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Atomic Scale Mechanisms of the Reduction of Nickel–Magnesium Aluminate Spinels
Author(s) -
Hill Brenden E.,
Misture Scott T.
Publication year - 2013
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12538
Subject(s) - spinel , materials science , nial , crystallite , nickel , rietveld refinement , aluminate , stoichiometry , metal , magnesium , phase (matter) , inorganic chemistry , mineralogy , crystallography , metallurgy , crystal structure , chemistry , intermetallic , alloy , organic chemistry , cement
The dynamics of the reduction reaction of Ni x Mg 1− x Al 2 O 4 to form nickel metal and a remnant oxide was quantified to understand spinel behavior in catalysis applications. X‐ray diffraction, thermogravimetry, and pycnometry were employed to track the evolution of high‐ Ni spinels to metastable nonstiochiometric spinels during reduction, but before the phase transformation to theta alumina. Rietveld refinements of X‐ray diffraction data were used to quantify structural changes in the spinel and the phase fraction, crystallite size, and microstrain of all phases during H 2 reduction. During reduction, one O 2− is lost for each Ni 2+ reduced to Ni metal. Ni 0.25 Mg 0.75 Al 2 O 4 and Ni 0.5 Mg 0.5 Al 2 O 4 were shown to form Ni metal and a non‐stoichiometric spinel of the same Mg ‐ Al ratio as the starting composition. NiAl 2 O 4 and Ni 0.75 Mg 0.25 Al 2 O 4 were found to become unstable as full reduction was approached, and metastable spinel, Θ‐ Al 2 O 3 , and α‐ Al 2 O 3 formed sequentially given sufficient time at temperature.