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Precipitation and Solid Solubility in the System NiO‐Cr 2 O 3
Author(s) -
CHEN CHINGHWA,
NOTIS MICHAEL R.,
WILLIAMS DAVID B.
Publication year - 1983
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/j.1151-2916.1983.tb10092.x
Subject(s) - non blocking i/o , materials science , precipitation , dissolution , solubility , nucleation , nichrome , solvus , phase (matter) , solid solution , analytical chemistry (journal) , crystallography , metallurgy , thermodynamics , microstructure , superalloy , chemistry , chromatography , biochemistry , physics , organic chemistry , meteorology , catalysis
The precipitation of NiCr 2 O 4 and the solid solubility of Cr 3+ in NiO were investigated. Homogeneous precipitation occurs in this system, and the decomposition of NiO‐Cr 2 O 3 solid solution involves only one stable equilibrium phase, NiCr 2 O 4 . The small lattice misfit between precipitate and matrix results in the formation of randomly distributed spherical precipitates about 3 to 10 nm in diameter in the initial stage of growth. Above that size, precipitates form as ellipsoidal plates lying on (100) with all directions of the precipitate and matrix mutually parallel. Strain‐energy effects provide a rational explanation for the observed precipitate morphology during nucleation and subsequent growth. The precipitates grow along 100 to a size at which coherency is no longer maintained. The loss of coherency is associated with the development of interfacial dislocations, and the critical size at which coherency is lost is ∼300 nm. Dissolution of coherent precipitates and growth of semicoherent precipitates was directly observed to occur si multaneously when both are present. The NiO‐NiCr 2 O 4 two‐phase boundary (the NiO(Cr)(ss) solvus line) was experimentally determined between 950° and 1150°C. Concentration profiles measured at two‐phase interfaces indicate that the growth of the NiCr 2 O 4 phase is controlled by volume diffusion. In the present study, interface concentrations obtained from coherent precipitates are indistinguishable from those obtained from semicoherent precipitates. The maximum solubility of Cr in NiO was found to be 0.98°0.10 at 950°, 1.80°0.15 at 1050°, and 3.60°0.31 at 1150°C.