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et al
., 2010). These photographs clearly show that
these sample textures were formed from melt
during quenching in the Fe-FeS system at high
pressures.
The heating efficiency during laser heating is
also a criterion for melting detection. Anomalous
power-temperature relations are often observed
in the laser-heating experiments associated with
melting. Lord
et al
. (2009) observed a plateau in
temperature during the increase in laser power
and inferred that this corresponds to the melting
of the sample (Fe-Fe
3
C). They interpreted that the
change in the heating efficiency could be caused
by the latent heat of melting. Similarly, Asanuma
et al
. (2010) observed a jump in heating efficiency
because of melting. Figure 8.5(a) shows examples
for the heating efficiency change due to melting.
They detected a jump in the heating efficiency
associated with melting of Pt at ambient pressure.
A similar jump was also observed in the FeSi
sample heated at 28 GPa as shown in Figure 8.5(b).
In situ X-ray diffraction (XRD) is the ideal tech-
nique to detect melting at high pressure and
temperature; the disappearance of XRD peaks in-
dicates melting for crystalline materials, and we
can observe the appearance of the halo of the XRD
from the liquid. Reappearance of the diffraction
peaks after cooling is also an important indication
for confirming melting. This technique was used
successfully to identify melting using a large vol-
ume press (e.g., Morard
et al
., 2008). Although the
uniaxial nature of the diamond anvil cell made
it difficult to detect melting by in situ XRD, in-
tensive efforts to improve the cell configurations
and laser heating optics made it possible to de-
tect melting using the XRD method. Campbell
et al
. (2007) successfully detected melting of the
Fe-Fe
3
S system up to 61.1 GPa by performing
in situ XRD. Terasaki
et al
. (2011) and Kamada
(2011) extended the pressure range of melting
experiments to the pressures above 120 GPa. Re-
cent results of the melting experiments of Fe and
FeSi alloys and those of iron-sulfur systems de-
termined by these melting criteria are shown in
Figures 8.6 and 8.7, respectively.
(b) Melting relations of iron and iron-light-
element systems
The Fe-S system has been
most intensively studied by the static experi-
ments. The eutectic point of the system has been
determined at various pressures (e.g., Stewart
et al
., 2007; Morard
et al
., 2008), and is summa-
rized in Figure 8.8. Kamada (2011) extended the
solidus curve of the Fe-Fe
3
S system to 182 GPa.
He observed disappearance of Fe
3
S at higher
temperatures, which was a clear indication of
melting of Fe
3
S; i.e., coexistence of hcp-iron and
2400
FeSi alloy, 21 GPa
Pt, 1 atm
2200
2200
Melting point (2042 K)
2000
2000
1800
9
10
11
12
48
50
52
54
Power, W
Power, W
(a)
(b)
Fig. 8.5
(a) Heating efficiency change due to melting of Pt at ambient pressure and (b) FeSi alloy at 21 GPa after
Asanuma
et al
. (2000). We observed a jump in temperature associated with melting of the sample.
