Advanced structural ceramics (Si3N4, SiC, A12O3, ZrO2) are rapidly being developed with sufficient fracture toughness to be considered for engineering applications such as internal combustion engine components, rotating turbine engine components, and heat recovery systems. X-ray computed tomography (CT) is a promising nondestructive evaluation method for these ceramics, but beam hardening presents a serious problem in the interpretation of CT images generated with polychromatic X-ray sources by creating artifacts . Dual-energy X-ray techniques have the potential to eliminate these problems. In addition, in theory, dual energy allows generation of quasimonochromatic equivalent images, which should allow verification of theoretically determined optimum energies. In using dual-energy methods, the high-and low-energy images are nonlinearly transformed to generate two energy-independent images characterizing the integrated Compton/photoelectric attenuation components. Characteristic linear combinations of these two "basis" images can serve to identify unknown materials and generate synthesized monoenergetic images.

The dual-energy method has been used to study structural ceramics as well as liquids that are close to ceramic materials in atomic number and mass density. The work was done on a Siemens DR-H CT machine with 85- and 125-kVp energy levels. Test samples included Si3N4 cylinders ranging from 10 to 50 mm in diameter, liquid Freon TF, and densified SiC.

The design of an x-ray detector suitable for use in tomography must be optimized for the intended application. Recently, we have developed microtomography applications that require resolution of -1 micron in three spatial dimensions and -1% statistical accuracy in the reconstruction of attenuation coefficients for each cubic micron volume element in a .1 cubic mm specimen. X-ray detector design for these applications must take into account much more than just the demanding micron spatial resolution requirement. The detector must be optimized to take into account the physical properties of the specimen to be measured, the characteristics of the x-ray beam available to probe the specimen, signal to noise ratios needed in the reconstructed image and requirements of the data processing algorithm. In addition, the detector design should be sufficiently flexible to allow significant variation in the kinds of specimens that can be examined.

As a technique for non-destructive materials analysis, computed tomography (CT) has been especially useful for studying the dependence of the structure of ceramics on manufacturing processes. CT also has been used for characterizing the lithology of reservoir cores while they are still contained in preservation material or a core barrel.

The parameter measured by CT is the X-ray attenuation coefficient, which is a function of both material density and material composition.

Analysis of serai conductor material and associated integrated circuits (IC) is imperative for ensuring quality products. Currently, routine circuit testing is dominated by measurement of the optical and electrical material/device properties through final device performance and parametric testing.

Characterization of the crystal microstructure still is not considered a routine process test. Structural characterization usually is based on double-crystal rocking curves, x-ray topography, or a combination of these techniques.