Andrew J. Allen

Ultra-small-angle X-ray scattering at the Advanced Photon Source

The design and operation of a versatile ultra-small-angle X-ray scattering (USAXS) instrument at the Advanced Photon Source (APS) at Argonne National Laboratory are presented. The instrument is optimized for the high brilliance and low emittance of an APS undulator source. It has angular and energy resolutions of the order of 10−4, accurate and repeatable X-ray energy tunability over its operational energy range from 8 to 18 keV, and a dynamic intensity range of 108 to 109, depending on the configuration. It further offers quantitative primary calibration of X-ray scattering cross sections, a scattering vector range from 0.0001 to 1 A−1, and stability and reliability over extended running periods. Its operational configurations include one-dimensional collimated (slit-smeared) USAXS, two-dimensional collimated USAXS and USAXS imaging. A robust data reduction and data analysis package, which was developed in parallel with the instrument, is available and supported at the APS.

The surface area of cement paste as measured by neutron scattering: evidence for two C-S-H morphologies

Abstract Small-angle neutron scattering was used to measure the effect of water-to-cement ratio (w/c) and cement batch variation on the surface area of ordinary Portland cement (OPC) paste after hydration for 28 days at room temperature, and to measure the development of surface area over the first 3 days of hydration at 30°C. The 28-day surface area was found to increase with w/c ratio in proportion to the volume of original water-filled space available for reaction product to form. The surface areas of different batches of type I OPC were quite similar, while that of a type II OPC was some 15% lower. Early surface area development at 30°C followed the heat evolution for the first 24 h of hydration and then leveled off, suggesting that further heat evolution was associated with reaction product, which added little to the surface area. These results support the theory that two different morphologies of the calcium-silicate-hydrate gel reaction product form during cement hydration.

Microstructural characterization of yttria-stabilized zirconia plasma-sprayed deposits using multiple small-angle neutron scattering

Density, electron microscopy, elastic modulus, and small-angle neutron scattering studies are used to characterize the microstructures of yttria-stabilized zirconia plasma-sprayed deposits as a function of both feedstock morphology and annealing. In particular, anisotropic multiple small-angle neutron scattering data are combined with anisotropic Porod scattering results to quantify each of the three main porous components in these thermal barrier coating materials: intrasplat cracks, intersplat lamellar pores and globular pores. An inverse correlation between the volume of porosity and its surface area is confirmed for the as-sprayed deposits, as is a preferential annealing of intrasplat cracks at elevated temperatures. The average elastic modulus is correlated with the total void surface area while the elastic anisotropy is related more closely to the intersplat porosity. However, depending on the feedstock morphology, globular pores are also shown to play a surprisingly significant role in post-anneal deposit microstructures and properties.  2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Measurement, standards, and data needs for CO2 capture materials: a critical review.

The commercial deployment of cost-effective carbon capture technology is hindered partially by the lack of a proper suite of materials-related measurements, standards, and data, which would provide critical information for the systematic design, evaluation, and performance of CO2 separation materials. Based on a literature search and conversations with the carbon capture community, we review the current status of measurements, standards, and data for the three major carbon capture materials in use today: solvents, solid sorbents, and membranes. We highlight current measurement, standards and data activities aimed to advance the development and use of carbon capture materials and major research needs that are critical to meet if innovation in carbon capture materials is to be achieved. The review reveals that although adsorbents are considered to have great potential to reduce carbon capture cost, there is no consensus on the experimental parameters to be used for evaluating sorbent properties. Another important finding is the lack of in situ experimental tools for the structural characterization of solid porous materials during CO2 adsorption, and computational methods that would enable a materials-by-design approach for their development.

Evolution of the void structure in plasma-sprayed YSZ deposits during heating☆

Abstract The evolution of the anisotropic void microstructure of plasma-sprayed yttria-stabilized zirconia (YSZ) deposits has been observed as a function of temperature by small-angle neutron scattering. Scattering experiments were carried out in-situ, in a furnace between 600 and 1400°C. The terminal slope (Porod scattering) of the scattering spectra was used to derive the specific surface area of the voids. For samples with sufficient scattering anisotropy, the two major void systems — intersplat (inter-lamellar) pores and intrasplat cracks — could be characterized separately. The pore and crack specific surface areas were found to depend on temperature differently. The specific surface area of the intrasplat cracks decreased markedly at temperatures below 1000°C, whereas the specific surface area of the intersplat pores began to decrease above 1000°C. This indicates important differences in the sintering of these two void systems probably related to their size and shape. Changes in the void surface were observed at temperatures as low as 800°C, a temperature comparable to, or less than, the usual operational temperature for this material.

Ultra-Small-Angle X-ray Scattering Instrument at the Advanced Photon Source: History, Recent Development, and Current Status

The 25-year history and development of an ultra-small-angle X-ray scattering (USAXS) instrument dedicated to serving materials research is presented and discussed. The instrument’s successful track record is attributed to three factors. The first, and surely the most important, is that all development has been driven by scientific research directions and opportunities. Second, the USAXS instrument is a core capability rather than an add-on facility, with measurement capability from micrometers to nanometers, which is precisely the size range where microstructures determine physical properties. The third is that the instrument’s range of capabilities has continually expanded, now including 2D collimation, imaging, and dynamics. And finally, USAXS has enjoyed the benefit of a management structure that has consistently appreciated the unique experimental measurement capabilities that USAXS delivers.

Effective pinhole-collimated ultrasmall-angle x-ray scattering instrument for measuring anisotropic microstructures

Small-angle scattering is widely used for measuring materials microstructure in the 1–100 nm size range. Ultrasmall-angle x-ray scattering (USAXS), typically achieved through crystal collimation, extends this size range to include features over 1 μm in size. This article reports on USAXS on the UNICAT beam line 33-ID at the Advanced Photon Source. The instrument makes use of a six-reflection crystal pair as a collimator and another six-reflection crystal pair as an analyzer. First principle absolute calibration and a broad scattering vector range make this a very effective instrument, limited only by the fact that the measurement of anisotropic microstructures is excluded due to slit smearing from the crystal collimation. This limitation has recently been removed by adding a horizontally reflecting crystal before and another after the sample. This creates a USAXS instrument with collimation in two orthogonal directions. We call this configuration effective pinhole USAXS. Now, anisotropic materials are pro...

In situ quasi-elastic scattering characterization of particle size effects on the hydration of tricalcium silicate

The effects of different particle size distributions on the real-time hydration of tricalcium silicate cement paste were studied in situ by quasi-elastic neutron scattering. The changing state of water in the cement system was followed as a function both of cement hydration time and of temperature for different initial particle size distributions. It was found that the length of the initial, dormant, induction period, together with the kinetics of hydration product nucleation and growth, depends on the hydration temperature but not on the particle size distribution. However, initial particle size does affect the total amount of cement hydrated, with finer particle size producing more hydrated cement. Furthermore, the diffusion-limited rate of hydration at later hydration time is largely determined by the initial tricalcium silicate particle size distribution.

Selective Adsorption of CO2 from Light Gas Mixtures by Using a Structurally Dynamic Porous Coordination Polymer

The selective adsorption of CO{sub 2} from mixtures with N{sub 2}, CH{sub 4}, and N{sub 2}O in a dynamic porous coordination polymer (see monomer structure) was evaluated by ATR-FTIR spectroscopy, GC, and SANS. All three techniques indicate highly selective adsorption of CO{sub 2} from CO{sub 2}/CH{sub 4} and CO{sub 2}/N{sub 2} mixtures at 30 C, with no selectivity observed for the CO{sub 2}/N{sub 2}O system.

Dispersion stabilization of silver nanoparticles in synthetic lung fluid studied under in situ conditions

Abstract The dispersion stabilization of silver nanoparticles (AgNPs) in synthetic lung fluid was studied to interrogate the effects on colloidal stability due to the principal constituents of the fluid. The colloidal stability of 20 nm citrate-AgNPs dispersed in the presence of each constituent of the synthetic lung fluid (individually, the complete fluid, and without additives) was observed during titration of increasing sodium chloride concentration. A variety of complementary in situ measurement techniques were utilized, including dynamic light scattering, ultraviolet-visible absorption spectroscopy, atomic force microscopy, and small-angle X-ray scattering, which provided a collective set of information that enabled far better understanding of the dispersion behavior in the fluid than any one technique alone. It was observed that AgNPs continued to adsorb bovine serum albumin (BSA) protein from the synthetic lung fluid solution as the sodium chloride concentration increased, until a maximum BSA coating was achieved prior to reaching the physiological sodium chloride concentration of 154 mmol L−1. BSA was determined to be the constituent of the synthetic lung fluid that is required to provide colloidal stability at high salt loadings, though the phospholipid constituent exerts a subtle effect. Additionally, as AgNPs are a distinctly different class of nanoparticles apart from the carbon nanotubes and titanium dioxide nanoparticles initially reported to be dispersible using this fluid, this work also demonstrates the broad applicability of synthetic lung fluid in providing stable dispersions for engineered nanoparticles for use in biological assays.