Dense Amorphous Zirconia–Alumina by Low‐Temperature Consolidation of Spray‐Pyrolyzed Powders

Low-temperature fabrication of Al 2 O 3 -ZrO 2 (Y 2 O 3 ) nanocomposites through hot pressing of amorphous powders

“…The lower true density of amorphous phase was related to weaker atomic binding and looser atomic configuration; therefore, plastic deformation was easier to occur in amorphous phase, which had been explained via shear banding [34], structural densification [35] and free volume theory [36,37]. As plastic deformation occurred in amorphous phase, the densification of amorphous powders was highly promoted; that was why amorphous powders could be consolidated into dense forms under moderate high pressures of 500 to 1000 MPa and low temperatures no higher than 800°C [38,39]. Besides, as the plastic deformation of amorphous particles could eliminate continuous pores [38], the particle packing was more homogenous in the amorphous bulk than in the green body of nanocrystalline powders; according to Azar [19], the better homogeneity of particle packing could promote the particles rearrangement, and were beneficial to the densification of transition powders.…”

“…As plastic deformation occurred in amorphous phase, the densification of amorphous powders was highly promoted; that was why amorphous powders could be consolidated into dense forms under moderate high pressures of 500 to 1000 MPa and low temperatures no higher than 800°C [38,39]. Besides, as the plastic deformation of amorphous particles could eliminate continuous pores [38], the particle packing was more homogenous in the amorphous bulk than in the green body of nanocrystalline powders; according to Azar [19], the better homogeneity of particle packing could promote the particles rearrangement, and were beneficial to the densification of transition powders. In present work, the plastic deformation probably occurred in amorphous powders, and leaded to the enhanced densification at low temperatures in Fig.…”

Preparation of dense amorphous Al2O3–ZrO2–Y2O3 by two-step hot pressing

“…Amorphous oxides are usually prepared by several "soft" chemistry routes, such as sol-gel synthesis [6] and spray pyrolysis [7], followed by thermal decomposition to combust the organics and yield homogeneous amorphous phases. Gandhi et al [7] first demonstrated that amorphous powders could be densified to neartheoretical densities at coexistence of moderately high pressures and low temperatures; bulk amorphous ZrO 2 -Al 2 O 3 [7,8] with densities up to 98% were obtained after hot pressing at 500 ∼ 750 MPa and 450 ∼ 600 • C without crystallization.…”

In Process Nanocrystalline Control Consolidation of the Amorphous ZrO<SUB>2</SUB>-20 mol%Al<SUB>2</SUB>O<SUB>3</SUB> Powder

“…Therefore, the bulk nanocrystalline synthesis has been the subject of much attention in the filed of nanoceramic processing. To the best of our knowledge, we are the first to find the solid state amorphization by mechanical alloying 1) the oxide ceramics powder mixture, ZrO 2 -20 mass%Al 2 O 3 , while there have been various amorphous powder production methods including the alkoxy method, 2) spray pyrolysis 3) and rapid quenching. 4) At the same time, we have successfully prepared the full-density product of the nanocrystal, as synthesized via crystallization, below 30 nm for the crystallite size by employing the spark pressure sintering, as we here use this term for the pulse electric discharge consolidation, of the amorphous powder.…”