Preparation and Characterization of Fibrous Alumina and Zirconia Toughened Alumina Ceramics with Gradient Porosity

Abstract

This paper investigated a synthesis process for highly porous Al2O3, Y-ZTA, and Ce-ZTA ceramic nanocomposites with gradient microstructure and improved mechanical properties. Ceramic nanofibres were synthesized as the starting material. The gradient microstructure was developed during spark plasma sintering using an asymmetric graphite arrangement that generated significant temperature differences (80–100 °C) between the opposite sides of the samples. Structural and mechanical properties of the fibrous ceramic composites were investigated. The effect of the temperature gradient on properties was also discussed. While the asymmetric configuration resulted in a gradient porosity, reference samples fabricated in standard graphite configuration were uniformly porous. The gradient structure and the ZrO2 addition led to improved hardness and compression strength of the sintered samples. However, the opposite sides of the samples exhibited considerable variations in both microstructure and in terms of properties. The upper part of the Ce-ZTA ceramic showed a highly porous structure with 18.2 GPa hardness, while the opposite side was highly densified with 23.0 GPa hardness. Compressive strength was 46.1 MPa and 52.1 MPa for Y-ZTA and Ce-ZTA sintered at 1300 °C, respectively, despite their high porosity. The research provided a promising approach to prepare highly porous ZTA composites with high strength for a wide range of applications.

Zirconia-Toughened Alumina (ZTA) Nanoceramics with a Gradient Microstructure: A Comparative Study of ZTA Ceramics with Fibrous and Granular Morphology

“…The temperatures of the top and bottom side of the samples are not considerably different for the STD configuration. The difference typically increases at higher sintering temperatures, as was also found in previous papers [ 21 , 22 , 23 ]. However, the maximum ΔT (ΔT = T 2 − T 1 ) was only 25 and 26 °C at 1300 °C sintering temperature for the fibrous and granular Y-ZTA samples, respectively.…”

“…The preparation method of ZTA fibres is detailed elsewhere [ 23 ]. Briefly, we dissolved the appropriate salts for Ce-ZTA and Y-ZTA in distilled water.…”

“…The raw nanofibers were heat-treated at 1200 °C for 1 h in an atmosphere of air. The average fibre diameters were 530 ± 23 and 520 ± 21 nm for Y-ZTA and Ce-ZTA composite fibres, respectively, determined by SEM image analysis in an earlier paper [ 23 ].…”

“…The following precursors were used for the synthesis: aluminium nitrate nonahydrate [Al(NO 3 ) The preparation method of ZTA fibres is detailed elsewhere [23]. Briefly, we dissolved the appropriate salts for Ce-ZTA and Y-ZTA in distilled water.…”

“…Several studies have reported that a temperature gradient can be developed either in the axial or radial direction [ 19 ] during SPS. A specially designed graphite tool [ 20 ], or a simple asymmetric graphite configuration [ 21 , 22 , 23 ], can produce inhomogeneous current distribution in the axial direction, and in turn, a temperature gradient in the samples [ 20 , 24 , 25 , 26 ]. The latter results in a gradient in porosity distribution [ 25 ].…”