Harold E. Burdette

High-Resolution Small-Angle X-ray Scattering Camera for Anomalous Scattering

The design and operation of a new small-angle X-ray scattering instrument, optimized for high throughput at a synchrotron source, high angular and wavelength resolution, large sample cross-sectional area, accurate energy tuning, excellent signal-to-noise ratio and harmonic rejection are presented. The principles of design and implementation are given, as are the details of primary calibration of absolute intensity and experimental desmearing. The instrument has been tested for application to anomalous-scattering measurements near the chromium K edge. Preliminary results on samples of a heat-treated steel are presented as a demonstration of the capability of this experiment to separate the microstructure evolution as a function of temperature of a chromium-rich precipitate from the thermal behavior of other precipitates in the steel.

X‐ray magnifier

A method for the magnification of x-ray radiographic images is described and demonstrated. This magnifier employs two successive asymmetric diffractions of an x-ray beam from highly perfect silicon crystals. The two diffractions magnify the beam in two perpendicular directions. A device with a magnification of 25x is demonstrated for Cu K(alpha) radiation. This device preserves and sometimes improves the resolution inherent in the radiographic technique. The x-ray magnifier is particularly useful in circumventing the relatively poor spatial resolution of electro-optical imaging systems needed for real-time observations. Basic limits on magnification and resolution using this method are described.

Asymmetric crystal topographic camera

The practical aspects of asymmetric crystal topography are described. In this technique, asymmetric Bragg diffraction is utilized to obtain a monochromatic and well collimated x‐ray beam large enough to cover the entire area of sample crystals. Thus, the recording of diffracted beams from a sample crystal provides topographic images of the entire sample crystal. Advantages of this technique are simplicity (no scanning device), excellent sensitivity to crystal imperfections (strain fields), and versatility. Information is given on the general alignment of the camera, magnification of the x‐ray beam width, preparation of the first crystal, and divergence of the beam due to the first crystal. The practical aspects of this topographic system are demonstrated using thick Cu and Ni crystals of various degrees of perfection. An inexpensive image intensifier is also described, which is used routinely to aid in the alignment of sample crystals.

Small-angle-scattering determination of the microstructure of porous silica precursor bodies

Small-angle X-ray and small-angle neutron scattering measurements were carried out on a series of porous silica precursor (unsintered) bodies with different starting chemistries. The samples were prepared from mixtures containing 10 to 30 wt% colloidal silica sol and 90 to 70 wt% potassium silicate. Particle-size distributions were derived from the data using a maximum-entropy technique. Scattering data from the porous silica samples are especially suitable for such an analysis because the colloidal particles and clusters and aggregates of these particles are verified in detail to be spherical, and the scattering instrument use for this study covered the entire range of sizes in this material and was very well calibrated. It was found that the lower the amount of colloidal silica, the broader the size distribution of the silica aggregates.

Real time observation of dendritic solidification in alloys by synchrotron microradiography

A third generation synchrotron x-ray source and advanced imaging facilities were used to study dendritic solidification in metallic alloys in real time. A digital camera and a video camera with different time and spatial resolution were tested to capture growing dendrites during solidification of Sn-13 wt%Bi and Al-25 wt%Cu alloys. The captured digital images show that the morphology of the dendrites can be resolved with satisfactory resolution and contrast. The trade-off between spatial resolution and time resolution was discussed. The effect of beam characteristics such as intensity, parallelism and coherency on both spatial and time resolution was analysed, and potential improvements with higher image quality with reduced exposure time were also discussed.

A study of the coarsening of liquid-solid mixtures using synchrotron radiation microradiography

The coarsening of liquid-solid mixtures with a high volume fraction of solid is an important process in metallurgy. The development of secondary arm spacings in castings and the sintering of powders using a liquid phase are but two examples. The theory of Ostwald ripening is widely used to model some of the events during these processes, yet microstructural details important at a high volume fraction of solid are usually ignored. The authors report preliminary studies on the coarsening of a liquid-solid mixture observed at temperature by microradiography using synchrotron radiation where local microstructural features can be examined in situ.

NBS materials science beamlines at NSLS

Abstract Synchrotron radiation beamlines for topography, spectroscopy and small angle scattering at energies from 5 to 20 keV, are described.

X-ray diffraction imaging of man-made and natural diamond

Abstract Natural diamond crystals, intended for use as substrates for chemical vapor deposition growth of homoepitaxial diamond films and man-made diamond crystals have been studied by X-ray diffraction imaging (topography) using the National Institute of Standards and Technology materials science X-ray beam line at the National Synchrotron Light Source. An examination of type Ia, type IIa and type IIb natural crystals has shown that, in general, type Ia material is less strained with a better-defined microstructure and with less variation among samples. The type II samples show a large degree of variation in residual strain and a disrupted microstructure resulting from a large number of crystalline imperfections. The high temperature, high pressure process for growth of man-made diamond yields crystals that are almost always superior to commercially available natural material.

Real time topography with X-ray image magnification

Abstract An X-ray optical configuration for real time synchrotron ratiation topography is described. Asymmetric diffraction from perfect Si crystals is used to control the beam size, wavelength, and collimation before the sample, and to magnify the X-ray image after the sample. Preliminary results using this system are reported. Video images of moving magnetic domain walls under a varying magnetic field were obtained from Ni single crystals in the anomolous transmission geometry.

Ultra-small-angle X-ray scattering to bridge the gap between visible light scattering and standard small-angle scattering cameras

Abstract This paper reports the performance of an ultra-small-angle X-ray scattering facility on beamline X23A3 at the National Synchrotron Light Source. Based on a Bonse-Hart double-crystal design, the instrument combines: continuously tunable optics with asymmetric first monochromator crystal, high-flux throughput, high-precision crystal rotators, independently-mounted reflecting crystals, photodiode detector and high-resolution X-ray video camera. This combination of features permits rapid small-angle X-ray scattering measurements in the scattering wave-vector range of 0.005–2.0 nm −1 (depending on the sample), with μm-positioning accuracy of a typical 3 × 3 mm 2 beam on the sample.