Characterization of Intergranular Phases in Doped Zirconia Polycrystals
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1.5 A120 3 11.2 B20 3 3.6 Na 2O3 0.4 K 20, and that of the barium silicate glass (mol%) was 45.8 SiO 2 2.1 A120 3 21.6 B20 3 29.3 BaO 0.5 As20 3. Zirconia powders processed without additives are designated 'Pure' 3Y-TZP or 8Y-CSZ. Details regarding specimen processing are reported elsewhere [4-6]. Following sintering and isostatic pressing, specimens were prepared for transmission electron microscopy by conventional grinding, polishing, and ion-milling techniques. Specimens were mounted on copper slotted washers and carbon-coated prior to examination. The analytical electron microscopy (AEM) described here was performed at the SHaRE User Facility, Oak Ridge National Laboratory. An EMiSPEC Vision integrated acquisition system interfaced to a Philips CM200FEG with an Oxford Super-ATW detector and XP3 pulse processor was used to acquire EDS spectrum lines (typically 20 points, 0.5 to 2.0 nm spacing, 10 s dwell/point) across edge-on grain boundaries and across grain-boundary triple-points. Probes were selected to maximize the EDS signal while considering beam damage effects and best spatial resolution; probes were typically of 0.5 nA (1.2 nm FWHM) to 1.5 nA (2 nm FWHM). Spectra were "post processed" interactively with the Vision software to yield profiles of background-subtracted integrated intensities. Additionally, some spectra were acquired for 100 s live-time with probes which were either stationary or rastered (to reduce beam damage) within a region of interest. Si0 2
RESULTS Shown in Figure 1 are results from the 'Pure' zirconias. The submicron grain size is apparent in the image from a 3Y-TZP specimen (Fig. la). The location where an EDS spectrum line profile was acquired across the edge-on grain boundary is marked. From this, background subtracted FWHM intensities of the Zr Ka and Y Ka reveal zirconium depletion and yttrium enrichment has occurred at the boundary (Fig. lb). The intensity ratios of the lines in Figure lb (3Y-TZP) and corresponding results from a grain boundary in an 8Y-CSZ specimen are presented in Figure 1c; these indicate the chemical width of both boundaries is approximately 4 nm FWHM. Away from the grain boundary, the observed higher Y Kca/Zr Kca ratio in the 8YCSZ compared to the 3Y-TZP is consistent with the higher overall yttria content (8 versus 3 mol%). EDS spectrum lines were acquired across grain boundaries of 8Y-CSZ with 1 wt% Si0 2 added. Zirconium depletion and yttrium enrichment at grain boundaries was observed (Figure 2a). Additionally, background fitting for Si K was obtained using a third-order polynomial fit to windows set below Si K and above Zr L peaks. However, this conventional profiling was complicated by the presence of Zr L and Y L peaks overlapping the Si K signal, resulting in a possibly unreliable Si K profile. (Note that the location of the maximum silicon signal at 8 nm does not correspond to the local extremes in the zirconium and yttrium signals at 9 nm.) However a spatial differencing technique was used to ascertain the presence or absence of silicon at the gr
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