Advanced Photon Source

A U.S. Department of Energy, Office of Science,
Office of Basic Energy Sciences national synchrotron x-ray research facility

Publications from year 2000

Surface modification of silica fillers formed in situ for the reinforcement of polydimethylsiloxane networks. B.T. Vu, J.E. Mark and D.W. Schaefer. Cited: Abstracts of Papers of the American Chemical Society, 2000, 220 Aug 20, p U356-U356.

Multilevel structure of reinforcing silica and carbon. Using small-angle x-ray (SAXS), neutron (SANS), x-ray diffraction and light scattering, we study the structure of colloidal silica and carbon on length scales from 4 Angstrom < q(-1) < 10(7) Angstrom where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 Angstrom, aggregated into micron-sized aggregates that in turn are agglomerated into 100 mu agglomerates.
The diffraction data show that the primary particles in precipitated silica are composed of highly defective amorphous silica with little intermediate-range order (order on the scale of several bond distances). On the next level of morphology, primary particles arise by a complex nucleation process in which primordial nuclei briefly aggregate into rough particles that subsequently smooth out to become the seeds for the primaries. The primaries aggregate to strongly bonded clusters by a complex process involving kinetic growth, mechanical disintegration and restructuring. Finally, the small-angle scattering (SAS) data lead us to postulate that the aggregates cluster into porous, rough-surfaced, non-mass-fractal agglomerates that can be broken down to the more strongly bonded aggregates by application of shear.
We find similar structure in pelletized carbon blacks. In this case we show a linear scaling relation between the primary and aggregate sizes. We attribute the scaling to mechanical processing that deforms the fractal aggregates down to the maximum size able to withstand the compaction stress.
Finally, we rationalize the observed structure based on empirical optimization by filler suppliers and some recent theoretical ideas due to Witten , Rubenstein and Colby.

D.W. Schaefer, T. Rieker, M. Agamalian, J.S. Lin, D. Fischer, S. Sukumaran, C.Y. Chen, G. Beaucage, C. Herd and J. Ivie. Cited: Journal of Applied Crystallography, 2000, 33 (1), Jun 1, p 587-591.

The ultra-small-angle x-ray scattering instrument on UNICAT at the APS. A new ultra-small-angle X-ray scattering (USAXS) instrument has been commissioned as part of the UNICAT facility on the 33-ID line at the Advanced Photon Source. The instrument offers continuously-tunable optics for anomalous USAXS, 1000 times the throughput of earlier USAXS instruments(1,2), high sensitivity and high resolution at low scattering vector, and a scattering vector range from below 0.00015 Angstrom(-1) to above 0.5 Angstrom(-1). Early results include USAXS from colloidal silica suspensions, and anomalous USAXS from rare- earth oxides in the presence of similarly-sized cavities in silicon nitride. The addition of side-reflection optics, in an optional configuration of this instrument, enables USAXS measurements of anisotropic as well as isotropic materials.

G.G. Long, A.J. Allen, J. Ilavsky, P.R. Jemian and P. Zschack. Cited: Synchrotron Radiation Instrumentation, 2000, 521

Cavitation creep in the next generation silicon nitride. F. Lofaj, S.M. Wiederhorn, G.G. Long and M.K. Ferber. Cited: Ceramic Materials and Components for Engines, 2000,

Complementary experimental techniques for multi-scale modeling of plasticity. Some recently-developed experimental techniques, such as in situ ultra-small-angle X-ray scattering (USAXS), have demonstrated a capability for measuring aspects of dislocation structure evolution that are inaccessible to other experimental methods. However, no single technique can provide the entire range of information required by theoretical and computational researchers. It is only through the synergy of several experimental techniques (such as USAXS, transmission electron microscopy, and X-ray diffraction imaging) that much of the required quantitative information can be obtained. Ultimately, the development of additional new experimental techniques will also be required.

L.E. Levine, G.G. Long and D.R. Black. Cited: Multiscale Phenomena in Materials-Experiments and Modeling, 2000, 578

Anomalous ultra-small-angle X-ray scattering from evolving microstructures during tensile creep. Ultra-small-angle X-ray scattering provides quantitative and statistically significant information on the size distribution of electron density inhomogeneities with dimensions between approximate to 100 Angstrom and approximate to 5 mu m. All sizes are sampled simultaneously with a single experiment, removing the possibility of observational bias, In a material such as commercial silicon nitride, where the inhomogeneities are due to populations of intergranular secondary phases and voids of similar dimensions, the scattering contains contributions from each individual population. A single USAXS scan cannot separate overlapping populations of scatterers due to the different contrasts of the microstructural components. Anomalous USAXS (A-USAXS) is an element-specific contrast variation method to vary the scattering contribution from one of the populations while holding that of the other populations fixed. To follow the size evolution under tensile creep of both the cavities and the Yb disilicate secondary phases, A-USAXS data was measured near the Yb L-III absorption edge. Creep cavity and disilicate size distributions were each determined as a function of deformation.

P.R. Jemian, G.G. Long, F. Lofaj and S.M. Wiederhorn. Cited: Applications of Synchrotron Radiation Techniques to Materials Science V, 2000, 590

Fracture Toughness of Poly(methyl Methcarylate) Bone Cement. A.H. Gomoll, A. Bellare, W. Fitz, R.D. Scott, T.S. Thornhill, P. Jemian and G.G. Long. Cited: Institute of Materials Communications, 2000, p