Median Pore Size Research Articles

Fabrication of Porous Al₂O₃ Ceramics with Submicron-Sized Pores Using a Water-Based Gelcasting Method.

The gelcasting method is usually employed to fabricate relatively dense ceramics. In this work, however, porous Al2O3 ceramics with submicron-sized pores were fabricated using the water-based gelcasting method by keeping the Al2O3 content at low levels. By controlling the water content in the ceramic slurries and the sintering temperature of the green samples, the volume fractions and the size characteristics of the pores in the porous Al2O3 can be readily obtained. For the porous Al2O3 ceramics prepared with 30 vol.% Al2O3 content in the slurries, their open porosities were from 38.3% to 47.2%, while their median pore sizes varied from 299.8 nm to 371.9 nm. When there was more Al2O3 content in the slurries (40 vol.% Al2O3), the porous Al2O3 ceramics had open porosities from 37.0% to 46.5%, and median pore sizes from 355.4 nm to 363.1 nm. It was found that a higher sintering temperature and Al2O3 content in the slurries increased the mechanical strength of the porous Al2O3 ceramics.

Energy efficient lightweight periclase-magnesium alumina spinel castables containing porous aggregates for the working lining of steel ladles

This study presents a new lightweight periclase-magnesium alumina spinel castable (LPSC) for the working lining of steel ladles using porous periclase-spinel aggregates to replace conventional dense magnesia aggregates. The porous periclase-spinel aggregates were produced by an in-situ decomposition technique resulting in an apparent porosity of 23.3% and a median pore size of 5.66 μm. Scanning electron microscopy revealed a better porous aggregate/matrix interface bonding in the LPSC, which significantly improved its strength and thermal shock resistance. Additionally, the higher amount of micropores of the porous aggregates in the LPSC absorbed more penetrated slag from the matrix, which enhanced the slag resistance. Thus, compared with conventional castables, the LPSC had a lower bulk density of 9.2–10.8% and a lower thermal conductivity of 18.8% (1000 °C) while at the same time a higher strength, thermal shock resistance and slag resistance was achieved.

Three-dimensional microstructure analysis of a polymer electrolyte membrane water electrolyzer anode

The anode catalyst layer of a PEM water electrolyzer is reconstructed using a combination of FIB-SEM tomography and ionomer modeling. The pore space is infiltrated with silicone, enabling good discrimination between pores and IrRuOx catalyst material, while the ionomer cannot be imaged. The reconstructed volume of 29 μm × 24 μm x 7 μm contains catalyst particles with a median size of 0.5 μm and has a porosity of 55%. By modeling different ionomer contents inside the pore space, the impact on microstructural and transport parameters is investigated. At an ionomer content of 40–50% of the pore volume, all transport parameters are in a reasonable range, confirming experimental results from literature. At an ionomer content of 48% the catalyst layer has a porosity of 29%, a median pore size of 0.94 μm, a permeability of the pore space of 1.8mD and a mean ionomer film thickness of 0.4μm. The tortuosities of the ionomer and the pore space are calculated to 3.5 and 6.7 at the corresponding phase fractions of 26% and 29% respectively. The electrochemically active surface area estimated from the tomography (1.0m2g−1) is considerably lower than literature values, indicating a roughness below FIB-SEM resolution.

Cyclic cold isostatic pressing and improved particle packing of coarse grained oxide ceramics for refractory applications

This study investigated the cold isostatic pressing of coarse grained alumina refractories applying either a cyclic pressure increase or a cycling at maximum pressure. Additionally the effects of the maximum pressure and the particle size distribution on physical, mechanical and thermomechanical properties were analyzed. The cyclic pressure increase resulted in a slightly higher apparent density and lower apparent porosity. A cycling at maximum pressure decreased the median pore size to some extent. Remarkably, an optimized particle size distribution resulted in a lower apparent porosity, lower median pore size and in a higher Young's modulus before and after thermal shock together with a slightly lower relative decrease of the Young's modulus. A higher pressing pressure which decreased the apparent porosity did not affect the Young's modulus. Thus, apparently the optimized particle size distribution improved the particle packing which was associated with a smaller median pore size. This smaller pore size increased the number of pores relative to the total porosity, which then acted as points of crack initiation and crack deflection limiting the length of propagating cracks in case of thermal shock. Thus, tailoring the pore size distribution is a promising starting point to improve the thermomechanical properties of refractories.

Characterization of adhesive interphase between epoxy and cement paste via Raman spectroscopy and mercury intrusion porosimetry

When exposed to harsh environmental conditions, the adhesive bond between epoxy and concrete was found to depend almost entirely on the effectiveness of the mechanical interlock which is contingent upon the ability of the adhesive to properly wet and penetrate the substrate. The current study is an investigation of the existence of a distinct interphase region within cement paste through the combined use of mercury intrusion porosimetry and Raman spectroscopy. A positive correlation between median pore size and depth of epoxy permeation into the cement paste substrate was observed. The Lucas-Washburn equation was found to accurately represent the driving mechanisms behind permeation of curing epoxy into the porous cement paste matrix. Interconnectivity of the capillary and gel pore structures was determined to play an important role in the permeation mechanisms. Analysis of relative conversion of epoxy via Raman spectroscopy in the interfacial region showed evidence of epoxy-cement paste interactions.

Effect of Al(OH)3 content on the microstructure and strength of porous cordierite-mullite ceramics prepared by an in-situ pore forming technique

Five porous cordierite-mullite ceramics with similar porosity and different neck characteristics were prepared from Al(OH)3, magnesite, silica and clay using an in-situ pore-forming technique. The phase composition, pore and neck characteristics and strength of the porous ceramics were investigated by an X-ray diffractometer (XRD), a scanning electron microscopy (SEM) and a microscopy measured method, etc. The experimental results showed that Al(OH)3 content had a significant effect on the pore size distribution and neck characteristics (neck size distribution, total value of neck size and phase composition) and then affecting the strength. With an increase in Al(OH)3 content, the median pore size decreased, the total length of necks and the uniformity of neck size increased, also the mullite content of necks increased, resulting in the increase of strength of the porous cordierite-mullite ceramics. When the Al(OH)3 content was 64.9 wt%, the porous cordierite-mullite ceramics had the best performance of high apparent porosity of 45.1 % and high compressive strength of 55.9 MPa.

An activated carbon derived from tobacco waste for use as a supercapacitor electrode material

A tobacco-derived activated carbon (TAC) was prepared from tobacco waste using KOH activation with a KOH/tobacco carbon mass ratio of 3 at 800 °C for 1 h, and was used as an electrode material for a supercapacitor. The tobacco waste was hydrothermally treated in a 10%(v/v) HCl solution to remove metallic impurities and carbonized before activation. The carbonized tobacco has a low Brunauer-Emmett-Teller (BET) surface area of 111.25 m2·g−1, a pore volume of 0.11 cm3·g−1, an average pore diameter of 1.77 nm and a specific capacitance of 37 F·g−1 at a current density of 0.5 A·g−1. The TAC has a high BET surface area of 1297.6 m2·g−1, a large pore volume of 0.52 cm3·g−1, and a pore size distribution with a median pore size of 0.52 nm. It has a specific capacitance of 148 F·g−1 at a current density of 0.5 A·g−1 in a 6 M KOH electrolyte, and an excellent cycling stability with no capacitance fade after 9,000 cycles at a current density of 1 A·g−1.

Modeling of the thermal and mechanical properties of clay ceramics incorporating organic additives

This paper presents the results of a combined experimental and theoretical study on a clay ceramic used for building applications. The thermal and mechanical properties of the clay ceramic were improved by addition of organic additives. The organic additives consisted of Olive Stone Flour (OSF), with round-shape particles of 55µm, and Wheat Straw (WS), with 877µm particles in the form of fibers. It was found that the combustion of OSF and WS resulted in a porosity formation during the firing process. The morphology of these pores corresponded to that of the organic additives. Therefore, the addition of small OSF particles decreased the median pore size of the clay ceramic. It improved the mechanical strength of the clay ceramic by 12% for an 8wt% addition of OSF. On the other hand, the WS fibers increased the clay ceramic anisotropy. This resulted in a 41% improvement of the thermal conductivity using an 8wt% addition of WS. Finally, a model was developed from these experimental results to predict the thermal conductivity and the mechanical strength of the clay ceramic with other organic additives. They were predicted from the parameters of the organic additives (i.e., true density, swelling degree, particle size distribution, particle shape factor). The predictions indicated that the thermal conductivity is improved by 50% with a 25% improvement of the mechanical strength using small organic fibers, which is a step forward in the development of fired clay bricks that can be used for both insulation and structure purposes in building applications.

Solute mixing regulates heterogeneity of mineral precipitation in porous media

AbstractSynchrotron X‐ray microtomography was used to track the spatiotemporal evolution of mineral precipitation and the consequent alteration of the pore structure. Column experiments were conducted by injecting CaCl2 and NaHCO3 solutions into granular porous media either as a premixed supersaturated solution (external mixing) or as separate solutions that mixed within the specimen (internal mixing). The two mixing modes produced distinct mineral growth patterns. While internal mixing promoted transverse heterogeneity with precipitation at the mixing zone, external mixing favored relatively homogeneous precipitation along the flow direction. The impact of precipitation on pore water flow and permeability was assessed via 3‐D flow simulations, which indicated anisotropic permeability evolution for both mixing modes. Under both mixing modes, precipitation decreased the median pore size and increased the skewness of the pore size distribution. Such similar pore‐scale evolution patterns suggest that the clogging of individual pores depends primarily on local supersaturation state and pore geometry.

Suspension- and solution-based freeze casting for porous ceramics

Abstract

High-Porosity Carbon Processed from Mixtures of Furfuryl Resin-Poly(ethylene glycol)-Benzenesulfonyl Chloride and Its Application for Catalyzing Tri-iodide Reduction

High-porosity carbon (HPC) was first prepared from a novel mixture system of furfuryl resin as carbon-yielding precursor, poly(ethylene glycol) with low molecular weight as pore-forming agent and benzenesulfonyl chloride (BSC) as cured catalyst, and then employed as catalyst for counter electrode in dye-sensitized solar cells (DSCs). The pore structures of HPC are tailored by changing BSC amount from 2% to 14%. Especially, when BSC amount ascends from 4% to 8%, the apparent porosity of HPC rises from 59.58% to 68.02% and the median pore size from 0.429 to 3.164 μm, except that some globular carbons initially occur on the carbon skeleton. Since the HPC derived from 4% BSC has high porosity and the most quantity of small-sized pores to enlarge its surface area allowing for the most catalytic active sites for tri-iodide reduction, the resulted counter electrode exhibits the best catalytic activity and the highest efficiency for use in DSCs.

Macroporous ceramic supports from natural clays. Improvement by the use of activated clays

Porous ceramicsupports were elaborated from natural kaolino-illitic clay, before and after acid activation, using uniaxial dry pressing method. The prepared supports were sintered at 850, 900 and 1000°C. The effect of sintering temperature on the mechanical strength, density, porosity, pore size distribution and permeability was evaluated. It was observed that with increase of sintering temperature, the mechanical strength, density and the median pore diameter increase while the porosity decreases. The effect of use of acid activated clay was noticeable; it improved the characteristic of the elaborated supports. In fact, the best mechanical strength was observed with the supports made of pressured acid activated clay, while the highest porosity was obtained with the supports made with clay acid activated under reflux. The best results were for the support made of acid activated clay under reflux sintered at 1000°C with a porosity of 35%, resistance to diametrical compression of 6.6MPa and median pore size of 0.28µm. It shown but a permeability of about 0.52cm3s−1cm−2bar−1 at 4.3bars.

Evaluating Sulphate Resistance of Cement-Based Systems by Sulphate Content Determination after Exposure

This paper describes approaches to evaluating the resistance of cement-based composites to sulphate attack. The conventional approach of evaluation by means of measuring expansion is discussed in comparison with the sulphate diffusion, which was quantified as a function of depth. Besides CSA Types GU and HS, a 30:70 blend of fly ash and cement Type GU was also examined. The specimens so produced were immersed in a sulphate solution as per ASTM C1012 and retrieved variously after 7, 14, 28, 56 and 84 days of exposure. As expected, Type HS cement performed best with minimum expansion and sulphate ingress. On the other hand, the Type GU cement showed lower expansion and sulphate ingress in comparison to the fly ash blended binder. Although bearing identical porosity, the blended binder had the smallest median pore size. Therefore, the sulphate ingress and consequent ettringite production likely cracks the blended system more than the other two. Significantly, after longer durations of sulphate exposure, the blended system showed higher tensile strength which implies a healing of cracks through ettringite formation.

An asymmetrical activated carbon electrode configuration for increased pore utilization in a membrane-assisted capacitive deionization system

A membrane-assisted capacitive deionization (CDI) system was developed for the purification of water containing sodium chloride using activated carbon fibers (ACFs) as capacitor electrode materials. The ACFs have different degrees of activation with different surface areas and pore size distributions. Their desalination performance for sodium or chloride ions was investigated. Results indicate that the salt removal efficiency and surface area-normalized electrosorption capacity for each ion depend on the surface area, pore depth and the match between the pore sizes of the ACFs and the radius of each hydrated ion. A high surface area and shallow pores favor the salt removal efficiency and a high surface area-normalized electrosorption capacity. The ACF with a median pore size of 0.69 nm performs best for sodium ion removal and those with median pore sizes of 1.09 and 1.52 nm are best for chloride ion removal, which could be ascribed to the fact that the radius of a hydrated sodium ion (0.66 nm) is smaller than that of a hydrated chloride ion (0.72 nm). An asymmetric electrode material configuration is needed to optimize both the anion and cation adsorption in the membrane-assisted CDI system.

The relationship between the pore size distribution and the thermo-mechanical properties of high alumina refractory castables

AbstractA series of high alumina refractory castables were prepared via casting with tabular alumina aggregates (0.088 – 5 mm), fine powders, and calcium aluminate cement as starting materials. The effect of the median diameter of alumina (D50 = 7.26 μm, 5.33 μm, 2.37 μm) on the thermo-mechanical properties of the refractory castables was investigated. The results indicate that the decrease in the alumina particle size from 7.26 μm to 2.37 μm has little influence on both the apparent porosity and bulk density of castables. However, the median pore size of castables fired after 1 600 °C decreased drastically from 4.7 μm to 2.4 μm correspondingly, which led to significant growth in the strength and thermal shock resistance of castables. The cold modulus of rupture and crushing strength were increased by 201 % and 120 %, respectively. At the same time, the hot modulus of rupture and elastic modulus were also increased by 143 % and 127 %, respectively. The residual elastic modulus was enhanced twice after three thermal cycles.

Controlled‐release drug carriers based hierarchical silica microtubes templated from cellulose acetate nanofibers

ABSTRACTWe report a facile method to synthesize hollow silica microtubes (SMTs) from electrospun cellulose acetate fiber precursors. Specific surface areas of up to 765 m2/g (Brunauer–Emmett–Teller) were measured for the SMTs, which had a typical wall thickness of ∼100 nm and submicron inner diameters. An average pore size of 4.6 nm and pore volume of 0.41 cm3/g were derived from Barrett–Joyner–Halenda fitting, whereas Horvath–Kawazoe pore size distribution analysis revealed microporous median pore size and maximum pore volume of 0.7 nm and 0.18 cm3/g, respectively. The as‐prepared SMTs featuring micro‐ and mesoporous structures in the walls where amino‐functionalized to facilitate a very high drug loading (15% by weight). Drug release profile revealed sustained release rates (79% of acetylsalicylic acid was released after 6 h). It is concluded that the high drug loading and sustained release resulted from the advantageous integration of SMTs' hollow structure and wall mesoporosity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42562.

Porous ceramic monoliths based on diatomite

Porous silica ceramics were obtained at low forming pressure and low sintering temperature by using diatomaceous earth as a silica source and boric acid as an inexpensive additive. The starting raw material, diatomite from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid up to 2wt%. Powder was compacted by using different pressures of 40, 60 and 80MPa. The pressed samples were sintered at 850, 1000, 1150, and 1300°C for 4h in air. A relatively high porosity in the range of 60–70% is obtained for the samples pressed at 40, 60 and 80MPa and sintered at 1000°C. Median pore size diameters are in the range of macroporous up to 2μm in the samples sintered at 1150 and 1300°C. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scaning electron microscopy (SEM) and mercury porosimetry measurements were employed to characterize the phases, functional groups, microstructure and pore size distribution of the obtained samples. In addition, measurements of densities and open porosities by immersion technique, according to Archimedes principle, were used. The relations between mechanical properties (Young modulus, Poisson ratio, and compressive strength) versus content of boric acid in the investigated samples were studied and disscussed.

Clogging Mechanism of Stormwater Filter Media by NaCl as a Deicing Salt

The effect of NaCl deicing salt on compost-included stormwater filtration media (SFM) has not been studied so far. This article presents results of an experimental and analytical study conducted to understand the mechanism of permeability reduction in two SFM caused by the application of a common deicing salt (NaCl). The two SFM used were made up of clayey silty sand with and without added compost (15% by mass). Constant-head flow experiments were conducted applying NaCl at two different concentrations. Permeability of SFM without compost reduced by an average of 19.1%, while the permeability of SFM with compost reduced by an average of 93.7%. Mercury intrusion porosimetry (MIP) tests and chemical analyses were conducted on representative samples of the media, both before and after salt application. MIP results showed that median pore sizes enlarged, while permeability reduced. This is counterintuitive, as we usually expect that permeability reduction would be caused by pore-size reduction. MIP results (enlarged pore sizes) suggest that deicing salts caused flocculation of aggregates. Based on analysis of our experimental results and comparison with similar results in the literature, we conclude that permeability reduction of SFM was due to blocking of pore throats by dispersed particles and biofilms. Permeability reduction of the SFM with compost was larger, because compost-salt interactions were comparatively greater than the soil-salt interactions. Results of this study suggest that salt-laden snow should not be piled up near the bioretention facilities built with compost-included SFM.

Silica-based strong anion exchange media for protein purification

The main objective of our research was to develop silica-based, polymer-functionalized ion exchange materials for single-use bioprocess applications, with the ultimate goal of achieving maximal binding capacity for target proteins. Herein we report the utilization of Grace® wide pore silica gel and bonding the silica with cationic polymers. The strong anion exchange materials have been prepared by a two-step process involving initial bonding with two trimethoxysilanes and subsequent aqueous solution radical polymerization with quaternary ammonium ion containing monomers and an azo initiator. Using the binding capacities for bovine serum albumin (BSA), a model protein for the evaluation of the new materials, we optimized the processes with regard to the median pore size of the silica gel, as well as polymer composition and ratios, which were determined by reagent ratios and reaction conditions. The products were also characterized by both chemical and physical methods. It has been found that higher binding capacities are associated with lower ligand density and higher molecular weight for the attached polymers, with over 20% higher in both static and dynamic binding capacity values with the same amount of attached polymers. The advantages of a large pore size distribution and optimal median pore size for the base silica are discussed. Optimal pore size range of 500–1500Å and distribution of Span 90 for over 1.0 give the highest BSA binding capacities. Silica-based strong anion exchange materials showed excellent flow characteristics when packed into a column and were superior to commercial agarose-based strong anion exchange material with respect to dynamic binding capacity, elution of proteins, and baseline separation of a mixture of three model proteins.

Preparation and characterization of clay-based porous ceramics with boric acid as additive

Intention of this work was to obtain porous silicon dioxide ceramics by using boric acid as an inexpensive additive at low forming pressure and low sintering temperature. Starting raw material, smectite clay from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid in amount of 0.5, 1 and 2wt%. Powder was compacted by using different pressures: 40, 60 and 80MPa. Pressed samples were sintered at 850, 1000, 1150, and 1300°C for 4h in air. A relatively high porosity of nearly 40% is obtained for the samples pressed at 40, 60 and 80MPa and sintered at 1000°C. Median pore size diameters are in the range of macroporous up to 0.2μm and 10μm in the samples sintered at 1150 and 1300°C, respectively. X-ray diffraction (XRD), scaning electron microscopy (SEM), and porosimetry measurements were employed to characterize the phases and microstructure of the obtained ceramics. The relations between mechanical characteristics of samples (Young modulus and Poisson ratio) and content of boric acid were studied.