd
Ni(OH)2-Pd
Ni45Pd55
Co13Pd87
Ni15Pd85
+0.84(10)
+1.47(16)
+2.53(8)
13
13
13
CNP-MgO15
MgO
NiPd
CoPd
Ni(OH)2-Pd
Ni62Pd38
Co4Pd96
Ni6P94
+0.40(16)
+3.16(63)
+3.68(34)
15
15
15
CNP-MgO24
MgO
NiPd
CoPd
Ni(OH)2-Pd
Ni66Pd44
Co5Pd95
Ni7P93
+0.33(8)
+2.76(16)
+3.52(42)
24
24
24
CNP-MgO33
MgO
NiPd
CoPd
Ni(OH)2-Pd
Ni31Pd69
Co16Pd84
Ni26Pd74
+1.44(10)
+1.12(18)
+1.73(13)
33
33
33
CNP-Pyr-12 Pyrex
NiPd
CoPd
Ni(OH)2-Pd
Ni42Pd58
Co19Pd81
Ni40Pd60
+0.96(14)
+0.75(8)
+1.04(6)
12
12
12
CNP-Pyr-26 Pyrex
NiPd
CoPd
Ni(OH)2-Pd
Ni32Pd68
Co15Pd85
Ni36Pd64
+1.42(5)
+1.18(16)
+1.22(13)
26
26
26
CNP-MgO13
Au80Pd20
CoPd
Al2O3+
8µl H2O
Ni(OH)2Pd
Pressure
medium
(MgO or Pyrex)
NiPd
1mm
Fig. S1: Diagrammatic cross-section of the capsule design for “CNP” experiments.
Powdered and crushable Al2O3 were used to separate the sensors from each other as
well as to prevent from contact with the capsule walls.
“C-diff” experiments
The carbon diffusion experiments “C-diff” were carried out in order to assess the
degree of carbon and boron contamination for a single Au80Pd20 capsule in
combination with different packing materials: Al2O3, MgO or Pyrex acting as
‘barriers’. The common source of carbon in experimental runs is elemental graphite
from the furnace, which may infiltrate through microfractures in pressure medium
material and then into the capsule, oxidizing to CO/CO2 and imposing an ƒO2 on the
experimental charge. The diffusion (or permeability) rate of carbon may be linked to
the physical properties of packing/sleeve materials such as porosity or plastic
behaviour at high-pressure conditions. The obvious source of boron is the packing
material itself (BN or Pyrex) and a crucial factor may be the availability of elemental
boron as opposed to the oxidized B2O3 species.
Experimental procedure
Au80Pd20 capsules of ø=3mm were used, filled with 9µg of Bishop Tuff rhyolite
powder (Table 2S) and 1µl H2O. Experiments were carried out at 1GPa and 1000°C
using different packing materials: crushable Al2O3, MgO or Pyrex. Run durations
were 3 and 7 days. Post-run capsules were prepared for analytical procedure using the
same technique described in the paper. Polished samples were gold coated for SIMS
analyses.
Experimental results
The C and B contents of glasses are presented in Table 3S. Overall CO2 (C is assumed
to be converted to molecular CO2 or carbonate in the glass) contents increased with
increasing run duration. On average, experiments run for 7 days contain 2-3 times
more CO2 than those run for 3 days. Pyrex was found to be the best material to
impede carbon infiltration. Glasses in experiments carried out with Pyrex contain 2 or
3 times less CO2 than those performed with MgO and Al2O3 packing materials
respectively. Carbon distribution within glasses was found to be heterogeneous in Cdiff-A3 and C-diff-A6 experiments; areas close to capsule walls contain about 70 ppm
more CO2 than those near the capsule cores.
Backscattered electron images of AuPd capsules from 7 day experiments were made
in order to evaluate the capsule corrosion. An experiment with a Pyrex sleeve
demonstrates minimal capsule degradation, whereby use of MgO led to slightly
heavier corrosion with visible blacking of walls caused by carbon infiltration (Fig.
3a,b main document). Crushable alumina showed the highest corrosion with
conspicuous blackening of capsule materials (Fig. 3c main document). A significant
amount of Au metal is present in the pore spaces of the crushable alumina spacer,
possible due to reaction of Pdalloy with C as a catalyst.
Boron contamination was measured in experiments employing a Pyrex sleeve. Traces
of boron (≤65ppm) were detected in glasses from experiments run for 1 and 3 days,
whereas samples run for 7 days showed significantly higher concentrations
(≤1100ppm).
Table 2S: Composition of Bishop Tuff rhyolite, used as a starting material in “C-diff”
experiments. Vales are given in wt.% and numbers in brackets refer to 2
reproducibility based on X analyses.
Na2O
2.7
(0.2)
MgO
0.06
(0.04)
Al2O3
14.1
(1.7)
SiO2
72.4
(2.4)
K2O
5.6
(0.3)
CaO
0.55
(0.05)
TiO2
<0.08
MnO
<0.01
FeO
0.33
(0.15)
Total
95.8
Table 3S: Concentration of CO2 and B2O3 in glasses from C-diff experiments
performed at 1000°C and 1GPa in ppm.
Sample
CO2 [ppm] in
glass, rim/core
1259/1294
C-diff-M3
C-diff-M7
C-diff-P3
C-diff-P7
C-diff-P1-WS
Pressure
medium
Crushable
Al2O3
Crushable
Al2O3
MgO
MgO
Pyrex
Pyrex
Pyrex
C-diff-P3-F
Pyrex
C-diff-A3
C-diff-A6
B
[ppm], Run duration
rim/core
[days]
3
1672/1738
6
755
1683
440
1326
820
64
905/1113
48
3
7
3
7
1
926//918
26043/19144
3
“JG” experiments
The experimental series “JG” was carried out in order to assess the suitability of
Jakobsson’s (2012) setup for controlling ƒO2 in high-temperature H2O-saturated
experiments.
Experimental method
Starting composition
The starting composition (GBA307) replicates basaltic andesite 307 (Thirlwall et al.,
1996) from Mount Granby-Fedon's Camp on Grenada, Lesser Antilles (see table 4S).
The starting material was made in two batches, one high in Fe2+ (added as FeO) and
one with high Fe3+ content (added as Fe2O3), from mixtures of synthetic oxides (SiO2,
TiO2, Al2O3, FeO, Fe2O3, MnO, MgO, NiO, Cr2O3), carbonates (Na2CO3, K2CO3,
CaCO3) and Ca3(PO4)2 in powder form. SiO2, TiO2, Al2O3, and MgO were dried at
1000ºC for 24 hours to drive off any residual moisture, and the carbonates were stored
overnight at 200ºC in a drying oven. Initial mixes of SiO2, TiO2, Al2O3, MgO and
carbonates were weighed out in the appropriate proportions and homogenised by
grinding under ethanol in an agate mortar, before being decarbonated in a vertical
furnace at 600 - 1000ºC for four hours in a Pt crucible. MnO, Ca3(PO4)2, NiO, Cr2O3
and Fe2O3 or FeO were added to the decarbonated powder and the mixtures were
rehomogenised in an agate mortar.
Experimental setup
All experiments were run using the double capsule technique of Jakobsson (2012)
(see Fig. S2A) in an attempt to impose the ƒO2 of various redox buffers on hydrous
samples. Approximately 15mg of starting material was inserted into an Au80Pd20 alloy
inner capsule (o.d. 2 mm, wall thickness 0.1 mm), with the two starting powders
mixed in proportion so that Fe3+/ Fe2+ was approximately equal to the anticipated ratio
in a fully molten melt for the buffer imposed in the experiment, calculated using
Kress & Carmichael (1991) (table 2). Distilled H2O was added to the anhydrous
starting composition in the inner capsule with a micro-syringe prior to welding. The
inner capsule was then pressed and inserted into a Pt outer capsule (o.d. 4 mm, wall
thickness 0.15 mm). To obviate the problem of metal alloying between the Au80Pd20
inner capsule and transition metals in the redox buffer at high temperature, the buffer
was physically separated from the inner capsule by crushable alumina powder and a
Pt capsule. 15 mg H2O was added to 60 mg of redox buffer in the outer capsule using
a microsyringe before welding. Both capsules were weighed before and after welding
the capsule to check for volatile loss.
Piston cylinder experiments were carried out using 1.27 cm (half-inch) end-loaded
piston cylinders at the Research School of Earth Sciences at the Australian National
University at pressures of 1.0 GPa and 1300ºC with run times of 6 hours. The
assembly comprised an NaCl-cell with a Pyrex sleeve, straight graphite furnace and
inner spacers of MgO (Fig. S2B). Experiments were performed using the `hot pistonin' method. An initial sample pressure of ~0.2 GPa was applied before the sample was
simultaneously pressurized and heated at a rate of 100ºC min-1. Sample pressure was
kept constant during runs to ±0.05 GPa with manual adjustment when necessary.
Temperatures were measured using a Pt-Rh (B-type) thermocouple inserted axially
into the capsule using two-bore, high purity Al2O3 (hot end) and mullite (cold end)
tubing (as described in Mallmann and O’Neill, 2007). No allowance was made for the
effect of pressure on e.m.f. Experiments were terminated by turning off the power to
the apparatus; initial quench rates were typically in the order of 70ºC s-1.
All quenched samples were mounted in epoxy before being cut in half on a diamond
saw. The sample was polished using abrasive paper, followed by diamond pastes to 1
µm grade.
Experiments were H2O saturated with initial H2O-content = 20 wt %, calculated for
composition GBA307 using the model of Papale et al. (2006) and run with five
different redox buffers chosen to cover a wide spread of ƒO2.
Results
Glass composition and texture
Initial major element composition was consistent for all superliquidus experiments
and variation in glass chemistry was confined to FeO. Absolute Fe loss, as determined
by mass balance, across all experiments ranged between 0.3 - 3.4 wt % (4 -51 %
relative), resulting in Mg# (Mg/[Mg + ∑Fe]= 0.54 - 0.71.
H2O content of glasses
Experiments contained glasses with two distinct populations of vesicles (Fig. S3B).
Larger bubbles (ø<5 µm) are distributed evenly throughout the sample. Interstitial to
these are microvesicles of ø<1 µm. Rare experiments have a ø ~ 1 mm void at the
base of the Au80Pd20 capsule. The presence of large vesicles suggests experiments
were fluid saturated, but the smaller vesicles show that the full water content of the
melt was not retained on the quench. As a result it is difficult to measure a meaningful
glass water content. There was also evidence of CO2 related FTIR peaks in the glass,
so the ‘excess fluid’ composition was almost certainly not pure H2O.
Fe3+/∑Fe of glass
Fe3+/∑Fe as analysed by µXANES in H2O-saturated experimental glasses varies
between 0.41 - 0.86 (see Fig. 5 in main text). For all H2O-saturated experiments,
measured Fe3+/∑Fe is higher than the initial ratio set in the starting composition,
which was determined by Kress & Carmichael (1991) for each redox buffer, and does
not show systematic variation with the intended ƒO2. The most oxidised experiment
occurred with an NNO buffer, where there was an Fe3+/∑Fe increase of 0.73 from a
starting ratio of 0.13.
The formulation of Kress & Carmichael (1991) has been shown to accurately predict
Fe3+/∑Fe of anhydrous (Moore et al., 1995; Partzsch et al., 2004; Cottrell et al., 2009,
Stamper et al., 2014) and hydrous (Sisson and Grove, 1993; Gaillard et al., 2001,
2003; Botcharnikov et al., 2005) basaltic glass at 1 atm and high pressure for given
redox conditions. Therefore, for our experiments, there should also be a tractable and
direct relationship between measured Fe3+/∑Fe and ƒO2. Utilising this fact, the range
of Fe3+/∑Fe in all experimental glasses analysed by µXANES experiments is 0.41 0.86, which corresponds to an inner capsule ƒO2 = NNO + 3.1 to + 7.7 (using Kress
& Carmichael (1991)). This illustrates the failure of this particular cell design to
impose an ƒO2 at the desired buffer value in a 6 hours run at 1300°C.
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FeO and Fe2O3 components in hydrous silicic melts under oxidizing conditions.
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the ferric–ferrous ratio of silicic melts. Chem Geol 174 (1): 255–273
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Table 4S: Comparison of experimental glass analyses (anhydrous totals) with whole
rock analysis of starting composition.
wt.% 307* GBA307
SiO2 57.57 58.49(99)
TiO2 0.74 0.73(4)
Al2O3 17.34 18.47(56)
FeO
6.66 4.93(95)
MnO 0.16 0.16(2)
MgO 3.92 3.86(13)
CaO 7.63 7.95(19)
Na2O 4.17 4.21(16)
K2O
1.54 0.94(27)
P2O5 0.22 0.22(5)
Cr2O3 0.01 0.02(1)
NiO
0.01 0.02(2)
Total 100.0 100.0
* Whole rock major element analysis of basaltic andesite 307 by Thirlwall et al.
(1996)
Numbers in parentheses are standards deviation of ten experiments (σ) x 100 as
measured by electron probe microanalyses (EPMA)
A
B
4mm
Pt-Rh
thermocouple
MgO spacers
Redox buffer
Pt cap
Graphite furnace
32mm
8mm
Au80Pd20
capsule
Crushable
alumina
powder
Noble metal capsule
NaCl sleeve
Starting
material
Pyrex sleeve
5.9 mm
Pt capsule
12.7 mm
FIGURE S2: A) Double capsule setup of Jakobsson (2012). B) 1.27 cm (half-inch)
salt-pyrex piston cylinder assembly.
A
B
AuPd
gl
Crushable alumina
gl
100 µm
C
Ni
NiO
1 mm
200 µm
Figure S3: Back scattered electron SEM images of an H2O-saturated experiment run
with a Ni-NiO (NNO) redox buffer. A) Au80Pd20 inner capsule containing vesicular
glass and one large (ø = 1 mm) void. Capsule is surrounded by crushable alumina
powder. B) Close up of glass texture (position on large image marked by white box).
There are two populations of vesicles: larger bubbles are ø < 5µm; microvesicles are ø
< 1 µm. C) NNO buffer in outer capsule compartment displaying interlocking texture
of Ni and NiO blebs.