Grain Growth in UO<sub>2</sub>‐Al,O<sub>3</sub> in the Presence of a Liquid Phase

Lay, K. W.

doi:10.1111/j.1151-2916.1968.tb11896.x

Cited by 91 publications

(20 citation statements)

References 3 publications

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“…However, with progress of grain growth, the liquid phase layer became thicker and thicker and a possible transformation of mechanism from solution-reprrecipitation process to diffusion of atoms through the Bi 2 O 3 -rich liquid layer would occur. In this case, the grain growth rate would be expressed by dG/dt = 2DSMσ/kTρδ(G/(G 0 − 1)) (where D is the diffusion constant of the solid in the liquid, S the solubility of a flat surface, σ the solid-liquid surface energy, ρ the density of the solid, δ the thickness of the liquid layers, and G 0 is the critical grain radius below which the grains dissolve and above which they grow) [24]. It means that grain growth rate is dependent on the thickness of the liquid phase layer.…”

Section: Discussionmentioning

confidence: 99%

“…Grain growth kinetics can be expressed by the relation D n t − D n 0 = k 0 t exp(−Q/RT ) (where D t is the average grain size at time t, D 0 the initial grain size, n the kinetic grain growth exponent, Q the apparent activation energy, k 0 the coefficient, R and T are ideal gas constant and absolute temperature) [24,25]. This equation clearly indicates that, at a given time and temperature, the final grain size is related to the activation energy Q associated with the specific grain growth.…”

Section: Discussionmentioning

confidence: 99%

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Development of magneto-dielectric materials based on Li-ferrite ceramics

Teo

Kong

et al. 2008

Journal of Alloys and Compounds

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Development of magneto-dielectric materials based on Li-ferrite ceramics

Teo

Kong

et al. 2008

Journal of Alloys and Compounds

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“…If the grains remained separated, then several existing treatments would be applicable. [6,29,51] However, the concomitant loss of solid-liquid interface with grain agglomeration, along with grain coalescence, is a major complication. German [7,52] empirically isolated a liquid volume fraction effect on the grain growth rate constant in liquid phase sintering.…”

Section: Introductionmentioning

confidence: 99%

Modeling grain growth dependence on the liquid content in liquid-phase-sintered materials

German

Olevsky

1998

Metall Mater Trans A

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A model for grain growth during liquid-phase sintering (LPS) is presented. A Rayleigh grain size distribution is assumed based on both experimental and theoretical results. This asymmetric distribution provides a continuous driving force for coarsening. The model uses the solid grain contiguity to calculate the relative solid-state and liquid-phase contributions to coarsening. The level of grain agglomeration affects both the mean diffusion distance and interface area over which diffusion occurs. A cumulative grain growth rate is calculated assuming independent solid and liquid contributions to coarsening. Consequently, only the liquid volume fraction and solid-liquid dihedral angle are required to predict the change in grain coarsening rate with solid-liquid ratio. A prior empirical correlation between the grain growth rate constant and the liquid volume fraction is compared to the resulting analytic form, showing excellent agreement. The new model is projected to be generically applicable to microstructure coarsening in multiple phase materials, including porous structures.

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“…For example, lead-base solders are liquid-phase sintered at temperatures barely exceeding 500 K, tungsten-nickel-iron composites, tungsten-nickel-copper composites, and carbide-metal composites at about 1750 K, and an UO2-A12C>3 ceramic 5 at about 2500 K.…”

Section: Introductionmentioning

confidence: 99%

Anomalous sintering behavior in the 95% W--3.5% Ni--1.5% Fe composite

Zukas¹,

Sheinberg²

1974

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ABSTRACT[hiring liquid-phase sintering of W-Ni-Fe composites, single crystal spheroids of essentially pure tungsten form in a W-Ni-Fe matrix. These spheroids grow in a systematic way if either the sintering time is increased, or if the sintering temperature is raised. The generally accepted mechanism of spheroid growth is the dissolution of the small spheroids with simultaneous reprecipitation of tungsten frora the molten matrix onto the larger ones, the reaction being driven by surface energy differences between the small and large spheroids. It has been shown theoretically that for such reactions, the plot of log diameter-log cime will give a straight line of slope 1/3. This theory has been modified to include a rearrangement process for achieving densification during the early stages of sintering and a coalescence process for combining solid spheroids during the latter stages of sintering. Furthermore, sintering at different temperatures should proceed with a single-valued activation energy since a single growth mechanism is rate controlling.We studied the sintering behavior of a low volume matrix alloy (95% W-3.5X Hi-1.5% Fe) and found that the slope of the log diameter-log time plot was less than 1/4, and that the growth process could not be represented by a single-valued activation energy. These experiments as well as those generally published in the literature have several shortcomings in that they do not consider the effect of solid state reactions during presintering, nor the effect of sintering temperature on the spheroid nucleation size. Furthermore, determining activation energies after a constant sintering time does not evaluate structural differences. To overcome these objections, we ran n second series of experiments where the baseline material had already been liquid-phase sintered, and the growth rates determined after additional sintering. Activation energies were determined from the tines required at the different sintering temperatures to achieve equivalent structures. In these tests, the log diameter-log time plots had slopes less than 1/4 and the activation energies were different for different sintering conditions. These results indicate that the dissolution-reprecipitation process is not rate controlling in the 95% W-3.5% Ni-1.552 Fe composite. We feel that the growth rates are too fast for such a process to be rate controlling, and that "coalescence", i.e., the joining of two or more spheroids that come into contact at the proper crystallographic orientation and form a single spheroid, is much more important even during the initial stages of sintering. The rate for such a growth mechanism would depend on some degree of matrix circulation, and the probability for proper spheroid contact. Thermal activation, then, would mean an increase in the matrix circulation and perhaps a greater acceptable angle of contact for welding. Since such a process is not diffusion controlled, but depends on probability, growth rates would behave in a systematic way, but not in accordance with any particular g...

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Grain Growth in UO₂‐Al,O₃ in the Presence of a Liquid Phase

Cited by 91 publications

References 3 publications

Development of magneto-dielectric materials based on Li-ferrite ceramics

Development of magneto-dielectric materials based on Li-ferrite ceramics

Modeling grain growth dependence on the liquid content in liquid-phase-sintered materials

Anomalous sintering behavior in the 95% W--3.5% Ni--1.5% Fe composite

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Grain Growth in UO2‐Al,O3 in the Presence of a Liquid Phase

Cited by 91 publications

References 3 publications

Development of magneto-dielectric materials based on Li-ferrite ceramics

Development of magneto-dielectric materials based on Li-ferrite ceramics

Modeling grain growth dependence on the liquid content in liquid-phase-sintered materials

Anomalous sintering behavior in the 95% W--3.5% Ni--1.5% Fe composite

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Product

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Grain Growth in UO₂‐Al,O₃ in the Presence of a Liquid Phase