Browsing by Author "Hwang, Bing"

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    Calculation of x‐ray intensity from a rough sample based on a statistical model
    Hwang, Bing; Houska, Charles R. (American Institute of Physics, 1988-06-01)
    An x‐ray intensity correction is developed which begins with a roughness model that is often used to describe real surfaces. This is based upon a normal distribution of surface asperities relative to a mean plane. Pair correlation between absorbing elements along x‐ray paths either entering or leaving the sample with respect to the signal producing element is accomplished by means of an exponential autocorrelation function. This allows the degree of roughness to be varied on a local scale to fit specific surfaces using statistical data. Equations are developed to describe x‐ray fluorescence and diffraction signals for symmetric and asymmetric beam optics. Theory is compared with experiment using a roughened, fully stabilized zirconia sample.
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    Residual strain gradients in a fully stabilized zirconia sample
    Hwang, Bing; Houska, Charles R.; Ice, Gene E.; Habenschuss, Anthony (American Institute of Physics, 1988-06-01)
    Polished and severely ground fully stabilized zirconia samples are examined using primarily x‐ray diffraction(XRD). The XRD (111) profile reflections from both samples were broadened asymmetrically compared to that of an annealed sample. The asymmetry results from a d‐spacing gradient extending from the free surface into undisturbed bulk material. There are two possible origins of this depth gradient, i.e., variations in residual strain or chemical composition. The latter is eliminated by means of x‐ray photoelectron spectroscopy which did not reveal a chemical gradient. d‐spacing profiles for both samples are obtained nondestructively using a trial and error fitting procedure. A maximum compressive strain of ∼4% is obtained at the surface of the ground sample which decreases gradually to zero at greater depths. The overall zone is ∼1–2 μm. A similar but smaller compressive zone is found in the polished sample which is followed by a zone of tension. The maximum compressive strain at the surface is ∼5% and the overall zone of residual strain is ∼0.1 μm.