Model and data work together to reveal microscopic structures of materials

Abstract

Microscopic compositional distributions are important in determining the bulk properties of materials.1 In one application dealing with anticorrosive primers for metals, the distributions of corrosion inhibitor and filler particles in a polymer matrix are major factors governing the degree of protection under corrosive conditions.2 In another application in the field of geosciences, knowledge of the microscopic distributions of mineral phases in various rock formations is critical in the oil and gas industry.3, 4 While the value of this structural information is self-evident, the experimental techniques available for obtaining it are generally costly and destructive to the sample. X-ray computed tomography (CT) has been used as a nondestructive method to probe the internal structures of materials. However, x-ray CT only gives a microscopic map of the radiation’s amplitude attenuation and phase shift and is usually inadequate to determine compositional distributions within heterogeneous materials by the usual image-rendering process.5 Data-constrained modeling (DCM) has extended the reach of x-ray CT techniques to more directly determine a sample’s material composition. By combining a generic model with sample-specific CT data taken under multiple x-ray beam conditions, we have shown that DCM can provide microscopic details of compositional distributions in a wide range of samples.6–9 DCM for predictive modeling of microscopic compositions is based on a number of assumptions. The total volume of a voxel (3D pixel) is the sum of the partial volumes of its constituent material compositions (including void). A voxel’s total x-ray interaction (including amplitude attenuation and phase shift) is the sum of the interactions of its constituent compositions. Its composition is also determined statistically by that of its Figure 1. DCM-software user interface with predicted compositional microstructure for a rock sample composed of quartz (blue) and calcite (red). The display corresponds to a sample size of 1.5 1 0.36mm3.