Precipitation and solid solubility in the system NiO-Cr/sub 2/O/sub 3/

Journal Article · Mon Aug 01 00:00:00 EDT 1983 · J. Am. Ceram. Soc.; (United States)

DOI:https://doi.org/10.1111/j.1151-2916.1983.tb10092.x· OSTI ID:6461357

Chen, C H; Notis, M R; Williams, D B

The precipitation of NiCr/sub 2/O/sub 4/ and the solid solubility of Cr/sup 3 +/ in NiO were investigated. Homogeneous precipitation occurs in this system, and the decomposition of NiO-Cr/sub 2/O/sub 3/ solid solution involves only one stable equilibrium phase, NiCr/sub 2/O/sub 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 The precipitates grow along (100) to a size at which coherency is no longer maintained.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 approx. =300 nm. Dissolution of coherent precipitates and growth of semicoherent precipitates was directly observed to occur simultaneously when both are present. The NiO-NiCr/sub 2/O/sub 4/ twophase boundary (the NiO(Cr)(ss) solvus line) was experimentally determined between 950/sup 0/ and 1150/sup 0/C. Concentration profiles measured at two-phase interfaces indicate that the growth of the NiCr/sub 2/O/sub 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 + or - 0.10 at 950/sup 0/, 1.80 + or - 0.15 at 1050/sup 0/, and 3.60 + or - 0.31 at 1150/sup 0/C.

• Research Organization: Department of Metallurgy and Materials Engineering, Lehigh University, Bethlehem, Pennsylvania
• OSTI ID: 6461357
• Journal Information: J. Am. Ceram. Soc.; (United States), Vol. 66:8
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM COMPOUNDS
PHASE STUDIES
CHROMIUM OXIDES
NICKEL OXIDES
CHEMICAL REACTION YIELD
CHROMATES
CRITICAL SIZE
CRYSTAL GROWTH
CRYSTAL LATTICES
DECOMPOSITION
DIFFUSION
DISSOLUTION
EQUILIBRIUM
INTERFACES
NICKEL COMPOUNDS
NUCLEATION
PRECIPITATION
SOLID SOLUTIONS
SOLUBILITY
STRAINS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTAL STRUCTURE
DISPERSIONS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
SIZE
SOLUTIONS
TRANSITION ELEMENT COMPOUNDS
YIELDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies