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Fast Sintering of Nano Ceria and Ato...

Tong, Wen.

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Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary./
作者:	Tong, Wen.
面頁冊數:	194 p.
附註:	Source: Dissertation Abstracts International, Volume: 74-07(E), Section: B.
Contained By:	Dissertation Abstracts International74-07B(E).
標題:	Materials science. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3555435
ISBN:	9781267969903

Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary.
Tong, Wen.

Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary. - 194 p.

Source: Dissertation Abstracts International, Volume: 74-07(E), Section: B.

Thesis (Ph.D.)--University of California, Davis, 2012.

This item is not available from ProQuest Dissertations & Theses.

In the late 1970s, a new sintering technique called spark plasma sintering (SPS) was patented in the US and the first SPS machine was made in Japan. In SPS, high Joule heat is generated by running an enormous amount of current through a conductive graphite die, and fast heat transfer is enabled through direct contact to a green body inside the die, making it possible to reach a heating rate orders of magnitude higher than that in commercial sintering. SPS can densify sintered objects to higher densities in shorter times and at lower temperatures than commercial sintering while retaining the original grain size of the powder. These advantages make SPS a favored method to sinter refractory and nano-materials.

ISBN: 9781267969903Subjects--Topical Terms:

543314
Materials science.

Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary.
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245 1 0 $a Fast Sintering of Nano Ceria and Atomic Structure of Ceria Grain Boundary.
300 $a 194 p.
500 $a Source: Dissertation Abstracts International, Volume: 74-07(E), Section: B.
500 $a Adviser: Nigel Browning.
502 $a Thesis (Ph.D.)--University of California, Davis, 2012.
506 $a This item is not available from ProQuest Dissertations & Theses.
520 $a In the late 1970s, a new sintering technique called spark plasma sintering (SPS) was patented in the US and the first SPS machine was made in Japan. In SPS, high Joule heat is generated by running an enormous amount of current through a conductive graphite die, and fast heat transfer is enabled through direct contact to a green body inside the die, making it possible to reach a heating rate orders of magnitude higher than that in commercial sintering. SPS can densify sintered objects to higher densities in shorter times and at lower temperatures than commercial sintering while retaining the original grain size of the powder. These advantages make SPS a favored method to sinter refractory and nano-materials.
520 $a In this thesis, SPS was applied to sinter nano-CeO2, and a systematic study of the effects of heating temperatures, heating rate, hold time, and pressures on the sintered product was conducted. The applied high pressure and fast heating rate promoted densification of CeO2 ceramics at much lower temperatures for shorter holding times with limited grain growth. Furthermore, the results show that the control of microstructure with a desired grain size is possible through the appropriate choice of SPS parameters. Pure CeO2 is rarely used in real applications, and a higher oxide ionic conductivity is found when CeO2 electrolytes are doped with rare earth oxides. For that reason the Dy2O3-CeO2 system was also examined.
520 $a CeO2 has proved to be a superior electrolyte to yttrium stabilized zirconia (YSZ) because of its higher ionic conductivity in medium temperature ranges (500-800 °C) and better phase stability, but its ionic conductivity has not yet reached the level required for fuel cell commercialization. It is known that grain boundaries play a significant role in determining ionic conductivity, and resolving the structure of grain boundaries is necessary in order to find the interaction between grain boundary structure and ionic conductivity in CeO2.
520 $a STEM can reach sub-Angstrom resolution and concurrent electron energy loss spectroscopy (EELS) can perform atom by atom chemical analysis. In the current research, high angular annular dark field (HAADF) STEM was utilized to resolve the grain boundary structure of CeO2 at an atomic scale. When the electron probe is on a low index orientation of the materials in HAADF, the contrast is proportional to a scattering factor which scales with the Z2 of the elements within the atomic columns, thus, HAADF is also called Z contrast imaging. HAADF STEM contains no coherency information and the atomic position in the grain boundary can be directly determined. In the same mode, an EELS spectrum can be obtained from atomic locations defined in the image by analyzing the inelastically scattered electrons passing through the center of HAADF detector. These characteristics make STEM the favored method for grain boundary and interface research.
520 $a In this research, the grain boundary structures of [111] and [100] tilt grain boundaries over the entire tilt angle range were obtained by HAADF STEM. Through structural unit analysis, the favored structural units were obtained and all grain boundary structures were decomposed into combinations of these basic structural units. Surprisingly, a high similarity among the grain boundary structure of primary cubic materials, e.g. CeO2, SrTiO3, YSZ and face centered cubic (FCC) metals was discovered and a crystallographic explanation for the similarity of the structural units among these materials was given. This result implies that lattice structure similarity can extend to grain boundary structure similarity. Such similarity leads to the possibility to predict unknown grain boundary structures through referring to grain boundaries with a similar lattice. (Abstract shortened by UMI.).
590 $a School code: 0029.
650 4 $a Materials science. $3 543314
650 4 $a Condensed matter physics. $3 3173567
650 4 $a Inorganic chemistry. $3 3173556
690 $a 0794
690 $a 0611
690 $a 0488
710 2 $a University of California, Davis. $b Materials Science and Engineering. $3 3174061
773 0 $t Dissertation Abstracts International $g 74-07B(E).
790 $a 0029
791 $a Ph.D.
792 $a 2012
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3555435