Open Porous Materials Research Articles

Succinic Acid Removal and Recovery from Aqueous Solution Using Hydrotalcite Granules: Experiments and Modeling

Hydrotalcites (layered double hydroxides) are an alternative for anion removal due to their adsorption and ion exchange properties, e.g., in biotechnology. The applicability of powdered hydrotalcite in columns under dynamic conditions is impossible due to the small particle size and the low specific density. Therefore, the material was granulated for application as inorganic adsorbent in commercially available chromatographic columns. The calcination of a granulated hydrotalcite/betonite water mixture led to an open-porous material with a specific surface area of 153 m2/g. The average adsorption capacity of the hydrotalcite granules for succinic acid in column experiments was estimated at 0.4 mol/kg over 12 succeeding ad- and desorption cycles (pH 6.5). Up to 98% of the bound succinic acid could be recovered. The granules were characterized concerning their pore structure and adsorption equilibrium. The obtained results were included in a mathematical model simulating adequately the breakthrough behavior ...

Development of New Ni-Al Porous Alloys for Metal-Supported Solid Oxide Fuel Cells

The technique of synthesis of Ni+16mass%Al open cell type porous intermetallic materials that can be treated in inert or regenerative atmospheres at temperature up to 1600 K without changing their functional properties has been developed. Materials with Ni3Al + NiAl phase composition, porosity of 42 %, sizes of transport pores up to 10 μm, sizes of core elements equal to 40 μm, and specific surface of open porosity of 90 mm-1 have been produced. It is demonstrated that after complete oxidation of the given materials, the NiO-NiAl2O4 composite is formed, whose reduction in hydrogen flux results in the formation of Ni-NiAl2O4 cermet; the shape of the porous material in the course of oxidation/reduction does not change.

Anion and solvent responsive copolymeric gels – Morphology, annealing, and surfactant stimuli

The phase diagram of the pseudo-ternary aqueous 1-propanol (50:50 H2O:1-propanol by weight), ionic liquid acrylate, 1-(11-acryloyloxyundecyl)-3-methyl imidazolium tetrafluorborate (ILBF4), and methyl methacrylate (MMA) system is mapped for weight fractions of ILBF4 less than 0.75 at 25 °C and at 60 °C. The mapped region is composed of a very large single-phase microemulsion domain and an appreciable multi-phase (emulsion) domain. This emulsion domain shrinks in size with increasing temperature, in contrast to the homologous bromide system (ILBr) with an emulsion domain that is insensitive to temperature. Microemulsion polymerization of the 0.70/0.15/0.15 composition in this solvent/ILBF4/MMA system produces a solvogel that is further examined for its solvent and anion stimuli responsiveness. Aqueous-DMSO solvent exchange of the PF6− exchanged materials shows nearly reversible, but dissipative behavior on a macro-scale. Transformation of transparent gel to open cell porous material by anion exchange with PF6− is found to exhibit a (third) long time-scale behavior, wherein anion exchange is limited by ionic diffusion through condensed polymeric chains. The accompanying spinodal decomposition is also demonstrated to be driven by an amphiphilic anion, bis(2-ethylhexyl)sulfosuccinate, with interesting material effects to produce more pliable porous material than obtained by exchange with PF6−. Thermal and solvent annealing treatments show that these porous materials can be activated to lower their internal specific surface area, while retaining free volume available for stimuli-induced poration.

Technical Notes: Evaluation of Two Alternative Procedures for Measuring Airflow Resistance of Sound Absorbing Materials

Abstract It is well known that sound absorption and sound transmission properties of open porous materials are highly dependent on their airflow resistance values. Low values of airflow resistance indicate little resistance for air streaming through the porous material and high values are a sign that most of the pores inside the material are closed. The laboratory procedures for measuring airflow resistance have been stan- dardized by several organizations, including ISO and ASTM for both alternate flow and continuous flow. However, practical implementation of these standardized methods could be both complex and expensive. In this work, two indirect alternative measurement procedures were compared against the alternate flow standardized technique. The techniques were tested using three families of eco-friendly sound absorbent materials: recycled polyurethane foams, coconut natural fibres, and recycled polyester fibres. It is found that the values of airflow resistance measured using both alternative methods are very similar. There is also a good correlation between the values obtained through alternative and standardized methods.

A phenomenological elastoplastic model for porous metal fiber sintered sheets

Metal fiber sintered sheets (MFSSs) are a type of layered open cell porous materials and are transversely isotropic. Their stress–strain responses to uniaxial tension and compression and simple shear loading in different directions (i.e., in the in-plane and transverse directions) were measured. A set of characteristic stress and strain was defined and employed to formulate an elastoplastic constitutive model for the infinitesimal deformation of MFSSs subject to monotonic proportional loading. The elastoplastic potential in the constitutive model was calibrated with the measured stress–strain responses in terms of the defined characteristic stress and strain, without a need to know the yield surface and its evolution a priori. A successful application of the developed model to the multiaxial mechanical responses of MFSSs was demonstrated.

Vibroacoustic response sensitivity due to relative alignment of two anisotropic poro-elastic layers

The effects of relative alignment of two different types of anisotropic open cell porous materials are investigated in terms of the acoustic response of a multi-layered configuration. Numerical experiments, where gradient based optimization techniques were used, are conducted to find possible extremal values. It is shown that, depending on the degree of anisotropy of the porous material properties, their angular orientations have a significant and frequency dependent influence on the measured response. The results highlight the importance of further advancing the knowledge of anisotropic porous material behavior.

Synergistic Effect of Copolymer Particle and Surfactant on the Morphology of Macroporous Materials Based on High Internal Phase Emulsion

The open porous materials (PolyHIPEs) based on high internal phase emulsions (HIPEs) stabilized by copolymer particles had been prepared through adding small quantity (about 0.5 wt% relative to the external phase) of cationic surfactant, cetyltrimethylammonium bromide (CTAB), into the oil (external) phase. The effect of copolymer particle concentration, surfactant concentration and CTAB position in HIPEs on the morphologies of PolyHIPEs was investigated. All these factors could tune the internal structures of the Poly- HIPEs and some of them generated pore throats on the pore wall. Obvious synergistic interaction between the negative-charged particles and cationic surfactant CTAB in HIPE was displayed: CTAB could not only adsorb on the oil-water interface competitively with the copolymer particles but also cross the interface to absorb on the particle surface, which changed the particle hydrophilicity. The further investigation on the stability of HIPE proved that the HIPEs with CTAB in the oil phase were more prone to form open porous materials after polymerizing the monomer in the external phase. Keywords: Cetyltrimethylammonium bromide, High internal phase emulsions, PolyHIPE, Particle stabilized emulsion, chromatographic aluminum oxide, copolymerization, dihalide anion radical, stationary trans-cis isomer ratio.

Ring opening metathesispolymerisation of emulsion templated dicyclopentadiene giving open porous materials with excellent mechanical properties

Surfactant stabilized emulsions of dicyclopentadiene and 50%, 60%, 70% or 80% of water were cured using ring opening metathesis polymerisation. All formulations gave open porous architectures featuring excellent mechanical properties which change upon oxidation.

Development of a stable open-porous structure in the solvent-crazed high-density polyethylene

It is demonstrated that the tensile drawing of high-density polyethylene (HDPE) films in the presence of physically active media via the mechanism of delocalized crazing results in the development of an open-porous structure in the polymer. Depending on tensile strain, overall volume porosity can reach ∼55%. Here, the parameters of the porous structure (pore and fibril diameters) are in the nanometer range. It is also demonstrated that the nanoporous structure with a highly developed surface formed via delocalized crazing is thermodynamically unstable and the related relaxation processes result in the reduction or complete elimination of porosity. Efficient ways of stabilization and preservation of open porosity and parameters of the porous structure of deformed samples of polyethylene are related to complete removal of the liquid medium from the polymer samples and annealing. This approach makes it possible to obtain open-porous materials based on polyolefins with stable characteristics, which is of a significant practical interest.

Theoretical analysis of moisture transport in wood as an open porous hygroscopic material

Abstract Moisture transport in an open porous hygroscopic material such as wood is a complex system of coupled processes. For seasoned wood in natural climate three fully coupled processes active in the moisture transport are readily identified: (1) diffusion of vapor in pores; (2) phase change from one state to another, also called moisture sorption; and (3) diffusion of bound water in wood tissue (in the cell wall). A mathematical model for predicting moisture transport in wood for a given condition must at least consider the dominating active processes simultaneously to be considered accurate. In this study, a theoretical investigation is conducted on the influence of the model parameters on the model response to a known step change of ambient vapor pressure. The objective is twofold. First, to investigate if model simplification can be conducted in a transparent and stringent manner, not compromising required model accuracy and precision. Second, to show model characteristics that could enable tailored experimental studies to verify or discard variations of this type of transport model. The model sensitivity analyses clearly showed that there are large differences on the degree of influence of the three processes on the outcome of the coupled model. Least significant is the bound water diffusion. Based on the results from the sensitivity analyses, a simplified model for moisture transport in wood is proposed.

Drying of aerogel-bonded sands

The drying of foundry sands bonded by polymeric aerogels is of essential importance for their industrial application and of general interest in the context of drying theories for porous media, since in these new materials the interstices between the sand grains are partially filled with an open porous nanostructured material, the aerogel. We describe measurements on the drying of various foundry sands with different amounts of aerogelic binder made from resorcinol and formaldehyde in which we also varied the drying temperature. The results suggest that the nanostructured aerogel dictates completely the drying behaviour. Sand type and sand grain size are of minor relevance. A simple qualitative picture is developed describing the observations.

Gas Pressure Dependence of the Heat Transport in Porous Solids with Pores Smaller than 10 μm

To elucidate the gaseous heat transfer in open porous materials with pore sizes below 10 μm, an experimental setup for hot-wire measurements at high gas pressures was designed and tested. The samples investigated were organic, resorcinol–formaldehyde-based aerogels with average pore sizes of about 600 nm and 7μm. The range in gas pressure covered was 10 Pa to 10 MPa. To avoid effects due to mass transport along the inner surface of the porous backbone of the samples, He and Ar, i.e., gases with very low interaction with the sample surface at ambient temperature, were chosen. The study reveals a significant contribution of coupling effects to the thermal transport in nanoporous media. A model has been developed that qualitatively describes the observed gas pressure dependence of the heat transport.

Variation of the mechanical properties of PMMA to suit osteoporotic cancellous bone

Poly(methyl methacrylate) (PMMA) is by far the most frequently used bone substitute material for vertebroplasty. However, there are serious complications, such as cement leakage and an increased fracture rate of the adjacent vertebral bodies. The latter may be related to the mechanical properties of the augmented segment within the osteoporotic spine. A possible counter-measure is prophylactic augmentation at additional levels, but this aggravates the risk for the patient. Introduction of pores is a possible method to reduce the inherent high stiffness of PMMA. This study investigates the effect of porosity on the mechanical properties of PMMA bone cement. Different fractions of a highly viscous liquid were mixed into the PMMA during preparation. An open-porous material with adjustable mechanical properties resulted after removal of the aqueous phase. Different radiopacifiers were admixed to investigate their suitability for vertebroplasty. The final material was characterized mechanically by compressive testing, microscopically and radiologically. In addition, the monomer release subsequent to hardening was measured by means of gas chromatography. The Young's modulus in compression could be varied between 2800 ± 70 MPa and 120 ± 150 MPa, and the compression ultimate strength between 170 ± 5 MPa and 8 ± 9 MPa for aqueous fractions ranging between 0 and 50% of volume. Only a slight decrease of the Young's modulus and small changes of ultimate strength were found when the mixing time was increased. An organic hydrophilic and lipophilic radiopacifier led to a higher Young's modulus of the porous material; however, the ultimate strength was not significantly affected by adding different radiopacifiers to the porous cement. The radiopacity was lost after washing the aqueous phase out of the pores. No separation occurred between the aqueous and the PMMA phase during injection into an open porous ceramic material. The monomer released was found to increase for increasing aqueous fractions, but remained comparable in magnitude to standard PMMA. This study demonstrates that a conventional PMMA can be modified to obtain a range of mechanical properties, including those of osteoporotic bone.

熱間等方加圧（ＨＩＰ）法による開気孔質多孔体の作製とその焼結メカニズム

Open-pore porous materials can be produced by the capsule-free Hot Isostatic Pressing (HIPing) process. In this paper, sintering mechanisms, features and applications of capsule-free HIPed open-porous materials are discussed. During sintering powder compacts by capsule-free HIPing process, high pressure gas penetrates inside of the green bodies, and forms pores. There are two mechanisms to explain this phenomenon. Surface-diffusion is enhanced during capsule-free HIPing, because high frequency gas-collision with pore surfaces, forms grown necks between raw powder particles, and enhances pore formation. Another possible mechanism is the matter of spatial compatibility of gas atoms and sintered material. For the shrinkage of pores, i. e., for the densification of the green bodies, the high pressure gas, or the high density gas must be removed from inside of pores. The higher density requires the higher energy to remove high density gas. At the end of the sintering process, the gas must be removed from pores to ambient pressure to make those pores to be open pores. The above mentioned sintering mechanisms provide higher open porosity, more grown necks, smoother pore surfaces and narrower pore size distribution in capsule-free HIPed materials compared with those in conventionally sintered porous materials. As a consequence, high Young's modulus, high fracture strength, high fluid permeability are obtained by the capsule-free HIP process. The porous materials fabricated by the capsule-free HIPing can be applied for filters, grinding wheels, electrochemical electrodes and others with better performance than conventional products.

Development of Modelling Methods for Materials to be Used as Bone Substitutes

The demand in the medical industry for load bearing materials is ever increasing. The techniques currently used for the manufacture of such materials are not optimized in terms of porosity and mechanical strength. This study adopts a microstructural shape design approach to the production of open porous materials, which utilizes spatial periodicity as a simple way to generate the models. A set of triply periodic surfaces expressed via trigonometric functions in the implicit form are presented. A geometric description of the topology of the microstructure is necessary when macroscopic properties such as mechanical strength, stiffness and isotropy are required to be optimised for a given value of volume fraction. A distinction between the families of structures produced is made on the basis of topology. The models generated have been used successfully to manufacture both a range of structures with different volume fractions of pores and samples of functional gradient material using rapid prototyping.

Positronium annihilation data and actual free-volume distribution in polymers

Determination of the size distribution of free-volume holes in solids, in particular, polymers, is an important physicochemical problem. The positron annihilation technique has been proposed for this purpose. The central point in this technique is the quantitative interpretation of data, especially, for substances with a high specific surface area. A developed free-volume system in open-pore membrane materials, such as poly(trimethylsilylpropyne) PTMSP and the spirocyclically bound benzodioxane polymer PIM-1, and polymeric sorbents (hypercrosslinked polystyrenes) makes it possible for the first time to compare the sorption characteristics and positron annihilation data on the character of size distribution of nanopores in these polymers. In combination with the results of mathematical simulation of the structure and radiothermoluminescence measurements, the array of data indicate the structural inhomogeneity of the test amorphous materials. It was shown that this inhomogeneity in relation to the positron annihilation technique is expressed in the insufficiency of the representation of the orthopositronium decay curve by one component that takes into account the Gaussian lifetime distribution (symmetrical pore size distribution) and in the necessity of use of several decay components. The feasibility of revealing a nonrandom character of pore size distribution gives the positron annihilation technique an advantage over other approaches (inverse gas chromatography, 129Xe NMR) to investigation of nanopores in polymers.

Thermoelectric ceramics for generators

The manufacturing of thermoelectric modules from conventional materials is well established and widely commercially available. However, fabrication of modules based on oxide materials has been recently emerging and there exist very few reports on their performance. The oxide nature of the thermoelectric elements and the processing specifications involving very high temperatures make the fabrication a difficult task and different from that of conventional thermoelectric modules. In this work we describe (i) the fabrication of thermoelectric modules based on oxide bulk and foam materials of Ca 3Co 4O 9 and Ca 0.95Sm 0.05MnO 3 and (ii) the metal to ceramic contact preparation. The open porous foam structures of thermoelectric materials make it possible to design efficient thermoelectric modules for waste heat sources involving gaseous and liquid media. The possibility of direct large area physical contact of thermoelectric foam elements with hot media will make them efficient electric power generators. The open porous thermoelectric materials with introduced porosities can be good candidates to confine phonons (lattice vibrations) in order to reduce the thermal conductivity if the pores can be made sufficiently small. The performances of the modules were evaluated and possible factors limiting their theoretical performance are discussed. A parameter representing the quality of the modules termed the manufacturing factor (MF) representing the cumulative effect of various factors involved in the fabrication process is introduced and evaluated for the modules and compared to other reported modules.

Development of Ceramic Thermoelectric Oxides for Generator

In this work we describe (i) the fabrication of thermoelectric modules based on oxide bulk and foam materials of Ca3Co4O9 and Ca0.95Sm0.05MnO3(ii) and the metal to ceramic contacts preparation. The open porous foam structures of thermoelectric materials can result in designing efficient thermoelectric modules for waste heat sources involving gaseous and liquid media. The possibility of direct large area physical contact of thermoelectric foam elements with hot media will make them efficient electric power generators. The open porous thermoelectric materials with holes can be a good candidate to confine phonons (lattice vibrations) in order to reduce the thermal conductivity if the pores can be made sufficiently small. The performances of the modules were evaluated and possible factors limiting their theoretical performance are discussed. A parameter representing the quality of the modules termed as manufacturing factor (MF) representing the cumulative effect of various factors involved in the fabrication process is introduced and evaluated for the modules and compared to the reported modules.

Synthesis of open porous emulsion-templated monoliths using cetyltrimethylammonium bromide

In recent years, open porous materials (polyHIPEs) have attracted more and more attention because of their specific properties and applications in biological tissue scaffolds, catalysis supports and ion-exchange resin. However, the surfactants used in this type material were limited to nonionic surfactants or the mix of nonionic surfactant and ionic surfactant. In this work, firstly well-defined polyHIPEs were synthesized by W/O emulsions with ionic surfactant alone (e.g., CTAB). Furthermore, the polyHIPEs with much higher pore volume (14.7 cm 3 g −1), uniform pore diameter and cell size were obtained by this method. Both the median pore diameter and average cell size of the polyHIPEs rose with increase of DVB concentration and/or water fraction.

Relationship between pore size and the gas pressure dependence of the gaseous thermal conductivity

In porous materials, such as foams or pressed powder boards, the thermal conductivity via the gas phase represents at ambient temperatures a significant or even dominant contribution to the total thermal conductivity. The variation of the thermal conductivity of an open porous material with gas pressure is a function of the pore size. In the pressure range below 1 bar, measurement of thermal conductivity offers a non-destructive probe of pore sizes larger than 100 nm. If the thermal conductivity setup also allows for measurements at higher pressures, the pore size range can be extended to even smaller values. Experimental data for a variety of different porous materials such as open porous foams, granular porous and nonporous materials and aerogels, porous solids with an adjustable mean pore size in the meso- or macro-pore range, are presented. The pore characteristics determined from thermal conductivity measurements are compared to morphological data derived from nitrogen sorption and small angle X-ray scattering data. The potential and limits of this method in terms of the extraction of an average pore size and a pore size distribution are discussed.