
Assessment of temperature gradients in multianvil assemblies using spinel layer growth kinetics
Author(s) -
van Westrenen Wim,
Van Orman James A.,
Watson Heather,
Fei Yingwei,
Watson E. Bruce
Publication year - 2003
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2002gc000474
Subject(s) - spinel , octahedron , rhenium , oxygen , materials science , atmospheric temperature range , mineralogy , graphite , temperature gradient , thermodynamics , crystallography , analytical chemistry (journal) , geology , metallurgy , chemistry , crystal structure , physics , organic chemistry , chromatography , quantum mechanics
We present an empirical equation to link the thickness of a MgAl 2 O 4 spinel layer growing at the interface between MgO and Al 2 O 3 multianvil high‐pressure assembly pieces to pressure ( P ), temperature ( T ), and time ( t ), extending the recent study of Watson et al. [2002] to the pressure range 6–16 GPa and temperature range 1673–2273 K. For the spinel thickness Δ X we obtain This equation can be used to assess the thermal gradient in any multianvil assembly where MgO and Al 2 O 3 filler pieces are in contact at P ‐ T conditions within the MgAl 2 O 4 spinel stability field. As an illustration, we show that the central hot spot, in which temperatures can be considered constant, is close to 1 mm long in a common octahedral multianvil assembly with 8 mm edge length and rhenium furnace, while it extends to 3 mm long in an octahedron with 18 mm edge length using a straight graphite heating element. In addition, we present the results of a spinel growth experiment performed at 2273 K and 15 GPa with 18 O enriched MgO, which shows that oxygen is mobile at a length scale exceeding that of the spinel layer. This finding raises the possibility that under some circumstances growth of spinel (and of reaction‐product layers in other oxide systems) might be accomplished by concurrent fluxes of oxygen and cations. This “mobile oxygen” model differs from the more conventional Mg‐Al exchange model proposed by Watson and Price [2002] for the lower‐pressure experiments and might explain the observed differences in systematics between the high‐ and low‐pressure data sets.