This article reviews the use of x-ray computed tomography (XRCT) to investigate the structure and properties of cellular solids. In the first section, the possibilities offered by XRCT are presented. Examples of tomographic images are shown for the three classes of material (polymers, metals, and ceramics). Different characterizations of cellular solids performed thanks to XRCT images are shown: calculation of morphological parameters, in situ and ex situ mechanical tests, and use of the tomographic images to perform finite element (FE) modeling. The second part of the paper presents the existing methods to create the meshes from tomographic images and highlights some interesting results from the FE simulations.

Ice templating is able to do much more than macroporous, cellular materials. The underlying phenomenon—the freezing of colloids—is ubiquitous, at a unique intersection of a variety of fields and domains, from materials science to physics, chemistry, biology, food engineering, and mathematics. In this review, I walk through the seemingly divergent domains in which the occurrence of freezing colloids can benefit from the work on ice templating, or which may provide additional understanding or inspiration for further development in materials science. This review does not intend to be extensive, but rather to illustrate the richness of this phenomenon and the obvious benefits of a pluridisciplinary approach for us as materials scientists, and for other scientists working in areas well outside the realms of materials science.

A new technology to coat open-celled foams homogeneously by using a vertical centrifuge and shear-thinning slurries is presented. The technology is exemplified by a complex multilayer-coated foam for catalytic applications (Fig. 3). Furthermore, a new calculation model for the estimation of coating thickness and for quality assessment is introduced and proved by comparing the calculated and experimental data. Based on these results, various material combinations are shown, e.g., layers made of rough particles, zeolites, activated carbon, γ-Al2O3, perovskites, mullite, and yttria–alumina–garnet on SiC–, Al2O3–, or cordierite foams. Theses “functionalized foams” can be used for a wide variety of practical applications, e.g., as adsorbents and catalysts in environmental engineering, as preforms for metal matrix composites, and for special purpose applications that require corrosion and oxidation resistance.

Carbon-bonded alumina filters for steel melt filtration are increasingly used by industries. Their potential regarding the material characteristics and the filtration efficiency appears, however, not used in full measure up to now. In the course of the present work, a new approach, due to the application of active oxide coatings, whose chemical phase equates to that of the nonmetallic oxidic inclusions in the steel melt, was created. The main emphasis consists of the generation of cold-applied, active alumina, spinel, and mullite coatings. Coatings have been developed due to the variation of sintering temperatures and a thermal pretreatment, which lead to increasing cold crushing strength. A basic understanding regarding the adhesion and the interface between the oxide coating and the carbon-bonded filter substrate has been created. Therefore, the essential factor is traceable back to thermal-related mechanisms.

Ceramic parts possessing an ordered porosity were produced for the first time by powder-based three-dimensional printing of a preceramic polymer followed by pyrolysis in an inert atmosphere. The main parameters involved in the process were investigated, and the precision of the printed and ceramized parts was assessed by means of scanning electron microscopy and micro computed tomography. The influence of two different printing solvents was investigated and the use of a mixture of 1-hexanol and hexylacetate in particular allowed the production of parts with a relative density of 80% both in the polymeric and in the ceramic state. The mixing of a cross-linking catalyst directly with the printing liquid greatly simplified the process, minimizing the necessity of preprocessing the starting powder. Three-dimensional printing of a preceramic polymer not containing any inert or active fillers was proved to be a feasible, convenient and precise process for the production of porous ceramic possessing a complex, ordered structure, such as stretch-dominated lattices.

Zeolite-based supports for inorganic membranes intended for gas separation have the potential to increase the resistance to thermal shock-induced cracking compared with ceramic or metallic substrates. We have studied the effect of exposure at 90 °C of hierarchically porous silicalite-I substrates to aqueous solutions at pH 2.0, 10.6, and 13.0 for periods up to 168 h. Silicalite-I supports were produced in binder-free form by pulsed current processing and using clay-binders by conventional thermal treatment. Long-term (168 h) acid and alkali treatment of the silicalite-I substrates results in a slight removal of silicon (in acid) and aluminum (in alkali) and does not affect the specific surface area and the crystalline microporous structural features but broadens the size distribution of the macropores. The mechanical strength remains unchanged after exposure to both alkaline and acidic solutions and the binder-free substrates display more than 20 times higher strength than the binder-containing materials.

Incorporation of porosity into a monolithic material decreases the effective thermal conductivity. Porous ceramics were prepared by different methods to achieve pore volume fractions from 4 to 95%. A toolbox of analytical relations is proposed to describe the effective thermal conductivity as a function of solid phase thermal conductivity, pore thermal conductivity, and pore volume fraction (νp). For νp < 0.65, the Maxwell–Eucken relation for closed porosity and Landauer relation for open porosity give good agreement to experimental data on tin oxide, alumina, and zirconia ceramics. For νp > 0.65, the thermal conductivity of kaolin-based foams and calcium aluminate foams was well described by the Hashin Shtrikman upper bound and Russell’s relation. Finally, numerical simulation on artificially generated microstructures yields accurate predictions of thermal conductivity when fine detail of the spatial distribution of the phases needs to be accounted for, as demonstrated with a bio-aggregate material.

Reusable thermal protection systems of reentry vehicles are adopted for temperatures ranging between 1000 and 2000 °C, when gas velocity and density are relatively low; they exploit the low thermal conductivity of their constituent materials. This paper presents a new class of light structural thermal protection systems comprised of a load bearing structure made of a macroporous reticulated SiSiC, filled with compacted short alumina/mullite fibers. Their manufacturing process is very simple and does not require special devices or ambient conditions. The produced hetoroporous heterogeneous ceramics showed high radiations shielding capabilities up to 2000 °C in vacuum. Even after repeated exposures at higher temperatures, a significant degradation of the SiSiC scaffold was not observed.

The mechanical properties of porous ceramics are greatly influenced by their microstructure. Therefore, mechanical behavior of highly porous ceramics is different from that of dense ceramics. In this work, we evaluate different mechanical testing methods such as static compression, Brazilian disc test and 3-point bending on their suitability for comparison of highly porous ceramic materials. It is shown that 3-point bending is more suitable than static compression or Brazilian disc testing, as the material exhibits no critical crack propagation under compressive loading. With 3-point bending tests, a quantitative comparison of the mechanical properties of foams with different microstructures and porosities is possible. Under cyclic compression the foams exhibit a very high degree of crack tolerance in combination with preservation of their structural integrity even at high strains of 10%.

The crushing strength or compression strength is a fundamental mechanical property for reticulated ceramic foams. There are essential influencing variables such as the rate of the applied load, the size of the applied load area, the sample size, and the strut homogeneity of the samples. In this work, the impact of the variation of the testing parameters on the crushing strength measurement was evaluated with the help of industrially produced ceramic foams made of Al2O3, ZrO2, SiC, and fused silica. The results indicate that the rate of the applied load has no significant influence on the crushing strength of the ceramic foams. Whereas the size of the applied load area and the sample size have an evident influence. The experimental results were compared with the minimum principal stress distribution calculated with FEM.

Atomic force microscopy (AFM) has proven useful in the investigation of porous surfaces due to its nanoscale spatial resolution, micron scale range, compatibility with nonconducting materials, and even applicability ability to biological systems since it can operate in fluids. Since AFM directly measures the surface by contact, it is particularly suited for quantifying the roughness, and more appropriately for porous and particulate materials, the surface area. In this work, a multi-scale porous material, human molar dentin, was studied with AC mode AFM (both in-air and in-liquid), enabling extensive analyses both for plain dentin as well as specimens exposed to nanoparticle TiO2 containing toothpaste to approximate personal dental hygiene. Finally, high speed AFM is also demonstrated in vitro with equivalent results, except that the time required per image is reduced by several orders of magnitude from tens of minutes to as little as 6 s. Careful implementation of AFM, both at standard and high speeds, is therefore effective for investigating highly porous materials, including biological tissue, in environmentally or physiologically relevant conditions.

During the advance of the nuclear fission reaction, fission products accumulate and form pores (gas bubbles) that decrease the thermal conductivity of the nuclear fuel, potentially leading to overheating of the fuel element. To investigate this important phenomenon, a finite-element method is used to simulate the effect of 3-dimensional (3D) distributions of pores on the thermal transport in a nuclear fuel element consisting of uranium oxide (UO2) nuclear fuel pellet and Zircaloy cladding. Spherical pores ranging in size from 70 to 172 µm are introduced to create up to 30 vol% total porosity. The simulations demonstrate that the centerline temperature increases with the total porosity and the increase is nonlinear. The results also show that the centerline temperature, at fixed total porosity, weakly depends on the pore size distribution. This method can provide useful information regarding the effect of high porosity levels that may occur in off-normal operation conditions.

A physical model is developed for the enhancement of the Seebeck coefficient (S) in a porous thermoelectric material with inhomogeneous porosity. The pores are assumed to be hole and of spherical shape. We take into account the presence of trap centers situated at pore/medium interfaces and neglect changes in the carrier effective mass due to the band-bend. We show that the porosity always leads to an increase in the absolute value of S. A simple relation is derived for S in nondegenerate n-type semiconducting materials in the case when the main contribution in the carrier relaxation time at zero porosity is from the scattering on acoustic phonons. We have shown that the value of S does not depend on the orientation of the porosity gradient with respect to the direction of the temperature gradient. The relative growth of the Seebeck coefficient compared to its value in the bulk material of the same volume is examinated for different number of the pore groups with different characteristic sizes at various pore size distributions.

In the present study, aminofunctionalized mesoporous silica (AFMS) was synthesized using the anionic surfactant N-lauroylsarcosine sodium as template and 3-aminopropyltrimethoxysilane as costructure directing agent. The synthesized mesoporous silica was characterized by the Fourier transform infrared spectra, x-ray diffraction, N2 adsorption-desorption, scanning electron microscopy, and transmission electron microscopy techniques. The application for the removal of Ni2+ from aqueous solution using the synthesized mesoporous silica as adsorbent was investigated. It was found that the solution pH affected adsorption of Ni2+ greatly. The kinetic data of adsorption showed that the removal rate of Ni2+ was substantially high. The adsorption isotherms were fitted using the Sips, Langmuir, and Freundlich models, respectively, and the results showed that the Sips model was the best one to describe the experimental data. From the data of Sips, the maximum adsorption capacity of Ni2+ in respect of the extracted sample is 2.48 mmol/g, much higher than those reported in other literature. The possible adsorption mechanism of Ni2+ on the AFMS was proposed.

Adsorption of Escherichia coli (E. coli) cells on red mud (RM) is important in the interactions between RM and bacteria. The objective of this work is to study adsorption of E. coli onto RM and to determine its influence in relation to the surface properties of RM. The effects of different calcination temperatures on the surface properties of red mud were investigated by thermogravimetric analysis, x-ray diffraction, scanning electron microscopy, Brunauer, Emmett, Teller (surface measurement)/N2 adsorption method, and zeta potential analysis. A higher adsorption capacity was observed from RM calcinated at 700 °C (RM700) due to larger pores formed on the surface of RM. The correlation between the adsorption efficacy and surface properties of RM is discussed and the extended Derjaguin-Landau-Verwey-Overbeek theory suggests that when the adsorption reaches equilibrium, the increased adsorption of E. coli onto RM is due to the smaller energy barrier between E. coli and RM700 as compared with that between E. coli and raw RM (RM0).

Porous thermoplastic polyurethane (TPU) membranes were produced by the electrospinning process. Two different TPUs and their blends were used to investigate the effects of material composition, solution concentration, and rheological properties on the microstructure, fiber diameter, and fiber diameter distribution of the electrospun membranes. The ratios of hard and soft segments in the solutions were adjusted by varying the blend ratios of TPUs dissolved in N, N-dimethylformamide. The solutions with higher TPU concentrations and more hard segments exhibited a higher viscosity, larger storage and loss moduli, and greater electrospun jet stability. Solutions with concentrations around the critical chain entanglement concentration (Ce) produced bead or beaded fiber structures, while bead-free fibers of a uniform diameter were obtained when the concentration increased to about two times that of Ce. Relationships between the electrospun fiber diameter, the Berry number, and the normalized concentration of the solutions were studied as well.

Nano-cellular foams were successfully produced from blends of styrenic and acrylic polymers by a two-step batch foaming process using carbon dioxide as the blowing agent. Addition of poly(ethyl methacrylate) or poly(methyl methacrylate-co-ethyl acrylate) to styrene-acrylonitrile copolymers, even at a low level, resulted in very homogeneous foams with smaller cell size and narrower cell size distribution than with the individual polymers. The best nanofoams produced from miscible blends have average cell sizes below 100 nm, cell densities up to 5 × 1015 cm−3 and medium-to-low relative densities (void fraction between 60 and 70%). Contrary to previous studies, it was found that blends with lower CO2 solubility gave higher cell density nanofoams. This suggests new mechanisms for the nucleation of foams from these blends at the nanoscale.

In this paper, a process to introduce nanoscale cells in homogeneous polyetherimide (PEI) is presented. The nanofoams produced have a bulk porosity (void fraction) in the range of 25–64%, with the average cell sizes in the range of 40–100 nm. Uniform nucleation of cells throughout the volume of the PEI specimen was observed. Supercritical CO2 at 20 MPa was used as the blowing agent and the specimens were foamed in a hot press to ensure flatness for further processing and characterization. Sorption studies showed that at 20 MPa, PEI can absorb about 10% CO2 by weight and that a 1-mm thick specimen can reach an equilibrium concentration in approximately 100 h at 45 °C. The effects of desorption time, foaming temperature, clamping pressure, and foaming time were investigated. Several nanoscale morphologies were observed through changes in the foaming temperature, which ranged from 165 to 210 °C. In one experiment, it was found that when the clamping force is increased from 1 to 10 tons, the average cell size increased from 40 to 4000 nm or by a factor of 100. This points to the clamping force as an important process variable to control the nanostructure introduced in PEI. Optimal processing conditions for the production of defect-free nanofoams are presented.

Microcellular foams, with cells of the order 10 μm, have been studied for over two decades. But little research has been done to study the effect of molecular weight on solid-state microcellular foaming. In this study, polyethylene terephthalate (PET) with a range of intrinsic viscosity (IV) 0.68–0.81 dL/g was used to investigate the effect of molecular weight on microcellular foaming process and resulting foam microstructures and properties. In the saturation step, IV showed negligible effect on sorption and desorption of CO2 in PET for all the conditions explored. In the foaming step, we found relative density increased with increasing IV. Also, as IV increased, cell size decreased and cell nucleation density increased. We hypothesize that lower chain mobility in higher IV samples led to more localized cell nucleation, resulting in a higher nucleation density, and also more constraints for cell growth, resulting in a smaller cell size. In addition, higher IV foams were found to have smaller skin thicknesses.