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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Hanford Tank Waste Particle Atlas

Several methods have been utilized to perform solid phase characterization. Polarized light microscopy (PLM) is used to identify individual particles based on size, shape, color, and optical properties (e.g., refractive index1, birefringence, extinction positions, and interference figures). Scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) is used to detect which elements are present in individual particles and to infer chemical phase identification based on the metals present in combination with the size and shape of the particles. Powder X-ray diffraction (XRD) is used to identify crystalline phases present in bulk samples by matching the X-ray patterns with a library of known patterns for pure phases. Transmission electron microscopy (TEM) is used to identify individual particles by their X-ray diffraction patterns. RAMAN analysis is used to identify bulk sample compositions by matching RAMAN spectra with a library of known patterns. Other specialized techniques have not been employed routinely for Hanford tank waste samples.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

Characteristics of kinetic sprayed Ta in terms of the deposition behavior, microstructural evolution and mechanical properties: Effect of strain-rate-dependent response of Ta at high temperature

Highlights: • The effect of high-temperature rate-dependent response of BCC Ta on the deposition state of kinetic sprayed Ta particles with synergistic effect of powder oxidation • Abnormal increase of dislocation density above certain powder preheating temperature under the lower condition (N{sub 2} carrier gas), whereas considerable occurrence of grain refinement under the higher condition (He carrier gas). • Most significant dislocation density with the smallest volume-averaged domain size under the condition of 600 {sup o}C powder pre-heating with N{sub 2} carrier gas due to characteristic response of Ta. - Abstract: Numerous efforts have been focused on the fundamental research regarding kinetic spraying processes, but previous studies were biased to only few kinds of metallic materials. In particular, for Ta with body-centered cubic crystal structure, systematic studies are currently lacking in the literature. In this study, the characteristic deposition behaviors, microstructures, and mechanical properties of kinetic sprayed Ta under various impact conditions were systematically investigated. Generally, unusual features were usually related to strain-rate-dependent response (i.e. Peierls-Nabarro short range barriers) of Ta at high-temperature. This made thermal softening effect to be saturated above a certain degree of temperature, contributing to inferior deposition efficiency for the pre-heating at 600 °C than those of 400 and 500 °C by creating synergy with powder oxidation. In terms of microstructural evolutions, the dislocation density was abnormally increased at a certain powder preheating temperature (i.e., 600 °C), owing to the strain-rate-dependent response of Ta at high-temperature. On the other hand, grain refinement generated by rotational dynamic recrystallization was mainly observed under the higher kinetic energy condition (He carrier gas) at RT. Especially, the dislocation density and volume-average domain size evaluated via high-resolution X-ray diffraction peak profile analysis were corresponding to the results of the microstructural observations. Additionally, the nanomechanical properties (i.e., nanohardness and elastic modulus) evaluated via nanoindentation tests were in good agreement with the results from transmission electron microscopy investigations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Magnetostructural martensitic transformations with large volume changes and magneto-strains in all-d-metal Heusler alloys

The all-d-metal Mn{sub 2}-based Heusler ferromagnetic shape memory alloys Mn{sub 50}Ni{sub 40−x}Co{sub x}Ti{sub 10} (x = 8 and 9.5) are realized. With a generic comparison between d-metal Ti and main-group elements in lowering the transformation temperature, the magnetostructural martensitic transformations are established by further introducing Co to produce local ferromagnetic Mn-Co-Mn configurations. A 5-fold modulation and (3, −2) stacking of [00 10] of martensite are determined by X-ray diffraction and HRTEM analysis. Based on the transformation, a large magneto-strain of 6900 ppm and a large volume change of −2.54% are observed in polycrystalline samples, which makes the all-d-metal magnetic martensitic alloys of interest for magnetic/pressure multi-field driven applications.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structure and optical properties of [In{sub 1−2x}Sn{sub x}Zn{sub x}]GaO{sub 3}(ZnO){sub m}

Compounds of [In{sub 1−2x}Sn{sub x}Zn{sub x}]GaO{sub 3}(ZnO){sub 1} (x≤0.22) and [In{sub 1−2x}Sn{sub x}Zn{sub x}]GaO{sub 3}(ZnO){sub 2} (x≤0.42) were prepared by solid state processing proving a substantial solid solution of Sn in the layered compounds InGaO{sub 3}(ZnO){sub m} (m=1, 2). Single crystal X-ray diffraction of the compounds reveals two In{sup 3+} ions to be substituted by one Sn{sup 4+} and one Zn{sup 2+} at the octahedral layer preserving the average charge of +3 at these sites. The substitution does not lead to an ordering of the ions but proves for the first time that the octahedral site can be occupied by different ions while all characteristics of the layered structures remain unchanged. Consequences of indium substitution are (i) decrease of the a axis compared to InGaO{sub 3}(ZnO){sub m} according to smaller ionic radii of Sn{sup 4+} and Zn{sup 2+} compared to In{sup 3+} and (ii) shift of the optical band gap to higher energies shown by UV–vis measurements. - Graphical abstract: Substitution limits of indium in InGaO{sub 3}(ZnO){sub m} (IGZO) by Sn and Zn are studied for m=1, 2 by single crystal X-ray diffraction and micro-chemical analysis. - Highlights: • New Oxides [In{sub 1−2x}Sn{sub x}Zn{sub x}]GaO{sub 3}(ZnO){sub m} (m=1, 2) with IGZO type structure. • Sn and Zn substitute for In at octahedral sites. • Crystal structures were characterized by single crystal X-ray diffraction. • Optical band gap energies were determined by UV–vis spectroscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Orientation epitaxy of Ge 1–x Sn x films grown on single crystal CaF 2 substrates

Ge 1–x Sn x films were grown via physical vapor deposition below the crystallization temperature of Ge on single crystal (111) and (100) CaF 2 substrates to assess the role of Sn alloying in Ge crystallization. By studying samples grown at several growth temperatures ranging from 250 °C to 400 °C we report temperature-dependent trends in several of the films' properties. X-ray diffraction theta vs. two-theta (θ/2θ) scans indicate single orientation Ge 1–x Sn x (111) films are grown on CaF 2 (111) substrates at each temperature, while a temperature-dependent superposition of (111) and (100) orientations are exhibited in films grown on CaF2(100) above 250 °C. This is the first report of (111) oriented Ge 1–x Sn x grown on a (100) oriented CaF 2 substrate, which is successfully predicted by a superlattice area matching model. These results are confirmed by X-ray diffraction pole figure analysis. θ/2θ results indicate substitutional Sn alloying in each film of about 5%, corroborated by energy dispersive spectroscopy. In addition, morphological and electrical properties are measured by scanning electron microscopy, atomic force microscopy and Hall mobility measurements and are also shown to be dependent upon growth temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Accessing alkali-free NASICON-type compounds through mixed oxoanion sol–gel chemistry: Hydrogen titanium phosphate sulfate, H{sub 1−x}Ti{sub 2}(PO{sub 4}){sub 3−x}(SO{sub 4}){sub x} (x=0.5–1)

We report a direct sol–gel synthesis and characterization of new proton-containing, rhombohedral NASICION-type titanium compounds with mixed phosphate and sulfate oxoanions. The synthetic conditions were established by utilizing peroxide ion as a decomposable and stabilizing ligand for titanyl ions in the presence of phosphates in a strong acidic medium. Thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), induction-coupled plasma optical emission spectroscopic (ICP-OES) elemental analysis, and Raman and {sup 1}H magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopic studies have determined the presence of sulfate and proton ions in the structure, for which the compositional range has been found to be H{sub 1−x}Ti{sub 2}(PO{sub 4}){sub 3−x}(SO{sub 4}){sub x} (x=0.5–1). The particulate products exhibit a nanocrystalline nature observed through characterization with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The N{sub 2} sorption isotherm measurements and subsequent Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) analyses confirmed the presence of the textural meso- and macropores in the materials. Future studies would determine the potential of the new compounds in various applications as battery materials, proton conductors and solid acid catalysts. - Graphical abstract: A series of proton-containing NASICON-type compounds, H{sub 1−x}Ti{sub 2}(PO{sub 4}){sub 3−x}(SO{sub 4}){sub x} (x=0.5–1), were discovered through a new sol–gel synthetic method that utilizes peroxide ion as a decomposable and stabilizing ligand for titanyl ions in the presence of phosphates in a strong acidic medium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

High-frequency millimeter wave absorption of indium-substituted ε-Fe{sub 2}O{sub 3} spherical nanoparticles (invited)

In this work, we prepared indium-substituted ε-iron oxide (ε-In{sub x}Fe{sub 2−x}O{sub 3}) spherical nanoparticles by a combination method of reverse-micelle and sol-gel techniques. The powder X-ray diffraction pattern with Rietveld analysis shows that ε-In{sub x}Fe{sub 2−x}O{sub 3} has an orthorhombic crystal structure (space group: Pna2{sub 1}), and the In{sup 3+} ions mainly replace the Fe{sup 3+} ions at B site among the four nonequivalent Fe{sup 3+} sites (A–D sites). The magnetic measurements show that the coercive field (H{sub c}) at 300 K decreases with increasing x, i.e., H{sub c} = 21.9 kOe (x = 0), 12.2 kOe (x = 0.04), 11.6 kOe (x = 0.09), 7.8 kOe (x = 0.13), and 5.9 kOe (x = 0.18). Millimeter wave absorption was measured by terahertz time-domain spectroscopy, and the decrease of resonance frequency (f{sub r}) is observed, i.e., f{sub r} = 182 GHz (x = 0), 160 GHz (x = 0.04), 143 GHz (x = 0.09), 123 GHz (x = 0.13), and 110 GHz (x = 0.18). This decrease in the f{sub r} value is understood by the decrease of magnetic anisotropy, which is caused by the replacement of Fe{sup 3+} (S = 5/2) with nonmagnetic In{sup 3+} (S = 0) at B site contributing to the magnetic anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Intercalation of Nanopolyaniline with Nanobentonite and Manganese Oxide Nanoparticles as a Novel Nanocomposite to Remediate Cobalt/Zinc and Their Radioactive Nuclides {sup 60}Co/{sup 65}Zn

A novel nanocomposite based on the combination of nanobentonite with nanopolyaniline and nanomanganese oxide (N-Bent–NPANI–NMn{sub 3}O{sub 4}) was synthesized and investigated to extract Co/Zn ions from water using batch technique and {sup 60}Co/{sup 65}Zn radionuclides from radioactive wastewater using column techniques. Characterization was established by High resolution-transmission electron microscopy (HR-TEM), Scanning electron microscope, X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and Fourier transform infrared spectrophotometer. The image of HR-TEM indicated that the produced nanocomposite was ranged from 59.07 to 83.38 nm. Solution pH, time of reaction, amount of solid and metal concentration, all of these parameters were inspected and optimized as fundamental factors during the extraction process. The obtained results implied that the ideal conditions for extraction were pH 6 and 7, reaction time 10 and 20 min, for Co and Zn ions, respectively. The highest removal capacities were found 255.28 and 202.22 mg g{sup −1} for Co and Zn, respectively by using 5 mg nanocomposite. Excellent recoveries were obtained as 94.0–94.5% and 92.0–93.0% for removal of Co–{sup 60}Co and of Zn–{sup 65}Zn ions, respectively from the examined samples. Graphical Abstract: .

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Structural properties of barium stannate

Here BaSnO 3 has attracted attention as a transparent conducting oxide with high room temperature carrier mobility. We report a series of measurements that were carried out to assess the structure of BaSnO 3 over a variety of length scales. Measurements included single crystal neutron and x-ray diffraction, Rietveld and pair distribution analysis of neutron powder diffraction, Raman scattering, and high-pressure x-ray diffraction. Results from the various diffraction probes indicate that both the long-range and local structures are consistent with the cubic symmetry. The diffraction data under pressure was consistent with a robustly cubic phase up to 48.9 GPa, which is supported by density functional calculations. Additionally, transverse phonon velocities were determined from measured dispersion of the transverse acoustic phonon branches, the results of which are in good agreement with previous theoretical estimates and ultrasound measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Novel silica stabilization method for the analysis of fine nanocrystals using coherent X-ray diffraction imaging

High-energy X-ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron-based technique used to quantitatively reconstruct the three-dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub-100?nm size regimes ? a size routinely achievable by chemical synthesis ? despite the spatial resolution of the BCDI technique being 20?30?nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction data sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20?nm and AuPd nanocrystals in the size range 60?65?nm were investigated with BCDI measurement at beamline 34-ID-C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre-requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Formation and Acid–Base Surface Properties of Highly Dispersed η-Al{sub 2}O{sub 3} Nanopowders

Highly dispersed η-Al{sub 2}O{sub 3}-based nanopowders have been prepared via glycine–nitrate combustion followed by heat treatment in air. The resultant materials have been characterized by X-ray diffraction, Fourier transform IR spectroscopy, scanning electron microscopy, simultaneous thermal analysis, and other techniques. We have optimized the glycine-to-nitrate ratio (G/N = 0.2) and found heat treatment conditions for combustion products (isothermal holding at a temperature of 700°C for 6 h) that allow one to obtain single- phase nanocrystalline η-Al{sub 2}O{sub 3} powders with an average particle size of 5 ± 1 nm and specific surface area of 54 ± 5 m{sup 2}/g. The acid–base surface properties of the η-Al{sub 2}O{sub 3} nanopowder have been analyzed using pyridine sorption–desorption processes as an example. The specific concentrations of weak, intermediate, and strong Lewis acid centers on the surface of the η-Al{sub 2}O{sub 3} nanocrystals have been shown to markedly exceed those on the surface of commercially available γ-Al{sub 2}O{sub 3} (A-64). The synthesized nanopowders can thus be used as effective supports of acid catalysts.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Study on Nanocellulose Properties Processed Using Different Methods and Their Aerogels

In this paper the effects of different mechanical methods including homogenization, ultrasonication and grinding on the properties of the nanocellulose materials and their aerogels, were investigated. The cellulose nanocrystal products, (CNC-H) and (CNC-U), were prepared by homogenization and ultrasonication of the acid hydrolyzed pulps, respectively. The aerogel products were produced by solvent exchanging of nanocellulose hydrogels with tertiary butyl alcohol and followed by freeze drying. The nanocellulose materials were studied using transmission electron microscopy, field emission scanning electron microscopy (FE-SEM), Fourier transformed infrared spectroscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA). Size distribution and surface charges of the nanocellulose suspensions were measured by zetasizer. Also, the morphology, the porosity properties and surface area of the CNCs and CNF aerogels were investigated via FE-SEM and nitrogen adsorption–desorption isotherms. The results showed that CNC-H has higher surface charge, suspension stability (− 41.8 mV), crystallinity index (74.7%) and better size dispersion than CNC-U and CNF with an average particle size of 122 nm. CNC-H microstructures demonstrated homogeneous network structure with smaller nanometer dimensions (15–30 nm width and 60–400 nm length). However, the CNC-H showed lower thermal stability compared to CNC-U and CNF. Larger average pore size (16.32 nm), pore volume (0.42 cc/g) and high specific surface area (> 100 m{sup 2} g{sup −1}) in CNC-H aerogel were obtained. Graphical Abstract: Suspensions of nanocellulose (NC) were prepared by different mechanical methods: Homogenizing, Ultrasonic and grinding. The NC products were investigated and their differences in morphology and other characteristics were studied. The aerogels were prepared from the nanocellulose hydrogels. The nitrogen physisorption was used to study the pore characteristics of the aerogels. .

36 MATERIALS SCIENCE↗
DOE OSTI2024

Restructuring of the Lewis Acid Sites in Y-Modified Dealuminated Beta-Zeolite by Hydrothermal Treatment

Yttrium-modified dealuminated Betazeolite (Y-BEA) represents a type of Lewis acid zeolite that has gained attention for its potential to efficiently catalyze the conversion of biomass-derived oxygenates. The structure of the Y active sites and their dynamics during biomass conversion reactions, which normally involve substantial amounts of water, necessitate thorough investigation for the rational design of more active and stable catalysts. Here, we conducted a study where a series of Y-BEA catalysts with different yttrium loadings (1–7 wt.%) were subjected to hydrothermal treatment (450 °C, 20% water) and investigated for their structural and catalytic activity changes through a combination of multiple characterizations and kinetic measurements. The number of acid sites of Y-BEA decreased without a change in acid strength following the hydrothermal treatment, which was confirmed by the results of acid site titration, infrared spectroscopy of probe molecules, and kinetic measurements for probe reactions (acetone aldol condensation). Structural analysis using X-ray diffraction (XRD), specific surface area measurement, X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) demonstrated that both the zeolite structure and the isolation status of the Y site remain intact after hydrothermal treatment. Further, the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) spectra, thermogravimetric analysis (TGA), and operando 1 H and 29 Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) revealed the dehydroxylation of Y-BEA induced by hydration-rearrangement-condensation restructuring during the high-temperature steam treatment. Dehydroxylation affects the structure of Y sites by reducing their vicinal silanol sites. In conclusion, this conversion of Lewis acidic Y sites into nonacidic sites is the primary factor behind the change in acid site quantity and catalytic activity on Y-BEA.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A nanoporous 3D zinc(II) metal–organic framework for selective absorption of benzaldehyde and formaldehyde

A new 3D nanoporous metal–organic framework (MOF), [[Zn{sub 4}O(C{sub 24}H{sub 15}N{sub 6}O{sub 6}){sub 2}(H{sub 2}O){sub 2}]·6H{sub 2}O·DMF]{sub n} (1) based on 4,4′,4″-s-triazine-1,3,5-triyltri-p-aminobenzoate (TATAB) ligand was solvothermally synthesized and characterized by single–crystal X-ray diffraction, Powder X-ray diffraction (PXRD), infrared spectroscopy (IR) and Brunauer–Emmett–Teller (BET) analyses. X-ray single crystal diffraction analysis reveals that 1 exhibits a 3D network with new kvh1 topology. Semi-empirical (AM1) calculations were carried out to obtain stable conformers for TATAB ligand. In addition, the absorption of two typical aldehydes (benzaldehyde and formaldehyde) in the presence of 1 was investigated and the effect of the aldehyde concentration, exposure time and temperature was studied. It was found that compound 1 has a potential for the absorption of aldehydes under mild conditions. - Graphical abstract: Absorption of two typical aldehydes (formaldehyde and benzaldehyde) by solvothermally synthesized of a 3D nano-porous MOF based on TATAB tricarboxylate ligand and Zn (NO{sub 3}){sub 2}·6H{sub 2}O. - Highlights: • We present a 3D Zn(II)-MOF with TATAB linker by solvothermal method. • The framework possesses a new kvh1 topology. • The framework displays formaldehyde and benzaldehyde absorption property. • Conformational analysis was performed to determine the stable linker geometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Analyzing the scale of the bainitic ferrite plates by XRD, SEM and TEM

Since the major strengthening mechanisms in nanocrystalline bainitic steels arise from the exceptionally small size of the bainitc ferrite plate, accurate determination of this parameter is fundamental for quantitative relating the microstructure to the mechanical properties. In this work, the thickness of the bainitic ferrite subunits obtained by different bainitic heat treatments was determined in two steels, with carbon contents of 0.3 and 0.7 wt.%, from SEM and TEM micrographs. As these measurements were made on 2D images taken from random sections, the method includes some stereological correction factors to obtain accurate information. Finally, the determined thicknesses of bainitic ferrite plates were compared with the crystallite size calculated from the analysis of X-ray diffraction peak broadening. Although in some case the values obtained for crystallite size and plate thickness can be similar, this study confirms that indeed they are two different parameters. - Highlights: •Bainitic microstructure in a nanostructured and sub-micron steel •Bainitic ferrite plate thickness measured by SEM and TEM •Crystallite size determined by X-ray analysis.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Diffused phase transitions in Pb(Zr{sub 0.65}Ti{sub 0.35})O{sub 3}-Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3} multiferroics

The solid solutions of (1−x)Pb(Zr{sub 0.65}Ti{sub 0.35})O{sub 3}-xPb(Fe{sub 2/3}W{sub 1/3})O{sub 3} in different ratios were fabricated by a high-temperature solid-state reaction method using high-purity oxides for possible multi-ferroic applications. Structural analysis using x-ray diffraction powder patterns of the system by Rietveld refinement method exhibits the formation of rhombohedral phase with R3c space group. Detailed studies of dielectric permittivity as a function of temperature of the systems show that the frequency independent dielectric maximum temperature shifts toward room temperature on increasing x. In addition to this, the degree of diffuseness of the permittivity anomaly is more pronounced for higher content of Pb(Fe{sub 2/3}W{sub 1/3})O{sub 3}, implying the existence of a composition-induced diffuse phase transition for the limited range of compositional ratios. Detailed impedance spectroscopy analysis shows the contributions of grain, grain boundary, and interfacial polarizations in the resistive characteristics and conduction mechanism of the materials. The weak ferromagnetic and saturated ferroelectric loops indicate that system with x = 0.1, 0.2 have good multiferroic characteristics, and may be useful for future spintronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Quantitative Analysis of Micro-structural Changes in a Bituminous Coal After Exposure to Supercritical CO{sub 2} and Water

High-volatile bituminous coal samples were reacted in deionized water with supercritical CO{sub 2} (ScCO{sub 2}–water) under simulated in situ pressure and temperature conditions (8 MPa and 40 °C) in unconfined stress state for 14 days, in order to characterize potential CO{sub 2}–water–coal reactions. Micro-structural changes were identified pre- and post-experiment using X-ray powder diffraction (XRD) analysis for powdered coal (mineralogical changes), optical microscopy and scanning electron microscopy (SEM) for polished thin sections (surface feature changes) and micro-CT scanning for a small core (porosity and permeability changes). XRD analysis revealed that carbonic acid leaches out mineral matters in coal, including carbonates (calcite) and silicate minerals (albite, illite and kaolinite). Optical microscopy, SEM and CT images confirmed that the interaction of coal with ScCO{sub 2}–water causes an abundance of micro-cracks to open or propagate in unconfined coal samples. Most micro-cracks preferably propagated along maceral–mineral and maceral–maceral interfaces, which demonstrates that the micro-cracking was caused by differential swelling of different coal lithotypes. Wormhole formation was observed in coal caused by mineral dissolution and hydrocarbon mobilization, which significantly increases coal porosity compared with swelling-induced cracking. 3-D pore network models extracted from CT images show that ScCO{sub 2}–water treatment enlarges the pore and throat size, increases the numbers of pores and throats and improves pore network connectivity. Overall, CO{sub 2}–water–coal interactions under unconfined conditions enhance coal porosity, connectivity and permeability, which can be attributed to the combined effect of micro-cracking, mineral dissolution and hydrocarbon mobilization.

58 GEOSCIENCES↗