Yuan Zhong

Assembled nano-structures from micron-sized precursors

Oriented assembly of small crystals to form larger structures are common in nature and full understanding and control of such process would be beneficial for the forthcoming nano-technologies. Such bottom-up assembly of nano-structures most often requires a precursor of nano-sized crystals. Here we demonstrate a novel laser sintering process that can rupture a submicron-sized zirconia precursor into nano-sized crystals, followed by a rapid oriented assembly of these small crystals. A detailed structure study has been carried out to understand the complex process and a model has been proposed. Such a process sheds light on a new way of fabricating nano-materials using commercialized oxide materials.

Tougher zirconia nanoceramics with less yttria

ABSTRACT Reducing the grain size in zirconia ceramics has shown to decrease its toughness by size-dependent stabilisation of the tetragonal phase that, in turn, hinders the stress-induced phase transformation from tetragonal to monoclinic. The stability of the tetragonal phase increases with the decrease of grain size but decreases with the reduction of the amount of yttria added, implying the need for adjustment of the yttria content when a nano-grained structure is of concern. In this study, low-yttria compositions were investigated. The ceramics were prepared with two sintering methods namely spark plasma sintering (SPS) and pressureless sintering. A clear tendency was noted for the indentation toughness increase with the reduction of yttria content, and a higher toughness achieved in as-SPSed samples in comparison with the annealed samples. The origins of the increased toughness were discussed in terms of yttria content, carbon contamination and increased oxygen vacancies after sintering at reducing atmosphere in SPS.

Dense and strong ZrO2 ceramics fully densified in l 15 min

ABSTRACT Crack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600–1700°C for 3–5u2005min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300–1200u2005nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244u2009±u2009139u2005MPa, 13.3u2009±u20090.3u2005GPa and 5.5u2009±u20090.1u2005MPau2005m1/2, respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.