Volume Fraction Of Macropores Research Articles

Research on the mechanical properties and microstructure of fly ash-based geopolymers modified by molybdenum tailings

The environmental and economic problems caused by the accumulation of molybdenum tailings (MT) have become increasingly prominent. Therefore, a cost-effective method is urgently needed to realize the resource utilization of MT. In this paper, the mechanism of action of MT on fly ash-based geopolymers were systematically researched. The effects of MT on the macro-properties of fly ash-based geopolymers were researched in terms of fluidity, setting time, drying shrinkage and mechanical strength. The reaction mechanism of fly ash-based geopolymers modified by MT were analyzed from the perspective of microstructure and micromorphology by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric (TG) and nitrogen adsorption/desorption (NAD) methods. The results show that the addition of MT could effectively improve the fluidity of fly ash-based geopolymer paste, appropriately delay its setting time and increase its drying shrinkage; When the content of MT was 20%, the bending strength of fly ash-based geopolymers were significantly improved, and the flexural strength at 3, 7 and 28 days were increased by 79.2%, 47.4% and 19% respectively. The SEM, FTIR and TG results confirmed that the main product was glassy sodium calcium aluminum silicate hydrate (N(C)-A-S-H) gel, which was used as a binder to connect residual raw material particles and form hardened geopolymer materials. The XRD results show that the addition of MT would not lead to the formation of new crystal phases in the fly ash-based geopolymers, and when the addition of MT was 20%, the diffraction peak intensity of the crystal phase structure of the fly ash-based geopolymers basically were not changed obviously. The NAD results show that the addition of 20% MT could significantly improve the pore structure of fly ash-based polymers, increased the volume fraction of micropores, and reduced the volume fraction of macropores. The SEM/EDS results show that the MT could be dissolved in alkali activator to form nanorods to fill the pore structure of fly ash-based geopolymers, thus reducing the cracks and defects of fly ash-based geopolymers and improving the compactness of the microstructure.

Ion corrosion behavior of tunnel lining concrete in complex underground salt environment

In this study, the ion corrosion behavior of tunnel lining concrete in complex underground salt corrosion environment was investigated using a self-designed corrosion simulation test device in a complex underground environment. The results indicated the following: the corrosion of flowing water leads to the dissolution of lining concrete, and the load promotes the development of cracks in the tensile area of lining concrete and inhibits the development of defects in the compression area, resulting in the transmission speed of chloride and sulfate ions in lining concrete under different corrosion conditions given as follows: concrete in tensile zone under flowing corrosive solution and load > flowing corrosion solution acting alone > static corrosion solution > concrete in compression zone under flowing corrosive solution and load. When the flowing corrosion solution alone and flowing corrosion solution and load act on the concrete in the tensile zone, the pore volume fraction of gel decreases and the macropore volume fraction increases. Under the combined action of static corrosion solution and flowing groundwater and load, the pore volume fraction of gel in the pressurized area increases and the harmless pore volume fraction decreases.

Anisotropy of soil water diffusivity of hillslope soil under spruce forest derived by X-ray CT and lab experiments

The idea of the study is to indicate direction-dependent differences in hydraulic conductivity, K(Se), and soil water diffusivity, D(θ), as function of the volume fraction related to the fractional capillary potential for each of the characteristic pore size classes by extended anisotropy factors. The study is exemplary focused on a BwC horizon of a Dystric Cambisol under spruce forest formed on the weathered and fractured granite bedrock in the mountainous hillslopes Uhlirska catchment (Czech Republic). Thus, undisturbed soil samples were taken in vertical (0°, y = x-axis) and horizontal (90°, z-axis) direction. The D(θ) values and especially the D(θ)-weighted anisotropy ratios showed that anisotropy increases with the volume fraction of macropores, MaP (d > 0.03 mm), with r2 between 0.89 and 0.92. The X-ray computer tomography (CT) based anisotropy ratio (ACT) is larger for the horizontal sampled soil core with 0.31 than for the vertical with 0.09. This underlines the existence of a predominantly horizontally oriented pore network and the fact that weathered bedrock strata can initiate lateral preferential flow. The study results suggest that combining the hydraulic conductivity as intensity and the capacity parameter by means of diffusivity results in an extended anisotropy ratio which unveils the role of the soil hydraulic characteristics in generation of small-scale lateral preferential flow. In future, the small-scale direction-dependent differences in the soil hydraulic capacity and intensity parameter will be used for model-based upscaling for better understanding of preferential flow at the catchment scale.

Microstructure and mechanical behaviors of engineered cementitious composites with high-volume fly ash

To study the effects of fly ash, polyvinyl alcohol (PVA) fibers and curing schemes on the microstructure and mechanical behaviors of Engineered Cementitious Composites (ECC) with high-volume fly ash, two kinds of fly ash and two PVA fibers were used in ECC. Besides, two curing schemes were adopted. The microstructure and mechanical properties of ECC were investigated by mercury intrusion porosimetry (MIP), scanning electron microscope (SEM), uniaxial compression test and three-point bending test. The results show that curing schemes and adding PVA fibers have a great influence on the differential curves of the pore size distribution of ECC and matrix in the range of 0–100 nm. There is a positive relationship between the deflection capacity or ultimate tensile strain of ECC and its macro pore volume fraction. Number of cracks increases with increasing the capillary pore volume fraction. On the contrary, the deflection capacity, ultimate tensile strain and number of cracks decrease when the transitional pore volume percent in ECC increases.

Microstructure and transport properties of cement-based material enhanced by graphene oxide

The microstructure and transport properties of mortars made with graphene oxide (GO) and cement and with similar consistency were experimentally investigated and compared with those of control mortars made using Portland cement. Polycarboxylate superplasticiser was used to improve the consistency of GO-modified mortars and the dispersibility of GO nanosheets. Compared with the control samples, the GO-modified mortars with similar consistency showed a 33·2% reduction in the chloride migration coefficient and a 61·6% reduction in the initial rate of water absorption. These improvements are due to the addition of GO particles in the mortars, which inhibit crack growth, change the morphology of hydrated crystals and refine the pore structure. Very small amounts of GO additives were found to significantly decrease the macropore volume fraction and the critical and average pore diameters. In an attempt to understand the correlation between the pore size distribution and the macroscopic transport performance, both the critical pore diameter and the macropore volume fraction were found to be exponentially dependent on the chloride migration coefficient. The average pore diameter was found to be linearly related to the initial absorption rate of the mortars, but was independent of the secondary absorption rate.

Anisotropy of unsaturated hydraulic properties of compacted mineral capping systems seven years after construction

The mechanical compaction of soil material of mineral landfill systems affects the continuity and connectivity of the complex soil pore network. A horizontally-oriented layering is intended to generate a slope-induced lateral water flow out of mineral capping systems that is sufficient to minimise the statutory required vertical percolation through the underlying waste body and the potential leachate.In this case, soil compaction affects both the porosity and water retention as capacity values and the hydraulic conductivity as intensity parameter. The idea of this study was to combine information on both soil properties in an extended anisotropy factor based on the soil water diffusivity. The analysis is focused on the direction-dependent soil hydraulic properties of a mechanically compacted landfill capping system.In particular, the volume fractions were related to the fractional capillary potential for each of the characteristic pore size classes. Three different soil profiles of top, middle, and bottom slopes of the mineral capping system of the Rastorf landfill in Northern Germany were sampled seven years after construction. Undisturbed soil cores of 100 cm3 and 438 cm3 were extracted in vertical (ver) and horizontal directions (hor) in depths of 20, 50, and 80 cm representing the main layers. The soil water retention and unsaturated hydraulic conductivity, K, functions were determined by suctions plates, permeameter, and the evaporation method. In the coarse pores range (pressure head values of h ≥ −300 hPa), the standard anisotropy ratio, AR, (K(Se)hor/K(Se)ver) as a function of effective saturation, Se, in the sealing liner in 80 cm depth was larger than 1, indicating higher horizontal than vertical K(Se) values. Thus, AR-values above 1 in the range close to water saturation especially in 80 cm depth suggest the tendency of lateral water flow out of mineral capping system due to a sufficient hydraulic potential and thus its reasonable functionality, even seven years after construction.The anisotropy factor was extended in two steps; for AR* and AR**, the pore size class-related matric flux potential, ϕ, and the soil water diffusivity, D(θ), were proposed to combine intensity parameters with capacity-based volume fractions of pore size classes and the fractional capillary potential. The ϕ- and D(θ)-weighted anisotropy ratios, AR* and AR**, indicate that anisotropy increases with the volume fraction of macropores (r2AR* of 0.69−0.77; r2AR** of 0.71−0.80) and wide coarse pores (r2AR* of 0.57−0.78; r2AR** of 0.79−0.89) in both directions. The results suggest that by combining both the intensity and the capacity parameters of the soil hydraulic properties in an extended anisotropy ratio improves the information on compacted mineral capping systems.

Modelling of anion-exchange membrane transport properties with taking into account the change in exchange capacity and swelling when varying bathing solution concentration and pH

In this paper we take into account the variation of anion-exchange membrane swelling and effective exchange capacity with changing the concentration and/or pH of the bathing solution when simulating membrane transport characteristics (the electric conductivity, diffusion permeability and ion transport numbers). Two main structural elements of the membrane are distinguished: a microporous polyelectrolyte gel assumed homogeneous, and macropores including structural defects and voids. It is supposed that only microporous gel exerts osmotic pressure, which causes membrane swelling described in our model by the Gregor equation, which employs the mole fractions of free and bound water. Three types of ion-exchange functional groups, namely, the secondary, tertiary and quaternary amino groups are taken into account. The degree of dissociation of these groups depends on the internal solution pH, which is described by equilibriums between protonated and deprotonated forms. The Donnan equations and electroneutrality condition are used to calculate the ion concentration in the membrane. The microheterogeneous model based on the Nernst-Planck equations is used to describe the ion transport. We take into account that the ion diffusion coefficients depend on the degree of gel swelling, this dependence is described by the Mackie-Meares equation. The model parameters include the equivalent volume of dry polyelectrolyte gel, the volume fraction of macropores, the structural parameters and others.The results of calculations are compared with experimental data on the electric conductivity, diffusion permeability and ion transport numbers for two heterogeneous anion-exchange membranes MA-40 and MA-41 (Shchekinoazot, Russia) differed by the fractions of the weakly basic functional groups. A good quantitative agreement between the theory and experiment is found for both membranes using the same set of ion hydration numbers and chemical equilibrium constants for secondary and tertiary amino groups. In particular, it is shown that with increasing pH of the bathing solution, the membrane diffusion permeability passes through a maximum, which is explained by the corresponding maximum of water content. A higher water content results in larger membrane pores, which leads to higher values of ion diffusion coefficients and higher amount of sorbed electrolyte. Together with varying water content, the variation in membrane effective exchange capacity as a function of external solution pH, determines a non-trivial behavior of electric conductivity, diffusion permeability and ion transport numbers in the membrane equilibrated with NaCl solutions of different concentration and pH.

Interfacial modification and ultra-low concentration sol impregnation: A combined approach for tailoring the pore structure and improving the thermal insulation performance of fumed silica compact

Fumed silica compacts for buildings show outstanding thermal insulation performance. However, the completely elimination of macropores within the fumed silica compacts under the condition of optimum level of compaction is rather difficult, which has a negative impact on its thermal insulation property. Here, a novel method of interfacial modification combined with ultra-low concentration sol impregnation is proposed to tailor the pore structure and reduce the thermal conductivity of fumed silica compacts. The result shows that, compared with the general sol impregnation treatment (without interfacial modification)，the thermal conductivity of the resulting fumed silica compact after interfacial modification and ultra-low concentration sol impregnation significantly decreases from 26.6 mW/(m·K) to 22.0 mW/(m·K), as the pore diameter and the volume fraction of macropores decreases from 100 nm to 37 nm and from 64.91% to 30.32%, respectively. The decrease in the amount of silanols on the surface of the fumed silica matrix effectively inhibits the interfacial adhesion of the colloidal particles introduced by the ultra-low concentration impregnation and thus promoting the formation of new mesoporous networks of the silica aerogel, which further improving the pore structure and reducing the thermal conductivity of fumed silica compacts at the optimum level of compaction.

Using the X‐ray computed tomography method to predict the saturated hydraulic conductivity of the upper root zone in the Loess Plateau in China

Core Ideas Computed tomography (CT)‐measured properties were in the order: soil under Q. liaotungensis > P. tabuliformis > C. korshinskii > M. sativa. The parameters measured by CT could help estimate saturated hydraulic conductivity (Ksat) in the Loess Plateau. Macropore quantity has a higher R2 for predicting Ksat than the morphology of macropores. The recovery of natural vegetation significantly improves soil macroporosity through root decay and biological activity. Macropores are preferential pathways for the movement of water to deep soil. However, the quantification of soil macropore structure and its relationship with soil hydraulic conductivity (Ksat) are not well understood. We characterized the macropores under different vegetation types to evaluate the effects of macropores on Ksat. Undisturbed soil cores were collected from four treatments: areas dominated by Quercus liaotungensis Koidz.(QLI), Pinus tabuliformis Carrière (PTA), Caragana korshinskii Kom. (CKO), and Medicago sativa L.(MSA). A medical computed tomography (CT) scanner was used to acquire images with a voxel size of 0.977 by 0.977 by 1.000 mm for depths of 0 to 360 mm. We used ImageJ software to quantify the macropore properties. Soil structure and Ksat improved with the succession of vegetation. The mean macropore volume fraction across the soil cores for the QLI, PTA, CKO, and MSA treatments were 6.6, 3.5, 1.3, and 0.6% within a 4900‐mm2 area, respectively. Macropore quantity (volume fraction and number) had a higher R2 for predicting Ksat than macropore morphology (branch density, connectivity density, and junction density). Moreover, the grayscale values were negatively correlated with Ksat and accounted for 78.8% of the variation in Ksat. Grayscale values, volume fraction, and the number of macropores were the best combination of CT‐measured parameters for predicting Ksat, accounting for 81.9% of the variation in Ksat. The CT‐measured parameters could be used to estimate Ksat in the upper root zone in the Loess Plateau.

A simple model for the response of an anion-exchange membrane to variation in concentration and pH of bathing solution

Swelling is an important property of charged gels and membranes. The size of pores and, therefore, membrane properties such as conductivity, diffusion and hydraulic permeability, permselectivity depend on water content and degree of swelling. In this paper we propose a simple model for equilibrium swelling of an ion-exchange membrane, allowing calculation of water content and membrane thickness as functions of the concentration and pH of the bathing solution. The model parameters include the equivalent volume of dry polyelectrolyte gel, the volume fraction of macropores and others. Three types of ion-exchange functional groups, namely, the secondary, tertiary and quaternary amino groups in an anion-exchange membrane are taken into account. The osmotic pressure exerted by micro- and mesopores, appearing in the gel when swelling, is expressed using the Gregor equation, which employs the mole fractions of free and bound water. The equilibria between protonated and deprotonated amino groups are assumed as well as the Donnan and ion-exchange equilibria between the membrane and bathing solution. The results of calculations are compared with experimental data on the membrane thickness and effective exchange capacity obtained for two heterogeneous anion-exchange membranes MA-40 and MA-41 (Shchekinoazot) differed by the composition of functional groups. The procedure of determining membrane structural and thermodynamic parameters is described. A good quantitative agreement between the theory and experiment is found for both membranes using the same set of ion hydration numbers and chemical equilibrium constants for secondary and tertiary amino groups. In particular, it is shown that with increasing pH of the bathing solution, the membrane thickness (and, hence, water content) pass through a local maximum and a local minimum. The simplicity of the model, which does not reduce adequacy, would enable it to be included later in other models describing the transport of ions and water to account for the swelling and change in the membrane structure with a change in pH and concentration of the bathing solution.

Preparation and Characterization of Fe2O3-CaO-SiO2 Porous Glass Ceramics for Bacteria Immobilization

In this work we present a study of porous glass ceramics towards bacteria-immobilization applications for water filtration. Sol-gel synthesized glass samples were processed into Fe2O3-CaO-SiO2 porous glass ceramics by introducing a pore forming agent. The crystal phase composition, morphology, and pore structure of the ceramics were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption measurements, and mercury intrusion porosimetry. By varying the pore forming agent and process conditions, varied pore size distributions are produced. The volume fraction of macropores is overall large while the volume fraction of meso-pores and micropores is overall comparably small. All samples display good biocompatability and compressive strength, making them suitable for bacteria immobilization. The macropore sizes were determined primarily by the size of pore forming agent, enabling control. The results provide a basis for optimizing the preparation of porous glass ceramics for bacteria immobilization.DOI: http://dx.doi.org/10.5755/j01.ms.23.4.16763

The influence of thermal treatment on the microstructure and thermal insulation performance of silica aerogels

In this work, thermal treatment to the as-prepared silica aerogels was explored as a strategy to reduce the macropores in aerogels, thus to improve the thermal insulation performance. The experimental results show that the pore size exhibits a slight shift to the value lower than the pore size of no-heat-treated silica aerogels and the macropore volume fraction experiences sharp decline from 63.05 to 24.82% after thermal treatment at 800 °C. The thermal conductivity doesn't increase with the enhancement of density but decreases from 0.0090 W/(mK) for the no-heat-treated sample to 0.0080 W/(mK) for the 400 °C- treated aerogels. The reason is that the reduction of macropores results in the restriction degree of gaseous thermal transfer being enhanced in aerogels, which is proved through theoretical calculation by two models. However, the thermal conductivity dramatically climbs to 0.030 W/(mK) after 800 °C owing to the pore structures being damaged and solid heat transfer gets significantly enhanced, which is confirmed by the theoretical calculation. This study suggests that appropriate high-temperature treatment to the as-prepared aerogels could improve the thermal insulation performance and the usability of silica aerogels at room temperature.

Improvement of thermal insulation performance of silica aerogels by Al2O3 powders doping

Abstract Silica aerogel is deemed as a kind of high-performance thermal insulation materials. However, the existence of macropores in the structure is always ignored in the research and application of aerogels. Thus the thermal insulation performance of silica aerogels could be further improved if the macropores are reduced. In this work, nano-sized Al2O3 powders are explored as nano fillers to reduce the macropore volume fraction in silica aerogels by filling the big voids among the silica aggregates, and further lower the thermal conductivity. The experimental results showed that the macropore volume fraction ( V MAC ) was dramatically reduced from 63.05% to 23.12% with the addition of Al2O3 powders ranging from 0.0 g to 1.0 g. This trend was also verified by the variation of (VT*-VBET) and (VBET/VT*). Accordingly, the thermal insulation performance was improved due to the reduction of macropores in aerogels. The lowest thermal conductivity of Al2O3-doped aerogels reached 7.41 mW/(m K) in contrast with that of pure silica aerogels (9.00 mW/(m K)), which was a significant decline for aerogel-based materials due to the gaseous heat transfer being further weakened. Moreover, the increment of thermal conductivity from 7.41 to 9.71 mW/(m K) with the Al2O3 powders increasing could be attributed to the enhancement of solid heat transfer in the system. The variation of experimental thermal conductivity was in good agreement with the result of theoretical calculation. This study proposed an innovative idea to improve the thermal insulation of aerogel under ambient conditions.

Room temperature and high temperature sealing properties and compression properties of compressive gaskets made of micrometric vermiculite particles

Vermiculite gaskets obtained by pressing vermiculite powders in the range of 17.7–80MPa, were studied for their sealing (leak rate measurements) and compressive properties (compressibility and resiliency). The in plane permeability at room temperature was found to decrease strongly through increasing elaboration pressure, that reduced both the median pore radius (<30nm) and the macropore volume fraction (<45%), measured by mercury intrusion. After annealing at temperatures of up to 600°C, the out of plane permeability (measured at room temperature) was increasing from ~10−20 (at 200°C) to ~10−24 due to the increase in anisotropy related to the densification and the formation of interlayer bonds. The global leak rate was found to be determined exclusively by the contact leak rate and independent of the material's permeability. The leak rates measured at room temperature were also found to be dependent on the gasket's resiliency values. The global helium leak rate (2.5×10−2atm·cm3·s−1·m−1, for 35MPa working pressure, under 5bar helium pressure) was relied neither on the working temperature (25°C to 800°C) nor the material porosity for gaskets pressed at 200°C and 80MPa. The resiliency (~5%) and compressibility (9%) values of these gaskets were reduced, as heating the materials to 800°C due to the densification induced by both pressure and temperature, increasing their rigidity.

Triple hierarchical micro–meso–macroporous carbonaceous foams bearing highly monodisperse macroporosity

The limited coalescence phenomenon occurring in Pickering emulsions stabilized by solid particles allows preparing monolithic silica foams with nearly monodisperse macroscopic voids and also meso- and microporosities. After soaking of these foam hard templates with a phenolic resin, partially graphitized interconnected porous carbon monoliths can be obtained easily. Like the silica templates, these carbon monoliths possess a hierarchical, triple porosity. Mercury intrusion porosimetry reports a macropore volume fraction of 45–70% with a narrow pore size distribution, while their specific surface area values lie between 700 and 900m2g−1 and their mesopore specific surface area between 200 and 500m2g−1. This approach allows preparing hierarchical porous carbon whose mesoporosity does not require using any soft template to organize the resin precursor.

Design of Bi-Tortuous, Anisotropic Graphite Anodes for Fast Ion-Transport in Li-Ion Batteries

Thick Li-ion battery electrodes with high ion transport rates could enable batteries that cost less and that have higher gravimetric and volumetric energy density, because they require fewer inactive cell-components. Finding ways to increase ion transport rates in thick electrodes would be especially valuable for electrodes made with graphite platelets, which have been shown to have tortuosities in the thru-plane direction about 3 times higher than in the in-plane direction. Here, we predict that bi-tortuous electrode structures (containing electrolyte-filled macro-pores embedded in micro-porous graphite) can enhance ion transport and can achieve double the discharge capacity compared to an unstructured electrode at the same average porosity. We introduce a new two-dimensional version of porous-electrode theory with anisotropic ion transport to investigate these effects and to interpret the mechanisms by which performance enhancements arise. From this analysis we determine criteria for the design of bi-tortuous graphite anodes, including the particular volume fraction of macro-pores that maximizes discharge capacity (approximately 20 vol.%) and a threshold spacing interval (half the electrode's thickness) below which only marginal enhancement in discharge capacity is obtained. We also report the sensitivity of performance with respect to cycling rate, electrode thickness, and average porosity/electroactive-material loading.

Thermal management using the bi-disperse porous medium approach

Thermal management of distributed electronics similar to data centers is studied using a bi-disperse porous medium (BDPM) approach. The BDPM channel comprises heat generating micro-porous square blocks, separated by macro-pores. Laminar forced convection cooling fluid of Pr = 0.7 saturates both the micro- and macro-pores. Bi-dispersion effect is induced by varying the macro-pore volume fraction ϕ E , and by changing the number of porous blocks N 2, both representing re-distribution of the electronics. When 0.2 ⩽ ϕ E ⩽ 0.86, the heat transfer Nu is enhanced twice (from ∼550 to ∼ 1100) while the pressure drop Δ p ∗ reduces almost eightfold. For ϕ E < 0.5, Nu reduces quickly to reach a minimum at the mono-disperse porous medium (MDPM) limit ( ϕ E → 0). Compared to N 2 = 1 case, Nu for BDPM configuration is high when N 2 ≫ 1, i.e., the micro-porous blocks are many and well distributed. The Nu increase with Re changes from non-linear to linear as N 2 increases from 1 to 81, with corresponding insignificant pumping power increase.

Natural Convection Inside a Bidisperse Porous Medium Enclosure

Bidisperse porous medium (BDPM) consists of a macroporous medium whose solid phase is replaced with a microporous medium. This study investigates using numerical simulations, steady natural convection inside a square BDPM enclosure made from uniformly spaced, disconnected square porous blocks that form the microporous medium. The side walls are subjected to differential heating, while the top and bottom ones are kept adiabatic. The bidispersion effect is generated by varying the number of blocks (N2), macropore volume fraction (ϕE), and internal Darcy number (DaI) for several enclosure Rayleigh numbers (Ra). Their effect on the BDPM heat transfer (Nu) is investigated. When Ra is fixed, the Nu increases with an increase in both DaI and DaE. At low Ra values, Nu is strongly affected by both DaI and ϕE. When N2 is fixed, at high Ra values, the porous blocks in the core region have negligible effect on the Nu. A correlation is proposed to evaluate the heat transfer from the BDPM enclosure, Nu, as a function of Raϕ, DaE, DaI, and N2. It predicts the numerical results of Nu within ±15% and ±9% in two successive ranges of modified Rayleigh number, RaϕDaE.

Preparation and properties of macroporous brushite bone cements

In the present work a macroporous brushite bone cement for use either as an injected or mouldable paste, or in the shape of preformed grafts, has been investigated. Macropores have been introduced by adding to the powder single crystals of mannitol which worked as a porogen. The size of the crystals was in the range of 250–500 μm in diameter, suitable for cell infiltration, with a shape ratio between 3 and 6. From compression tests on cylindrical samples an elastic modulus in the range 2.5–4.2 GPa and a compressive strength in the range 17.5–32.6 MPa were obtained for a volume fraction of macropores varying between 15 and 0%. Thus the compressive strength exceeded in all tests the maximum value currently attributed to cancellous bone.

Phase Separation in Alkylene-Bridged Polysilsesquioxane Sol-Gel Systems

AbstractPolymerization-induced phase separations and concurrent sol-gel transitions in the hydrolysis and polycondensation of alkylene-bridged polysilsesquioxane system resulted in the formation of co-continuous macroporous gels. Gel morphology with co-continuous macropores and micrometer-sized gel skeletons was obtained in the composition region containing much higher amount of water compared with the case with other alkyltrialkoxysilane sol-gel systems. A narrow pore size distribution and high volume fraction of macropores were obtained in the median size range from few micrometers down to 0.1μm.