Synthesis and characterization of mullite–zirconia nanostructured composite by combined mechanical activation and reaction sintering

• Mechanical activation of zircon–alumina powders up to 60 h led to no phase change.
• Zircon decomposition and mullite formation occurred after sintering at 1400 °C.
• The amount of formed mullite increased by increasing mechanical activation time.
• Produced mullite–zirconia composite had a hardness value of 11.1 Gpa.

The objective of present study was to produce mullite–zirconia nanostructured composite by mechanical activation of zircon–alumina powder mixture followed by reaction sintering. The results showed that mechanical activation up to 60 h led to no phase change. Complete formation of mullite–zirconia composite was observed after 60 h of mechanical activation and subsequent reaction sintering at 1400 °C for 2 h. This temperature is about 200–250 °C lower than the temperatures commonly used in the reaction sintering of zircon–alumina powder mixture. Density measurements showed that the relative density of green bodies was ∼78%, which increased to values above 90% after reaction sintering. It was also observed that the relative density of reaction sintered samples increased with an increase in the mechanical activation time. The produced composite showed a hardness value of 11.1 GPa, which is comparable with the hardness value of mullite–zirconia composites obtained by other methods.

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