Controlling sintering and grain growth of nanoceramics

Abstract

Sintering and grain growth are fundamental processes affecting microstructural evolution of ceramics. The phenomenological models describing these processes as found in textbooks are simplifications of the very dynamic set of system’s parameters, which lead to limited predictability and the need for extensive empirical analyses for process optimization. One such simplification is the underestimation of interfacial energies and their relationships with diffusion paths and growth control. The goal of this paper is to clarify how thermodynamics of interfaces can provide opportunities for a more refined control of ceramic processing. On the first part of this paper we discuss the relevance of grain boundary energies in grain growth, showing that although grain boundary mobility is the preferred parameter choice for designing of grain growth inhibition, recent studies demonstrate dopants can be selected to annihilate the process driving force and enable thermally (meta)stable nanoceramics. In the second part of the paper, we point out shortcomings from the current sintering theory and discuss that both surface and grain boundary energies with their associated rates of interfacial area evolution represent a more comprehensive sintering description. This perspective offers tunable parameters that may set a new foundation for the design of sintering aids for optimal densification.

Low‐temperature sintering of magnesium aluminate spinel doped with manganese: Thermodynamic and kinetic aspects

“…The 2°. An increase in dihedral angle can be interpreted as an increase in sintering stress 34 , which is aligned with the previous discussion on the effect of Mn on sintering 18 . That is, the fact that the grain boundary energy is dramatically reduced favors grain boundary formation at the initial stages of sintering, while de-stabilizing isolated pores at the final stage, whose stability is directly dependent on dihedral angles 53 .…”

“…While the mechanism of the dopant effects is still under debate and is so far system specific, it is generally accepted that dopants can change interfacial energies and/or affect diffusion mechanisms. While doping effects on diffusion mechanisms have been discussed for years 17 , only more recently the role of interfacial energies on sintering and microstructural evolutions has been demonstrated to be very relevant both experimentally 18,19 and by modelling 20 .…”

Thermodynamics and kinetics of sintering of Y2O3

“…It has been thus suggested that the actual effect of additives on the chemical potential differences will dictate the effectiveness of a dopant. 66 In alignment with Lange et al's theories of thermodynamics of sintering, an increase in dihedral angle shall cause an increased driving force for mass flow towards neck formation and densification. 27 The relevance of the dihedral angle on densification has been demonstrated in SnO 2 by Chang et al 67 It was shown that a change in the dihedral angle as small as 7° can reverse the mass flow from a non-densification to a densification mechanism.…”

Site Inversion Induces Thermodynamic Stability against Coarsening in Zinc Aluminate Spinel

“…It has thus been proposed that sintering can be slowed down by increasing the grain boundary energy and decreasing the surface energy itself. This would lead to an increase in the interface energy equilibrium angle at the contact of two particles, known as the dihedral angle, retarding the coalescence of particles regardless of the mass transport mechanism …”

“…This would lead to an increase in the interface energy equilibrium angle at the contact of two particles, known as the dihedral angle, retarding the coalescence of particles regardless of the mass transport mechanism. 15 There are only a few experimental studies on the measurement of surface energy in zinc aluminate spinel. Quach et al have reported the room-temperature anhydrous surface energy of ZnAl 2 O 4 by water adsorption microcalorimetry as 1.36 J/m 2 .…”