HR: 0800h
AN: V31D-0683 [Abstracts]
TI: Determination of Partial Molar Volume of Ferrous Iron in Silicate Melts
AU: * Dwyer, C A
EM: cdwyer@u.washington.edu
AF: Earth and Space Sciences, University of Washington, Seattle, WA 98195, United States
AU: Kress, V C
EM: kress@u.washington.edu
AF: Earth and Space Sciences, University of Washington, Seattle, WA 98195, United States
AB:
The density of silicate liquids and partial molar volumes of oxide components have been a topic of intense study
over several decades. Nevertheless, only a handful of density measurements have been performed in ferrous-
iron dominated melts. Ferrous iron is among the most important elements in the crust and mantle. Knowledge of
the partial molar volume of ferrous iron is critical to calculating phase saturation, exchange equilibrium, density
etc. in major rock-forming phases as a function of pressure. We have developed a protocol
for measuring density of silicate melts under reducing conditions using a single-bob Archimedean device. We
are currently performing density measurements in the CaO-FeO-Al2O3-SiO2 system with the goal of
accurately constraining the partial molar volume of ferrous iron as a function of temperature and composition.
The device as currently configured uses a Mo crucible and Mo bob assembly. Preliminary work in mildly reducing
melts suggest that up to 3 mol% Mo oxide in the silicate melt can coexist with Mo metal. On quench, Mo
comes out of solution forming globular "micro-nuggets" and/or dendritic crystals. Under more reducing
conditions in Fe-rich compositions, Fe in the silicate reacts with Mo metal to form "micro-nuggets" of equilibrium
immiscible Fe-Mo liquid alloy. We believe that under these conditions the Fe content of the melt and the formation
of "micro-nuggets" are governed by the reactions:
\begin{eqnarray}
{Mo(s) + \frac{y}{2} O2 \ (\!g)}
&↔& {MoO y \ (\! silicate \
melt) ↔ Mo(\! alloy) + \frac{y}{2}
O2 \
(\!g)}\nonumber
{FeO(\! silicate \ melt)} &↔& {\rm
Fe(\! alloy) + \frac{1}{2}O2 \ (\!g)}\nonumber
\end{eqnarray}
A review of the literature suggests that redox chemistry might also be controlling the formation of "micro-nuggets"
of alloys of Fe and other transition metals. We will perform drop quench experiments into water, air, and air
slowly to investigate this hypothesis. Since the crucible acts as an infinite reservoir of Mo, the maximum Fe
content of the silicate melt is defined by saturation with the Fe-Mo alloy. Changing the oxygen fugacity also
changes the Fe and Mo content of the alloy. This will permit resolution of both Fe and Mo partial molar volume
independently.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 3694 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting