A software package is presented for performing reduction and analysis of small-angle neutron scattering (SANS) and ultra-small-angle neutron scattering (USANS) data. A graphical interface has been developed to visualize and quickly reduce raw SANS and USANS data into one- or two-dimensional formats for interpretation. The resulting reduced data can then be analyzed using model-independent methods or non-linear fitting to one of a large and growing catalog of included structural models. The different instrumental smearing effects for slit-smeared USANS and pinhole-smeared SANS data are handled automatically during analysis. In addition, any number of SANS and USANS data sets can be analyzed simultaneously. The reduction operations and analysis models are written in a modular format for extensibility, allowing users to contribute code and models for distribution to all users. The software package is based on Igor Pro, providing freely distributable and modifiable code that runs on Macintosh and Windows operating systems.

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Reduction and analysis of SANS and USANS data using IGOR Pro

Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion

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 defining the chemically active (C–S–H) surface area within cement, and for predicting concrete properties.

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Composition and density of nanoscale calcium–silicate–hydrate in cement

Porosity plays a clearly important role in geology. It controls fluid storage in aquifers, oil and gas fields and geothermal systems, and the extent and connectivity of the pore structure control fluid flow and transport through geological formations, as well as the relationship between the properties of individual minerals and the bulk properties of the rock. In order to quantify the relationships between porosity, storage, transport and rock properties, however, the pore structure must be measured and quantitatively described. The overall importance of porosity, at least with respect to the use of rocks as building stone was recognized by TS Hunt in his “Chemical and Geological Essays” (1875, reviewed by JD Dana 1875) who noted:

> “Other things being equal, it may properly be said that the value of a stone for building purposes is inversely as its porosity or absorbing power.”

In a Geological Survey report prepared for the U.S. Atomic Energy Commission, Manger (1963) summarized porosity and bulk density measurements for sedimentary rocks. He tabulated more than 900 items of porosity and bulk density data for sedimentary rocks with up to 2,109 porosity determinations per item. Amongst these he summarized several early studies, including those of Schwarz (1870–1871), Cook (1878), Wheeler (1896), Buckley (1898), Gary (1898), Moore (1904), Fuller (1906), Sorby (1908), Hirschwald (1912), Grubenmann et al. (1915), and Kessler (1919), many of which were concerned with rocks and clays of commercial utility. There have, of course, been many more such determinations since that time.

There are a large number of methods for quantifying porosity, and an increasingly complex idea of what it means to do so. Manger (1963) listed the techniques by which the porosity determinations he summarized were made. He separated these into seven methods for …

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Characterization and Analysis of Porosity and Pore Structures

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

How Nano Are Nanocomposites

An ultra-high-resolution small-angle neutron scattering (USANS) double-crystal diffractometer (DCD) is now in operation at the NIST Center for Neutron Research (NCNR). The instrument uses multiple reflections from large silicon (220) perfect single crystals, before and after the sample, to produce both high beam intensity and a low instrument background suitable for small-angle scattering measurements. The minimum detector background to beam intensity ratio (noise-to-signal, N/S) for q ≥ 5 × 10−4 A−1 is 4 × 10−7. The instrument uses 2.38 A wavelength neutrons on a dedicated thermal neutron beam port, producing a peak flux on the sample of 17300 cm−2 s−1. The typical measurement range of the instrument extends from 3 × 10−5 A−1 to 5 × 10−3 A−1 in scattering wavevector (q), providing information on material structure over the size range from 0.1 µm to 20 µm. This paper describes the design and characteristics of the instrument, the mode of operation, and presents data that demonstrate the instrument's performance.

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Design and performance of a thermal-neutron double-crystal diffractometer for USANS at NIST

The ORNL Ultra-Small-Angle Neutron Scattering (USANS) facility at the High Flux Isotope Reactor (HIFR) has been recently upgraded, using the Bonse–Hart technique. Si(111) triple-bounce channel-cut single crystals have been used for both the monochromator and analyzer. The total width of the rocking curve of the analyzer is about 1.6′′ and the wavelength of the primary neutron beam is 2.59 A. It has been demonstrated that, owing to the low neutron absorption of silicon, the wings of the rocking curve are generally contaminated by neutrons propagating and diffracting inside the walls of channel-cut crystals. This parasitic intensity has been eliminated by the cutting of a groove in the long wall and the insertion of a cadmium absorber (0.6 mm thick). This modification effectively suppresses the wings of the rocking curve by over two orders of magnitude and thus dramatically improves the sensitivity of the diffractometer. The upgraded facility has been tested with several samples, including a polystyrene latex with a radius of 2.50 × 104 A as determined by optical microscopy. The average radius calculated from USANS data is 2.48 × 104 A, in excellent agreement with independently determined dimensions. The minimum accessible scattering vector of the upgraded USANS facility is Qmin ≃ 2 × 10−5 A−1, which corresponds to a maximum resolvable real-space dimension of 2π/Qmin ≃ 3 × 105 A (30 μm).

Optimization of a Bonse–Hart Ultra-Small-Angle Neutron Scattering Facility by Elimination of the Rocking-Curve Wings

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 A < q-1 < 107 A where q is the magnitude of the scattering vector. These materials consist of primary particles of the order of 100 A, aggregated into micron-sized aggregates that in turn are agglomerated into 100 µ 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.

Multilevel Structure of Reinforcing Silica and Carbon

Ultra-small-angle neutron scattering is a powerful new tool to quantitatively characterize the morphology of materials on length scales from 0.1 to 50 μm. The technique has already been used on a wide range of materials from hydrogels to geologic specimens. The data reveal a surprising richness of previously undetected morphological features.

Ultra-small-angle neutron scattering: a new tool for materials research

Bonse-Hart double-crystal diffractometers (DCD) with multibounce channel-cut crystals show rocking curves which depart dramatically in their wings from dynamical diffraction theory. This intrinsic background is many orders of magnitude higher than the predictions of dynamical diffraction theory. This effect has been studied at the ultra-small-angle neutron scattering (USANS) facility at Oak Ridge National Laboratory by the measurement of rocking curves from different volume elements of a thick single-bounce Si(lll) perfect crystal and from triple-bounce channel-cut Si(lll) crystals. Analysis of these data, together with the rocking curves from an X-ray Bonse-Hart DCD, allows it to be established that the rocking curve of the multibounce channel-cut crystals contains parasitic scattering generated at the surface of the crystals. The intensity of this component can be reduced by very deep etching of the crystal surface. Using this technique, the signal-to-noise ratio of the Bonse-Hart DCD at the ORNL USANS facility has been improved by one order of magnitude to ~,5 x 105 [I(0)/I(0 = 10")].

M. Agamalian

Papers

Design and performance of a thermal-neutron double-crystal diffractometer for USANS at NIST

Optimization of a Bonse–Hart Ultra-Small-Angle Neutron Scattering Facility by Elimination of the Rocking-Curve Wings

Multilevel Structure of Reinforcing Silica and Carbon

Ultra-small-angle neutron scattering: a new tool for materials research

Surface-Induced Parasitic Scattering in Bonse-Hart Double-Crystal Diffractometers