Abstract
Rapid development of nanotechnology often requires verification of existing phase diagrams, which were suitable for bulk materials. This work presents a new phase map (phase diagram) for Al2O3-ZrO2 crystalline powders including the role of the nanoscale particles. Al2O3-ZrO2 composites are relevant for industry for applications demanding high hardness. The nanopowders were manufactured via co-precipitation process followed by microwave hydrothermal synthesis (MHS) at 270 °C, drying at room temperature and annealing in the temperature range 300–1500 °C. The phase composition was investigated using X-ray diffraction (XRD) and Rietveld refinement analysis. The grain size and size distribution were calculated using Rietveld refinement analysis and using transmission electron microscopy (TEM). A particular feature of the composites was the nanoisolation, separation of different phases on a nanoscale. This feature limited grain growth during annealing and permitted the phase diagram for a nano-enabled system to be determined, which turned out to be different from that of conventional composites. In particular, considerable solubility of Al3+ in ZrO2 was found for temperatures less than 1000 °C.
Highlights
Rapid development of nanotechnology often requires verification of existing phase diagrams, which were suitable for bulk materials
The present method of particles preparation ensured that the grain size of particles was in the nano range from room temperature up to 1000 °C for the identified several phases present for the composition range from 0% Al to 100% Al
The Boehmite (AlOOH) grain size evaluated by Rietveld refinement analysis for as-synthesized samples was found to be above 100 nm
Summary
Rapid development of nanotechnology often requires verification of existing phase diagrams, which were suitable for bulk materials. Alumina-toughened zirconia (ATZ- ZrO2-Al2O3) and zirconia-toughened alumina (ZTA- Al2O3-ZrO2) are important materials for high-temperature structural[1,2,3] and functional[4,5,6,7] applications thanks to their exceptional mechanical properties, and high temperature stability. ZrO2-Al2O3 materials using 4-step method: (I) co-precipitation of precursors, (II) microwave hydrothermal synthesis (MHS), (III) drying materials in room temperature, and (IV) annealing[11,12]. This method allows producing highly crystalline nanoparticles with a narrow particle size distribution. According to Kimmel et al.[13], nanoscale grain size leads to formation of phases and structures which do not appear for ZrO2-Al2O3 conventional composites and/or are metastable. These findings are consistent with several earlier reports[14,15,16,17]
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