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 2006

Changes in Pore Size Distribution upon Thermal Cycling of TATB-based Explosives Measured by Ultra-Small Angle X-ray Scattering. T.M. Willey, J. Handly, B.L. Weeks, T. Van Buuren, J. Ilavsky, J.R.I. Lee, G.E. Overturf and J.H. Kinney. Cited: Propellents, Explosives, and Pyrotechnics, 2006, p

Effect of chemical structure on the volume-phase transition in neutral and weakly charged poly(N-alkyl(meth)acrylamide) hydrogels studied by ultrasmall-angle X-ray scattering. Neutral poly(N-isopropylacrylamide) (PIPAAm), poly(N,N-diethylacrylamide) (PDEAAm), and poly(N-isopropylmethacrylamide) (PIPMAm) hydrogels and their weakly charged counterparts prepared by copolymerizing with sodium methacrylate (x(MNa)=0,0.025,0.05) were studied using ultrasmall-angle x-ray scattering. The volume-phase transition in hydrogels was observed as an increase in the inhomogeneity correlation length of the networks. The change in inhomogeneity correlation length was abrupt in neutral PIPAAm and PIPMAm gels with increase in temperature but was continuous in neutral PDEAAm gels. Addition of ionic comonomer to the network backbone suppressed the volume-phase transition in poly(N-alkylacrylamide)s but not in PIPMAm. The observed differences in temperature-induced volume change of these three polymers in water cannot be rationalized based on their relative hydrophobicity and are instead explained by considering the hydrogen-bonding constraints on their thermal fluctuations. Both PIPAAm and PDEAAm undergo volume collapse since their thermal fluctuations are constrained by hydrogen bonding with water to an extent that beyond a critical temperature they seek entropic compensation. Although thermal fluctuations in both PIPAAm and PIPMAm are equally constrained, thermal energy of the latter can be relaxed via the rotation of alpha-methyl groups allowing it greater flexibility. Compared to N-alkylacrylamides, N-alkylmethacrylamide can thus sustain hydrogen bonding to relatively higher temperatures before seeking entropic compensation by undergoing volume collapse. (c) 2006 American Institute of Physics.

V.R. Tirumala, J. Ilavsky and M. Ilavsky. Cited: Journal of Chemical Physics, 2006, 124 (23), Jun 21, p -.

Small-angle X-ray scattering measurements of helium-bubble formation in borosilicate glass. Small-angle X-ray scattering (SAXS) measurements have been performed to study helium-bubble formation in borosilicate glass. Helium was introduced by He+ implantation over an energy range of 1 to 2 MeV to give a uniform distribution over similar to 1 mu m depth. The implanted dose was varied from 9 x 10(13) to 2.8 x 10(16) ions cm(-2), corresponding to a local concentration range of 40 to 11200 atomic parts per million (a.p.p.m.) averaged over the implantation depth. The SAXS response was fit with the Percus-Yevick hard-sphere interaction potential to account for interparticle interference. The fits yield helium-bubble radii and helium-bubble volume fractions that vary from 5 to 15 angstrom and from 10(-3) to 10(-1), respectively, as the dose increased from 9 x 10(13) to 2.8 x 10(16) cm(-2). The SAXS data are also consistent with maximum helium solubility with respect to bubble formation between 40 and 200 a.p.p.m. in the borosilicate glass matrix.

A.Y. Terekhov, B.J. Heuser, M.A. Okuniewski, R.S. Averback, S. Seifert and P.R. Jemian. Cited: Journal of Applied Crystallography, 2006, 39 Oct, p 647-651.

The combined effects of crosslinking and high crystallinity on the microstructural and mechanical properties of ultra high molecular weight polyethylene. Ultra high molecular weight polyethylene (PE) has been used for more than forty years as the bearing surface in total joint replacements. In recent years, there have been numerous advances in processing conditions that have improved the wear resistance of this material. In particular, crosslinking has been shown to dramatically improve the wear behavior of this orthopedic polymer in simulator studies. This benefit to wear resistance, however, is accompanied by a decrease in mechanical properties such as ultimate tensile strength, ductility, toughness and fatigue resistance. This degradation to mechanical properties may have serious implications for devices with high stress concentrations or large cyclic contact stresses. Tailoring microstructure for improved structural performance is essential for implant design. In this work we examined the role of crystallinity and crosslinking on the microstructure and mechanical properties of PE. Crystallinity was increased with a high pressure process and crosslinking was obtained with gamma irradiation. Crystallinity was beneficial to fatigue crack propagation resistance and when coupled with crosslinking a polymer with both wear and fatigue resistance was obtained. (C) 2005 Elsevier Ltd. All rights reserved.

K.S. Simis, A. Bistolfi, A. Bellare and L.A. Pruitt. Cited: Biomaterials, 2006, 27 (9), Mar, p 1688-1694.

New generation precipitated silica for elastomer reinforcement. D.W. Schaefer, D.J. Kohls, E. Feinblum and A. Vorobiev. Cited: Fall 170th Technical Meeting of the Rubber Division, American Chemical Society (Conf. Proc.) October 10-12, 2006 (Cincinnati, OH), Vol. 170 (paper 69), Ed., American Chemical Society, 2006, p. paper 69.

Influence of geometrical and spatial characteristics of the porosity on the thermal conductivity of EB-PVD TBCs. A.F. Renteria. Cited: Journal of Thermal Spray Technology, 2006, 15 (1), Mar, p 29-30.

Microstructure and rheology of thermoreversible nanoparticle gels. Naive mode coupling theory is applied to particles interacting with short-range Yukawa attractions. Model results for the location of the gel line and the modulus of the resulting gels are reduced to algebraic equations capturing the effects of the range and strength of attraction. This model is then applied to thermo reversible gels composed of octadecyl silica particles suspended in decalin. The application of the model to the experimental system requires linking the experimental variable controlling strength of attraction, temperature, to the model strength of attraction. With this link, the model predicts temperature and volume fraction dependencies of gelation and modulus with five parameters: particle size, particle volume fraction, overlap volume of surface hairs, and theta temperature. In comparing model predictions with experimental results, we first observe that in these thermal gels there is no evidence of clustering as has been reported in depletion gels. One consequence of this observation is that there are no additional adjustable parameters required to make quantitative comparisons between experimental results and model predictions. Our results indicate that the naive mode coupling approach taken here in conjunction with a model linking temperature to strength of attraction provides a robust approach for making quantitative predictions of gel mechanical properties. Extension of model predictions to additional experimental systems requires linking experimental variables to the Yukawa strength and range of attraction.

S. Ramakrishnan and C.F. Zukoski. Cited: Langmuir, 2006, 22 (18), Aug 29, p 7833-7842.

Advanced neutron and X-ray techniques for insights into the microstructure of EB-PVD thermal barrier coatings. The ongoing quest to increase gas turbine efficiency and performance (increased thrust) provides a driving force for materials development. While improved engine design and usage of novel materials provide solutions for increased engine operating temperatures, and hence fuel efficiency, reliability issues remain. Thermal barrier coatings (TBCs), deposited onto turbine components using the electron-beam physical vapor deposition (EB-PVD) process, exhibit unique pore architectures capable of bridging the technological gap between insulation/life extension and prime reliance. This article explores the potential of advanced X-ray and neutron techniques for comprehension of an EB-PVD TBC coating microstructure. While conventional microscopy reveals a hierarchy of voids, complementary advanced techniques allow quantification of these voids in terms of component porosities, anisotropy, size and gradient through the coating thickness. In addition, the derived microstructural parameters obtained both further knowledge of the nature and architecture of the porosity, and help establish its influence on the resultant thermal and mechanical properties. (c) 2006 Elsevier B.V. All rights reserved.

A. Kulkarni, A. Goland, H. Herman, A.J. Allen, T. Dobbins, F. Decarlo, J. Ilavsky, G.G. Long, S. Fang and P. Lawton. Cited: Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, 2006, 426 (1-2), Jun 25, p 43-52.

Mechanical properties of rubbers reinforced with porcellinite-derived precipitated silica. D.J. Kohls, D.W. Schaefer, E. Feinblum, A. Vorobiev and R. Kosso. Cited: Fall 170th Technical meeting of the Rubber Division, American Chemical Society (Conf. Proc.) October 10-12, 2006 ( Cincinnati , OH ), Vol. 170 (paper 68), Ed., American Chemical Society, 2006, p. paper 68.

On the Nature of Variations in Density and Composition within TATB-based Plastic Bonded Explosives. J.H. Kinney, T.M. Willey and G.E. Overturf. Cited: 13th International Detonation Symposium (Conf. Proc.) ( Norfolk , VA ), Vol. Ed., 2006,

Relation of thermal conductivity with process induced anisotropic void systems in EB-PVD PYSZ thermal barrier coatings. Thermal barrier coatings (TBCs) deposited by Electron-beam physical deposition (EB-PVD) protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task is to optimize the properties of PYSZ-based TBC by tailoring its microstructure. Thermal conductivity of the EB-PVD produced PYSZ TBCs is influenced mainly by the size, shape, orientation and volume of the various types of porosity present in the coatings. These pores can be classified as open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within the three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization is very complex and requires the use of sophisticated methods. In this work, three different EB-PVD TBC microstructures were manufactured by varying the process parameters, yielding various characteristics of their pores. The corresponding thermal conductivities in as-coated state and after ageing at 1100C/1h and 100h were measured via Laser Flash Analysis Method (LFA). The pore characteristics and their individual effect on the thermal conductivity are analysed by USAXS which is supported by subsequent modelling and LFA methods, respectively. Evident differences in the thermal conductivity values of each microstructure were found in as-coated and aged conditions. In summary, broader columns introduce higher values in thermal conductivity. In general, thermal conductivity increases after ageing for all three investigated microstructures, although those with initial smaller pore surface area show smaller changes.

A. Flores Renteria, B. Saruhan-Brings and J. Ilavsky. Cited: (Conf. Proc.) (Cocoa Beach, FL, United States), Vol. 27 (3-15), Ed., American Ceramic Society, Westerville, OH 43081, United States, 2006, p. 3-15.

Scattering for mixtures of hard spheres: Comparison of total scattering intensities with model. The angular dependence of the intensity of x-rays scattered from binary and ternary hard sphere mixtures is investigated and compared to the predictions of two scattering models. Mixture ratio and total volume fraction dependent effects are investigated for size ratios equal to 0.51 and 0.22. Comparisons of model predictions with experimental results indicate the significant impact of the role of particle size distributions in interpreting the angular dependence of the scattering at wave vectors probing density fluctuations intermediate between the sizes of the particles in the mixture.

B.J. Anderson, V. Gopalakrishnan, S. Ramakrishnan and C.F. Zukoski. Cited: Physical review E, 2006, 73 (3), Mar, p -.