TABLE 2.

Advanced analytical techniques used to determine the physicochemical characteristics of aggregates^a

Method	Sample size	Resolution	Limitations	Information collected	Reference(s)
SANS	150-μm-thick sections	1 nm to 0.8 μm	Technique relies on the contrasting agent (D2O/H2O), diffusion of contrasting agent to estimate pore connectivity, requires a long time to collect data, and pore geometry is assumed for when analyzing natural samples	Particle size distribution, pore vol, surface roughness, surface area, and interconnected porosity	143
USANS	150-μm-thick sections	60 nm to 20 μm
FIB-T	10 μm3	10 nm to 0.1 μm	Small sample volume used in analysis, and the technique is destructive, which limits reproducibility	Pore vol, porosity, pore size statistics, and connected and unconnected pore network; also, data can be correlated to elemental composition using EDS	144, 145
ET	100-nm needle	<1 nm to 0.05 μm	Small sample volume, fixed-needle geometry, and technique relies on image analysis and 3D reconstruction	Pore geometry and connectivity; pore data can be cross-correlated with elemental composition using EDS	146
BSEM	Thin sections	100 nm to ∼500 μm	2D analysis of a 3D geometry requires sample prep, and technique relies on image analysis to distinguish intra- and intergrain porosity	Pore geometry and connectivity; pore data can be cross-correlated with elemental composition using EDS	145
XCT	1 mm by 5-mm cylinders to 10-cm-diam cores	300 nm to 100 μmb	Technique relies on image analysis and 3D reconstruction	Results allow for full reconstruction of pore network	147
MIP	3.38 cm3	2 nm to 500 μm	Technique only measures connected porosity and assumes pore geometry	Results provide details on pore vol, pore size distribution, and surface area	148
PGA	Powder samples	0.5 nm to 0.2 μm	Technique only measures connected porosity and assumes pore geometry	Results provide details on pore vol, pore size distribution, and surface area	149

^aSANS, small-angle neutron scattering; USANS, ultrasmall-angle neutron scattering; FIB-T, focused ion beam tomography; ET, electron tomography; BSEM, backscattered scanning electron microscopy; XCT, X-ray computed tomography; MIP, mercury intrusion porosimetry; PGA, physical gas adsorption; EDS, energy dispersive spectroscopy. Table adapted from Zachara et al. (89).

^bActual detectable pore size resolution will vary depending upon X-ray source, optics, and material.