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Alumina Density, p, g/cm

FIGURE 13.6 Correlation of NMR image data with porosity for Al2O3 cold-pressed specimen.

(XCT) imaging [16-18]. XCT imaging is a highly developed technology that has seen rapid developments over the past several years primarily through advances in more effective X-ray detectors and higher speed computers making image generation faster. Figure 13.7 is a schematic diagram of a typical XCT system. What is desirable about image data from XCT systems is the relative insensi-tivity to part shape. While conventional transmission X-ray imaging using film is a method in reasonably common practice [22, 28], reliable use of film radiography for detecting flaws in complex shaped components such as blades and vanes from a gas turbine is very difficult. Solid-state X-ray detectors [29] and fast computers have been shown to allow data to be acquired for an entire three-dimensional X-ray image in less than 6 min and images generated in less than 1 s. Figure 13.8 shows a 23-cm diameter radial flow monolithic ceramic rotor and one X-ray tomographic image from fast data acquisition with one slice reconstructed in less than 1 s. Features as small as 200 ^m have been detected using such XCT systems.

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