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 2007

Composition and density of nanoscale calcium-silicate-hydrate in cement. Although Portland cement concrete is the world's most widely used manufactured material, basic questions persist regarding its internal structure and water content, and their effect on concrete behaviour. Here, for the first time without recourse to drying methods, we measure the composition and solid density of the principal binding reaction product of cement hydration, calcium silicate-hydrate (C-S-H) gel, one of the most complex of all gels. We also quantify a nanoscale calcium hydroxide phase that coexists with C-S-H gel. By combining small-angle neutron and X-ray scattering data, and by exploiting the hydrogen/deuterium neutron isotope effect both in water and methanol, we determine the mean formula and mass density of the nanoscale C-S-H gel particles in hydrating cement. We show that the formula, (CaO)(1.7)(SiO2)(H2O)(1.80), and density, 2.604 Mg m(-3), differ from previous values for C-S-H gel, associated with specific drying conditions. Whereas previous studies have classified water within C-S-H gel by how tightly it is bound, in this study we classify water by its location-with implications for de. ning the chemically active (C-S-H) surface area within cement, and for predicting concrete properties. A.J. Allen, J.J. Thomas and H.M. Jennings. Cited: Nature Materials, 2007, 6 (4), Apr, p 311-316.

Ultrasmall-Angle X-ray Scattering (USAXS) Studies of Morphological Trends in High Energy Milled NaAlH4 Powders. T. Dobbins, E.B. Bruster, E.U. Oteri and J. Ilavsky. Cited: Journal of Alloys and Compounds, 2007

Determination of the relation between the process controlled variations of anisotropic void system and thermal conductivity of electron beam physical vapour deposited (EB-PVD) PYSZ thermal barrier coatings. A. Flores Renteria, B. Saruhan-Brings and J. Ilavsky. Cited: (Conf. Proc.) Vol. 27(3) (3-16), Ed., John Wiley &Sons. Inc., Hoboken, New Jersey, 2007, p. 3-16.

Simplified tube form factor for analysis of small-angle scattering data. R.S. Justice, D.H. Wang, L.-S. Tan and D.W. Schaefer. Cited: Applied Crystallography, 2007, 40 (s1), p 88-92.

Iron K-edge anomalous small-angle scattering at 15-ID-D at the Advanced Photon Source. N. Kirby, D. Cookson, C. Buckley, E. Bovell and T. St Pierre. Cited: Journal of Applied Crystallography, 2007, 40 p

Mechanical Properties of rubbers reinforced with porcelainite-derived precipitated silica. D.J. Kohls, D.W. Schaefer, R. Kosso and I. Tsyganova. Cited: Rubber World, 2007, 236 (1), April.

Porcellanite-derived precipitated silica: Syntheses & properties. D.J. Kohls, D.W. Schaefer, R. Kosso and I. Tsyganova. Cited: Rubber Asia, 2007, 21 (3), May-June.

Structure of Low-Density Nanoporous Dielectrics Revealed by Low-Vacuum Electron Microscopy and Small-Angle X-ray Scattering. Abstract: Aerogels (AGs) are ultralow-density nanoporous solids that have numerous potential applications. However, as most AGs are strong insulators with poor mechanical properties, direct studies of the complex nanoporous structure of AGs by methods such as atomic force and conventional scanning electron microscopy (SEM) have not proven feasible. Here, we use low-vacuum SEM to image directly the ligament and pore size and shape distributions of representative AGs over a wide range of length scales (~100-105 nm). The structural information obtained is used for unambiguous, real-space interpretation of small-angle X-ray scattering curves for these complex nanoporous systems. Low-vacuum SEM permits imaging of both cross-sections and skin layers of AG monoliths. Images of skin layers reveal the presence of microcracks, which alter the properties of cast monolithic AGs. S.O. Kucheyev, M. Toth, T.F. Baumann, A.V. Hamza, J. Ilavsky, W.R. Knowles, C.K. Saw, B.L. Thiel, V. Tileli, T. Vanbuuren, Y.M. Wang and T.M. Willey. Cited: Langmuir, 2007, 23 (2), p 353-356.

Self-assembly of carbon black into nanowires that form a conductive three dimensional micronetwork. The authors have used mechanical self-assembly of carbon-black nanoparticles to fabricate a three dimensional, electrically connected micronetwork of nanowires embedded within an insulating, supporting matrix of poly(methyl methacrylate). The electrical connectivity, mean wire diameter, and morphological transitions were characterized as a function of the carbon-black mass fraction. Conductive wires were produced with mean diameters as low as 24 nm with lengths up to 100 μm. © 2007 American Institute of Physics. L.E. Levine, G.G. Long, J. Ilavsky, R.A. Gerhardt, R. Ou and C.A. Parker. Cited: Applied Physics Letters, 2007, 90 (1), p 014101.

Determination of static microstructure of dilute and concentrated suspensions of anisotropic particles by ultra-small-angle X-ray scattering. Ultra- small -angle X-ray scattering was performed on suspensions of anisotropic polystyrene particles of varying degrees of anisotropy. The wave vector dependence of particle form factors is well described by a model developed by Debye for the scattering from fused spheres. As volume fraction is raised, all suspensions undergo a disorder/order phase transition. The scattering from disordered and ordered suspensions of anisotropic particles is the same as that of spheres up to volume fractions of 0.45, suggesting that, in the dilute crystalline phase, the anisotropic particles order into a rotator or plastic crystal phase, where the particle centers of mass are ordered, but the particle directors are randomly distributed. Further increase in particle volume fraction leads to differences in scattering between homonuclear dicolloids and spheres, implying that the homonuclear dicolloids form a body-centered tetragonal phase with both positional and directional order. This conclusion is supported by real-space imaging of dried films of the particles. E.B. Mock and C.F. Zukoski. Cited: Langmuir, 2007, 23 (17), Aug 14, p 8760-8771.

Nanostructural features in silica-polyvinyl acetate nanocomposites characterized by small-angle scattering. Small-angle scattering (SAS) experiments were carried out on nanocomposites of poly(vinyl acetate) (PVAc) and fumed silica nanoparticles with different surface areas and chemical treatment, in the wave-vector (Q) range: 0.0002-1 A-1 . SAS data on composites with matrices of two different molecular weights indicate that the particle aggregation is independent of the molecular weight of the matrix for a fixed filler concentration and surface treatment. Particle size distributions derived from the SAS data suggest that particle aggregation is reduced when the native surface hydroxyl groups are blocked by various surface treatments, which also reduce the bonding strength to the polymer matrix. The unified exponential/power-law analysis of the SAS data shows three levels of hierarchy in the organization of silica particles. The first level consists of small aggregates of silica particles. At the second level we observe polydispersed aggregates resembling mass-fractal objects that is corroborated by TEM. The polydispersed aggregates further associate to form agglomerates at the third level. The relevance of these findings to the mechanism of nanofiller reinforcement of linear amorphous polymers above Tg is discussed. R.A. Narayanan, P. Thiyagarajan, A.-J. Zhu, B.J. Ash, M.L. Shofner, L.S. Schadler, S.K. Kumar and S.S. Sternstein. Cited: Polymer, 2007, 48 (19), p 5734-5741.

Application of USAXS analysis and non-interacting approximation to determine the influence of process parameters and ageing on the thermal conductivity of electron-beam physical vapor deposited thermal barrier coatings. Electron-beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) display a lower thermal conductivity compared with the deposited bulk material. This effect is achieved due to the presence of pores within these films. The spatial and geometrical characteristics of the porosity influence directly the magnitude of the achieved reduction of the thermal conductivity. In this work, three EB-PVD coating containing different microstructures were manufactured by varying the manufacturing process parameters during the deposition process. Their corresponding thermal conductivities were measured via the laser flash analysis method (LFA) in both the as-coated state and after ageing (1100 °C/100 h). Analysis of the pore formation during processing was carried out by ultrasmall-angle X-ray scattering (USAXS). This technique is supported with a computer based modeling developed by researchers at Advanced Photon Source (APS) in ANL, USA, and in National Institute of Standards and Technology (NIST), USA. The model enables the characterization of the size, shape, volume and orientation of each of the pore populations in EB-PVD TBCs. The effect of these spatial and geometrical characteristics of the porosity on the thermal conductivity of the EB-PVD coatings were studied via a non-interacting approximation based on Maxwell's model. Results of LFA measurements and the applied approximation indicate an interrelation between the microstructure and the thermal properties of the analyzed EB-PVD coatings. Microstructures containing a higher volume fraction of fine anisotropic intra-columnar pores, and larger voids between feather-arms oriented at lower angles toward the substrate plane correspond to lower thermal conductivity values. Inter-columnar gaps do no significantly contribute to lowering the thermal conductivity due to their orientation parallel to the heat flux and their lower volume fraction compared with the volume occupied by the primary columns. On heat treatment, the deepest section of the gaps between feather-arms break-up into arrays of nano-sized low aspect ratio voids. The anisotropic, elongated intra-columnar pores evolve toward low aspect ratio shapes that are less effective in reducing the thermal conductivity. © 2006 Elsevier B.V. All rights reserved. A.F. Renteria, B. Saruhan, J. Ilavsky and A.J. Allen. Cited: Surface and Coatings Technology, 2007, 201 (8), p 4781-4788.

How nano are nanocomposites? Composite materials loaded with nanometer-sized reinforcing fillers are widely believed to have the potential to push polymer mechanical properties to extreme values. Realization of anticipated properties, however, has proven elusive. The analysis presented here traces this shortfall to the large-scale morphology of the filler as determined by small-angle X-ray scattering, light scattering, and electron imaging. We examine elastomeric, thermoplastic, and thermoset composites loaded with a variety of nanoscale reinforcing fillers such as precipitated silica, carbon nanotubes (single and multiwalled), and layered silicates. The conclusion is that large-scale disorder is ubiquitous in nanocomposites regardless of the level of dispersion, leading to substantial reduction of mechanical properties (modulus) compared to predictions based on idealized filler morphology. D.W. Schaefer and R.S. Justice. Cited: Macromolecules, 2007, 40 (24), Nov 27, p 8501-8517.

New Precipitated Silica for Rubber Reinforcement. D.W. Schaefer, D.J. Kohls, E. Feinblum, R. Kosso and A. Vorobiev. Cited: Rubber and Plastics News, 2007, April 30.

How do orientation fluctuations evolve to crystals? Z. Xiao, J. Ilavsky, G.G. Long and Y.A. Akpalu. Cited: Lecture Notes in Physics: Progress in Understanding of Polymer Crystallization, 2007, 714

Directed Assembly of Quantum Dots in a Diblock Copolymer Matrix. F.L. Beyer, C.R. Ziegler, K. Sill, T. Emrick, N.M. Benetatos and K.I. Winey. Cited: ARL Technical Report 2007, 2007, (ARL-TR-4204),