Catalytic properties, densification and mechanical properties of nanocrystalline yttria-zirconia-based materials

Alumina, titania, ceria and manganese oxide were either coated onto or doped in cubic 7 mol% Y203-ZrO2 (7YZ) nanocrystals to form nanocomposites for methane combustion. These novel catalysts were very active and thermally stable. In particular, 25 wt% Mn203-coated 7YZ and 25 wt% Mn203-doped 7YZ showed remarkably low light-off temperatures of 3750C and 3580C, respectively. These catalysts were highly attractive as they were competitive with the much more expensive supported noble metal catalysts. Their catalytic activity could be attributed to the availability of active surface oxygen species, which facilitated the methane activation at low temperatures. Nanocrystalline 3 mol% and 8 mol% Y203-ZrO2 (3YZ and 8YZ) were successfully densified with an ultrafine grain size of < 90 nm by pressureless sintering at 11000C and 11500C, respectively. The low-temperature sinterability could be attributed to the well-defined nanocrystalline particles obtained via hydrothermal synthesis, and the effective elimination of secondary porosity through the dry compact processing. Submicron-sized 3 mol% Y203-ZrO2 ceramics with a grain size of - 150 nm was also obtained with commercial TOSOHC powders. Grain growth during densification of TOSOH© powders was successfully suppressed by presintering to 93% density under an argon atmosphere, followed by hot isostatic pressing at a temperature lower than the presintering temperature. The grain sizes of dense 3YZ and 8YZ ceramics were controlled between 100 nm and 5 glm. This allowed for the systematic study of 3YZ and 8YZ in indentation hardness, Young's modulus and fracture toughness as a function of grain size through micro-indentation and instrumented nano-indentation.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Cui, Jianyi

Advisor dc:contributor.advisor

• Jackie Y. Ying.

• Materials Science and Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/41679

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/41679