Grain Growth Kinetics in Liquid‐Phase‐Sintered Zinc Oxide–Barium Oxide Ceramics

Abstract

Grain growth of ZnO in the presence of a liquid phase of the ZnO-BaO system has been studied for temperatures from 1300" to 1400°C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence three-dimensional grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature.All regressions between G" and time for n = 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n = 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol. [

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

“…[62] Figure 1 compiles several analyses to show the general agreement to the proposed distribution for LPS materials. [3,44,50,55,59,[63][64][65][66][67][68][69] In these fits, the standard error between the Rayleigh distribution and the measured grain size data ranges from 0.5 to 1.3 pct. Most significant are the results of Aboav and Langdon, [64] who measured over 10,000 grains in MgO-LiF compositions, where the curve fit has a standard error of 0.5 pct.…”

“…Even for zero dihedral angle systems, coalescence is observed at 2 pct of the grain contacts. [50] Likewise, grain growth occurs where there is no solubility of solid in the liquid, such as in WCu. [48] These observations show solid-state grain growth is an important mechanism of coarsening during LPS.…”

Review: liquid phase sintering

“…Amorphous particles will coalesce, since there is no grain boundary [146]. For crystalline solids, there is a 5-10% probability that a random grain contact will form with a low-angle grain boundary that favors coalescence.…”

“…Several of these parameters change with temperature. Subsequent treatments [124,[138][139][140] assume a liquid or viscous film on the grain boundary [109,[141][142][143][144][145], but it is missing when grains are coalescing [146]. Figure 40 plots two examples of solution-reprecipitation data for shrinkage versus time on a log-log basis [10,147].…”

Microstructural effects on distortion and solid-liquid segregation during liquid phase sintering under microgravity conditions

“…[23] Liquid-phase-sintered systems can consist of a com- bination of bonded and nonbonded grains. [24] The tendency for the particles to bond is related to the dihedral angle, which depends on the liquid phase's degree of saturation with the solid phase. [25,26] In systems such as W-Cu that have negligible solubility between the solid and liquid phases, the liquid cannot dissolve grain boundaries, so the particles are rigidly bonded.…”