Brook - ECerS nano ceramics paper.pdf (2.82 MB)
Processing of bulk nanostructured ceramics
journal contribution
posted on 2008-03-17, 10:01 authored by J.G.P. Binner, Vaidhy VaidhyanathanVaidhy VaidhyanathanConventional ceramic forming routes have been adapted for the processing of ~16 nm, 3 mol% yttria
stabilized zirconia nanopowders leading to the production of ~99% dense nanostructured ceramics that
display average grain sizes as fine as ~65 nm. The precursor material is in the form of ~5 vol% solids
content nanosuspensions produced commercially; these can now be concentrated up to ~37 vol% whilst
retaining the viscosity at ~0.05 Pa s. A patent application has been submitted related to the process. The
concentrated suspensions have then been used to produce granulated powders suitable for dry forming via
spray-freeze drying. Whilst powders have been produced that will yield green bodies with densities of
~50% of theoretical, currently the powders suffer from either poor flow and low fill densities or granules
that are too strong to crush during pressing, even at pressures up to 500 MPa. The same suspensions have
also been slip cast into extremely homogeneous green bodies with densities of ~54% of theoretical after
drying using a humidity drier. Higher densities are currently blocked by cracking of the samples during
drying and/or burnout of the organics if the solids content of the suspensions exceeds ~20 vol%.
Radiant and hybrid pressureless sintering experiments have been performed on the dry and wet processed
green bodies using both conventional single step and two-step sintering cycles. Whilst densities >98% of
theoretical were achievable by all combinations, a nanostructure could only be retained using the two
stage sintering approach. With hybrid heating the average grain sizes for die pressed samples were in the
range 70 – 80 nm whilst for the more homogeneous slip cast samples a final average grain size of just 64
nm was achieved for a body with a final density of ~99.5%. It is believed that the primary advantage
offered by hybrid heating is the ability to use a much faster initial heating rate, 20 versus just 7oC min-1,
without risking damage to the samples. Whilst detailed characterisation of the properties of these
nanostructured ceramics has begun, preliminary results have suggested that the toughness is lower and
hardness roughly equivalent to submicron grain-sized 3-YSZ, although the resistance to wear and
hydrothermal ageing may have been improved. As a result of detailed crystallographic characterisation this is believed to be due to a grain size dependent shift in the phase boundary composition for nano YSZ
ceramics leading to ‘over stabilisation’ at any given yttria content. Current work is focused on
investigating the effect of both yttria content and average grain size on the properties of these new
materials.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Materials
Citation
BINNER, J.G.P. and VAIDHYANATHAN, B., 2008. Processing of bulk nanostructured ceramics. Journal of the European Ceramic Society, 28, pp. 1329–1339Publisher
© ElsevierPublication date
2008Notes
This is article was published in the journal, Journal of the European Ceramic Society [© Elsevier]. The definitive version (doi:10.1016/j.jeurceramsoc.2007.12.024) is available at: http://www.elsevier.com/locate/jeurceramsocISSN
0955-2219Language
- en