Abstract
A new "solid-state" oxygen buffering reaction (WC-COW), WC + 1/2O2 ⇌ CO + W, is presented. At atmospheric pressure, the oxygen fugacity in equilibrium with this buffer is approximated in the range of 600-1200 °C by logfO2 =1.53-21008TK±0.13bar. A simple method for maintaining oxygen fugacity in standard muffle furnaces using this buffer in off-the-shelf ceramic crucibles is described. The utility of the experimental arrangement in controlling oxygen fugacity during solid-state synthesis of iron-bearing silicates is demonstrated by rapid synthesis of fayalite, Fe2SiO4, from oxide starting mixtures at 1050 °C.
Highlights
High-temperature sample synthesis of transition-metal bearing oxide compounds often requires the control of redox conditions to ensure that the correct valence state is maintained
These metal–oxide mixtures are contained in an outer capsule, which surrounds a second capsule containing the sample, and f O2 is communicated by diffusion of oxygen through the wall of the inner capsule
In “un-buffered” experiments, the carbon–carbon monoxide (C–CO) (French and Eugster, 1965) buffer often defines the oxygen fugacity as graphite is a common component of furnaces and capsules in solid-state experiments at pressure up to about 5 GPa, (C − CO) : C + 1/2O2 ↽⇀ CO
Summary
High-temperature sample synthesis of transition-metal bearing oxide compounds often requires the control of redox conditions to ensure that the correct valence state is maintained. The utility of the experimental arrangement in controlling oxygen fugacity during solid-state synthesis of iron-bearing silicates is demonstrated by rapid synthesis of fayalite, Fe2SiO4, from oxide starting mixtures at 1050 ○C.
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