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.

No abstract

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 Å−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.

Numerical simulations are used in this work to investigate aspects of microstructure and microseg-regation during rapid solidification of a Ni-based superalloy in a laser powder bed fusion additive manufacturing process. Thermal modeling by finite element analysis simulates the laser melt pool, with surface temperatures in agreement with in situ thermographic measurements on Inconel 625. Geometric and thermal features of the simulated melt pools are extracted and used in subsequent mesoscale simulations. Solidification in the melt pool is simulated on two length scales. For the multicomponent alloy Inconel 625, microsegregation between dendrite arms is calculated using the Scheil-Gulliver solidification model and DICTRA software. Phase-field simulations, using Ni–Nb as a binary analogue to Inconel 625, produced microstructures with primary cellular/dendritic arm spacings in agreement with measured spacings in experimentally observed microstructures and a lesser extent of microsegregation than predicted by DICTRA simulations. The composition profiles are used to compare thermodynamic driving forces for nucleation against experimentally observed precipitates identified by electron and X-ray diffraction analyses. Our analysis lists the precipitates that may form from FCC phase of enriched interdendritic compositions and compares these against experimentally observed phases from 1 h heat treatments at two temperatures: stress relief at 1143 K (870 °C) or homogenization at 1423 K (1150 °C).

Abstract-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. 

No abstract

No abstract

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.