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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

From core-scale experiment to reservoir-scale modeling: A scale-up approach to investigate reaction-induced permeability evolution of CO2 storage reservoir and caprock at a U.S. CO2 storage site

Mineral dissolution and secondary mineral precipitation can cause porosity and permeability changes of CO 2 storage reservoirs and caprocks after injection of CO 2 . In this paper, a 3-step approach (core-scale experiment →core-scale modeling →reservoir-scale modeling) is developed to simulate reservoir-scale porosity and permeability evolution of CO 2 storage formation and caprock at a model CO 2 storage site. The model site is based on characteristics of a real site in Mississippi, USA. Important chemical and permeability modeling parameters in the reservoir-scale model are validated by core-scale experimental and reactive transport modeling results. The reservoir-scale model predicts a maximum 3.2% permeability increase of the CO 2 storage formation and a maximum 1.1% permeability increase of the caprock after 1000 years of exposure to CO 2 -rich brine, while the core-scale model predicts 7% permeability decrease for a small CO 2 storage formation core and 296% permeability increase for a small caprock core after 180-day exposure to CO 2 -rich brine. The discrepancy between permeability results of reservoir-scale model and core-scale model is attributed to strong pH buffering effect of CO 2 storage formation with large mass of H+-consuming minerals. Therefore, using core-scale experiments/models only is not sufficient to elucidate reservoir-scale permeability evolution. Variations of key model parameters have a small effect on permeability evolution of both CO 2 storage formation and caprock, except for variations of K eq (SiO 2 (am)) and the exponent n in permeability-porosity correlation. SiO 2 (am) is a key mineral that governs permeability evolution of CO 2 storage formation and caprock, given the characteristics of the model CO 2 storage site.

58 GEOSCIENCES↗
DOE OSTI2018

Analysis of textural properties of CaO-based CO 2 sorbents by ex-situ USAXS

Here in this work, the micro-textural properties of CaO-based CO 2 sorbents prepared in a thermo-gravimetric reactor were investigated by ex situ synchrotron-based Small Angle X-ray Scattering (SAXS), Ultra Small Angle X-ray Scattering (USAXS) and Wide Angle X-ray Scattering (WAXS). Six sorbent samples were produced by calcination in vacuum at different temperatures and durations of the heating step; additionally, four partially carbonated samples were produced, after calcination in vacuum, at different CaO conversions. The scattering intensity profiles were analyzed by means of the Unified Fit model. Bimodal pore size distributions (micro-pores and meso-pores) were identified and the micro-textural properties (porosity, specific surface and pore radius of gyration) of each of the two pore populations were quantified both for the calcined and for the carbonated samples. The micro-textural properties of a few calcined samples were compared with N 2 -adsorption measurements. For each pore population, the trends of porosity, specific surface and pore radius of gyration, in addition to the pore number density and sphericity factor, were obtained versus time during the calcination and versus the CaO conversion during the carbonation. The relevance of micro-pores with respect to macro-pores was assessed both as far as the porosity impact on the CO 2 capture capacity and as far as the specific surface impact on the carbonation kinetics. For the calcined samples, the micro-textural properties of a partially calcined sample were compared with those of the completely calcined samples, and pore correlation distances were determined. Finally, for the carbonated samples, the specific surface per unit of particle volume results linearly dependent on the CaO conversion and, if expressed per unit of mass of unreacted CaO, does not change significantly for most of the CaO carbonation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Controllable oxygen vacancy defect engineering of BiVO 4 porous structures for room temperature NH 3 detection

Controlling structural features of sensing material while judiciously introducing vacancy defect states for revamping the electronic properties of the sample to obtain its superior gas sensing performance, is quite rare. Herein, we report for the first time, the room temperature (RT) ammonia (NH 3 ) detection of peanut-like porous bismuth vanadate (BiVO 4 ) with a stable monoclinic phase. The developed BiVO 4 possess abundant oxygen vacancies and porosity by virtue of calcinations (400–800 ℃). BiVO 4 calcined at 400 ℃ exhibits high selectivity towards NH 3 with a maximum response of 1421 @ 270 ppm at RT, which is 2.5 fold enhanced compared to without calcined BiVO 4 (response of 547 @ 270 ppm NH 3 ). The oxygen defective BiVO 4 appeared highly durable and stable even under high humid conditions (∼60 %). Besides, the porosity of BiVO 4 not only enhances the specific surface area (19.8 m 2 /g) but also results in fast diffusion of NH 3 molecules, leading to a reduction in the decay time (34 s for 90 ppm NH 3 ). The density functional theory (DFT) uncovers that the oxygen vacancy formation in BiVO 4 augments the NH 3 sensing capabilities by enhancing the adsorption energy of NH 3 . This work provides insight into the sensing mechanism of increased response caused by defect engineering and porosity, which will be favourable for fabricating high-performance NH 3 sensors at RT.

DFT analysis↗
DOE OSTI2025

Additive manufacturing of mullite ceramic by digital light processing

Mullite material was successfully additively manufactured using digital light processing (DLP). The printed geometry involves a one-step process of pyrolysis, de-binding, and sintering under a plain atmosphere to achieve an average of 76 % ceramic yield and linear shrinkage of 12 %. Furthermore, the thermal profile was carefully controlled to obtain consistent phases in which the XRD shows a mullite phase. Here, in addition, the Weibull analysis was conducted on the sintered flexural specimens, showing a Weibull modulus (m) of 13.05 with a characteristic strength (σ 0 ) of 94.96 MPa. Synchrotron microtomography was performed on the sintered specimens, which showed two distinct porosity distributions (small and large). Large porosity (non-spherical elongated) is the primary cause of decreased material strength, while small porosity (spherical) is the sintering product. The measured thermal conductivity of the specimens was in the range of 2.7–3.1 W/m∙k and decreased with an increase in temperature. Lastly, large-scale prototypes were printed concurrently with a fine resolution of 25 μm without any compromise on the predetermined design and structure.

Additive manufacturing↗
DOE OSTI2017

Probabilistic Risk Assessment of CO2 Trapping Mechanisms in a Sandstone CO2-EOR Field in Northern Texas, USA

This study employs a polynomial chaos expansion (PCE) technique to develop the reduced order models (ROMs) integrated with the Monte Carlo simulations to quantify uncertainties of CO 2 storage associated with enhanced oil recovery (EOR) in a commercial-scale CO 2 -EOR field. The Morrow B sandstone at the Farnsworth Unit (FWU) EOR field in northern Texas was selected as a case study. A 3-D reservoir model, including simulation of a five-spot injection/production well pattern, was constructed based on the data from well logs and cores, and an updated seismic interpretation in the FWU. Porosity and permeability were considered as sources of uncertainty. The 1000-realization heterogeneous random fields of porosity and permeability were generated based on the variogram analysis on the core measurements of the FWU. Three model outputs of interest include the amount of CO 2 trapped by three trapping mechanisms, i.e. hydrodynamic trapping, oil dissolution trapping, and aqueous dissolution trapping. The total of 25 runs were conducted with the simulations of a 20-year CO 2 -EOR period, and a 20-year monitoring period to develop the ROMs between uncertain model input parameters (i.e., porosity and permeability in this study) and model outputs at the end of simulation for each grid cell using PCE approach. The high coefficient of determination (R 2 ) and small normalized root mean square error (NRMSE) between the simulated (using reservoir modeling) and predicted (using ROMs) CO 2 storage indicate that the ROMs are acceptable and reliable to be used for the predictions. Given the 1000 Monte Carlo samplings of the model input parameters, cumulative distribution functions (CDFs) and uncertainty bounds (10 th and 90 th percentiles) of model outputs were estimated based on ROMs. At the end of simulation, the most injected CO 2 at the FWU was stored by hydrodynamic trapping (between 121,400 and 166,860 tonnes), followed by oil dissolution trapping (between 55,303 and 76,816 tonnes), and aqueous dissolution trapping (between 1979 and 2751 tonnes).

58 GEOSCIENCES↗
DOE OSTI2015

Probing water distribution in compressed fuel-cell gas-diffusion layers using X-ray computed tomography

X-ray computed tomography was used to investigate geometrical land and channel effects on spatial liquid-water distribution in gas-diffusion layers (GDLs) of polymer-electrolyte fuel cells under different levels of compression. At low compression, a uniform liquid-water front was observed due to water redistribution and uniform porosity; however, at high compression, the water predominantly advanced at locations under the channel for higher liquid pressures. Lastly, at low compression, no apparent correlation between the spatial liquid water and porosity distributions was observed, whereas at high compression, a strong correlation was shown, indicating a potential for smart GDL architecture design with modulated porosity.

25 ENERGY STORAGE↗
DOE OSTI2021

Microfracture-pore structure characterization and water-rock interaction in three lithofacies of the Lower Eagle Ford Formation

The microfracture-pore structures and water-rock interactions of eight samples of three typical lithofacies (three limestone, three wackestone, and two mudstone) from the Lower Eagle Ford Formation have been investigated using an integrated methodology. The methods used were X-ray diffraction (XRD), total organic carbon (TOC) content, pyrolysis, thin-section petrography, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), spontaneous water imbibition, and water vapor & nitrogen physisorption. Petrophysical properties such as organic richness, maturity, mineral composition, types and patterns of microfractures and pores, porosity, pore-throat size distribution, pore size distribution, pore connectivity, water adsorption and desorption behavior were determined from these methods, and the results compared among the three lithofacies. For example, the three limestone EAS samples and three wackestone DM samples show a low porosity range from 2.02–3.35%, whereas the two mudstone VRU samples exhibit a much large average porosity of 11.7% by MIP results. Nitrogen physisorption results show that pore size distributions have a good similarity in N2 adsorption volume for the samples with similar lithology. Microfractures are morphologically divided into seven types, with their definitions & pictorial examples presented and possible formation mechanisms proposed. In addition, the water vapor physisorption behavior and their controlling factors are discussed. Here, the water adsorption capacity shows a positive relationship (R 2 = 0.90) with clay content and a negative relationship (R 2 = 0.99) with carbonate content. In general, this integrated study of microfracture-pore structure characterization and water-rock interaction provides some insights of water vapor adsorption behavior in different lithofacies and whether microfractures could be an important pathway for fluid flow.

58 GEOSCIENCES↗
DOE OSTI2018

Solvent-pore interactions in the Eagle Ford shale formation

In this work, the effect of solvent extraction on pore space was examined on a suite of samples from the Eagle Ford Shale Formation with varying lithologies and maturities. Several solvents -toluene, cyclohexane, methanol, dichloromethane, and hydrochloric acid- were contacted with shale samples, extracting the compatible organic matter. The porosity in these extracted shale samples was compared to unmodified samples. The amount and type of organic matter extracted were determined using Gas Chromatography - Mass Spectrometry, and the porosity was determined by (Ultra) Small Angle Neutron Scattering. Mostly alkanes and aromatics were detected in the extracts, but other portions of bitumen may also have been present. Only higher molecular weight alkanes were extracted with hydrochloric acid, suggesting that physical dissolution of carbonate minerals may have liberated this portion of organic matter and the solvent was not able to penetrate the bitumen and kerogen to extract the lower molecular weight alkanes. Lastly, a decrease in porosity with extraction was observed and attributed to a dominant mechanism of kerogen swelling due to kerogen-solvent interaction.

02 PETROLEUM↗
DOE OSTI2022

Multimodal study of the impact of stimulation pH on shale pore structure, with an emphasis on organics behavior in alkaline environments

The tight nature of shale formations calls for hydraulic fracturing techniques able of altering the pore architecture to facilitate the production of hydrocarbon resources. The composition, pH, salinity, density and chemistry of Hydraulic Fracturing Fluids (HFF) vary substantially depending on reservoir characteristics. pH is among the most important stimulation fluid properties, ranging from very acidic, for carbonate reservoirs, to basic, in the case of clay-rich formations. pH regulates what geochemical reactions take place between the stimulation fluid and shale, as well as pore architecture alteration. The dissolution of carbonates and pyrite, and the precipitation of common minerals such as barite, gypsum and iron oxides in acidic environments have been extensively documented. In contrast, alkali stimulation environments and the role of organic components have received less attention. This research provides insight into the role of both minerals and organic components during alkaline stimulation, and the resulting pore architecture alterations. Here, a set of reactive experiments are performed using three different shales, with varying organic matter (OM) content, at different pH (3, 6, 8, 10, 12). The analysis of pore architecture alteration induced by the reaction was performed via nitrogen (N2) gas adsorption and Time-Domain Nuclear Magnetic Resonance (TD-NMR). Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) was used to measure the composition of the stimulation fluid post-reaction. The system with a larger impact on the pore architecture (pH 12) underwent a more extensive analysis through the application of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and x-ray Diffraction (XRD). Results show that mineral dissolution contributed to the creation of secondary porosity, mainly through dissolution of clays and silicates. We show that the abundance and distribution of organic matter both play a significant role in changes in pore architecture. Most samples showed an increase in inter-organic porosity, likely due to the organic acids within kerogen reacting with the stimulation fluid. Samples with a larger amount and more widespread distribution of organic matter show the most significant alterations. Finally, we also highlight the dissolution process of iron-rich minerals, including framboidal pyrite, as another important source of secondary porosity.

04 OIL SHALES AND TAR SANDS↗
DOE OSTI2018

Advanced manufacturing—A transformative enabling capability for fusion

Additive Manufacturing (AM) can create novel and complex engineered material structures. Features such as controlled porosity, micro-fibers and/or nano-particles, transitions in materials and integral robust coatings can be important in developing solutions for fusion subcomponents. A realistic understanding of this capability would be particularly valuable in identifying development paths. Major concerns for using AM processes with lasers or electron beams that melt powder to make refractory parts are the power required and residual stresses arising in fabrication. A related issue is the required combination of lasers or e-beams to continue heating of deposited material (to reduce stresses) and to deposit new material at a reasonable built rate while providing adequate surface finish and resolution for meso-scale features. Some Direct Write processes that can make suitable preforms and be cured to an acceptable density may offer another approach for PFCs.

Additive Manufacturing, fusion energy, Fusion Mate↗
DOE OSTI2023

Investigation of methane mass transfer and sorption in Marcellus shale under variable net-stress

Natural gas in shale exists as free and adsorbed gas, subject to prevailing pore pressures and stress conditions. Accordingly, to accurately estimate/predict the shale gas recovery potential, a central requirement is to represent gas transport and sorption behavior under varying stress conditions. The objective of this work is to facilitate the interpretation of laboratory-scale experiments, at relevant conditions, in an attempt to bridge the gap in scales between laboratory- and field-scale observations. We have conducted a series of high-pressure experiments on a full-diameter core sample from the Marcellus shale. These include gas loading (pressure-decay) and depletion (production) experiments with pure methane (CH 4 ) at variable stress conditions to characterize transport and sorption behavior under reservoir-relevant conditions. Here we have formulated and applied a novel integral model for mass transfer and storage in multi-porosity shale systems that allows us to effectively investigate transport and sorption phenomena: We delineate gas transport by interpreting helium (He) pressure-decay experiments and demonstrate how to use the information gained to calculate the relevant transport coefficients of CH 4 and other gases. A separate measurement of the CH 4 sorption isotherm on a smaller sample (a shale cube) was interpreted and combined with the transport description to predict the production behavior of CH 4 from the experiments with the full-diameter core. Our experiments demonstrate that the representation of sorption hysteresis is crucial for predicting and guiding shale gas production: At the end of both gas production experiments, approximately 20% of the initial gas in place remained in the core. Without accounting for sorption hysteresis, our modeling demonstrates that the CH 4 production could be overestimated by 10%. We demonstrate that our integral, triple-porosity model provides an effective approach for the interpretation and prediction of gas transport and sorption behavior during loading and production experiments on shale cores under variable net-stress conditions. In summary, our work combines measurements and modeling of mass transfer and sorption in shales at different scales to validate a characterization approach that facilitates an improved understanding of shale gas production. Furthermore, the triple-porosity model utilized in our work defines a potential pathway for the translation of laboratory-scale experimentation to larger-scale applications.

58 GEOSCIENCES↗
DOE OSTI2013

Natural CO 2 accumulations in the western Williston Basin: A mineralogical analog for CO 2 injection at the Weyburn site

The Devonian carbonates of the Duperow Formation on the western flank of the Williston Basin in southwest Saskatchewan contain natural accumulations of CO 2 , and may have done so for as long as 50 million years. These carbonate sediments are characterized by a succession of carbonate cycles capped by anhydrite-rich evaporites that are thought to act as seals to fluid migration. The Weyburn CO 2 injection site lies 400 km to the east in a series of Mississippian carbonates that were deposited in a similar depositional environment. That long-term isolation of natural CO 2 can be accomplished within carbonate strata has motivated the investigation of the Duperow rocks as a potential natural analog for storage of anthropogenic CO 2 in carbonate lithologies. For the Duperow strata to represent a legitimate analog for Midale injection and storage, the similarity in lithofacies, whole rock compositions, mineral compositions and porosity with the Midale Beds must be established. Here we compare lithofacies, whole rock compositions, mineralogy and mineral compositions from both locales. The major mineral phases at both locales are calcite, dolomite and anhydrite. In addition, accessory pyrite, fluorite, quartz and celestine (strontium sulfate) are also observed. Dawsonite, a potential CO 2 -trapping mineral, is not observed within the CO 2 -bearing horizons of the Duperow Formation, however. The distribution of porosity in the Midale Vuggy units is similar to that of the Duperow Formation, but the Marly units of the Midale have significantly higher porosity. The Duperow Formation is topped by the Dinesmore evaporite that is rich in anhydrite, and often contains authigenic K-feldspar. The chemistry of dolomite and calcite from the two localities also overlaps. Silicate minerals are in low abundance (<3%) within the analyzed Duperow samples, with quartz and K-feldspar the only silicates observed petrographically or in X-ray diffraction patterns. The Midale Beds contain significantly higher silica/silicate concentrations (Durocher et al., 2003), but the paucity of mono- and divalent cations that can be derived from dissolution of these silicate minerals likely precludes significant carbonate mineral formation. Therefore physical and solution trapping are likely to be the primary CO 2 trapping mechanisms at both sites.

58 GEOSCIENCES↗
DOE OSTI2013

Sensitivity of injection costs to input petrophysical parameters in numerical geologic carbon sequestration models

Numerical simulations are widely used in feasibility studies for geologic carbon sequestration. Accurate estimates of petrophysical parameters are needed as inputs for these simulations. However, relatively few experimental values are available for CO2-brine systems. Hence, a sensitivity analysis was performed using the STOMP numerical code for supercritical CO2 injected into a model confined deep saline aquifer. The intrinsic permeability, porosity, pore compressibility, and capillary pressure-saturation/relative permeability parameters (residual liquid saturation, residual gas saturation, and van Genuchten alpha and m values) were varied independently. Their influence on CO2 injection rates and costs were determined and the parameters were ranked based on normalized coefficients of variation. The simulations resulted in differences of up to tens of millions of dollars over the life of the project (i.e., the time taken to inject 10.8 million metric tons of CO2). The two most influential parameters were the intrinsic permeability and the van Genuchten m value. Two other parameters, the residual gas saturation and the residual liquid saturation, ranked above the porosity. These results highlight the need for accurate estimates of capillary pressure-saturation/relative permeability parameters for geologic carbon sequestration simulations in addition to measurements of porosity and intrinsic permeability.

Cost estimate↗
DOE OSTI2019

CO 2 storage in the Paluxy formation at the Kemper County CO 2 storage complex: Pore network properties and simulated reactive permeability evolution

The Paluxy formation is being considered as a prospective CO 2 reservoir at the Kemper County CO 2 Storage Complex. Herein, the pore and pore-throat size distributions and connectivity of the Paluxy formation is evaluated through analysis of 3D X-ray Computed Tomography images. In spite of resolution limitations that constrain the pore-throat sizes detectable by imaging, the permeability contributing pore-throats are successfully characterized through 3D imaging analysis. Image-obtained pore and pore-throat size distributions and pore connectivity are then utilized to construct pore network models and simulate permeability. After CO 2 is injected, it will dissolve into formation brine and create conditions favorable for dissolution of primary minerals and precipitation of secondary minerals. These reactions will alter the porosity and permeability of the system to varying degrees depending on the spatial location of reactions. In this research, the possible porosity-permeability evolution is simulated using pore network models considering mineral reactions occurring uniformly and non-uniformly throughout the network. For a given change in porosity, there is a large range of possible permeability outcomes. Depending on the extent and spatial location of mineral reactions, permeability may decrease by more than one order of magnitude as minerals precipitate. During dissolution, simulated permeability increases as much as 500%.

03 NATURAL GAS↗
DOE OSTI2021

Bimodal particle distributions with increased thermal conductivity for solid particles as heat transfer media and storage materials

Solid particles are being considered in several high temperature thermal energy storage systems and as heat transfer media in a variety of advanced power generation systems, particularly in concentrated solar power plants. The downside of such an approach is the low overall heat transfer coefficients caused by the inherently low thermal conductivity values of the low-cost solid media when coupled to heat exchanger for the power cycle working fluid. Choosing the right particle size distribution, emittance, and material of the solid media can all make a substantial difference in packed bed thermal conductivity. Current research though exclusively focuses on continuous unimodal distributions of particles. Here, in this work, we propose the use of a binary particle system with a bimodal size distribution to significantly increase packed bed thermal conductivity by reducing packed bed porosity. This is the first study related to ceramic solid particle heat transfer that has considered the thermal conductivity of non-unimodal size distributions at room and elevated temperatures. The following study found that for the binary particle system using Carbo particles CP 16/30 – CP 70/140 where the large particle volume fraction was 50% there was an 17–47% increase in packed bed thermal conductivity when compared with a nearly unimodal particle size distribution of CP 16/30 between 50 and 300 °C. Two different porosity and effective thermal conductivity models were studied, with one providing better prediction of porosity but both effective thermal conductivity models providing less predictive capacity. Importantly this approach can have a substantial impact of thermal performance, with little to no impact on the particle cost.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nature-inspired lotus-shaped fins combined with hybrid nanoparticles and metal foam for high-performance latent heat thermal energy storage

Latent heat thermal energy storage (LHTES) systems play a critical role in renewable energy integration by providing high energy density and nearly isothermal operation during phase transitions. However, their performance is often limited by slow melting/charging rates, which motivates the search for enhanced heat transfer designs. This study investigates the melting behavior of RT-82 phase change material (PCM) using novel lotus-shaped fins combined with copper metal foam and conductive graphene nanoparticles and carbon nanotubes. A two-dimensional enthalpy-porosity model in ANSYS Fluent was developed to simulate the charging/melting process, capturing non-thermal equilibrium between the foam and PCM/nano-PCM. In this study, effects of fin geometry, nanoparticle concentration, and foam porosity on melting dynamics and cost-performance trade-offs were investigated. Results showed that natural convection accelerated melting by ~12% compared to conduction-only scenarios. Optimized lotus-shaped fins with higher fin density (T3F4 and T3F10) achieved up to 63% faster melting relative to sparse configurations. Graphene nanoparticles improved thermal conductivity, with a 6% volume fraction, by reducing melting time by ~6.9%, while their combination with 75% porosity foam achieved a maximum reduction in the melting time of ~51% compared to pure PCM. Cost-performance analysis identified T3F4 as the most balanced design, offering rapid thermal response without excessive material costs, while moderate-density designs like T3S6 provided economical alternatives with acceptable performance. These results highlight the performance enhancement that can be achieved by integrating bio-inspired fins, nanoparticles, and foams, into compact and efficient LHTES for solar heating, building thermal management, and industrial waste-heat recovery applications.

25 ENERGY STORAGE↗
DOE OSTI2021

A mechanistic damage model for solid oxide fuel cell ceramic materials - Part I: Constitutive modeling

A multiscale mechanistic damage model for solid oxide fuel cell (SOFC) ceramics that combines micromechanics of stiffness reduction due to material porosity change and microcracking with a continuum damage mechanics (CDM) description for the evolution of microcracks up to fracture is developed in this work. The model also accounts for volumetric swelling of the anode due to redox cycling. Porosity change and swelling during redox combined with normal operating thermomechanical loads could increase the stress, strain and damage distributions in SOFC stacks leading them to failure. The proposed model involves three governing parameters: (i) the porosity in terms of the pore or void volume fraction, (ii) material swelling magnitude prescribed at a given loading step, and (iii) the damage variable that describes microcracking caused by thermomechanical loads and swelling. Pores and microcracks in the ceramics are modeled as randomly distributed ellipsoidal inclusions with negligible stiffness by an Eshelby-Mori-Tanaka formulation combined with an inclusion orientation distribution method. Microcracking damage evolution is described by a CDM formulation. Volumetric swelling is treated in a similar way to thermal expansion in the constitutive relations. After validation and numerical checks, the damage model is used to analyze a simplified SOFC positive-electrode/electrolyte/negative-electrode (PEN) structure subjected a redox cycle in addition to thermomechanical loads experienced during normal operation of a SOFC stack.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2016

Densification of W–Ni–Fe powders using laser sintering

In this paper, Laser Sintering (LS) of 90%W–7%Ni–3%Fe (wt.%) powders have been investigated, with the goal to understand the influence of final density by laser power, scanning speed, laser trace width, and the number of scanning passes. The results suggest that the laser power and scanning speed are the most important factors influencing density; the influence of trace width and number of scanning passes are not significant. With the increase of laser power and decrease of scanning speed, higher density can be achieved. Additionally, the microstructure analysis indicated that the porosity changed from open porosity to closed porosity with higher laser energy input. Energy-Dispersive X-ray Spectroscopy (EDX) analysis shows that during the sintering process, W was not melted but dissolved into the Ni–Fe matrix. Contact flattening and grain accommodation of W grains have been observed. It suggests that both rearrangement and solution-reprecipitation mechanisms are responsible for the densification. The sintered density with respect to laser power and scanning speed was modeled by continuum modeling theory and compared with experimental results.

42 ENGINEERING↗