Microporosity Formation Research Articles

Synthetic biodegradable microporous hydrogels for in vitro 3D culture of functional human bone cell networks

Generating 3D bone cell networks in vitro that mimic the dynamic process during early bone formation remains challenging. Here, we report a synthetic biodegradable microporous hydrogel for efficient formation of 3D networks from human primary cells, analysis of cell-secreted extracellular matrix (ECM) and microfluidic integration. Using polymerization-induced phase separation, we demonstrate dynamic in situ formation of microporosity (5–20 µm) within matrix metalloproteinase-degradable polyethylene glycol hydrogels in the presence of living cells. Pore formation is triggered by thiol-Michael-addition crosslinking of a viscous precursor solution supplemented with hyaluronic acid and dextran. The resulting microporous architecture can be fine-tuned by adjusting the concentration and molecular weight of dextran. After encapsulation in microporous hydrogels, human mesenchymal stromal cells and osteoblasts spread rapidly and form 3D networks within 24 hours. We demonstrate that matrix degradability controls cell-matrix remodeling, osteogenic differentiation, and deposition of ECM proteins such as collagen. Finally, we report microfluidic integration and proof-of-concept osteogenic differentiation of 3D cell networks under perfusion on chip. Altogether, this work introduces a synthetic microporous hydrogel to efficiently differentiate 3D human bone cell networks, facilitating future in vitro studies on early bone development.

Microporosity evolution in polymer‐derived SiOC glasses pyrolyzed in different atmospheres

AbstractPolymer‐derived ceramics (PDCs) are a class of advanced materials obtained by pyrolysis in a controlled atmosphere of an organosilicon polymer. Their functional as well as mechanical properties originate from the peculiar nanostructures developed during the pyrolysis. Herein, we investigate the formation of transient microporosity in a model PDC (methyl‐silsesquioxane) obtained in Ar, Ar–5%H2, CO2, and air. It is shown that a common evolution can be detected up to 700°C. At this temperature, the structure of the material in terms of chemical bonds is marginally changed (only redistribution reactions take place), but the medium‐range order is clearly modified moving the system to a more disordered state (detected by small angle x‐ray scattering [SAXS]) and causing the formation of a large amount of open micropores sized at about 1.2–1.7 nm. In the 700–800°C range, the proper ceramization starts causing the formation of a new class of small (around 1 nm) open micropores. These partially annihilate at 900°C in Ar and Ar–H2 (i.e., in the second part of the ceramization process), whereas they totally collapse in CO2 due to the formation of a more silica‐like SiOC (less polymerized and viscous). Finally, SAXS points out the persistence of relatively large closed nanovoids of about 1 nm at 1250°C for the samples treated in Ar and Ar–H2. These might explain anomalies in terms of density, elastic modulus, and thermal conductivity of this class of ceramics as reported in the literature.

Abnormal improvement of high-temperature stress rupture life in a new low cost Ni-based single crystal superalloy by adding minor nitrogen

Generally, elevated nitrogen (N) content promotes the precipitation of nitrides, which increase the size and quantity of porosity and thus degrade the mechanical performance of superalloys. However, in this study, N content was found to have a beneficial impact on the stress rupture property of single-crystal (SX) superalloys. The results indicated that as the N content increased from 5 ppm to 35 ppm, the porosity first decreased and then increased. The porosity of the sample with 14 ppm N was the lowest, 0.072% ± 0.011%, which was mainly attributed to the TiN phases in interdendritic pools that compensated for volume shrinkage by lattice expansion. The addition of N reduced the volume fraction and antiphase boundary energy of the γ′ phase because TiN nitride formation consumed Ti in large quantities. Additionally, the rupture life at 1100 °C/130 MPa was abnormally improved to 251.67 h ± 19 h as the N content was increased to 14 ppm, while it was markedly decreased as the N content was continuously increased to 35 ppm. The improved stress fracture life of the alloy was primarily attributed to the formation of TiN with a small size, which retarded microporosity formation and effectively impeded dislocation movement in γ channels. Moreover, during the stress rupture test, the size of the tertiary γ′ phase first reduced to a minimum in the alloy containing 14 ppm N, which increased the resistance to dislocation movement. However, excessive addition of N drastically reduced the stress fracture life as the precipitation and solid solution strengthening in the γ′ phase weakened. In addition, the agglomeration of nitride inclusions formed defects that aggravated crack nucleation and propagation. The overall N impact was studied, and the optimal N content was ascertained to provide further instructions for the commercial development of Re-free second-generation SX alloys.

To the ontogenesis of aeschynite in feldspar vein no. 31 оf the Vishnevye Gory, Southern Urals

Small grains of accessory aeschynite in feldspar vein no. 31 of Vishnevye Mountains (South Urals) co-crystallize with late growth zones of feldspar crystals, as well as with ilmenite, titanomagnetite, muscovite, zircon, monazite, thorite, rutile, columbite and other minerals. Crystallization of aeschynite was followed by its metamict decay and formation of a nanocrystalline structure and further repeated dissolution and metasomatosis along microfractures of the mineral aggregate. Metasomatosis of aeschynite was accompanied by the formation of microporosity in muscovite-ilmenite aggregates at the contact with aeschynite grains.

Uncovering the effects of Ce and superheat temperature on Fe-rich intermetallic and microporosity formation in aluminum alloy

The continuous accumulation of Fe impurities in recycled aluminum is a major obstacle for its wide application in fatigue sensitive parts due to the formation of Fe intermetallics and micropores. In this paper, we study the effects of rare earth elements and superheat temperature on the crystal structure of Fe-rich intermetallic and morphology of microporosity using micron-resolution phase-contrast lens magnification based X-ray computed tomography (XCT). Using image registration and U-net convolutional neural networks (CNN) algorithm, we first segmented the morphology of Fe-rich intermetallic and quantified their distribution as a function of Ce additions and superheating temperature. It was found that the addition of Ce elements promoted the microstructure refinement and restricted the growth of β-Fe intermetallics effectively. Lowering the superheat temperature from 780 °C to 680 °C does not show a linear relationship between porosity level and the reduction of the intermetallic volume fraction. In fact, we have found the size of eutectic Si and Fe-rich intermetallic is the smallest at 730 °C and the tensile strength at as-cast condition with a superheating at 730 °C and Ce addition can give the greatest elongation at 4.26%, and yield and tensile strengths at 175.3and 249.5 MPa, respectively. • Rare earth Ce refines microstructure of Al-Si-Mg alloys and thus reduces pore size. • Non-linear relationship between superheat and pore size were found. • 3D Segmentation of α-Fe and β-Fe intermetallics using U-net CNN algorithm were developed for CT data. • Minimizing negative impacts of Fe-intermetallics and pores on properties is achieved.

Dual-template approach to designing nitrogen functionalized, hierarchical porous carbons for efficiently selective capture and separation of SO2

As the typically corrosive and toxic waste gas, sulfur dioxide (SO2) is derived from many industrial processes, its efficient elimination shows great significance for flue gas desulfurization. Herein, a class of hierarchically porous carbons with large BET surface areas (∼1192 m2/g), tunable nanoporosity and high-concentrated nitrogen base sites (6.5 at%) were developed, which were applied for selective capture and separation of sulfur dioxide via enhanced base-acid interaction. The nitrogen functionalized, porous carbons were prepared from a new dual-template route, which was realized from carbonization of a mixture containing zinc gluconate and urea (DT-NPC-xs, where x stands for the ratio of urea to zinc gluconate). In this process, the evaporation of zinc site at high temperature results in formation of abundant microporosity; while the decomposition of urea releases large amount of gas templates and nitrogen dopants, which create tunable meso-macroporosity and versatile nitrogen base sites in DT-NPC-x. The synthesized DT-NPC-xs show SO2 capacity as high as 11.8 mmol/g at 25 °C and 1.0 bar, and the SO2/N2 (0.1/0.9) and SO2/CO2 (0.1/0.9) IAST selectivities were up to 198.7 and 21.5. Breakthrough tests demonstrate the superior elimination of trace SO2 (∼2150 min/g) from ternary mixed gas (SO2/CO2/N2 = 0.6/15/84.4). The overall performance of DT-NPC-3 in SO2 adsorption and separation were superior to many reported adsorbents (e.g. activated carbon, g-C3N4) applied in the field.

Simulation and experimental characterization of microporosity during solidification in Sn-Bi alloys

The formation of microporosity during solidification of Sn-Bi alloys is investigated through experiments and simulations. Samples of varying composition with 20, 30, 47 and 58 wt% Bi are solidified in a copper mould and the pore fraction is measured through scanning electron microscopy. Finite element models are derived from X-ray micro computed tomography data and a material model is implemented to capture the effect of liquid pressure and volumetric swelling. The experimental assessment of solidification porosity shows a strong dependency on alloy composition. The round morphology of porosity found in the Sn-20 wt% Bi alloy indicates its formation in the terminal stage of solidification. Microporosity formation is computed by means of Finite Element simulations and the results correlate with experimental findings. The analysis confirms volumetric shrinkage in the liquid state of confined eutectic domains as the mechanism for pore formation and determines the composition dependency of Sn-Bi alloys.

Structural two-phase evolution of aminosilica-based silver-coordinated membranes for increased hydrogen separation

Hybrid organosilica membranes of silver-doped bis [3-(trimethoxysilyl) propyl] amine (BTPA) were prepared via sol-gel processing followed by coordination reactions to improve the permeability and separation performance. The evolution of silver in two phases as silver ions and as nanoparticles was observed during modification of the aminosilica networks; the silver ions coordinated with amine moieties while the silver nanoparticles developed following reduction on the aminosilica surface. The silver/amine mole ratio was evaluated against the formation of coordinated and particulate species during modification in the range of 0.1–0.5 mol mol−1. The formation of microporosity was successfully developed from 2.36 to 115 m2 g−1 by increasing the silver mole ratio. Furthermore, silver-modified aminosilica membranes showed a hydrogen (H2) permeance of 1.46 × 10−6 mol m−2 s−1 Pa−1, which was 65-fold higher than pure BTPA with excellent selectivity for H2/propane (C3H8) separation of 1500. It is evident that the proposed modification method via the two-phase structural evolution of silver coordination and nanoparticles reorganized the organosilica framework and improved the separation in the dehydrogenation of propane.

Preparation and Characterization of Intrinsic Porous Polyamides Based on Redox-Active Aromatic Diamines with Pentiptycene Scaffolds.

The electrochromic (EC) polyamides (Ether-PentiTPA1 and Ether-PentiTPA8) from the electroactive pentiptycene-derived triphenylaminediamine monomers (PentiTPA1 and PentiTPA8) were designed and prepared via polycondensation. The incorporation of rigid and contorted H-shaped pentiptycene scaffolds could restrain polymer chains from close packing and further form intrinsic microporosity in the polymer matrix which could be confirmed by the measurements of WXRD, BET, and PALS. With the existence of intrinsic microporosity, the diffusion rate of counterions between the electroactive polymer film and electrolyte can be promoted during the electrochemical procedure. Therefore, the prepared polyamide Ether-PentiTPA1 exhibits enhanced EC behaviors, such as lower driving potential (1.11 V), smaller redox potential difference ΔE (0.24 V), and shorter switching response time (3.6/5.2 s for coloring/bleaching). Consequently, the formation of intrinsic microporosity can be a useful approach for the enhancement of EC response performance.

Quantifying the effects of cooling rates and alloying additions on the microporosity formation in Al alloys

Microporosity in aluminum alloy castings is detrimental to the final mechanical properties such as fatigue life. Previous studies have shown that alloying additions in sand casting have a large impact on the percentage of porosity but no systematic studies on the effects of cooling rates and alloying additions have been reported. In this study, we investigate the porosity formation in three alloys with different cooling conditions using X-ray computed tomography (XCT). The microporosities of the three aluminum alloys at different cooling rates were visualized and statistically analyzed. When the cooling rate increased from 0.7 to 4.2 °C/s, the average equivalent diameter of microporosity in Al-7.3Si-1.5Cu decreased from 149.8 μm to 61.3 μm, with a size reduction of about 60 %; At a cooling rate of 0.7 °C/s, the average equivalent diameter of microporosity increased nearly three times with the increase of Si content to 7.3 wt.%. Comparing to three-dimensional (3D) cellular automata (CA) model predictions of porosity evolution in Al-Cu and Al-Si-Cu alloys, it was found that high cooling rates can increase the nucleation rate of microporosity and adding Cu and Si will give rise to the low solubility of hydrogen in the interdendritic liquid region during solidification. Therefore, robust casting components can be achieved by controlling the chemistry and applying non-equilibrium solidification conditions which change the interdendritic liquid flow and hydrogen supersaturations.

Development of technology for modification of heat-resistant nickel alloy ЖС3ДК-ВІ with titanium carbonitride ultrafine powders

Purpose. To study the effect of modification by the titanium carbonitride Ti(C, N) ultrafine particles additives in the form of powder and briquettes on the structure and physical-mechanical properties of the ЖС3ДК-ВІ alloy used for the manufacture of aircraft engine turbines cast rotor blades.
 Research methods. Preliminary high-temperature treatment of the melt was carried out on a VIP-10 installation.
 On the UPPF-3M installation with the alkaline melting pot, the ЖС3ДК-ВІ alloy was modified with ultrafine particles of titanium carbonitride Ti(C,N) in an amount of 60...80 g in the form of briquettes or powder wrapped in nickel foil.
 The samples were subjected to homogenization at a temperature of 1210 °C with a holding time of 3.5 hours and air cooling.
 The chemical composition of investigated alloys was determined. The macrostructure was studied on plates ~ 4 mm thick after chemical etching. The microstructure was evaluated on microsections before and after etching in the Marble reagent.
 Microhardness, ultimate strength, elongation and contraction, impact strength were determined at room temperature. Long-term strength tests were carried out at 850 °C under a load of 350 MPa. The bending test of the blades was carried out on a manual screw press in accordance with GOST 14019-80.
 Results. The microstructure of Ti+TiCN briquettes has been studied by optical and electron microscopy. X-ray microanalysis of specimen fractures confirmed a fairly uniform distribution of titanium carbonitride in the volume of briquettes.
 The chemical composition, macro- and microstructure of the experimental alloy have been studied. A fracto-graphic study of the samples fracture structure was carried out.
 The modifying effect of titanium carbonitride ultrafine particles on the dendritic structure, distribution and change in the morphology of primary carbides, the number and distribution of carbonitride particles has been established.
 A comparative analysis of the mechanical and heat-resistant properties of the ЖС3ДК-ВІ alloy of standard composition and modified with ultradispersed Ti(C,N) particles has been carried out. Bending tests of turbine rotor blades were carried out.
 Scientific novelty. It is shown that the use of ultrafine titanium carbonitride powders for bulk modification of the heat-resistant nickel alloy ЖС3ДК-ВІ makes it possible to increase the mechanical and heat-resistant properties of the material. Increasing the amount of modifier promotes grain refinement.
 More stable properties and favorable structure are provided by melt modification with ultrafine Ti(C,N) particles in the form of briquettes. It was found that modification with powdered Ti(C,N) leads to a decrease in the impact toughness values due to the formation of boundary microporosity.
 Practical value. The technology of the heat-resistant nickel alloy ЖС3ДК-ВІ, used for the manufacture of cast rotor blades of gas turbine engines, modification with additives of titanium carbonitride Ti(C,N) ultrafine particles, providing an increased level of performance properties of finished products, has been developed.

Characterization on the formation of porosity and tensile properties prediction in die casting Mg alloys

The 3D visualization of the porosity in high-pressure die casting (HPDC) Mg alloys AZ91D and Mg4Ce2Al0.5Mn (EA42) was investigated by X-ray computed tomography. It was demonstrated that the volumetric porosity at the near-gate location for alloy EA42 was significantly higher than that far from the gate location. This difference resulted from the low valid time during intensified casting pressure conditions. Specimens of alloy EA42 exhibited a narrow pore distribution in the side view (∼0.5 mm) compared to the wide distribution (∼1.8 mm) of alloy AZ91D, which was mainly attributed to the formation mechanism of the defect band. The formation of microporosity in the defect band of alloy EA42 was inhibited because of the significant latent heat released by a large amount of the Al11Ce3 phase segregated in the defect band during solidification. Additionally, an effective estimator (Z-Propagation) was introduced, which is proposed to predict the projected area fraction of the porosity (f) involved during tensile failure with better effectiveness compared with traditional methods based on the actual fractured surface. By coupling the Z-Propagation method with the critical local strain model, the logarithmic fracture strain and true fracture stress of the specimens were predicted within 3.03% and 1.65% of the absolute value of the average relative error (AARE), respectively.

Investigation on the Microporosity Formation of IN718 Alloy during Laser Cladding Based on Cellular Automaton.

Porosity is one of the most common defects in the laser cladding of Inconel 718 (IN718) alloy, which can reduce the strength and fatigue performance of the components. However, the dynamic formation of microporosity is challenging to observe through experiments directly. In order to explore the formation mechanism of porosities and dynamically reproduce the competitive growth between porosities and dendrite, a multi-scale numerical model was adopted, combined with a cellular automaton (CA) and finite element method (FEM). The decentered square algorithm was adopted to eliminate crystallographic anisotropy and simulate dendrite growth in different orientations. Afterward, based on the formation mechanism of microporosity during solidification, equiaxed and columnar dendrites with porosities were simulated, respectively. Dendrite morphology, porosity morphology, and distribution of solute concentration were obtained during the solidification process. The simulation results were reasonably compared with experimental data. The simulation results of the equiaxed crystal region are close to the experimental data, but the columnar crystal region has a relative error. Finally, the interaction effects of porosities and dendrites under different environmental conditions were discussed. The results suggested that with the increase in the cooling rate, the quantity of porosity nucleation increased and the porosity decreased.

Influence of DVB as linker molecule on the micropore formation in polymer-derived SiCN ceramics

In this work, the formation of transient microporosity during the polymer-to-ceramic conversion in polymer-derived ceramics was studied using a commercially available poly(vinyl)silazane precursor which was modified with divinylbenzene (DVB) as linker molecule during crosslinking. After pyrolysis treatments between 400 and 700 °C, the resulting materials not only showed distinct changes in elemental composition and structural features upon introduction of the linker molecule, but also a shift in micropore size, e.g. shifting from 0.84 nm to 0.70 nm after pyrolysis at 600 °C. Due to hindrance of transamination reactions in the low-temperature region, the nitrogen content in linker-containing samples was significantly higher, leading to a different composition of micropore-forming entities and, in case of the system studied, to smaller pores. These findings are a first step towards the clarification of the mechanisms leading to the pore formation in PDCs during pyrolytic conversion, which is essential for their use in prospective applications.

Nodule Count, End of Solidification Cooling Rate, and Shrinkage Porosity Correlations in High Silicon Spheroidal Graphite Iron

High-silicon spheroidal graphite (SG) irons present higher changes of density during the solidification process when compared to normal SG irons. This special behavior is particularly significant in the last stages of solidification, where the graphite expansion may become insufficient to compensate the contraction of the austenite and the risk of microporosity formation increases. The goal of this laboratory research was to establish correlations between the different levels of nodule count obtained using five commercial inoculants, the cooling rate at the end of solidification, and the shrinkage porosity propensity. The analysis was conducted on thermal analysis cups that were sectioned and evaluated for microstructure by optical metallography and by 2D analysis with the Image J software to quantify the size of the microporosity region. It was found that a higher nodule count, associated with higher cooling rate at the end of solidification, generates lower porosity. SEM analysis was conducted to study the nature of nuclei. Complex (MgSiAl)N nitrides were found as the main nucleation sites for graphite.

Modeling of gas porosity and microstructure formation during dendritic and eutectic solidification of ternary Al-Si-Mg alloys

A two-dimensional (2-D) multi-component and multi-phase cellular automaton (CA) model coupled with the Calphad method and finite difference method (FDM) is proposed to simulate the gas pore formation and microstructures in solidification process of hypoeutectic Al-Si-Mg alloys. In this model, the pore growth, and dendritic and eutectic solidification are simulated using a CA technique. To achieve the equilibrium among multiple phases during ternary Al-based alloy solidification, the phase transition thermodynamics and kinetics are evaluated by adopting the Calphad method. The diffusion equations of hydrogen and two solutes are solved by FDM. The developed CA-FDM coupled model can be used for simulating the evolution of gas microporosity and microstructures, involving dendrites and irregular binary and ternary eutectics, of ternary hypoeutectic Al-Si-Mg alloys. It has the capability of reproducing the interactions between the hydrogen microporosity formation and the growth of dendrites and eutectics, the competitive growth among the growing gas pores of different sizes, together with the time-evolving concentration fields of hydrogen and solutes. The simulated morphology of gas pore and microstructure has a good agreement with the experimental observation. The influences of the initial hydrogen concentration and cooling rate on the microporosity formation are investigated. It is found that the main portion of porosity formation occurs in the eutectic solidification stage through analyzing the profiles of porosity percentage and solid fraction varying with solidification time. The varying features of simulated porosity percentage, the maximum and average pores radii indicate that increasing initial hydrogen concentration promotes the formation of higher final porosity percentage and larger pores, while the size of gas pores will significantly reduce with increasing cooling rate, leading to a lower final porosity percentage.

Evaluation of dental caries, tooth crack, and age-related changes in tooth structure using optical coherence tomography.

Optical coherence tomography (OCT) is an imaging technique that can visualize the internal biological structure without X-ray exposure. Swept-source OCT (SS-OCT) is one of the latest version of OCT, wherein the light source is a tunable laser that sweeps near-infrared wavelength light to achieve real-time imaging. The imaging depth of OCT is highly influenced by the translucency of the medium. The medium that does not transmit light and the deeper structure beyond the range of light penetration depth are not relevant for OCT imaging. In OCT, sound enamel is almost transparent at the OCT wavelength range, and enamel and dentin can be distinguished from each other as the dentin–enamel junction (DEJ) appears as a dark border. Demineralized enamel and dentin are imaged as bright zones because of the formation of numerous micro-porosities where the backscatter of OCT signal is increased. In cavitated caries at interproximal or occlusal hidden zone, the upper margin of the cavity reflects the signal showing a distinct bright border in the SS-OCT image. SS-OCT is capable of determining crack penetration depth even when the cracks extended beyond the DEJ. SS-OCT has a high degree of sensitivity and specificity for the detection of dental caries and tooth cracks. SS-OCT is also capable of detecting non-carious cervical lesions and occlusal tooth wear in cross-sectional views to estimate the amount of tooth structure loss.

Features of hardening and structure formation of concrete with high-dispersion mineral additives

The article deals with the effect of micro-filler additives on the properties of high-strength concrete. The effectiveness of microcements – mixtures based on highly dispersed cement and silica fume – has been substantiated. Using the methods of thermokinetic analysis and thermoporometry, the processes of heat release and the formation of microporosity during the hardening of ordinary cement and microcements without additives and with the addition of silica fume are studied. The positive effect of silica fume on the hydration and formation of the structure of cement stone is proved. It is shown that the nature of the hydration interaction in the system of “microcement - silica fume” contributes to the compaction of the structure and reduce the development of shrinkage phenomena. It was revealed that the use of microcementives allows to increase the workability of concrete mixtures and to accelerate the rate of curing of high-strength concrete. According to the results of the studies, the high efficiency of the use of components of the type “microcement – silica fume” in the technology of high-strength and durable concrete has been proved.

Improving the flexibility and compostability of starch/poly(butylene cyclohexanedicarboxylate)-based blends

Fully biobased blends of thermoplastic starch and a poly(butylene cyclohexanedicarboxylate)-based random copolyester containing 25 % of adipic acid co-units (PBCEA) are prepared by melt blending and direct extrusion film casting. The obtained films are characterized from the physicochemical and mechanical point of view and their fragmentation under composting conditions is evaluated. The results demonstrate that the introduction of adipic acid co-units in the PBCE macromolecular chains permits to decrease the blending temperature, thus avoiding unwanted starch degradation reactions. Moreover, the presence of small amounts of citric acid as compatibilizer further improves the interfacial adhesion between the two components and promotes the formation of micro-porosities within the films. The synergistic combination of these factors leads to the development of materials showing an elastomeric behavior, i.e. no evident yield and elongation at break higher than 450 %, good moisture resistance and fast fragmentation in compost.

Hierarchical Structural Changes During Redox Cycling of Fe-Based Lamellar Foams Containing YSZ, CeO2, or ZrO2.

Several high-temperature energy conversion and storage technologies rely on redox cycling of Fe-based materials, including storage materials in solid-oxide Fe-air batteries and oxygen carriers in chemical-looping combustion. The materials' macroporosity necessary for gas flow is, however, irreversibly diminished during redox cycling due to (i) large volume changes during the redox transformations, (ii) foam sintering at elevated operating temperature (550-900 °C), and (iii) formation and growth of Kirkendall microporosity. To address these challenges, we use directional freeze-casting to create highly porous, lamellar, Fe-composite foams containing uniformly distributed sintering inhibitor (SI) particles-either Y2O3-stabilized ZrO2 (YSZ), CeO2, or ZrO2-at 0, 5, 10, or 15% of the solid volume. We characterize these foams before, during, and after redox cycling (Fe/FeO/Fe3O4, via H2O and H2) at 800 °C using operando synchrotron X-ray microtomography, metallography, and scanning electron microscopy. Shrinkage of the foam volume and formation of a gas-blocking shell surrounding the foam are reduced as the SI fraction increases. Volumetric shrinkage after the first five redox cycles is decreased from 66% (for pure-Fe foams) to 45% (for all Fe-composites containing 5 vol % SI). Foams containing 15 vol % YSZ show no volumetric shrinkage after five cycles, although, after 20 cycles, they have shrunk 53%. Post-cycling analysis reveals segregation of the SI particles to the cores of individual lamellae, surrounded by thick layers of sintered Fe on the lamellae surfaces. This segregation occurs due to Fe diffusion through FeO to the lamellae surfaces during oxidation, leaving behind the SI particles, which are then pushed into clusters by FeO/Fe3O4 contraction during reduction. The SI is thus rendered ineffective, which explains why foam densification is delayed (compared with pure-Fe foams), rather than fully prevented, after repeated cycling.