Processing of Nanostructured Ceramics

By Prof. Jon Binner

Background

There is considerable current interest in learning how to process genuinely nanostructured ceramics since they offer the potential for significantly enhanced properties. However, it is often difficult to make large enough components to allow more than the most basic of property measurements.

Aims and Objectives of the Research

The goal of the work at Loughborough is to learn how to produce a range of different ceramics with mean grain sizes <100 nm in size and that are fully dense using process routes that will be easily adaptable by industry.

Current Research Outcomes

The bulk of the work done to date is with yttria stabilised zirconia (YSZ). It is now possible to produce fully dense, sintered nanostructured ceramics with mean grain sizes in the range 60 - 250 nm that measure up to 50 mm in diameter by two different processing routes, viz. pressing and slip casting. The former involves the production of flowable, crushable granules that have already been demonstrated to be suitable for industrial presses. In terms of the properties, the strengths are very similar to those of conventional, submicron ceramics, viz. ~1 GPa, although the fracture mechanism is different. Toughness measurements indicate that nano 1.5YSZ ceramics are crack, or damage, initiation resistant rather than crack propagation resistant, with toughness values up to 14.5 MPa m^1/2 being observed. The wear mechanism of nano YSZ is different to that of submicron YSZ and the wear rates are lower, particularly under wet conditions

However, most excitingly, these nanostructured YSZ ceramics can be completely immune to hydrothermal ageing. Whilst conventional submicron 3YSZ will typically survive <2 weeks at 140°C or <1 hour at 245°C before a crystallographic transformation renders them into a pile of damp powder, the new nanostructured 3YSZ has been observed to survive at least 3 weeks (504 hrs) at 245°C with no detectable trace of the transformation even starting to occur. Work is underway based on nanostructured alumina, zirconia toughened alumina and barium titanate, whilst work on nanostructured yttrium aluminium garnet (YAG) is due to start in April 2010.

Figure: a) A 3YSZ ceramic with a mean grain size of ~65 nm; b) Die pressed components made of nanostructured 3YSZ (die pressing courtesy of Dynamic Ceramic) and c) A screen printed nanostructured BaTiO₃ layer (screen printing courtesy of Syfer Technology).

Research Significance

The work on nano YSZ has led to 3 patents being filed and the work is now being scaled up via both Royal Society and TSB grants, whilst a prototype valve component for the oil industry will be produced under a new EPSRC Collaboration Fund grant; work to begin in June 2010. Simultaneously, samples are being produced for a number of companies around the world, including for applications in dental ceramics. The work on Al₂O₃ and YAG potentially has applications in ceramic armour via a joint EPSRC project with Oxford University, whilst the work on barium titanate could result in very much smaller electronic ceramic components.

Numerous papers have been published and presented at international conferences. It is anticipated that the first commercialisation of the work could easily happen within 2010.

References

1. Binner JGP and Vaidhyanathan B. J. Eur. Ceram. Soc. 28 1329-1339 (2008)
2. Binner J, Vaidhyanathan B, Paul A, Annaporani K & Raghupathy B, Int. J. Appl. Ceram. Techn; available online at http://www3.interscience.wiley.com/journal/120126106/issue

Loughborough University

The Department of Materials, formerly named the Institute of Polymer Technology and Materials Engineering has roots going back virtually 40 years and throughout this time we have been contributing to the advancement and application of knowledge in Materials Science and Engineering by means of teaching, scholarship and research. Our philosophy is based on the engineering application and use of materials which, when processed, are altered in structure and properties. This encompasses design considerations and business implications.