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Research Papers

Mechanical Properties of Gelcast Cerium Dioxide From 23 to 1500 °C

[+] Author and Article Information
Stephen J. Sedler

Department of Mechanical Engineering,
University of Minnesota—Twin Cities,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: sedl0033@umn.edu

Thomas R. Chase

Department of Mechanical Engineering,
University of Minnesota—Twin Cities,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: trchase@umn.edu

Jane H. Davidson

Department of Mechanical Engineering,
University of Minnesota—Twin Cities,
111 Church Street SE,
Minneapolis, MN 55455
e-mail: jhd@umn.edu

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received July 22, 2016; final manuscript received September 15, 2016; published online October 27, 2016. Assoc. Editor: Hareesh Tippur.

J. Eng. Mater. Technol 139(1), 011008 (Oct 27, 2016) (9 pages) Paper No: MATS-16-1209; doi: 10.1115/1.4034925 History: Received July 22, 2016; Revised September 15, 2016

This work reports the elastic modulus and four-point flexural strength of a gelcast ceramic, cerium dioxide (ceria), with a microporosity of nominally 20% and a grain size of 11 μm from 23 to 1500 °C. The data augment the sparse data published for ceria and extend previous results by 150 °C. The ceria tested is representative of that constituting the ligaments of a reticulated porous ceramic. The elastic modulus decreases from 90 GPa at 23 °C to 16 GPa at 1500 °C. The flexural strength is 78 MPa below 900 °C and then decreases rapidly to 5 MPa at 1500 °C. These trends are consistent with data reported for other ceramics. Comparing the measured elastic modulus to prior data obtained for lower porosity shows the minimum solid area (MSA) model can be used to extend the modulus data to other porosities. Similarly, the flexural strength data agree with prior data when the effects of specimen size, porosity, and grain size are taken into account.

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Figures

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Fig. 1

Measured elastic moduli of gelcast ceria from 23 to 1500 °C. The data obtained in the current study have a maximum measurement error of ±2.9 GPa based on specimen dimensions and load cell uncertainty. Error bars are not shown because they span only within the markers. The curve fit to the data is represented by Eq. (4).

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Fig. 2

Load versus crosshead displacement curve for one of the specimens tested at 1500 °C. Note the nonlinear behavior in the region of the maximum load. The superimposed line is based on the E value deduced from this curve.

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Fig. 3

Measured flexural strength along with a curve fit to the experimental data using Eq. (5). The data obtained in the present study have a maximum measurement error of ±1.8 MPa. Error bars are not shown because they span only within the markers.

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Fig. 4

Ceria RPC consisting of a series of interconnected ligaments and macroscale pore spaces

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Fig. 5

Scanning electron micrographs of a broken ligament of a ceria RPC. The internal void, having the shape of a Plateau border [54], constitutes a macroscale feature; e.g., the porosity of the ligament material does not include this void. The inset micrograph clarifies the microscale porosity of the ligament material.

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Fig. 6

Example microstructure of a ceria test specimen that was not heated beyond room temperature following fabrication. (a) Photographic image of the polished cross section and (b) thresholded mask of the cross section shown in Fig. 6(a).

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Fig. 7

Histogram of pores' areas on the imaged cross section of each specimen type. The tail of the histogram is cutoff, since all pore area bins greater than 100 μm2 have frequencies less than 0.01.

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Fig. 8

Examples of fitting ellipses to pore areas. For each pore area, the best fit ellipse axes' lengths and orientation are determined using a Newton-based Pratt fit [64].

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Fig. 9

Histogram of pore roundness measured in each specimen type

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Fig. 10

Image of a polished cross section of gelcast ceria after chemical etching to reveal the grain boundaries. The grain boundaries have been emphasized for clarity.

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Fig. 11

Comparison of elastic moduli for ceria from different sources. Published data from Wygant [27] (calculated assuming Poisson's ratio of 0.3), Sato et al. [28,29], Lipińska-Chwałek et al. [30], and Wang et al. [31] are shown superimposed on the data generated in the present study. The values from the literature are adjusted to an equivalent porosity of 0.20 using Eq. (11) with b = 3.0. (A base porosity value of zero was used instead of the specimen porosity of 0.06 for Wang et al. [31] because they used nanoindentation and the indents fell entirely within single grains.) The original specimen porosities are shown in the legend. The curve fit to the data for gelcast ceria (Eq. (4)) is also shown.

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Fig. 12

Fracture surface of an example flexural specimen tested at 1200 °C with a subsurface fracture origin. The top edge of the cross section in this photo was in the surface under tension during the test.

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Fig. 13

Normalized flexural strength compared to those of Akopov and Poluboyarinov [33]. The normalized curve fit for gelcast ceria, resulting from Eq. (5), is also included.

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